**4.3 SHARON-Anammox process**

A Single reactor system for High activity Ammonium Removal Over Nitrite (SHARON) is a treatment process, which utilizes partial nitrification process for the degradation of ammonia and organic nitrogen components from wastewaters. The process results in stable nitrite formation, rather than complete oxidation to nitrate. The process relies on controlling the pH, temperature, and retention time to prevent the nitrate formation by nitrite-oxidizing bacteria, e.g. Nitrobacter. The wastewater denitrification that employs SHARON reactors can proceed with an anoxic reduction, such as Anammox. In the Anammox process (anaerobic ammonium oxidation), nitrite and ammonium are converted into nitrogen gas under anaerobic conditions without the need to add an external carbon source. In comparison with conventional N-removal processes, the SHARON process results in a reduction of required aeration energy and carbon source.

The application of the successive SHARON-Anammox processes was tested to treat the wastewater from a fish cannery plant. The effluents generated from the anaerobic digestion are characterized by their salinity up to 8000–10,000 g NaCl m−3, organic carbon content (1000–1300 g TOCm−3), and high ammonium content (700–1000 g NH+4− Nm−3). In the SHARON reactor, nearly half the ammonia is oxidized to NO− 2-N via partial nitrification. Then, SHARON effluent was directed to feed the Anammox reactor. The system was reported to attain average nitrogen removal of 68%. The bacterial population distribution in the Anammox reactor, followed by FISH analysis and batch activity assays, did not change significantly despite the continuous entrance to the system of aerobic ammonium oxidizers coming from the SHARON reactor. Most of the bacteria corresponded to the Anammox population and the rest with slight variable shares to the ammonia oxidizers. Despite the continuous variations in the amounts of ammonium and nitrite in the feed wastewater, the Anammox reactor showed an unexpected robustness. Only in

the period when NO<sup>−</sup> 2-N concentration was higher than the NH+ 4-N concentration did the process destabilized and it took 14 days until the nitrogen removal percentage decreased to 34% with concentrations in the effluent of 340 g NH+ 4-Nm−3 and 440 g NO<sup>−</sup> 2-N m−3, respectively. That study concluded that this successive application of SHARON-Anammox reactors is successful in treating high nitrogen and saline effluents with acceptable control on the ratio between the NO− 2-N and NH<sup>+</sup> 4-N [13].
