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The methane potential and biodegradability of different ratios of acetate and lignin-rich effluents from a neutral sulfite semi-chemical (NSSC) pulp mill were investigated. Results showed ultimate methane yields up to 333±5mLCH4/gCOD when only acetate-rich substrate was added and subsequently lower methane potentials of 192±4mLCH4/gCOD when the lignin fraction was increased. The presence of lignin showed a linear decay in methane production, resulting in a 41% decrease in methane when the lignin-rich feed had a 30% increase. A negative linear correlation between lignin content and biodegradability was also observed. Furthermore, the effect of hydrotalcite (HT) addition was evaluated and showed increase in methane potential of up to 8%, a faster production rate and higher soluble lignin removal (7-12% higher). Chemical oxygen demand (COD) removal efficiencies between 64 and 83% were obtained for all samples.

Three hydrotalcites of M 2+ -Mg-Al were synthesized using the co-precipitation method, where M 2+ was Fe 2+ , Zn 2+ and Fe 2+ + Zn 2+ . The hydrotalcites and their calcined form of mixed oxides obtained by their thermal decomposition were characterized by FTIR, XRD and SEM. Subsequently their effect on the methane potential of synthetic wastewater comprised of sucrose and sulfur was evaluated in a multiple batch system at 37 ± 0.5 °C. The best methane potential was observed from the Fe-Zn-Mg-Al hydrotalcite at 500 mg/L yielding 3712mL CH 4 /gVS which corresponds to an 8.1% increment against the control. The better performance of the Fe-Zn-Mg-Al hydrotalcite can be attributed to the Zn 2+ ions. These react with S 2in the substrate to yield zinc sulfide and therefore prevent it from forming H 2 S by sulfate reducing bacteria, meanwhile reducing competition for methanogens to form methane. Calcined hydrotalcites neither stimulated nor inhibited the methane production which suggests that the enhancement of methane produced by the Fe-Zn-Mg-Al hydrotalcite was related to the presence of Fe 2+ and Zn 2+ cations incorporated and immobilized in the layered sheet structure of the hydrotalcite.Hoban, D.

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