The share of electrochemical reduction, hydrogenotrophic and heterotrophic denitrification in nitrogen removal in rotating electrobiological contactor (REBC) treating wastewater from soilless cultivation systems

Abstract

There is a growing global environmental problem of agricultural wastewater from soilless plant cultivation systems. In most countries dominate open fertilization systems, in which excess of nutrient solution is discharged in an uncontrolled way into the ground inside greenhouses or adjacent areas. Wastewater from such systems is characterized by a very high concentration of nitrogen and phosphorus compounds and their discharge into the environment causes significant pollution of the water and soil environment. The goal of the research was to determine the contribution of electrochemical reduction of nitrogen, hydrogenotrophic and heterotrophic denitrification in the process of nitrogen removal in a rotating electrobiological contactor (REBC) depending on hydraulic retention time (HRT) and electric current density (J). Synthetic sewage with characteristics corresponding to wastewater from soilless cultivation of tomatoes was the subject of the research. The first part of the experiment included determination of the effect of HRT on the effectiveness of bio-processes of nutrients removal in a rotating biological contactor (RBC). The second concerned the effect of HRT and J on the effectiveness of nutrients removal in a rotating electrochemical contactor (RECC), while the third part - the effect of HRT and J on the effectiveness of nutrients removal in REBC. RBC was characterized by low efficiency of denitrification (6.2 to 9.2%). The effectiveness of nitrogen removal in RECC was determined by both electric current density and hydraulic retention time. The highest efficiency was 53.4%. REBC nitrogen removal effectiveness was higher than in RBC and in RECC. The nitrogen removal efficiency increased along with increasing values of HRT, reaching the maximum value of 68.6% for J=10.0A/m² and HRT=24h. The contribution of hydrogenotrophic denitrification in total nitrogen removal increased with the increase of electric current density.

Keywords: Electrochemical treatment; Hydrogenotrophic denitrification; Nutrients removal; Rotating electrobiological contactor; Tomatoes soilless cultivation wastewater.