Treatment of dyehouse effluents using sequential combinations of electrochemical oxidation, membrane separation, and activated sludge

Abstract

Reducing water demand in textile sector is one of the important environmental concerns. In this study, individual and combined effects of selected operational parameters on a full‐scale electrochemical oxidation (ECO) process treating dyehouse effluent were investigated experimentally. Combinations of variables including current density, wastewater pH, and conductivity resulting in maximum color removal efficiency were determined using the Box‐Behnken design method. In addition to color removal, variations in wastewater organic composition before and after ECO were also examined critically. Removal and/or generation of 22 polycyclic aromatic hydrocarbons (PAHs) before and after ECO were investigated under variable operational conditions. Treatability of ECO effluent using conventional activated sludge process was investigated by both full‐scale monitoring studies and batch‐scale nitrification tests. Toxicity impact of raw, ozonized, and electrochemically treated wastewaters on nitrifiers were also determined and compared. Water reuse and salt recovery alternatives were assessed by full‐scale tests in a pilot plant which is composed of nanofiltration (NF), reverse osmosis (RO), and activated sludge processes. Advantages and disadvantages of applying ECO process as a pretreatment prior to membrane‐based or biological methods were critically evaluated. The average flux values of NF and RO membranes without ECO were 39 ± 2 and 19.5 ± 1 L m−2 h−1, respectively. The average flux values of NF and RO membranes without ECO were 39 ± 2 and 19.5 ± 1 L m−2 h−1, respectively. The permeability of the membranes for raw dyehouse effluent (without ECO) were estimated to be 6.0 ± 11 and 0.73 ± 0.6 L m−2 h−1 bar−1 Another important observation was formation of some PAHs including naphthalene, acenaphtylene, anthracene, benzo(a)anthracene, and benzo(g,h,i)perylene as a function of operational conditions maintained in ECO process. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 472–481, 2014