Investigation on the improved electrochemical and bio-electrochemical treatment processes of soilless cultivation drainage (SCD)

The soilless crop cultivation under cover generates wastewater called soilless cultivation drainage (SCD), being a nutrient-rich overflow. The average concentration of phosphorus- and nitrogen-based pollutants from soilless tomato cultivation usually ranges from 35.4 to 104.0 mg P/L and from 270.0 to 614.9 mg N/L, respectively. In bio-electrochemical reactors, nitrogen and phosphorus are removed via biological denitrification, electrochemical nitrate reduction, bio-electrochemical reduction, and electrocoagulation. The novelty of this study is due to the use of alternating current (AC), which can both mitigate the corrosion on the anode and solve the issue of insoluble oxide build-up on the cathode. Additionally, and crucially, it promotes bacterial growth and activity. The aim of the present study was to determine (1) the effectiveness of soilless cultivation drainage treatment methods that employ biological and electrochemical processes, with consideration given to (2) the quantity and quality of the produced sludge as a potential nutrient-rich product. The bio-electrochemical reactor proved more effective than the electrochemical one and ensured a high TP and TN removal efficiency exceeding 97% and 66%, respectively. The resulting sludge was rich in such elements as calcium, potassium, carbon, phosphorus, and nitrogen, and as such may serve as a viable alternative to conventional mineral fertilizers.