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/m/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 (HS) content in produced gas, resulting in marginally improved hydrogen (H) and methane (CH) 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 1 and 2 reactors, respectively.

High methanogenic activity of a three-stage UASB in relation to the granular sludge formation.

A new UASB (upflow anaerobic sludge blanket) system with three-stage concept and granular sludge formation was developed to provide a very high process activity, in terms of a high energy yield and a large optimum COD loading rate, from ethanol wastewater at 37 °C and a controlled pH of 5.5 in the first bioreactor with recirculation of the final overflow from the third to the first two bioreactors to lower the amount of sodium hydroxide used for pH control in the first bioreactor and to increase the total alkalinity of the whole system. The proper volumetric ratio of the three-stage UASB with flocculant sludge provided the dominance of the three sequencial steps of acidogenesis, acetognesis and methanogenesis to occur in the respective bioreactors, causing a higher process performance and giving the optimum COD loading rate of 15 kg/md.