Development and optimisation of VFA driven DEAMOX process for treatment of strong nitrogenous anaerobic effluents

The recently proposed DEAMOX (DEnitrifying AMmonium OXidation) process combines the anammox reaction with autotrophic denitrifying conditions using sulphide as an electron donor for the production of nitrite from nitrate within an anaerobic biofilm. This paper firstly presents a feasibility study of the DEAMOX process using synthetic (ammonia + nitrate) wastewater where sulphide is replaced by volatile fatty acids (VFA) as a more widespread electron donor for partial denitrification. Under the influent N-NH₄⁺/N-NO₃⁻ and COD/N-NO₃⁻ ratios of 1 and 2.3, respectively, the typical efficiencies of ammonia removal were around 40% (no matter whether a VFA mixture or only acetate were used) for nitrogen loading rates (NLR) up to 1236 mg N/l/d. This parameter increased to 80% by increasing the influent COD/N-NO₃⁻ ratio to 3.48 and decreasing the influent N-NH₄⁺/N-NO₃⁻ ratio to 0.29. As a result, the total nitrogen removal increased to 95%. The proposed process was further tested with typical strong nitrogenous effluent such as reject water (total N, 530–566 mg N/l; total COD, 1530–1780 mg/l) after thermophilic sludge anaerobic digestion. For this, the raw wastewater was split and partially (∼50%) fed to a nitrifying reactor (to generate nitrate) and the remaining part (∼50%) was directed to the DEAMOX reactor where this stream was mixed with the nitrified effluent. Stable process performance up to NLR of 1,243 mg N/l/d in the DEAMOX reactor was achieved resulting in 40, 100, and 66% removal of ammonia, NO_x⁻, and total nitrogen, respectively.