Reclamation and reuse of wastewater by membrane-based processes in a typical midstream petrochemical factory: a techno-economic analysis

In the present study, a techno-economic analysis for the reclamation of wastewater in a midstream petrochemical factory (the Miaoli factory of the China Petrochemical Development Company in Taiwan) was investigated. Caprolactam is the main product in this factory. The wastewater to be reclaimed and recycled as cooling water replenishment was the effluent from organic- and inorganic-based wastewater treatment plants, the concentrate from cooling tower units, and water for rinsing use from other units. In addition to the current primary treatment process (Scheme 1), other treatment methods involving various combinations of membrane-based processes of microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO), and electrodialysis reversal (EDR) were proposed, depending on the quality of the wastewater. The three schemes include the combination of MF and EDR (Scheme 2), UF and RO (Scheme 3), and MF, UF and RO (Scheme 4). Based on the capacities and operating costs of various membrane modules, an economic analysis on Schemes 2–4 by the net present worth method demonstrated that Scheme 3 was the best choice under the range of source water price studied (U$ 0.45–0.62/m³). In this case, the total amount of wastewater reclaimed notably increased from 6.6% by the current treatment scheme (Scheme 1) to 30.9% by Schemes1 and 3. Moreover, Scheme 3 had an advantage over Scheme 1 when the source water price exceeds U$ 0.51/m³.