Use of polishing pond effluents to cultivate lettuce (Lactuca sativa) in a hydroponic system

The sanitary quality and productivity of hydroponic lettuce (Lactuca sativa L.) plants cultivated under greenhouse conditions and treated with effluent from anaerobic reactor + polishing pond followed by physical-chemical treatment was evaluated. Two hydroponic cultivations were performed at summer and winter time at Vitoria-ES, Brazil. The treatments for both cultivations were: T1) conventional nutrient solution, T2) effluent from physical-chemical treatment, T3) effluent from polishing pond, and T4) effluent from polishing pond with 50% dilution. The plants were evaluated for microbial contamination, productivity and nutrient content. In all cases, no significant microbial contamination of lettuce was detected and the levels of macronutrients in the shoot system were similar to those in published reports. In the experiments from summer season, the treatments T1 and T2 resulted in higher production than the T3 and T4 treatments. Plants from T3 and T4 had a less developed root system as a result of reduced oxygenation from competition with the higher algae biomass content from the polishing pond effluent. In the winter season, the effect of the algal biomass was pronounced only in the T3 treatment (undiluted effluent from polishing pond). In conclusion, hydroponic cultivation of lettuce with pond effluent is suitable as a complement to water and nutrients for plants.