© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0 Submerged biological filters to treat landfill leachate. A laboratory experience A, Matarti, M.A. G6mez, A. Ramos, M. Zamorano & E. Hontoria Civil Engineering Department. Granada Universip, Spain. Abstract Leachate treatment systems installed at landfill sites have advanced a great deal in sophistication and reliability, Leachate recirculation, biological and physiochemical treatment processes are used to treat this wastewater but all treatment technologies seem to need a combination of two or more methods to obtain an effluent with suitable properties to eliminate environmental problems, A system for leachate disposal must be simply and economic; it must require the least possible amount of energy to operate and minimum staff involvement. Biological biofilm filters could be a new solution to treat landfill leachate with standard characteristics. Aerobic and anaerobic systems could be used to treat landfill leachate with biological filters. Results obtained for two pilot plants show that this treatment could be an efficient alternative, with COD and suspended solids removal depending on hydraulic loading rate under aerobic or anaerobic conditions. A new pilot plant, with aerobic and anaerobic reactors, is necessary to determine the design parameters of the system. 1 Introduction Wastes in landfill undergo physical, chemical and biological changes resulting in solubilisation or suspension of high concentrations of organic matter in a liquid phase called Ieachate (l). Landfill Ieachate is a complex wastewater and it always contains a high strength of pollutants which have an adverse effect on the enviromnent (2). The composition of these Ieachates depends on waste composition and age, landfill surface, landfill operation and climatic conditions. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0 690 Waste Management and the En~irownent The most important characteristics of leachate which could influence treatment are: high concentration of organic and inorganic substances, irregular production depending on the amount of rainfall, variations in the biodegradable fraction of organic substance depending on the age of landfill, and the low or negligible concentration of phosphorous (3) These Ieachate characteristics impose operational difficulties on treatment processes not normally found when treating wastewater of high strength and volume. Different treatment strategies are therefore required to match a treatment to the changing Ieachate volumes and strengths during the filling phase and aftercare of a landfill (3). In an effort to control the pollution caused by landfill leachate, many treatment processes have been studied, such as leachate recircultaion, biological methods and physiochemical methods. Leachate recirculation is a process to enhance stabilisation of active landfills and in-situ treatment of problematic Ieachates. Pohland & Kim (4) have documented the benefits of increasing landfill moisture content and liquid movement through the fill; these benefits are associated with increasing gas utilisation opportunities, reduced leachate treatment requirements, avoidance of long-term monitoring and liability, and potential for landfill mining and reuse (5). Biological methods include aerobic and anaerobic processes (3,6). Leachate from landfill may contain substances which are able to limit biological treatment efficiency, such as: metals, carbon compounds, ammonia, chloride and sulphide. However, the sensitivity of biological treatment processes in the presence of toxic compounds is reduced by several factors (3). Aerobic and anaerobic treatment processes used with landfill leachate are: aerated lagoons, activated sludge plants, trickling filters, rotating biological contractors, anaerobic lagoons, anaerobic digesters and anaerobic filters. Physiochemical treatment processes have been tested by many researchers that have studied different treatment with sanitary landfill Ieachate such as: flocculation-precipitation (7), elimination of heavy metals and suspended solids (8), chemical oxidation to eliminate cyanide, phenol and other organic pollutants (9), active carbon to adsorption of some organic compounds or to nitrogen reduction (10) and stripping with vapour to remove ammonia (11). One of the new developments of Ieachate treatment is the separation process with membrane, as: nanofiltration (8), microfiltration and ultrafiltration (12) and reverse osmosis (13). All discussed and tested treatment technologies seem to present a non suitable substitute for biological Ieachate treatment. One solution could be an optimum combination of two or more methods or the development of other treatment technologies. A system proposed for leachate disposal must be simply and economic; it must require the least possible amount of energy to operate and minimum staff involvement. Submerged biological filters have support materials to biofilm grown; this support is not moving and completely submerged in wastewater, running always as a filter (13). Some of the advantages of this treatment are: treatment plants can be built inside structure, no secondary clarification is needed, is a simply system © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0 Waste Management and the En~’irownent 69] and requires a low amount of energy to operate and minimum staff involvement, it has no moving parts and a high density filter medium with the possibility to get high organic removal rate per unit volume (14,15). Landfill leachate may contain substances which are able to limit biological treatment efficiency but the main characteristic of the system and its application to treat wastewater with high salt concentration (16) or with pollutants as phenol or heavy metals (17) and its application to industrial wastewater with similar composition make to think that submerged biofilters could be use to treat landfill leachate. The objective of this research was to know the possibility of an application of submerged filter to treat landfill leachate. This research has been developed with two laboratory pilot plant. 2 Materials and Methods 2.1 Laboratory pilot plants The laboratory pilot plants used in this study consisted of two submerged biological filters reactors; the fwst running in aerobic conditions and the second in anaerobic conditions. Both reactors had the same dimensions: height of reactors, 30 cm and diameter of reactors, 6.5 cm. Leachate without previous treatment was introduced on the top of the pilot plants from a 50 Iitre deposit with a peristaltic pump. Treated effluents were collected tiom the bottom of the reactors. The aerobic system used a compressor to introduce air at the bottom of the reactor. A schematic diagram of these plants is shown in Figure 1, INFFLUENT INFFLUENT \ ii PERISTALTIC PUMP T * \ i -f AEROBIC REACTOR LEACHATE DEPOSIT ANAEROBIC REACTOR Figure 1: Pilot plants schematic diagram Both reactors were packed with clayey schists (2-7 mm average size, 1.78 g/cm3 apparent relative density and 2,18 g/cm3 real relative density), a ceramic material, with high surface area and special shapes, from brick industrial waste. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Waste Management and the Environment, D Almorza, CA Brebbia, D Sales & V Popov (Editors). ISBN 1-85312-907-0 692 Waste Management and the En~irownent Aerobic and anaerobic reactors were running with several hydraulic loading rates (O.18 to 0.7 m3/m2/d)by changing leachate flow. Several recirculation rates (200, 400 and 800%) were assayed as well with 0.36 m3/m2/dhydraulic loading for both reactors. A continuous air flow (6.79 m3/m2/d ) was maintained in aerobic reactor. 2.2 Landfill leachate characterisation Landfill leachate used in this research was taken from a landfill facility in Granada, Spain (Loma de Manzanares, Alhendh); it is a high density landfill where wastes are disposed from an urban waste comporting and recovery plant. Average parameters of this leachate show that this is a young leachate: COD 17.045 + 1.045 mg 02/1, total nitrogen 976 ~ 15 mg/1, pH 7.87 ~ 0.26, conductivity 14.84 ~ 3,79 S/cm and suspended solids 676 + 97 mg/1. 2.3 Analytical methods Every 24 hours, water samples (50 ml) were collected flom the inlet and the outlet of the columns, obtaining three replicates for each assay, COD, pH, total nitrogen and suspended solid were routinely monitored in all samples. Chemical Oxygen Demand was measured using COD closed reflux micro method (18), Absorbance of the digestate was measured calorimetrically at 600 nm and the COD concentration was calculated tlom a calibration curve, prepared with potassium acid phthalate. Chloride interference was avoided with silver nitrate. Previous to nitrogen determination, total nitrogen was oxidised to nitrate by boric and persulfate digestion. Nitrate was measured using an ion