Microbial community structure and dynamics in a mixotrophic nitrogen removal process using recycled spent caustic under different loading conditions.

abstract A laboratory-scale Bardenpho process was established to investigate the proper nitrogen loading rate(NLR) when modified spent caustic (MSC) is applied as electron donor and alkalinity source for denitri-fication. MSC injection induced autotrophic nitrogen removal with sulfur as electron donor and hetero-trophic denitrification. The nitrogen removal rate (NRR) did not increase proportionally to NLR. Basedon the total nitrogen concentration in the effluent observed in the trials with MSC, the NLR in the influentshould not exceed 0.15 kg N/m 3 d in order to satisfy water quality regulations. Microbial communities inthe anoxic reactors were characterized by pyrosequencing of 16S rRNA gene sequences amplified by thepolymerase chain reaction of DNA extracted from sludge samples. Microbial diversity was lower as MSCdosage was increased, and the injection of MSC caused an increase in SOB belonging to the genus Thio-bacillus which is responsible for denitrification using sulfur. 2011 Elsevier Ltd. All rights reserved.