Enrichment strategies of heavy metals in the O/H/O process composed of biological fluidized bed for wastewater treatment: A case study of Cu and Zn

Abstract

Municipal sludge can be utilized as a resource despite its polluting nature. However, the presence of heavy metals lowers its resource value, and their uniform dispersion in conventional biological processes because of sludge reflux poses enormous difficulties for the subsequent separation/recovery. In this study, the enrichment strategies of Cu and Zn in simulated wastewater based on a new biological process named oxic-hydrolytic & denitrification-oxic (O1/H/O2 or O/H/O) combination were investigated and the influence mechanisms of pH, chelate, operating parameters, and denitrification reaction control were illustrated. Results showed that the amount Cu and Zn in the sludge of H reactor exceeded those of both O1 and O2 when pH of O1＜6.5. The maximum sludge-water partition coefficients (Kd) of Cu and Zn in H reactor were 3128 and 3421 times when the influent concentration of NH3–N was at a certain value (210 mg/L NH4Cl for Cu and 140 mg/L NH4Cl for Zn). This was ascribed to the control of nitrification rate, ammonification/nitrosation in the O1 reactor, anaerobic ammonia oxidation combined with autotrophic denitrification in the H reactor, optimal hydraulic retention time (HRT) and sludge retention time (SRT). Under the pre-set conditions of water quality and operation parameters, the precipitates in the sludge were found to be Cu(OH)2, Zn(OH)2, CuS, ZnS which were theoretically and instrumentally characterized. In sum, the joint regulation of biological combination and biochemical reaction will provide new enrichment/separation strategies for heavy metals in municipal sludge management.