Role of free nitrous acid on waste activated sludge bio-electrolysis and key microflora shift

It is a major bottleneck as efficient energy recovery from waste activated sludge (WAS) often require long treatment time during traditional anaerobic fermentation. In order to further enhance the resource utilization efficiency and shorten the treatment time, bio-eletrolysis, i.e., microbial electrolysis cells (MECs), assisted with free nitrous acid (FNA) was employed for WAS treatment in this study. The performance of current and hydrogen generation during bio-eletrolysis from FNA-treated WAS was compared with that obtained from un-pretreated sludge. FNA significantly boosted the hydrolysis and acidification of WAS in MECs, in detail, the concentrations of soluble carbohydrates, proteins and volatile fatty acids (VFAs) were much higher than that of un-pretreated sludge. The utilization efficiency of VFAs was higher than 97% in the MEC-FNA test with the increase of current (1.9mA) and hydrogen yield (0.86mL/g VSS), which were 3.8 and 5.1 folds higher than that in the control. What's more, pyrosequencing revealed that the abundance of anaerobic fermentation bacteria, electrochemically active bacteria and nitrate-reducing bacteria were notably enhanced. © 2019, Editorial Board of China Environmental Science. All right reserved.