Hydrogenotrophic denitrification process efficiency and the number of denitrifying bacteria (MPN) in the sequencing batch biofilm reactor (SBBR) with platinum and carbon anodes

ABSTRACT

This work reports on the effect of electric current density and anode material (platinum, carbon) on the concentration of oxidized and mineral forms of nitrogen, on physical parameters (pH, redox potential, electrical conductivity) and the number of denitrifying bacteria in the biofilm (MPN). Experiments were conducted under anaerobic conditions without and with the flow of electric current (with density of 79 mA·m⁻² and 132 mA·m⁻²). Results obtained in the study enabled concluding that increasing density of electric current caused a decreasing concentration of nitrate in the reactor with platinum anode (R1) and carbon anode (R2). Its concentration depended on anode material. The highest hydrogenotrophic denitrification efficiency was achieved in R2 in which the process was aided by inorganic carbon (CO₂) that originated from carbon anode oxidation and the electrical conductivity of wastewater increased as a result of the presence of HCO₃⁻ and CO₃²⁻ ions. Strong oxidizing properties of the platinum anode (R1) prevented the accumulation of adverse forms of nitrogen, including nitrite and ammonia. The increase in electric current density affected also a lower number of denitrifying bacteria (MPN) in the biofilm in both reactors (R1 and R2). Metal oxides accumulated on the surface of the cathode had a toxic effect upon microorganisms and impaired the production of a hydrogen donor.

KEYWORDS:

• Carbon anode
• electrolysis
• hydrogenotrophic denitrification
• number of denitrifying bacteria (MPN)
• platinum anode
• sequencing batch biofilm reactor (SBBR)

Funding

This study was financed under Project No. 0811–0882 of the University of Warmia and Mazury in Olsztyn, Poland.