Production of unburned calcium silicon filter material (UCSFM) from oyster shell and its performance investigation in an A/O integrated biological aerated filter reactor (A/O-BAF)

Abstract

A considerable amount of the oyster shells as a waste product of mariculture is produced every year, which leads to a major disposal problem with coastal regions of China. This work researched the feasibility of utilizing oyster shell as raw materials to produce unburned calcium silicon filter material (UCSFM) in an unburned process. The chemical composition, physical property and microstructure of UCSFM were determined. The results indicated that oyster shells could be utilized to produce the UCSFM, which belongs to alkaline filter material. The UCSFM was invoked as a bio-carrier in an A/O integrated biological aerated filter reactor (A/O-BAF) for wastewater treatment, and its processing performance was investigated at different ammonia nitrogen loads. The CODcr and NH₃–N removal rates of UCSFM BAF were slightly higher than UCSFM A/O-BAF, but UCSFM A/O-BAF showed a higher TN removal rate of ammonia nitrogen loads between 0.130 kg (m³ d)⁻¹ and 0.496 kg (m³ d)⁻¹ and the average TN removal rates of UCSFM A/O-BAF and UCSFM BAF were 41.88% and 7.48%, respectively. Pyrosequencing analysis of the 16S rRNA gene in anoxic/oxic zones of A/O-BAF process indicated that the microbial communities were quite different from different ammonia nitrogen loads. Thiobacillus, Thiothrix, Hydrogenophaga, Flavobacterium were the dominant genera shared in the oxic zones, while VadinHA17_norank, Desulfobacter, Aeromonas and SB-1_norank were the dominant genera shared in the anoxic zones. The microbial population and physicochemical properties of the UCSFMs explained the excellent performance of the UCSFM A/O-BAF reactor well. Therefore, the UCSFM produced from the oyster shell was appropriate for serving as a bio-carrier in A/O-BAF reactors.