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Integrated chemical treatment of municipal wastewater using waste hydrogen peroxide and ultraviolet light
Physics and Chemistry of the Earth 36 (2011) 459–464
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Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce
Integrated chemical treatment of municipal wastewater using waste hydrogen peroxide and ultraviolet light Zulfiqar Ahmed Bhatti a, Qaisar Mahmood a, Iftikhar Ahmad Raja a, Amir Haider Malik a, Naim Rashid a, Donglei Wu b,* a b
Department of Environmental Sciences, COMSATS Institute of Information Technology, Abbottabad 22060, Pakistan Department of Environmental Engineering, Zhejiang University, Hangzhou 310029, PR China
a r t i c l e
i n f o
Article history: Received 30 May 2009 Received in revised form 8 November 2009 Accepted 9 March 2010 Available online 12 March 2010 Keywords: Advance Oxidation Process Biological oxygen demand Biodegradable fraction Chemical oxygen demand Integrated chemical treatment Waste hydrogen peroxide
a b s t r a c t Dilemmas like water shortage, rapid industrialization, growing human population and related issues have seriously affected human health and environmental sustainability. For conservation and sustainable use of our water resources, innovative methods for wastewater treatment are continuously being explored. Advance Oxidation Processes (AOPs) show a promising approach to meet specific objectives of municipal wastewater treatment (MWW). The MWW samples were pretreated with Al2(SO4)48H2O (Alum) at different doses 4, 8, 12–50 mg/L to enhance the sedimentation. The maximum COD removal was observed at alum treatments in range of 28–32 mg/L without increasing total dissolved solids (TDS). TDS were found to increase when the alum dose was increased from 32–40 mg/L. In the present study, the optimum alum dose of 30 mg/L for 3 h of sedimentation and subsequent integrated H2O2/UV treatment was applied (using 2.5 mL/L of 40% waste H2O2 and 35% fresh H2O2 separately). Organic and inorganic pollutants, contributing towards chemical oxygen demand (COD), biological oxygen demand (BOD), turbidity and total dissolved solids were degraded by H2O2/UV. About 93% COD, 90% BOD and 83% turbidity reduction occurred when 40% waste H2O2 was used. When using fresh H2O2, 63% COD, 68% BOD and 86% turbidity reduction was detected. Complete disinfection of coliform bacteria occurred by using 40% H2O2/UV. The most interesting part of this research was to compare the effectiveness of waste H2O2 with fresh H2O2. Waste H2O2 generated from an industrial process of disinfection was found more effective in the treatment of MWW than fresh 35% H2O2. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Chemically enhanced methods, in conjunction with Advanced Oxidation Processes (AOPs) provides an efficient and promising alternative to conventional methods for the treatment of MWW. These techniques can be used in combination with the conventional methods to increase the overall performance of the wastewater treatment plant (WWTP). Various studies have shown that AOPs can be utilized to decompose substances such as insecticides, dyes, surfactants and organochlorides into relatively harmless substances such as carbondioxide and water (Pelezetti and Schiavello, 1991; Fox and Dulay, 1993; Taner et al., 2006). Treatment with alum beforehand may further enhance the wastewater treatment using AOPs. Velasco and Juan (2007), studied the effect of aluminum sulphate and Poly Aluminum Chloride (PAC1) (Qiu et al., 2008) as a coagulant for the removal of dissolved organic carbon of surface waters. It was found that the efficiency of alum was * Corresponding author. Tel.: +86 13805739113; fax: +86 571 86971898. E-mail address: [email protected] (D. Wu). 1474-7065/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2010.03.024
highly dependant on operational conditions such as pH and dose. The pH tends to affect the solubility of aluminum in coagulation, which is favored under more acidic conditions since acceptable residual aluminum concentration is achieved, whereas aluminum solubility increases and therefore pH effect must be balanced (Sarkar et al., 2005). In another study, alum and aluminum hydroxide was used for the removal of phosphates from wastewater, which are the major contributors of the eutrophication of water bodies (Georgantas and Grigoropoulou, 2007). Alum was found to be a better chemical for phosphate removal even though the active coagulant formed was Al(OH)3. Temperature did not affect alum action but aluminum hydroxide showed variations with the change of temperature. In Tunisia, the domestic wastewater was proposed to be treated using hydrogen peroxide so as to meet the problem of water shortage and recycle the wastewater for further reuse. According to the research, 30% H2O2 increase the biodegradability of some water pollutants and an optimum dose of 2.5 mL/L was sufficient to destroy majority of the risks even though it may vary according to the amount of organic matter present in water. COD reduction
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achieved was about 85%. Significant decrease in BOD5 was also observed as well as exponential inactivation of fecal coliform was achieved (Kisibi, 2006; Rosal et al., 2008). In another research, domestic wastewater was treated in batch and continuous mode using H2O2/UV/O3. Beforehand, the water was pretreated using three different methods for turbidity removal, which might hinder the effect of the latter treatment, namely; plain sedimentation. The results showed that neither plain sedimentation nor filtration showed substantial results, but aluminum sulfate at an optimum pH of 7 and optimum dose of 60 mg/L showed appreciable reduction in COD (39%) and turbidity (84%). This resulted in better effluent COD as opposed to raw wastewater. No doubt, H2O2 concentration was an important parameter, and the greatest decrease in COD was found to be at 100 mg/L. The process greatly reduced the reaction time due to UV lamps and enormous decrease in the amount of residual COD. In addition, the water microbial count was also significantly reduced (Taner et al., 2006; Teresa et al., 2006). In another study, use of ozone increased the level of hydroxyl radicals and increased the rate of degradation of organic pollutant in domestic wastewater (Ligrini et al., 1993). However, the use of fresh H2O2 may be costly. Moreover, the H2O2 alone or in combination with alum coagulation cannot effectively remove microbial loads from treated MWW which would be reused. The specific objectives of this study were to compare the effectiveness of used and fresh H2O2 to treat the MWW and to reduce the alum dose for chemical sedimentation. The combination of H2O2 with UV light was investigated to observe the effectiveness of integrated treatment of organic matter and coliform bacteria in wastewater. 2. Materials and methods 2.1. Wastewater sampling MWW samples were obtained from Shaikhul-bandi Abbottabad, Pakistan. For this purpose, 50 L plastic container was conditioned properly using running MWW. After sample collection it was corked and taken to the laboratory for further analysis and treatment. Its characteristics are given in Table. 1. Waste H2O2 was collected from drain of Tetra Brik Aseptic (TBA) machine in a food factory located in Hattar Industrial Estate, Hattar near Abbottabad, Pakistan. During TBA machine operation process fresh 35% H2O2 is changed to 40% H2O2 which is wasted and drained. MWW comprised of effluents from kitchen, washrooms, washing, laundry etc. It contained a large quantity of organic pollution with 0.9 biodegradable fractions (George, 2004). UV lamp was used for ultraviolet disinfection with specification of 240–280 nm, 16,000–32,000 microwatt-second per square with water depth range 2–3 in., brand light source USA. 2.2. Optimization of H2O2 dose In order to evaluate the optimum amount of 40% H2O2 for BOD, COD removal and total plate count reduction, a series of experiments were conducted with optimized doses of alum and then
treated with hydrogen peroxide, 28–32 mg/L and 2.5 mL/L. During pretreatment alum was tested as 4, 8, 12–50 mg/L, the alum dose between 28 and 32 mg/L was found the most effective in the removal of COD and BOD without increasing TDS of effluent. In these experiments, BOD, COD removal and reduction of total plate count were measured throughout the reaction period of 30, 60, 90, and 120 min. 2.3. Treatment system A mixer with variable rotational speed of 0–500 rotations per minute (rpm) was used to mix the sample thoroughly. One-liter of raw MWW was treated in batch reactor at mixing speed of 500 rpm. As a first step, it was treated with alum dose 28– 32 mg/L during Chemically Enhanced Primary Sedimentation (CEPS) and decant of CEPS was used further to treat with two different concentrations of H2O2/UV (35% fresh H2O2 and 40% waste or used H2O2), at the concentration (v/v) of 2.5 mL/L applied to various samples of wastewater, with continuous stirring at 500 rpm. Before starting mixing, at time zero, 35% and 40% H2O2 doses were separately added and samples were drawn at time intervals of 30, 60, 90 and 120 min after the addition to test their effectiveness. All the experiments were conducted at ambient temperature of 25 + 2 °C. Fig. 1 shows the process flow sheet and the treatment outline. 2.4. Microbial count The membrane filter technique was used for microbial analysis (Verstrate, 1998). For this purpose, various dilutions (10 3–10 6) were made of the wastewater sample. Nutrient agar (2%) was used as solidifying medium in sterilized petri dishes. 100 mL diluted municipal wastewater sample was filtered through filter paper (0.45 lm porosity) and incubated at 35 °C for 24 h. The colonies were counted under the compound microscope at magnification power of 10–15. 2.5. Analytical procedures All the analytical procedures used were the standard methods for water and wastewater analysis (APHA). Wastewater samples were analyzed prior to and after the treatment with 40% waste and 35% fresh H2O2 during separate treatment. Biological oxygen demand (BOD5) was measured by using standard method (APHA, 2005), Chemical oxygen demand (COD) was determined by closed reflux colorimetric method using digester (HACH – LTG 082.99.40001) (APHA). The wastewater sample, digestion solution and sulfuric acid were digested in vials for two hours at 150 °C. After digestion, absorbance was measured at wavelength 605 nm in a spectrophotometer (LOVIBOND tintometer GMBH, 44287 DORTMUND). The pH meter (HANNA, HI – 991003) was used for pH determination. Hydrogen peroxide was measured according to Tetra Pack Technical data manual by using hydrometer and temperature. Hydrogen peroxide value was obtained after connecting temperature and hydrometer reading on third scale of H2O2 W/ W (Tetra Pack). Fresh hydrogen peroxide was purchased from local
Table 1 Pre and post experimental analysis. Parameters
Raw WW
Alum treatment
Fresh 35% H2O2 treatment
Waste 40% H2O2 treatment
pH TDS (ppm) COD (ppm) BOD (ppm) Turbidity (NTU)
8–8.5 563–600 245–295 170–200 166–186
7.49–7.9 530–580 171–132 85–88 25.66–48
9 504 98.66 58 24
7.8 572 20 19 30
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A
1) Domestic Wastewater collection (Sample) 2) Natural Sedimentation For 1hour Chemically Enhanced Primary Sedimentation (CEPS) Alum treatment 30 mg/L (3 hrs sedimentation)
3) Chemical oxidation of CEPS effluent with Waste H 2O2 40% (collected from Food Industry) and 35 % fresh H2O2 minutes of mixing i. Sample collected after 30 and 60 minutes of mixing
ii. Sample collected after 90 minutes of mixing
4. Sample collected after 120 minutes of H2O2 mixing
B wastewater
Mixer
UV Lamp
Effluent, Water Quality within NEQs
Influent, Domestic WW
Alum Treatment
H2O2 /UV Treatment
Fig. 1. (A) Steps involved in proposed treatment process of low cost treatment of domestic wastewater. (B) Major steps involved in MWW treatment.
market 35% concentration. Various steps of the treatment have been illustrated in Fig. 1. 3. Results and discussion
reaction occur due to mixing of H2O2 and leads basic by product like HCO3 (pH 8). It seemed that pH values of MWW did not fluctuate significantly after dosing with alum and subsequent treatment with H2O2 and thus should not be considered in the process design.
3.1. Effect on pH 3.2. Changes in turbidity During high turbidity and subsequent alum dosing, the MWW pH is likely to drop because alum reacts with carbonates and hydroxyl species therefore removing base from solution. Upon its addition to water, calcium and magnesium bicarbonate alkalinity reacts with the alum to form an insoluble aluminum hydroxide precipitate. Owing to its acidic nature of alum, its addition to the wastewater slightly decreases in pH from 8.03 to about 7.4 after the addition of alum 28–32 mg/L (Table 2). The changes in pH with respect to time were inconsequential. Only a slight increase in pH was observed which may be due to the oxidation of organic dissolved solids in effluent. The pH changed from about 7.4–7.8 after 120 min when using waste H2O2 and 8–8.7 pH with fresh H2O2 (Fig. 2). The pH indicates the degradation
Natural sedimentation and CEPS with alum greatly reduced the turbidity of wastewater. By increasing the dose of alum, turbidity was reduced to 71.08% (Fig. 3) from 166 NTU to 48 NTU. The basic purpose of the alum addition was to form flocks and remove enough particulate matter to make further disinfection with H2O2 more effective. During subsequent step, H2O2/UV treatment could be effective only if particulate matter had removed in CEPS process. Turbidity removal in the range of 82.7–86.36% was observed after treating with 40% waste H2O2 and 35% fresh H2O2 when mixed for 120 min at a retention time of 12 h. Fig. 3 showed that fresh H2O2 was more effective to reduce the turbidity when compared with waste H2O2.
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Table 2 The changes in pH after treating with fresh and waste H2O2 in combination with UV light. pH
Raw ww
NS
Alum treated
30 min
60 min
90 min
120 min
Peroxide 35% Peroxide 40%
8.0 8.03
8.1 8.03
7.9 7.49
8.8 7.43
8.9 7.56
9.0 7.7
9.0 7.82
Percentage removal of some important parameters at different treatment steps.
Fig. 2. Effect of fresh H2O2 treatment on pH with the passage of time.
Fig. 3. Decrease in turbidity after treating with alum and H2O2/UV.
Turbidity removal with alum (71.08%) was observed in CEPS process and second further decrease in turbidity after 120 min of mixing with H2O2 Fig. 3. Fig. 3 shows that the maximum effect of fresh H2O2 was observed in reduction of turbidity while in Table 1 waste H2O2 was most effective against COD and BOD removal than the turbidity. 3.3. Effect on COD and BOD after treating with 35% fresh H2O2/UV and 40% waste H2O2/UV Noteworthy reduction in the COD and BOD of the DWW was seen more effective reduction by 40% waste peroxide treatment. Fig. 4 shows that both BOD and COD reductions were different when treating the wastewater samples with two different concentration of peroxide separately. Natural sedimentation and alum treatment had similar effects as shown in Fig. 4. Reduction in COD and BOD observed was up to 87% and 89% after the 30 min mixing of 40% waste H2O2 and both parameters reduced further to 96% and 90% after 60 min of mixing. After 120 min no further decrease in COD and BOD was observed. COD reduction was very sharp with in 30 min mixing of 40% waste peroxide. Effective reduction in COD and BOD occurred by treating same sample with 35% fresh H2O2 after 120 min of mixing. In this treatment, the use
of fresh H2O2/UV caused continuous decrease of COD and BOD after120 min of mixing. While using waste H2O2/UV treatment, there was continuous decrease in COD and BOD values till 60 min as 20 and 19 mg/L, after 60 min no further decrease was observed. It indicated that using waste H2O2 was effective for 60 min than fresh H2O2. Where as the obtained results of COD and BOD were 98 mg/L and 58 mg/L with fresh H2O2 showing effective results after 120 min. H2O2 is one of the most powerful known oxidizer and results in the formation of hydroxyl radicals (OH), which reacts with the pollutants such as iron, sulfide, solvents and gasoline as well as pesticides present in MWW, thus, reducing the contamination level in water. UV radiation provides the necessary energy for carrying the various chemical, physical and biological processes for the oxidizing the pollutants. These oxidations entail an array of direct and indirect photoreactions which are initiated by the absorbed UV radiation. Moreover, UV light can also disinfect the water samples. Table 1 shows the characteristics of MWW prior to and after integrated chemical treatment. A comparison of degradability of fresh and waste hydrogen peroxide has been given in Fig. 4. It is clear that when using 40% waste hydrogen peroxide with UV light, 30 min of mixing can be sufficient for the reduction of COD and BOD while fresh peroxide with UV needs more than 2.5 mL of per-
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Fig. 4. Reduction of COD and BOD after treating with 35% fresh and 40% waste H2O2 along with UV light.
Table 3 Inactivation of micro organisms after treating with waste hydrogen peroxide at different treatment steps. Microbial count Dilutions 10 10 10 10 10 a b
1 2 3 4 5
Raw water sample
Water sample NS
Water sample
After 30 min
After 60 min
After 120 min
TNTCa TNTC TNTC TNTC TNTC
TNTC TNTC TNTC TNTC TNTC
TNTC TNTC TNTC 201 CFU/10 mL 16 CFU/10 mL
4 CFU/10 mL 1 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL
0 CFUb/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL
0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL
TNTC = Too numerous to count. CFU = Colony forming units.
oxide and a longer time to reach the 90% removal efficiency. In another study (Kisibi, 2006) more than 90% COD removal efficiency was achieved by 3 mL of fresh peroxide without using UV light. In our previous studies (Bhatti et al., 2009), alum alone was not sufficient to decrease COD and BOD. 3.4. Microbial activity UV treatment with peroxide can easily inactivate, even with low UV doses, chlorine resistant species such as Giardia and Cryptosporidium which a dangerous human pathogens. UV is a green technology as it is chemical free and produces no disinfection byproducts. Hence, the most significant effect was observed during the inactivation of fecal coliform, which decreased to 0 CFU/10 mL after 60 min of peroxide/UV treatment. Even after 30 min the microbial count had fallen to 4 CFU/10 mL of wastewater from too numerous to count at dilution series of 10 1. Using primary and secondary wastewater treatment processes alone for the reduction of enteric organism my results in 90–99.9% elimination, and tertiary treatment may further decimate these pathogens, the treated wastewater could still be contaminated by high microbial numbers. Henceforth, further disinfection of this treated wastewater may be necessary. For this purpose, integrated H2O2/UV treatment can be used. Table 3 showed that after using waste hydrogen peroxide along with UV light resulted in the disappearing of all coliform bacteria (CFU). According to studies, H2O2 is thought to attach with microbial cell walls, membranes and enzymatic or transport systems (Kisibi, 2006). As a result, the microbial repair mechanism, required to repair minor damage, may become overloaded, leading to their inability to repair the injuries and subsequent death. The present investigation showed that CEPS may not be sufficient alone to treat complex wastewaters especially industrial effluents. Some additional treatment technologies especially anaerobic/aerobic treatments may be employed for the effective
treatment. Further research work is required to investigate the unit cost of operations. 4. Conclusion The present study compared the effectiveness of used and fresh H2O2 to treat the domestic waste and to reduce the alum dose for chemical sedimentation. The combination of H2O2 with UV light was found very effective to decrease BOD, COD, turbidity and coliform bacteria in MWW Waste H2O2 generated from an industrial process of disinfection was found more effective in the treatment of MWW than fresh 35% H2O2. The waste hydrogen peroxide can be applied in combinations with UV light to treat MWW effectively. Acknowledgements The Chinese Major projects on control and management technology of water pollution under contract No. 2008ZX07317-008 financially supports this work. References APHA, 2005. Standard Methods for the Examination of Water and Wastewater, 21st ed. American Public Health Association, Inc., New York, USA. Bhatti, Z.A., Mahmood, Q., Raja, I.A., 2009. Sewage water pollutants removal efficiency correlates to the concentration gradient of amendments. Journal of Chemical Society of Pakistan 31 (4), 665–673. Fox, M.A., Dulay, M.T., 1993. Heterogeneous photocatalyst. Chemical Reviews 93, 341–358. Georgantas, D.A., Grigoropoulou, H.P., 2007. Orthophosphate and metaphosphate ion removal from aqueous solution using alum and aluminum hydroxide. Journal of Colloid and Interface Science (315), 70–79. George, T., 2004. Wastewater Engineering Treatment and Reuse, fourth ed. McGraw-Hill Companies Inc. pp. 1196–1200. Kisibi, M., 2006. Chemical oxidation with hydrogen peroxide for domestic wastewater treatment. Chemical Engineering Journal (119), 161–165. Ligrini, O., Oliveros, E., Braun, A.M., 1993. Photochemical process for water treatment. Chemical Reviews 93, 671–698.
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Pelezetti, E., Schiavello, M. (Eds.), 1991. Photochemical Conversion and Storage of Solar Energy. Kluwer Academic Publisher. Qiu, Z., Jiang, W., He, Z., 2008. Post-treatment of banknote printing wastewater using polysilicate ferro-aluminum sulfate (PSFA). Journal of Hazardous Materials (166), 740–745. Rosal, R., Rodriguez, A., Perdigon-Melon, J., Peter, A., Garcia-Calvo, E., 2008. Oxidation of dissolved organic matter in the effluent of a sewage treatment plant using ozone combined with hydrogen peroxide (O3/H2O2). Chemical Engineering Journal (149), 311–318. Sarkar, B., Chakrabarti, P.P., Vijaykumar, A., Kale, V., 2005. Wastewater treatment in dairy industries-possibility of reuse. Desalination (195), 141–152.
Taner, Y., Kadir, K., Nuri, A., 2006. Treatability study on domestic wastewater using UV/H2O2 process. Applied Catalysis. B: Environmental 67 (3–4), 223–228. Teresa, Z., Gunther, G., Fernando, H., 2006. Chemical oxygen demand reduction in coffee wastewater through chemical flocculation and advanced oxidation processes. Journal of Environmental Science 19 (3), 300–305. Velasco, U., Juan, R., 2007. Enhanced coagulation under changing alkalinityhardness conditions and its implications on trihalomethane precursors removal and relationship with UV absorbance. Separation and Purification Technology (55), 368–380. Verstrate, W., 1998. Microbial Ecology, Practical Course Notes. Ghent University, Belgium.
Contents lists available at ScienceDirect
Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce
Integrated chemical treatment of municipal wastewater using waste hydrogen peroxide and ultraviolet light Zulfiqar Ahmed Bhatti a, Qaisar Mahmood a, Iftikhar Ahmad Raja a, Amir Haider Malik a, Naim Rashid a, Donglei Wu b,* a b
Department of Environmental Sciences, COMSATS Institute of Information Technology, Abbottabad 22060, Pakistan Department of Environmental Engineering, Zhejiang University, Hangzhou 310029, PR China
a r t i c l e
i n f o
Article history: Received 30 May 2009 Received in revised form 8 November 2009 Accepted 9 March 2010 Available online 12 March 2010 Keywords: Advance Oxidation Process Biological oxygen demand Biodegradable fraction Chemical oxygen demand Integrated chemical treatment Waste hydrogen peroxide
a b s t r a c t Dilemmas like water shortage, rapid industrialization, growing human population and related issues have seriously affected human health and environmental sustainability. For conservation and sustainable use of our water resources, innovative methods for wastewater treatment are continuously being explored. Advance Oxidation Processes (AOPs) show a promising approach to meet specific objectives of municipal wastewater treatment (MWW). The MWW samples were pretreated with Al2(SO4)48H2O (Alum) at different doses 4, 8, 12–50 mg/L to enhance the sedimentation. The maximum COD removal was observed at alum treatments in range of 28–32 mg/L without increasing total dissolved solids (TDS). TDS were found to increase when the alum dose was increased from 32–40 mg/L. In the present study, the optimum alum dose of 30 mg/L for 3 h of sedimentation and subsequent integrated H2O2/UV treatment was applied (using 2.5 mL/L of 40% waste H2O2 and 35% fresh H2O2 separately). Organic and inorganic pollutants, contributing towards chemical oxygen demand (COD), biological oxygen demand (BOD), turbidity and total dissolved solids were degraded by H2O2/UV. About 93% COD, 90% BOD and 83% turbidity reduction occurred when 40% waste H2O2 was used. When using fresh H2O2, 63% COD, 68% BOD and 86% turbidity reduction was detected. Complete disinfection of coliform bacteria occurred by using 40% H2O2/UV. The most interesting part of this research was to compare the effectiveness of waste H2O2 with fresh H2O2. Waste H2O2 generated from an industrial process of disinfection was found more effective in the treatment of MWW than fresh 35% H2O2. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Chemically enhanced methods, in conjunction with Advanced Oxidation Processes (AOPs) provides an efficient and promising alternative to conventional methods for the treatment of MWW. These techniques can be used in combination with the conventional methods to increase the overall performance of the wastewater treatment plant (WWTP). Various studies have shown that AOPs can be utilized to decompose substances such as insecticides, dyes, surfactants and organochlorides into relatively harmless substances such as carbondioxide and water (Pelezetti and Schiavello, 1991; Fox and Dulay, 1993; Taner et al., 2006). Treatment with alum beforehand may further enhance the wastewater treatment using AOPs. Velasco and Juan (2007), studied the effect of aluminum sulphate and Poly Aluminum Chloride (PAC1) (Qiu et al., 2008) as a coagulant for the removal of dissolved organic carbon of surface waters. It was found that the efficiency of alum was * Corresponding author. Tel.: +86 13805739113; fax: +86 571 86971898. E-mail address: [email protected] (D. Wu). 1474-7065/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2010.03.024
highly dependant on operational conditions such as pH and dose. The pH tends to affect the solubility of aluminum in coagulation, which is favored under more acidic conditions since acceptable residual aluminum concentration is achieved, whereas aluminum solubility increases and therefore pH effect must be balanced (Sarkar et al., 2005). In another study, alum and aluminum hydroxide was used for the removal of phosphates from wastewater, which are the major contributors of the eutrophication of water bodies (Georgantas and Grigoropoulou, 2007). Alum was found to be a better chemical for phosphate removal even though the active coagulant formed was Al(OH)3. Temperature did not affect alum action but aluminum hydroxide showed variations with the change of temperature. In Tunisia, the domestic wastewater was proposed to be treated using hydrogen peroxide so as to meet the problem of water shortage and recycle the wastewater for further reuse. According to the research, 30% H2O2 increase the biodegradability of some water pollutants and an optimum dose of 2.5 mL/L was sufficient to destroy majority of the risks even though it may vary according to the amount of organic matter present in water. COD reduction
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achieved was about 85%. Significant decrease in BOD5 was also observed as well as exponential inactivation of fecal coliform was achieved (Kisibi, 2006; Rosal et al., 2008). In another research, domestic wastewater was treated in batch and continuous mode using H2O2/UV/O3. Beforehand, the water was pretreated using three different methods for turbidity removal, which might hinder the effect of the latter treatment, namely; plain sedimentation. The results showed that neither plain sedimentation nor filtration showed substantial results, but aluminum sulfate at an optimum pH of 7 and optimum dose of 60 mg/L showed appreciable reduction in COD (39%) and turbidity (84%). This resulted in better effluent COD as opposed to raw wastewater. No doubt, H2O2 concentration was an important parameter, and the greatest decrease in COD was found to be at 100 mg/L. The process greatly reduced the reaction time due to UV lamps and enormous decrease in the amount of residual COD. In addition, the water microbial count was also significantly reduced (Taner et al., 2006; Teresa et al., 2006). In another study, use of ozone increased the level of hydroxyl radicals and increased the rate of degradation of organic pollutant in domestic wastewater (Ligrini et al., 1993). However, the use of fresh H2O2 may be costly. Moreover, the H2O2 alone or in combination with alum coagulation cannot effectively remove microbial loads from treated MWW which would be reused. The specific objectives of this study were to compare the effectiveness of used and fresh H2O2 to treat the MWW and to reduce the alum dose for chemical sedimentation. The combination of H2O2 with UV light was investigated to observe the effectiveness of integrated treatment of organic matter and coliform bacteria in wastewater. 2. Materials and methods 2.1. Wastewater sampling MWW samples were obtained from Shaikhul-bandi Abbottabad, Pakistan. For this purpose, 50 L plastic container was conditioned properly using running MWW. After sample collection it was corked and taken to the laboratory for further analysis and treatment. Its characteristics are given in Table. 1. Waste H2O2 was collected from drain of Tetra Brik Aseptic (TBA) machine in a food factory located in Hattar Industrial Estate, Hattar near Abbottabad, Pakistan. During TBA machine operation process fresh 35% H2O2 is changed to 40% H2O2 which is wasted and drained. MWW comprised of effluents from kitchen, washrooms, washing, laundry etc. It contained a large quantity of organic pollution with 0.9 biodegradable fractions (George, 2004). UV lamp was used for ultraviolet disinfection with specification of 240–280 nm, 16,000–32,000 microwatt-second per square with water depth range 2–3 in., brand light source USA. 2.2. Optimization of H2O2 dose In order to evaluate the optimum amount of 40% H2O2 for BOD, COD removal and total plate count reduction, a series of experiments were conducted with optimized doses of alum and then
treated with hydrogen peroxide, 28–32 mg/L and 2.5 mL/L. During pretreatment alum was tested as 4, 8, 12–50 mg/L, the alum dose between 28 and 32 mg/L was found the most effective in the removal of COD and BOD without increasing TDS of effluent. In these experiments, BOD, COD removal and reduction of total plate count were measured throughout the reaction period of 30, 60, 90, and 120 min. 2.3. Treatment system A mixer with variable rotational speed of 0–500 rotations per minute (rpm) was used to mix the sample thoroughly. One-liter of raw MWW was treated in batch reactor at mixing speed of 500 rpm. As a first step, it was treated with alum dose 28– 32 mg/L during Chemically Enhanced Primary Sedimentation (CEPS) and decant of CEPS was used further to treat with two different concentrations of H2O2/UV (35% fresh H2O2 and 40% waste or used H2O2), at the concentration (v/v) of 2.5 mL/L applied to various samples of wastewater, with continuous stirring at 500 rpm. Before starting mixing, at time zero, 35% and 40% H2O2 doses were separately added and samples were drawn at time intervals of 30, 60, 90 and 120 min after the addition to test their effectiveness. All the experiments were conducted at ambient temperature of 25 + 2 °C. Fig. 1 shows the process flow sheet and the treatment outline. 2.4. Microbial count The membrane filter technique was used for microbial analysis (Verstrate, 1998). For this purpose, various dilutions (10 3–10 6) were made of the wastewater sample. Nutrient agar (2%) was used as solidifying medium in sterilized petri dishes. 100 mL diluted municipal wastewater sample was filtered through filter paper (0.45 lm porosity) and incubated at 35 °C for 24 h. The colonies were counted under the compound microscope at magnification power of 10–15. 2.5. Analytical procedures All the analytical procedures used were the standard methods for water and wastewater analysis (APHA). Wastewater samples were analyzed prior to and after the treatment with 40% waste and 35% fresh H2O2 during separate treatment. Biological oxygen demand (BOD5) was measured by using standard method (APHA, 2005), Chemical oxygen demand (COD) was determined by closed reflux colorimetric method using digester (HACH – LTG 082.99.40001) (APHA). The wastewater sample, digestion solution and sulfuric acid were digested in vials for two hours at 150 °C. After digestion, absorbance was measured at wavelength 605 nm in a spectrophotometer (LOVIBOND tintometer GMBH, 44287 DORTMUND). The pH meter (HANNA, HI – 991003) was used for pH determination. Hydrogen peroxide was measured according to Tetra Pack Technical data manual by using hydrometer and temperature. Hydrogen peroxide value was obtained after connecting temperature and hydrometer reading on third scale of H2O2 W/ W (Tetra Pack). Fresh hydrogen peroxide was purchased from local
Table 1 Pre and post experimental analysis. Parameters
Raw WW
Alum treatment
Fresh 35% H2O2 treatment
Waste 40% H2O2 treatment
pH TDS (ppm) COD (ppm) BOD (ppm) Turbidity (NTU)
8–8.5 563–600 245–295 170–200 166–186
7.49–7.9 530–580 171–132 85–88 25.66–48
9 504 98.66 58 24
7.8 572 20 19 30
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A
1) Domestic Wastewater collection (Sample) 2) Natural Sedimentation For 1hour Chemically Enhanced Primary Sedimentation (CEPS) Alum treatment 30 mg/L (3 hrs sedimentation)
3) Chemical oxidation of CEPS effluent with Waste H 2O2 40% (collected from Food Industry) and 35 % fresh H2O2 minutes of mixing i. Sample collected after 30 and 60 minutes of mixing
ii. Sample collected after 90 minutes of mixing
4. Sample collected after 120 minutes of H2O2 mixing
B wastewater
Mixer
UV Lamp
Effluent, Water Quality within NEQs
Influent, Domestic WW
Alum Treatment
H2O2 /UV Treatment
Fig. 1. (A) Steps involved in proposed treatment process of low cost treatment of domestic wastewater. (B) Major steps involved in MWW treatment.
market 35% concentration. Various steps of the treatment have been illustrated in Fig. 1. 3. Results and discussion
reaction occur due to mixing of H2O2 and leads basic by product like HCO3 (pH 8). It seemed that pH values of MWW did not fluctuate significantly after dosing with alum and subsequent treatment with H2O2 and thus should not be considered in the process design.
3.1. Effect on pH 3.2. Changes in turbidity During high turbidity and subsequent alum dosing, the MWW pH is likely to drop because alum reacts with carbonates and hydroxyl species therefore removing base from solution. Upon its addition to water, calcium and magnesium bicarbonate alkalinity reacts with the alum to form an insoluble aluminum hydroxide precipitate. Owing to its acidic nature of alum, its addition to the wastewater slightly decreases in pH from 8.03 to about 7.4 after the addition of alum 28–32 mg/L (Table 2). The changes in pH with respect to time were inconsequential. Only a slight increase in pH was observed which may be due to the oxidation of organic dissolved solids in effluent. The pH changed from about 7.4–7.8 after 120 min when using waste H2O2 and 8–8.7 pH with fresh H2O2 (Fig. 2). The pH indicates the degradation
Natural sedimentation and CEPS with alum greatly reduced the turbidity of wastewater. By increasing the dose of alum, turbidity was reduced to 71.08% (Fig. 3) from 166 NTU to 48 NTU. The basic purpose of the alum addition was to form flocks and remove enough particulate matter to make further disinfection with H2O2 more effective. During subsequent step, H2O2/UV treatment could be effective only if particulate matter had removed in CEPS process. Turbidity removal in the range of 82.7–86.36% was observed after treating with 40% waste H2O2 and 35% fresh H2O2 when mixed for 120 min at a retention time of 12 h. Fig. 3 showed that fresh H2O2 was more effective to reduce the turbidity when compared with waste H2O2.
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Table 2 The changes in pH after treating with fresh and waste H2O2 in combination with UV light. pH
Raw ww
NS
Alum treated
30 min
60 min
90 min
120 min
Peroxide 35% Peroxide 40%
8.0 8.03
8.1 8.03
7.9 7.49
8.8 7.43
8.9 7.56
9.0 7.7
9.0 7.82
Percentage removal of some important parameters at different treatment steps.
Fig. 2. Effect of fresh H2O2 treatment on pH with the passage of time.
Fig. 3. Decrease in turbidity after treating with alum and H2O2/UV.
Turbidity removal with alum (71.08%) was observed in CEPS process and second further decrease in turbidity after 120 min of mixing with H2O2 Fig. 3. Fig. 3 shows that the maximum effect of fresh H2O2 was observed in reduction of turbidity while in Table 1 waste H2O2 was most effective against COD and BOD removal than the turbidity. 3.3. Effect on COD and BOD after treating with 35% fresh H2O2/UV and 40% waste H2O2/UV Noteworthy reduction in the COD and BOD of the DWW was seen more effective reduction by 40% waste peroxide treatment. Fig. 4 shows that both BOD and COD reductions were different when treating the wastewater samples with two different concentration of peroxide separately. Natural sedimentation and alum treatment had similar effects as shown in Fig. 4. Reduction in COD and BOD observed was up to 87% and 89% after the 30 min mixing of 40% waste H2O2 and both parameters reduced further to 96% and 90% after 60 min of mixing. After 120 min no further decrease in COD and BOD was observed. COD reduction was very sharp with in 30 min mixing of 40% waste peroxide. Effective reduction in COD and BOD occurred by treating same sample with 35% fresh H2O2 after 120 min of mixing. In this treatment, the use
of fresh H2O2/UV caused continuous decrease of COD and BOD after120 min of mixing. While using waste H2O2/UV treatment, there was continuous decrease in COD and BOD values till 60 min as 20 and 19 mg/L, after 60 min no further decrease was observed. It indicated that using waste H2O2 was effective for 60 min than fresh H2O2. Where as the obtained results of COD and BOD were 98 mg/L and 58 mg/L with fresh H2O2 showing effective results after 120 min. H2O2 is one of the most powerful known oxidizer and results in the formation of hydroxyl radicals (OH), which reacts with the pollutants such as iron, sulfide, solvents and gasoline as well as pesticides present in MWW, thus, reducing the contamination level in water. UV radiation provides the necessary energy for carrying the various chemical, physical and biological processes for the oxidizing the pollutants. These oxidations entail an array of direct and indirect photoreactions which are initiated by the absorbed UV radiation. Moreover, UV light can also disinfect the water samples. Table 1 shows the characteristics of MWW prior to and after integrated chemical treatment. A comparison of degradability of fresh and waste hydrogen peroxide has been given in Fig. 4. It is clear that when using 40% waste hydrogen peroxide with UV light, 30 min of mixing can be sufficient for the reduction of COD and BOD while fresh peroxide with UV needs more than 2.5 mL of per-
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Fig. 4. Reduction of COD and BOD after treating with 35% fresh and 40% waste H2O2 along with UV light.
Table 3 Inactivation of micro organisms after treating with waste hydrogen peroxide at different treatment steps. Microbial count Dilutions 10 10 10 10 10 a b
1 2 3 4 5
Raw water sample
Water sample NS
Water sample
After 30 min
After 60 min
After 120 min
TNTCa TNTC TNTC TNTC TNTC
TNTC TNTC TNTC TNTC TNTC
TNTC TNTC TNTC 201 CFU/10 mL 16 CFU/10 mL
4 CFU/10 mL 1 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL
0 CFUb/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL
0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL 0 CFU/10 mL
TNTC = Too numerous to count. CFU = Colony forming units.
oxide and a longer time to reach the 90% removal efficiency. In another study (Kisibi, 2006) more than 90% COD removal efficiency was achieved by 3 mL of fresh peroxide without using UV light. In our previous studies (Bhatti et al., 2009), alum alone was not sufficient to decrease COD and BOD. 3.4. Microbial activity UV treatment with peroxide can easily inactivate, even with low UV doses, chlorine resistant species such as Giardia and Cryptosporidium which a dangerous human pathogens. UV is a green technology as it is chemical free and produces no disinfection byproducts. Hence, the most significant effect was observed during the inactivation of fecal coliform, which decreased to 0 CFU/10 mL after 60 min of peroxide/UV treatment. Even after 30 min the microbial count had fallen to 4 CFU/10 mL of wastewater from too numerous to count at dilution series of 10 1. Using primary and secondary wastewater treatment processes alone for the reduction of enteric organism my results in 90–99.9% elimination, and tertiary treatment may further decimate these pathogens, the treated wastewater could still be contaminated by high microbial numbers. Henceforth, further disinfection of this treated wastewater may be necessary. For this purpose, integrated H2O2/UV treatment can be used. Table 3 showed that after using waste hydrogen peroxide along with UV light resulted in the disappearing of all coliform bacteria (CFU). According to studies, H2O2 is thought to attach with microbial cell walls, membranes and enzymatic or transport systems (Kisibi, 2006). As a result, the microbial repair mechanism, required to repair minor damage, may become overloaded, leading to their inability to repair the injuries and subsequent death. The present investigation showed that CEPS may not be sufficient alone to treat complex wastewaters especially industrial effluents. Some additional treatment technologies especially anaerobic/aerobic treatments may be employed for the effective
treatment. Further research work is required to investigate the unit cost of operations. 4. Conclusion The present study compared the effectiveness of used and fresh H2O2 to treat the domestic waste and to reduce the alum dose for chemical sedimentation. The combination of H2O2 with UV light was found very effective to decrease BOD, COD, turbidity and coliform bacteria in MWW Waste H2O2 generated from an industrial process of disinfection was found more effective in the treatment of MWW than fresh 35% H2O2. The waste hydrogen peroxide can be applied in combinations with UV light to treat MWW effectively. Acknowledgements The Chinese Major projects on control and management technology of water pollution under contract No. 2008ZX07317-008 financially supports this work. References APHA, 2005. Standard Methods for the Examination of Water and Wastewater, 21st ed. American Public Health Association, Inc., New York, USA. Bhatti, Z.A., Mahmood, Q., Raja, I.A., 2009. Sewage water pollutants removal efficiency correlates to the concentration gradient of amendments. Journal of Chemical Society of Pakistan 31 (4), 665–673. Fox, M.A., Dulay, M.T., 1993. Heterogeneous photocatalyst. Chemical Reviews 93, 341–358. Georgantas, D.A., Grigoropoulou, H.P., 2007. Orthophosphate and metaphosphate ion removal from aqueous solution using alum and aluminum hydroxide. Journal of Colloid and Interface Science (315), 70–79. George, T., 2004. Wastewater Engineering Treatment and Reuse, fourth ed. McGraw-Hill Companies Inc. pp. 1196–1200. Kisibi, M., 2006. Chemical oxidation with hydrogen peroxide for domestic wastewater treatment. Chemical Engineering Journal (119), 161–165. Ligrini, O., Oliveros, E., Braun, A.M., 1993. Photochemical process for water treatment. Chemical Reviews 93, 671–698.
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