Growth of Lettuce in Hydroponics Fed with Aerobic- and Anaerobic–Aerobic-Treated Domestic Wastewater

Abstract

Reusing water and nutrients from municipal wastewater can conserve resources and reduce wastewater treatment costs. In this study, the suitability of different qualities of treated wastewater for plant production in a hydroponic flow-through system was investigated. Lettuce (Lactuca sativa L.) was grown in hydroponic lines fed with treated wastewater, i.e., conventional effluent from aerobic wastewater treatment by the activated sludge process (CE), ozonised CE (CEO), anaerobically pre-treated and nitrified wastewater (AN) and biological activated carbon filtered AN (ANC) in comparison with a modified Hoagland nutrient solution. In CEO, AN and ANC, the lettuce reached a similar weight and elemental composition as that in HS. The low N and P concentrations in CE and CEO were quickly depleted, resulting in limited plant development at the ends of these lines. The lower water content in the CE shoots was probably related to hypoxia that occurred at higher temperatures. In the CEO line, this condition did not arise due to the constant decay of O3. At lower temperatures, the CEO shoot dry weight was 90% higher than that in CE. This was possibly an effect of residual ozone and/or oxygen supersaturation. AN produced the highest yield, while carbon filtration lowered the content of cations in ANC, inducing deficiency of Fe > Mn > Cu > Zn > K. Coupling wastewater treatment with hydroponics allows for efficient nutrient recovery, and thus could reduce the energy and reactor volume needed for N and P elimination.