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.

Waste settlement in bioreactor landfill models.

Prediction of landfill settlement is one of the important parameters that affects the design and maintenance of bioreactor landfills. Due to the large number of variables involved in the settlement mechanism, accurate prediction of landfill settlement is a real challenge. The operational protocol of a landfill, the presence of municipal sludge from treatment plants, the addition of soybean peroxidase (SBP) enzymes, and the fraction of organic matter in the municipal solid waste (MSW) have to be reflected in the parameters of any model used to predict the settlement of MSW. In this work, a biodegradation-induced settlement model incorporating two parameters (A and B) was developed. The settlement data of two researchers were used to estimate the parameter values with two different approaches; the first considered the overall experiment and results, and the second separated the aerobic phase, if present, from the anaerobic phase. The rate of initial settlement occurring under aerobic conditions has been greater than that under anaerobic conditions. Parameters increased with the increase in the concentration of enzymes and with the presence of sludge in both aerobic and anaerobic stages. Increasing organic content of MSW has resulted in the enhancement of the biodegradation rate and settlement. This has been reflected on the higher values of the parameters compared to their values in the absence of organic waste.

A comparison of acute toxicity of biodiesel, biodiesel blends, and diesel on aquatic organisms.

The increased demand of alternative energy sources has created interest in biodiesel and biodiesel blends; biodiesel is promoted as a diesel substitute that is safer, produces less harmful combustion emissions, and biodegrades more easily. Like diesel spills, biodiesel can have deleterious effects on the aquatic environments. The effect of neat biodiesel, biodiesel blends, and diesel on Oncorhynchus mykiss and Daphnia magna was evaluated using acute toxicity testing. Static nonrenewal bioassays of freshwater organisms containing B100, B50, B20, B5, and conventional diesel fuel were used to compare the acute effects of biodiesel to diesel. Mortality was the significant end point measured in this study; percent mortality and lethal concentration (LC50) at different exposure times were determined from the acute toxicity tests performed. Trials were considered valid if the controls exhibited > 90% survival. Based on percentage of mortality and LC50 values, a toxicity ranking of fuels was developed.