Sulfur-siderite autotrophic denitrification system for simultaneous nitrate and phosphate removal: From feasibility to pilot experiments.

Siderite (FeCO3) is one kind of abundant and cheap carbonate minerals, but it has never been used as inorganic carbon sources and pH buffer in the sulfur autotrophic denitrification before. In this study, sulfur-siderite autotrophic denitrification (SSAD) system was formed. Batch, column and pilot experiments of the SSAD system showed that siderite could provide inorganic sources and pH buffer for sulfur autotrophic denitrification. The optimal volume ratio of sulfur and siderite was 1:3 for the SSAD system. Siderite could not be used as an electron donor by the sulfur autotrophic denitrifiers. The SSAD column removed 28 mg/L NO3--N and 3.1 mg/L PO43--P completely at 12 h HRT. The SSAD pilot biofilter during treating secondary effluent obtained stable NO3- and PO43- removal, and controlled effluent NO3--N and PO43--P around 4 and 0.2 mg/L, respectively, at 4 h HRT, and no blocking occurred in operation of 401 days. In the SSAD system, the main bacteria were Thiobacillus (67.8%), Sulfurimonas (20.0%), and Simplicispira (3.5%); and Sulfurimonas (29.4%), Ferritrophicum (15.2%), and Thiobacillus (10.3%) during treating synthetic wastewater and secondary effluent, respectively. PO43- was removed through iron phosphate precipitate. The SSAD system was a promising way to remove NO3- and PO43- simultaneously from wastewater lack of organic carbon sources.