Denitrification of industrial wastewater: Influence of glycerol addition on metabolic activity and community shifts in a microbial consortium

• The wastewater are characterized by a high concentration of nitrates.
• The denitrification rate was at 44 mg N g−1 d m d−1.
• The microbial consortium were characterized by a diverse metabolic activity.
• Shifts in the bacterial community dynamics of the consortium could be observed.

The wastewater originating from explosives manufacturing plants are characterized by a high concentration of nitrates (3200 mg N L−1), sulfates (1470 mg L−1) and low pH (1.5) as well as the presence of organic compounds, such as nitroglycerin (1.9 mg L−1) and nitroglycol (4.8 mg L−1). The application of glycerol (C/N = 3) at such a high concentration enabled complete removal of nitrates and did not cause the anaerobic glycerol metabolic pathway of the DNC4 consortium to activate, as confirmed by the low concentrations of 1,3-propanediol (0.16 g L−1) and acetic acid (0.11 g L−1) in the wastewater. Increasing the glycerol content (C/N = 5) contributed to a notable increase in the concentration of both compounds: 1.12 g L−1 for acetic acid and 1.82 for 1,3-PD (1,3-propanediol). The nitrate reduction rate was at 44 mg N g−1 biomass d−1. In order to assess the metabolic activity of the microorganisms, a method to determine the redox potential was employed. It was established, that the microorganisms can be divided into four groups, based on the determined denitrification efficiency and zero-order nitrate removal constants. The first group, involving Pseudomonas putida and Pseudomonas stutzeri, accounts for microorganisms capable of the most rapid denitrification, the second involves rapid denitrifying microbes (Citrobacter freundi and Pseudomonas alcaligenes), the third group are microorganisms exhibiting moderate denitrification ability: Achrobactrum xylosoxidans, Ochrobactrum intermedium and Stenotrophomonas maltophila, while the last group consists of slow denitrifying bacteria: Rodococcus rubber and Sphignobacterium multivorum.