Treatment and toxicity reduction of textile dyeing wastewater using the electrocoagulation-electroflotation process.

A pilot-scale study was conducted using the electrocoagulation-electroflotation (EC-EF) process to treat textile dyeing raw wastewater to evaluate treatment performance. The effects of some key factors, such as current density, hydraulic retention time (HRT), and removal of conductivity, total suspended solids (TSS), chemical oxygen demand (COD), and color were investigated. The operating variables were current density of 0-300 A m(-2), HRT of 0-30 min, and a coagulant (anionic polyacrylamide (A-PAM)) dosage of 0-30 mg L(-1). Daphnia magna was used to test acute toxicity in raw and treated wastewater. Under the operating conditions without added coagulant, maxima of 51%, 88%, 84%, and 99% of conductivity, TSS, COD, and color were removed, respectively, with a HRT of 30 min. The coagulant enhanced removal of all wastewater parameters. Removal maxima of 59%, 92%, 94%, and 98% for conductivity, TSS, COD, and color were observed, respectively, with an optimal dosage of 30 mg L(-1) and a shortened HRT of 20 min. The 48 h-LC50 D. magna test showed that the raw wastewater was highly toxic. However, the EC-EF process decreased toxicity of the treated samples significantly, and >70% toxicity reduction was achieved by the EC-EF process with the addition of 15-30 mg L(-1) coagulant, HRT of 20 min, and current density of 150-300 A m(-2). The pilot scale test (0.3 m(3 )h(-1)) shows that the EC-EF process with added coagulant effectively treated textile dyeing wastewater.

Treatment of tannery wastewater with high nitrogen content using anoxic/oxic membrane bio-reactor (MBR).

Bench scale membrane bio-reactors were operated to investigate the treatment efficiency of tannery wastewater with high organic and nitrogen contents and the optimum operating conditions were derived. The optimum ratio of the volume of anoxic denitrification tank to aerobic nitrification tank was 50% when denitification/nitrication MBR process was used to treat tannery wastewater. It was also found that supplementation of phosphorus to maintain COD:T-P ratio of 100:1 was needed to achieve the best performance. Under these conditions, the effluent COD and T-N were 160 and 54 mg/L, respectively which satisfied the effluent limits for the tannery wastewater.