Carbon and nitrogen removal from low-strength domestic wastewater with a two-stage submerged biological filter

The aim of the present study was to evaluate the secondary and tertiary treatment of low -strength domestic wastewater with submerged biological filters (BFs). The experiments were carried out with a two-stage pilot plant consisting of two subsequent filter columns. In the first aerated reactor, the removal of carbon and nitrification was accomplished (secondary nitrification); while, in the second anoxic reactor a post-denitrification process with methanol as external carbon source was performed. During the 3 months of experimental period, in average terms, Total Suspended Solids (TSS) concentrations of 156 mg/L were reduced to 5 mg/L; Chemical Oxygen Demand (COD) concentrations of 179 mg/L were reduced to 43 mg/L. In the secondary nitrification, mean influent NH4+ concentrations of 6.1 mg/L were reduced to average values of 1.8 mg/L. During the post-denitrification, mean influent NO3- concentrations of 12.0 mg/L were reduced to average values of 6.1 mg/L. The overall process produced a backwashing effluent with an average concentration of about 175 mg/L of TSS.