Mathematical modelling of MSW biodegradation in bioreactor landfills operating under saline environment

A mathematical model was developed to simulate the biodegradation of municipal solid waste (MSW) in bioreactor landfills operating under saline conditions and to predict the leachate strength (aqueous organic and volatile fatty acid (VFA)), and the volume of landfill gas (CH4 and CO 2) produced. The model described the biodegradation of MSW into methane and carbon dioxide in three steps. These steps were hydrolysis, acidogenesis, and methanogenesis. The hydrolysis step was assumed to follow first order kinetics whereas the Monod kinetics were used to describe the growth rate of acidogenic and methanogenic biomass. The inhibition of salt content was linked to the hydrolysis rate constant and methanogenic bacteria. A competitive inhibition term to simulate the effect of saline environment was included in the Monod kinetics to simulate the methanogenic biomass. Sensitivity analysis indicates that the hydrolysis rate constant, methanogenic kinetics (μM, kdM, KSM), and initial concentration of methanogenic biomass had a significant impact on peaks of the VFA and daily methane produced, as well as the time required to reach them. The model has been calibrated by comparing the simulation results to experimental 1D bioreactor measurements. The results of methane production showed good agreement between the model and experimental data. Both the model kinetics and the fitting parameters for salt inhibition (K, and m) were determined from these simulations

Effect of saline water and sludge addition on biodegradation of municipal solid waste in bioreactor landfills

Bioreactor landfills require sufficient moisture to optimize the biodegradation processes and methane generation. In arid regions, this is problematic given the lack of fresh water supplies. Saline water can be used but may inhibit the biodegradation of the municipal solid waste (MSW) in landfills. Sludge may be used to enhance the biodegradation of MSW under saline conditions. For this study, two groups of laboratory-scale bioreactor cells were used to study the impact of saline water and sludge addition on the biodegradation of MSW in bioreactor landfills. The first group (four bioreactors) operated without sludge addition. The second group (four bioreactors) operated with the addition of sludge. The salt concentrations in the two groups were 0, 0.5, 1 and 3% (w/v), respectively. All bioreactors were operated at neutral pH levels with leachate recycling. The methane yield was 70.6, 61.7 and 47.5 L kg-1 dry waste for bioreactors R1, R2 and R4, respectively; and 84.7, 78.7, 72.6 and 59 L kg-1 dry waste for bioreactors R5, R6, R7 and R8, respectively. The high salt content (3%) inhibited the MSW biodegradation as evidenced by the methane yield, the percentage reduction in leachate concentration and the settlement that occurred during the study. Sludge addition was able to improve the methane yield at all salt concentrations