Windhoek/Goreangab Direct Potable Water Reuse, Case Study Namibia

Abstract

Long-term experience in Windhoek (55 years) shows that treated, domestic used water (secondary effluent) can be both safely and cost-efficiently utilized for direct potable reuse (DPR). The advanced water reclamation process employed is resilient and produces purified water of a quality that constantly meets all the required drinking water standards. In addition, non-regulated (emerging) constituents such as micro-pollutants, antibiotic-resistant bacteria, and genes are removed to below the limit of detection. Bioassays in combination with chemical footprint analysis provide a further indication regarding the safety of the purified (reclaimed) water, which accounts for approximately 25% of the drinking water supply. Consequently, this source is an essential part of integrated water resource management in Windhoek and has contributed substantially to the city’s social, economic, and environmental development. A multiple barrier approach ensures the highest possible safety levels, which are consistently achieved. Three differing barrier types are employed with non-treatment, treatment, and operational functions. The non-treatment barriers consist of comprehensive source control, the strict separation of domestic and industrial effluents, and the blending of the reclaimed water with treated dam and ground water. The main treatment barriers are comprised by the Gammams Sewage Treatment Works (a nutrient removal plant) and the New Goreangab Water Reclamation Plant, an advanced multiple barrier purification system, which is based on ozonation and biological activated carbon filtration (a “non-reverse osmosis process”). One example of an operational barrier is the dosing of powdered activated carbon in the case of inadequate source water quality.

The public acceptance of direct potable reuse is mainly driven by the lack of other affordable alternatives and the fact that since DPR commenced 55 years ago, no health problems related to reclaimed water have been experienced. Other contributory factors are an open information policy, excellent public education practices, and consumer confidence in both the quality management and the advanced water treatment technology used, which after more than 20 years of operation in the current facility remains unchanged.