Recycling nutrients from municipal wastewater

A commercial hydroponic system is being adapted for studying the potential recycling of nutrients from settled primary domestic wastewater to produce value-added crops. The system is 3 m long, with small gullies used for easily manageable plants like lettuce and capsicum, and large gullies for large plants like corn and tomato. Primary treated effluent is being used to irrigate lettuce in one series, and a commercial nutrients solution is being used to irrigate the same type of lettuce in another series as a control. The crops grown in these systems have shown a remarkable ability to remove nitrogen and phosphorous from settled primary sewage. Studies are continuing to improve hydroponic design and to accommodate other crops. Early results have shown that lettuce will remove over 77% of the phosphorous and 80% of the nitrogen. The crops irrigated with sewage without disinfection appear healthy compared to the control using commercial nutrients but yield plants which are up to 50% less mass. At the end of the cropping period, the plants were harvested to quantify total nutrient uptake and to test for heavy metals in the edible portion of the vegetables.