- Email: [email protected]
Disinfection and solubilization of sewage sludge using the microwave enhanced advanced oxidation process
Journal of Hazardous Materials 181 (2010) 1143–1147
Contents lists available at ScienceDirect
Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Disinfection and solubilization of sewage sludge using the microwave enhanced advanced oxidation process Y. Yu, W.I. Chan, P.H. Liao, K.V. Lo ∗ Department of Civil Engineering, University of British Columbia, 6250 Applied Science Lane, Vancouver, BC V6T 1Z4, Canada
a r t i c l e
i n f o
Article history: Received 5 January 2010 Received in revised form 7 April 2010 Accepted 30 May 2010 Available online 4 June 2010 Keywords: Microwave radiation Disinfection Fecal coliforms regrowth Nutrient release
a b s t r a c t The microwave enhanced advanced oxidation process (MW/H2 O2 -AOP) was used to treat municipal sewage sludge for solids disintegration, nutrient solubilization, with an emphasis on pathogen destruction and regrowth. Pathogen reduction, in terms of fecal coliform concentrations were found below detection limit (1000 CFU/L) immediately after treatment when sludge was treated at 70 ◦ C with more than 0.04% of H2 O2 (w/w). Significant regrowth of fecal coliforms was observed for the treated samples after 72 h. However, no regrowth was observed for samples treated at 70 ◦ C with 0.08% H2 O2 or higher, suggesting a complete elimination of fecal coliforms. The range of hydrogen peroxide used did not have a significant effect on orthophosphate release regardless of temperature. Ammonia release at these low temperatures was found to be insignificant. The soluble chemical oxygen demand increased with an increase of hydrogen peroxide dosage at 70 ◦ C. However, there was no clear trend of soluble chemical oxygen demand over varying hydrogen peroxide dosage at 55 ◦ C. The MW/H2 O2 -AOP is a novel process for the pasteurization and stabilization of sewage sludge to meet and maintain Class A biosolids criteria. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The treatment and disposal of waste activated sludge is a major concern for municipal wastewater treatment facilities due to its health and environmental impacts, as well as handling and disposal costs. Sludge typically contains high levels of organic matters, nutrients, and metals [1]; hence they can be used as fertilizers for agricultural land applications. 54% of the produced sludge was applied to agricultural, horticultural, forest, and reclamation land in USA [2]; however, it poses a health threat because of the possible increase in soil-borne diseases associated with the land application of sludge. Pathogens entering the soil may also lead to both surface and ground water contamination since any member of the allochthonous or indigenous microbiota in soil will eventually end up in an aquatic environment or be dispersed in aerosols [3,4]. When sludge is used as fertilizers or soil conditioners, they may come into contact with fruits or vegetables, and induce food-borne diseases. Sludge now must meet stringent pathogen reduction regulations, which is specified in the Standards for the Use or Disposal of Sewage Sludge, before it can be used for land applications [5]. The pathogen reduction requirements are divided into two levels, Class A and Class B, depending on the extent of pathogen reduction. In Class B, disinfection is incomplete; fecal coliform levels are
∗ Corresponding author. Tel.: +1 604 822 4880; fax: +1 604 822 6901. E-mail address: [email protected] (K.V. Lo). 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.05.134
reduced to below 2 million colony forming units (CFU) per gram of total solids dry weight [5]. Disinfection is more complete in Class A, where fecal coliform levels are less than 1000 most probable numbers (MPN) per gram of total solids dry weight [5]. Microwave radiation has recently been applied to sludge for disinfection purposes [6]. It was found that 45 kW s (90 s at 500 W) of microwave radiation produced approximately a 4.8 log reduction of Escherichia coli. Complete inactivation of fecal coliform (to below detection limits) immediately after treatment, could be achieved with 60 kW s and 90 kW s (1 kW for 60 s and 90 s) for primary and waste activated sludge, respectively [7,8]. It should also be noted that the microwave at a frequency of 2450 MHz and less are also capable of denaturing DNA molecules and disassociating organic chemical bonds [9]. Hydrogen peroxide is well known for its antiseptic properties. It had been tested as a means of disinfection when applied independently or in combination with other chemicals. In a study where hydrogen peroxide was used in combination with iron (II) sulfate (Fenton’s reagent) to treat pig and cattle slurry, the total fecal coliform level was reduced by 99.9% [10]. Wagner et al. also found that hydrogen peroxide can effectively reduce fecal coliform in wastewater effluent to the target level of 10,000 CFU/100 mL, but the high dosage and long contact time required clearly made the option uneconomical [11]. No attempt to check for the regrowth of fecal coliform has been found in these studies either. The microwave enhanced advanced oxidation process (MW/H2 O2 -AOP) utilizes both microwave radiation and hydrogen
1144
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
peroxide simultaneously, generating hydroxyl radicals which could significantly improve nutrient solubilization for treating sludge and other substrates [12–15]. The synergistic effect of microwave radiation and hydrogen peroxide on the process was more pronounced at higher temperatures. In terms of pathogens destruction, microwaves alone could cause significant inactivation of fecal coliforms and Salmonella spp. in wastewater sludge [8]. A strong synergistic effect of microwave heating and hydrogen peroxide was observed in the destruction of E. coli pure culture [16]. However, the combined treatment with hydrogen peroxide and microwave radiation has not been tested for the destruction of pathogens in sewage sludge. Another important factor is coliform regrowth, which is an essential aspect to truly meeting Class A biosolids requirements as well as the safety of the operators while handling what is perceived as “disinfected sludge”. Due to the large quantities of sludge handling, a small percentage of regrowth constitutes up to an unsafe number of fecal coliforms in aerosols or contactable areas to the operator. Consequently, the purpose of this study was to investigate sludge disinfection with the consideration for pathogen regrowth and nutrient solubilization using the MW/H2 O2 -AOP. Low hydrogen peroxide dosages (0.02–0.1%) and a low temperature regime (55–70 ◦ C) were chosen to economize the process and create treatment temperature conditions to be more comparable to that of conventional thermal treatment conditions. 2. Materials and methods 2.1. Microwave apparatus The Milestone Ethos TC closed vessel Microwave Labstation (Milestone Inc., USA) was used in this study. It operates at a frequency of 2450 MHz with a maximum power output of 1000 W. The Labstation has the capacity of handling up to 12 vessels for the microwave treatment in a single run: 1 reference vessel and 11 sample vessels, each with a volume of 100 mL. A thermocouple is inserted into the reference vessel and is connected to the control panel, thus providing real time temperature monitoring during the runs. A magnetic mixing device allows for the stirring of the samples in the vessels during the microwave process. The microwave system can attain a maximum temperature of 220 ◦ C and a pressure up to 30 bars. 2.2. Experimental design Fresh secondary aerobic activated sludge with a sludge retention time of approximately 17 days was obtained from the activated sludge wastewater treatment pilot plant located at the south campus of the University of British Columbia. Characteristics of the secondary aerobic sludge are listed in Table 1. For the treatment process, the experiments were divided into two parts, i.e., with and without the microwave treatments. For the first part, two different temperatures of 55 ◦ C and 70 ◦ C, and six levels of hydrogen peroxide dosage (0–0.1% as (w/w) in 0.02% increments) were selected. Five replicates at each treatment condition were heated in the microwave Labstation at a temperature increTable 1 Characteristics of raw sludge. Parameters
Concentration
SCOD (mg/L) TCOD (mg/L) TS (%) TP (mg/L) TKN (mg/L) FC counts (CFU/L)
59–70 3967–4076 0.32 155–176 405–459 5.8 × 106 to 10.0 × 106
ment rate of approximately 20 ◦ C/min, up to the desired treatment temperature, and the samples were subsequently held for 5.5 min at the set temperature within the Labstation. The procedures have been developed through our previous studies and other research groups have also adopted similar ones [12–15]. For the second part, sludge samples were treated by the same varying dosages of hydrogen peroxide for 4 h at ambient temperature (approximately 22–23 ◦ C) without microwave radiation. For the part of the pathogen disinfection and regrowth of this study, fecal coliforms were chosen as indicator organisms for the MW/H2 O2 -AOP. Samples were prepared immediately after the treatment for microbial examinations. Sludge samples treated with microwave radiation at 70 ◦ C were retained in closed sterile bottles and stored at ambient temperature for 72 h for fecal coliform regrowth. Fecal coliform concentrations were compared to the concentrations immediately after the treatment. 2.3. Chemical analysis and microbial examination Unfiltered, raw sludge samples were analyzed for total chemical oxygen demand (TCOD), total phosphate (TP), total Kjeldahl nitrogen (TKN) and total solids (TS) according to the Standard Methods [17]. Three of the five treated replicate samples were centrifuged at 4000 rpm for 10 min and the supernatant was subsequently collected and passed through a 1.6 m fibreglass filter paper. The supernatant was analyzed for ammonia (ammonia-N), orthophosphate (ortho-P), and soluble chemical oxygen demand (SCOD). Ortho-P, ammonia-N concentrations were determined using the flow injection analysis (Lachat Quick-Chem 8000 Automated Ion Analyzer, Lachat Instruments, USA), and SCOD was determined using the colorimetric method according to that outlined in Standard Methods [17]. Fecal coliform concentrations were determined using the membrane filtration technique, which is described in Standard Methods Part 9222D [17]. Two of five treated sludge samples were appropriately diluted to six different dilutions with distilled water, so that the fecal coliform colonies count in each diluted sample cultured in the next stage was between 10 and 200. The diluted samples were passed through 0.45 m sterilized, gridded membranes where microorganisms were retained. Petri dishes containing agar and DifcoTM mFC broth base were prepared according to the manufacturer’s instruction. The filters were then placed on the prepared Petri dishes and incubated at 45 ◦ C for 24 ± 2 h. Fecal coliform colonies were counted after incubation. The dilutions with fecal coliform colonies counts (at least 2) within the range were averaged and tabulated. The fecal coliforms concentrations were reported in colony forming units per liter (CFU/L). The detection limit for the analyses was 1000 CFU/L. 3. Results and discussion 3.1. Nutrient release The results of nutrient release and COD release are summarized in Table 2. The ortho-P release decreased from 27.4 mg/L to 15.7 mg/L as hydrogen peroxide dosage increased from 0% to 0.1% at 70 ◦ C. The decrease in ortho-P concentration further confirms the previous report that polyphosphate was formed when sludge was treated by microwave radiation and H2 O2 at intermediate temperatures between 60 ◦ C and 80 ◦ C [18–20]. The addition of hydrogen peroxide did not have much influence on ortho-P release at 55 ◦ C, indicating limited interaction between microwave radiation and hydrogen peroxide. The synergistic effects of microwave radiation and hydrogen peroxide are more pronounced at high microwave treatment temperatures [15]. The results from previous studies and
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
1145
Table 2 Results of organic matter and nutrients solubilization after treatments. H2 O2 dosage (%)
0 0.02 0.04 0.06 0.08 0.1 a
Microwave at 55 ◦ C
Without microwave
Microwave at 70 ◦ C
SCOD (mg/L)
Ortho-P (mg/L)
Ammonia-N (mg/L)
SCOD (mg/L)
Ortho-P (mg/L)
Ammonia-N (mg/L)
SCOD (mg/L)
Ortho-P (mg/L)
Ammonia-N (mg/L)
– 59.1(7.2)a 52.8(15.0) 63.7(12.6) 61.0(6.9) 61.0(5.8)
– 10.1(0.4) 10.3(0.3) 15.6(0.8) 21.5(0.9) 25.0(0.9)
– 5.6(0.2) 7.1(0.2) 4.1(2.7) 2.1(0.3) 8.8(0.4)
353(10.9) 370(20.6) 407(23.5) 302(20.4) 309(15.5) 331(12.3)
14.0(0.9) 16.2(0.7) 18.6(1.4) 12.9(0.6) 12.2(0.4) 12.9(1.3)
2.7(0.1) 2.7(0.3) 3.3(0.4) 2.5(0.2) 2.6(0.1) 2.4(0.1)
450(52.8) 713(84.9) 812(11.0) 847(11.0) 924(22.0) 996(12.5)
27.4(0.1) 17.7(0.8) 17.0(0.7) 15.4(1.5) 18.2(0.4) 15.7(0.9)
3.5(0.0) 3.2(0.1) 3.5(0.2) 3.2(0.9) 4.8(1.0) 2.6(1.1)
Mean (standard deviation) of three replicates.
Table 3 Comparison of solubilization results with previous studies. TS (%)
H2 O2 (% by wt.)
H2 O2 :TS
Temperature (◦ C)
P release (%)
COD release (%)
Kenge et al. [18]
2.9 1.8 1.1
7.2 3.7 2.2
2.5:1 2.1:1 2.0:1
80 80 80
14–16 8–9 9–10
19–25 18–22 25–28
Lo et al. [19]
1.0 1.0
1.0 1.0
1:1 1:1
60 80
15 9
15 18
This study
0.32
0.02–0.1
0.06:1–0.31:1
70
9–10
17–25
this study are listed in Table 3. The nutrient release levels were comparable to past studies, even with much lower hydrogen peroxide dosage in this study. As mentioned earlier, microwave temperature was a significant factor for ortho-P release; the hydrogen peroxide dosage was not a factor for its solubilization at these low treatment temperatures and a short treatment time. It was therefore concluded that high releases of ortho-P could not be achieved in low temperatures regimes (60–80 ◦ C), regardless of the hydrogen peroxide dosage applied. When the sludge was treated by H2 O2 alone at ambient temperature, ortho-P release remained relatively constant until H2 O2 dosages exceeded 0.04%, at which point ortho-P concentration increased with an increase in H2 O2 dosage. The highest concentration of ortho-P of 25 mg/L was obtained at 0.1% of H2 O2 (Table 2). However, it should be noted that the samples were treated for 4 h, thus, the higher ortho-P release could be solely due to hydrogen peroxide treatment over a longer treatment time. In general, the release of ammonia is low at the tested temperatures. The highest concentration of soluble ammonia was less than 4.8 mg/L, obtained at 70 ◦ C with a dosage of 0.08% H2 O2 for the MW/H2 O2 -AOP, while the highest yield was 8.8 mg/L at a dosage of 0.1% H2 O2 , with a longer reaction time of 4 h ambient temperature without microwave radiation (Table 2). No clear trend was observed for ammonia yield in this narrow range of H2 O2 dosages and low treatment temperatures. The SCOD remained relatively constant for H2 O2 treatments at ambient temperature without microwave radiation, regardless of H2 O2 dosage. When sludge was treated at a microwave temperature of 55 ◦ C, the COD release was in the range of 300–400 mg/L. The increase of hydrogen peroxide dosages did not affect the COD release significantly (Table 2). It was obvious that the addition of hydrogen peroxide increased the COD release at 70 ◦ C (Table 2). The maximum SCOD concentration was approximately 1000 mg/L (∼25% of TCOD of the initial sludge) at 0.1% H2 O2 . Previous studies showed that treatment temperature was the dominant factor affecting COD solubilization [21]. At lower treatment temperatures under 100 ◦ C, little interaction between hydrogen peroxide and microwave radiation took place, so soluble COD concentration was not expected to be high. It could also be concluded that at low temperatures (60–80 ◦ C) high dosages of hydrogen peroxide was not necessary for the disintegration of solids and nutrient release in MW/H2 O2 -AOP (Table 3).
3.2. Destruction of fecal coliforms The results of fecal coliform destruction were depicted in Fig. 1. The efficiency of fecal coliform destruction was dictated by the combined interactions of temperature, hydrogen peroxide dosage and microwave radiation. Hydrogen peroxide is a powerful oxidant with disinfection powers. However, the fecal coliform reduction was not significant at a low dosage of hydrogen peroxide without microwave radiation (Fig. 1). Although hydrogen peroxide is an excellent antiseptic, it rapidly decomposes into oxygen and water when it comes into contact with organic matters. When hydrogen peroxide was added to sewage sludge, it quickly reacts with the rich organic matters present, instead of destructing fecal coliforms specifically. Hydrogen peroxide will not induce protein, lipid or nucleic acid alteration without the catalysts for hydroxyl radical formation [22]. The inhibition of microbial growth and damage to microorganisms by hydrogen peroxide is rather a result of the toxic radicals rather than its own oxidative properties in its molecular state [23]. The formation of free radicals usually requires the presence of catalysts such as metal ions (e.g., Fenton’s reagent), UV, ozone, or microwaves [24]. In this case, the sole addition of hydrogen peroxide limits the chances of free radicals formation and therefore reduces the
Fig. 1. Fecal coliform reduction after treatments with/without microwave radiation.
1146
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
effectiveness of fecal coliforms destruction. In addition, Labas et al. discovered that the inactivation of pure E. coli culture was ineffective when the H2 O2 dosage was less than the limiting hydrogen peroxide concentration of 25 mg/L [23]. Similarly, such limiting hydrogen peroxide dosage in disinfection could also exist when sewage sludge is used as substrate instead of pure E. coli culture. Hence, another explanation for the poor fecal coliform inactivation in the treatment of sludge with H2 O2 alone is that the amount of H2 O2 used here was below the limiting dosage. Limited fecal coliforms reduction was achieved by microwave heating at 55 ◦ C, but as the addition of hydrogen peroxide increased, the reduction of fecal coliforms increased; however, the reduction levelled off when the hydrogen peroxide dosage reached 0.06%. This result was similar to the SCOD solubilization results in that they both suggested limited interaction between hydrogen peroxide and microwave radiation at lower temperatures. The limited reduction of fecal coliforms at 55 ◦ C shows a contrast to the results obtained for 70 ◦ C, where the fecal coliform counts decreased from 5.1 log to 3 log (detection limit) as hydrogen peroxide dosage increased from 0% to 0.04%. No fecal coliform colonies were detected in all samples treated with more than 0.04% hydrogen peroxide dosage at 70 ◦ C. This indicated some synergistic effect between hydrogen peroxide and microwave heating in the destruction of fecal coliforms even though the hydrogen peroxide dosages were low. Koutchma and Ramaswamy have reported similar synergistic effects when microwave radiation and hydrogen peroxide were used to destruct K-12 E. coli culture. The strongest synergistic effect for the tested range was observed at 0.075 g/100 g (H2 O2 /E. coli culture) with a microwave heating temperature of 60 ◦ C [16]. Although sewage sludge was used in this study instead of pure E. coli culture, similar synergistic effects of combined hydrogen peroxide and microwave radiation can still be seen. The results of the MW/H2 O2 -AOP for the disinfection of fecal coliforms were similar to the microwave radiation process reported by Hong et al. [7]. When comparing their microwave disinfection results to those with conventional heating methods, the microwave process was more efficient for the treatment of primary sludge, and equally efficient for the waste activated sludge. The microwave treatment could achieve disinfection in the order of minutes, instead of hours in the case of conventional heating. The destruction of fecal coliform was completed in a very short period for the MW/H2 O2 -AOP. The efficiency of pathogen destruction is typically dictated by a combination of time and temperature for both the MW/H2 O2 -AOP and sole microwave radiation process. Hydrogen peroxide dosage also increases the overall efficiency of the disinfection for the MW/H2 O2 -AOP. The results proved that the MW/H2 O2 -AOP could be used as means of disinfection and the stabilization of sludge, at the same time, recover useful resources via sludge solids disintegration and nutrient release. The treated sludge could also meet the Class A biosolids criteria. 3.3. Regrowth of fecal coliforms Reduced concentrations of fecal coliforms found immediately after treatment could be deceiving because the regrowth of microorganisms and pathogens could take place rapidly when the conditions become favorable again. The results are shown in Fig. 2. For samples treated with less than 0.08% hydrogen peroxide dosage, significant regrowth of fecal coliforms was observed. The fecal coliform counts surpassed the initial counts by approximately three orders of magnitude, even though the fecal coliform count for some samples were below detection limit immediately after the MW/H2 O2 -AOP treatment. The regrowth of fecal coliforms could be attributed to: (1) multiplication of survived bacteria; (2) elimination of competitive species. As we discussed earlier, nutri-
Fig. 2. Fecal coliform regrowth of samples treated at 70 ◦ C microwave temperature.
ents contained in the biomass were released into the solution, which became readily available to fecal coliforms and other viable microorganisms and therefore helping their regrowth. Some of the bacteriophages that would otherwise have been capable of infecting and eliminating E. coli bacteria, have also been destroyed from the microwave heating. Sanborn et al. reported that complete inactivation of bacteriophage T4, was achieved when the phage was exposed to a household microwave for 3 min [25]. Therefore, the lack of competition could be another explanation to the significant regrowth of fecal coliforms after microwave treatment. However, no regrowth was observed for samples treated with microwave heating with over 0.08% hydrogen peroxide dosage. The results suggest that the complete elimination of fecal coliforms was achieved at these conditions. The problem with pathogenic microorganisms regrowth could be avoided with the combined treatment of microwave radiation at specific temperatures along with sufficient hydrogen peroxide addition (>0.08% in this case). Based on the results obtained in this study, it can be postulated that for different substrates, complete elimination of pathogenic organisms can also be achieved with adequate microwave radiation and hydrogen peroxide addition. This could be considered a novel process of pasteurization and stabilization of sewage sludge for generating true Class A biosolids. The economic feasibility has not been performed for the MW/H2 O2 -AOP. The cost and benefit of the process for a laboratoryscale operation cannot be assessed comprehensively, since it is significantly more costly per unit of sludge to run a laboratory-scale operation than a full-scale operation. A study will be conducted for the economic feasibility of the pilot-scale MW/H2 O2 -AOP operated in a continuous mode after its installation. 4. Conclusions The MW/H2 O2 -AOP could be an efficient means to disinfect or stabilize sewage sludge. Complete destruction of fecal coliforms could be achieved with hydrogen peroxide dosage higher than 0.08% at 70 ◦ C, which would eliminate the problem of coliform regrowth. The MW/H2 O2 -AOP could be a promising technology in producing sludge that meets and maintains Class A biosolids requirements. The MW/H2 O2 -AOP displayed its capabilities to release nutrients and disintegrate solids from sewage sludge at low microwave temperatures with low H2 O2 dosages. A high hydrogen peroxide dosage was not necessary for the solubilization of phosphorus and organic matters in the lower treatment temperature regime. The synergistic effects between microwave heating and hydrogen peroxide could be observed in terms of SCOD release at 70 ◦ C. The interaction between microwave heating and hydrogen peroxide,
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
however, was very limited at 55 ◦ C, hence resulting in poor COD solubilization.
[12]
Acknowledgments [13]
The authors wish to acknowledge research funding from the Natural Science and Engineering Research Council of Canada (NSERC) and the UBC Bridge Program.
[14] [15]
References [16] [1] Metcalf, Eddy, Wastewater Engineering Treatment Disposal and Reuse, 4th ed., McGraw-Hill, New York, 2003. [2] USEPA. Land Application of Biosolids, Office of Inspector General Status Report 2002-S-000004; 2002. [3] J. Santamaria, G.A. Toranzos, Enteric pathogens and soil: a short review, Int. Microbiol. 6 (2003) 5–9. [4] D.G. Boyer, G.C. Pasquarell, Agricultural land use impacts on baceterial water quality in a Karst groundwater aquifer, J. Am. Water Resour. Assoc. 35 (1999) 291–300. [5] USEPA. Standards for the Use or Disposal of Sewage Sludge, Code of Federal Regulations, Part 503, Title 40; 1999. [6] D.I. Martin, I. Margaritescu, E. Cirstea, I. Togoe, D. Ighigeanu, M.R. Nemtanu, C. Oproiu, N. Iacob, Application of accelerated electron beam and microwave irradiation to biological waste treatment, Vacuum 77 (2005) 501–506. [7] S.M. Hong, J.K. Park, N. Teeradej, Y.O. Lee, Y.K. Cho, C.H. Park, Pretreatment of sludge with microwaves for pathogen destruction and improved anaerobic digestion performance, Water Environ. Res. 78 (2006) 76–83. [8] S.A. Pino-Jelcic, S.M. Hong, J.K. Park, Enhanced anaerobic biodegradability and inactivation of fecal coliforms and Salmonella spp. in wastewater sludge by using microwaves, Water Environ. Res. 78 (2006) 209–216. [9] R.S. Reimers, J.E. Holland, J.J. Shelton, W.S. Bankston, J.C. Burnham, J.H. Meckling, Application of applied-field in the disinfection of water and waste, in: Proceedings of the Water Environment Federation, Disinfection 2000, New Orleans, LA, 2003. ´ D. Milic, ´ The hydrogen peroxide, as a [10] A. Tofant, M. Vuˇcemiloa, Zˇ . Paviˇcica, potentially useful slurry disinfectant, Livest. Sci. 102 (2006) 243–247. [11] M Wagner, D. Brumelis, R. Gehr, Disinfection of wastewater by hydrogen peroxide or peracetic acid: development of procedures for measurement of residual
[17]
[18]
[19]
[20]
[21]
[22] [23]
[24]
[25]
1147
disinfectant and application to a physicochemically treated municipal effluent, Water Environ. Res. 74 (2002) 33–50. P.H. Liao, W.T. Wong, K.V. Lo, Advanced oxidation process using hydrogen peroxide/microwave system for solubilization of phosphate, J. Environ. Sci. Health Part A: Toxic/Hazard. Subst. Environ. Eng. 40 (2005) 1753–1761. A. Qureshi, K.V. Lo, D.S. Mavinic, P.H. Liao, F. Koch, H. Kelly, Dairy manure treatment, digestion and nutrient recovery as a phosphate fertilizer, J. Environ. Sci. Health Part B 41 (2006) 1221–1235. W.I. Chan, K.V. Lo, P.H. Liao, Solubilization of blood meal to be used as a liquid fertilizer, J. Environ. Sci. Health Part B 42 (2007) 417–422. C. Eskicioglu, A. Prorot, J. Marin, R.L. Droste, K.J. Kennedy, Synergetic pretreatment of sewage sludge by microwave irradiation in presence of H2 O2 for enhanced anaerobic digestion, Water Res. 42 (2008) 4674–4682. T. Koutchma, H.S. Ramaswamy, Combined effects of microwave heating and hydrogen peroxide on the destruction of Escherichia coli, Lebensm. Wiss. Technol. 33 (2000) 30–36. APHA, AWWA, WRF, Standard Methods for the Examination of Water and Wastewater, 20th ed., American Public Health Association, Washington, DC, 1998. A.A. Kenge, P.H. Liao, K.V. Lo, Role of mixing on microwave-enhanced advanced oxidation process in treating sewage sludge, J. Environ. Sci. Health Part A: Toxic/Hazard. Subst. Environ. Eng. 43 (2008) 1431–1440. K.V. Lo, P.H. Liao, G.Q. Yin, Sewage sludge treatment using microwaveenhanced advanced oxidation processes with and without ferrous sulfate addition, J. Chem. Technol. Biotechnol. 83 (2008) 1370–1374. W.T. Wong, W.I. Chan, P.H. Liao, K.V. Lo, D.S. Mavinic, Exploring the role of hydrogen peroxide in the microwave advanced oxidation process: solubilization of ammonia and phosphates, J. Environ. Eng. Sci. 5 (2006) 459–465. W.T. Wong, W.I. Chan, P.H. Liao, K.V. Lo, A hydrogen peroxide/microwave advanced oxidation process for sewage sludge treatment, J. Environ. Sci. Health Part A 41 (2006) 2623–2633. B.J. Juven, M.D. Pierson, Antibacterial effects of hydrogen peroxide and methods for its detection and quantitation, J. Food Protect. 59 (1996) 1233–1241. M.D. Labas, C.S. Zalazara, R.J. Brandia, A.E. Cassano, Reaction kinetics of bacteria disinfection employing hydrogen peroxide, Biochem. Eng. J. 38 (2008) 78– 87. S. Parsons, M. Williams, Introduction, in: S. Parsons (Ed.), Advanced Oxidation Processes for Water and Wastewater Treatment, IWA Publishing, London, UK, 2004, pp. 1–6. M.R. Sanborn, S.K. Wan, R. Bulard, Microwave sterilization of plastic tissue culture vessels for reuse, Appl. Environ. Microbiol. 44 (1982) 960–964.
Contents lists available at ScienceDirect
Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Disinfection and solubilization of sewage sludge using the microwave enhanced advanced oxidation process Y. Yu, W.I. Chan, P.H. Liao, K.V. Lo ∗ Department of Civil Engineering, University of British Columbia, 6250 Applied Science Lane, Vancouver, BC V6T 1Z4, Canada
a r t i c l e
i n f o
Article history: Received 5 January 2010 Received in revised form 7 April 2010 Accepted 30 May 2010 Available online 4 June 2010 Keywords: Microwave radiation Disinfection Fecal coliforms regrowth Nutrient release
a b s t r a c t The microwave enhanced advanced oxidation process (MW/H2 O2 -AOP) was used to treat municipal sewage sludge for solids disintegration, nutrient solubilization, with an emphasis on pathogen destruction and regrowth. Pathogen reduction, in terms of fecal coliform concentrations were found below detection limit (1000 CFU/L) immediately after treatment when sludge was treated at 70 ◦ C with more than 0.04% of H2 O2 (w/w). Significant regrowth of fecal coliforms was observed for the treated samples after 72 h. However, no regrowth was observed for samples treated at 70 ◦ C with 0.08% H2 O2 or higher, suggesting a complete elimination of fecal coliforms. The range of hydrogen peroxide used did not have a significant effect on orthophosphate release regardless of temperature. Ammonia release at these low temperatures was found to be insignificant. The soluble chemical oxygen demand increased with an increase of hydrogen peroxide dosage at 70 ◦ C. However, there was no clear trend of soluble chemical oxygen demand over varying hydrogen peroxide dosage at 55 ◦ C. The MW/H2 O2 -AOP is a novel process for the pasteurization and stabilization of sewage sludge to meet and maintain Class A biosolids criteria. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The treatment and disposal of waste activated sludge is a major concern for municipal wastewater treatment facilities due to its health and environmental impacts, as well as handling and disposal costs. Sludge typically contains high levels of organic matters, nutrients, and metals [1]; hence they can be used as fertilizers for agricultural land applications. 54% of the produced sludge was applied to agricultural, horticultural, forest, and reclamation land in USA [2]; however, it poses a health threat because of the possible increase in soil-borne diseases associated with the land application of sludge. Pathogens entering the soil may also lead to both surface and ground water contamination since any member of the allochthonous or indigenous microbiota in soil will eventually end up in an aquatic environment or be dispersed in aerosols [3,4]. When sludge is used as fertilizers or soil conditioners, they may come into contact with fruits or vegetables, and induce food-borne diseases. Sludge now must meet stringent pathogen reduction regulations, which is specified in the Standards for the Use or Disposal of Sewage Sludge, before it can be used for land applications [5]. The pathogen reduction requirements are divided into two levels, Class A and Class B, depending on the extent of pathogen reduction. In Class B, disinfection is incomplete; fecal coliform levels are
∗ Corresponding author. Tel.: +1 604 822 4880; fax: +1 604 822 6901. E-mail address: [email protected] (K.V. Lo). 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.05.134
reduced to below 2 million colony forming units (CFU) per gram of total solids dry weight [5]. Disinfection is more complete in Class A, where fecal coliform levels are less than 1000 most probable numbers (MPN) per gram of total solids dry weight [5]. Microwave radiation has recently been applied to sludge for disinfection purposes [6]. It was found that 45 kW s (90 s at 500 W) of microwave radiation produced approximately a 4.8 log reduction of Escherichia coli. Complete inactivation of fecal coliform (to below detection limits) immediately after treatment, could be achieved with 60 kW s and 90 kW s (1 kW for 60 s and 90 s) for primary and waste activated sludge, respectively [7,8]. It should also be noted that the microwave at a frequency of 2450 MHz and less are also capable of denaturing DNA molecules and disassociating organic chemical bonds [9]. Hydrogen peroxide is well known for its antiseptic properties. It had been tested as a means of disinfection when applied independently or in combination with other chemicals. In a study where hydrogen peroxide was used in combination with iron (II) sulfate (Fenton’s reagent) to treat pig and cattle slurry, the total fecal coliform level was reduced by 99.9% [10]. Wagner et al. also found that hydrogen peroxide can effectively reduce fecal coliform in wastewater effluent to the target level of 10,000 CFU/100 mL, but the high dosage and long contact time required clearly made the option uneconomical [11]. No attempt to check for the regrowth of fecal coliform has been found in these studies either. The microwave enhanced advanced oxidation process (MW/H2 O2 -AOP) utilizes both microwave radiation and hydrogen
1144
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
peroxide simultaneously, generating hydroxyl radicals which could significantly improve nutrient solubilization for treating sludge and other substrates [12–15]. The synergistic effect of microwave radiation and hydrogen peroxide on the process was more pronounced at higher temperatures. In terms of pathogens destruction, microwaves alone could cause significant inactivation of fecal coliforms and Salmonella spp. in wastewater sludge [8]. A strong synergistic effect of microwave heating and hydrogen peroxide was observed in the destruction of E. coli pure culture [16]. However, the combined treatment with hydrogen peroxide and microwave radiation has not been tested for the destruction of pathogens in sewage sludge. Another important factor is coliform regrowth, which is an essential aspect to truly meeting Class A biosolids requirements as well as the safety of the operators while handling what is perceived as “disinfected sludge”. Due to the large quantities of sludge handling, a small percentage of regrowth constitutes up to an unsafe number of fecal coliforms in aerosols or contactable areas to the operator. Consequently, the purpose of this study was to investigate sludge disinfection with the consideration for pathogen regrowth and nutrient solubilization using the MW/H2 O2 -AOP. Low hydrogen peroxide dosages (0.02–0.1%) and a low temperature regime (55–70 ◦ C) were chosen to economize the process and create treatment temperature conditions to be more comparable to that of conventional thermal treatment conditions. 2. Materials and methods 2.1. Microwave apparatus The Milestone Ethos TC closed vessel Microwave Labstation (Milestone Inc., USA) was used in this study. It operates at a frequency of 2450 MHz with a maximum power output of 1000 W. The Labstation has the capacity of handling up to 12 vessels for the microwave treatment in a single run: 1 reference vessel and 11 sample vessels, each with a volume of 100 mL. A thermocouple is inserted into the reference vessel and is connected to the control panel, thus providing real time temperature monitoring during the runs. A magnetic mixing device allows for the stirring of the samples in the vessels during the microwave process. The microwave system can attain a maximum temperature of 220 ◦ C and a pressure up to 30 bars. 2.2. Experimental design Fresh secondary aerobic activated sludge with a sludge retention time of approximately 17 days was obtained from the activated sludge wastewater treatment pilot plant located at the south campus of the University of British Columbia. Characteristics of the secondary aerobic sludge are listed in Table 1. For the treatment process, the experiments were divided into two parts, i.e., with and without the microwave treatments. For the first part, two different temperatures of 55 ◦ C and 70 ◦ C, and six levels of hydrogen peroxide dosage (0–0.1% as (w/w) in 0.02% increments) were selected. Five replicates at each treatment condition were heated in the microwave Labstation at a temperature increTable 1 Characteristics of raw sludge. Parameters
Concentration
SCOD (mg/L) TCOD (mg/L) TS (%) TP (mg/L) TKN (mg/L) FC counts (CFU/L)
59–70 3967–4076 0.32 155–176 405–459 5.8 × 106 to 10.0 × 106
ment rate of approximately 20 ◦ C/min, up to the desired treatment temperature, and the samples were subsequently held for 5.5 min at the set temperature within the Labstation. The procedures have been developed through our previous studies and other research groups have also adopted similar ones [12–15]. For the second part, sludge samples were treated by the same varying dosages of hydrogen peroxide for 4 h at ambient temperature (approximately 22–23 ◦ C) without microwave radiation. For the part of the pathogen disinfection and regrowth of this study, fecal coliforms were chosen as indicator organisms for the MW/H2 O2 -AOP. Samples were prepared immediately after the treatment for microbial examinations. Sludge samples treated with microwave radiation at 70 ◦ C were retained in closed sterile bottles and stored at ambient temperature for 72 h for fecal coliform regrowth. Fecal coliform concentrations were compared to the concentrations immediately after the treatment. 2.3. Chemical analysis and microbial examination Unfiltered, raw sludge samples were analyzed for total chemical oxygen demand (TCOD), total phosphate (TP), total Kjeldahl nitrogen (TKN) and total solids (TS) according to the Standard Methods [17]. Three of the five treated replicate samples were centrifuged at 4000 rpm for 10 min and the supernatant was subsequently collected and passed through a 1.6 m fibreglass filter paper. The supernatant was analyzed for ammonia (ammonia-N), orthophosphate (ortho-P), and soluble chemical oxygen demand (SCOD). Ortho-P, ammonia-N concentrations were determined using the flow injection analysis (Lachat Quick-Chem 8000 Automated Ion Analyzer, Lachat Instruments, USA), and SCOD was determined using the colorimetric method according to that outlined in Standard Methods [17]. Fecal coliform concentrations were determined using the membrane filtration technique, which is described in Standard Methods Part 9222D [17]. Two of five treated sludge samples were appropriately diluted to six different dilutions with distilled water, so that the fecal coliform colonies count in each diluted sample cultured in the next stage was between 10 and 200. The diluted samples were passed through 0.45 m sterilized, gridded membranes where microorganisms were retained. Petri dishes containing agar and DifcoTM mFC broth base were prepared according to the manufacturer’s instruction. The filters were then placed on the prepared Petri dishes and incubated at 45 ◦ C for 24 ± 2 h. Fecal coliform colonies were counted after incubation. The dilutions with fecal coliform colonies counts (at least 2) within the range were averaged and tabulated. The fecal coliforms concentrations were reported in colony forming units per liter (CFU/L). The detection limit for the analyses was 1000 CFU/L. 3. Results and discussion 3.1. Nutrient release The results of nutrient release and COD release are summarized in Table 2. The ortho-P release decreased from 27.4 mg/L to 15.7 mg/L as hydrogen peroxide dosage increased from 0% to 0.1% at 70 ◦ C. The decrease in ortho-P concentration further confirms the previous report that polyphosphate was formed when sludge was treated by microwave radiation and H2 O2 at intermediate temperatures between 60 ◦ C and 80 ◦ C [18–20]. The addition of hydrogen peroxide did not have much influence on ortho-P release at 55 ◦ C, indicating limited interaction between microwave radiation and hydrogen peroxide. The synergistic effects of microwave radiation and hydrogen peroxide are more pronounced at high microwave treatment temperatures [15]. The results from previous studies and
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
1145
Table 2 Results of organic matter and nutrients solubilization after treatments. H2 O2 dosage (%)
0 0.02 0.04 0.06 0.08 0.1 a
Microwave at 55 ◦ C
Without microwave
Microwave at 70 ◦ C
SCOD (mg/L)
Ortho-P (mg/L)
Ammonia-N (mg/L)
SCOD (mg/L)
Ortho-P (mg/L)
Ammonia-N (mg/L)
SCOD (mg/L)
Ortho-P (mg/L)
Ammonia-N (mg/L)
– 59.1(7.2)a 52.8(15.0) 63.7(12.6) 61.0(6.9) 61.0(5.8)
– 10.1(0.4) 10.3(0.3) 15.6(0.8) 21.5(0.9) 25.0(0.9)
– 5.6(0.2) 7.1(0.2) 4.1(2.7) 2.1(0.3) 8.8(0.4)
353(10.9) 370(20.6) 407(23.5) 302(20.4) 309(15.5) 331(12.3)
14.0(0.9) 16.2(0.7) 18.6(1.4) 12.9(0.6) 12.2(0.4) 12.9(1.3)
2.7(0.1) 2.7(0.3) 3.3(0.4) 2.5(0.2) 2.6(0.1) 2.4(0.1)
450(52.8) 713(84.9) 812(11.0) 847(11.0) 924(22.0) 996(12.5)
27.4(0.1) 17.7(0.8) 17.0(0.7) 15.4(1.5) 18.2(0.4) 15.7(0.9)
3.5(0.0) 3.2(0.1) 3.5(0.2) 3.2(0.9) 4.8(1.0) 2.6(1.1)
Mean (standard deviation) of three replicates.
Table 3 Comparison of solubilization results with previous studies. TS (%)
H2 O2 (% by wt.)
H2 O2 :TS
Temperature (◦ C)
P release (%)
COD release (%)
Kenge et al. [18]
2.9 1.8 1.1
7.2 3.7 2.2
2.5:1 2.1:1 2.0:1
80 80 80
14–16 8–9 9–10
19–25 18–22 25–28
Lo et al. [19]
1.0 1.0
1.0 1.0
1:1 1:1
60 80
15 9
15 18
This study
0.32
0.02–0.1
0.06:1–0.31:1
70
9–10
17–25
this study are listed in Table 3. The nutrient release levels were comparable to past studies, even with much lower hydrogen peroxide dosage in this study. As mentioned earlier, microwave temperature was a significant factor for ortho-P release; the hydrogen peroxide dosage was not a factor for its solubilization at these low treatment temperatures and a short treatment time. It was therefore concluded that high releases of ortho-P could not be achieved in low temperatures regimes (60–80 ◦ C), regardless of the hydrogen peroxide dosage applied. When the sludge was treated by H2 O2 alone at ambient temperature, ortho-P release remained relatively constant until H2 O2 dosages exceeded 0.04%, at which point ortho-P concentration increased with an increase in H2 O2 dosage. The highest concentration of ortho-P of 25 mg/L was obtained at 0.1% of H2 O2 (Table 2). However, it should be noted that the samples were treated for 4 h, thus, the higher ortho-P release could be solely due to hydrogen peroxide treatment over a longer treatment time. In general, the release of ammonia is low at the tested temperatures. The highest concentration of soluble ammonia was less than 4.8 mg/L, obtained at 70 ◦ C with a dosage of 0.08% H2 O2 for the MW/H2 O2 -AOP, while the highest yield was 8.8 mg/L at a dosage of 0.1% H2 O2 , with a longer reaction time of 4 h ambient temperature without microwave radiation (Table 2). No clear trend was observed for ammonia yield in this narrow range of H2 O2 dosages and low treatment temperatures. The SCOD remained relatively constant for H2 O2 treatments at ambient temperature without microwave radiation, regardless of H2 O2 dosage. When sludge was treated at a microwave temperature of 55 ◦ C, the COD release was in the range of 300–400 mg/L. The increase of hydrogen peroxide dosages did not affect the COD release significantly (Table 2). It was obvious that the addition of hydrogen peroxide increased the COD release at 70 ◦ C (Table 2). The maximum SCOD concentration was approximately 1000 mg/L (∼25% of TCOD of the initial sludge) at 0.1% H2 O2 . Previous studies showed that treatment temperature was the dominant factor affecting COD solubilization [21]. At lower treatment temperatures under 100 ◦ C, little interaction between hydrogen peroxide and microwave radiation took place, so soluble COD concentration was not expected to be high. It could also be concluded that at low temperatures (60–80 ◦ C) high dosages of hydrogen peroxide was not necessary for the disintegration of solids and nutrient release in MW/H2 O2 -AOP (Table 3).
3.2. Destruction of fecal coliforms The results of fecal coliform destruction were depicted in Fig. 1. The efficiency of fecal coliform destruction was dictated by the combined interactions of temperature, hydrogen peroxide dosage and microwave radiation. Hydrogen peroxide is a powerful oxidant with disinfection powers. However, the fecal coliform reduction was not significant at a low dosage of hydrogen peroxide without microwave radiation (Fig. 1). Although hydrogen peroxide is an excellent antiseptic, it rapidly decomposes into oxygen and water when it comes into contact with organic matters. When hydrogen peroxide was added to sewage sludge, it quickly reacts with the rich organic matters present, instead of destructing fecal coliforms specifically. Hydrogen peroxide will not induce protein, lipid or nucleic acid alteration without the catalysts for hydroxyl radical formation [22]. The inhibition of microbial growth and damage to microorganisms by hydrogen peroxide is rather a result of the toxic radicals rather than its own oxidative properties in its molecular state [23]. The formation of free radicals usually requires the presence of catalysts such as metal ions (e.g., Fenton’s reagent), UV, ozone, or microwaves [24]. In this case, the sole addition of hydrogen peroxide limits the chances of free radicals formation and therefore reduces the
Fig. 1. Fecal coliform reduction after treatments with/without microwave radiation.
1146
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
effectiveness of fecal coliforms destruction. In addition, Labas et al. discovered that the inactivation of pure E. coli culture was ineffective when the H2 O2 dosage was less than the limiting hydrogen peroxide concentration of 25 mg/L [23]. Similarly, such limiting hydrogen peroxide dosage in disinfection could also exist when sewage sludge is used as substrate instead of pure E. coli culture. Hence, another explanation for the poor fecal coliform inactivation in the treatment of sludge with H2 O2 alone is that the amount of H2 O2 used here was below the limiting dosage. Limited fecal coliforms reduction was achieved by microwave heating at 55 ◦ C, but as the addition of hydrogen peroxide increased, the reduction of fecal coliforms increased; however, the reduction levelled off when the hydrogen peroxide dosage reached 0.06%. This result was similar to the SCOD solubilization results in that they both suggested limited interaction between hydrogen peroxide and microwave radiation at lower temperatures. The limited reduction of fecal coliforms at 55 ◦ C shows a contrast to the results obtained for 70 ◦ C, where the fecal coliform counts decreased from 5.1 log to 3 log (detection limit) as hydrogen peroxide dosage increased from 0% to 0.04%. No fecal coliform colonies were detected in all samples treated with more than 0.04% hydrogen peroxide dosage at 70 ◦ C. This indicated some synergistic effect between hydrogen peroxide and microwave heating in the destruction of fecal coliforms even though the hydrogen peroxide dosages were low. Koutchma and Ramaswamy have reported similar synergistic effects when microwave radiation and hydrogen peroxide were used to destruct K-12 E. coli culture. The strongest synergistic effect for the tested range was observed at 0.075 g/100 g (H2 O2 /E. coli culture) with a microwave heating temperature of 60 ◦ C [16]. Although sewage sludge was used in this study instead of pure E. coli culture, similar synergistic effects of combined hydrogen peroxide and microwave radiation can still be seen. The results of the MW/H2 O2 -AOP for the disinfection of fecal coliforms were similar to the microwave radiation process reported by Hong et al. [7]. When comparing their microwave disinfection results to those with conventional heating methods, the microwave process was more efficient for the treatment of primary sludge, and equally efficient for the waste activated sludge. The microwave treatment could achieve disinfection in the order of minutes, instead of hours in the case of conventional heating. The destruction of fecal coliform was completed in a very short period for the MW/H2 O2 -AOP. The efficiency of pathogen destruction is typically dictated by a combination of time and temperature for both the MW/H2 O2 -AOP and sole microwave radiation process. Hydrogen peroxide dosage also increases the overall efficiency of the disinfection for the MW/H2 O2 -AOP. The results proved that the MW/H2 O2 -AOP could be used as means of disinfection and the stabilization of sludge, at the same time, recover useful resources via sludge solids disintegration and nutrient release. The treated sludge could also meet the Class A biosolids criteria. 3.3. Regrowth of fecal coliforms Reduced concentrations of fecal coliforms found immediately after treatment could be deceiving because the regrowth of microorganisms and pathogens could take place rapidly when the conditions become favorable again. The results are shown in Fig. 2. For samples treated with less than 0.08% hydrogen peroxide dosage, significant regrowth of fecal coliforms was observed. The fecal coliform counts surpassed the initial counts by approximately three orders of magnitude, even though the fecal coliform count for some samples were below detection limit immediately after the MW/H2 O2 -AOP treatment. The regrowth of fecal coliforms could be attributed to: (1) multiplication of survived bacteria; (2) elimination of competitive species. As we discussed earlier, nutri-
Fig. 2. Fecal coliform regrowth of samples treated at 70 ◦ C microwave temperature.
ents contained in the biomass were released into the solution, which became readily available to fecal coliforms and other viable microorganisms and therefore helping their regrowth. Some of the bacteriophages that would otherwise have been capable of infecting and eliminating E. coli bacteria, have also been destroyed from the microwave heating. Sanborn et al. reported that complete inactivation of bacteriophage T4, was achieved when the phage was exposed to a household microwave for 3 min [25]. Therefore, the lack of competition could be another explanation to the significant regrowth of fecal coliforms after microwave treatment. However, no regrowth was observed for samples treated with microwave heating with over 0.08% hydrogen peroxide dosage. The results suggest that the complete elimination of fecal coliforms was achieved at these conditions. The problem with pathogenic microorganisms regrowth could be avoided with the combined treatment of microwave radiation at specific temperatures along with sufficient hydrogen peroxide addition (>0.08% in this case). Based on the results obtained in this study, it can be postulated that for different substrates, complete elimination of pathogenic organisms can also be achieved with adequate microwave radiation and hydrogen peroxide addition. This could be considered a novel process of pasteurization and stabilization of sewage sludge for generating true Class A biosolids. The economic feasibility has not been performed for the MW/H2 O2 -AOP. The cost and benefit of the process for a laboratoryscale operation cannot be assessed comprehensively, since it is significantly more costly per unit of sludge to run a laboratory-scale operation than a full-scale operation. A study will be conducted for the economic feasibility of the pilot-scale MW/H2 O2 -AOP operated in a continuous mode after its installation. 4. Conclusions The MW/H2 O2 -AOP could be an efficient means to disinfect or stabilize sewage sludge. Complete destruction of fecal coliforms could be achieved with hydrogen peroxide dosage higher than 0.08% at 70 ◦ C, which would eliminate the problem of coliform regrowth. The MW/H2 O2 -AOP could be a promising technology in producing sludge that meets and maintains Class A biosolids requirements. The MW/H2 O2 -AOP displayed its capabilities to release nutrients and disintegrate solids from sewage sludge at low microwave temperatures with low H2 O2 dosages. A high hydrogen peroxide dosage was not necessary for the solubilization of phosphorus and organic matters in the lower treatment temperature regime. The synergistic effects between microwave heating and hydrogen peroxide could be observed in terms of SCOD release at 70 ◦ C. The interaction between microwave heating and hydrogen peroxide,
Y. Yu et al. / Journal of Hazardous Materials 181 (2010) 1143–1147
however, was very limited at 55 ◦ C, hence resulting in poor COD solubilization.
[12]
Acknowledgments [13]
The authors wish to acknowledge research funding from the Natural Science and Engineering Research Council of Canada (NSERC) and the UBC Bridge Program.
[14] [15]
References [16] [1] Metcalf, Eddy, Wastewater Engineering Treatment Disposal and Reuse, 4th ed., McGraw-Hill, New York, 2003. [2] USEPA. Land Application of Biosolids, Office of Inspector General Status Report 2002-S-000004; 2002. [3] J. Santamaria, G.A. Toranzos, Enteric pathogens and soil: a short review, Int. Microbiol. 6 (2003) 5–9. [4] D.G. Boyer, G.C. Pasquarell, Agricultural land use impacts on baceterial water quality in a Karst groundwater aquifer, J. Am. Water Resour. Assoc. 35 (1999) 291–300. [5] USEPA. Standards for the Use or Disposal of Sewage Sludge, Code of Federal Regulations, Part 503, Title 40; 1999. [6] D.I. Martin, I. Margaritescu, E. Cirstea, I. Togoe, D. Ighigeanu, M.R. Nemtanu, C. Oproiu, N. Iacob, Application of accelerated electron beam and microwave irradiation to biological waste treatment, Vacuum 77 (2005) 501–506. [7] S.M. Hong, J.K. Park, N. Teeradej, Y.O. Lee, Y.K. Cho, C.H. Park, Pretreatment of sludge with microwaves for pathogen destruction and improved anaerobic digestion performance, Water Environ. Res. 78 (2006) 76–83. [8] S.A. Pino-Jelcic, S.M. Hong, J.K. Park, Enhanced anaerobic biodegradability and inactivation of fecal coliforms and Salmonella spp. in wastewater sludge by using microwaves, Water Environ. Res. 78 (2006) 209–216. [9] R.S. Reimers, J.E. Holland, J.J. Shelton, W.S. Bankston, J.C. Burnham, J.H. Meckling, Application of applied-field in the disinfection of water and waste, in: Proceedings of the Water Environment Federation, Disinfection 2000, New Orleans, LA, 2003. ´ D. Milic, ´ The hydrogen peroxide, as a [10] A. Tofant, M. Vuˇcemiloa, Zˇ . Paviˇcica, potentially useful slurry disinfectant, Livest. Sci. 102 (2006) 243–247. [11] M Wagner, D. Brumelis, R. Gehr, Disinfection of wastewater by hydrogen peroxide or peracetic acid: development of procedures for measurement of residual
[17]
[18]
[19]
[20]
[21]
[22] [23]
[24]
[25]
1147
disinfectant and application to a physicochemically treated municipal effluent, Water Environ. Res. 74 (2002) 33–50. P.H. Liao, W.T. Wong, K.V. Lo, Advanced oxidation process using hydrogen peroxide/microwave system for solubilization of phosphate, J. Environ. Sci. Health Part A: Toxic/Hazard. Subst. Environ. Eng. 40 (2005) 1753–1761. A. Qureshi, K.V. Lo, D.S. Mavinic, P.H. Liao, F. Koch, H. Kelly, Dairy manure treatment, digestion and nutrient recovery as a phosphate fertilizer, J. Environ. Sci. Health Part B 41 (2006) 1221–1235. W.I. Chan, K.V. Lo, P.H. Liao, Solubilization of blood meal to be used as a liquid fertilizer, J. Environ. Sci. Health Part B 42 (2007) 417–422. C. Eskicioglu, A. Prorot, J. Marin, R.L. Droste, K.J. Kennedy, Synergetic pretreatment of sewage sludge by microwave irradiation in presence of H2 O2 for enhanced anaerobic digestion, Water Res. 42 (2008) 4674–4682. T. Koutchma, H.S. Ramaswamy, Combined effects of microwave heating and hydrogen peroxide on the destruction of Escherichia coli, Lebensm. Wiss. Technol. 33 (2000) 30–36. APHA, AWWA, WRF, Standard Methods for the Examination of Water and Wastewater, 20th ed., American Public Health Association, Washington, DC, 1998. A.A. Kenge, P.H. Liao, K.V. Lo, Role of mixing on microwave-enhanced advanced oxidation process in treating sewage sludge, J. Environ. Sci. Health Part A: Toxic/Hazard. Subst. Environ. Eng. 43 (2008) 1431–1440. K.V. Lo, P.H. Liao, G.Q. Yin, Sewage sludge treatment using microwaveenhanced advanced oxidation processes with and without ferrous sulfate addition, J. Chem. Technol. Biotechnol. 83 (2008) 1370–1374. W.T. Wong, W.I. Chan, P.H. Liao, K.V. Lo, D.S. Mavinic, Exploring the role of hydrogen peroxide in the microwave advanced oxidation process: solubilization of ammonia and phosphates, J. Environ. Eng. Sci. 5 (2006) 459–465. W.T. Wong, W.I. Chan, P.H. Liao, K.V. Lo, A hydrogen peroxide/microwave advanced oxidation process for sewage sludge treatment, J. Environ. Sci. Health Part A 41 (2006) 2623–2633. B.J. Juven, M.D. Pierson, Antibacterial effects of hydrogen peroxide and methods for its detection and quantitation, J. Food Protect. 59 (1996) 1233–1241. M.D. Labas, C.S. Zalazara, R.J. Brandia, A.E. Cassano, Reaction kinetics of bacteria disinfection employing hydrogen peroxide, Biochem. Eng. J. 38 (2008) 78– 87. S. Parsons, M. Williams, Introduction, in: S. Parsons (Ed.), Advanced Oxidation Processes for Water and Wastewater Treatment, IWA Publishing, London, UK, 2004, pp. 1–6. M.R. Sanborn, S.K. Wan, R. Bulard, Microwave sterilization of plastic tissue culture vessels for reuse, Appl. Environ. Microbiol. 44 (1982) 960–964.