Risks associated with treated wastewater in greenhouse cooling system

The hot climate in the Gulf region is forcing many farmers to use controlled environment agriculture by using evaporative coolers inside greenhouses. These coolers are consuming around 60% of the water used for the greenhouse. Replacing groundwater with treated wastewater will have a good impact in saving freshwater for other different applications. The problem is that treated wastewater is rich of nutrients that can support algae growth, block the cooling pads, and reduce the efficiency of the cooling system. Moreover, it is unclear if the water can be a source of any airborne diseases that could affect human health and crop quality. Unfortunately, few or no data is available related to the applications of treated wastewater in greenhouse cooling system. Therefore, the aim of this study is to evaluate the possibility of using treated wastewater in greenhouse cooling system and asses any potential risk to the environment that could affect human health and crop quality and safety. The greenhouse cooling system was connected to tertiary treated wastewater and the system was left to run for two months. Algae growth was observed in cooling pads. Samples from cooling pads, air, and water were taken for microbial analysis. The same sampling was made from other greenhouse running with freshwater. Using treated wastewater in cooling system did not show any negative impacts in plant growth. However, rapid growth of algae in cooling pad of treated wastewater was noticed compared to the groundwater cooling system. This could be mini-mized by covering cooling pads with shade net, or adding some anti-algae growth (CaSO₄) in cooling tanks, or using plastic cooling pads, or cleaning cooling pads from time to time. Moreover, more types of bacteria were found in treated wastewater cooling system but were not harmful for human and plants. Almost similar microbes were found in the air and water running in all greenhouses. Therefore, the study recommends the use of treated wastewater in the greenhouse cooling system with application of antifouling compounds or using plastic cooling pads that can be easily cleaned.