Water/Waste Processing - Feb 2012
identity is lost during the normal natural water cycle and during drinking water treatment There are several full scale operating indirect potable recycling systems in place that have demonstrated that appropriate technologies in combination provide multiple barriers to remove almost all constituents and do not allow microbial and chemical contaminants to reach finished water at levels of potential concern Well known examples of these large scale systems are Singapores New Water and Orange County Californias Groundwater Replenishment projects The specific technology combinations to be applied are dependent upon the source water composition and the intended use Although there is some remaining level of public resistance to reusing wastewater where there is human contact the attitudes of a well informed public toward planned direct and indirect potable water reuse have been changing rapidly when the need and benefits are explained There are still some toilet to tap emotional concerns but in fact the product water produced by these treatment trains for indirect or direct potable use is actually lower in microbial and inorganic content trace organic chemicals and total organic carbon than almost any natural waters and approaches rain water The planned projects yield waters very low in TDS and also low TOC with reduced precursors and therefore it would also generate much smaller quantities of disinfection byproducts DBPs when subjected to typical drinking water disinfection In some quarters treated water is expected to be returned to the environment to lose its original identity or for dilution but the capabilities of the current treatment technologies have made that concept archaic because it would actually degrade the treated water by mixing it with natural waters The only supporting rationales might be to provide storage capacity or a buffer and time delay in the event of a significant process upset However in that extreme and unusual temporary case there would be planned opportunities to temporally divert the flow so that there would be no public health risk Because of the potential contaminants in wastewater sources it is essential to have an appropriate HACCP type management system with critical control point monitoring employ appropriate reliable and multiple barrier redundant treatments and utilize as much as possible real time monitoring of targeted contaminants and surrogates to assure 24 7 365 performance However it is not necessary to be overly redundant in the treatment train given the known effectiveness and reliability of the available technologies For example RO is not necessary prior to SAT costly AOP may not be necessary especially when SAT will occur or additional treatment will be applied at a drinking water plant ozone alone provides significant oxidation of trace organics and UV alone can provide removal of nitrosodimethylamine NDMA if needed AOP ozone oxidation and UV disinfection prior to a storage reservoir prior to a drinking water treatment plant may also be unnecessary however excellent reduction of nitrogen and phosphorus nutrients would be essential to prevent eutrofication In the latter case 8 February 2012 Water Waste Processing www waterwaste com
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