With ongoing water shortage, is there a better method than reverse osmosis, that wastes over 50% water, to reduce total dissolved solids? Which one and what is your experience with it?
"over 50% water loss" would apply only to brines (extremely high levels of salt) and to poorly designed-operated-maintainedRO systems. Instead we develop, design and realize tailored high grade water reuse systems with overall over 90% water recovery = less than 10% water loss. Knowing that TDS = total dissolved solids, the first step is to remove all non-mineral solids by advanced biological treatment (without adding any chemicals other than nutrients if/as required). This results in ultra-low TOC, COD, BOD, TSS, turbidity (NTU) and SDI (silt density index) which minimizes irreversible fouling and power consumption of NF/RO membranes and doubles their economic lifetime. In the second step, some of the minerals could be removed by precipitation and/or air stripping. Finally after UF/cartridge pre-filtration and conditioning, the remaining TDS is retained by partial or full RO filtration as needed. I would like to add that some minerals such as sulfates, nitrates, ammonia, ... can also be removed in the first step by advanced biological treatment.
I will be interested to have the commercial details for such a system providing 1000 LPH with 70-80% of TDS reduction. You may write to water_india2005@yahoo.com
I do not think ion or resin based treatment is uneffective as the Softeners manufactured and marketed by Ion exchange India work very effectively against hard water.
Well if addressing TDS is the main concern then there are alternative methods that can be adopted. For instance universities in the U.S. have found that Moringa extracts can reduce tds in water by 30%. The contact time that has to be given is 3 hours. The water then needs to be skimmed from the top as the sludge settles at the bottom. RO is a good solution only to address high TDS. For other factors such as turbidity, removal of heavy metals, hardness and microbial contamination there are several options from Zeolite Filters, Template Assisted Crystallization technology and a wide array of biocides.
Water treated by RO still require a disinfectant present to eradicate microbial contamination and a biocide with residual presence in the water is the correct solution. Many RO filter suppliers provide a follow on UV treatment. UV treatment is good if the water is going to be consumed immediately, but if the water is going to be stored a biocide present in the water will provide greater safety.
Most RO purifiers reject 50-70% water in order to reduce the TDS by 70% or more and the reject water will have much higher TDS than the raw water TDS , which is not environment friendly.