Mineral and biological contamination of soil and Capsicum annuum irrigated with recycled domestic wastewater

Due to water scarcity in many arid countries, there is considerable interest in recycling wastewater streams such as treated urban wastewater for irrigation in the agricultural sector. The aim of this study is to assess the contamination of soil and Capsicum annuum (grown in pots) irrigated by domestic wastewaters treated by different wetland types between September 2013 and September 2014. The objectives were to assess (a) the suitability of the irrigation water for growth when using recycled wastewater contaminated by trace minerals and pathogens, (b) the impact of differently treated wastewaters on soil and fruits as a function of the wetland type, and (c) the marketable yield of the harvest as a function of mineral and biological contamination risk. Ortho-phosphate-phosphorus, ammonia-nitrogen, potassium and manganese concentrations in the irrigation water considerably exceeded the thresholds. High contamination levels by total coliforms, Salmonella spp. and Streptococcus spp. were detected. No mineral contamination was observed in the soils due to irrigation with treated wastewater. Results showed that slight to moderate zinc contamination was detected in some vegetables. Potassium accumulation in the yield showed the highest values followed by zinc. In contrast, the lowest mineral accumulation of the yield was observed for iron. No bacterial contamination was detected for fruits harvested from plants irrigated by wetland outflow water. In contrast, fruits harvested from those plants irrigated by preliminary treated wastewater showed high contamination by total coliforms, Streptococcus spp. and Salmonella spp. especially for fruits, which were located close to the contaminated soil surface. However, findings indicate that vegetables receiving wastewater treated with wetlands can be considered as safe compared to those receiving only preliminary treated wastewater. High yields in terms of economic return were associated with tap water and an organic growth medium, and a wetland with a small aggregate size and a low contact time. (C) 2016 Elsevier B.V. All rights reserved.