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Anaerobic treatment of real textile wastewater with a fluidized bed reactor
Water Research 37 (2003) 1868–1878
Anaerobic treatment of real textile wastewater with a fluidized bed reactor S. S- ena, G.N. Demirerb,* b
a Department of Civil and Environmental Engineering, San Diego State University, San Diego, CA 92182, USA Department of Environmental Engineering, Faculty of Engineering, Middle East Technical University, Inonu Bulvari, Ankara 06531, Turkey
Received 14 September 2001; received in revised form 11 November 2002; accepted 15 November 2002
Abstract Anaerobic treatability of a real cotton textile wastewater was investigated in a fluidized bed reactor (FBR) with pumice as the support material. The immobilized biomass or attached volatile solids level on the support material was 0.073 g VSS/g support material at the end of the 128-d start-up period. During the operation period, real cotton textile wastewater was fed to the anaerobic FBR both unsupplemented (in Stages 1 and 2) and supplemented (with synthetic municipal wastewater in Stage 3 and glucose in Stages 4–6). The effect of operational conditions such as organic loading rate (OLR), hydraulic retention time (HRT), influent glucose concentration as the co-substrate, etc. was investigated to achieve the maximum color removal efficiency in the reactor. Results indicated that anaerobic treatment of textile wastewater studied was possible with the supplementation of an external carbon source in the form of glucose (about 2 g/l). The corresponding maximum COD, BOD5 and color removals were found to be around 82%, 94% and 59%, respectively, for HRT of around 24 h and OLR of 3 kg COD/m3/d. Further increase in external carbon source added to real textile wastewater did not improve the color removal efficiency of the anaerobic FBR reactor. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Textile wastewater; Anaerobic; Decolorization; Fluidized bed reactor
1. Introduction Textile establishments receive and prepare fibers; transform fibers into yarn, thread, or webbing; convert the yarn into fabric or related products; and dye and finish these materials at various stages of production [1]. Textile manufacturing consumes a considerable amount of water in its manufacturing processes. The water is primarily utilized in the dyeing and finishing operations of the textile establishments. Considering both the volume generated and the effluent composition, the textile industry wastewater is rated as the most polluting among all industrial sectors.
*Corresponding author. E-mail address: [email protected] (G.N. Demirer).
Important pollutants in textile effluent are mainly recalcitrant organics, color, toxicants and inhibitory compounds, surfactants, chlorinated compounds (AOX), pH and salts. Dye is the most difficult constituent of the textile wastewater to treat. Azo dyes are the class of dyes most widely used industrially [2] having a world market share of 60–70%. Reactive azo dyes are becoming more popular in the textile industry, they are mainly used for cotton dyeing. However, reactive dyes hydrolyze easily, resulting in a high portion of unfixed (or hydrolyzed) reactive dyes, which have to be washed off during the dyeing process. As much as 50% of the initial dye load is present in the dye bath effluent [3]. Physico-chemical methods are applied for the treatment of this kind of wastewaters, achieving high dye removal efficiencies [4]. On the other hand, in recent
0043-1354/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0043-1354(02)00577-8
S. S - en, G.N. Demirer / Water Research 37 (2003) 1868–1878
years there is a tendency to use biological treatment systems to treat dye-bearing wastewaters [5]. The recalcitrant nature of azo dyes, together with their toxicity to microorganisms, makes aerobic treatment difficult. On the other hand, a wide range of azo dyes is decolorized anaerobically [6–9]. Under anaerobic conditions, azo dyes are readily cleaved via a four-electron reduction at the azo linkage generating aromatic amines. The required electrons are provided by electron donating carbon source such as starch, volatile fatty acids (VFA) or glucose. In addition, it is known that methanogenic and acetogenic bacteria in anaerobic microbial consortium contain unique reduced enzyme cofactors, such as F430 and vitamin B12 that could also potentially reduce azo bonds [10,11]. These steps remove color of the dye, however they do not completely mineralize the aromatic amines generated in the anaerobic environment [7,12,13] with a few exceptions [10,14]. Unfortunately, as suspect mutagens and carcinogens, the aromatic amines cannot be regarded as environmentally safe end products. On the other hand, it is known that most of the aromatic amines can be biodegraded under aerobic conditions [8,15,16]. Several high rate anaerobic reactor configurations have been developed for treating wastewaters at
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relatively short hydraulic retention times (HRT). Of these the anaerobic fluidized bed reactor (FBR) has been one of the technological advances. It has been successfully employed in a broad spectrum of wastewaters including both readily and hardly biodegradable wastes [17–19]. Although, in recent studies dealing with anaerobic treatment of textile wastewater several high rate anaerobic reactors such as upflow anaerobic sludge blanket reactors (UASB) and anaerobic baffled reactors (ABR) were used, no study was reported using FBR in textile wastewater treatment. Tables 1 and 2 provide summaries about performance of different anaerobic systems treating real and synthetic textile wastewater reported in the literature, respectively. Cotton manufacturing and dyeing are predominant in the Turkish textile sector which is one of the most important industrial sectors in the country both in terms of its contribution to economy and environmental emissions. Therefore, the aim of this study was to investigate the anaerobic treatability of a real cotton textile wastewater in a FBR. To this purpose, a FBR with pumice as the support material was operated. The effect of operational conditions such as OLR, HRT, influent glucose concentration as the co-substrate, etc. was also investigated.
Table 1 Performance of different anaerobic systems treating real textile wastewater Anaerobic system
Co-substrate
Influent COD (mg/l)
Baffled reactor
Two stage UASB
GAC amended UASB+SCAS UASB
OLR
HRT
color
Reference
COD
color
20 h
70
90
[32]
[9]
Sucrose+ peptone+nutrient (90%v/v) Tapiaco (black line)
1000
500 mg/l 1000 mg/l 1500 mg/l
646 1172 1675
155 SU
12 h
74 87 90
67 71 69
(red line) 0 200 mg/l 500 mg/l
408 619 940
150 SU
12 h
27 40 45
39 58 57
96 300 602 6000
150 SU
12 h
48 52 56 75
[38]
80
[31]
(blue line) 0 200 mg/l 500 mg/l No co-substrate
1200
1.2 g COD/l d
Removal rates (%)
0.8 OD (500 nm) 500 dil. factor
3.6 g COD/l d
1–2 d
13 73 84 80
2–2.4 g COD/ m3 d
8–10 h
60
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Table 2 Performance of different anaerobic systems treating simulated (synthetic) textile wastewater Dye
Dye type
Reactor type
Dye conc.
HRT
Mordant Blue 13 Mordant Black Basic Red Acid Yellow 151
Mono azo
Batch
100 mg/l
42 d
Direct Red 7 Acid Red 114 Direct Blue 15 Direct Yellow 12 Reactive Black 5 Acid Blue 113
Diazo
92 62 83 75 81 94
Direct Black 19 Direct Black 22 Reactive Blue 19 Acid Blue 80 Acid Blue 25 Basic Blue 22
Polyazo
51 61 70 7 67 62
Direct Yellow 11 Reactive Blue 21 Basic Blue 3 Acid Orange 3 Basic Yellow 28 MY3 Acid Red 27 4-Hydroxyazobenzene-4’sulphonic acid Acid Yellow 23 Acid Yellow 21 Reactive Yellow 16 Reactive Red 198 Reactive Red 141 Reactive Blue 220 Reactive Yellow 95 Reactive Orange 12 Reactive Red 218 Reactive Orange 13 Reactive Red 24 Reactive Brown 11 Reactive Black 39 Reactive Black 5 Reactive Blue 49 Blue PB Black SG Reactive Blue 38 Reactive Blue 21 Reactive Blue 72 Acid Orange 7 Acid Orange 8 Acid Orange 10 Acid Red 14 Acid Yellow 17 Basic Blue 3 Basic Red 2 Remazol Golden Yellow
Anthraquinone
Stilbene Phthalocyanine Oxazine Nitro Methine Azo
Batch
0.5 mmol/l
72 h
Azo
Batch
100 mg/l
Diazo Anthraquinone Metal complex
Batch
100 mg/l
Azo
FBR
5 mg/l
Azo Phenoxazine Acridine Azo
UASB
40 mg/l
6.5 h 2h 4.5 h 1h — 23 h 32 h 50 h 32 h 23 h 5.5 h 4.5 h 2h 2h 7.5 h 4.5 h 4.5 h 50 h 24 h 12 h 12 h 24 h 8–20 h
Batch
500 mg/l
24 h
Phthalocyanine
Color rem. (%) 83 77 92 88
53 36 62 62 35 51 37 43 6 98 80–90 85–90 85–90 90–95 0 90–95 90–95 85–90 90–97 90 70–75 80–85 7–10 98 75–80 40 85–90 25–30 90 98 81 86 20 72 78 78
Reference [7]
[37]
[8]
[16]
[36]
[40]
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Table 2 (continued) Dye
Dye type
Remazol Navy Blue GG Remazol Red RB Remazol Blue B Remazol Black B Cibracon Orange CG Cibracon Red C-2G Disperse Navy D2GR Remazol Turquoise Blue G113 Remazol Black B Mordant Orange 1 Mordant Orange 1 (MO1) Azodisalicylate (ADS) Azodisalicylate Acid Orange 7 Acid Yellow 36 Acid dye Acid Red 114 Acid Blue 25 Acid Yellow 27 Acid Yellow 151 Acid Back 24 Direct Red 7 Direct Blue 14 Direct Blue 15 Direct Yellow 12 Direct Yellow 50 Mordant Black 11 Mordant Black 9 Remazol Brilliant Violet 5R
Diazo
Phthalocyanine Diazo Azo
Reactor type
UAF UASB UASB
Batch
Reactive
Sequencing batch reactor Anaerobic filter reactor
Maxilon red BL-N
Basic
Acid Yellow 17 Pricion Red H-E7B
Acid Azo
UASB
Remazol Black B
Reactive anthraquinone oxazine
Sequencing batch reactor
Acid Yellow 17 Basic Blue 3 Basic Red 2 Orange II
Azo
200 mg/l
6–8.6 h
>99
[34]
16 h
No rem. 55–77
[35]
25 mg/l 150–450 mg/ l 20 mg/l
UASB
40 mg/l
Semicontinuous
100 mg/l
2.1. Fluidized bed reactor A 5.2 cm inner diameter, 73 cm long plexiglass tube was fused to a 15 cm inner diameter, 25 cm long tube to form the 4 l reactor body (Fig. 1). The enlarged top
Reference
90 mg/l
25 mg/l
2. Materials and methods
Color rem. (%)
48 h 8h 8h 8h 24 h 28 d 7d 28 d 7d 21 d 56 d 14 d 14 d 28 d 7d 7d 7d 35 d 7d 7d 15 d
UASB
Black 3HN
HRT
80 89 76 67 79 88 68 8 >95 95 >99 98.8 88.9 97 97 100 100 100 57 >90 100 98 >90 100 100 100 99 100 90
500 mg/l 100 mg/l 100 mg/l 75 mg/l 75 mg/l 100 mg/l
Azo
Remazol Blue R Cibacron Blue CR Pricon Blue H-EGN Azodisalicylate (ADS)
Dye conc.
18 h
0.33 d
61 57 67 44 91 95 20 72 78 >99
[41] [33] [5]
[15]
[39]
[42]
[5] [31]
[28]
>99
section was used as a gas–solid separator. The bottom of the reactor was flat with symmetrically placed four pores through which flow was equally distributed into the reactor. Five sampling ports were installed on the reactor wall to obtain solid samples. The effluent was collected by gravity through a loop connected to a port on the top section of the reactor. The recycle flow was
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Water trap
Effluent collection
Feed solution
Recycling pump
Magnetic stirrer
Sampling ports
Feeding pump
Inlet structure
Fig. 1. Schematic diagram of the anaerobic fluidized bed reactor (FBR) system.
drawn from the top section (5 cm below the free liquid surface) using a peristaltic pump and then fed upward into the reactor. Gas produced in the reactor was transferred through water trap to prevent the intake of oxygen from the atmosphere. Reactor was placed in a temperature-controlled room at 35721C. Pumice (HESS Pumice Products, Inc., Malan, Idaho, USA), with a diameter of 0.25–1.4 mm and particle density of 1764 kg/m3 was used as support material in the FBR. The start-up and operation periods of the anaerobic FBR are described below. 2.2. Start-up period The aim of the start-up period was to acquire biofilm formation on the support material. Mixed anaerobic cultures with mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) concentrations of 72.776.8 and 26.0371.37 g/l, respectively, was obtained from the anaerobic sludge digesters of the Ankara wastewater treatment plant. The feed contained methanol, glucose and yeast extract as well as basal medium (BM) during the start-up period. BM
contained all the necessary micro- and macro-nutrients for an optimum anaerobic microbial growth [20]. The composition of the BM was as follows (concentrations of the constituents are given in brackets as mg/l): NH4Cl (1200), MgSO4 7H2O (400), KCl (400), Na2S 9H2O (300), CaCl2 2H2O (50), (NH4)2 HPO4 (80), FeCl2 4H20 (40), CoCl2 6H20 (10), KI (10), MnCl2 4H20 (0.5), CuCl2 2H20 (0.5), ZnCl2 (0.5), AlCl3 6H20 (0.5), NaMoO4 2H2O (0.5), H3BO3 (0.5), NiCl2 6H20 (0.5), NaWO4 2H2O (0.5), Na2SeO3 (0.5), cysteine (10) and NaHCO3 (3000). During the start-up period the COD loading was gradually raised by increasing the feed rate while keeping the influent COD constant at around 5000 mg/ l. The yeast extract concentration in the feed was 20 mg/l and the remaining COD was supplied by methanol and glucose at different ratios (Table 3). Methanol which provided 50% of the total influent COD (5000 mg/l) initially encouraged the growth of methanosarcina [21]. The contribution of methanol in the total influent COD was decreased to 25%, 12.5%, and 0% on days 25, 38, and 46, respectively, by replacing it with glucose. Moreover, NH4Cl concentration was gradually increased to its value in BM (1200 mg/l) to obtain high initial C/N ratios during the start-up period to encourage extracellular polymer production, which aids bacterial attachment on solid surface (Table 3). 2.3. Operation period In the operation period, the reactor was fed with the real textile wastewater obtained from dye bath effluent of a dye house in Ankara, Turkey. Wastewater characterization was done for wastewater in each different container that was used for experimental practice (Table 4). In the dye house, reactive dyes namely Remazol, Everzol and Levafix types of dyes are commonly used. FBR was operated under 6 different operational conditions. These conditions are tabulated in Table 5. 2.4. Analytical methods pH measurements were performed with a pH meter (Model 2906, Jenway Ltd., UK) and a pH probe (G05992-55, Cole Parmer Instrument Co., USA). COD of samples were measured by Hach spectrophotometer (Model no P/N 45600-02) and vials for 0–1500 mg/l COD. Suspended solids and volatile suspended solids were measured as described in Standard Methods 2540 D, E. Total phosphorus and total Khjeldahl nitrogen concentrations were also determined by Standard Methods 4500-P-E and 4500-Norg, respectively [22]. To measure the immobilized biomass, sample from the expanded bed material was collected in a ceramic dish through a sampling port (5–10 ml). Suspended biomass
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Table 3 Organic load and percentage of methanol and ammonium chloride during the start-up Time (days)
COD loading (kg COD/m3 d)
Methanol (% of total COD)
Glucose+yeast (% of total COD)
NH4Cla
0–24 25–37 38–45 46–128
0–3.75 3.75–10 10–15 15–22
50 25 12.5 0
50 75 87.5 100
50 75 100 100
a
% of its value at the end of the start-up.
Table 4 Characteristics of real textile wastewater Parameters
Container 1
Container 2
Container 3
Container 4
pH BOD5 (mg/l) COD (mg/l) SS (mg/l) TKN (mg/l) PO4 3 (mg/l) SO4 2 (mg/l) Cl 1 (mg/l) Color (at 669 nm)
9.91 170714.14 1029767.4 180716 22.5172.05 2.3970.09 2.3670.38 609.8 0.21
9.9 162.570 1157.57100 11079 20.7870.55 2.1670.08 1.9470.33 594.8728.3 0.18
8.9 90721 1062.67760.7 13075 57.0674.51 1.4270.07 4.2370.06 557.33710.6 0.16
8.9 97.573.5 1018711.3 180784.8 55.8170.5 0.9270.07 6.4370.14 569.877.07 0.15
Table 5 Different operational conditions applied to the FBR Container no and on which day it was used
Stage
Operation days
OLR (kg COD/ m3 d)
HRT (h)
Feed composition
Influent COD conc. (mg/l)
1-1–14 2-15–46 3-47–86 4-87–118
1 2 3 4 5 6
1–46 47–62 63–77 78–91 92–105 106–118
1 0.5 0.38 1.3 3 5
24 50 50 24 24 24
TW TW TW: SMW (3:1) TW+glucose TW+glucose TW+glucose
1030 1162 850 1500 3000 6000
in the mixed liquor was removed by gentle wash then, it was dried at 1051C for 24 h. The dried sample was then muffled at 6001C for 1 h. The difference between two dried weights would yield the weight of immobilized biomass as attached volatile solids (AVS). Color was measured by UV–Vis spectrophotometer (Varian Cary 100 Conc, Australia) at peak absorption wavelength of real textile wastewater (669 nm). Before analysis, samples were filtered through 0.45 mm filters to remove suspended matters.
3. Results and discussion Start-up period was completed in 128 d. The AVS concentration (0.0732 g VSS/g support) attained at the end of the start-up period was within the typical range
reported in the literature such as 0.074–0.11 [23], 0.039 [43], 0.05 [24], and 0.0375–0.429 g VSS/g support [25]. Table 6 shows operational parameters obtained at the end of start-up period. The bed expansion was 19% during the start-up period. It was increased to and kept between 35% and 40% in the operation period which is in the typical range reported in the literature [26,27]. After the start-up period, the real textile wastewater was fed to the reactor. The corresponding organic loading rate (OLR), HRT, effluent pH, VFA and alkalinity values, influent and effluent COD and BOD5 values, COD and BOD5 removal, influent and effluent color and color removal are depicted in Fig. 2. As seen in Table 5, the FBR was operated under 6 different operating conditions (stages) with the aim of increasing the color removal efficiency in the reactor for a 118-d period.
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Table 6 Operational parameters at the end of start-up period for FBR Operational parameters 3
OLR (kg COD/m d) HRT (h) Upflow velocity (m/h) Qrecycle =Qfeed Expansion (%) Volume of expanded bed (cm3) Msupport (g) g VSS/g support Total VSS (g) g VSS/l expanded bed
FBR 23 5.7 19 295 19 700 620 0.0732 45.4 64.8
Providing an optimum growth condition for methanogens is critical for color removal. It is known that methanogenic and acetogenic bacteria in anaerobic cultures contain unique reduced enzyme cofactors, such as F430 and vitamin B12 that could also potentially reduce azo bonds. It is therefore, not surprising that azo reduction rates are sensitive to the amount of available substrate in an anaerobic system as well as the loading rate, since catabolism of these substrate is responsible for the production of reduced enzyme cofactor [5]. As a result, low color removal with low COD removal performance was an expected outcome. 3.2. Stage 2 (days 47–62)
3.1. Stage 1 (days 1–46) In this stage, real textile wastewater was fed to the reactor without any additional carbon and nutrient source, only alkalinity was added (with different concentrations, see Fig. 2e) prior to feeding. Average COD concentration of real textile wastewater was 1100 mg/l. During Stage 1, OLR was kept at around 1 kg COD/ m3 d. HRT applied to the reactor was around 24 h (Fig. 2b). pH of the effluent was around 9 (Fig. 2c), which did not vary much during the operation period. The optimum reactor operation conditions were achieved in anaerobic systems when pH and alkalinity values are greater than 6.5 and 800 mg/l (as CaCO3), respectively and when VFA concentration is lower than 250 mg/l. Effluent alkalinity concentration was between 580 and 750 mg/l (as CaCO3) (Fig. 2e) and VFA concentration in the effluent was lower than 100 mg/l during the operation period (Fig. 2e). Both VFA and alkalinity data supported that the reactor was operating properly. As seen in Fig. 2g, COD removal in the reactor during Stage 1 varied over time. COD removal efficiency decreased from 59% to 27% between day 10 and 18, possibly due to the toxic effect of real textile wastewater. After acclimation of anaerobic microorganisms to real textile wastewater, a gradual increase in the COD removal rate was recorded. On day 33, COD removal rate reached to 68% and from that point on it did not change much. Fig. 2h and i depict that BOD5 removal rate in Stage 1 showed the same pattern with COD removal. On day 10, BOD5 removal was 98%, however it decreased to 45% in 7 d. After the cultures were acclimated to the feed, the BOD5 removal increased to 84% on day 25 and did not vary considerably for the rest of this stage. During the first 24 d, no color removal was observed in the effluent (Fig. 2j and k). This period was considered as the acclimation period after which the onset of color removal was observed with the increase in COD removal rate (Fig. 2g and k). The color removal rate was 37% on day 41.
In Stage 2, HRT applied to the reactor was increased from 24 to about 50 h (Table 5) to observe the effect of this increase on the color removal efficiency of the system. Since the influent COD concentration was the same (around 1100 mg/l), the OLR decreased to 0.5 kg COD/m3 d with the increase in HRT. With the increase in HRT from 24 to 50 h, the COD and BOD removal rates decreased to about half of their values at the end of Stage 1. In other words, COD and BOD5 removal rates dropped to 35% and 39%, respectively. As seen from Fig. 2j and k the color removal rate also decreased to 19% during Stage 2 (day 61). Decrease in COD, BOD5 and color removal performances with the decrease in OLR is understandable due to low synthesis of unique reduced enzyme cofactors (F430 and vitamin B12) responsible for color reduction under anaerobic conditions. Therefore, it can be stated that an increase in HRT alone did not result in the increased color removal. 3.3. Stage 3 (days 63–77) Combined treatment of textile and municipal wastewater was simulated in this stage. This practice is advantageous wherever applicable. Because many treatment problems such as flow, alkalinity, temperature extremes and fluctuations are solved by treating textile and municipal wastewater together. Furthermore, municipal wastewater may supply the necessary nutrients for the biological growth. In this period, textile wastewater was mixed with synthetic municipal wastewater (SMW) at 3:1 ratio. The composition of the SMW solution was 500 mg/l glucose, 27 mg/l urea, 22 mg/l KH2PO4 and 1000 mg/l Na2CO3. COD and BOD of the mixture were between 800–900 and 90 mg/l, respectively. HRT was kept constant at about 50 h (Fig. 2b), OLR decreased to about 0.38 kg COD/m3 d. Upon this change in the feed composition, the BOD5 removal rate increased to 90% while COD removal rate remained around 40% in this stage.
HRT (hr)
OLR 3 (kg COD/m .d)
S. S - en, G.N. Demirer / Water Research 37 (2003) 1868–1878 Stage 2
Stage 3
OLR=0.5 HRT= 50 h
TW : SMW (3:1)
Stage 4
Stage 5
TW+glucose TW+glucose (3000 mg/L (1500 mg/L COD) COD)
Stage 6 TW+glucose (6000 mg/L COD)
(a)
6 4 2 0
(b)
60 40 20
(c)
10 pH
Stage 1 3 OLR=1 (kg COD/m .d) HRT= 1 d
1875
9 8
VFA (mg/L)
200
(d)
150 100
(mg CaCO3/L)
Color removal (as absorbance)
Absorbance @ 669 nm
BOD5 (mg/L) BOD5 COD removal removal (%) (%)
COD (mg/L)
Alkalinity
50 0 (e)
1500 1000 500 0 6000
(f)
4000 2000 120 100 80 60 40 20 6000
(g)
(h)
4000 2000 100 80 60 40 20
(i)
0.25 0.20 0.15 0.10 0.05 0.00 80 60 40 20 0
(j)
(k)
0
10
20
30
40
50
60
70
80
90
100
Time (days) Influent alkalinity
Effluent Influent
Fig. 2. Operation period for FBR treating real textile wastewater.
110
120
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As seen from Fig. 2j and k, color removal decreased sharply to zero, then increased to 12% (day 76) as the maximum value in this stage. It is evident that color removal performance of the reactor was adversely effected from this change in the influent composition. Combined treatment of textile and municipal wastewater did not result in any gain in terms of color removal over the treatment of textile wastewater alone (Stage 2). 3.4. Stage 4 (days 78–91) In Stage 4, an external carbon source was added to the textile wastewater in the form of glucose at a concentration of about 500 mg/l yielding an influent COD concentration of about 1500 mg/l (Table 5). At the same time the HRT of the reactor was decreased from 50 to about 24 h which resulted in an OLR of 1.3 kg COD/ m3 d. With the addition of 500 mg/l of glucose as the external carbon source and corresponding increase in the influent COD concentration, BOD5 and COD removals increased to 94% and 62–66%, respectively. While the color removal increased to 40–44% (Fig. 2k). A significant increase in the color removal performance of the FBR is noteworthy in this stage. This improvement was due to the addition of external carbon source, which helps to ascertain a reducing environment and possibly increase the concentration of enzyme cofactors, such as F430 and vitamin B12 in the reactor that could also potentially reduce azo bonds [5] and hence resulting in better color removal. 3.5. Stage 5 (days 92–105) After observing the stimulative effect of the addition of 500 mg/l of glucose as the external carbon source in Stage 4, glucose concentration was increased to about 2 g/l to observe the effect of increasing the concentration of the external carbon source. With this increase in the glucose concentration, the influent COD concentration and OLR applied to the reactor increased to about 3000 mg/l and 3 kg COD/m3 d, respectively (Table 5). COD and color removal rates increased to 78–82% and 54–59% from earlier values of 62–66% and 40– 44%, respectively (Fig. 2g and k). While the BOD5 removal rate in the reactor was around 94%. From these figures it was clear that increasing the glucose concentration from 500 to 2000 mg/l resulted in significantly better performance of the FBR both in terms of organics and color removal. 3.6. Stage 6 (days 106–118) In Stage 6, the concentration of glucose as the external carbon source was increased further to about 5000 mg/l
to observe any additional improvement in the performance of the FBR. As seen in Table 5, this change in the glucose concentration increased the influent COD concentration to around 6000 mg/l and the OLR to 5 kg COD/m3 d. In this stage although the COD and BOD5 removal rates increased to 89% and 99%, respectively, color removal did not increase significantly and stayed around 62% (Fig. 2j and k). As a result, it was observed that further increase in the glucose, thus influent COD concentration did not improve the color removal efficiency of the system considerably. Therefore, Stage 5 (textile wastewater with 2 g/l glucose addition) represented the optimum condition for maximum color removal in the real textile wastewater investigated in this study.
4. Conclusions Apart from the aesthetic deterioration and obstruction for penetration of dissolved oxygen into the natural water bodies caused by the presence of color, some of the dyes, dye precursors and the dye degradation products are carcinogenic and mutagenic in nature [28]. Existing physico-chemical methods for decolorization such as advanced oxidation processes like the use of Fenton’s reagent (H2O2+Fe2+), hydrogen peroxide, ozonation are costly in terms of operation costs and produce problematic sludge. Coagulation–flocculation produce high amounts of sludge which pose handling and disposal problems. Activated carbon adsorption, membrane filtration, ion exchange, irradiation, and electrokinetic coagulation are also uneconomical and/ or not very established [4,28,29]. Biological treatment methods, on the other hand, provide efficient and low cost means of textile wastewater treatment [6,30]. Conventional aerobic treatment systems are not efficient [4,5,31]. Decolorization of dyes using pure (algal, fungal, and bacterial) cultures is impractical as most of the isolated cultures are dye specific [28]. However, decolorization of dyes and/or treatment of textile wastewaters under strict anaerobic conditions is well documented [5,7–9,15,28,30,32,33]. Because the textile sector in Turkey is one of the most important industrial sectors both in terms of its contribution to economy and environmental emissions, efficient and cost-effective treatment methods are needed. Therefore, anaerobic treatability of a real cotton textile wastewater was investigated in a FBR with pumice as the support material. The results indicated that the anaerobic treatability of the textile wastewater studied was found to be optimal upon the addition of an external carbon source in the form of 2 g/l glucose (with the influent COD concentration of 3000 mg/l). COD, BOD5 and color removals achieved were around 82%, 94% and 59%, respectively. The observed improvement
S. S - en, G.N. Demirer / Water Research 37 (2003) 1868–1878
in the color removal with the addition of 2 g/l of glucose is in agreement with the literature which underline the importance of external carbon source supplementation to anaerobic reactors treating dyes/textile wastewater [5,9,31,32,34,35]. Further increase in external carbon source adding to textile wastewater did not improve the color removal efficiency of the system. Finally, the requirement of glucose addition as the external carbon source to the textile wastewater with a concentration of 2 g/l might be a concern in terms of the practical applicability of anaerobic treatment. However, it should be kept in mind that anaerobic treatment compared to physico-chemical treatment methods still offers a viable option in terms of cost.
[11]
[12]
[13]
[14]
[15]
Acknowledgements This study was funded by the State Planning Organization of the Republic of Turkey. Dr. Metin M. Duran of Villanova University is deeply appreciated for his valuable suggestions and help in obtaining the support material used in the FBRs.
[16]
[17]
[18]
References [19] [1] EPA Office of Compliance Sector Notebook Project: Profile of the Textile Industry, EAA/310-R-97-009, September 1997. [2] Fitzgerald SW, Bishop PL. Two-stage anaerobic/aerobic treatment of sulfonated azo dyes. J Environ Sci Health A 1995;30:1251–76. [3] Shore J. Dyeing with reactive dyes. In: Cellulosics Dyeing. Oxford, Manchester, UK: The Alden Press, 1995. [4] Vandevivere PC, Bianchi R, Verstraete W. Treatment and reuse of wastewater from the textile wet-processing industry: Review of emerging technologies. J Chem Technol Biotech 1998;72:289–302. [5] Razo-Flores E, Luijten M, Donlon B, Lettinga G, Field J. Biodegradation of selected azo dyes under methanogenic conditions. Water Sci Technol 1997;36:65–72. [6] Banat IM, Nigam P, Singh D, Marchant R. Microbial decolorization of textile-dye-containing effluents: a review. Biores Technol 1996;58:217–27. [7] Brown D, Laboureur P. The degradation of dyestuffs: 1. Primary biodegradation under anaerobic conditions. Chemosphere 1983;12:397–404. [8] Carliell CM, Barclay SJ, Naidoo N, Buckley CA, Mulholland DA, Senior E. Microbial decolorization of a reactive azo-dye under anaerobic conditions. Water SA 1995; 21:61–9. [9] Chinwekitvanich S, Tuntoolvest M, Panswad T. Anaerobic decolorization of reactive dyebath effluents by a twostage UASB system with tapioca as a co-substrate. Water Res 2000;34:2223–32. [10] Razo-Flores E, Donlon B, Field J, Lettinga G. Biodegradability of N-substituted aromatics and alkylphenols under
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methanogenic conditions using granular sludge. Water Sci Technol 1996;33:47–57. Zaoyan Y, Ke S, Guangliang S, Fan Y, Jinshan D, Huanian M. Anaerobic-aerobic treatment of a dye wastewater by combination of RBC with activated sludge. Water Sci Technol 1992;26:2093–6. Kool HJ. Influence of microbial biomass on the biodegradability of organic compounds. Chemosphere 1984; 13:751–61. Zeyer J, Wasserfallen A, Timmis KN. Microbial mineralization of ring-substituted anilines through an ortocleavage pathway. Appl Environ Microbiol 1985;50: 447–53. O’Connor OA, Young LY. Effect of nitrogen limitation on the biodegradability and toxicity of nitrophenol and aminophenol isomers to methanogenesis. Arch Environ Contam Toxicol 1993;25:285–91. Brown D, Hamburger B. The degradation of dye stuffs: 3 Investigations of their ultimate degradability. Chemosphere 1987;16:1539–53. Seshadri S, Bishop PL, Agha AM. Anaerobic/aerobic treatment of selected azo dyes in wastewater. Waste Manage 1994;14:127–37. Denac M, Dunn IJ. Packed-bed and fluidized bed biofilm reactor performance for anaerobic wastewater treatment. Biotech Bioeng 1988;32:159–73. Henze M, Harremoes P. Anaerobic treatment of wastewater in fixed film reactors - a literature review. Water Sci Technol 1983;15:1–101. Hickey RF, Owens RW. Methane generation from high strength industrial wastes with the anaerobic biological fluidized bed, Biotech. Bioeng Suppl 1981;11:399–413. Demirer GN, Speece RE. Toxicity of acrylic acid to acetate-enriched methanosarcina cultures. J Environ Eng Div ASCE 1998;124:345–52. Boone DR, Bryant MP. Propionate-degrading bacteria from methanogenic ecosystems. 80th General Meeting of the American Society for Microbiology. Miami Beach, FL, USA: American Society for Microbiology, 1980. Standard Methods for the Examination of Water and Wastewater. 20th ed. Washington, DC: APHA, AWWA, WEF, 1997. Farhan MH, ChinHong PH, Keenan JD, Shieh WK. Performance of anaerobic reactors during pseudosteady-state operation. J Chem Technol Biotech 1997; 69:45–57. Garcia-Bernet D, Buffiere P, Elmaleh S, Moletta R. Application of the down-flow fluidized bed to the anaerobic treatment of wine distillery wastewater. Water Sci Technol 1998;38:393–9. Perez M, Romero LI, Sales D. Anaerobic thermophilic fluidized-bed treatment of industrial wastewater—effect of F-M relationship. Chemosphere 1999;38:3443–61. Balaguer MD, Vicent MT, Paris JM. Utilization of pumice stone as support for the anaerobic treatment of vinasse with a fluidized-bed reactor. Environ Technol 1991;12: 1167–73. Stronach SM, Diazbaez MC, Rudd T, Lester JN. Factors affecting biomass attachment during startup and operation of anaerobic fluidized-beds. Biotech Bioeng 1987;30: 611–20.
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[28] Manu B, Chaudhari S. Anaerobic decolorisation of simulated textile wastewater containing azo dyes. Biores Technol 2002;82:225–31. [29] Robinson T, McMullan G, Marchant R, Nigam P. Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative. Biores Technol 2001;77:247–55. [30] Beydilli MI, Pavlostathis SG, Tincher WC. Decolorization and toxicity screening of selected reactive azo dyes under methanogenic conditions. Water Sci Technol 1998;38:225–32. [31] Huren A, Yi Q, Xiasheng G. A way for water pollution control in dye manufacturing industry. 49th Purdue Industrial Waste Conference Proceedings, Chelsea, MI, USA: Lewis Publishers, 1994. [32] Bell J, Plumb JJ, Buckley CA, Stuckey DC. Treatment and decolorization of dyes in an anaerobic baffled reactor. J Environ Eng Div ASCE 2000;126:1026–32. [33] Donlon B, Razo-Flores E, Luijten M, Swarts H, Lettinga G, Field J. Detoxification and partial mineralization of the azo dye mordant orange 1 in a continuous upflow anaerobic sludge-blanket reactor. Appl Microbiol Biotech 1997;47:83–90. [34] Basibuy . uk . M, Forster CF. The use of sequential anaerobic/aerobic processes for the biotreatment of a simulated dyeing wastewater. Environ Technol 1997;18:843–8. [35] O’Neill C, Hawkes FR, Hawkes DL, Esteves S, Wilcox SJ. Anaerobic-aerobic biotreatment of simulated textile effluent containing varied ratios of starch and azo dye. Water Res 2000;34:2355–61.
[36] An H, Qian Y, Gu XS, Tang WZ. Biological treatment of dye wastewaters using an anaerobic-oxic system. Chemosphere 1996;33:2533–42. [37] Haug W, Schmidt A, Nortemann B, Hempel DC, Stolz A, Knackmuss HJ. Mineralization of the sulfonated azo dye mordant yellow-3 by a 6-aminonaphthalene-2-sulfonatedegrading bacterial consortium. Appl Environ Microbiol 1991;57:3144–9. [38] Kuai L, De Vreese I, Vandevivere P, Verstraete W. GACamended UASB reactor for the stable treatment of toxic textile wastewater. Environ Technol 1998;19:1111–7. [39] Lourenc-o ND, Novais JM, Pinheiro HM. Reactive textile dye color removal in a sequencing batch reactor. Water Sci Technol 2000;42:321–8. [40] Nigam P, Banat IM, Singh D, Marchant R. Microbial process for the decolorization of textile effluent containing azo, diazo and reactive dyes. Process Biochem 1996; 31:435–42. [41] Oxspring DA, McMullan G, Smyth WF, Marchant R. Decolourisation and metabolism of the reactive textile dye, remazol black B, by an immobilized microbial consortium. Biotech Lett 1996;18:527–30. [42] Panswad T, Luangdilok W. Decolorization of reactive dyes with different molecular structures under different environmental conditions. Water Res 2000; 34:4177–84. [43] Meraz M, Monroy O, Noyola A, Ilangovan K. Studies on the dynamics of immobilization of anaerobic bacteria on a plastic support. Water Sci Technol 1995;32:243–50.
Anaerobic treatment of real textile wastewater with a fluidized bed reactor S. S- ena, G.N. Demirerb,* b
a Department of Civil and Environmental Engineering, San Diego State University, San Diego, CA 92182, USA Department of Environmental Engineering, Faculty of Engineering, Middle East Technical University, Inonu Bulvari, Ankara 06531, Turkey
Received 14 September 2001; received in revised form 11 November 2002; accepted 15 November 2002
Abstract Anaerobic treatability of a real cotton textile wastewater was investigated in a fluidized bed reactor (FBR) with pumice as the support material. The immobilized biomass or attached volatile solids level on the support material was 0.073 g VSS/g support material at the end of the 128-d start-up period. During the operation period, real cotton textile wastewater was fed to the anaerobic FBR both unsupplemented (in Stages 1 and 2) and supplemented (with synthetic municipal wastewater in Stage 3 and glucose in Stages 4–6). The effect of operational conditions such as organic loading rate (OLR), hydraulic retention time (HRT), influent glucose concentration as the co-substrate, etc. was investigated to achieve the maximum color removal efficiency in the reactor. Results indicated that anaerobic treatment of textile wastewater studied was possible with the supplementation of an external carbon source in the form of glucose (about 2 g/l). The corresponding maximum COD, BOD5 and color removals were found to be around 82%, 94% and 59%, respectively, for HRT of around 24 h and OLR of 3 kg COD/m3/d. Further increase in external carbon source added to real textile wastewater did not improve the color removal efficiency of the anaerobic FBR reactor. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Textile wastewater; Anaerobic; Decolorization; Fluidized bed reactor
1. Introduction Textile establishments receive and prepare fibers; transform fibers into yarn, thread, or webbing; convert the yarn into fabric or related products; and dye and finish these materials at various stages of production [1]. Textile manufacturing consumes a considerable amount of water in its manufacturing processes. The water is primarily utilized in the dyeing and finishing operations of the textile establishments. Considering both the volume generated and the effluent composition, the textile industry wastewater is rated as the most polluting among all industrial sectors.
*Corresponding author. E-mail address: [email protected] (G.N. Demirer).
Important pollutants in textile effluent are mainly recalcitrant organics, color, toxicants and inhibitory compounds, surfactants, chlorinated compounds (AOX), pH and salts. Dye is the most difficult constituent of the textile wastewater to treat. Azo dyes are the class of dyes most widely used industrially [2] having a world market share of 60–70%. Reactive azo dyes are becoming more popular in the textile industry, they are mainly used for cotton dyeing. However, reactive dyes hydrolyze easily, resulting in a high portion of unfixed (or hydrolyzed) reactive dyes, which have to be washed off during the dyeing process. As much as 50% of the initial dye load is present in the dye bath effluent [3]. Physico-chemical methods are applied for the treatment of this kind of wastewaters, achieving high dye removal efficiencies [4]. On the other hand, in recent
0043-1354/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0043-1354(02)00577-8
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years there is a tendency to use biological treatment systems to treat dye-bearing wastewaters [5]. The recalcitrant nature of azo dyes, together with their toxicity to microorganisms, makes aerobic treatment difficult. On the other hand, a wide range of azo dyes is decolorized anaerobically [6–9]. Under anaerobic conditions, azo dyes are readily cleaved via a four-electron reduction at the azo linkage generating aromatic amines. The required electrons are provided by electron donating carbon source such as starch, volatile fatty acids (VFA) or glucose. In addition, it is known that methanogenic and acetogenic bacteria in anaerobic microbial consortium contain unique reduced enzyme cofactors, such as F430 and vitamin B12 that could also potentially reduce azo bonds [10,11]. These steps remove color of the dye, however they do not completely mineralize the aromatic amines generated in the anaerobic environment [7,12,13] with a few exceptions [10,14]. Unfortunately, as suspect mutagens and carcinogens, the aromatic amines cannot be regarded as environmentally safe end products. On the other hand, it is known that most of the aromatic amines can be biodegraded under aerobic conditions [8,15,16]. Several high rate anaerobic reactor configurations have been developed for treating wastewaters at
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relatively short hydraulic retention times (HRT). Of these the anaerobic fluidized bed reactor (FBR) has been one of the technological advances. It has been successfully employed in a broad spectrum of wastewaters including both readily and hardly biodegradable wastes [17–19]. Although, in recent studies dealing with anaerobic treatment of textile wastewater several high rate anaerobic reactors such as upflow anaerobic sludge blanket reactors (UASB) and anaerobic baffled reactors (ABR) were used, no study was reported using FBR in textile wastewater treatment. Tables 1 and 2 provide summaries about performance of different anaerobic systems treating real and synthetic textile wastewater reported in the literature, respectively. Cotton manufacturing and dyeing are predominant in the Turkish textile sector which is one of the most important industrial sectors in the country both in terms of its contribution to economy and environmental emissions. Therefore, the aim of this study was to investigate the anaerobic treatability of a real cotton textile wastewater in a FBR. To this purpose, a FBR with pumice as the support material was operated. The effect of operational conditions such as OLR, HRT, influent glucose concentration as the co-substrate, etc. was also investigated.
Table 1 Performance of different anaerobic systems treating real textile wastewater Anaerobic system
Co-substrate
Influent COD (mg/l)
Baffled reactor
Two stage UASB
GAC amended UASB+SCAS UASB
OLR
HRT
color
Reference
COD
color
20 h
70
90
[32]
[9]
Sucrose+ peptone+nutrient (90%v/v) Tapiaco (black line)
1000
500 mg/l 1000 mg/l 1500 mg/l
646 1172 1675
155 SU
12 h
74 87 90
67 71 69
(red line) 0 200 mg/l 500 mg/l
408 619 940
150 SU
12 h
27 40 45
39 58 57
96 300 602 6000
150 SU
12 h
48 52 56 75
[38]
80
[31]
(blue line) 0 200 mg/l 500 mg/l No co-substrate
1200
1.2 g COD/l d
Removal rates (%)
0.8 OD (500 nm) 500 dil. factor
3.6 g COD/l d
1–2 d
13 73 84 80
2–2.4 g COD/ m3 d
8–10 h
60
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Table 2 Performance of different anaerobic systems treating simulated (synthetic) textile wastewater Dye
Dye type
Reactor type
Dye conc.
HRT
Mordant Blue 13 Mordant Black Basic Red Acid Yellow 151
Mono azo
Batch
100 mg/l
42 d
Direct Red 7 Acid Red 114 Direct Blue 15 Direct Yellow 12 Reactive Black 5 Acid Blue 113
Diazo
92 62 83 75 81 94
Direct Black 19 Direct Black 22 Reactive Blue 19 Acid Blue 80 Acid Blue 25 Basic Blue 22
Polyazo
51 61 70 7 67 62
Direct Yellow 11 Reactive Blue 21 Basic Blue 3 Acid Orange 3 Basic Yellow 28 MY3 Acid Red 27 4-Hydroxyazobenzene-4’sulphonic acid Acid Yellow 23 Acid Yellow 21 Reactive Yellow 16 Reactive Red 198 Reactive Red 141 Reactive Blue 220 Reactive Yellow 95 Reactive Orange 12 Reactive Red 218 Reactive Orange 13 Reactive Red 24 Reactive Brown 11 Reactive Black 39 Reactive Black 5 Reactive Blue 49 Blue PB Black SG Reactive Blue 38 Reactive Blue 21 Reactive Blue 72 Acid Orange 7 Acid Orange 8 Acid Orange 10 Acid Red 14 Acid Yellow 17 Basic Blue 3 Basic Red 2 Remazol Golden Yellow
Anthraquinone
Stilbene Phthalocyanine Oxazine Nitro Methine Azo
Batch
0.5 mmol/l
72 h
Azo
Batch
100 mg/l
Diazo Anthraquinone Metal complex
Batch
100 mg/l
Azo
FBR
5 mg/l
Azo Phenoxazine Acridine Azo
UASB
40 mg/l
6.5 h 2h 4.5 h 1h — 23 h 32 h 50 h 32 h 23 h 5.5 h 4.5 h 2h 2h 7.5 h 4.5 h 4.5 h 50 h 24 h 12 h 12 h 24 h 8–20 h
Batch
500 mg/l
24 h
Phthalocyanine
Color rem. (%) 83 77 92 88
53 36 62 62 35 51 37 43 6 98 80–90 85–90 85–90 90–95 0 90–95 90–95 85–90 90–97 90 70–75 80–85 7–10 98 75–80 40 85–90 25–30 90 98 81 86 20 72 78 78
Reference [7]
[37]
[8]
[16]
[36]
[40]
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Table 2 (continued) Dye
Dye type
Remazol Navy Blue GG Remazol Red RB Remazol Blue B Remazol Black B Cibracon Orange CG Cibracon Red C-2G Disperse Navy D2GR Remazol Turquoise Blue G113 Remazol Black B Mordant Orange 1 Mordant Orange 1 (MO1) Azodisalicylate (ADS) Azodisalicylate Acid Orange 7 Acid Yellow 36 Acid dye Acid Red 114 Acid Blue 25 Acid Yellow 27 Acid Yellow 151 Acid Back 24 Direct Red 7 Direct Blue 14 Direct Blue 15 Direct Yellow 12 Direct Yellow 50 Mordant Black 11 Mordant Black 9 Remazol Brilliant Violet 5R
Diazo
Phthalocyanine Diazo Azo
Reactor type
UAF UASB UASB
Batch
Reactive
Sequencing batch reactor Anaerobic filter reactor
Maxilon red BL-N
Basic
Acid Yellow 17 Pricion Red H-E7B
Acid Azo
UASB
Remazol Black B
Reactive anthraquinone oxazine
Sequencing batch reactor
Acid Yellow 17 Basic Blue 3 Basic Red 2 Orange II
Azo
200 mg/l
6–8.6 h
>99
[34]
16 h
No rem. 55–77
[35]
25 mg/l 150–450 mg/ l 20 mg/l
UASB
40 mg/l
Semicontinuous
100 mg/l
2.1. Fluidized bed reactor A 5.2 cm inner diameter, 73 cm long plexiglass tube was fused to a 15 cm inner diameter, 25 cm long tube to form the 4 l reactor body (Fig. 1). The enlarged top
Reference
90 mg/l
25 mg/l
2. Materials and methods
Color rem. (%)
48 h 8h 8h 8h 24 h 28 d 7d 28 d 7d 21 d 56 d 14 d 14 d 28 d 7d 7d 7d 35 d 7d 7d 15 d
UASB
Black 3HN
HRT
80 89 76 67 79 88 68 8 >95 95 >99 98.8 88.9 97 97 100 100 100 57 >90 100 98 >90 100 100 100 99 100 90
500 mg/l 100 mg/l 100 mg/l 75 mg/l 75 mg/l 100 mg/l
Azo
Remazol Blue R Cibacron Blue CR Pricon Blue H-EGN Azodisalicylate (ADS)
Dye conc.
18 h
0.33 d
61 57 67 44 91 95 20 72 78 >99
[41] [33] [5]
[15]
[39]
[42]
[5] [31]
[28]
>99
section was used as a gas–solid separator. The bottom of the reactor was flat with symmetrically placed four pores through which flow was equally distributed into the reactor. Five sampling ports were installed on the reactor wall to obtain solid samples. The effluent was collected by gravity through a loop connected to a port on the top section of the reactor. The recycle flow was
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Water trap
Effluent collection
Feed solution
Recycling pump
Magnetic stirrer
Sampling ports
Feeding pump
Inlet structure
Fig. 1. Schematic diagram of the anaerobic fluidized bed reactor (FBR) system.
drawn from the top section (5 cm below the free liquid surface) using a peristaltic pump and then fed upward into the reactor. Gas produced in the reactor was transferred through water trap to prevent the intake of oxygen from the atmosphere. Reactor was placed in a temperature-controlled room at 35721C. Pumice (HESS Pumice Products, Inc., Malan, Idaho, USA), with a diameter of 0.25–1.4 mm and particle density of 1764 kg/m3 was used as support material in the FBR. The start-up and operation periods of the anaerobic FBR are described below. 2.2. Start-up period The aim of the start-up period was to acquire biofilm formation on the support material. Mixed anaerobic cultures with mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) concentrations of 72.776.8 and 26.0371.37 g/l, respectively, was obtained from the anaerobic sludge digesters of the Ankara wastewater treatment plant. The feed contained methanol, glucose and yeast extract as well as basal medium (BM) during the start-up period. BM
contained all the necessary micro- and macro-nutrients for an optimum anaerobic microbial growth [20]. The composition of the BM was as follows (concentrations of the constituents are given in brackets as mg/l): NH4Cl (1200), MgSO4 7H2O (400), KCl (400), Na2S 9H2O (300), CaCl2 2H2O (50), (NH4)2 HPO4 (80), FeCl2 4H20 (40), CoCl2 6H20 (10), KI (10), MnCl2 4H20 (0.5), CuCl2 2H20 (0.5), ZnCl2 (0.5), AlCl3 6H20 (0.5), NaMoO4 2H2O (0.5), H3BO3 (0.5), NiCl2 6H20 (0.5), NaWO4 2H2O (0.5), Na2SeO3 (0.5), cysteine (10) and NaHCO3 (3000). During the start-up period the COD loading was gradually raised by increasing the feed rate while keeping the influent COD constant at around 5000 mg/ l. The yeast extract concentration in the feed was 20 mg/l and the remaining COD was supplied by methanol and glucose at different ratios (Table 3). Methanol which provided 50% of the total influent COD (5000 mg/l) initially encouraged the growth of methanosarcina [21]. The contribution of methanol in the total influent COD was decreased to 25%, 12.5%, and 0% on days 25, 38, and 46, respectively, by replacing it with glucose. Moreover, NH4Cl concentration was gradually increased to its value in BM (1200 mg/l) to obtain high initial C/N ratios during the start-up period to encourage extracellular polymer production, which aids bacterial attachment on solid surface (Table 3). 2.3. Operation period In the operation period, the reactor was fed with the real textile wastewater obtained from dye bath effluent of a dye house in Ankara, Turkey. Wastewater characterization was done for wastewater in each different container that was used for experimental practice (Table 4). In the dye house, reactive dyes namely Remazol, Everzol and Levafix types of dyes are commonly used. FBR was operated under 6 different operational conditions. These conditions are tabulated in Table 5. 2.4. Analytical methods pH measurements were performed with a pH meter (Model 2906, Jenway Ltd., UK) and a pH probe (G05992-55, Cole Parmer Instrument Co., USA). COD of samples were measured by Hach spectrophotometer (Model no P/N 45600-02) and vials for 0–1500 mg/l COD. Suspended solids and volatile suspended solids were measured as described in Standard Methods 2540 D, E. Total phosphorus and total Khjeldahl nitrogen concentrations were also determined by Standard Methods 4500-P-E and 4500-Norg, respectively [22]. To measure the immobilized biomass, sample from the expanded bed material was collected in a ceramic dish through a sampling port (5–10 ml). Suspended biomass
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Table 3 Organic load and percentage of methanol and ammonium chloride during the start-up Time (days)
COD loading (kg COD/m3 d)
Methanol (% of total COD)
Glucose+yeast (% of total COD)
NH4Cla
0–24 25–37 38–45 46–128
0–3.75 3.75–10 10–15 15–22
50 25 12.5 0
50 75 87.5 100
50 75 100 100
a
% of its value at the end of the start-up.
Table 4 Characteristics of real textile wastewater Parameters
Container 1
Container 2
Container 3
Container 4
pH BOD5 (mg/l) COD (mg/l) SS (mg/l) TKN (mg/l) PO4 3 (mg/l) SO4 2 (mg/l) Cl 1 (mg/l) Color (at 669 nm)
9.91 170714.14 1029767.4 180716 22.5172.05 2.3970.09 2.3670.38 609.8 0.21
9.9 162.570 1157.57100 11079 20.7870.55 2.1670.08 1.9470.33 594.8728.3 0.18
8.9 90721 1062.67760.7 13075 57.0674.51 1.4270.07 4.2370.06 557.33710.6 0.16
8.9 97.573.5 1018711.3 180784.8 55.8170.5 0.9270.07 6.4370.14 569.877.07 0.15
Table 5 Different operational conditions applied to the FBR Container no and on which day it was used
Stage
Operation days
OLR (kg COD/ m3 d)
HRT (h)
Feed composition
Influent COD conc. (mg/l)
1-1–14 2-15–46 3-47–86 4-87–118
1 2 3 4 5 6
1–46 47–62 63–77 78–91 92–105 106–118
1 0.5 0.38 1.3 3 5
24 50 50 24 24 24
TW TW TW: SMW (3:1) TW+glucose TW+glucose TW+glucose
1030 1162 850 1500 3000 6000
in the mixed liquor was removed by gentle wash then, it was dried at 1051C for 24 h. The dried sample was then muffled at 6001C for 1 h. The difference between two dried weights would yield the weight of immobilized biomass as attached volatile solids (AVS). Color was measured by UV–Vis spectrophotometer (Varian Cary 100 Conc, Australia) at peak absorption wavelength of real textile wastewater (669 nm). Before analysis, samples were filtered through 0.45 mm filters to remove suspended matters.
3. Results and discussion Start-up period was completed in 128 d. The AVS concentration (0.0732 g VSS/g support) attained at the end of the start-up period was within the typical range
reported in the literature such as 0.074–0.11 [23], 0.039 [43], 0.05 [24], and 0.0375–0.429 g VSS/g support [25]. Table 6 shows operational parameters obtained at the end of start-up period. The bed expansion was 19% during the start-up period. It was increased to and kept between 35% and 40% in the operation period which is in the typical range reported in the literature [26,27]. After the start-up period, the real textile wastewater was fed to the reactor. The corresponding organic loading rate (OLR), HRT, effluent pH, VFA and alkalinity values, influent and effluent COD and BOD5 values, COD and BOD5 removal, influent and effluent color and color removal are depicted in Fig. 2. As seen in Table 5, the FBR was operated under 6 different operating conditions (stages) with the aim of increasing the color removal efficiency in the reactor for a 118-d period.
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Table 6 Operational parameters at the end of start-up period for FBR Operational parameters 3
OLR (kg COD/m d) HRT (h) Upflow velocity (m/h) Qrecycle =Qfeed Expansion (%) Volume of expanded bed (cm3) Msupport (g) g VSS/g support Total VSS (g) g VSS/l expanded bed
FBR 23 5.7 19 295 19 700 620 0.0732 45.4 64.8
Providing an optimum growth condition for methanogens is critical for color removal. It is known that methanogenic and acetogenic bacteria in anaerobic cultures contain unique reduced enzyme cofactors, such as F430 and vitamin B12 that could also potentially reduce azo bonds. It is therefore, not surprising that azo reduction rates are sensitive to the amount of available substrate in an anaerobic system as well as the loading rate, since catabolism of these substrate is responsible for the production of reduced enzyme cofactor [5]. As a result, low color removal with low COD removal performance was an expected outcome. 3.2. Stage 2 (days 47–62)
3.1. Stage 1 (days 1–46) In this stage, real textile wastewater was fed to the reactor without any additional carbon and nutrient source, only alkalinity was added (with different concentrations, see Fig. 2e) prior to feeding. Average COD concentration of real textile wastewater was 1100 mg/l. During Stage 1, OLR was kept at around 1 kg COD/ m3 d. HRT applied to the reactor was around 24 h (Fig. 2b). pH of the effluent was around 9 (Fig. 2c), which did not vary much during the operation period. The optimum reactor operation conditions were achieved in anaerobic systems when pH and alkalinity values are greater than 6.5 and 800 mg/l (as CaCO3), respectively and when VFA concentration is lower than 250 mg/l. Effluent alkalinity concentration was between 580 and 750 mg/l (as CaCO3) (Fig. 2e) and VFA concentration in the effluent was lower than 100 mg/l during the operation period (Fig. 2e). Both VFA and alkalinity data supported that the reactor was operating properly. As seen in Fig. 2g, COD removal in the reactor during Stage 1 varied over time. COD removal efficiency decreased from 59% to 27% between day 10 and 18, possibly due to the toxic effect of real textile wastewater. After acclimation of anaerobic microorganisms to real textile wastewater, a gradual increase in the COD removal rate was recorded. On day 33, COD removal rate reached to 68% and from that point on it did not change much. Fig. 2h and i depict that BOD5 removal rate in Stage 1 showed the same pattern with COD removal. On day 10, BOD5 removal was 98%, however it decreased to 45% in 7 d. After the cultures were acclimated to the feed, the BOD5 removal increased to 84% on day 25 and did not vary considerably for the rest of this stage. During the first 24 d, no color removal was observed in the effluent (Fig. 2j and k). This period was considered as the acclimation period after which the onset of color removal was observed with the increase in COD removal rate (Fig. 2g and k). The color removal rate was 37% on day 41.
In Stage 2, HRT applied to the reactor was increased from 24 to about 50 h (Table 5) to observe the effect of this increase on the color removal efficiency of the system. Since the influent COD concentration was the same (around 1100 mg/l), the OLR decreased to 0.5 kg COD/m3 d with the increase in HRT. With the increase in HRT from 24 to 50 h, the COD and BOD removal rates decreased to about half of their values at the end of Stage 1. In other words, COD and BOD5 removal rates dropped to 35% and 39%, respectively. As seen from Fig. 2j and k the color removal rate also decreased to 19% during Stage 2 (day 61). Decrease in COD, BOD5 and color removal performances with the decrease in OLR is understandable due to low synthesis of unique reduced enzyme cofactors (F430 and vitamin B12) responsible for color reduction under anaerobic conditions. Therefore, it can be stated that an increase in HRT alone did not result in the increased color removal. 3.3. Stage 3 (days 63–77) Combined treatment of textile and municipal wastewater was simulated in this stage. This practice is advantageous wherever applicable. Because many treatment problems such as flow, alkalinity, temperature extremes and fluctuations are solved by treating textile and municipal wastewater together. Furthermore, municipal wastewater may supply the necessary nutrients for the biological growth. In this period, textile wastewater was mixed with synthetic municipal wastewater (SMW) at 3:1 ratio. The composition of the SMW solution was 500 mg/l glucose, 27 mg/l urea, 22 mg/l KH2PO4 and 1000 mg/l Na2CO3. COD and BOD of the mixture were between 800–900 and 90 mg/l, respectively. HRT was kept constant at about 50 h (Fig. 2b), OLR decreased to about 0.38 kg COD/m3 d. Upon this change in the feed composition, the BOD5 removal rate increased to 90% while COD removal rate remained around 40% in this stage.
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As seen from Fig. 2j and k, color removal decreased sharply to zero, then increased to 12% (day 76) as the maximum value in this stage. It is evident that color removal performance of the reactor was adversely effected from this change in the influent composition. Combined treatment of textile and municipal wastewater did not result in any gain in terms of color removal over the treatment of textile wastewater alone (Stage 2). 3.4. Stage 4 (days 78–91) In Stage 4, an external carbon source was added to the textile wastewater in the form of glucose at a concentration of about 500 mg/l yielding an influent COD concentration of about 1500 mg/l (Table 5). At the same time the HRT of the reactor was decreased from 50 to about 24 h which resulted in an OLR of 1.3 kg COD/ m3 d. With the addition of 500 mg/l of glucose as the external carbon source and corresponding increase in the influent COD concentration, BOD5 and COD removals increased to 94% and 62–66%, respectively. While the color removal increased to 40–44% (Fig. 2k). A significant increase in the color removal performance of the FBR is noteworthy in this stage. This improvement was due to the addition of external carbon source, which helps to ascertain a reducing environment and possibly increase the concentration of enzyme cofactors, such as F430 and vitamin B12 in the reactor that could also potentially reduce azo bonds [5] and hence resulting in better color removal. 3.5. Stage 5 (days 92–105) After observing the stimulative effect of the addition of 500 mg/l of glucose as the external carbon source in Stage 4, glucose concentration was increased to about 2 g/l to observe the effect of increasing the concentration of the external carbon source. With this increase in the glucose concentration, the influent COD concentration and OLR applied to the reactor increased to about 3000 mg/l and 3 kg COD/m3 d, respectively (Table 5). COD and color removal rates increased to 78–82% and 54–59% from earlier values of 62–66% and 40– 44%, respectively (Fig. 2g and k). While the BOD5 removal rate in the reactor was around 94%. From these figures it was clear that increasing the glucose concentration from 500 to 2000 mg/l resulted in significantly better performance of the FBR both in terms of organics and color removal. 3.6. Stage 6 (days 106–118) In Stage 6, the concentration of glucose as the external carbon source was increased further to about 5000 mg/l
to observe any additional improvement in the performance of the FBR. As seen in Table 5, this change in the glucose concentration increased the influent COD concentration to around 6000 mg/l and the OLR to 5 kg COD/m3 d. In this stage although the COD and BOD5 removal rates increased to 89% and 99%, respectively, color removal did not increase significantly and stayed around 62% (Fig. 2j and k). As a result, it was observed that further increase in the glucose, thus influent COD concentration did not improve the color removal efficiency of the system considerably. Therefore, Stage 5 (textile wastewater with 2 g/l glucose addition) represented the optimum condition for maximum color removal in the real textile wastewater investigated in this study.
4. Conclusions Apart from the aesthetic deterioration and obstruction for penetration of dissolved oxygen into the natural water bodies caused by the presence of color, some of the dyes, dye precursors and the dye degradation products are carcinogenic and mutagenic in nature [28]. Existing physico-chemical methods for decolorization such as advanced oxidation processes like the use of Fenton’s reagent (H2O2+Fe2+), hydrogen peroxide, ozonation are costly in terms of operation costs and produce problematic sludge. Coagulation–flocculation produce high amounts of sludge which pose handling and disposal problems. Activated carbon adsorption, membrane filtration, ion exchange, irradiation, and electrokinetic coagulation are also uneconomical and/ or not very established [4,28,29]. Biological treatment methods, on the other hand, provide efficient and low cost means of textile wastewater treatment [6,30]. Conventional aerobic treatment systems are not efficient [4,5,31]. Decolorization of dyes using pure (algal, fungal, and bacterial) cultures is impractical as most of the isolated cultures are dye specific [28]. However, decolorization of dyes and/or treatment of textile wastewaters under strict anaerobic conditions is well documented [5,7–9,15,28,30,32,33]. Because the textile sector in Turkey is one of the most important industrial sectors both in terms of its contribution to economy and environmental emissions, efficient and cost-effective treatment methods are needed. Therefore, anaerobic treatability of a real cotton textile wastewater was investigated in a FBR with pumice as the support material. The results indicated that the anaerobic treatability of the textile wastewater studied was found to be optimal upon the addition of an external carbon source in the form of 2 g/l glucose (with the influent COD concentration of 3000 mg/l). COD, BOD5 and color removals achieved were around 82%, 94% and 59%, respectively. The observed improvement
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in the color removal with the addition of 2 g/l of glucose is in agreement with the literature which underline the importance of external carbon source supplementation to anaerobic reactors treating dyes/textile wastewater [5,9,31,32,34,35]. Further increase in external carbon source adding to textile wastewater did not improve the color removal efficiency of the system. Finally, the requirement of glucose addition as the external carbon source to the textile wastewater with a concentration of 2 g/l might be a concern in terms of the practical applicability of anaerobic treatment. However, it should be kept in mind that anaerobic treatment compared to physico-chemical treatment methods still offers a viable option in terms of cost.
[11]
[12]
[13]
[14]
[15]
Acknowledgements This study was funded by the State Planning Organization of the Republic of Turkey. Dr. Metin M. Duran of Villanova University is deeply appreciated for his valuable suggestions and help in obtaining the support material used in the FBRs.
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