Techno-economic assessment of a hybrid forward osmosis and membrane distillation system for agricultural water recovery

Despite the potential of forward osmosis (FO) and membrane distillation (MD) to treat difficult waste streams, these technologies have not yet been applied on a large scale in industry. Also, economic analyses which are crucial in a commercialization of these technologies are not presently available. In this work a techno-economic study of water recovery from anaerobic digested (AD) effluents by a FO-MD hybrid process was performed. OPEX and CAPEX calculations were used to estimate a final water treatment cost based on experimental laboratory results which demonstrated that the FO-MD process can yield a high water quality for AD effluents. However the obtained water fluxes (< 2 Lm^-2h^-1) were too low for industrial application in the present form of the FO-MD process. The energy consumption of the FO-MD system was 0.52 kWh m^-3 which is 100 times lower than the electricity produced from 1 m³ of AD effluents based on methane energy yields. The cost of water produced by the FO-MD system was 1.29 $ m^-3, assuming water flux of 10 Lm^-2h^-1 and membrane cost of 36 $ m^-2. Sensitivity analysis shows that the cost of membrane module has a high influence on water cost at fluxes < 8 Lm^-2h^-1. Analysis shows that for the FO-MD system to be cost efficient, the water flux must exceed 14 Lm^-2h^-1. Thus our techno-economic assessment shows directions where the technology should be improved in order to be technically feasible and industrially applicable.