How Rhodococcus ruber accelerated denitrification with soybean-processing wastewater as the electron donor

Total nitrogen removal is a bottleneck for achieving acceptable effluent quality for many municipal wastewater treatment plants (WWTPs). Inadequate denitrification is often the cause of insufficient total-nitrogen removal, and a deficiency of electron donor is a frequent cause. Soybean-processing wastewater (SPW) is potential electron donor. SWP contains electron donors to drive denitrification, but they are polymers that need to be hydrolyzed first. This work evaluated how bioaugmentation with a small amount of Rhodococcus ruber accelerated denitrification with soluble SWP. Compared with normal acclimated denitrifying biomass alone, addition of 0.45% (w/w) R. ruber accelerated the NO₃⁻–N removal rate by 22%, and it also led to greater release of NH₄⁺–N from the breakdown of amino acids in SWP. The acceleration was attributed to the proteins and polysaccharides being more rapidly hydrolyzed, since R. ruber contained the genes for a variety of protein and polysaccharide hydrolases. Hydrolysis released simple amino acids and carbohydrates that could be oxidized by the denitrifying biomass, as well as by R. ruber. While R. ruber also could oxidize amino acids and carbohydrate via oxygen and nitrate respirations, its main role in bioaugmentation was to accelerate the first step, hydrolysis. This work introduces the practice novelty that bioaugmentation with R. ruber could accelerate denitrification and the fundamentals novelty that R. ruber accelerated denitrification by catalyzing hydrolysis of proteins and polysaccharides in SPW.