Combining Vermifiltration with Hydroponics to Treat Organic Wastewaters and Produce Food

Abstract

Pork is extensively consumed worldwide. Large-scale pig farming responds to the consumer demand but also generates great amounts of waste, rich in pathogenic bacteria, organic matter, nitrogen and phosphorus. The typical piggery waste treatment is insufficient to eliminate the risk of pollution. Vermicomposting and vermifiltration have shown capacity to remove organic matter, control pathogens and promote ammonia and nitrite oxidation in animal wastes and wastewaters. Hydroponic plants have shown ability to remove nitrate and phosphorus from wastewaters and decrease eutrophication risks. A partially continuous pilot-scale system combining a trickling vermifilter with a downstream hydroponic deep-water culture unit was built. Organic matter, faecal pathogens, and forms of nitrogen were analysed in the vermifiltration stage; nitrogen and phosphorus were the focus of hydroponic treatment analysis. Nitrifying bacterial communities were analysed in different sampling spots in the system. A reflection on the possibility to upscale the system for real-life use was presented. Vermifiltration removed ammonia (≤100%), nitrite (≤100%), organic matter (≤83% BOD5), and coliform bacteria (≤54%). A variety of pointed cabbage and radicchio initially grew hydroponically but showed signs of nutrient deficiencies, stalled growth and death over time. Modest abundances of AOB and NOB were found in the liquid phase of the system, and further study of solids and biofilms are needed. Hydroponic treatment of the vermifilter effluent removed more BOD5 (≤83%), ammonia (≤98%), nitrite (≤99%) and phosphorus (≤55%), removal limited probably by ecological factors. Nitrate was not efficiently removed by hydroponic treatment. Coliforms recovered in the hydroponic unit. The results suggest the need to monitor and correct physical conditions and nutrient content in the feed, and to control the micro-organisms throughout the system. Batch systems are advisable for preliminary studies. Implementation of similar systems on pig farms facilities is possible, although requiring investment in construction, monitoring, maintenance and personnel.