Application of a pilot-scale pulsed electrocoagulation system to pulp mill OE stage bleaching effluent

摘要

Pulp mill is water use intensive, requiring substantial amount of water to produce a ton of product. The hindrances toward fuller reuse of the post-treatment effluents are mostly related to residual ionic species and coloration from ligneous fragments and dissolved organic solids. A pilot-scale study was conducted using pulsed electrocoagulation technology to treat the wastewater of an OE bleaching effluent, with the purpose of evaluating its treatment performance. The operating variables were a current density of 0-233.7 A/m~2, a hydraulic retention time (HRT) of 6.5-16.25 min. Water quality indicators investigated were electrical conductivity, suspended solids (SS), chemical oxygen demand (COD), true color and hardness. The results obtained during pilot-scale studies were encouraging. Under the operating conditions studied, the removals of all water quality indicators always increased with an increase either in current density or HRT. The highest removals obtained at 266.7 A/m~2 and an HRT of 16.25 min for conductivity, SS, COD, true color and hardness were 63.2%, 92.9%, 75.7%, 86.4% and 89.5% for aluminum electrode and 70.1%, 96.4%, 81.1%, 86.6% and 79.6% for iron electrode, respectively. Evaluation of the economy efficiency suggested that the OE bleaching effluent could be effectively treated using a current density of 266.7 A/m~2 and HRT of 16.25 min at operational costs of US$ 0.1109 and 0.094/ton for the aluminum and iron electrode sets, respectively. The study showed that electrocoagulation technology can be used to treat effluent of an OE bleaching stage for water reuse.