JOURNAL OF ENGINEERING RESEARCH AND TECHNOLOGY, VOLUME 2, ISSUE 2, JUNE 2015 122 Comparison and Optimization of ozone – Based Advanced Oxidation Processes in The Treatment of Stabilized Landfill Leachate Salem S. Abu Amr* 1 , Hamidi Abdul Aziz 1, 2 , Mohammed J.K. Bashir 3 Shuokr Qarani Aziz 4 , Tamer M. Alslaibi 5 1 School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia 2 Solid Waste Management Cluster, Engineering Campus, Universiti Sains Malaysia, 14300 Penang, Malaysia 3 Department of Environmental Engineering, Faculty of Engineering and Green Technology, UniversitiTunku Abdul Rahman, 31900 Kampar, Perak,Malaysia. 4 Department of Civil Engineering, College of Engineering, University of Salahaddin–Erbil, Iraq. 5 1 Environment Quality Authority, General Administrator of Natural Resources, Water Recourse Department, Gaza Strip, Palestine *Corresponding author: Dr. Salem S. Abu Amr Tel: + 60-45996215; Fax: +60-45941009. E-mail: sabuamr@hotmail.com ABSTRACT-Leachate pollution is one of the main problems in landfilling. Among the most problematic parameters in stabilized leachate are COD, ammonia, and color. The treatment technology that can be used may differ based on the type of leachate produced. Even after treatment, the effluent characteristics are always hard to comply with the discharge standard. Ozonation is one of the chemical processes that can be used in the treatment of landfill leachate. However, its performance when use alone is low; its effectiveness can be improved using advanced oxidants. To date, application of Fenton and persulfate reagents separately to improve ozonation process in one ozone reactor was not well established. The study aimed to evaluate and compare the performance of the three treatment processes, namely ozone, ozone/Fenton and ozone/persulfate in treating stabilized leachate separately at different experimental conditions. The performance of the three methods in the treating stabilized leachate was compared. According to the results, the performance of ozone alone was poor, and utilizing new advanced oxidation material during ozonation of such leachate was required to improve leachate treatability. Ozone/Fenton process is a viable choice for degrading and decolourizing stabilized leachate. Furthermore, ozone/persulfate process has higher performance in ammonia removal as well as it has good removal efficiency of COD and color from stabilized leachate. Suitable data for establishing fully stabilized leachate treatment plant using ozone/Fenton and ozone/persulfate was suggested. The final effluent of ozone/Fenton process complied with the discharge standard for COD and colour. Index Terms - Advanced oxidation process, Ozonation, Fenton, Persulfate, treatment efficiency. Abu Amr et al.,/ Comparison and Optimization of ozone – Based Advanced Oxidation Processes in The Treatment of Stabilized Landfill Leachate (2015) 123 I. Introduction Growing population and industrial development have increased waste generated by urban areas and otherwise. In most countries, sanitary landfilling is the most common way of eliminating municipal solid waste (MSW) (Renou et al., 2008) [1]. MSW is waste from domestic, commercial, and industrial activities in urban areas (Bartone 1990) [2]. Sanitary landfilling is the most economical and environment-friendly method for disposing municipal and industrial solid waste (Tengrui et al., 2007)[3]. Malaysia generates about 6.2 million tons of solid waste per year, which equals approximately 25,000 tons per day. This amount is expected to increase to more than 31,000 tons per day by 2020 because of increasing population and per capita waste generation (Yahya 2012)[4]. Food, paper, and plastic constitute 80% of the overall weight of Malaysian waste (Manaf et al., 2009)[5]. The average amount of MSW generated in Malaysia is 0.5 kg/capita/day to 0.8 kg/person/day, and that in major cities is as high as 1.7 kg/capita/day (Kathirvale et al., 2003)[6]. Despite the many advantages of landfilling, the resulting highly polluted leachate has been a cause of significant concern, especially because landfilling is the most common technique of solid waste disposal (Ghafari et al., 2005)[7]. Landfill leachate is liquid that has seeped through solid waste in a landfill and extracted dissolved or suspended materials in the process. The environmental impact of leachate depends on leachate strength, proper leachate collection, and the efficiency of leachate treatment. Leachate contains high amounts of organic compounds, ammonia, and heavy metals and sometimes contaminates ground and surface water (Christensen et al., 2001)[8]. Landfill leachate usually contains a complex variety of materials and organic compounds, such as humic substances, fatty acids, heavy metals, and many other hazardous chemicals (Schrab et al., 1993)[9]. Researchers worldwide are still searching for a total solution to the leachate problem. Multiple-stage treatments are still required to remove leachate pollution thoroughly. No single method can effectively remove all pollutants simultaneously. Treatment by a conventional water treatment system (i.e., a combination of sedimentation, biological treatment, filtration, and carbon adsorption) cannot remove salts or organics, such as harmful recalcitrant compounds. This research aims to establish new technology and knowledge in stabilized leachate treatment by using ozone – based advanced oxidation processes (ozone, ozone/Fenton, and ozone/persulfate) to reduce treatment time and improve the efficiency of treatment by increasing oxidation potential. II. Materials and methods A. ozone oxidation Ozone experiments were conducted in a 2 L sample using an ozone reactor with a height of 65 cm and an inner diameter of 16.5 cm. The reactor was supported by a cross column ozone chamber to enhance the ozone gas diffusion (Figure 3.8 A and B). The water bath and cooling system supported the ozone reactor in keeping the internal reaction temperature at <15 °C as an optimal half-life of the dissolved ozone (30 min) in water (Lenntech, Water treatment solution, 2012). Ozone was produced by a BMT 803 generator (BMT Messtechnik, Germany) fed with pure dry oxygen with recommended gas flow rate of 200–1000 ml/min ± 10% under 1 bar pressure. The recommended input ozone gas concentration (30 – 80 in g/m 3 non-thermal plasma (NTP) ± 0.5%) was measured by an ultraviolet gas ozone analyzer (BMT 964). The initial pH of leachate samples was adjusted at different pH values ranges between 3 and 11, in order to investigate an optimal initial pH in treating stabilized leachate by ozone. The reaction time was varied between 10 and 120 min to determine an optimal ozonation time (Tizaoui et al., 2007)[10]. B. Ozone/Fenton in the advanced oxidation process Fenton reagent (H2O2/Fe 2+ ) was employed in the advanced oxidation during the ozonation of stabilized leachate. H2O2 (30%) and ferrous sulfate heptahydrate (Fe2SO4∙7H2O, 278.02 g/mol) were used in preparing the Fenton reagent, which was then added to the leachate sample in the ozone reactor as one reaction process. C. Ozone/persulfate in the advanced oxidation process Persulfate (S2O8 2− ) as sodium persulfate (Na2S2O8, M = 238 g/mol) was employed in the advanced oxidation during the ozonation of stabilized leachate, which was added to the sample in the ozone reactor as one reaction process Abu Amr et al.,/ Comparison and Optimization of ozone – Based Advanced Oxidation Processes in The Treatment of Stabilized Landfill Leachate (2015) 124 D. Biodegradable and soluble COD fractions The effects of the three ozonation treatment processes such as ozone alone, ozone/Fenton and ozone/persulfate on biodegradable and soluble characteristics of stabilized solid waste leachate were investigated in this research. The fractions of biodegradable COD(bi), non-biodegradable COD(ubi), soluble COD(s), biodegradable soluble COD(bsi), non-biodegradable soluble COD(ubsi), and particulate COD (PCOD) were examined and calculated before and after each ozonation treatment processes. III. Results and dissection A. Comparison of the three oxidation processes The comparison of different ozone oxidation processes is of interest to determine the best removal performance of COD, colour and ammonia, as well as enhancing of biodegradability and their effects on COD fractions of stabilized leachate. The aim of this study was to evaluate the above mentioned approaches in terms of reduced organic load and ammonia, decreases colour, and enhances the biodegradable characteristics of stabilized leachate. To investigate the performance of combined ozone application and two advanced oxidant reagents, stabilized leachate was treated with ozone oxidation alone, ozone/Fenton and ozone/persulfate in the AOPs, respectively. 1. Comparison on COD, colour and NH3-N removal The three ozone oxidation processes are compared in Figure 1 in terms of COD, colour, and ammonia reduction based on optimal operational conditions. In the O3/H2O2/Fe 2+ system, the Fenton ions reacted with H2O2, resulting in the formation of hydroxyl radicals (∙OH) (Eq. (1)). •OH has the potential to destroy and degrade organic pollutants (Hermosilla et al., 2009)[11]. Fe 2+ +H2O2→Fe 3+ +OH- + OH. (1) The reaction of ozone with H2O2 generates .OH radicals. H2O2 is also dissolved in water and dissociates into the hydroperoxide ion (HO 2- ), which rapidly reacts with ozone to initiate a radical chain mechanism that generates hydroxyl radicals (Staehelin et al., 1982; Glaze et al., 1987)[12,13] . The removal efficiency of the target parameters was generally decreased with increasing Fenton molar ratio. In Ozone/persulfate reaction; the Na2S2O8 dosage was fixed as a COD/S2O8 2− ratio (g/g), namely, 1/1 to 1/10 during 60 min ozonation of leachate (Fig. 3), to evaluate the role of S2O8 2− in ozonation improvement. Persulfate oxidation can be enhanced by the release of sulfate radicals, which have powerful effects on the oxidation of organics (Watts 2011)[14]. The generation of sulfate radicals during oxidation can be significantly enhanced by catalysts, such as heat and UV radiation (Eq. 2 - 4), which were found to improve the persulfate oxidation potential (Gao et al., 2012; Abu Amr and Hamidi 2012)[15, 16]. + → (2) (3) (300C10 years) leachate is >0.3, 0.1 to 0.3, and <0.1, respectively (Schiopu et al. 2010). Stabilized leachate with very low biodegradability (BOD5/COD=0.034 to 0.05) and very strong organics made the biological treatment difficult. Different ozone applications have been used to enhance the biodegradability of landfill leachate (Tizaoui et al., 2007; Bila et al., 2004; Cortez et al., 2011b; Cortez et al., 2011a) [10, 27 – 29]. However, the performance of ozone alone in improving the ratio was still very low. Based on the results, the ozone/persulfate process is an efficient method for enhancing the biodegradability of stabilized leachate (Table 1). TABLE 1 Comparison the effect of the three ozone applications on biodegradability Process BOD5/COD Raw leachate 0.034 – 0.05 Ozone alone 0.06 Ozone/Fenton 0.14 Ozone/Persulfate 0.29 4. Comparison the effect of COD fractions COD fractionation is the most important parameter for leachate quality. However, the effects of ozone applications on these fractions have not been evaluated. The effects of the three ozone applications on COD fractions in stabilized leachate are compared in this section (Table 2). The quantity of biodegradable and soluble COD fractions in raw leachate was relatively low, whereas that of non-biodegradable, non-soluble, and particulate fractions was high. As shown in Table 2, each treatment process improved the biodegradable soluble and biodegradable soluble COD fractions but reduced the non-biodegradable, particulate, and non- biodegradable soluble fractions. Based on the results, ozone/persulfate is an efficient process to improve biodegradability and solubility of organics in stabilized leachate. TABLE 2 Comparison the effect of the three ozone applications on COD fractions Process Fraction R a w le a c h a te O z o n e O n ly O z o n e /F e n t o n O z o n e /P e r s u lf a te Biodegradable COD (%) 24 28 36 39 Non-biodegradable COD (%) 76 72 68 61 Soluble COD (%) 59 65 72 72 Particulate COD (%) 41 35 28 28 Biodegradable soluble COD (%) 40 43 51 55 Non-biodegradable soluble COD (%) 60 57 49 45 0 100 200 300 400 500 600 Raw leachate Ozone only Ozone /Fenton oxidation Ozone/Persulfate oxidation S u lf a te r e si d u a l co n ce n tr a ti o n ( m g /L ) Treatment process Sulfate residual (mg/L) Abu Amr et al.,/ Comparison and Optimization of ozone – Based Advanced Oxidation Processes in The Treatment of Stabilized Landfill Leachate (2015) 127 5. Comparison on ammonia removals during aeration as a post treatment stage The removal of ammonia from leachate before and after ozonation during batch aeration as a post- treatment stage was documented to evaluate and compare the performance of the three ozonation processes. In raw stabilized leachate, full removal of ammonia was obtained after 7 days of aeration, but ammonia removal did not significantly improve after the ozone-alone process (Figure 4). In the ozone/Fenton process, ammonia was completely removed after 4 day of aeration, and removal significantly improved during the first day of aeration (69%) (Figure 5). Therefore, the performance of Fenton oxidation alone in ammonia removal was much poorer. In the ozone/persulfate process, ammonia was completely removed after only 2 days of aeration (Figure 6). Around 92% removal rate of ammonia was also achieved after the first 24 h of aeration compared with the 52% and 69% after the ozone-alone and ozone/Fenton processes, respectively. Moreover, the performance of persulfate oxidation alone in ammonia removal was much poorer. Different applications have been reported for ammonia removal during aerobic and anaerobic biological processes of leachate. Gotvajn et al. (2009)[30] obtained an 86% removal rate for ammonia after 50 h of aeration at pH of 11. Figure 4: Ammonia removal from leachate before and after ozone alone by aeration process Figure 5: Ammonia removal from leachate before and after ozone/Fenton treatment by aeration process Figure 6: Ammonia removal from leachate before and after ozone/persulfate treatment by aeration process Leachate is formed when water mainly from rain infiltrates deposited waste. As the liquid moves through the landfill, many organic and inorganic compounds, such as ammonia and heavy metals, are 0% 20% 40% 60% 80% 100% 0 100 200 300 400 500 600 700 800 900 0 1 2 3 4 5 6 7 N H 3 -N r e m o v a l ( % ) N H 3 -N ( m g /L ) Aeration time (day) NH3-N in raw leachate (mg/L) NH3-N after O3 (mg/L) NH3-N removal in raw leachate (%) NH3-N removal after O3 (%) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 100 200 300 400 500 600 700 800 900 0 1 2 3 4 5 6 7 N H 3 -N r e m o v a l (% ) N H 3 -N ( m g /L ) Aeration time (day) NH3-N in raw leachate (mg/L) NH3-N after O3/Fenton (mg/L) NH3-N removal in raw leachate (%) NH3-N removal after O3/Fenton (%) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 100 200 300 400 500 600 700 800 900 0 1 2 3 4 5 6 7 N H 3 -N r e m o v a l ( % ) N H 3 -N ( m g /L ) Aeration time (day) NH3-N in raw leachate (mg/L) NH3-N after O3/Persulfate (mg/L) NH3-N removal in raw leachate (%) NH3-N removal after O3/Persulfate (%) Abu Amr et al.,/ Comparison and Optimization of ozone – Based Advanced Oxidation Processes in The Treatment of Stabilized Landfill Leachate (2015) 128 transported into the leachate. The leachate then moves to the surface or base of the landfill cell and may pollute the surface and groundwater, which may affect human health and aquatic environment. Many factors affect the quality and quantity of leachate, such as seasonal weather variation, landfilling technique, waste type and composition, and landfill structure (Mohajeri, 2010)[20]. Leachate pollution in Malaysia is very serious, and the high generation of landfill leachate in tropical areas such as Malaysia is mainly attributed to the high amount of rainfall (Lema et al., 1988)[31]. IV. Conclusion The performance of the three ozonation techniques in AOP, namely, ozone alone, ozone/Fenton, and ozone/persulfate treating stabilized leachate was investigated and compared. According to the results, the performance of ozone alone was poor, and utilizing new advanced oxidation material during ozonation of such leachate was required to improve leachate treatability. Ozone/Fenton in AOP is a viable choice for degrading and decolourizing stabilized leachate. This process was found to be ideal because it can achieve 99% of colour removal and 79% of COD removal and up to 50% reduction in treatment time compared with the classical combination of Fenton and ozone processes. The removal efficiency was also higher. The process achieved a desired OC value for COD removal (0.29 Kg/Kg COD) compared with other methods. Furthermore, the process reduced iron ions (3.5 mg/L) to lower than the maximum acceptable levels (5 mg/L). Moreover, biodegradability (BOD5/COD ratio) was significantly improved, as were biodegradable and soluble organic fractions. Ozone/persulfate in AOP significantly removed NH3–N, COD, and colour. The process achieved high biodegradability (BOD5/COD; 0.29) compared with other treatment methods, which suggests further organic degradation via biological process as a post-treatment. The performance of the ozone/persulfate process to improving biodegradable and soluble organic fractions in stabilized leachate was better than that of other processes. Furthermore, the process completely removed iron ions from stabilized leachate and produced no undesirable sludge. Sulfate ions are not harmful to the environment, and sulfates can decompose in further biological processes. biodegradability (BOD5/COD) enhanced from 0.034 to 0.05, 0.14 and 0.29, after ozone alone, ozone/Fenton and ozone/persulfate, respectively. The results reveal that ozone/persulfate in AOP achieved higher ratio among the three treatment process which recommended suggesting biological process as a post treatment for further organic degradation and ammonia removal. The effect of the three ozonation processes on COD fractions in stabilized leachate was documented in this research. 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Dr. Salem Abu Amr is a post doctorate in Civil/Environmental engineering, University sciences Malaysia (USM), he has a Ph.D in Environmental Engineering from the USM in 2013. He obtained his B.Sc. in Environment and Earth Sciences in 2001 and his M.Sc. in Water Resources Management from Faculty of civil engineering, Islamic University, Gaza in 2005. He acquired practical experience working on various environmental engineering aspects including water/wastewater treatment and management, Drinking water and sanitary sewer distribution system monitoring, and development of advanced water/wastewater treatment technologies. He has reported over 35 publications in several international conferences and ISI journals: 20 articles in referred ISI & Scopus index journals, 5 international articles, 10 publications in international conference proceedings in this field. Dr. Hamidi Abdul Aziz is a professor in environmental engineering in the School of Civil Engineering of Universiti Sains Malaysia. Professor Aziz received his PhD degree in civil engineering (environmental engineering) from the University of Strathclyde in Scotland in 1992. To date, he has published over 200 refereed articles in professional journals and proceedings, 16 chapters in refereed international books, and 8 chapters in refereed national books. He has also published 9 research books. Dr Aziz continues to serve as a peer reviewer for more than 40 international journals. To date, he has reviewed 400 international papers. He also serves as a guest editor of the special issue on landfill leachate management and control of the International Journal of Environment and Waste Management (IJEWM). Professor Aziz currently serves as the editor-in-chief of the International Journal of Scientific Research in Environmental Sciences (IJSRES). He also serves as the managing editor of the International Journal of Environment and Waste Management, IJEWM and the International of Journal of Environmental Engineering, IJEE. Aside from these, he is a member of the editorial board of 10 other international journals in the environmental discipline. Professor Aziz's research focuses on alleviating problems associated with water pollution issues from industrial wastewater discharges and from solid waste management via landfilling, such as landfill leachate. Advanced oxidation processes is one of his research focuses. Dr Mohammed J.K. Bashir is an Assistant Professor in environmental engineering at the faculty of engineering and green technology, Universiti Tunku Abdul Rahman (UTAR), Malaysia. Dr. Bashir received his B.Sc. degree in Civil Engineering from Islamic University of Gaza, Palestine. He received M.Sc and Ph.D in Environ. Eng. from School of Civil Engineering, Universiti Sains Malaysia. He received several award and has published many refereed articles in professional journals/proceedings. Dr. Bashir's research has focused on wastewater treatment, solid and hazardous waste management, environmental sustainability. Dr. Shuokr Qarani Aziz is Asst. Professor in the Civil Engineering Department, College of Engineering, Salahaddin University-Erbil, Iraq. Currently, he is Head of Civil Engineering Department. He received B.Sc. degree in Civil Engineering and M.Sc. in Sanitary Engineering from Salahaddin University-Erbil, Iraq; PhD in Environmental Engineering from Universiti Sains Malaysia (USM), Malaysia. He has more than 40 published works in the fields of water and wastewater treatment, solid waste management and noise pollution. Dr.Tamer M. Alslaibi has a Ph.D in Water Resources Engineering from Universiti Sains Malaysia under The World Academy of Sciences (TWAS) fellowship. Has M.Sc. in Water Resources Engineering from the Islamic University of Gaza. One of the winners of the Energy Globe World Award prize as a best practical project for water category in 2014. Marquis Who's Who, as a testament to his hard work, has selected his biographical profile for inclusion in the new Who's Who in the World® 2015 (32nd Edition). Water and wastewater treatment, activated carbon production, adsorption and solid waste management are the area of his primary research interest. Authored or co-authored several papers in ISI journals and international conference proceedings in the fields of his interest. Currently, works as a director of water quality department in Palestinian Environment Quality Authority and as a reviewer in more than ten high impact factor journals (ISI). A member in International Water Association (IWA) and American Institute of Chemical Engineering (AICHE). javascript:AL_get(this,%20'jour',%20'Water%20Sci%20Technol.');