Effects of feed solutions on refuse hydrolysis and landfill leachate characteristics

Tap water, aerobically pre-treated leachate, and anaerobically pre-treated leachate, were each fed into the top of a series of three simulated landfills columns, filled with municipal solid waste collected in Shanghai, China. Changes in leachate, including pH, total organic carbon (TOC), and volatile fatty acids (VFAs), and the produced biogas were monitored over time. The tap-water-fed columns had a low hydrolysis rate that yielded an acidic environment (pH 4.8-5.4) in the leachate that inhibited methanogenesis reaction in the refuse. When aerobically pre-treated leachate was fed into the columns, the hydrolysis rate of total organic carbon fluctuated between 200 and 400 mg d-1 and methanogenesis in the refuse column was only partly activated. The hydrolysis rate of refuse fed with anaerobically pre-treated leachate was the highest among the three solutions. The high alkaline levels of the anaerobically pre-treated leachate and its methanogenic bacteria led to an early activation of methanogenesis in the refuse columns. The VFAs contributed approximately 40-60% of TOC in tap-water-fed columns, 60-80% of TOC in the columns fed aerobically pre-treated leachate, and up to 70-90% of TOC in columns fed with anaerobically pre-treated leachate. The feed solution had considerably affected leachate characteristics, and then the build-up of the methanogenesis in the refuse column and the composition of fermentation products in the leachate. The success of a bioreactor landfill depends on whether the recycled leachate could yield a favorable methanogenic environment in the top refuse layer, or whether an appropriate pre-treatment is adopted to modify the leachate characteristics.