Risk management during effluent application for irrigation

Abstract

Reuse of treated wastewater is a favourable direction for solving water shortage problems and meeting environmental quality criteria. Domestic wastewater in isolated communities in arid regions can be treated efficiently in a stabilization pond system. The effluent quality can be further improved when stored in a series of stabilization reservoirs. However the salinity of the wastes in the ponds will increase due to evaporation. There is a series of parameters that characterize the effluent quality for agricultural reuse. The conventional biological parameters include faecal coliforms as a microbial indicator. The use of faecal coliforms does not reflect the viral pollution of the effluent due to the poor correlation with virus occurrence. Therefore, phages are proposed as enteric virus pollution indicators. Phages exhibit similar behaviour and survival in an aquatic environment, and their quantitative assessment is easy and a reliable enteric virus measure. Field results from the treatment plant of the City of Arad (Israel) reveal the possibility of characterizing the effluent quality in stabilization ponds and additional reservoir systems. The field data also allows the type of reactor of which the system consists to be defined, and the kinetic expressions for further forecasting of the treatment system behaviour and removal rate of the pathogens. Health risks to consumers due to the consumption of agricultural products irrigated with reclaimed wastewater were assessed by numerical simulation. The analysis is based on defining of an Exposure Model (EM), which takes into account several parameters: (i) the quality of the applied effluent; (ii) the irrigation method used; (iii) the elapsed times between irrigation, harvest, and product consumption, and; (iv) the consumers’ habits of consuming these agricultural products. The exposure model is used for numerical simulation of human consumers’ risks by running the Monte Carlo simulation method. Although some deviations in the numerical simulation, which are probably due to uncertainty (impreciseness in quality of input data) and variability due to diversity among populations, reasonable results were obtained. Accordingly, there is a several orders of magnitude difference in the risk of infection between the different exposure scenarios with the same water quality. Extra data are required to decrease uncertainty in the risk assessment. Future research needs to include definite acceptable risk criteria, more accurate dose-response modeling, information regarding pathogen survival in treated wastewater, additional data related to the passage of pathogens into and in the plants during irrigation, and information referring to the consuming habits of the human community.