Using recycled water from municipal wastewater treatment processes as a source of irrigation water is an important strategy to ensure water security in many arid and semi-arid regions of the world. A long drought in Australia has had a profound impact on its domestic, agricultural and horticultural water supply, as well as environmental water flows.
The research reported in this paper was commissioned to investigate a method for providing a secure supply of irrigation water to the Werribee irrigation district, a major horticultural food growing district near Melbourne.
Economic and technical feasibility was determined using data collected from a pilot-scale plant, from which salt removal, water recovery, and overall process economics were calculated.
The pilot plant consisted of a pre-treatment multimedia filtration unit (MMF) and an electrodialysis reversal (EDR) system with a capacity of approximately 144 kL/day. Treated effluent from a wastewater treatment plant (WWTP) was used as feed water for the desalination pilot plant.
Water quality guidelines for horticulture specify an upper limit for total dissolved solids (TDS) of 375 mg/L. The EDR process reduced TDS from 1104 mg/L to 328 mg/L.
In addition, the process reduced the conductivity of recycled water by 72%, including the removal of 84% calcium, 76% chloride, 59% fluoride, 64% alkalinity, and 60% phosphate. This demonstrates that the EDR treated water is a viable alternative supply.
The power consumption of the EDR plant was found to be 0.6 kWh/kL, and for the media filtration was 0.4 kWh/kL. The total operating cost was estimated to be 18 cents/kL to deliver 82% water recovery.