Effect of Internal Recycle on Nitrogen Removal in a Novel Anoxic/oxic Integrated Biofilm Reactor Treating Low C/N Ratio Domestic Sewage

In this work, a novel integrated anoxic/oxic biofilm reactor was proposed to treat rural domestic sewage with low carbon to nitrogen (C/N) ratio. Effects of internal recycle (R) on pre-denitrification and biomass production in anoxic zones of the integrated reactor were mainly investigated to tap the potentials of efficiency and economy. The experimental results obtained during a 98-day period showed that: the nitrogen removal efficiencies of 69.3%, 74.6%, 79.2%, 80.1% on average were realized under R of 200%, 250%, 300%, 350%, respectively. Relatively long anoxic hydraulic retention time (7.2 h) promoted the utilization of easily biodegradable carbon source in influent and facilitated the occurrence of endogenous denitrification by heterotrophic denitrifying bacteria, which lowered the anoxic observed sludge yield to simplify the wasted sludge disposal. For practical application in rural areas, R of 250-300% was appropriate with respect to a comprehensive consideration.