Cost Reduction in the Process of Biological Denitrification by Choosing Traditional or Alternative Carbon Sources

Biological denitrification is a generally economically viable and reliable technology for nitrate (NO 3 − -N) and nitrite (NO 2 − -N) removal from wastewater. Nitrate/nitrite reduction requires an electron donor, which can be supplied from influent wastewater organic compounds, added as an external carbon source, or by endogenous respiration. Decisions regarding the selection of an external carbon source should take into consideration its cost, sludge generation quantity, the rate and efficiency of denitrification, and chemical storage safety. The expense of waste management and external carbon sources accounts for up to 50% of the overall cost of wastewater treatment. The carbon source characteristics required for biological denitrification affect the microbial community structure, denitrification rate, and intermediate products. This review is based on a bibliometric analysis and a systematic literature review providing information and insight into the topic of the denitrification process using different carbon sources. In this review, the main focus was on discussing alternative carbon sources vs. traditional carbon sources in terms of the carbon source price, C/N ratio, denitrification efficiency and rate, operational parameters, and advantages and disadvantages, as well as the limitations in the denitrification process. Future perspectives may include the operating parameters influencing the stability of the removal performance; the maintenance and improvement of nitrate removal; a study of the diversity of the microbial community; research on the application of new alternative carbon sources in denitrification; and N 2 O emission detection and minimisation.