Risk assessment of using output effluent of urban wastewater treatment plants (Case study: Northern Isfahan wastewater treatment plant)

Given the scarcity of water resources in many parts of the country, the increasing need for water, and increased volume of urban wastewater, planning to use the effluent of urban wastewater treatment plants by considering the environmental aspects as an appropriate solution is regarded to compensate for some of these scarcities and to reduce the pollutions. The recycled urban wastewater effluent is associated with many benefits and risks for human and environmental health. This research is aimed to evaluate the risk of using effluent in demanding sectors with respect to the priority of risk reduction.

In 2016, this research was conducted with the aim of assessing the risk of using the output effluent of the Northern Isfahan wastewater treatment plant. The statistical information of effluent quality was collected monthly and averaged from the laboratories of the relevant organizations. Considering six major qualitative parameters (pH, COD, BOD, TSS, TDS, and TC) and using environmental standards related to these parameters, an index was evaluated to assess the quality of treated wastewater as the Comprehensive Pollution Index (CPI). Then, using the library studies, regional studies, as well as specialized meetings with experts with knowledge about the status of output effluent of this treatment plant, risk and control checklists were prepared in the form of a questionnaire. The checklists were completed by 69 experts, and by generalizing the Frank and Morgan method, the Risk Index (RI) was calculated for potential effluent use in the study area and compared with the pollution index.

Results of the completed checklists showed that the agricultural sector had the highest risk score against the industrial sector and the industrial sector had the highest control score against the agricultural sector. In general, the mean score of 6-item risk checklist in the agricultural sector was higher than all sectors and the risks posed to humans in all four sectors had a higher score than other risks. Comparison of the qualitative standards of using effluent and quality of output effluent of the wastewater treatment plant also showed that the measured coliform parameter had the highest distance to its standard limit compared to other parameters. Therefore, the significance of this parameter in public health and community safety had a great impact on the calculation of pollution and risk indices. Hence, the risk index for the four sectors of agriculture, green space, natural resources, and industry was 54.71%, 23.97%, 15.1%, 6.22%, respectively, and the relative pollution index was 43%, 28%, 21%, and 8%, respectively. The results of these two indices were completely matched and the agricultural sector had the highest pollution and risk indices and accounted for the priority of risk reduction, and the effluent usage in the industrial, natural resources, and green space sectors will have lower risks to humans and the environment.

According to the results of this study, using the effluent of the wastewater treatment plant in the current conditions has lower risks for industrial use and natural resources (non-desertification) than agricultural use and green space irrigation. In general, the effluent use in water-based industries and growing unproductive plants will be followed by increased access of farmers to higher quality water resources and improved human and environmental health.