Abstract
Using a 23L methane fermentor incorporating an Ultra Filter membrane system and a rolled sieve as a fixed bed to maintain a high concentration of methane microbes, Shochu (one of the Japanese distilled spirits) distillery wastewater was used to find its improvement and suitable operating conditions. During the preliminary experiments, it was observed that the increase in NH4+ concentration due to the low C/N of the wastewater reduced the concentration of methane microbes, after that the digested gas production rate was decreased. To avoid the inhibition of methane fermentation by NH4+, the wastewater was diluted 1.6 times with water based on the nitrogen balance. However, NH4+ still gradually increased and the methane fermentation was inhibited in the subsequent runs. This NH4+ increase was considered to be induced by the decomposition of microbes in the fermentor. For the purpose of reducing the biological stress and the decomposition of microbes, the low pH value of the diluted wastewater was adjusted to the neutral range with Ca(OH)2. During this improved experiment, the methane microbes was increased and stability of the digested gas production could be observed, even when the concentration of NH4+ was maintained at ca. 3800mg/L. Based on these results, the operational conditions of 5.8kg-VS/m3·d of Lvs (loading rate of volatile solids) and 9.6 days of HRT (hydraulic retention time) were proposed as a suitable operational condition. This condition could perform 80% of the VA (volatile acid) removal ratio and 0.5m3/kg-VS of the digested gas yield.
