Enhancement of methanogenic activity by micronutrient control: Micronutrient availability in relation to sulfur transport.

The main purpose of this research was to clarify the influence of the addition of iron (Fe) alone (0-100 mg/L) or 50 mg/L of Fe with 2 mg/L each of cobalt (Co), copper (Cu) and nickel (Ni) on the methanogenic activity of a mesophilic two-stage UASB system treating ethanol wastewater at a fixed chemical oxygen demand (COD) loading rate of 16 kg/m3/day under a continuous mode of operation and steady state condition. The addition of Fe provided the dual benefits of a reduction in both the dissolved sulfide and the hydrogen sulfide (H2S) content in produced gas, resulting in marginally improved hydrogen (H2) and methane (CH4) productivities. When the Fe dosage was increased beyond the optimum value of 50 mg/L, the process performance drastically declined, as a consequence of the high total volatile fatty acid (VFA) concentrations that inhibited both the acidogens and methanogens predominantly present in the 1st and 2nd reactors, respectively. The chemical precipitation of iron sulfide was responsible for the reduction of produced H2S in both the aqueous and gaseous phases as well as the minimization of added amounts of all other micronutrients to fulfil the sufficiency of all micronutrients for anaerobic digestion (AD). The addition of 2 mg/L each of Co, Cu and Ni together with 50 mg/L Fe resulted in the greatest enhancement in process performance, as indicated by the improved CH4 yield (mL/g COD applied) to about 42.3%, compared to that without micronutrient supplement.

Enhancement of biogas production from swine manure by a lignocellulolytic microbial consortium.

Anaerobic digestion of lignocellulosic wastes is limited by inefficient hydrolysis of recalcitrant substrates, leading to low biogas yield. In this study, the potential of a lignocellulolytic microbial consortium (LMC) for enhancing biogas production from fibre-rich swine manure (SM) was assessed. Biochemical methane potential assay showed that inoculation of structurally stable LMC to anaerobic digestion led to increase biogas production under mesophilic and thermophilic conditions. The greatest enhancement was observed at 37°C with a LMC/SM ratio of 1.5:1 mg VSS/g VS leading to biogas and methane yields of 355 and 180 ml/g VS(added) respectively, equivalent to 40% and 55% increases compared with the control. The LMC was shown to increase the efficiency of total solid, chemical oxygen demand removal and degradation of cellulose and hemicelluloses (1.87 and 1.65-fold, respectively). The LMC-supplemented process was stable over a 90 d biogas production period. This work demonstrates the potential of LMC for enhancing biogas from lignocellulosic wastes.