Intervention And Fate Of Roxarsone In Biological Nitrogen Removal Processes

Roxarsone (4-hydroxy-3-nitrobenzenearsenic), a widely used feed addtive in livestock and poultry industry, was scarcely transformed within animals and entered into the environment through excretion. In the environment, roxarsone can be converted into inorganic arsenic which is more toxic and mobile through biotic and abiotic transformation. Eventually, roxarsone and its transformation products entered into the soil by applying manure, entered into the nature water with the scour of the stormwater or seeped into underground aquifer during the outdoor compost which would cause potential environment risks. Otherwise, microbial toxicity of roxarsone is likely to cause adverse effects to the biological treatment of animal wastewater containing roxarsone. In this paper, from the perspective of interaction of roxarsone and the microorganism, we made a systematical study of the intervention and fate of roxarsone in biological nitrogen removal processes. Specifically, it includes acute intervention of roxarsone to biological nitrogen removal processes, long-term ecological effects of roxarsone to biological nitrogen removal system and influence of roxarsone on horde structural of the activated sludge microbe.According to the research, we obtained several important conclusions as follows:(1) Roxarsone and its biotransformation products could adversely affect the biological nitrogen removal processes significantly and a period of acclimatization did not weaken the inhibitory effect of roxarsone. Compared with nitrification, biological denitrification was restrained in more extent for the generation of inorganic arsenic in denitrification stage. (2) Roxarsone can hardly be removed and biotransformed during the biological nitrogen removal processes even after a long-term domestication. Trace of roxarsone was converted into 4-hydroxy-3-aminobenzenearsenic acid (HAPA) and inorganic arsenic and that increased inorganic arsenic content in the micro-ecological environment of microorganisms. Enrichment of inorganic arsenic in activated sludge leaded to higher arsenic level in extracellular polymeric substance (EPS) and cytoplasm of microorganisms and eventually it weakened the respiration and a variety of enzyme activities of microbe. (3) Long-term stress of roxarsone declined biodiversity and changed the community structure of activated sludge microbe. The dominant of Acinetobacter was gradually displaced by Methylophilaceae and Aeromonas which were the new predominance species in activated sludge.