Potable water reuse - a sustainable water management option
Direct and indirect potable reuse (DPR and IPR respectively) is needed in many cases in order to secure a sustainable drinking water supply.The Windhoek/Namibia experience shows that treated domestic sewage can be successfully used for direct potable reuse. The advanced process employed produces reclaimed water of a quality that constantly meets all the required drinking water standards. Approximately 25 % of the potable water supply consists of reclaimed water. Therefore, this source is an essential part of integrated water resource management and has contributed greatly to the social and economic development of the city.A multiple barrier strategy is employed in order to attain the highest possible safety levels. There are three types of barriers comprised by non-treatment, treatment and operational barriers.The main reasons for public acceptance of potable reclamation and reuse are the lack of other affordable choices and the fact that since the beginning of potable reuse, no reclaimed water related health problems have been experienced. Further important factors have been the open information policy employed from the start of the project in 1968, the excellent public education practice and the consumer confidence in both the quality management and the advanced water treatment technology employed. In recent years, indirect potable water reuse has also been a topic in India. Operational experience from the Windhoek New Goreanagab Water Reclamation Plant (NGWRP) and results from lab scale tests conducted with municipal tertiary effluent from an Indian sewage treatment plant is used for the design of an IPR treatment train employing ozone (H2O2 optional), ceramic membranes, biological active carbon filters (BAC), activated carbon adsorption (GAC) and disinfection.Although the used water (tertiary effluent) under study contained large amounts of bromide (700 – 1,350 μg/L), when dosed stepwise in low concentrations, ozone can be applied without the massive formation of bromate. This is due to the fact that hardly any ozone is available for reactions with bromine species. Nevertheless, micro-pollutants are degraded by nearly 50 %. This is the result of the formation of highly reactive hydroxyl radicals during the reaction of ozone with the organic matter of the tertiary effluent. In many water stressed regions, potable reuse (DPR and IPR)has beensustainablypracticed,and also in Indiait constitutes a great opportunity for a safe and secured drinking water supply.