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Treatment of a low strength landfill leachate with peat Corbett, John Richard Ernest

Abstract

The Burns Bog landfill is the largest solid waste landfill in the province of British Columbia. It is situated on a peat bog in the Municipality of Delta. Leachate is generated by the passage of rainwater through the layers of refuse. Due to consolidation of the underlying peat bed the leachate rises to the ground surface near the toe of the landfill where it enters peripheral ditches and subsequently flows into Crescent Slough and the Fraser River. The purpose of this research was to investigate the treatment of this leachate to an acceptable quality for release to the receiving environment using peat as an adsorption/filtration medium. The peat used in this research was obtained from the Burns Bog peat bog near the landfill site. Column tests were run in the laboratory using a 29.2 cm I.D. plexiglass column containing 793 gm of dry peat. Leachate was pumped to the top of the column and allowed to percolate through the peat. The effluent from the column was then collected and analyzed. Six column runs were made to determine the effects of influent pH, influent concentration, and 'resting' the peat on the removal of pollutants by the peat. The removal of pollutants from the leachate by the peat is believed to occur through a combination of adsorption or exchange of dissolved pollutants and filtration of precipitated and suspended materials. The optimum pH for the adsorption of metals, was 7.1. At pH 4.8, adsorption decreased dramatically. At pH 8.4, adsorption was not as great as at pH 7.1, however, the total removal of metals was greater due to the precipitation and filtration of metal complexes. At the 95 per cent treatment level (i.e. 95 per cent of the metals entering the column are removed) the removal capacity of the peat at pH 7.1 was 11.4 mg/gm of dry peat. In order to treat the Burns Bog leachate to the proposed P.C.B. 'AA' level guidelines for specific discharges, a treatment level of 94.0 per cent would be required at the optimum pH of 7.1. This would require a dry weight of approximately 159 kg of peat per 1000 liters of leachate. Resting the peat for one month following initial leachate throughput appeared to slightly restore some of the adsorptive capacity of the peat. However, this restoration was not sufficient to allow reuse of the peat for leachate treatment. Reuse may be possible if longer rest periods (6 to 12 months) are used. Desorption of pollutants does occur by the percolation of water through the expended peat. This may cause a pollution problem following the termination of leachate treatment and should be studied in greater detail before a full-scale treatment system is constructed. Chemical treatment using lime and ferric chloride produced Fe, Mn, and Ca removals of greater than 90 per cent but did not reduce the N or Cl concentrations. Combined chemical and peat treatment did not produce any advantage over peat treatment alone. The 96 hr. TLm value for the natural leachate was 7.0 per cent vol/vol. Rapid Toxicity Assessments (RTA) run on the treatment effluents showed that it is possible to treat the leachate to a non-toxic level using peat treatment. Ammonia nitrogen and pH are believed to be major factors affecting leachate toxicity. It is felt that peat treatment may be an effective and economical method of treating the Burns Bog leachate. A spray-irrigation treatment system utilizing the final peat/clay cover of the landfill is considered to be the most suitable full-scale treatment method. Pilot-scale research at the landfill site is thought to be the logical next step in determining the feasibility of peat treatment of the Burns Bog leachate.

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