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 816 mg L−1 and 20,862 mg COD L−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 0 mV was used successfully as an indicator for optimum sulfide addition which consistently provided an appreciable reduction in effluent concentrations to less than 1 and 2 mg L−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 11.8 g COD L−1 day−1 with an average efficiency of 92%. Methane production and biomass yield were 0.32 L (g CODremoved)−1 and 0.014 g VSS (g CODremoved)−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 2.50 g COD L−1 day−1 or 2.13 g BOD L−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 38 mg L−1, respectively. This integrated treatment scheme was proven to be an effective approach for highly polluted and toxic rubber thread wastewater.