- Email: [email protected]
Improvement of anaerobic biological treatment effect by catalytic micro-electrolysis for monensin production wastewater
Chemical Engineering Journal 296 (2016) 260–267
Contents lists available at ScienceDirect
Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Improvement of anaerobic biological treatment effect by catalytic micro-electrolysis for monensin production wastewater Suqing Wu a, Yuanfeng Qi a,b, Chunzhen Fan a, Bibo Dai b, Jungchen Huang a, Weili Zhou a, Shengbing He a,⇑, Lei Gao a a b
School of Environmental Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, PR China Shandong ATK Environmental Engineering Company Limited, Jinan 250101, PR China
h i g h l i g h t s Novel catalytic-ceramic-filler (CCF) prepared from solid waste (scrap iron) and clay. Catalytic micro-electrolysis (CME) with CCF used as monensin wastewater pretreatment. About 98.44% of monensin residue and 37.07% of COD were removed by the CME reactor. The UASB efficiency (methane yield and COD removal) improved by the CME pretreatment. The coupled CME-UASB-AS system removed about 98% of COD and 95% of chroma.
a r t i c l e
i n f o
Article history: Received 3 January 2016 Received in revised form 27 March 2016 Accepted 28 March 2016 Available online 1 April 2016 Keywords: Catalytic-ceramic-filler Catalytic micro-electrolysis Improvement UASB Monensin production wastewater
a b s t r a c t Monensin discharged with the animal wastes and wastewater can cause harmful effect to the environment and human health. In this study, catalytic micro-electrolysis (CME) reactor filled with novel catalytic-ceramic-filler was utilized as pretreatment to improve the anaerobic biological treatment effect for the real monensin wastewater. The CME reactor as a possible pretreatment process had satisfactory effect, with 98.44% of monensin residue and 37.07% of chemical oxygen demand (COD) removals at the optimum hydraulic retention time (HRT) of 3.0 h and dissolved oxygen (DO) of about 1.5 mg L 1. Subsequently, as the secondary biological treatment, the Up-FLOW Anaerobic Sludge Blanket (UASB) reactor treatment effect was greatly improved by the CME pretreatment, with approximately 80% of COD removal at the optimum organic loading rate (OLR) of 3.5 kg m 3 d 1, which had higher methane yield (about 0.33 m3 kg 1 COD 1) and lower volatile fatty acids (VFA) concentration (about 300 mg L 1) than that of the UASB reactor without pretreatment. Finally, an activated sludge (AS) reactor was utilized as the last biological treatment and the coupled CME-UASB-AS system had high COD and chroma removal (about 98% and 95%, respectively), the final effluent (COD and chroma of about 200 mg L 1 and 40, respectively) with no residual monensin met the national discharged standard, which provided a reliable system for the practical monensin production wastewater treatment. Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction Monensin, as a kind of polyether ionophoric antibiotics, has been widely used in animal feeding operations [1]. It is usually added to ruminant diets to improve the efficiency of feed utilization, and may be subsequently released to the environment with animal wastes through overflow or leakage from storage structures or land application [2,3]. Moreover, monensin productive process usually generates large amount of wastewater, which contains ⇑ Corresponding author. Tel.: +86 21 34203734; fax: +86 21 54740825. E-mail addresses: [email protected], [email protected] (S. He). http://dx.doi.org/10.1016/j.cej.2016.03.140 1385-8947/Ó 2016 Elsevier B.V. All rights reserved.
high concentration of monensin residue. Monensin derived from streptomyces species has been considered as high risk compound, which comprises of complex molecules with high molecular weight [4]. Whether animal wastes or the wastewater is discharged, the contained monensin will cause harmful effect to the environment and human health. Therefore, it is significant to dispose of the monensin production wastewater to prevent environmental pollution from the discharged monensin. Catalytic micro-electrolysis (CME), based on traditional microelectrolysis, has been attracted much attention from researchers in the past several years, probably due to its advantage in refractory wastewater treatment. It can improve traditional micro-
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
261
Nomenclature ME CF HRT DO AS BOD EC50
micro-electrolysis ceramic filler hydraulic retention time (h) dissolved oxygen (mg L 1) activated sludge biochemical oxygen demand (mg L 1) concentration for 50% of maximal effect
electrolysis, lower concentrations of toxic components in aqueous solution and enhance the biodegradability of wastewater. Fe/Cu bimetal system, as a kind of CME, can accelerate corrosion of Fe0 and hence improve the micro-electrolysis ability. Therefore, Fe/ Cu catalytic micro-electrolysis has been utilized to remove many pollutants, such as hexavalent chromium [5], nitrate [6], indigo blue [7], and trichloroethene [8], etc. It is well known that filler plays a key role in a CME system, which determines the treatment efficiency and practical application of CME. Therefore, a new type of cost-effective and easily applicable filler is urgently needed to overcome disadvantages of traditional fillers (short-circuiting and clogging during operation) and improve the Fe/Cu CME technology. As a kind of anaerobic biological treatment technology, Up-flow Anaerobic Sludge Blanket (UASB) was firstly invented by Professor G. Lettinga in 1977 [9], and characterized by high organic and hydraulic loading, short hydraulic retention time, high active biomass concentrations, easily controlling and operating, energy- and cost-efficient, etc [10]. When applied in the wastewater treatment, a UASB system usually degrades the organic pollutants through four stages in turn, including hydrolysis, acidogenesis, acetogenesis, and methanogenesis, and the organic pollutants are finally transformed into methane and carbon dioxide [11,12]. At present, UASB has been widely applied in high concentrated organic wastewater treatment, including textile wastewater [13], 3,4,5-trimethoxybenzaldehyde and Di-bromo-aldehyde manufacturing wastewater [14], cheese whey wastewater [15], chloronitrobenzenes wastewater [16], potatojuice wastewater [17], palm oil mill effluent [18], etc. Thus, UASB is a cost-effective and high-efficiency technology for treating the industrial wastewater with high concentration. In this study, a coupled CME-UASB-AS system was applied in the real monensin production wastewater treatment. Firstly, the prepositive CME system was utilized as the pretreatment to remove the monensin residue in the wastewater, which could reduce the negative effect of monensin on the anaerobic system (UASB) and enhance the treatment effect of the UASB system. Subsequently, the later biological treatments (UASB + AS) were applied to degrade the organics after the CME pretreatment, which could completely and effectively depose of the real monensin production wastewater. Therefore, the objectives of this study were to: (1) fill novel catalytic-ceramic-filler (CCF) in a catalytic micro-electrolysis (CME) system for monensin production wastewater pretreatment and determine the optimum operating conditions for the CME system; (2) investigate the influence of CME pretreatment on methane yield and chemical oxygen demand (COD) removal by a Up-flow Anaerobic Sludge Blanket (UASB) system for the secondary wastewater treatment and determine the optimum operating conditions for the UASB system with the CME pretreatment; (3) couple the CME, UASB and aerobic activated sludge (AS) system for the monensin production wastewater systematic treatment and make the final effluent meet the requirement of the national discharged standard (COD 6 300 mg L 1 and chroma 6 60, C standard of CJ 343-2010, China).
LC50 CME CCF UASB COD VFA
lethal concentration of 50% catalytic micro-electrolysis catalytic-ceramic-filler Up-flow Anaerobic Sludge Blanket chemical oxygen demand (mg L 1) volatile fatty acids (mg L 1)
2. Materials and methods 2.1. Preparations of fillers Ceramic filler (CF) and catalytic-ceramic-filler (CCF) were prepared for micro-electrolysis (ME) and catalytic micro-electrolysis (CME) respectively according to our previous study [19]. Clay (obtained from the mountainous area in Zibo city of Shandong Province, China) and scrap iron (obtained from a machinery plant in Jinan city of Shandong Province, China) were utilized to prepare ceramic filler (CF) for the ME reactor, while copper sulfate (CuSO45H2O, purchased from Sigma–Aldrich, St. Louis, MO) solution (Cu2+ of 5.0 g L 1) was added to sinter the catalytic-ceramic-filler (CCF) for the CME reactor. The chemical components of the clay are shown in Table S1, and the curved scrap iron (4.0–5.0 mm wide; 1.0 mm thick) had an average specific surface area of 0.13 m2 g 1. Firstly, the clay and scrap iron were oven dried at 105 °C for 4.0 h, crushed in a ball mill and sieved (the diameter of the sieve mesh was 0.154 mm). Subsequently, clay and scrap iron (3:2, w/w) were stirred in a dry powder stirrer for 10 min, followed by pouring into a pelletizer (DZ-20) to produce pellets (10.0% water added for CF; 10.0% copper sulfate solution added for CCF). Then, the raw pellets were sieved (the diameters were 5.0–6.0 mm) and stored in draught cupboard at room temperature (22 °C) for 24 h. Secondly, the dried pellets were rapidly transferred into an electric tube rotary furnace (KSY-4D-16) and sintered at 850 °C for 30 min in nitrogen atmosphere. Finally, the sintered pellets were kept in a vacuum drying oven to cool down to room temperature (22 °C). The appearance and microstructure of CF and CCF (Fig. S1) showed that CF and CCF had rough surfaces and porous frameworks, which might increase their specific surface area, improve water flow and enhance water mass transfer, resulting in the improvement of pollutants removal efficiency by the reactors packed with CF and CCF. Additionally, the results of the leaching tests of CF and CCF (Table S2) showed that the concentrations of all the detected metals (Cu, Zn, Pb, Cr, Cd, Hg, Ba, Ni, and As) in the lixivium were much lower than the limits of the national standards (GB 5085.3-2007, China, Hazardous Wastes Distinction Standard-Leaching Toxicity Distinction), revealing that utilization of CF and CCF would not cause harm to the water environment.
2.2. Reactors for the treatment system A pilot-scale system as shown in Fig. 1, consisting of five identical cylindrical columns made of polypropylene, was set up for the monensin production wastewater treatment. The first two reactors, with the diameter of 60 cm, height of 1.8 m and effective volume of 297 L, were placed in parallel to each other and used as the ME (packed with CF) and CME reactor (packed with CCF), respectively. From bottom to top, both ME and CME reactor were filled
262
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
Fig. 1. Schematic of the monensin production wastewater treatment system (unit: cm).
in sequence with 20 cm of space for water and air distribution, 30 cm of cobble stone as supporting layer and 100 cm of fillers (CF and CCF, respectively) as media layer, leaving a 30 cm headspace to retain fillers during the backwashing process. If necessary, air was introduced into the reactors by an air pump and distributed through a filter plate at the bottom of the supporting layer. The third and fourth reactors placed in parallel to each other, with the length of 80 cm, width of 80 cm and height of 3.5 m, were utilized as the UASB reactors (with and without CME pretreatment, respectively) for the secondary biological treatment, the wastewater was introduced into the anaerobic reactors through the bottom inlet and uniformly distributed by the water distributor, followed by flowing through the three-phase separator (with the height of 70 cm) and discharging from the anaerobic reactors by the upper outlet. The fifth reactor (1.0 m 1.0 m 1.2 m), with effective volume of about 1.1 m3, was used as the AS reactor for the aerobic biological treatment, the wastewater and air were simultaneously introduced into the aerobic reactor through the bottom inlets and uniformly distributed by the water and air distributor, respectively. The final effluent was discharged through the upper outlet.
2.3. Operating conditions for the system The monensin production wastewater used in this study was mainly derived from the monensin production process in a monensin manufacturing factory (Zhejiang province, China), and the main features of the wastewater were shown in Table 1, suggesting that the main indexes of the wastewater were much higher than the limit of the national discharged standard, and some monensin residue existed in the wastewater, revealing that the wastewater might not be easily treated by the traditional biological treatment. Before being installed into the ME and CME reactors, the CF and CCF were soaked in the wastewater for about one week to prevent adsorption effect by the fillers. After the pH was adjusted to about 3.0 by adding HCl solution (1 M) due to the promotion effect under acidic condition which has been proven in our previous study [21], the monensin wastewater was introduced into the up-flow ME and CME reactors. Then, the comparison between the traditional ME and CME operated in continuous mode was carried out for the
Table 1 The main features of the monensin production wastewater and the national discharged standard. Index 1
COD, mg L BOD5, mg L 1 BOD5/COD Monensin, mg L Chroma (color) pH
1
Raw wastewater
CJ 343-2010
9917–10,384 1061–1163 0.107–0.114 27.38–35.62 764–831 5.03–5.74
6300 6150 – – 660 6.5–9.5
The limited concentration of monensin which may cause harmful effect to the environment: EC50 for decreasing the growth of the floating aquatic macrophyte, Lemna gibba was 998 lg L 1; EC50 of 980 lg L 1 was proved to reduce the biomass of the green algae, Selenastrum capricornutum; 48 h EC50 based on immobility of the crustacean, Daphnia magna was 10.7 mg L 1 and 96 h LC50 on the fish Oncorhynchus mykiss and Lepomis macrochirus were 9.0 and 16.6 mg L 1, respectively [20].
wastewater pretreatment, the influences of hydraulic retention time (HRT) and dissolved oxygen (DO) were studied to select the suitable pretreatment process and determine the optimum conditions determined by the residual monensin and COD removal efficiency. During the whole experiment, the reactors were backwashed according to the effluent quality. Subsequently, the wastewater was pumped into the up-flow UASB reactors after the pH was adjusted to about 7.0 with NaHCO3 addition, which was beneficial for the anaerobic biological process, especially for methanogenesis process [22]. The comparison between the UASB reactor with and without pretreatment was carried out to study the influence of pretreatment on the UASB efficiency. Before the introduction of the wastewater, the UASB reactors were inoculated with granule sludge obtained from a local starch factory at a concentration of approximately 18.3 g VSS L 1, and seeded with the synthetic starch wastewater (about 5000 mg L 1 of COD) at an organic loading rate (OLR) of approximately 0.5 kg m 3 d 1 to maintain the sludge activity. After two weeks, the two UASB reactors were seeded with the raw wastewater and the pretreatment effluent respectively, meanwhile, the volatile fatty acids (VFA) concentration, methane (CH4) yield and COD removal rate were studied. Then, the OLR continued to increase at a rate of about 30.0% every five days until the optimum OLR reached according to COD removal and CH4 yield, when the
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
263
UASB reactors were controlled at pH of about 7.0 and temperature of approximately 35.0 °C through a temperature controller and heating rot. Finally, the UASB effluent was introduced into a activated sludge (AS) reactor, which was inoculated with activated sludge obtained from the same starch factory, with a solids concentration of approximately 5.1 g MLSS L 1. The OLR was about 0.2 kg m 3 d 1 at the starting stage and enhanced gradually until the optimum OLR reached according to the COD removal efficiency. During the whole experiment, according to Drewnowski and Makinia, the pH in bulk wastewater should be always in narrow range of 7 and 8 in the activated sludge system [23], therefore, the AS reactor was operated at pH of 7.0–8.0 by adding NaHCO3, DO of 2.0–4.0 mg L 1 and temperature of about 30.0 °C. After the aerobic treatment, the final effluent was discharged into local sewage treatment plant. 2.4. Analytical methods COD, BOD5 and chroma of the wastewater were measured according to the national standard methods (State Environmental Protection Administration of China, Monitoring and Analysis Methods of Water and Wastewater, fourth ed., China). VFA in the UASB effluent and CH4 yield were measured by GC–MS analysis (TSQ Quantum XLS, Thermo Fisher, USA). The residual monensin in the wastewater was detected by a HPLC system (LC-2010A, shimadzu, Japan). DO, pH and temperature were monitored by the DO meter (HQ30d, HACH, USA) and pH meter (HQ11d, HACH, USA), respectively. All measurements were conducted in five replicates.
Fig. 2. The influence of DO on monensin removal.
four-electron reduction, compete against organic compounds for the reactive OH and enhance the decomposition of H2O2 [24,26], resulting in the decreasing monensin removal of the reactors at DO of 1.5–2.5 mg L 1. Therefore, the optimum DO for the two reactors was 1.0–1.5 mg L 1 and the highest monensin removal could reach 56.35% (ME) and 99.49% (CME), respectively. Additionally, it is obviously that the CME reactor always had higher removal efficiency than the ME reactor, probably due to the acceleration of Fe corrosion and the increase of OH generation by the catalytic decomposition of H2O2 by Cu catalysis [27].
3. Results and discussion 3.1. Pretreatment by the catalytic micro-electrolysis Specific pretreatment was essential to the monensin production wastewater due the residual monensin, and the biodegradability could be improved by the pretreatment, which was beneficial for the later biological treatment. Therefore, a comparison between the traditional ME and CME reactors was carried out to determine the optimum pretreatment process and the optimum operating conditions of the pretreatment. 3.1.1. Influence of dissolved oxygen Dissolved oxygen (DO) plays a key role in the micro-electrolysis process, thus, six DOs (0, 0.5, 1.0, 1.5, 2.0 and 2.5 mg L 1) were selected to investigate the influence of DO on monensin removal of ME and CME reactors. The results at HRT of 4.0 h are shown in Fig. 2, suggesting that the monensin removal of ME and CME reactors were both increased as DO was increased from 0 to 1.0 mg L 1, the main reasons could be summarized as three respects. Firstly, the redox potential was enhanced by aeration, which could accelerate the electrode reactions, resulting in faster corrosion rate of Fe and higher reactive energy for the reactions [19,21]. Secondly, under aerating conditions, oxygen could compete as the electron acceptor, leading to the generation of H2O2, which could combine with Fe2+ released by the micro-electrolysis reactions to form Fenton’s reagent [24]. Hydroxyl radical (OH) generated from Fenton reactions could oxidize organic compounds (including monensin) in the wastewater. Thirdly, aerating in the reactor might enhance the mass transfer effect, which could also increase the treatment efficiency of the reactor [25]. Therefore, the monensin removal was increased by the above three effects under aerating conditions. However, it is noteworthy that the removal of the reactors decreased gradually when DO exceeded 1.5 mg L 1, it is likely that excessive oxygen might enhance the reaction to form H2O via a
3.1.2. Influence of hydraulic retention time Hydraulic retention time (HRT) affects the treatment effect of the ME and CME reactors directly, therefore, seven HRTs (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 4.0 h) were selected to study the influence of HRT on monensin and COD removal by the ME and CME reactors. During this experiment, DO was kept at about 1.5 mg L 1. Fig. 3A shows variation trend of the monensin removal by the two reactors as HRT increased from 0 to 4.0 h, revealing that the variation trend of the monensin removal by the CME reactor was similar with the ME reactor, and the monensin removal increased firstly followed by keeping almost constantly. In the two reactors, the monensin was mainly removed or degraded by two effects from the reactors, including reduction effect by active radical ([H]), Fe0 and Fe2+ from iron corrosion process and oxidation effect by Fenton reactions under aerating conditions [28]. It is noteworthy that the monensin removal by the ME reactor varied slightly when HRT exceeded 2.0 h, but it by the CME reactor increased continually until HRT reached 3.0 h, the reason might be that the corrosion of iron was accelerated by Cu catalysis, resulting in the strengthening of reduction effect by active radical ([H]), Fe0 and Fe2+ [29]. Therefore, to obtain high monensin removal, HRT of the ME and CME reactor should not be lower than 2.0 and 3.0 h, respectively. The variation of COD removal by the two reactors with the increasing HRT is shown in Fig. 3B, suggesting that the variation of COD removal by the ME reactor was also similar with the CME reactor. The COD removal increased gradually as HRT was lower than 2.5 h, followed by the slight variation after 2.5 h. When HRT was lower than 2.5 h, the two reactors were both operated under acid conditions, the COD removal was mainly derived from oxidation effect by reactive OH, which was generated from Fenton’s reagent during the micro-electrolysis reactions. This oxidation effect by OH could be strengthened by Cu catalysis, resulting in higher COD removal by the CME reactor than that by the ME reac-
264
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
Fig. 4. Methane yield of UASB reactor with and without CME pretreatment.
Fig. 3. The influence of HRT on monensin (A) and COD (B) removal.
tor. Then, OH oxidation effect was weakened as HRT exceeded 2.5 h due to the neutral and alkaline conditions of the reactors. Therefore, HRT should not be lower than 2.5 h to obtain high COD removals. To sum up, the CME reactor was more suitable for the monensin production wastewater treatment according to the higher contaminants removal, the monensin and COD removal by the CME reactor could reach about 98.44% and 37.07% respectively at the optimum HRT of 3.0 h.
kg 1 COD 1) after about 7 days, although it had a small fluctuation at the staring stage (1–7 d) due to the accommodation stage of anaerobic bacteria for the introduced wastewater. However, the methane yield by the UASB reactor without the CME pretreatment decreased rapidly until almost no methane was generated, it is likely that high concentration of monensin residue (27.38– 35.62 mg L 1) was existed in the wastewater without the CME pretreatment, resulting in the inhibition of methanogens and the decrease of methane yield. It has been verified that monensin might inhibit the production of methane precursors responsible for providing substrates to methanogens (e.g., hydrogen and formate) [30]. Moreover, the VFA concentration in the UASB reactor without the CME pretreatment increased rapidly as the reactor was continually fed with the raw wastewater without pretreatment (shown in Fig. 5), and the percentage of propionic acid in the total VFA was also increased gradually. The reason may be that the monensin residue selected in favour of propionate forming Selenomonas species and thus caused a strong inhibition on the methanogenic association, resulting in rapid production of VFA, particularly propionic acid [1]. However, the UASB reactor with the CME pretreatment had stable concentration of the effluent VFA (about 300 mg L 1), suggesting the stability of this UASB reactor. Besides that, it could be seen from Fig. 6 that the UASB reactor with the CME pretreat-
3.2. Anaerobic biological treatment with and without pretreatment Anaerobic biological treatment is essential for the highconcentration wastewater due to its high-efficiency and costeffective performance, therefore, the UASB reactor was selected as the secondary biological treatment after the CME pretreatment. Meanwhile, the comparison between the UASB treatment effect with and without CME pretreatment was carried out to demonstrate the pretreatment effect by the CME reactor. During this experiment, the CME reactor was operated at the optimum conditions (DO of about 1.5 mg L 1, HRT of 3.0 h), and the OLR of the two UASB reactors were all kept at about 0.5 kg m 3 d 1. Fig. 4 shows methane yield of the UASB reactor with and without the CME pretreatment, suggesting that the UASB with the CME pretreatment had high and stable methane yield (about 0.33 m3 -
Fig. 5. The VFA concentration in UASB reactor with and without CME pretreatment.
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
265
Fig. 7. The operating of the UASB reactor with CME pretreatment. Fig. 6. The COD removal by UASB reactor with and without CME pretreatment.
ment could keep the stable COD removal (about 85%), comparing with the continual decrease of COD removal by the UASB reactor without the CME pretreatment (decreased from about 85% to 25%), probably due to the inhibition of methanogens by the monensin residue. Through this experiment, it could be concluded that the performance of the UASB reactor could be greatly improved by the CME pretreatment, which could make the UASB reactor keep high methane yield (about 0.33 m3 kg 1 COD 1) and COD removal (about 85%), low VFA concentration (about 300 mg L 1). It might be due to that the monensin residue in the wastewater has been removed or degraded by the CME pretreatment, meanwhile, the ratio of BOD5 to COD (BOD5/COD) was increased from about 0.11 to 0.33 by the pretreatment, resulting in the improvement of biodegradability of the wastewater, which could make the UASB system accommodate the wastewater easily and keep stable operation. 3.3. Optimal conditions for anaerobic biological treatment The comparison between the UASB reactor with and without the CME pretreatment demonstrated that the CME pretreatment was feasible, effective and essential for the monensin production wastewater treatment. Subsequently, the optimum operating conditions should be determined to optimize the UASB system for the secondary wastewater treatment. During this experiment, the CME reactor was also operated at the optimum conditions (DO of about 1.5 mg L 1, HRT of 3.0 h), and the subsequent UASB reactor was operated at a starting OLR of about 0.5 kg m 3 d 1 and a increasing rate of about 30.0% every five days. Fig. 7 shows variation of the COD removal by the UASB reactor with the CME pretreatment when OLR was increased gradually, the results reveals that the COD removal decreased slightly (only about 5.0%) as OLR was increased from 0.5 to 3.5 kg m 3 d 1 (1–45 d), meanwhile, the methane yield and effluent VFA concentration was almost constant, suggesting that the UASB system could accommodate the pretreated wastewater and the methanogens were not inhibited. However, when OLR was increased to about 4.0 kg m 3 d 1 (45–50 d), COD removal decreased rapidly with the fast decrease of methane yield and increase of the effluent VFA concentration, and the poor performance did not ease in the following operation. It is likely that the UASB reactor was operated in the overloading stage and the biological toxicants (e.g., trace monensin residue) might accumulate, and the accumulated VFA
led to the decrease of pH, these results could all inhibit the methanogenesis in the UASB reactor [31]. Subsequently, the OLR was adjusted back to 3.5 kg m 3 d 1 (50–60 d), all the COD removal, methane yield and effluent VFA concentration recovered to the previous level, suggesting that the UASB reactor was recovered to normal operation stage. Therefore, 3.5 kg m 3 d 1 should be selected as the optimum OLR of the UASB reactor and about 80% of COD removal was obtained, further demonstrating the effective CME pretreatment for the monensin production wastewater. 3.4. Aerobic treatment effect After the CME + UASB treatment, the majority of monensin residue and COD in the wastewater was removed and the biodegradability of the wastewater might be greatly improved accordingly, thus, an AS reactor was selected as the final biological treatment to remove the residual COD and make the final effluent reach the requirement of the national standard (COD 6 300 mg L 1). During this experiment, the CME and UASB reactors were operated on the optimum conditions determined by the above experiments. The operation of the AS reactor with the increasing OLR is shown in Fig. 8, the results reveals that the aerobic reactor had stable COD removal efficiency (only decreased from about 92% to 85%, 1–40 d) as OLR was increased from about 0.5 to 1.2 kg m 3 d 1, suggesting that the biodegradability of the wastewater has
Fig. 8. The operating of the aerobic reactor after CME + UASB treatment.
266
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
been greatly improvement by the prepositive CME and UASB treatments, and the aerobic reactor could accommodate the wastewater well, resulting in the sufficient degradation of the colloidal and dissolved organic matter residue by the suspended microorganisms in the reactor, which could satisfy energetic needs (catabolism) for the suspended microorganisms [32]. But, when the OLR was increased to about 1.6 kg m 3 d 1 (40–45 d), COD removal decreased rapidly and could not recover in the following five days, it might be that the aerobic reactor entered into the overloading stage and the suspended microorganisms could not bear the impact of too much organics, leading to the inhibition of the suspended microorganisms and insufficient degradation of the residual organics. Consequently, the OLR was adjusted to about 1.2 kg m 3 d 1 (45–60 d), the COD removal increased gradually back to the previous level (about 85%), revealing that the aerobic reactor has recovered to the normal operation. To summary, the optimum OLR for the AS reactor should be selected as 1.2 kg m 3 d 1, when about 85% of COD removal was obtained and the COD in the final effluent (about 200 mg L 1) met the requirement of the national discharged standard (COD 6 300 mg L 1). Finally, the coupled CME-UASB-AS system could remove about 98% of COD in the raw monensin production wastewater. 3.5. Color removal by the coupled system Chroma (color) is an important index for wastewater and high colored wastewater is forbidden to discharge into the environment. Therefore, the decolorization rate of the coupled system was also investigated, and the result shows that the coupled system had high decolorization rate (approximately 95%) for the monensin production wastewater and the chroma in the final effluent (about 40) reached the requirement of the national discharged standard (chroma 6 60). It is noteworthy that the majority of chroma (94%) in the raw wastewater was removed by the CME reactor, four potential mechanisms were involved to explain the high decolorization rate by the CME reactor, including reduction, oxidation, precipitation and adsorption. Firstly, active radical ([H]), Fe0 and Fe2+ derived from the fillers and the CME reactions might reduce colored organic pollutants to colorless substances [33]. Secondly, a strong oxidizing agent (OH radicals) generated from the CME reactions could attack the chromophores of macromolecular and colored substances and finally mineralize them to CO2, H2O and mineralized products under the aerating and acid conditions [34]. Thirdly, iron(II) and iron(III) oxides/hydroxides generated from Fe corrosion might remove some colored substances by the precipitation effect [35]. Fourthly, the fillers could also remove some colored substances by adsorption effect, but this adsorption effect might be slight and weakened gradually, probably due to the soaking of the fillers in the raw wastewater for about one week before the starting of the whole experiment. It should be noted that the reduction, oxidation and precipitation reactions could be strengthened by Cu catalysis during the CME pretreatment, finally resulting in the high decolorization rate of the CME reactor. Additionally, during the whole study (about 150 d), the CME reactor could keep high and stable contaminants removal rate (about 98% of monensin residue, 37% of COD and 94% of chroma, data not shown), indicating that the CCF could keep active and the CME reactor operated effectively during the long-term operation. 3.6. Economic analysis of the CME-UASB-AS treatment process Economic analysis of the CME-UASB-AS treatment process is crucial for application of the system in practical projects. During the pilot-scale experiment in this study, the operating cost of the
coupled CME-UASB-AS system in this study mainly included three sections: (1) chemical agent cost, including HCl (for CME reactor) and NaHCO3 addition (for UASB and AS reactors), was about 0.31 Chinese Yuan for per ton wastewater; (2) electric charge, mainly resulting from the running of water pumps (for all reactors) and air pumps (for CME and AS reactors), reached approximately 11.56 Chinese Yuan for per ton wastewater; (3) heating cost, mainly utilized for wastewater heating (for UASB and AS reactors), was about 6.32 Chinese Yuan for per ton wastewater. To summary, the total operating cost of the whole CME-UASB-AS treatment process was about 18.19 Chinese Yuan (about 2.79 dollar) for per ton wastewater. 4. Conclusion In this study, novel fillers (CCF) prepared from solid waste (scrap iron), clay and copper sulfate solution were filled into the CME reactor and applied as the pretreatment to improve the anaerobic treatment effect for the real monensin production wastewater. The results showed that the CME reactor packed with the CCF had effective pretreatment effect, with about 98.44% and 37.07% of monensin residue and COD removal respectively at the optimum HRT of 3.0 h and DO of about 1.5 mg L 1. Subsequently, the effect of the UASB reactor applied as the secondary treatment was greatly improved by the CME pretreatment, with approximately 80% of COD removal at the optimum OLR of 3.5 kg m 3 d 1, which had higher methane yield and lower VFA concentration than that of the UASB reactor without pretreatment. This result suggested that the CME pretreatment before the UASB reactor was feasible, effective and essential for the wastewater treatment. Finally, the activated sludge (AS) process was utilized as the aerobic treatment after the UASB reactor, obtaining about 85% of COD removal at the optimum OLR of 1.2 kg m 3 d 1. To summary, the coupled CME-UASB-AS system applied as the real monensin production wastewater treatment progress was feasible and satisfactory, with a total COD and chroma removal of approximately 98% and 95% respectively, and the final effluent (COD and chroma of about 200 mg L 1 and 40, respectively) met the requirement of the national discharged standard (COD 6 300 mg L 1 and chroma 6 60), suggesting a promising potential system for the practical monensin production wastewater treatment projects. Acknowledgements The study was supported by the Science and technology project of Zhejiang Province (No. 2015F50059); The National Natural Science Foundation of China (No. 51378306 and No. 51478262); Shanghai Jiaotong University ‘Chenxing Plan (SMC-B)’; Shandong provincial environmental protection industry projects for technology research and development (No. SDHBYF-2012-12). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.cej.2016.03.140. References [1] J. Thaveesri, G. Boucneau, W. Verstraete, Effect of monensin on UASB-reactor performance, Environ. Technol. 15 (1994) 491–496. [2] C.A. Dellinger, J.G. Ferry, Effect of monensin on growth and methanogenesis of Methanobactericum formicium, Appl. Environ. Microb. 48 (1984) 680–682. [3] N. Yoshida, M. Castro, C. du Mortier, A.F. Cirelli, Environmental behavior of antibiotic monensin: preliminary studies in Argentina, Environ. Chem. Lett. 5 (2007) 157–160. [4] S.A. Hussain, S.O. Prasher, R.M. Patel, Removal of ionophoric antibiotics in free water surface constructed wetlands, Ecol. Eng. 41 (2012) 13–21.
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267 [5] M. Rivero-Huguet, W.D. Marshall, Reduction of hexavalent chromium mediated by micro- and nano-sized mixed metallic particles, J. Hazard. Mater. 169 (2009) 1081–1087. [6] S. Mossa Hosseini, B. Ataie-Ashtiani, M. Kholghi, Nitrate reduction by nano-Fe/ Cu particles in packed column, Desalination 276 (2011) 214–221. [7] J. Trujillo-Reyes, V. Sánchez-Mendieta, A. Colín-Cruz, R.A. Morales-Luckie, Removal of indigo blue in aqueous solution using Fe/Cu nanoparticles and C/Fe/Cu nanoalloy composites, Water. Air. Soil. 207 (2009) 307–317. [8] Y.H. Kim, E.R. Carraway, Reductive dechlorination of TCE by zero valent bimetals, Environ. Technol. 24 (2003) 69–75. [9] G.S. Veeresh, P. Kumar, I. Mehrotra, Treatment of phenol and cresols in upflow anaerobic sludge blanket (UASB) process: a review, Water Res. 39 (2005) 154– 170. [10] M.A. Latif, R. Ghufran, Z.A. Wahid, A. Ahmad, Integrated application of upflow anaerobic sludge blanket reactor for the treatment of wastewaters, Water Res. 45 (2011) 4683–4699. [11] Y. Chen, J. He, Y. Mu, Y.-C. Huo, Z. Zhang, T.A. Kotsopoulos, R.J. Zeng, Mathematical modeling of upflow anaerobic sludge blanket (UASB) reactors: Simultaneous accounting for hydrodynamics and bio-dynamics, Chem. Eng. Sci. 137 (2015) 677–684. [12] T.G. Kim, J. Yun, K.S. Cho, The close relation between Lactococcus and Methanosaeta is a keystone for stable methane production from molasses wastewater in a UASB reactor, Appl. Microbiol. Biotechnol. 99 (2015) 8271– 8283. [13] F.J. Cervantes, R. Gomez, L.H. Alvarez, C.M. Martinez, V. Hernandez-Montoya, Efficient anaerobic treatment of synthetic textile wastewater in a UASB reactor with granular sludge enriched with humic acids supported on alumina nanoparticles, Biodegradation 26 (2015) 289–298. [14] W.C. Li, H. Chen, Y. Jin, H. Zhang, Q.G. Niu, W.K. Qi, Y.L. Zhang, Y.Y. Li, Y.X. Gao, Treatment of 3,4,5-trimethoxybenzaldehyde and Di-bromo-aldehyde manufacturing wastewater by the coupled Fenton pretreatment and UASB reactor with emphasis on optimization and chemicals analysis, Sep. Purif. Technol. 142 (2015) 40–47. [15] J. Carrillo-Reyes, L.B. Celis, F. Alatriste-Mondragón, E. Razo-Flores, Decreasing methane production in hydrogenogenic UASB reactors fed with cheese whey, Biomass. Bioenerg. 63 (2014) 101–108. [16] L. Zhu, J. Jin, H. Lin, K. Gao, X. Xu, Succession of microbial community and enhanced mechanism of a ZVI-based anaerobic granular sludge process treating chloronitrobenzenes wastewater, J. Hazard. Mater. 285 (2015) 157– 166. [17] C. Fang, K. Boe, I. Angelidaki, Biogas production from potato-juice, a byproduct from potato-starch processing, in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors, Bioresour. Technol. 102 (2011) 5734–5741. [18] A. Ahmad, R. Ghufran, Z. Abd, Wahid, Role of calcium oxide in sludge granulation and methanogenesis for the treatment of palm oil mill effluent using UASB reactor, J. Hazard. Mater. 198 (2011) 40–48.
267
[19] S. Wu, Y. Qi, S. He, C. Fan, B. Dai, W. Zhou, L. Gao, J. Huang, Preparation and application of novel catalytic-ceramic-filler in a coupled system for TNT manufacturing wastewater treatment, Chem. Eng. J. 280 (2015) 417–425. [20] Derek.G. Hillis, Linda. Lissemore, Paul.K. Sibley, K.R. Solomon, Effects of Monensin on Zooplankton Communities in Aquatic Microcosms, Environ. Sci. Technol. 41 (2007) 6620–6626. [21] S. Wu, Y. Qi, Y. Gao, Y. Xu, F. Gao, H. Yu, Y. Lu, Q. Yue, J. Li, Preparation of ceramic-corrosion-cell fillers and application for cyclohexanone industry wastewater treatment in electrobath reactor, J. Hazard. Mater. 196 (2011) 139–144. [22] Y.L. He, Anaerobic biological treatment of wastewater, China Light Industry Press, 1998. [23] J. Drewnowski, J. Makinia, The role of biodegradable particulate and colloidal organic compounds in biological nutrient removal activated sludge systems, Int. J. Environ. Sci. Te. 11 (2014) 1973–1988. [24] D. Ying, J. Peng, X. Xu, K. Li, Y. Wang, J. Jia, Treatment of mature landfill leachate by internal micro-electrolysis integrated with coagulation: a comparative study on a novel sequencing batch reactor based on zero valent iron, J. Hazard. Mater. 229–230 (2012) 426–433. [25] N. Sangkil, G.T. Paul, Reduction of azo dyes with zero-valent iron, Water Res. 34 (2000) 1837–1845. [26] Y. Du, M. Zhou, L. Lei, The role of oxygen in the degradation of p-chlorophenol by Fenton system, J. Hazard. Mater. 139 (2007) 108–115. [27] X. Liu, J.H. Fan, L.M. Ma, Oxidative degradation of EDTA in aqueous solution by the bimetallic Fe-Cu, Water. Air. Soil. 224 (2013) 1583. [28] M. Stieber, A. Putschew, M. Jekel, Treatment of pharmaceuticals and diagnostic agents using zero-valent iron-kinetic studies and assessment of transformation products assay, Environ. Sci. Technol. 45 (2011) 4944–4950. [29] J.H. Fan, L.M. Ma, The pretreatment by the Fe-Cu process for enhancing biological degradability of the mixed wastewater, J. Hazard. Mater. 164 (2009) 1392–1397. [30] V.H. Varel, A.G. Hashimoto, Effect of dietary monensin or chlortetracycline on methane production from cattle waste, Appl. Environ. Microb. 41 (1981) 29– 34. [31] R. Dai, Y. Liu, X. Liu, X. Zhang, C. Zeng, L. Li, Investigation of a sewageintegrated technology combining an expanded granular sludge bed (EGSB) and an electrochemical reactor in a pilot-scale plant, J. Hazard. Mater. 192 (2011) 1161–1170. [32] R. Hreiz, M.A. Latifi, N. Roche, Optimal design and operation of activated sludge processes: State-of-the-art, Chem. Eng. J. 281 (2015) 900–920. [33] O. Impert, A. Katafias, P. Kita, A. Mills, A. Pietkiewicz-Graczyk, G. Wrzeszcz, Kinetics and mechanism of a fast leuco-Methylene Blue oxidation by copper (ii)–halide species in acidic aqueous media, Dalton. T. (2003) 348–353. [34] X. Sun, T. Kurokawa, M. Suzuki, M. Takagi, Y. Kawase, Removal of cationic dye methylene blue by zero-valent iron: Effects of pH and dissolved oxygen on removal mechanisms, J. Environ. Sci. Heal. A. 50 (2015) 1057–1071. [35] B.H. Thomas, G.H. Cornelis, B.H. Stefan, H. Christof, P.S. René, Complete Reduction of TNT and Other (Poly)nitroaromatic Compounds under IronReducing Subsurface Conditions, Environ. Sci. Technol. 33 (1999) 1479–1487.
Contents lists available at ScienceDirect
Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Improvement of anaerobic biological treatment effect by catalytic micro-electrolysis for monensin production wastewater Suqing Wu a, Yuanfeng Qi a,b, Chunzhen Fan a, Bibo Dai b, Jungchen Huang a, Weili Zhou a, Shengbing He a,⇑, Lei Gao a a b
School of Environmental Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, PR China Shandong ATK Environmental Engineering Company Limited, Jinan 250101, PR China
h i g h l i g h t s Novel catalytic-ceramic-filler (CCF) prepared from solid waste (scrap iron) and clay. Catalytic micro-electrolysis (CME) with CCF used as monensin wastewater pretreatment. About 98.44% of monensin residue and 37.07% of COD were removed by the CME reactor. The UASB efficiency (methane yield and COD removal) improved by the CME pretreatment. The coupled CME-UASB-AS system removed about 98% of COD and 95% of chroma.
a r t i c l e
i n f o
Article history: Received 3 January 2016 Received in revised form 27 March 2016 Accepted 28 March 2016 Available online 1 April 2016 Keywords: Catalytic-ceramic-filler Catalytic micro-electrolysis Improvement UASB Monensin production wastewater
a b s t r a c t Monensin discharged with the animal wastes and wastewater can cause harmful effect to the environment and human health. In this study, catalytic micro-electrolysis (CME) reactor filled with novel catalytic-ceramic-filler was utilized as pretreatment to improve the anaerobic biological treatment effect for the real monensin wastewater. The CME reactor as a possible pretreatment process had satisfactory effect, with 98.44% of monensin residue and 37.07% of chemical oxygen demand (COD) removals at the optimum hydraulic retention time (HRT) of 3.0 h and dissolved oxygen (DO) of about 1.5 mg L 1. Subsequently, as the secondary biological treatment, the Up-FLOW Anaerobic Sludge Blanket (UASB) reactor treatment effect was greatly improved by the CME pretreatment, with approximately 80% of COD removal at the optimum organic loading rate (OLR) of 3.5 kg m 3 d 1, which had higher methane yield (about 0.33 m3 kg 1 COD 1) and lower volatile fatty acids (VFA) concentration (about 300 mg L 1) than that of the UASB reactor without pretreatment. Finally, an activated sludge (AS) reactor was utilized as the last biological treatment and the coupled CME-UASB-AS system had high COD and chroma removal (about 98% and 95%, respectively), the final effluent (COD and chroma of about 200 mg L 1 and 40, respectively) with no residual monensin met the national discharged standard, which provided a reliable system for the practical monensin production wastewater treatment. Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction Monensin, as a kind of polyether ionophoric antibiotics, has been widely used in animal feeding operations [1]. It is usually added to ruminant diets to improve the efficiency of feed utilization, and may be subsequently released to the environment with animal wastes through overflow or leakage from storage structures or land application [2,3]. Moreover, monensin productive process usually generates large amount of wastewater, which contains ⇑ Corresponding author. Tel.: +86 21 34203734; fax: +86 21 54740825. E-mail addresses: [email protected], [email protected] (S. He). http://dx.doi.org/10.1016/j.cej.2016.03.140 1385-8947/Ó 2016 Elsevier B.V. All rights reserved.
high concentration of monensin residue. Monensin derived from streptomyces species has been considered as high risk compound, which comprises of complex molecules with high molecular weight [4]. Whether animal wastes or the wastewater is discharged, the contained monensin will cause harmful effect to the environment and human health. Therefore, it is significant to dispose of the monensin production wastewater to prevent environmental pollution from the discharged monensin. Catalytic micro-electrolysis (CME), based on traditional microelectrolysis, has been attracted much attention from researchers in the past several years, probably due to its advantage in refractory wastewater treatment. It can improve traditional micro-
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
261
Nomenclature ME CF HRT DO AS BOD EC50
micro-electrolysis ceramic filler hydraulic retention time (h) dissolved oxygen (mg L 1) activated sludge biochemical oxygen demand (mg L 1) concentration for 50% of maximal effect
electrolysis, lower concentrations of toxic components in aqueous solution and enhance the biodegradability of wastewater. Fe/Cu bimetal system, as a kind of CME, can accelerate corrosion of Fe0 and hence improve the micro-electrolysis ability. Therefore, Fe/ Cu catalytic micro-electrolysis has been utilized to remove many pollutants, such as hexavalent chromium [5], nitrate [6], indigo blue [7], and trichloroethene [8], etc. It is well known that filler plays a key role in a CME system, which determines the treatment efficiency and practical application of CME. Therefore, a new type of cost-effective and easily applicable filler is urgently needed to overcome disadvantages of traditional fillers (short-circuiting and clogging during operation) and improve the Fe/Cu CME technology. As a kind of anaerobic biological treatment technology, Up-flow Anaerobic Sludge Blanket (UASB) was firstly invented by Professor G. Lettinga in 1977 [9], and characterized by high organic and hydraulic loading, short hydraulic retention time, high active biomass concentrations, easily controlling and operating, energy- and cost-efficient, etc [10]. When applied in the wastewater treatment, a UASB system usually degrades the organic pollutants through four stages in turn, including hydrolysis, acidogenesis, acetogenesis, and methanogenesis, and the organic pollutants are finally transformed into methane and carbon dioxide [11,12]. At present, UASB has been widely applied in high concentrated organic wastewater treatment, including textile wastewater [13], 3,4,5-trimethoxybenzaldehyde and Di-bromo-aldehyde manufacturing wastewater [14], cheese whey wastewater [15], chloronitrobenzenes wastewater [16], potatojuice wastewater [17], palm oil mill effluent [18], etc. Thus, UASB is a cost-effective and high-efficiency technology for treating the industrial wastewater with high concentration. In this study, a coupled CME-UASB-AS system was applied in the real monensin production wastewater treatment. Firstly, the prepositive CME system was utilized as the pretreatment to remove the monensin residue in the wastewater, which could reduce the negative effect of monensin on the anaerobic system (UASB) and enhance the treatment effect of the UASB system. Subsequently, the later biological treatments (UASB + AS) were applied to degrade the organics after the CME pretreatment, which could completely and effectively depose of the real monensin production wastewater. Therefore, the objectives of this study were to: (1) fill novel catalytic-ceramic-filler (CCF) in a catalytic micro-electrolysis (CME) system for monensin production wastewater pretreatment and determine the optimum operating conditions for the CME system; (2) investigate the influence of CME pretreatment on methane yield and chemical oxygen demand (COD) removal by a Up-flow Anaerobic Sludge Blanket (UASB) system for the secondary wastewater treatment and determine the optimum operating conditions for the UASB system with the CME pretreatment; (3) couple the CME, UASB and aerobic activated sludge (AS) system for the monensin production wastewater systematic treatment and make the final effluent meet the requirement of the national discharged standard (COD 6 300 mg L 1 and chroma 6 60, C standard of CJ 343-2010, China).
LC50 CME CCF UASB COD VFA
lethal concentration of 50% catalytic micro-electrolysis catalytic-ceramic-filler Up-flow Anaerobic Sludge Blanket chemical oxygen demand (mg L 1) volatile fatty acids (mg L 1)
2. Materials and methods 2.1. Preparations of fillers Ceramic filler (CF) and catalytic-ceramic-filler (CCF) were prepared for micro-electrolysis (ME) and catalytic micro-electrolysis (CME) respectively according to our previous study [19]. Clay (obtained from the mountainous area in Zibo city of Shandong Province, China) and scrap iron (obtained from a machinery plant in Jinan city of Shandong Province, China) were utilized to prepare ceramic filler (CF) for the ME reactor, while copper sulfate (CuSO45H2O, purchased from Sigma–Aldrich, St. Louis, MO) solution (Cu2+ of 5.0 g L 1) was added to sinter the catalytic-ceramic-filler (CCF) for the CME reactor. The chemical components of the clay are shown in Table S1, and the curved scrap iron (4.0–5.0 mm wide; 1.0 mm thick) had an average specific surface area of 0.13 m2 g 1. Firstly, the clay and scrap iron were oven dried at 105 °C for 4.0 h, crushed in a ball mill and sieved (the diameter of the sieve mesh was 0.154 mm). Subsequently, clay and scrap iron (3:2, w/w) were stirred in a dry powder stirrer for 10 min, followed by pouring into a pelletizer (DZ-20) to produce pellets (10.0% water added for CF; 10.0% copper sulfate solution added for CCF). Then, the raw pellets were sieved (the diameters were 5.0–6.0 mm) and stored in draught cupboard at room temperature (22 °C) for 24 h. Secondly, the dried pellets were rapidly transferred into an electric tube rotary furnace (KSY-4D-16) and sintered at 850 °C for 30 min in nitrogen atmosphere. Finally, the sintered pellets were kept in a vacuum drying oven to cool down to room temperature (22 °C). The appearance and microstructure of CF and CCF (Fig. S1) showed that CF and CCF had rough surfaces and porous frameworks, which might increase their specific surface area, improve water flow and enhance water mass transfer, resulting in the improvement of pollutants removal efficiency by the reactors packed with CF and CCF. Additionally, the results of the leaching tests of CF and CCF (Table S2) showed that the concentrations of all the detected metals (Cu, Zn, Pb, Cr, Cd, Hg, Ba, Ni, and As) in the lixivium were much lower than the limits of the national standards (GB 5085.3-2007, China, Hazardous Wastes Distinction Standard-Leaching Toxicity Distinction), revealing that utilization of CF and CCF would not cause harm to the water environment.
2.2. Reactors for the treatment system A pilot-scale system as shown in Fig. 1, consisting of five identical cylindrical columns made of polypropylene, was set up for the monensin production wastewater treatment. The first two reactors, with the diameter of 60 cm, height of 1.8 m and effective volume of 297 L, were placed in parallel to each other and used as the ME (packed with CF) and CME reactor (packed with CCF), respectively. From bottom to top, both ME and CME reactor were filled
262
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
Fig. 1. Schematic of the monensin production wastewater treatment system (unit: cm).
in sequence with 20 cm of space for water and air distribution, 30 cm of cobble stone as supporting layer and 100 cm of fillers (CF and CCF, respectively) as media layer, leaving a 30 cm headspace to retain fillers during the backwashing process. If necessary, air was introduced into the reactors by an air pump and distributed through a filter plate at the bottom of the supporting layer. The third and fourth reactors placed in parallel to each other, with the length of 80 cm, width of 80 cm and height of 3.5 m, were utilized as the UASB reactors (with and without CME pretreatment, respectively) for the secondary biological treatment, the wastewater was introduced into the anaerobic reactors through the bottom inlet and uniformly distributed by the water distributor, followed by flowing through the three-phase separator (with the height of 70 cm) and discharging from the anaerobic reactors by the upper outlet. The fifth reactor (1.0 m 1.0 m 1.2 m), with effective volume of about 1.1 m3, was used as the AS reactor for the aerobic biological treatment, the wastewater and air were simultaneously introduced into the aerobic reactor through the bottom inlets and uniformly distributed by the water and air distributor, respectively. The final effluent was discharged through the upper outlet.
2.3. Operating conditions for the system The monensin production wastewater used in this study was mainly derived from the monensin production process in a monensin manufacturing factory (Zhejiang province, China), and the main features of the wastewater were shown in Table 1, suggesting that the main indexes of the wastewater were much higher than the limit of the national discharged standard, and some monensin residue existed in the wastewater, revealing that the wastewater might not be easily treated by the traditional biological treatment. Before being installed into the ME and CME reactors, the CF and CCF were soaked in the wastewater for about one week to prevent adsorption effect by the fillers. After the pH was adjusted to about 3.0 by adding HCl solution (1 M) due to the promotion effect under acidic condition which has been proven in our previous study [21], the monensin wastewater was introduced into the up-flow ME and CME reactors. Then, the comparison between the traditional ME and CME operated in continuous mode was carried out for the
Table 1 The main features of the monensin production wastewater and the national discharged standard. Index 1
COD, mg L BOD5, mg L 1 BOD5/COD Monensin, mg L Chroma (color) pH
1
Raw wastewater
CJ 343-2010
9917–10,384 1061–1163 0.107–0.114 27.38–35.62 764–831 5.03–5.74
6300 6150 – – 660 6.5–9.5
The limited concentration of monensin which may cause harmful effect to the environment: EC50 for decreasing the growth of the floating aquatic macrophyte, Lemna gibba was 998 lg L 1; EC50 of 980 lg L 1 was proved to reduce the biomass of the green algae, Selenastrum capricornutum; 48 h EC50 based on immobility of the crustacean, Daphnia magna was 10.7 mg L 1 and 96 h LC50 on the fish Oncorhynchus mykiss and Lepomis macrochirus were 9.0 and 16.6 mg L 1, respectively [20].
wastewater pretreatment, the influences of hydraulic retention time (HRT) and dissolved oxygen (DO) were studied to select the suitable pretreatment process and determine the optimum conditions determined by the residual monensin and COD removal efficiency. During the whole experiment, the reactors were backwashed according to the effluent quality. Subsequently, the wastewater was pumped into the up-flow UASB reactors after the pH was adjusted to about 7.0 with NaHCO3 addition, which was beneficial for the anaerobic biological process, especially for methanogenesis process [22]. The comparison between the UASB reactor with and without pretreatment was carried out to study the influence of pretreatment on the UASB efficiency. Before the introduction of the wastewater, the UASB reactors were inoculated with granule sludge obtained from a local starch factory at a concentration of approximately 18.3 g VSS L 1, and seeded with the synthetic starch wastewater (about 5000 mg L 1 of COD) at an organic loading rate (OLR) of approximately 0.5 kg m 3 d 1 to maintain the sludge activity. After two weeks, the two UASB reactors were seeded with the raw wastewater and the pretreatment effluent respectively, meanwhile, the volatile fatty acids (VFA) concentration, methane (CH4) yield and COD removal rate were studied. Then, the OLR continued to increase at a rate of about 30.0% every five days until the optimum OLR reached according to COD removal and CH4 yield, when the
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
263
UASB reactors were controlled at pH of about 7.0 and temperature of approximately 35.0 °C through a temperature controller and heating rot. Finally, the UASB effluent was introduced into a activated sludge (AS) reactor, which was inoculated with activated sludge obtained from the same starch factory, with a solids concentration of approximately 5.1 g MLSS L 1. The OLR was about 0.2 kg m 3 d 1 at the starting stage and enhanced gradually until the optimum OLR reached according to the COD removal efficiency. During the whole experiment, according to Drewnowski and Makinia, the pH in bulk wastewater should be always in narrow range of 7 and 8 in the activated sludge system [23], therefore, the AS reactor was operated at pH of 7.0–8.0 by adding NaHCO3, DO of 2.0–4.0 mg L 1 and temperature of about 30.0 °C. After the aerobic treatment, the final effluent was discharged into local sewage treatment plant. 2.4. Analytical methods COD, BOD5 and chroma of the wastewater were measured according to the national standard methods (State Environmental Protection Administration of China, Monitoring and Analysis Methods of Water and Wastewater, fourth ed., China). VFA in the UASB effluent and CH4 yield were measured by GC–MS analysis (TSQ Quantum XLS, Thermo Fisher, USA). The residual monensin in the wastewater was detected by a HPLC system (LC-2010A, shimadzu, Japan). DO, pH and temperature were monitored by the DO meter (HQ30d, HACH, USA) and pH meter (HQ11d, HACH, USA), respectively. All measurements were conducted in five replicates.
Fig. 2. The influence of DO on monensin removal.
four-electron reduction, compete against organic compounds for the reactive OH and enhance the decomposition of H2O2 [24,26], resulting in the decreasing monensin removal of the reactors at DO of 1.5–2.5 mg L 1. Therefore, the optimum DO for the two reactors was 1.0–1.5 mg L 1 and the highest monensin removal could reach 56.35% (ME) and 99.49% (CME), respectively. Additionally, it is obviously that the CME reactor always had higher removal efficiency than the ME reactor, probably due to the acceleration of Fe corrosion and the increase of OH generation by the catalytic decomposition of H2O2 by Cu catalysis [27].
3. Results and discussion 3.1. Pretreatment by the catalytic micro-electrolysis Specific pretreatment was essential to the monensin production wastewater due the residual monensin, and the biodegradability could be improved by the pretreatment, which was beneficial for the later biological treatment. Therefore, a comparison between the traditional ME and CME reactors was carried out to determine the optimum pretreatment process and the optimum operating conditions of the pretreatment. 3.1.1. Influence of dissolved oxygen Dissolved oxygen (DO) plays a key role in the micro-electrolysis process, thus, six DOs (0, 0.5, 1.0, 1.5, 2.0 and 2.5 mg L 1) were selected to investigate the influence of DO on monensin removal of ME and CME reactors. The results at HRT of 4.0 h are shown in Fig. 2, suggesting that the monensin removal of ME and CME reactors were both increased as DO was increased from 0 to 1.0 mg L 1, the main reasons could be summarized as three respects. Firstly, the redox potential was enhanced by aeration, which could accelerate the electrode reactions, resulting in faster corrosion rate of Fe and higher reactive energy for the reactions [19,21]. Secondly, under aerating conditions, oxygen could compete as the electron acceptor, leading to the generation of H2O2, which could combine with Fe2+ released by the micro-electrolysis reactions to form Fenton’s reagent [24]. Hydroxyl radical (OH) generated from Fenton reactions could oxidize organic compounds (including monensin) in the wastewater. Thirdly, aerating in the reactor might enhance the mass transfer effect, which could also increase the treatment efficiency of the reactor [25]. Therefore, the monensin removal was increased by the above three effects under aerating conditions. However, it is noteworthy that the removal of the reactors decreased gradually when DO exceeded 1.5 mg L 1, it is likely that excessive oxygen might enhance the reaction to form H2O via a
3.1.2. Influence of hydraulic retention time Hydraulic retention time (HRT) affects the treatment effect of the ME and CME reactors directly, therefore, seven HRTs (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 4.0 h) were selected to study the influence of HRT on monensin and COD removal by the ME and CME reactors. During this experiment, DO was kept at about 1.5 mg L 1. Fig. 3A shows variation trend of the monensin removal by the two reactors as HRT increased from 0 to 4.0 h, revealing that the variation trend of the monensin removal by the CME reactor was similar with the ME reactor, and the monensin removal increased firstly followed by keeping almost constantly. In the two reactors, the monensin was mainly removed or degraded by two effects from the reactors, including reduction effect by active radical ([H]), Fe0 and Fe2+ from iron corrosion process and oxidation effect by Fenton reactions under aerating conditions [28]. It is noteworthy that the monensin removal by the ME reactor varied slightly when HRT exceeded 2.0 h, but it by the CME reactor increased continually until HRT reached 3.0 h, the reason might be that the corrosion of iron was accelerated by Cu catalysis, resulting in the strengthening of reduction effect by active radical ([H]), Fe0 and Fe2+ [29]. Therefore, to obtain high monensin removal, HRT of the ME and CME reactor should not be lower than 2.0 and 3.0 h, respectively. The variation of COD removal by the two reactors with the increasing HRT is shown in Fig. 3B, suggesting that the variation of COD removal by the ME reactor was also similar with the CME reactor. The COD removal increased gradually as HRT was lower than 2.5 h, followed by the slight variation after 2.5 h. When HRT was lower than 2.5 h, the two reactors were both operated under acid conditions, the COD removal was mainly derived from oxidation effect by reactive OH, which was generated from Fenton’s reagent during the micro-electrolysis reactions. This oxidation effect by OH could be strengthened by Cu catalysis, resulting in higher COD removal by the CME reactor than that by the ME reac-
264
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
Fig. 4. Methane yield of UASB reactor with and without CME pretreatment.
Fig. 3. The influence of HRT on monensin (A) and COD (B) removal.
tor. Then, OH oxidation effect was weakened as HRT exceeded 2.5 h due to the neutral and alkaline conditions of the reactors. Therefore, HRT should not be lower than 2.5 h to obtain high COD removals. To sum up, the CME reactor was more suitable for the monensin production wastewater treatment according to the higher contaminants removal, the monensin and COD removal by the CME reactor could reach about 98.44% and 37.07% respectively at the optimum HRT of 3.0 h.
kg 1 COD 1) after about 7 days, although it had a small fluctuation at the staring stage (1–7 d) due to the accommodation stage of anaerobic bacteria for the introduced wastewater. However, the methane yield by the UASB reactor without the CME pretreatment decreased rapidly until almost no methane was generated, it is likely that high concentration of monensin residue (27.38– 35.62 mg L 1) was existed in the wastewater without the CME pretreatment, resulting in the inhibition of methanogens and the decrease of methane yield. It has been verified that monensin might inhibit the production of methane precursors responsible for providing substrates to methanogens (e.g., hydrogen and formate) [30]. Moreover, the VFA concentration in the UASB reactor without the CME pretreatment increased rapidly as the reactor was continually fed with the raw wastewater without pretreatment (shown in Fig. 5), and the percentage of propionic acid in the total VFA was also increased gradually. The reason may be that the monensin residue selected in favour of propionate forming Selenomonas species and thus caused a strong inhibition on the methanogenic association, resulting in rapid production of VFA, particularly propionic acid [1]. However, the UASB reactor with the CME pretreatment had stable concentration of the effluent VFA (about 300 mg L 1), suggesting the stability of this UASB reactor. Besides that, it could be seen from Fig. 6 that the UASB reactor with the CME pretreat-
3.2. Anaerobic biological treatment with and without pretreatment Anaerobic biological treatment is essential for the highconcentration wastewater due to its high-efficiency and costeffective performance, therefore, the UASB reactor was selected as the secondary biological treatment after the CME pretreatment. Meanwhile, the comparison between the UASB treatment effect with and without CME pretreatment was carried out to demonstrate the pretreatment effect by the CME reactor. During this experiment, the CME reactor was operated at the optimum conditions (DO of about 1.5 mg L 1, HRT of 3.0 h), and the OLR of the two UASB reactors were all kept at about 0.5 kg m 3 d 1. Fig. 4 shows methane yield of the UASB reactor with and without the CME pretreatment, suggesting that the UASB with the CME pretreatment had high and stable methane yield (about 0.33 m3 -
Fig. 5. The VFA concentration in UASB reactor with and without CME pretreatment.
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
265
Fig. 7. The operating of the UASB reactor with CME pretreatment. Fig. 6. The COD removal by UASB reactor with and without CME pretreatment.
ment could keep the stable COD removal (about 85%), comparing with the continual decrease of COD removal by the UASB reactor without the CME pretreatment (decreased from about 85% to 25%), probably due to the inhibition of methanogens by the monensin residue. Through this experiment, it could be concluded that the performance of the UASB reactor could be greatly improved by the CME pretreatment, which could make the UASB reactor keep high methane yield (about 0.33 m3 kg 1 COD 1) and COD removal (about 85%), low VFA concentration (about 300 mg L 1). It might be due to that the monensin residue in the wastewater has been removed or degraded by the CME pretreatment, meanwhile, the ratio of BOD5 to COD (BOD5/COD) was increased from about 0.11 to 0.33 by the pretreatment, resulting in the improvement of biodegradability of the wastewater, which could make the UASB system accommodate the wastewater easily and keep stable operation. 3.3. Optimal conditions for anaerobic biological treatment The comparison between the UASB reactor with and without the CME pretreatment demonstrated that the CME pretreatment was feasible, effective and essential for the monensin production wastewater treatment. Subsequently, the optimum operating conditions should be determined to optimize the UASB system for the secondary wastewater treatment. During this experiment, the CME reactor was also operated at the optimum conditions (DO of about 1.5 mg L 1, HRT of 3.0 h), and the subsequent UASB reactor was operated at a starting OLR of about 0.5 kg m 3 d 1 and a increasing rate of about 30.0% every five days. Fig. 7 shows variation of the COD removal by the UASB reactor with the CME pretreatment when OLR was increased gradually, the results reveals that the COD removal decreased slightly (only about 5.0%) as OLR was increased from 0.5 to 3.5 kg m 3 d 1 (1–45 d), meanwhile, the methane yield and effluent VFA concentration was almost constant, suggesting that the UASB system could accommodate the pretreated wastewater and the methanogens were not inhibited. However, when OLR was increased to about 4.0 kg m 3 d 1 (45–50 d), COD removal decreased rapidly with the fast decrease of methane yield and increase of the effluent VFA concentration, and the poor performance did not ease in the following operation. It is likely that the UASB reactor was operated in the overloading stage and the biological toxicants (e.g., trace monensin residue) might accumulate, and the accumulated VFA
led to the decrease of pH, these results could all inhibit the methanogenesis in the UASB reactor [31]. Subsequently, the OLR was adjusted back to 3.5 kg m 3 d 1 (50–60 d), all the COD removal, methane yield and effluent VFA concentration recovered to the previous level, suggesting that the UASB reactor was recovered to normal operation stage. Therefore, 3.5 kg m 3 d 1 should be selected as the optimum OLR of the UASB reactor and about 80% of COD removal was obtained, further demonstrating the effective CME pretreatment for the monensin production wastewater. 3.4. Aerobic treatment effect After the CME + UASB treatment, the majority of monensin residue and COD in the wastewater was removed and the biodegradability of the wastewater might be greatly improved accordingly, thus, an AS reactor was selected as the final biological treatment to remove the residual COD and make the final effluent reach the requirement of the national standard (COD 6 300 mg L 1). During this experiment, the CME and UASB reactors were operated on the optimum conditions determined by the above experiments. The operation of the AS reactor with the increasing OLR is shown in Fig. 8, the results reveals that the aerobic reactor had stable COD removal efficiency (only decreased from about 92% to 85%, 1–40 d) as OLR was increased from about 0.5 to 1.2 kg m 3 d 1, suggesting that the biodegradability of the wastewater has
Fig. 8. The operating of the aerobic reactor after CME + UASB treatment.
266
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267
been greatly improvement by the prepositive CME and UASB treatments, and the aerobic reactor could accommodate the wastewater well, resulting in the sufficient degradation of the colloidal and dissolved organic matter residue by the suspended microorganisms in the reactor, which could satisfy energetic needs (catabolism) for the suspended microorganisms [32]. But, when the OLR was increased to about 1.6 kg m 3 d 1 (40–45 d), COD removal decreased rapidly and could not recover in the following five days, it might be that the aerobic reactor entered into the overloading stage and the suspended microorganisms could not bear the impact of too much organics, leading to the inhibition of the suspended microorganisms and insufficient degradation of the residual organics. Consequently, the OLR was adjusted to about 1.2 kg m 3 d 1 (45–60 d), the COD removal increased gradually back to the previous level (about 85%), revealing that the aerobic reactor has recovered to the normal operation. To summary, the optimum OLR for the AS reactor should be selected as 1.2 kg m 3 d 1, when about 85% of COD removal was obtained and the COD in the final effluent (about 200 mg L 1) met the requirement of the national discharged standard (COD 6 300 mg L 1). Finally, the coupled CME-UASB-AS system could remove about 98% of COD in the raw monensin production wastewater. 3.5. Color removal by the coupled system Chroma (color) is an important index for wastewater and high colored wastewater is forbidden to discharge into the environment. Therefore, the decolorization rate of the coupled system was also investigated, and the result shows that the coupled system had high decolorization rate (approximately 95%) for the monensin production wastewater and the chroma in the final effluent (about 40) reached the requirement of the national discharged standard (chroma 6 60). It is noteworthy that the majority of chroma (94%) in the raw wastewater was removed by the CME reactor, four potential mechanisms were involved to explain the high decolorization rate by the CME reactor, including reduction, oxidation, precipitation and adsorption. Firstly, active radical ([H]), Fe0 and Fe2+ derived from the fillers and the CME reactions might reduce colored organic pollutants to colorless substances [33]. Secondly, a strong oxidizing agent (OH radicals) generated from the CME reactions could attack the chromophores of macromolecular and colored substances and finally mineralize them to CO2, H2O and mineralized products under the aerating and acid conditions [34]. Thirdly, iron(II) and iron(III) oxides/hydroxides generated from Fe corrosion might remove some colored substances by the precipitation effect [35]. Fourthly, the fillers could also remove some colored substances by adsorption effect, but this adsorption effect might be slight and weakened gradually, probably due to the soaking of the fillers in the raw wastewater for about one week before the starting of the whole experiment. It should be noted that the reduction, oxidation and precipitation reactions could be strengthened by Cu catalysis during the CME pretreatment, finally resulting in the high decolorization rate of the CME reactor. Additionally, during the whole study (about 150 d), the CME reactor could keep high and stable contaminants removal rate (about 98% of monensin residue, 37% of COD and 94% of chroma, data not shown), indicating that the CCF could keep active and the CME reactor operated effectively during the long-term operation. 3.6. Economic analysis of the CME-UASB-AS treatment process Economic analysis of the CME-UASB-AS treatment process is crucial for application of the system in practical projects. During the pilot-scale experiment in this study, the operating cost of the
coupled CME-UASB-AS system in this study mainly included three sections: (1) chemical agent cost, including HCl (for CME reactor) and NaHCO3 addition (for UASB and AS reactors), was about 0.31 Chinese Yuan for per ton wastewater; (2) electric charge, mainly resulting from the running of water pumps (for all reactors) and air pumps (for CME and AS reactors), reached approximately 11.56 Chinese Yuan for per ton wastewater; (3) heating cost, mainly utilized for wastewater heating (for UASB and AS reactors), was about 6.32 Chinese Yuan for per ton wastewater. To summary, the total operating cost of the whole CME-UASB-AS treatment process was about 18.19 Chinese Yuan (about 2.79 dollar) for per ton wastewater. 4. Conclusion In this study, novel fillers (CCF) prepared from solid waste (scrap iron), clay and copper sulfate solution were filled into the CME reactor and applied as the pretreatment to improve the anaerobic treatment effect for the real monensin production wastewater. The results showed that the CME reactor packed with the CCF had effective pretreatment effect, with about 98.44% and 37.07% of monensin residue and COD removal respectively at the optimum HRT of 3.0 h and DO of about 1.5 mg L 1. Subsequently, the effect of the UASB reactor applied as the secondary treatment was greatly improved by the CME pretreatment, with approximately 80% of COD removal at the optimum OLR of 3.5 kg m 3 d 1, which had higher methane yield and lower VFA concentration than that of the UASB reactor without pretreatment. This result suggested that the CME pretreatment before the UASB reactor was feasible, effective and essential for the wastewater treatment. Finally, the activated sludge (AS) process was utilized as the aerobic treatment after the UASB reactor, obtaining about 85% of COD removal at the optimum OLR of 1.2 kg m 3 d 1. To summary, the coupled CME-UASB-AS system applied as the real monensin production wastewater treatment progress was feasible and satisfactory, with a total COD and chroma removal of approximately 98% and 95% respectively, and the final effluent (COD and chroma of about 200 mg L 1 and 40, respectively) met the requirement of the national discharged standard (COD 6 300 mg L 1 and chroma 6 60), suggesting a promising potential system for the practical monensin production wastewater treatment projects. Acknowledgements The study was supported by the Science and technology project of Zhejiang Province (No. 2015F50059); The National Natural Science Foundation of China (No. 51378306 and No. 51478262); Shanghai Jiaotong University ‘Chenxing Plan (SMC-B)’; Shandong provincial environmental protection industry projects for technology research and development (No. SDHBYF-2012-12). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.cej.2016.03.140. References [1] J. Thaveesri, G. Boucneau, W. Verstraete, Effect of monensin on UASB-reactor performance, Environ. Technol. 15 (1994) 491–496. [2] C.A. Dellinger, J.G. Ferry, Effect of monensin on growth and methanogenesis of Methanobactericum formicium, Appl. Environ. Microb. 48 (1984) 680–682. [3] N. Yoshida, M. Castro, C. du Mortier, A.F. Cirelli, Environmental behavior of antibiotic monensin: preliminary studies in Argentina, Environ. Chem. Lett. 5 (2007) 157–160. [4] S.A. Hussain, S.O. Prasher, R.M. Patel, Removal of ionophoric antibiotics in free water surface constructed wetlands, Ecol. Eng. 41 (2012) 13–21.
S. Wu et al. / Chemical Engineering Journal 296 (2016) 260–267 [5] M. Rivero-Huguet, W.D. Marshall, Reduction of hexavalent chromium mediated by micro- and nano-sized mixed metallic particles, J. Hazard. Mater. 169 (2009) 1081–1087. [6] S. Mossa Hosseini, B. Ataie-Ashtiani, M. Kholghi, Nitrate reduction by nano-Fe/ Cu particles in packed column, Desalination 276 (2011) 214–221. [7] J. Trujillo-Reyes, V. Sánchez-Mendieta, A. Colín-Cruz, R.A. Morales-Luckie, Removal of indigo blue in aqueous solution using Fe/Cu nanoparticles and C/Fe/Cu nanoalloy composites, Water. Air. Soil. 207 (2009) 307–317. [8] Y.H. Kim, E.R. Carraway, Reductive dechlorination of TCE by zero valent bimetals, Environ. Technol. 24 (2003) 69–75. [9] G.S. Veeresh, P. Kumar, I. Mehrotra, Treatment of phenol and cresols in upflow anaerobic sludge blanket (UASB) process: a review, Water Res. 39 (2005) 154– 170. [10] M.A. Latif, R. Ghufran, Z.A. Wahid, A. Ahmad, Integrated application of upflow anaerobic sludge blanket reactor for the treatment of wastewaters, Water Res. 45 (2011) 4683–4699. [11] Y. Chen, J. He, Y. Mu, Y.-C. Huo, Z. Zhang, T.A. Kotsopoulos, R.J. Zeng, Mathematical modeling of upflow anaerobic sludge blanket (UASB) reactors: Simultaneous accounting for hydrodynamics and bio-dynamics, Chem. Eng. Sci. 137 (2015) 677–684. [12] T.G. Kim, J. Yun, K.S. Cho, The close relation between Lactococcus and Methanosaeta is a keystone for stable methane production from molasses wastewater in a UASB reactor, Appl. Microbiol. Biotechnol. 99 (2015) 8271– 8283. [13] F.J. Cervantes, R. Gomez, L.H. Alvarez, C.M. Martinez, V. Hernandez-Montoya, Efficient anaerobic treatment of synthetic textile wastewater in a UASB reactor with granular sludge enriched with humic acids supported on alumina nanoparticles, Biodegradation 26 (2015) 289–298. [14] W.C. Li, H. Chen, Y. Jin, H. Zhang, Q.G. Niu, W.K. Qi, Y.L. Zhang, Y.Y. Li, Y.X. Gao, Treatment of 3,4,5-trimethoxybenzaldehyde and Di-bromo-aldehyde manufacturing wastewater by the coupled Fenton pretreatment and UASB reactor with emphasis on optimization and chemicals analysis, Sep. Purif. Technol. 142 (2015) 40–47. [15] J. Carrillo-Reyes, L.B. Celis, F. Alatriste-Mondragón, E. Razo-Flores, Decreasing methane production in hydrogenogenic UASB reactors fed with cheese whey, Biomass. Bioenerg. 63 (2014) 101–108. [16] L. Zhu, J. Jin, H. Lin, K. Gao, X. Xu, Succession of microbial community and enhanced mechanism of a ZVI-based anaerobic granular sludge process treating chloronitrobenzenes wastewater, J. Hazard. Mater. 285 (2015) 157– 166. [17] C. Fang, K. Boe, I. Angelidaki, Biogas production from potato-juice, a byproduct from potato-starch processing, in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors, Bioresour. Technol. 102 (2011) 5734–5741. [18] A. Ahmad, R. Ghufran, Z. Abd, Wahid, Role of calcium oxide in sludge granulation and methanogenesis for the treatment of palm oil mill effluent using UASB reactor, J. Hazard. Mater. 198 (2011) 40–48.
267
[19] S. Wu, Y. Qi, S. He, C. Fan, B. Dai, W. Zhou, L. Gao, J. Huang, Preparation and application of novel catalytic-ceramic-filler in a coupled system for TNT manufacturing wastewater treatment, Chem. Eng. J. 280 (2015) 417–425. [20] Derek.G. Hillis, Linda. Lissemore, Paul.K. Sibley, K.R. Solomon, Effects of Monensin on Zooplankton Communities in Aquatic Microcosms, Environ. Sci. Technol. 41 (2007) 6620–6626. [21] S. Wu, Y. Qi, Y. Gao, Y. Xu, F. Gao, H. Yu, Y. Lu, Q. Yue, J. Li, Preparation of ceramic-corrosion-cell fillers and application for cyclohexanone industry wastewater treatment in electrobath reactor, J. Hazard. Mater. 196 (2011) 139–144. [22] Y.L. He, Anaerobic biological treatment of wastewater, China Light Industry Press, 1998. [23] J. Drewnowski, J. Makinia, The role of biodegradable particulate and colloidal organic compounds in biological nutrient removal activated sludge systems, Int. J. Environ. Sci. Te. 11 (2014) 1973–1988. [24] D. Ying, J. Peng, X. Xu, K. Li, Y. Wang, J. Jia, Treatment of mature landfill leachate by internal micro-electrolysis integrated with coagulation: a comparative study on a novel sequencing batch reactor based on zero valent iron, J. Hazard. Mater. 229–230 (2012) 426–433. [25] N. Sangkil, G.T. Paul, Reduction of azo dyes with zero-valent iron, Water Res. 34 (2000) 1837–1845. [26] Y. Du, M. Zhou, L. Lei, The role of oxygen in the degradation of p-chlorophenol by Fenton system, J. Hazard. Mater. 139 (2007) 108–115. [27] X. Liu, J.H. Fan, L.M. Ma, Oxidative degradation of EDTA in aqueous solution by the bimetallic Fe-Cu, Water. Air. Soil. 224 (2013) 1583. [28] M. Stieber, A. Putschew, M. Jekel, Treatment of pharmaceuticals and diagnostic agents using zero-valent iron-kinetic studies and assessment of transformation products assay, Environ. Sci. Technol. 45 (2011) 4944–4950. [29] J.H. Fan, L.M. Ma, The pretreatment by the Fe-Cu process for enhancing biological degradability of the mixed wastewater, J. Hazard. Mater. 164 (2009) 1392–1397. [30] V.H. Varel, A.G. Hashimoto, Effect of dietary monensin or chlortetracycline on methane production from cattle waste, Appl. Environ. Microb. 41 (1981) 29– 34. [31] R. Dai, Y. Liu, X. Liu, X. Zhang, C. Zeng, L. Li, Investigation of a sewageintegrated technology combining an expanded granular sludge bed (EGSB) and an electrochemical reactor in a pilot-scale plant, J. Hazard. Mater. 192 (2011) 1161–1170. [32] R. Hreiz, M.A. Latifi, N. Roche, Optimal design and operation of activated sludge processes: State-of-the-art, Chem. Eng. J. 281 (2015) 900–920. [33] O. Impert, A. Katafias, P. Kita, A. Mills, A. Pietkiewicz-Graczyk, G. Wrzeszcz, Kinetics and mechanism of a fast leuco-Methylene Blue oxidation by copper (ii)–halide species in acidic aqueous media, Dalton. T. (2003) 348–353. [34] X. Sun, T. Kurokawa, M. Suzuki, M. Takagi, Y. Kawase, Removal of cationic dye methylene blue by zero-valent iron: Effects of pH and dissolved oxygen on removal mechanisms, J. Environ. Sci. Heal. A. 50 (2015) 1057–1071. [35] B.H. Thomas, G.H. Cornelis, B.H. Stefan, H. Christof, P.S. René, Complete Reduction of TNT and Other (Poly)nitroaromatic Compounds under IronReducing Subsurface Conditions, Environ. Sci. Technol. 33 (1999) 1479–1487.