Nitrification of vegetable waste using nitrifying bacteria

Current inorganic chemical-based fertilizers for soils have adverse impacts on human health and environment. In the present work, two nitrifying bacteria, i.e. Nitrosomonas sp. DSM 28437 and Nitrobacter sp. DSM 10236, were explored for the production of nitrate in vegetable wastes. For this purpose, the nitrite production by Nitrosomonas sp. and nitrate production by Nitrobacter sp. in two synthetic media containing ammonium and nitrite, respectively were investigated. Also, simultaneous growth of both bacteria in a single synthetic medium containing ammonium was investigated. Finally, the performance of both bacteria in a mixture of vegetable wastes, where a consortia of microorganisms present in cattle-based compost produced ammonium, were investigated. Highest concentration of nitrite (13.2 ppm) and nitrate (1600 ppm) in Nitrosomonas sp. and Nitrobacter sp. inoculated synthetic media were achieved after 12 and 28 days, respectively. The simultaneous growth of both bacteria in synthetic media and both bacteria along with compost microorganisms in vegetable wastes resulted in 12 and 20 ppm nitrate, respectively. Also, it was observed that with increasing time, the optical density of Nitrobacter sp. population increased from 0.04 to 0.72 after 35 days, but for Nitrosomonas sp., until 12 days, the optical density increased 0.3 from to 0.6 and then decreased to 0.2 on day 21 because of nitrite toxicity to the microorganism. The transformation of ammonium to nitrate using Nitrosomonas sp. and Nitrobacter sp. in synthetic media and a mixture of vegetable wastes was studied to develop a new organic fertilizer containing nitrogen source.