Wastewater reuse and risk: definition of key objectives

Wastewater reclamation holds promise as an important water resource as the desire to develop arid regions continues to place increasing demands on finite water resources. The debate surrounding the consumption of reclaimed wastewater finds risk managers pondering the question of what types of water quality standards might be set in order to provide the proper level of safety associated with the use of reclaimed wastewater. We propose quality categories for different reuses such as irrigation or indirect aquifer recharge with different requirements towards microbial and chemical parameters. Based on recent existing guidelines and risk estimations, microbial and chemical limits for each category were compiled. Since economic calculations are very important, analytical costs are included and measurements frequency is proposed. Biological parameters have to indicate all potential pathogenic organisms including viruses, bacteria and parasites from different origins. The selected biological indicator parameters most used in rules and regulations are coliforms and E. coli, indicating the occurrence of a former faecal contamination and the possible presence of all pathogens occurring in faeces of warm-blooded animals. In the case of wastewater reuse, biological parameters have to indicate all potential pathogens causing infection diseases and/or intoxication in all living beings including plants and animals. The large number of possible chemical parameters in relation with wastewater reclamation and reuse has to be adapted and minimized with respect to the origin of the sewage, the extent of the treatment process and the intended use. These parameters must cover a broad spectrum of toxicological and ecological risks as well as possible technical disorders. Risk assessment and risk management are also necessary.