Development of a novel process for anoxic ammonia removal with sulphidogenesis

A novel process for anoxic ammonia removal with sulphidogenesis was developed in a 1.75 l capacity up-flow hybrid reactor in anoxic conditions (ORP = −225 ± 25 mV) for simultaneous removal of ammonia, organic carbon and sulphate. The process was operated for a total of 240 days. Synthetic feed was used during the first 220 days. After start-up and acclimatization of the process for 120 days, loading rate studies were carried out in continuous operation (at COD/SO42− ratio = 1.3) at HRT of 1 day. The reactor performance decreased at a high organic loading rate of 3.75 kg COD/m3/d due to sulphide inhibition. The continuous injection of air at a rate of 0.2 l/min at 40 cm height from the bottom of reactor helped in sulphide oxidation within the anoxic zone and this helped to increase the removals of NH4+, COD and SO42− substantially. Application of the developed process for the treatment of primary treated combined tannery effluent was carried out during the final phase at an organic loading rate of 3.9 kg COD/m3/d (COD/SO42− ratio = 1.3) and at an ammonia loading rate of 0.3 kg NH4+/m3/d. The percentage removals of NH4+, COD and SO42− were in the ranges of 65.9–89.4, 51.9–70.7 and 70.8–83.1, respectively. The specific rates of sulphate reduction and anoxic ammonia removal of the reactor biomass were 0.36 kg SO42−/kgMLVSS/d and 0.07 kg NH4+/kgMLVSS/d, respectively.