Study on isolation and identification of heterotrophic nitrifying bacteria and optimal denitrification conditions

Abstract: Aerobic composting of livestock and poultry manure, decomposing organic matter and releasing heat by microorganisms, can be harmless and thoroughly decomposed, as well as realize the utilization of solid waste. However, in the process of composting, a large amount of ammonia gas is generated, which pollutes the surrounding air seriously. It is essential to select microorganisms with high nitrogen removal ability. Through continuous enrichment and domestication of shake flask, a strain named Z53 with high-efficiency removal of ammonia nitrogen was isolated from the activated sluge of garbage leachate plant. Through identification of morphology characteristics as well as gene sequences of 16SrRNA, the strain Z53 was identified as Paracoccus denitrificans. The nitrogen removal conditions were optimized by orthogonal test, detecting the temperature(30, 35 or 40 ℃), pH value(7, 8 or 9) , and the liquid volume (40, 60 or 80 mL in 250 mL conical flask), and the results showed that the optimal carbon source of the strain was disodiam succinate, the best C/N ratio was 15, and the optimal removal conditions of ammonia nitrogen included shaking speed of 160 r/min, liquid volume of 40 mL in 250 mL conical flask, temperature of 30 ℃ as well as pH value 7.0. When inoculating 1% of the bacterial solution under optimal conditions, the strain Z53 removed (191.4±0.7) mg/L ammonia nitrogen completely within 11 h, and the average removal rate was 17.4 mg/(L·h). The determination of nitrogen morphology displayed that strain Z53 not only owned the ability of heterotrophic digestion (which can oxidize the ammonia nitrogen to nitrate nitrogen without accumulation of nitrite nitrogen) but also had the ability of denitrification to transform nitrate nitrogen into nitrite nitrogen under aerobic conditions. The average removal rate of nitrate nitrogen was 16.8 mg/(L·h), while under the anaerobic conditions, it could produce N2, and the average removal rate of nitrate nitrogen was 9.8 mg/(L·h). The strain Z53 could convert ammonia nitrogen into nitrate nitrogen through nitrification, and then converted nitrate nitrogen into intracellular nitrogen or gaseous product through denitrification, which had strong removal ability of ammonia nitrogen. During the high-temperature aerobic composting process in the composting plant, the microorganisms decompose the nitrogen-containing organic matter to produce large amounts of ammonia gas. In order to remove the ammonia gas, the gas in the composting plant could be collected and passed into the bio-trickling filter with inoculating strain Z53. The removal of ammonia nitrogen in this way could achieve the purpose of reducing pollution of ammonia gas. Moreover, the strain Z53 could also be inoculated into the compost material, which removed part of the ammonia nitrogen in the heap before the compost was warmed up. In addition, the nitrogen content in the compost leachate was high, and the accumulation of nitrate would lead to eutrophication of the water body. Because the strain Z53 can remove nitrate nitrogen efficiently, the strain Z53 also has a good potential of application in the denitrification of water body of leachate in the composting plant.