Comparative Microbial Risk Assessment of Centralized and Decentralized Wastewater Treatment as Health Risk Barrier for Irrigation in Ghana

Worldwide, at least 3.5 to 4 million hectares of agricultural fields in 50 countries are irrigated with raw, partially diluted and treated wastewater. Wastewater irrigation, apart from the valuable plant nutrients it provides, also serves as conduit for e mployment generation, food security and environmental sustainability. At the same time, the practice can lead to severe public health consequences, particularly in developing countries where the microbial contamination of wastewater is high. Reducing the health risk associated with the practice while optimizing its benefits thus remains a major challenge for several local and international organizations. At the forefront of balancing the disparate aspects of the practice of wastewater irrigation is the Wo rld Health Organization (WHO). The WHO, has since 1971, developed three guidelines to mitigate the health risk of wastewater irrigation with the most recent one in 2006. The recent guidelines stipulate microbial guidelines of 1000 Escherichia coli/100ml a nd <1 helminth egg/100ml to assure tolerable health risk for farmers using wastewater for irrigation and consumers of wastewater irrigated vegetables that are eaten raw. However, in most developing countries like Ghana, where centralized wastewater treatm ent plants are either non-existent, non-functional or operating sub-optimally, achieving this microbial standard for wastewater irrigation can be very challenging. An alternative to highly technical and costly centralized wastewater treatment system is d ecentralized systems. This study, is designed to assess the microbial impact and hence the health cost of a change from centralized to decentralized wastewater treatment systems as health risk barrier for wastewater irrigation. The study focuses on Ghana where various decentralized and centralized wastewaer treatment systems are presently being explored for urban vegetable irrigation.