Progress on the Use of Hydroponics to Remediate Hog Farm Wastewater after Vermifiltration Treatment

Abstract

Hog farm wastewater may require novel biological treatment techniques to improve efficiency and reduce costs. Previous studies combining vermifiltration with downstream hydroponics showed the need for a balanced wastewater nutrient content, particularly the nitrogen-to-phosphorus ratio. Here, a deep-water culture hydroponic system, growing lettuce as model culture, was used to remediate hog farm wastewater after an initial vermifiltration stage, aiming to produce an effluent suitable for irrigation. Supplemented vermifiltered wastewater (SVW) with added nutrients was tested against unsupplemented vermifiltered wastewater (VW) over 35 days, using a synthetic nutrient solution (NS) as a control. Supplementation was shown to improve lettuce growth, light use efficiency, and water use efficiency. Nutrient analysis over time showed a better-balanced phosphorus and nitrogen removal in SVW than in VW; in all treatments nitrogen and phosphorus content was reduced to legally acceptable levels for treated wastewater reuse in irrigation: nitrate 5 mgN L−1 in VW and undetectable in SVW and NS; ammonia undetectable in all treatments; and total phosphorus 2.4 mg L−1 in SVW, 0.9 mg L−1 in NS and undetectable in VW. Coliforms increased in VW and SVW during hydroponic treatment, which should be solved by disinfection. Overall, combining vermifiltration with downstream hydroponic culture proved to be a promising treatment to remediate nutrients in hog farm effluent to make it suitable to be reused for irrigation.