| In intensive and intensive freshwater aquaculture,incomplete utilization of feed residues and accumulation of animal feces lead to serious nitrogen pollution in aquaculture water.In order to solve the problem that traditional physical-chemical nitrogen removal method has many equipment,high cost and is not suitable for large-scale treatment,it is an effective way to improve the water quality of aquaculture water to remove nitrogen in aquaculture water by using environmentally friendly and sustainable biological agents.This study from a strain screening to the activated sludge of heterotrophic aerobic denitrifying bacteria,through morphology observation,physiological and biochemical test and combining with molecular biology methods for strain identification,the physical and chemical mutagenesis method is adopted to composite mutagenesis screening mutant strains of strains,explore the denitrifying characteristic of the mutant strains,and applied to simulate aquaculture wastewater,has obtained the good effect of removing nitrogen.The main research results are as follows:1.A strain of aerobic denitrifying bacteria Q-9 with good denitrification ability was screened from the soil of the test field.Through morphological observation,physiological and biochemical indexes determination,and combined with 16S rDNA sequence analysis.The strain Q-9 was identified as Klebsiella quasipneumoniae.2.Determination of denitrifying capacity of denitrifying bacteria Q-9.With nitrate as the sole nitrogen source,the removal rate of nitrate and total nitrogen within 48h was 99.71%and 41.35%respectively.With the accumulation of nitrite at a certain concentration,the denitrification rate of nitrate was 2.88 mg·L-1h-1.When nitrite was the only nitrogen source,the removal rate of nitroso was 24.8%,the total removal rate was 21.4%,and the removal rate of nitroso was 0.52 mg·L-1h-11 within 48h.3.Taking strain Q-9 as the starting strain,a mutant strain T-2 with higher removal rate of nitroso and total nitrogen was obtained by UV-DES-MW combined mutation.With nitrite as the sole nitrogen source,the removal rate of nitrate nitrogen within 48 hours was 81.2%,the total nitrogen removal rate was 70.8%,and the removal rate of nitrite nitrogen was 1.72mg·L-1h-1,which was 3.3 times of the original strain,and had good genetic stability.4.The mutant T-2 was analyzed for denitrification and nitrogen removal.The effects of carbon sources,C/N ratio,metal ions and culture conditions on denitrification were studied by using single factor experiment.On the basis of single factor test results,the Box-Behnken response surface Design method was used to optimize the factors?speed,temperature and initial pH?that have a great influence on the denitrification rate,with denitrification rate as the response value.Results show that the suitable carbon source for sodium citrate,carbon and nitrogen ratio systematically,divalent metal ions for zinc ione,the age of 24h,1.5%inoculated quantity,initial pH7.4 slightly,temperature 32.6?,the speed of 192 r/min.Under these conditions,the removal rates of nitroso and total nitrogen were 99.8%and 95.89%,respectively,which were 17%and 24.49%higher than the original strains.Q-9,T-2 and mixed bacteria were used in simulated aquaculture wastewater treatment. |
PDF Full Text Request