Anaerobic Biotransformation of Organoarsenicals and Its Inhibition on Anaerobic Digestion

Extensive use of organoarsenic feed additives has caused organoarsenicals to be detected in animal manure and wastewater, and further within anaerobic digestion systems. Anaerobic organoarsenical biodegradation is initiated with the reduction of electron-withdrawing groups, followed by the cleavage of C–As bonds or the reduction of arsenate group. Electrochemical stimulation can accelerate the degradation of the organoarsenicals with electron-donating groups. The biotransformation of organoarsenicals can be significantly affected by microbial compositions and property, and environmental factors such as co-existing organic matter. Due to the equipment of arsenate or nitro groups in organoarsenicals and their anaerobic degradation products, methanogenic activity, especially the acetoclastic methanogenic activity can be inhibited, and anaerobic sludge characteristics including physiochemical properties and microbial structure are remodeled. In response to the stress of organoarsenicals at environment-relevant levels, anaerobic granular sludge can protect itself through accelerating the excretion of extracellular polymeric substances. Two inhibition alleviation strategies that rely on sulfate reduction and zero-valent iron mediation, respectively, can enhance organoarsenical degradation and immobilize the generated inorganic arsenic simultaneously. The understanding of organoarsenical-induced inhibition on anaerobic digestion and the development of the corresponding mitigation techniques can achieve highly efficient arsenic removal and biogas production during anaerobic digestion of animal manure and wastewater.