The release of depolymerization products of lignin during the degradation of lignocellulsic material under sulfate reducing condition was investigated. In addition, we investigated the fate of the most common (beta-O-4) link present in lignin under sulfate reducing condition, using a lignin model compound. The method of investigation was based on the selective inhibition of microbial uptake of released aromatic phenolic compounds, depolymerization product of lignin, by toluene. Eight different aromatic phenolic compounds were identified. Until day 17 only 3 phenolic compounds were regularly detected, thereafter 7 aromatic phenolic compounds could be regularly identified. The accumulation of identified phenolic acid was not linear with time. The lignin model compound was completely degraded within 13 days when either Avicel cellulose or newspaper was present as alternate source of carbon. On the other hand when lignin model compound was present as the sole source of carbon, it took more than 22 days for its complete degradation. But in either case complete degradation of lignin model compound was observed. Four degradation byproducts of lignin model compound were identified, but the two most significant compounds identified were vanillic acid and 3-methoxy-4-hydroxy benzene propionic acid. The GC/MS analysis of the degradation by products of lignin model compound indicated that beta-O-4 link was cleaved under sulfate reducing condition and the presence of additional carbon source enhanced this process.

A mathematical model was developed to simulate methane and carbon dioxide production from simulated landfill column reactors operated under sulfate reducing and methane producing conditions. The model incorporated governing equations which describe the chemical and biochemical processes responsible for the degradation of organic waste materials. These processes were hydrolysis, acidogenesis, methanogenesis and sulfidogenesis. The differential equations were numerically solved using Stella Researcher Software. The model was calibrated and verified using 700 days of gas production data from the simulated landfill column reactors. The calibrated hydrolysis rate constants for newspaper and sludge were found to be higher in sulfate reducing reactors as compared to methane producing reactors. The simulated methane production was quite accurate in all the reactors, but the predicted carbon dioxide production in the sulfate reducing reactors was not so accurate for the first 100 days, which may be attributed to the necessity of further governing equations. According to the sensitivity analysis, hydrolysis rate constants and moisture factors were the two most sensitive parameters controlling the gas production.

The degradation of cellulose and lignocellulosic material was investigated in simulated landfill column reactors under sulfate reducing and methanogenic conditions. In the sulfate reducing reactors, methane gas production was effectively suppressed. The carbon dioxide produced during the sulfate reduction was dissolved in leachate as IC, leading to low carbon dioxide emission from sulfate reducing reactors. Higher COD in the leachate from the sulfate reducing reactors was probably due to higher solubilization rate of cellulose and lignocellulosic material. In a batch experiment, the hydrolysis of Avicel-cellulose, filter paper and newspaper was faster under sulfate reducing conditions. The percentage of organic carbon biodegradation in sulfate reducing conditions was higher than that in methanogenic conditions.

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The initial decomposition rates of cellulose and hemicellulose were measured using toluene to specifically inhibit the microbial uptake of hydrolysis products during the degradation of newspaper under sulfate reducing and methane producing conditions. The amount of glucose and xylose accumulation in the first 2 weeks of incubation period was higher in the sulfate reducing condition compared to the methane producing condition. It was estimated that 28 and 6% of initially loaded cellulose in the sulfate reducing condition and the methane producing condition was hydrolyzed, respectively. Accordingly, the newspaper-cellulose hydrolysis rate constant was estimated to be 6.7 times higher in sulfate reducing condition than in methane producing condition. Based on the glucose accumulation patterns, when sulfate reducing bacteria (SRB) were inhibited by anthraquinone and molybdate (Na2MoO4), it may be suggested that SRB might have contributed to the hydrolysis of cellulose, while their effect on the hydrolysis of hemicellulose could not be elucidated.