Treatment of Wastewater from Rubber Thread Manufacturing by a Combination of Chemical and Biological Processes

Abstract

After adjustment of pH to 5, Zn²⁺ in rubber thread wastewater was removed by coagulation with Na₂S•9H₂O. The molar ratio of added Na₂S to residual Zn²⁺ at pH 5 was 1:1. The amount of sludge generated was about 450 mg (l of wastewater)⁻¹. After the removal of Zn²⁺, the wastewater was treated anaerobically by an upflow anaerobic filter process (UAFP). The removal efficiency of TOC was about 79% at a TOC loading rate of 10 g l¹ d⁻¹, corresponding to a hydraulic retention time (HRT) of about 6 h. The anaerobically treated wastewater with a TOC concentration of 510 mg l⁻¹ was subjected to aerobic treatment by activated sludge. At a TOC loading rate of 0.4 g l⁻¹ d⁻¹, corresponding to a HRT of 31 h, the effluent TOC from the aerobic treatment was less than 30 mg l⁻¹, equivalent to a BOD of less than 20 mg l⁻¹. Total biological treatment time of both the anaerobic and aerobic processes to produce an effluent suitable for water course discharge was only 37 h. In a separate comparative experiment, rubber thread wastewater without Zn²⁺ was three-fold diluted with tap-water and treated aerobically just by activated sludge. The TOC concentration was about 20 mg l⁻¹ at a TOC loading rate of 0.6 g l⁻¹ d⁻¹, corresponding to a HRT of 4.1 days.

Keywords:

• rubber thread wastewater
• removal of Zn2+
• biological treatment
• upflow anaerobic filter process
• combination of chemical and biological processes