Nitrogen Removal Processes for Wastewater Treatment

Nitrogen-containing compounds are among the pollutants that can cause serious environmental hazards. One of these hazards is nutrients enrichment of rivers that can result in eutrophication, decreased water quality, and potential health hazards for humans and animals, when released in the environment. Nitrate removal methods can be generally classified into physical, biological, and chemical reduction methods. The most commonly used methods in this regard are biological denitrification, ion exchange, electrodialysis, reverse osmosis, chemical denitrification, adsorption, electrocoagulation, nanotechnology, and redox reaction. The first four methods have been used in the industry. Biological denitrification is an effective method because of the conversion of nitrate into N2 gas and the absence of secondary pollutant production. However, it is not widely used in the removal of nitrate from drinking water sources and underground water due to microbial contamination and rather is mostly used for wastewater treatment. The purpose of this study is to present a brief introduction on the use of physiochemical methods for the removal of nitrate from water and wastewater.

Pollution of water resources, such as nitrogen compounds, nitrate, and ammonium is increasingly expanding. A wide range of physico-chemical and biological methods are conducted for decreasing nitrate compounds and the amount of wastewaters. Due to low selectivity of nitrate, high costs, and the need for pre and post purification processes, the physico-chemical method is not effective for this purpose. However, biological methods are highly efficient in the removal of nitrogen compounds, and due to their advantages, they are widely used in wastewater purification. These methods include simultaneous nitrification and denitrification (SND), Anammox, and partial nitrification which are reviewed in the following chapter.

Normally, the food industry produces wastewater containing high organic matter and nitrogen compounds. Along with organic matter removal from these streams, also, nitrogen compounds should be removed. Nitrogen can be removed biologically from wastewater using conventional and novel processes. Although, conventional nitrification/denitrification is an established system for nitrogen removal but the costs of treatment by this system are high because of: high oxygen requirement for nitrification, the addition of external carbon source for denitrification (in the case of wastewaters with low C/N ratio), slow growth rate of microorganisms responsible for both processes, and needing two successive reactor or difficult control of one-reactor system. These disadvantages led to conduction of substantial studies to find better alternatives. Therefore, different novel processes were studied and used for nitrogen removal. Many autotrophic processes including SHARON, ANAMMOX, SHARONANAMMOX, CANON, and OLAND were discovered to be more economical than conventional nitrification/denitrification system. Also, more studies on combination of novel processes with a part of conventional nitrification/denitrification process led to the development of other novel processes such as heterotrophic nitrification-aerobic denitrification, NOx, and DEAMOX processes. Details of both conventional and novel processes were discussed in this chapter. Finally, the possibility of using these processes to remove nitrogen from food industry wastewater is discussed. Because of co-existence of both carbon and nitrogen compounds in food industry wastewater, the use of novel autotrophic processes for mainstream wastewater treatment is impossible. So, carbonaceous contaminants should be removed using anaerobic digestion or high load conventional activated sludge, and then effluent of these processes with high nitrogen contents (low C/N ratio) can be treated using novel autotrophic processes. It should be noted that there are two alternatives including heterotrophic nitrificationaerobic denitrification process and organic-laden DEAMOX process that can be used for mainstream food industry wastewater treatment but the exact characteristics of these processes are unclear and should be accurately studied in laboratory, pilot and full-scale before use.

The entrance of various pollutants into the environment and the resulting problems led to the use of new methods for the purification of these pollutants and the recovery of energy contained therein. Nowadays, bioelectrochemical systems (BES) are considered as a new technology in the generation of electricity and wastewater treatment. Also, the use of fossil fuels, especially oil and gas, has accelerated in recent years resulting in a global energy crisis. Bio-Renewable energy is considered as one of the ways to reduce the current global warming climate. Modern production of electricity from renewable sources without much carbon dioxide emissions is much more favorable. The purpose of this chapter is to present a brief introduction on the use of bioelectrochemical systems and its various types including Microbial Fuel Cells (MFC), Enzymatic Biofuel Cells (EFC) and Microbial Electrolysis Cell (MEC).

In recent years Bioelectrochemical systems (BESs) as a new approach represent an energy-efficient way for wastewater treatment, metal/nutrient recovery, and transformation of wastes to valuable products such as hydrogen. These unique characteristics of BESs are provided by a flexible platform for oxidation-reduction reactions. Although this process is still not fully developed but it can be nominated as a future trend of green energy and cleaner biochemical production pathway along with the waste remediation. Conversion of organic wastes into electricity and hydrogen/chemical products occurs in microbial fuel cells (MFCs) and microbial electrolysis cells (MECs), respectively. Different aspects of the process such as biological communities, physical configuration, and electrochemical conditions can affect a good performance of BES. In the present chapter review, the different fundamental mechanisms of BESs with emphasis on nitrogen removal have been reviewed. The behavior of affecting parameters on nitrogen and organic removal was discussed, including content pH, electrode material, level of supernatant concentration, the distance between electrodes and applied current, salinity and other operating conditions. Moreover, reported pathways and the theory of denitrification in BESs were described. Considering the finding, BES can be nominated as an alternative technology to the minimization of waste and a good way to generate electrical energy and valuable chemicals.