| In the early stage of development, the intensification of aquaculture promoted the rapid development of aquaculture in our country. It played an irreplaceable role and brought substantial economic benefits. But, with the constant improvement of the degree of breeding, the disadvantages of the intensification of aquaculture also gradually revealed. High bait casting led to deterioration of water quality, disease or death. In addition, the lack of effective aquaculture wastewater treatment led to discharge of a large number of aquaculture wastewater in the process of breeding. It has brought serious challenges to the ecological environment. Circulating water aquaculture had the characteristics of water-saving, environmental protection and strong controllability. Therefore, it was widely used in the intensification of aquaculture. The core of the circulating water aquaculture was the control problem of water quality. Conventional water treatment methods mainly included physical filtration, biological filtration, add oxygen, sterilization and disinfection, etc. Among them, the biological filtration is an important link in aquaculture water treatment. Biological membrane was of the advantages of strong shock load capability and good treatment effect. Therefore, it was widely used in the treatment process of aquaculture water quality. Probiotics were mostly made with the probiotics to splash in the rearing pond directly. It caused secondary pollution easily. Because the use of beneficial bacteria was mainly single strain and its proliferation was effected by competition from other microorganisms in the aquaculture water, they led to the single applying effect, less number of effective living bacterium and unsatisfactory treatment effect. Mixed bacteria could use the synergy of the strains to overcome the disadvantages of single species appeared. But mixed bacteria were mainly applied in industrial wastewater treatment, the research reports were very few in the circulating water aquaculture wastewater treatment. So we need to select mixed bacteria which are suitable for aquaculture wastewater treatment with good effect, and they are applied to the biological membrane sewage treatment technology to improve the efficiency of aquaculture wastewater treatment and realize "zero emissions" of the real meaning.This research mainly designed the test content of the following aspects according to the above questions:1) The separation and purification of target microorganisms (Bacillus subtilis, lactic acid bacteria and yeast) of the strong degradation ability; 2) Study on ability of the target single strains(Bacillus subtilis, lactic acid bacteria and yeast) degradating ammonia nitrogen and the nitrate nitrogen in the water, and the strains of the strong capability of denitrification were identified; 3) Compared the ability of single strain and mixed strains (yeast+bacillus subtilis, bacillus subtilis+lactic acid bacteria, yeast+lactic acid bacteria, bacillus subtilis+ lactic acid bacteria+yeast) degradating ammonia nitrogen and the nitrate nitrogen as well as the hanging condition of the biofilm; 4) Study on the effects of temperature and hydraulic retention time (HRT) in mixed bacteria wastewater treatment system. The author hoped microorganisms which was of the function of promoting denitrification was isolated, and the isolated single strain and mixed strains were inoculated in the biological filter. The best combination of microbial bacteria were filtrated, at the same time, the optimal temperature and HRT of the mixed bacteria were studied by the experiment of effect of the biofilter operating under different temperature and HRT to fill the vacancy of the application of the mixed bacteria in aquaculture wastewater treatment and improve the ability of biofilter treating aquaculture wastewater. It will provide a scientific basis for efficient operation of the biofilter and the optimization of circulating water aquaculture wastewater treatment technology. The main research results of this experiment were as follows:1. The screening of good bacteriaThis experiment purificated out of 8 strains of microorganisms from purchased powder by using the method of enrichment culture and purification from buying the fungus powder and test the denitrification ability.3 strains of best degradation effect were screened out. By gram staining and molecular identification of 16S rDNA technology.3 strains were identified. There were Bacillus subtilis OL-14, Lactobacillus sp. JCM 8693 and Saccharomycetes sp.OHZ67 respectively.3 strains laid the foundation for the research of single strain and mixed strains for of bacteria to deal with aquaculture wastewater in the next step.2. The effects of single bacteria and mixed strains in aquaculture wastewater treatment systemThe wastewater purification effect of Bacillus subtilis, yeast, lactobacillus and mixed strains were evaluated in order to optimize the biofilm technology in circulating water aquaculture system. The experiments were carried out for 35 days. Eight treatments were set up and sterile saline was set as control. Results show that the concentrations of ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2-N) were significantly lower in treatments than control, respectively (P<0.05). The removal rate of NH4+-N and NO2--N were both more than 90% in mixed strains treatment systems, which were significantly higher than other treatments (P<0.05). Significant lower phosphate were observed in treatments inoculated with Bacillus subtilis (0.2mg/L) than treatments without Bacillus subtilis (0.59mg/L) (P<0.05). The concentration of chemical oxygen demand (CODMn) were significantly lower in treatments compared the control (P<0.05), but there were no significant differences among the treatments (P>0.05). The mixed strains treatment systems had the highest removal rate of CODMn (76.9%). In conclusion, the most efficient purification ability are attained in the treatment with mixture of three kinds of strains and mixed strains treatment systems are superior to single bacteria treatment systems.3. The effect of temperature and HRT on the biofilter operatingThe experiment studied the removal efficiency of NH4+-N, NO2-N, CODMn and TP under different temperature and HRT in the biofilter.4 temperature gradients were set up on the test the effects of temperature in the biofilter. they respectively were 15℃,20℃,25℃ and 30℃. Results showed that the microbial quantity of the surface of biofilm increased gradually with the longer duration of hanging membrane, the color of the biofilm also gradually deepened. The microbial quantity of the surface of biofilm in 15℃ treatment group were 3.29×104 cfu/mg (bacillus subtilis),4.11×104 cfu/mg (yeast),5.89×104 cfu/mg (lactic acid bacteria).6.51×103 cfu/mg (nitrifying bacteria) and 7.91 ×103 cfu/mg (ammonia oxidation bacteria). It was lower 1-2 orders of magnitude than 20℃,25℃ and 30℃ treatment group. And the proportion of ammonia oxidizing bacteria and denitrifying bacteria was significantly lower than other three groups (P<0.05). In addition, the effect of temperature on biofilter purification effect was significant, especially for NH4+-N and NO2-N. For the treatment effect of NH4+-N,20℃,25℃ and 30℃ treatment groups were significantly better than 15℃ group (P<0.01), and there was no significant difference in 20℃,25℃ and 30℃ treatment groups (P>0.05). The removal rate were above 80%. For the treatment effect of NO2--N,20℃, The effects of 25℃ and 30℃ treatment groups were significantly superior to 15℃ treatment group (P<Q.01). The effects of 25℃ and 30℃ treatment groups were significantly better than that of 20℃ treatment group (P<0.05), while the differences between 25℃ and 30℃ treatment groups were not significant (P>0.05). For the treatment effect of CODMn and TP, more than 25℃ treatment groups were significantly better than below 25℃ treatment groups (P>0.05). The removal rate could reach more than 60%. As a result, the temperature of the biofilter at 25～30℃ could ensure the high efficient of biofilter.HRT were designed four different gradients in treating simulating aquaculture wastewater. They were 0.25h,0.5h,0.75h and 1h. Results showed that the removal efficiency of NH4+-N、 NO2-N、CODMn and TP increased significantly with the increase of HRT in the biofilter. The treatment effects of 0.75h and 1h treatment groups were superior to that of 0.25h and 0.5h treatment groups (P<0.05). The differences of them were no significant (P>0.05), but the scores of aquacultural environment of 0.75h treatment group was highest. Therefore, the best HRT was 0.75 h in this system. |
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