Effect of influent pH on biological denitrification using biodegradable PHBV/PLA blends as electron donor

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/poly (lactic acid) (PHBV/PLA), a biodegradable polymer blend, was used as both carbon source and biofilm carrier in a packed-bed bioreactor. The effect of influent pH on denitrification performance in PHBV/PLA supported denitrification system was further investigated. Results showed that the nitrate removal efficiency kept high level under an alkaline influent while largely decreased under an acidic influent. When the influent pH was 5.68, nitrate removal efficiency was about 34% of that on neutral or alkaline conditions. Meanwhile, dissimilatory nitrate reduction to ammonia process (DNRA) was enhanced on acidic condition. Furthermore, ΔpH (the difference between influent and effluent pH) and effluent TOC both increased on alkaline condition, and they sharply rose to 2.75 and 23.37 mg L−1 with an influent pH of 10.38. It was found that there were obvious positive correlations among influent pH, ΔpH and TOC. Moreover, based on the characteristics of microbial hydrolysis and denitrification processes, the effect mechanism of influent pH on nitrate removal was deeply explored. A better knowledge of the effect of influent pH on nitrate removal will be significant for the solid-phase denitrification in practice.