How does the entering of copper nanoparticles into biological wastewater treatment system affect sludge treatment for VFA production.

Usually the studies regarding the effect of engineered nanoparticles (NPs), which are released to wastewater treatment plant, on sludge anaerobic treatment in the literature have been conducted by directly adding NPs to sludge treatment system. Actually, NPs must enter into the wastewater treatment facility from influent before sludge being treated. Thus, the documented results can not reflect the real situations. During sludge anaerobic treatment for producing volatile fatty acids (VFA, the preferred carbon source for wastewater biological nutrient removal), it was found in this study that the entering of CuNPs to biological wastewater treatment system had no significant effect on sludge-derived VFA generation, while direct addition of CuNPs to sludge fermentation reactor caused a much lower VFA production, when compared to the control test. Further investigation revealed that the entering of CuNPs into wastewater biological treatment system improved sludge solubilization due to the decline of sludge particle size and the increase of sludge microorganism cells breakage. In addition, there was no obvious influence on hydrolysis, while significant inhibition was observed on acidification, resulting in the final VFA production similar to the control. When CuNPs were directly added to the fermentation system, the solubilization was little influenced, however the hydrolysis and acidification were seriously inhibited, causing the ultimate VFA generation decreased. Therefore, selecting proper method close to the real situation is vital to accurately assess the toxicity of nanoparticles on sludge anaerobic fermentation.