Co-Treatment of Transfer Station Wastewater and Aged Landfill Leachate Using a Two-Stage Anoxic/Oxic Process: Internal Carbon Utilization, Nitrogen Removal, and Microbial Community Response

Aged landfill leachate is difficult to treat biologically because of its low biodegradability and limited carbon availability. Carbon-rich transfer station wastewater is a potential co-substrate, but its use in staged biological co-treatment requires evaluation. This study examined coagulation pretreatment of transfer station wastewater followed by co-treatment with aged leachate in a two-stage anoxic/oxic system. Water-quality and optical analyses showed differences in biodegradable-carbon availability and dissolved organic matter composition: protein-like components were more prominent in transfer station wastewater, whereas humic- and fulvic-like components predominated in aged leachate. During 60 d of operation, average removal efficiencies for chemical oxygen demand, ammonium nitrogen, and total nitrogen were 93.4%, 91.12%, and 85.0%, respectively. Amphiplicatus was among the dominant bacterial taxa, and unclassified groups dominated the fungal community. Defluviicoccus was relatively more abundant in the first anoxic compartment, whereas Candida was more abundant in the final oxic compartment. The results support the use of transfer station wastewater as a carbon-rich co-substrate for biological treatment of aged leachate.