Biological denitrification is used to treat nitrogen-contaminated groundwater. During the water-treatment process, food sources containing carbon such as glucose, starch, methane, methanol and mixtures like sugar brewery waste are injected in the water to stimulate denitrification. Bacteria such as Pseudomas, Micromacus, Archromabacter, Thiobacilis and Bacilis are then used to decrease nitrates. The nitrate nitrogen in the water is utilized by the bacteria, in the absence of oxygen, and in the process it changes to nitrogen gas which escapes in the air. Biological denitrification is effective because it reduces nitrates in the water to 2 mg per liter of the total nitrogen, lower than the standard set by the Environmental Protection Agency (EPA) of 10 mg per liter of nitrate-nitrogen. However, biological denitification is hard to control, very slow and produces organic residue such as organic carbon, which leads to secondary pollution.
Reverse osmosis is a pressure-driven process where contaminants are removed by forcing untreated water through a semipermeable membrane. Purer water molecules move though the membrane, while the contaminants do not pass. The process is the reverse of natural osmosis, because the water moves from a more concentrated area to a less concentrated one. Reverse osmosis is not only specific to removal of nitrates but usually removes other minerals as well; thus it is more appropriate when you want to remove contents of excess hardness, salt or sulfate in water. The challenge associated with this process is membrane fouling, where solutes or particles deposit onto the membrane pores and degrade the membrane's performance. This can be solved by filtering the water to remove the particles before starting the reverse osmosis process.
In this process, water passes through a bed of synthetic resin beads to remove negative ions including nitrates, which are replaced by equal amounts of chloride ions. Saturate and remove the resin bed and regenerate using sodium chloride (brine) solution which transforms it to chloride form. Rinse the resin bed with clean water and reutilize. A concentrated brine solution of nitrate and counter-ion is produced after regeneration, and this brine is released in the sea or stored in landfills. When you release it in the sea, it increases the risk of future water contamination, thus the use of IX is not encouraged. Still, IX has a positive impact on water quality because it absorbs organic micropollutants (small concentrations of organic compounds) like aromatic compounds and is a simpler method than other types of denitrification processes.
Electrodialysis transfers ions by using direct current as a driving force. It uses ion-exchange resins that selectively transfer ions but not water. Cation- and anion-exchange membranes are arranged alternately between electrode cells at both ends, and desalination and concentration are carried out using the selectivity of these membranes. The anions migrate to the positive electrode (anodes) and the cations migrate to the negative electrodes. Two products are produced: concentrated water and dilute or ion-free water. The electric power required for this process is proportional to the number of ions that will be removed from the water. Treat the water before electrodialysis because the organic molecules can cause clogging. This is done by softening the water to remove hardness and filtering to remove any solids.