Closed loop hydroponics, where nutrient solution drainage is captured and reapplied to the crop, offers advantages over flow-through or single-pass systems by way of water and nutrient resource use efficiency. Increasing resource use efficiency reduces production costs and ultimately prevents environmental impacts associated with nutrient discharge to receiving water bodies.
Although there are many advantages, there are also production risks introduced when using a capture-and-reuse approach, namely, pathogen proliferation. There are many types of systems currently used in industry for treating fertigation water (irrigation water with fertilizer). Examples include but are not limited to sand filtration, ultraviolet light, chlorination, ozonation [O3(aq)], advanced oxidation processes, peracetic acid (C2H4O3), and hydrogen peroxide (H2O2).
In this experiment, recirculating nutrient solutions were treated using dimensionally stable anode (DSA)-based regenerative in situ electrochemical hypochlorination (RisEHc) in a deep water culture hydroponic lettuce (Lactuca sativa) production system. Phytotoxic effects were noted and attributed to the formation of chloramines in treated nutrient solutions containing ammonium. The study demonstrated that phytotoxic effects can be prevented with the use of regenerative in situ hypochlorination through proper management and monitoring techniques in recirculating hydroponic systems.
While the phytotoxicity caused by conventional chlorination has been well studied, there is no information regarding the effect of the novel RisEHC, with DSA, system examined herein, where the disinfecting agent is continuously regenerated. The objective of the presented research was to evaluate plant responses and possible phytotoxic effects caused by treating different recirculating nutrient solutions via RisEHC. Further, the efficacy of using a post-electrochemical ultraviolet application to reduce the phytotoxicity effects, as well as changing the nitrogen source of the fertilizer, were examined.
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