Effect of Leachate Recirculation on Municipal Solid Waste Biodegradation

Abstract Biological processes are known to reduce the organic fraction of municipal solid waste, but current landfilling practices have not been altered to reflect this knowledge. The advantages of enhancing degradation of solid waste include reduced period of leachate treatment, increased methane production, expedited landfill site reclamation through stabilized waste mining, and accelerated subsidence permitting recovery of valuable landfill air space. The techniques that can be used to enhance biological degradation include leachate recirculation, addition of nutrients, shredding, sludge and buffer solutions addition, lift design, temperature, and moisture content management. Manipulation of these variables promotes a more conducive environment for microbial activity. This paper presents the results of a leachate recirculation experiment into three pilots scale solid waste cells. A computer-operated pumping system controlled the rate of recirculated leachate into the solid waste cells. The leachate was recirculated over a period of 65 weeks, and effluent samples were obtained on a weekly basis and analyzed for pH, BOD, COD, TOC and heavy metal concentrations. The experimental results indicated that addition of supplemental materials to the leachate during recirculation has a positive effect on the rate of biological degradation of solid waste. The addition of primary sludge and supplemental nutrients resulted on a rapid increase in BOD and COD concentrations in the effluent samples. This rapid increase in BOD and COD concentrations suggests that following a lag phase prior to the methano-jenesis phase, a rapid decrease in the organic load in the leachate will be ichieved within a reasonable time frame. In addition, the results of this investigation indicates that the primary sludge is an excellent source of microbial inoculum. The addition of supplemental nutrients (nitrogen and phosphorus) with buffer also increases the concentration of the BOD and COD in the effluent samples, proving that a balance of pH and an increase in the available nutrients increases biological activities in the solid waste cells compared to the control cell.