Electro-osmotic thermal process model for performance enhancement of forward osmosis integrated with membrane distillation

摘要

An electroosmotic membrane bioreactor (eOMBR) is employed as the feed side of a forward osmosis (FO) unit for municipal wastewater treatment. Freshwater is drawn osmotically from the feed side to the draw side by desalination brine. The diluted brine is regenerated thermally by direct contact membrane distillation (DCMD). The combined eOMBR-DCMD process, referred to as electro-osmotic thermal process (eOTP), is modeled and its performance is assessed in terms of performance indicators including osmotic water permeation (J(w)), reverse salt diffusion flux (J(s)), and internal concentration polarization parameter (J(ICP)). These indicators depend on operating factors such as draw inlet concentration (c(d)), sludge retention time in eOMBR (SRT), diffusion coefficient in draw side (K-d), draw inlet flow rate (Q(d)), and ICP coefficient (K-ICP). eOTP performance is evaluated in terms of how electric field influences the relationship between the indicators and operating factors. c(d) and K-ICP are the most influential factors. Electric field improves the beneficial effect of c(d) on J(w) and reduces the adverse effect of K-ICP on J(w). Electric field also reduces the adverse effect of c(d) on J(ICP) but worsens the adverse effect of K-ICP on J(ICP). Electric field does not influence the sensitivity of J(s) to changes in K-ICP. Lower current density levels improve eOTP performance. The water productivity of eOTP is also improved by higher temperature levels at the draw side when the current density is 5 A/m(2). The cost of fresh water production by eOTP was estimated to be $1.90 per m(3). This theoretical assessment shows that electro-thermal effects provide a potential for wastewater and brine reuse.