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Coagulation-Flocculation As a Submerged Biological Filter Pre-Treatment with Landfill Leachate

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Coagulation-Flocculation As a Submerged Biological Filter Pre-Treatment with Landfill Leachate Coagulation-flocculation as a submerged biological filter pre-treatment with landfill leachate A. Gálvez Perez1,2, A. Ramos1,2,3, B. Moreno1,2,3 & M. Zamorano Toro1,2 1Department of Civil Engineering, Granada University, Spain 2MITA Research Group 3Institute of Water Research Abstract Landfill leachate may cause environmental problems if it is not properly managed and treated. An appropriate treatment process of landfill leachate often involves a combination of physical, chemical and biological methods to obtain satisfactory results. In this study, coagulation-flocculation was proposed as a pre- treatment stage of partially stabilized landfill leachate prior to submerged biological filters. Several coagulants (ferric, aluminium or organic) and flocculants (cationic, anionic or non-ionic) were assayed in jar-test experiments in order to determine optimum conditions for the removal of COD and total solids. Among the cationic flocculants, that of highest molecular weight and cationicity (CV/850) showed highest removal efficiencies (15% COD and 8% TS). Organic and aluminium coagulants showed better results than ferric coagulants. Coagulant removal efficiencies were between 9% and 17% for COD and between 10% and 15% for TS. Doses of 1 ml/l of coagulant were preferred. Some combinations of coagulant and flocculant enhanced the process. The best combinations obtained were FeCl3+A30.L, Ferriclar+A20.L, SAL8.2+A30.L and PAX-18+A30.L, which presented COD removal efficiencies between 24% and 37% with doses between 10 and 18 ml/l. Keywords: landfill leachate, coagulation-flocculation, submerged biological filter pre-treatment. Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-738-8 214 Waste Management and the Environment II 1 Introduction Landfills constitute one of the most common methods for the elimination of municipal waste but this type of waste disposal presents the problem of leaching [1]. Landfill leachate is generated as a result of precipitation, surface run-off and infiltration or intrusion of groundwater percolating through a landfill [2]. It has been identified as a potential source of soil, ground and surface water contamination if it is not properly collected, treated and safely disposed [3]. The composition of leachates determines their treatability [3]. The treatment processes used for landfill leachates often involve a combination of techniques involving physical, chemical and biological methods, since it is difficult to obtain satisfactory results by using any one of those methods alone [4,5]. Combined chemical and biological treatment has been investigated [6]. Coagulation-flocculation pre-treatment of landfill leachate may be applied as a useful pre-treatment step, especially for fresh leachate, prior to biological treatment, or as a post-treatment step for partially stabilized leachate [3]. Process efficiency for the treatment of leachate depends on leachate characteristics, pH, doses and type of chemical products used [5]. Aluminium sulphate, ferrous sulphate, ferric chloride and ferric chlorosulphate are commonly used as coagulants; iron salts have proved more efficient than aluminium ones, resulting in sufficient chemical oxygen demand (COD) reductions, up to 56%, whereas the corresponding values in the case of alum or lime addition have been lower, between 39% and 18% respectively [3,5]. Amokrane et al [7] and Tatsi et al [3] show that the percentage removal of COD and TS obtained by coagulation- flocculation is 10–25% with young leachates and 50-65%, with stabilised leachates or leachates pre-treated by biological processes. Submerged biological filters use support materials for the growth of biofilm; the support remains completely submerged, operating continually as a filter. The MITA research group from Granada University used this technology to treat landfill leachate in a laboratory pilot experiment. The experiment showed that the technology may be suitable as a substitute for other treatments of landfill leachate, although it would be necessary to define the design parameters [8]. After biological treatment, pollution parameters were often higher than reject requirements, so a combination of appropriate techniques was necessary. The objective of the present study is to examine the efficiency of coagulation- flocculation and precipitation processes for the treatment of landfill leachate as pre-treatment with a submerged biological filter. 2 Materials and methods 2.1 Landfill leachate The landfill leachate used in this study was taken from the sanitary landfill site at Alhendín (Granada, Southern Spain). A high density landfill connected to an urban waste composting and recovery plant; it has been in operation since 1999 and receives that part of the waste which cannot be recycled or recovered, Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-738-8 Waste Management and the Environment II 215 approximately 60% of the total entering the facility. The leachate produced in the landfill is collected through a drainage network into an artificial pond from which it is recirculated through the deposited landfill. For leachate characterization, the samples were analyzed for chemical and biological oxygen demand (COD, BOD5); total solids (TS), total suspended and dissolved solids (TSS, TDS); ammonia nitrogen (N-NH3), total Kjeldahl nitrogen (TKN) and pH in accordance with the Standard Methods for the Examination of Water and Wastewater [9]. The values of these main parameters are presented in Table 1. Table 1: Landfill leachate characterization. Parameters Values COD 24675 (mg/l) BOD5 8250 (mg/l) BOD5 /COD 0.33 TS 36444.42 (mg/l) TSS 573.17 (mg/l) TDS 35871.25 (mg/l) TKN 4049.34 (mg/l) N-NH3 3537.26 (mg/l) pH 7 2.2 Coagulation-flocculation studies Coagulation-flocculation studies were carried out in a conventional jar-test apparatus equipped with 6 beakers of 1 litre volume and with the following stages: rapid mixing, slow mixing and settle. The duration and speed of mixing are critical parameters in both the first and second stages. For the present study the following values were selected from the bibliography: in rapid mixing, 5 minutes at 150 rpm, used by Diamadopoulous [4] and Silva et al [10]; in slow mixing 15 minutes at 40 rpm, used by Amokrane et al [7] and Trebouet et al [11], and in the settle stage 60 minutes, used by Diamadopoulos [4], Yoon et al [12], Lin and Chang [10], Kargi and Yunus Pamukoglu [5] and Tatsi et al [3]. These samples were analyzed for COD, TS and pH in accordance with the Standard Methods for the Examination of Water and Wastewater [9]. Chemical reagents used in the experiments included several coagulants and flocculants supplied by Kemira® and Chemipol®. The coagulants supplied by Kemira® included two ferric coagulants (Ferric Chloride (d = 1.438 g/ml) and Ferriclar (d = 1.62 g/ml)) and two aluminium coagulants (PAX-18 (d = 1.36 g/ml) and SAL-8.2 (d = 1.32 g/ml). There was also a coagulant-flocculant supplied by Chemipol®, Chemifloc-PA/15, which was a polyamine. Among the flocculants supplied by Chemipol®, some were cationic (Chemifloc-CM/25, CM/80, CV/300 and CV/850), with different molecular weight and cationicity; some were anionic (Chemifloc-A/05.L, A/10.L, A20.L and A/30.L), and one was non-ionic (Chemifloc-N01.L). Experimental process stages and doses are summarized in Table 2. Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-738-8 216 Waste Management and the Environment II Table 2: Experimental process stages. Doses (ml/l) Stages Chemical products Coagulant Flocculant 1st:Cationic CM/25, CM/80,CV/300, CV/850 by 0, 0.5, 1, 2, flocculants Chemipol® 3, 4 FeCl , Ferriclar, PAX-18, SAL 8.2 by 0, 0.2, 0.4, 2nd : 3 Kemira® and PA/15 by Chemipol® 0.6, 0.8, 1, Coagulants 2, 3 rd FeCl3 Kemira® A05.L Chemipol® 3 : A10.L Chemipol® Coagulants Ferriclar Kemira® 0, 3.5, 7, A.20L Chemipol® 1 + PAX-18 Kemira® A.30L Chemipol® 10, 14, 18 flocculants SAL 8.2 Kemira® N01.L Chemipol® 3 Results and discussion 3.1 Experiments with different cationic flocculants Four cationic flocculants with different molecular weight and cationicity (CM/25, CM/80, CV/300 and CV/850) were used in different doses between 0 and 4 mg/l at free pH for COD and TS removal. The results of this experiment are shown in Figure 1. B A 18 18 16 16 14 14 12 12 10 10 8 8 6 6 4 TS (%) removal COD removal (%) removal COD 4 2 2 0 0 00.51234 00.51234 Flocculant dose (mg/l) Flocculant dose (mg/l) Figure 1: COD (A) and TS (B) removal efficiencies from landfill leachate for different flocculating agents and doses. “○” CM/25, “◊” CM/80, “■” CV/300 and “▲” CV/850. Figure 1(A) shows COD removal efficiency as a function of flocculant doses for the four chemical products tested. Percentage COD removals increased with increasing coagulant doses. Maximum COD removal efficiencies depend on the flocculants and doses, presenting results between 15.5% for CV/850 and 5.9% for CV/300. Percentage COD removals increased with increasing coagulant Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-738-8 Waste Management and the Environment II 217 doses but in some case efficiencies decreased after a maximum COD removal; optimal dose depends on the flocculant and ranges from 0.5 to 4 mg/l. Figure 1(B) shows TS removal efficiency as a function of flocculant doses for the four chemical products tested.
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