Composting Plant Leachate Treatment by Coagulation-Flocculation Process

This experimental study was conducted to investigate the effect of treatment of composting plant leachate by a coagulation-flocculation process. The effects of different dosages of coagulant and different pH values on the coagulation processes were compared. Ferric chloride and aluminium sulphate (alum) were tested as conventional coagulants. The experimental results show that a 18% removal of COD and 90% removal of heavy metals can be attained at pH 6.5 (optimum for alum) with the addition of 1400 mg L alum and -1 a 28% removal of COD and 86% removal of heavy metals can be attained at pH 10 (optimum for ferric chloride) with the addition of 2000 mg L ferric chloride. The comparison of these values with the Iranian guideline -1 for effluent discharge shows that the concentration of heavy metals in leachate did not exceed the maximum values allowed. Key word: Solid Waste Leachate Chemical treatment Heavy metals INTRODUCTION The specific composition of leachates determines its The growing production of domestic and industrial landfill leachates often involve a combination of wastes in the world causes serious disposal problems. appropriate techniques. They are designed as modular, Solid waste landfill sites are often defined as hazardous multi-stage units, capable of coping with the changing and heavily polluted wastewaters with considerable leachate characteristics over the years. Several processes, variations in both composition and volumetric flow [1]. drawn from wastewater and drinking water technology, Leachate is generated as a consequence of rainwater have been applied for the treatment of landfill leachates, percolation through wastes, chemical biological processes such as anaerobic and/or aerobic biological degradation, in waste and the inherent water content of wastes chemical oxidation, coagulation-precipitation, activated themselves [2]. The discharge of landfill leachate can carbon adsorption, photo-oxidation and membrane lead to serious environmental problems, since the processes [3, 5-7]. leachate contains a large amount of organic matter Coagulation/flocculation is an essential process in (both biodegradable and non-biodegradable carbon), water and in industrial wastewater treatment. Several ammonia-nitrogen, heavy metals, chlorinated organic and studies have been reported on the examination of inorganic salts [3, 4]. Although some of these pollutants coagulation–flocculation for the treatment of landfill can be degraded by microorganisms, the limitation of leachates, aiming at performance optimization, i.e. common biological processes (degradation is only a part selection of the most appropriate coagulant, determination of COD and limited removal of bio-refractory organic of experimental conditions, assessment of pH effect and pollutants) has made it difficult to meet the correlative investigation of flocculant addition [8]. Coagulation and discharge standard [4]. Therefore, alternative flocculation is a relatively simple technique that may be technologies based on physical-chemical stages are employed successfully in treating old landfill required. leachates [9]. Aluminum sulfate (alum), ferrous sulfate, relative treatability. The treatment processes used for Am-Euras. J. Agric. & Environ. Sci., 5 (5): 638-643, 2009 639 ferric chloride were commonly used as coagulants [4, 10]. FeCl .6H O. The influence of leachate pH [4-9] on Iron salts were proved to be more efficient than aluminum Coagulation/flocculation performances was studied. ones, resulting in sufficient chemical oxygen demand Coagulation with ferric chloride and aluminum sulfate as (COD) reductions (up to 56%), whereas the corresponding coagulant were performed to optimize the treatment values in case of alum or lime addition were lower conditions with respect to coagulant dosage and to (39 or 18%), respectively [3]. estimate the removal of COD, cupper, zinc, cadmium, Sanandaj is one of the most crowded cities in Iran. chromium and nickel. Everyday, municipality has to manage approximately 400 tons of solid waste generated from residential and RESULTS AND DISSCUSSION commercial sources and a composting plant receive whole of them. Field data indicate that a large amount of The characteristic values of main physico-chemical leachate is produced every day which is collected and pollution parameters for the examined leachate sample transferred by trucks to the nearest farmlands or are presented in Table 1. It is observed that this leachate unutilized. The aim of this study was the identification presents a relatively low value of pH. It can be deduced of Sanandaj composting plant leachate quality and the that leachates corresponded to the acidic phase of examination of coagulation/precipitation process decomposition. High concentration of COD was observed efficiency for the treatment of fresh (raw) leachates, ranging from 25762 to 45500 mg L . So, this leachate especially in terms of heavy metals removal. More displayed high concentrations of contaminants. Beside, specifically, the aim was the determination of most the average values of heavy metal concentrations in the appropriate coagulant type and dose, the examination of leachate are given in Table 1. The comparison of these pH effect on removal capacity and the identification values with the guidelines from Iranian Environmental of optimum experimental conditions for the efficient Protection Agency (for effluent discharge in the sewer) application of this process. and EPA (according to water irradiation standards) show MATERIALS AND METHODS and Ni) in leachate exceed the maximum values allowed. Leachate samples were collected once every week which is highly pH depended. for 6 months between December 2006 and June 2007 from Therefore, in order to determine the optimal pH value the composting plant of Sanandaj (Iran), which has been and coagulant dosage a standard jar test technique was in operation since 1982. The raw leachate samples were used. The best conditions for coagulation/flocculation obtained directly from the area where fresh solid wastes tests were evaluated considering COD and heavy metals were deposited. Samples were collected in 20-L plastic removal. The pH of initial samples was varied between carboys, transported to the laboratory and stored at 4 °C. 3 and 11 for each coagulant. Coagulation/flocculation The following parameters were analyzed: pH, COD, TS, process runs by the addition of 1400 mg L alum and TVS, TFS, metals as cupper, zinc, cadmium, chromium and nickel. All analyses were carried out according to Standard Methods [11]. All chemicals used for the analytical determinations were of analytical grade. Coagulation/flocculation and precipitation studies were performed in a conventional jar-test apparatus, equipped with 6 beakers of 1 L volume. The experimental process consisted of three subsequent stages: the initial rapid mixing stage took place for 5 min at 100 rpm, the following slow mixing stage for 15 min at 60 rpm, while the final settling step lasted for another 30 min. After the settling period, the supernatant was withdrawn from the beaker and was used for chemical analysis. Chemicals reagents used as coagulants included Al (SO )3.18H O, 2 4 2 3 2