Screening And Biological Characteristics Of Ammonia-oxidizing Molds In Aerobic Chicken Manure Composting

Heterotrophic ammonium oxidation is a process that ammonium nitrogen or negative trivalent organic nitrogen are oxidized into hydroxylamine, nitrite nitrogen or nitrate nitrogen by heterotrophic bacteria or molds. As an important part of global nitrogen cycle, heterotrophic ammonium oxidation plays a significant role in nitrogen transformation in systems containing high contents of organic compounds and nitrogen. Aerobic composting of solid waste, such as aerobic chicken manure composting is such a system in which ammonium volatilization resulted in serious nitrogen loss. The enhancement of heterotrophic ammonium oxidation is of significance in preventing nitrogen loss.In the study, nitrogen transformation activities of 10 strains of molds isolated from aerobic chicken manure composting were determined to screen ammonia-oxidizing molds and define high-effective strains. Culture conditions were changed to evaluate effects of environmental factors on the nitrogen transformation activity of high-effective strains. Finally, the high-effective strains were added into aerobic chicken manure composting to verify application effects. The objective of the study is to make clear the existence, characteristics of nitrogen transformation and application effects of ammonia-oxidizing molds in aerobic chicken manure composting, and to provide evidence for the inhibition of ammonium volatilization in the process of aerobic composting. The main results were as follows.(1) All of the 10 strains could oxidize ammonium nitrogen into nitrite and nitrate nitrogen, showing that they are ammonia-oxidizing molds, and indicating that ammonia-oxidizing molds are widely distributed in aerobic chicken manure composting. Both of the two defined high-effective strains, named M25-22 and M40-4, could decrease ammonium nitrogen by above 0.3mg·mL-1, and produce nitrite and nitrate nitrogen with a total concentration of 1.1×10-3mg·mL-1, 1.5×10-3mg·mL-1, respectively.(2) In media containing (NH4)2SO4 at a concentration of 5mg·mL-1, mycelium weight of M25-22 and its utilization ratio of ammonium nitrogen increased markedly during the first 5 days; nitrate concentration increased markedly from the 3rd to 5th day, and remained constant thereafter; nitrite concentration remained at a low level. Mycelium weight of M40-4 and its utilization ratio of ammonium nitrogen increased markedly during the first 3 days; nitrate concentration increased markedly from the 3rd to 5th day; nitrite was produced after 2 days, and remained constant after 4 days.(3) Both of the strain M25-22 and M40-4 showed the activity to oxidize ammonium nitrogen growing in media containing glucose, sucrose, starch or cellulose as the sole carbon source, and to oxidize the negative trivalent nitrogen of ammonium sulfate, peptone, acetamide, urea or L-aspartate. Slowly available carbon or nitrogen sources, such as starch, cellulose and peptone, were beneficial to ammonium oxidation by them. In media containing sucrose as the sole carbon source and ammonium sulfate as the sole nitrogen source, nitrate formation was the most pronounced with sucrose present at a concentration of 12g·L-1 and ammonium nitrogen present at a concentration of 2.438mg·mL-1, at the initial pH level of 7.5 and at 30℃by the strain M25-22, and with sucrose present at a concentration of 10g·L-1 and ammonium nitrogen present at a concentration of 2.014mg mL·-1, at the initial pH level of 7.0 and at 45℃.(4) After added into aerobic chicken manure composting, both of the two high-effective strains could decrease nitrogen loss and promote the maturity of compost, indicating that they have significant application value in aerobic composting of solid wastes such as chicken manure.