Integrated treatment scheme for rubber thread wastewater: sulfide precipitation and biological processes

In this study, acidic latex wastewater containing high average zinc and acetic contents of 816mgL(-1) and 20,862mgCODL(-1), respectively, was treated successfully by a series of chemical and biological processes without any addition of acid or base for pH adjustment. Total dissolved solids of the treated effluent increased by only 1.1-fold on average for sulfide precipitation as compared to 2.8-fold for the hydroxide strategy. The oxidation-reduction potential (ORP) value of 0mV was used successfully as an indicator for optimum sulfide addition which consistently provided an appreciable reduction in effluent concentrations to less than 1 and 2mgL(-1) for zinc and residual sulfide, respectively. The anaerobic filter was very stable in handling the chemically treated wastewater up to the organic loading rate of 11.8gCODL(-1)day(-1) with an average efficiency of 92%. Methane production and biomass yield were 0.32L(gCOD(removed))(-1) and 0.014gVSS (gCOD(removed))(-1), respectively. For the activated sludge process, the optimum sludge age and hydraulic retention time were 30 and 0.8 days, respectively, which are equivalent to the organic loading rates of 2.50gCODL(-1)day(-1) or 2.13gBODL(-1)day(-1). Under these optimum conditions, average removal efficiencies for COD and BOD were 96.6 and 99.4%. Average soluble COD, BOD and suspended solids in the effluent were 71, 11 and 38mgL(-1), respectively. This integrated treatment scheme was proven to be an effective approach for highly polluted and toxic rubber thread wastewater.