Treatment of Compost Leachate by Sequential Coagulation and Photo Fenton Process

Transcription

1 Treatment of Compost Leachate by Sequential Coagulation and Photo Fenton Process Monika Dubey 1 Mamta Awasthi 2 Centre for Energy and Environmental Engineering Centre for Energy and Environmental Engineering National Institute of Technology, Hamirpur National Institute of Technology, Hamirpur Himachal Pradesh, India Himachal Pradesh, India ABSTRACT A study on the effectiveness of sequential Coagulation Flocculation and Photo Fenton method on the treatment of Compost Leachate has been carried out. The effect of ph and Ferric Chloride (coagulant) dosage on the coagulation performance was investigated. Chemical Oxygen Demand (COD) and Turbidity removal efficiency was found to be 62% and 74%, respectively at an optimum dosage of 400 mgl -1 at ph 4. For the Photo Fenton process, the optimum value for the dosage of H 2 O 2, H 2 O 2 :Fe 2+ ratio, ph and reaction time were evaluated and were found to be 3000 mgl -1, 8:1, 3 and 2 hours, respectively. Pseudo-first order, pseudo-second order, balcerzak's model were developed for the optimum dosage by drawing linear graphs and corresponding regression coefficients were found. The COD removal efficiency for photo fenton Process was 93%. The total removal (percentage) and final leachate effluent concentration (mg/l) of COD, BOD, NH 3 -N, SS and total Phosphorus was 97.34% (81 mgl -1 ), 94% (27.1 mgl -1 ), 98.50% (20.02 mgl -1 ), 97.90% (25.20 mg/l -1 ) and 94.38% (0.84 mgl -1 ), respectively, which reached the local discharge standard. The kinetic study reveals that the photo fenton reaction follows Pseudo First Order Kinetics with regression coefficient of It was observed that by the process, the organic matter in the leachate was oxidized as the BOD/COD ratio increased from to So, it has been proved that the combination of coagulation-photo-fenton is a feasible technique and is recommended for compost leachate treatment. Keywords Compost Leachate, Ferric Chloride coagulation, Photo fenton. 1. INTRODUCTION Population growth and improvement in quality of the human life have led to an increase in waste production in many countries [1]. Over recent years, organic waste management policies have been encouraging recycling. The compost process is used widely to transform wastes to fertilizers. Leachate from composting is defined as the aqueous effluent generated as a consequence of rainwater percolation through wastes, biochemical processes in waste s cells and the inherent water content of wastes themselves. The compost leachate contains a high concentration of dissolved bio degradable and non-biodegradable compounds including heavy metals [2-3]. Leachate characteristics depends on a variety of parameters such as type of waste deposited, climatic conditions and mode of operation to count a few. It can be detrimental to surrounding soil, surface and sub-surface water resources. This makes the compost leachate treatment an important step [4-5]. Various combinations of physiochemical and biological processes have been applied for its treatment [6-9]. Nevertheless, difficulties occur in the biological treatment due to the presence of nonbiodegradable recalcitrant materials [10-11]. These methods are neither efficient, nor cost effective for the treatment of wastewaters containing toxic pollutants. This requires some novel technique to transfer highly toxic chemicals [12]. Over the past two decades, advance oxidation processes have become quite popular. The AOPs produce highly reactive hydroxyl radicals, which could degrade almost all the organic pollutants and oxide them to water and carbon dioxide [13]. Due to the ease of the process and its usage in different scales, it is broadly used for waste water remediation [14]. 558 Monika Dubey, MamtaAwasthi

2 Since the process involves high cost, an effort for the reduction in consumption of H 2 O 2 is very important. The photo-fenton process is the combination of Fenton (hydrogen peroxide and Iron (II) oxide ions) and UV. As UV increases the hydroxyl radical production, the efficiency of the process can be further be improved as compared to other AOPs methods [15-16]. Optimization of photo fenton process leads to reduction in consumption of H 2 O 2, Iron salt and electric power. This reduces the overall cost involved in the process. Detailed study on compost leachate has not been covered largely in scientific Literature. Amongst the chemical method found in the scientific literature, AOPs have shown good removal efficiencies in the treatment of MSW landfill leachate [17-18]. The main goal of the present study is the treatment of compost leachate in two phases. The first phase involves coagulation/flocculation process for the removal of COD and Turbidity from the compost leachate whereas the second phase involve Photo fenton process for removal of COD from the compost leachate. The specific aim of the study was to study the effect of operational parameters such as ph, coagulant dosage, concentration of H 2 O 2 and ferrous salt, and the optimum reaction time and to obtain a kinetic equation which the photo fenton reaction follows. 2. MATERIAL AND METHODS 2.1 Sampling and Leachate Characterization: The Leachate was collected from the compost plant in Hamirpur, Himachal Pradesh, India. The leachate was collected on weekly basis and characterized immediately after it was brought to the laboratory. For precision, testing was done in set of three. The concentrations were measured according to the standard methods (APHA, 1995). The characteristics of the leachate sample are shown in Table 1. Table 1. Characteristics of landfill leachate sample Characteristic Range Mean COD BOD SS NH 3 -N Total Phosphorus Lead NIL NIL The samples were taken to the laboratory in the sealed plastic barrels, stored at 4 for later analyses. The initial ph of the sample was determined by a ph meter (Model: HI 96107), the other parameters were determined following standard methods for the examination of water and wastewater (APHA AWWA- WEF, 1995). 2.2 Experimental Set up and Procedure The coagulant used in this study was Ferric Chloride (Merck, Germany). Sodium hydroxide (Merck, Germany) and sulfuric acid (Merck, Germany) were used to adjust ph of the solutions. 500ml of the sample were taken in 1L of beaker and ph adjusted from 3 to 8 at desired dose of coagulant and jar test was conducted. The samples were rapidly mixed at 200 r min -1 for two minutes, followed by 25 minutes of gentle agitation at a stirring speed of 25 r min -1. The flocs were allowed to settle for 2 hours and the supernatant was carefully removed by pipetting just below the surface of settled water. The supernatant was analysed for COD and Turbidity removal. At the optimum ph, the dosage of Ferric Chloride was varied from 50mg/L to 500 mg/l. Again, the supernatant was analysed for COD and turbidity removal. This gave the optimum ph and coagulant dose. For the photo fenton process, 30% Hydrogen peroxide (H 2 O 2 ) and ferrous sulphate (FeSO 4.7H 2 O) was used as the Fenton's reagent (Fe 2+ /H 2 O 2 ). The experimental setup for photo fenton reaction consist of a 40cm x 40cm x 70cm wooden box with an upper opening for incandescent lamp and a small exhaust fan at the side of the 559 Monika Dubey, MamtaAwasthi

3 box. At the top is a 100watt incandescent lamp. Inside the box, a beaker containing the leachate and the fenton reagent, is placed over the magnetic stirrer. The magnetic stirrer is to mix the fenton reagents in the leachate homogeneously. The exhaust helps to avoid any temperature rise inside the chamber and to vent off any gases if formed during the reaction. The door of the box is closed after when the fenton reagent is added. The schematic diagram of the setup is shown in figure 1. Figure 1. Schematic diagram of the photo fenton set up. COD was determined. Fenton reagent dosage, ph and the reaction time were optimized. H 2 O 2 concentration was optimized by varying the concentration from 1 g/l to 5 g/l at fixed Fe 2+ concentration of 500mg/L and ph = 4 with total reaction time of 2 hours. At this optimum dose of H 2 O 2, H 2 O 2 :Fe 2+ ratio was optimized for the same condition. Similarly, the optimum ph and reaction time was obtained. As the optimization of the photo fenton reaction is quiet time consuming, a Kinetic model representing the whole photo fenton reaction was required. This equation could easily help us to get the required amount of fenton reagents and reaction time for the required degree of treatment. The kinetic study was done at optimum dosage, at different time for photo fenton process. Pseudo first order, Pseudo Second order and Balcerzak s models were developed for optimum dosage by drawing linear graph and corresponding regression coefficients were found. 3. RESULTS AND DISCUSSION 3.1. Leachate Characterization The characteristics of compost Leachate is given in Table 1. All the parameters were found to be much higher than the discharge limits. The BOD/COD ratio of the raw Leachate was This suggests that the leachate possessed very less bio degradability. 3.2 Coagulation Effect of ph on COD and Turbidity Removal Efficiency To study the effect of initial ph on COD and Turbidity removal efficiency, the FeCl 3 dosage was fixed to 200 mg/l and the ph was varied from 3 to 8. Till ph 4, the percentage COD removal increased. Beyond ph 4, the removal efficiency decreased. The maximum COD removal is 45% at ph 4. The Turbidity removal efficiency increased from 59% to 68% at ph 4. After this ph, the Turbidity removal showed a clear declining pattern. The result is in agreement with those reported by Li et al. (2010) [19] and Maranon et al. (2008) [20]. They found in their studies found that COD removal was better for ferric chloride in acidic ph. Coagulation mechanism is highly ph dependent. Ferric ion in acidic condition hydrolyze to form polynuclearcation such as 560 Monika Dubey, MamtaAwasthi

4 Fe(OH) 2+, Fe 2 (OH) 2 4+, Fe 3 (OH) 4 5+ and other species with positive charges that interact with negative colloids causing charge neutralization and hence destabilization of colloid particles (Li et al., 2010) [19]. Fig 2. Effect of ph on COD and Turbidity removal efficiency Effect of FeCl 3 Dosage on COD Removal Efficiency As the dosage of FeCl 3 increased, the percentage removal of COD and Turbidity also increased. At 400 mg/l of FeCl 3 dosage, the percentage removal of COD and Turbidity was 62% and 74% respectively. Beyond this dosage, the percentage removal decreased. Similar trend has been reported by Wang et al., 2002 [21] and Rivas et al., 2004 [22]. There was no significant removal of COD at higher dosage which could be due to unavailability of surface particles for attachment of segments resulting from the destabilization of particles. Fig 3. Effect of FeCl 3 dosage on COD and Turbidity removal efficiency Photo fenton Process H 2 O 2 Dosage To study the effect of H 2 O 2 dosage on COD removal efficiency, 20ml of sample was added with 500 mg of Fe 2+ with varying concentrations of H 2 O 2 (1, 2, 3, 4, 5 g/l) and ph equal to 4. The effect of H 2 O 2 dosage on COD removal efficiency is shown in Fig 4. The COD removal percentage increased with increase in H 2 O 2 dosage till H 2 O 2 dosage of 3g/L. At 4g/L it became stable and thereafter showed a declining trend. The maximum COD removal was 86%. Thus, the optimum dose of H 2 O 2 for this reaction is 3000 mg/l. Similar results were observed by Zazouli et al. [23]. Zazouli et al reported the maximum COD removal was 84%. A low concentration of H 2 O 2 did not generateenough OH. in the solution. Besides, increasing H 2 O 2 concentration 561 Monika Dubey, MamtaAwasthi

5 had two opposite effects [24]. Thus, there was an optimum concentration of H 2 O 2 to achieve maximum removal of COD. Fig 4. Percentage COD removal versus H 2 O 2 dosage curve Effect of H 2 O 2 :Fe 2+ ratio 20mL sample was added with 3000 mg/l of H 2 O 2 and varying concentrations of H 2 O 2 : Fe 2+ (H 2 O 2 /Fe 2+ = 2:1, 4:1, 6:1, 8:1, 10:1) at ph equal to 4 and reaction time of 2h. The effect of H 2 O 2 :Fe 2+ ratio on COD removal efficiency is shown in Fig 5. The percentage COD removal showed an increase till H 2 O 2 :Fe 2+ ratio of 8:1. Beyond this ratio, the percentage removal decreased. At H 2 O 2 :Fe 2+ ratio of 10:1, the percentage COD removal is 72%. This wss probably because the oxidation process led to an increase in the production of Hydroxyl Radical up to certain concentration when the hydrogen peroxide ratio was increased. The hydroxyl radical was able to oxidize the almost all organic pollutant. When the H 2 O 2 wasincreased further, it started to react with hydroxyl radicals, acting as a free radical scavenger itself, decreasing the hydroxyl radical concentration and generating per hydroxyl radicals (HO 2. ) with much less oxidation capacities [24]. Hence, the removal rate decreased. The maximum percentage removal was 83%. 562 Monika Dubey, MamtaAwasthi Fig 5. Percentage COD removal versus H 2 O 2 :Fe 2+ ratio

6 Effect of ph The initial ph of the 20ml sample was varied (2, 3, 4, 5, 6) using dilute H 2 SO 4 and dilute NaOH solution at optimum dosage of H 2 O 2 equal to 3000mg/Land H 2 O 2 :Fe 2+ ratio of 8:1. Reaction time of 2h was given. The effect of initial ph on COD removal efficiency is shown in Fig 6. At the initial ph of 2, the percentage COD removal was 37%. The percentage removal increased drastically to 93% at ph equal to 3. Beyond this ph, COD showed a declining trend. At ph equal to 6, the percentage COD removal was just 24%. The optimum ph found in the study is 3. The results obtained agreed well with those reported by other authors except that for Hermosilla et al [25] that reported an optimal ph of 2.5 for photo fenton process. The ph affects the role in controlling the activity of the oxidant and the substrate, the speciation of Iron and the stability of Hydrogen Peroxide [26-27]. ph in the acidic range favours oxidation. Fig 6. COD removal percentage versus initial ph graph Effect of reaction Time 20mL sample was added with optimum dosage of 3000mg/L H 2 O 2. H 2 O 2 :Fe 2+ ratio of 8:1 at ph equal to 3 at varying reaction time (30, 60, 90, 120, 150 minutes). The effect of reaction time on the COD removal percentage is shown in Fig 4.6. The COD percentage removal for 30 minutes reaction time was 88%. This increased to 93% at reaction time of 2 hour. On further Increase in the reaction time, the percentage COD removal decreased to 89%. Similar trends in COD removal was observed by Ebrahiem, E.E. et al [28] where the optimum reaction time was 40 minutes. Electricity consumption represent 60% of the total operating costs in the photo fenton process. So, the reaction time needs to be the minimum possible. However, if the reaction time is too short, the intermediates remaining in the solution could structurally be similar to initial biorecalcitrant compounds. Also, at short photo treatment time, H 2 O 2 concentration may be high enough to inhibit the biological treatment if required as post treatment [28]. Fig 7. COD removal percentage versus Reaction Time graph 563 Monika Dubey, MamtaAwasthi

7 3.4 Kinetic Study Pseudo-first order, pseudo-second order, balcerzak's model were developed for the optimum dosage of H 2 O 2 : Fe 2+ ratio of 8:1, H 2 O 2 dosage = 3g/L at initial ph 3 and reaction time 2h, by drawing linear graphs and corresponding regression coefficients were found. Pseudo-first order reaction with respect to the COD value is given as: d[cod] / dt = - k 1 [COD] Regression coefficient is found to be The Pseudo-first order reaction model is: ln [COD] = t Pseudo-second order reaction with respect to the COD value is given as d[cod] / dt = - k 2 [COD] 2 Reaction constant, k = 5.0, Regression Coefficient (R 2 ) = is obtained. pseudo-second order reaction model is: y = 5E-05x Balcerzak's equation with respect to the COD value is given as: d[cod]/dt = - a [COD]t m where, a, m - Balcerzak's constants depending on initial reagent concentration. The balcerzak's constant a, m obtained from the plotted graph is and respectively. The regression coefficient obtained in balcerzak's model is Thus, the balcerzak's equation becomes: d[cod]/dt = [COD]t Fig. 8 ln [COD] vs Time graph for Pseudo First Order Reaction. Fig 9. 1/C versus Time graph 564 Monika Dubey, MamtaAwasthi

8 Fig 10. ln[ln(c 0 /C)] versus ln t graph 4. CONCLUSION Coagulation-Fenton process was used to treat compost leachate collected from Compost plant, Hamirpur, Himachal Pradesh, India. Results of the experiments revealed that: The optimum condition for coagulation was at ph equal to 4 and FeCl 3 dosage equal to 400 mg/l. At this dosage, the percentage COD and Turbidity removal was 62% and 74% respectively. For photo fenton process, the optimum dose of H 2 O 2 is 3000 mg/l, H 2 O 2 :Fe 2+ ratio of 8:1 at initial ph equal to 3 and reaction time equal to 2 hours. The total COD removal is %. Percentage removal of other parameters studied are shown in table 2. The reaction follows Pseudo First Order Kinetics with regression coefficient equal to The equation is ln [COD] = t The results of the present study have clearly delineated that coagulation combined with photo fenton provides a promising technique for the treatment of composting leachate. The initial, final and % removal of the characteristic parameters is shown in table 2. Table 2. The Initial, Final and Percentage Removal of various Characteristic Parameters. Parameter Initial (mg/l) Final (mg/l) % Removal COD BOD SS NH 4 -N Total Phosphorus REFERENCE [1] Abu Amr, S.S., Aziz, H.A., and Adlan, M.N. Optimization of stabilized leachate treatment using ozone/persulphate in advance oxidation process. Waste management Vol.33, Vol. 6, pp , DOI: /j.wasman (2013). [2] Aziz, S.Q., Aziz, H.A., Yusoff, M.S., Bashir, M.J.K., Landfill leachate treatment using powdered activated carbon augmented sequencing batch reactor (SBR) process: Optimization by response surface methodology, J. Hazard. Mater., 189, (2011). [3] Bu, L., Wang, K., Zhao, Q.L., Wei, L.L., Zhang, J., Yang, J.C., Characterization of dissolved organic matter during landfill leachate treatment by sequencing batch reactor, aeration corrosive cell-fenton, and granular activated carbon in series, J. Hazard. Mater., 179, (2010). [4] Jessica, M. M., Markus F., Hamid I., Patrick M. F., Curtis, H., Craig, G. C., Zhen, Q. S., Intermittent rainstorms cause pulses of nitrogen, phosphorus, and copper in leachate from compost in bioretention systems, Sci. Total. Environ., 537, (2015). [5] Kayleigh, B., Avik, J. G., Jillian, H., James, F., Anthony, Z., Membrane bioreactor technology: A novel approach to the treatment of compost leachate, Waste. Mange., 33, (2013). 565 Monika Dubey, MamtaAwasthi

9 [6]Dollerer, J. and Wilderer, P.A. Biological treatment of leachates from hazardous waste landfills using SBBR technology. Water Sci. Technol., 34: DOI: /S (96) (1996).. [7] Kargi, F. and Pamukoglu, M.Y. Adsorbent supplemented biological treatment of pre-treated landfill leachates by fed-batch operation. Bioresour. Technol., 94: DOI: /j.biortech (2004). [8] Lo, I. Characteristics and treatment of leachates from domestic landfills. Environ. Int., 22: DOI: / (96) (1996). [9] Kennedy, K.J. and Lentz, E.M. Treatment of landfill leachate using sequencing batch and continuous flow upflow anaerobic sludge blanket reactors. Water Res., 34: DOI: /S (00) (2000). [10] Cortez, S., Teixeira, P., Oliveira, R., Mota, M., Mature landfill leachate treatment by denitrification and ozonation, Process Biochem. 46, (2011). [11] Lim, S.J., Kim, T.H., Applicability and trends of anaerobic granular sludge treatment processes, Biomass Bioenerg., 60, (2014). [12] Swaminathan, M., Murugandham, M., and Sillanpaa, M. Advance oxidation processes for waste water treatment. International Journal of Photoenergy. Vol (2013), Article ID , p.3, DOI: /2013/ [13] Mahamuni, N.N. and Adewuyi,.G. Advance oxidation Processes involving ultrasound for waste water treatment: A review with emphasis on cost estimation. UltrasonicsSonochemistry. Vol. 17 No. 6, pp ,DOI: /j.ultsonch (2010). [14] Ahmadi, M., Vahabzadeh, F., Bonakdarpour, B., Mofarrah, E., and Mehranian, M Application of the central composite design and response surface methodology to the advance treatment of olive oil processing waste water using Fenton s peroxidation. Journal of Hazardous Materials, Vol 123, Nos. 1-3, pp DOI: /j.jhazmat (2005). [15] Babupunnoswami, A. and Muthukumar, K A review on Fenton and improvement to the Fenton Process of waste water treatment. Journal of environmental chemical engineering, Vo. 2 Issue 1, March 2014,pp , DOI: /j.jeee (2013). [16] Klamerth, N., Malato, S., Aguera, A., and Feranandez- Alba A. Photo- Fenton and modified Photo Fenton at neutral ph for the treatment of emerging contaminants in waste water treatment plant effluents A comparison. Water Research, Vol. 47, No. 2 p , DOI: /j.waters (2013) [17] Zhang, H., Choi, H.J., and Huang, C.-P. Optimization of Fenton process for the treatment of landfill leachate Journal of Hazardous materials, Vol. 125, Nos.1-3, pp ,doi: /j.jhazmat c(2005). [18] Umar, M., Aziz., H.A., and Yusoff, M.S. Trends in the use of Fenton, electro fenton and Photo fenton for the treatment of landfill leachate. Waste management, Vol. 54, No. 30, No. 11, pp , DOI: /j.wasman (2010). [19] W. Li, T. Hua, Q. Zhou, S. Zhang, F. Li Treatment of stabilized landfill leachate by the combined process of coagulation/flocculation and powder activated carbon adsorptiondesalination, 264 (2010), pp [20] E. Maranon, L. Castrillon, Y. Fernandez-Nava, A. Fernandez-Mendez, A. Fernandez-Sanchez. Coagulation flocculation as a pretreatment process at landfill leachate nitrification denitrification plantj. Hazard. Mater., 156 (2008), pp [21] Wang, ZP; Zhang, Z; Lin, YJ; Deng, NS; Tao, T; Zhuo, K; Landfill Leachate Treatment by a Coagulationphotooxidation process. J. Hazard. Mater. 95 (1/2), (2002). [22] F.J. Rivas, F. Beltran, F. Carvalho, B. Acedo, O. Gimeno, Stabilized leachate: sequential coagulation-flocculation + chemical oxidation process, Journal of Hazardous Materials,B116, pp , October [23]Mohammad Ali Zazouli, ZabihollahYousefi, Akbar Eslami and Maryam BagheriArdebilian. Iranian Journal of Environmental Health Science & Engineering2012 9:3 DOI: / [24] Primo O, Rivero MI, Ortiz I: Photo Fenton process as an efficient alternative to the treatment of landfill leachate. J Hazard Mater 2008,153: [25] Hermosilla D, CortijoM,Huang CP: Optimizing the treatment of landfill leachateby conventional fenton and photo fenton processes. Sci total Environ 2009, 407: [26] GoiA,Veressinina Y, Trapido M: Fenton process for landfill leachate treatment: evaluation of biodegradability and toxicity. JE nvironeng 2010,136:46-53 [27] Farrokhi M, Mousavy GR, Takdastan: The study on biodegradability enhancement of landfill leachate by Fenton oxidation. Iran J Health and Environ 2009, 2: [28] Ebrahim, M., Mustafa, Y. A., &Alwared, A. I. Removal of oil wastewater by advanced oxidation process/homogenous process. Journal of Engineering, 6(19) (2013). 566 Monika Dubey, MamtaAwasthi