Target of 95% Recovery in NEWater Production by using CDI based Process for RO Brine Treatment

In Singapore, NEWater is the product of a multiple barrier water reclamation process from secondary treated domestic effluent using MF/UF-RO and UV technologies. More than 20% brine is generated from the RO process. To increase the water recovery and treat the RO brine, a Capacitive Deionization (CDI) process with biological activated carbon (BAC) as pre-treatment was developed and tested with the treatment capacity up to 5,000 L d-1. The results show that ion concentrations in CDI product were quite low except SiO2. RO permeate (CDI product as feed) was of good quality including low SiO2 comparing with NEWater. It could be beneficial to use a dedicated RO operated at optimum conditions with better performance to recover the water. It was observed that the type of pre-treatment, the feed water chemistry and the cleaning technique and chemicals played important role in the sustainable operation. Enhanced pre-treatment and lowering pH could minimize the fouling. The CDI pressure increased faster with high TOC feed. BAC was able to achieve 15–27% TOC removal of RO brine; about 40% of TOC removal could be achieved when combined with membrane filtration. To control the organic fouling of CDI cells, 60% TOC removal could be the setting point for activated carbon regeneration or replacement. CDI had a water recovery of at least 80%, so CDI based RO brine treatment could improve overall water recovery of NEWater production over 90%. The CDI cells had energy consumption about 0.7 kwh m-3. It was found that organic fouling was the major cause of CDI pressure increase. Sustainable operation especially organic fouling control and effective cleaning is being investigated.