Seasonal variation in chemical properties and degradability by anaerobic digestion of landfill leachate at Benowo in Surabaya, Indonesia

Seasonal variations in the physical and chemical characteristics of leachate taken from Benowo landfill in Indonesia, including factors likely to inhibit anaerobic digestion, were investigated to determine the impacts on the stability of anaerobic treatment. To evaluate the biodegradability of the leachate, a continuous experiment was conducted by changing the organic loading rate (OLR). Chemical oxygen demand (COD) ranged between 2621 and 16,832 mg L^-1, and COD in the dry season was twice the level in the rainy season owing to reduced rainwater input and significant evaporation. COD, pH, and the concentrations of ammonium ion, and metals in the leachate were within acceptable ranges for decomposition by anaerobic digestion. However, the Na⁺ and Cl^- in the leachate are high enough to inhibit anaerobic digestion. From chemical investigation of leachate at six monitoring wells in Benowo, food waste accumulation and seawater intrusion might cause high salinity in the leachate. In the continuous experiment, COD removal efficiency was maintained at 40% regardless of OLR, suggesting that at least 40% of the leachate contained biodegradable substances. Based on these results, issues surrounding the biological treatment of saline and refractory substances in landfill leachate were discussed. It is suggested that high salinity and refractory substances in the leachate are common issues during the leachate treatment by anaerobic digestion as the implications for similar landfills in other countries around the world.