Simultaneous denitrification and phosphorus removal accomplished by denitrifying biofilters assembled with innovative sulphur-fly ash ceramic carriers.

Sulfur autotrophic denitrification (SAD) stands a cost-effective and organic-free denitrification technology contributing to carbon neutrality in deep wastewater treatment. However, SAD is usually accompanied with alkalinity depletion and incapable of phosphorus removal issues. Plus, fly ash (FA) is a large-volume industrial solid waste rich in Fe, Al, Ca, so how to leverage FA has always been a formidable challenge. In this study, two innovative SAD reactors have been conceivably established by packing with the composite ceramic carriers prepared by element S0 and FA (mass ratio: 1:1/1:2). The performance of SAD reactors is then comprehensively evaluated in terms of denitrification, phosphorus removal as well as its underlying microbial mechanisms. The operational results over 115 days indicated that the removal efficiencies of nitrogen and phosphorus were greater than 98 % and 94 %, respectively as hydraulic retention time (HRT) and influent NO3--N concentration changing from 3 to 12 h, 12-30 mg/L, respectively. The concentration of effluent PO43--P in two reactors were all less than 0.1 mg/L and pH maintained at 8.2-9.2. Also, no obvious nitrite accumulation was observed in either reactor. Hence, the enhanced SAD reactors were successfully constructed and demonstrated to be capable of carrying out excellent denitrification and phosphorus removal performance. Microbial community structure considerably depended on carrier type, influent NO3--N and HRT. Sulfurovum was significantly enriched and predominant genera serving for denitrification. This study might provide the new insights of the FA resourceful utilization (i.e., biofilm carriers) and also scientific supports for intensive simultaneous nitrogen and phosphorus removal by fortifying SAD processes.