The kinetics of urban solid waste anaerobic biodegradation under mesophilic conditions

In this research, a kinetic study of anaerobic biodegradation of urban solid waste (USW) generated in Dar es Salaam City (Tanzania) is presented. An experimental bioreactor simulating mesophilic conditions of USW dumpsites was developed. The goal of the study was to generate a kinetic order with respect to biodegradable organic matter and use it to model the biogas generation rate (BGR) from biodegradation of USW food-residues mixed with fruit-waste. The main controls were leachate re-circulation and initial-pH adjustments. A biodegradation rate law in differential form was proposed and the numerical values of kinetic order and rate constant were determined using initial rate method. The arithmetic average value of kinetic order determined was 0.994 and the rate constant was 0.3093 kgmol day-1. Results were in close agreement with literature and the kinetic model equation predicted reasonably well the BGR. In the second investigation, the goal was to examine the effect of different leachate-levels and ash-loading on BGR at various initial-pH values. Results showed that high ash-loading promotes BGR more than high leachate-level. In the third investigation the response surface methodology (RSM) was employed to optimize BGR. Results indicated that within the experimental range of factors applied there was a single factor significant effect of initial-pH and ash-loading on BGR while the two factor interactive-effect of initial-pH/ash-loading and leachate-level/ash-loading were significant (α < 0.05). Verification tests yielded maximum BGR values that were in good agreement with predicted values, thereby validating the model and confirming that the RSM was appropriate methodology.