Ensuring water re-use projects succeed — institutional and technical issues for treated wastewater re-use

Abstract

The increasing need for water in the arid areas of the world has resulted in the emergence of new water re-use technologies. The success of water re-use projects however, does not just depend on the effectiveness and suitability of the technology, but also on the presence of an institutional framework that ensures that the treated water can be distributed and used safely and efficiently. These two diverse issues were examined by MWH in projects carried out in Egypt and in the USA. One project in the East Bank of Cairo assessed the potential benefits of treated wastewater for irrigation in agricultural schemes. The project established a lack of clarity on ownership and management of the treated wastewater and outlined the institutional development and legislation necessary for the safe and controlled re-use of treated wastewater. The project demonstrated enhanced crop yields but that additional treatment of the wastewater was required to improve its microbiological quality to the standards required by both international and Egyptian legislation for safe re-use. Another project carried out in California, USA assessed the new technology of submerged membrane bioreactors (MBRs) for water re-use. MBRs combine activated sludge treatment with a membrane separation process. The project studied two commercially available submerged MBR systems at pilot scale. The project was designed to evaluate the feasibility of using permeate from the MBRs treating municipal wastewater as a feed source for thin film composite reverse osmosis (RO) membranes. The MBRs were examined in both nitrification and denitrification mode and both MBR systems showed good removal of BOD, TOC and microorganisms. They both produced a high quality effluent that could be used by the RO membranes for water re-use.