Research On Water Treatment Effect Of Self-cleaning Biological Filter With Fouling Intercepting Function

Biological filter is one of the core water treatment units in RAS,is the key to the successful operation of circulating aquaculture system,and plays a key role in the purification and recycling of aquaculture water.Although the traditional submerged biological filter has the function of intercepting suspended solids,its shortcomings such as being easily blocked,uneven distribution of water causing anoxic zone,and difficult removal of aging bacterial membranes,restrict its wide use.This experiment uses a new type of self-cleaning biological filter with dirt interception function,which not only has the function of intercepting suspended solids,but also can overcome the above shortcomings through the self-cleaning function.This experiment is aimed at the self-cleaning biological filter,and studies the water treatment effect of the biological filter by different filming methods,different self-cleaning frequencies,different N concentration potentials at the inlet and outlet of different biological filters,different decontamination precisions,and different filler filling rates.The main research results obtained are as follows:（1）Compared with natural film,adding different proportions of mature biofilm can effectively reduce the concentration of ammonia nitrogen and nitrite nitrogen.The highest ammonia nitrogen concentration reached by the natural membrane（S1）on the15th day is 1.2 mg/L,the highest ammonia nitrogen concentration reached by the addition of 10%mature bacterial membrane（S2）on the 13th day is 0.55 mg/L and the addition of 30%mature bacteria The membrane（S3）reached the highest ammonia nitrogen concentration on the 13th day of 0.36 mg/L;the S1 treatment group reached the highest nitrite nitrogen concentration on the 27th day of 4.6 mg/L,and the S2treatment group reached the highest on the 15th day The concentration of nitrite nitrogen was 0.72 mg/L,the highest concentration of nitrite nitrogen reached by the S3treatment group on the 9th day was 0.35 mg/L,the time for the ammonia nitrogen and nitrite nitrogen concentrations of the three treatment groups to reach the highest concentration in sequence Lag.The maturation time of the biofilms in the S1 treatment group,S2 treatment group and S3 treatment group were 35 days,25 days and 18 days,respectively.The data showed that the higher the proportion of mature biofilms,the shorter the time for the membrane to hang.Samples were taken for microbial sequencing when the ammonia nitrogen concentration decreased and the nitrite nitrogen concentration decreased.At the phylum level,it mainly contains the Proteobacteria,Firmicutes,Chlorophyta,Actinomycetes,Planktomycetes and Bacteroides.And the proportion of bacteria phyla decreased successively.The proportion of Proteobacteria when the nitrite nitrogen decreased was lower than that when the ammonia nitrogen concentration decreased,while the proportions of the green bacteria,actinomycetes and planktomycetes increased.（2）By designing three treatment groups with a cleaning frequency of 0.5 times/d,1 time/d and 2 times/d,the effect of cleaning frequency on the water treatment of the biological filter was studied.The results showed that all three treatment groups could reduce ammonia nitrogen and nitrite nitrogen to a lower level,and there was no significant difference.However,the treatment group with a cleaning frequency of 2times/d can significantly drain the suspended solids out of the system,and significantly reduces the nitrate nitrogen content in the system compared to the other two treatment groups.Nitrate nitrogen is the final product of nitrogen.The decrease in content indicates that the nitrogen content in the system is reduced,which reduces the water treatment load of the circulating water system.Therefore,the comprehensive cleaning frequency affects the nitrification performance and pollution interception capacity of the self-cleaning biological filter,and the cleaning frequency of the biological filter should be appropriately increased.Under the experimental conditions,the self-cleaning biological filter has a better self-cleaning frequency of 2 times/d.（3）The water treatment capacity of different flow circulating water systems is different.When the flow is controlled at 1200 L/h and 1500 L/h,it is beneficial to maintain the contact time between microorganisms and the aquaculture water body.Therefore,the biological filter has better water treatment capacity and can Transform ammonia nitrogen and nitrite nitrogen into nitrate nitrogen that is not sensitive to aquaculture organisms in time,where the flow rate is 1200 L/h（1₃¹cycles/h）,and the removal of chemical oxygen demand is higher than the flow rate.900 L/h（1 cycle volume/h）,but there is no significant difference compared with 1500 L/h（1₃²cycle volume/h）.Therefore,the effect is not significant when the flow rate reaches more than1200 L/h,and it is a better flow parameter to control the flow rate at 1200 L/h.（4）The filtering effect of a microfilter is related to the size of its mesh.The larger the mesh of the microfilter,the more particulate matter it can filter out and the stronger the water purification capacity.This experiment has a mesh size of 250 meshes.The filtration effect of the lower microfiltration machine is better than that of 120 mesh and200 mesh.The 250 mesh microfiltration machine removes a large amount of solid particles,which reduces the content of particles carried by the aquaculture water into the biological filter,thereby significantly reducing the ammonia nitrogen and nitrous acid in the water.The concentration of salt nitrogen and chemical oxygen demand improves the water treatment capacity of the self-cleaning biological filter.（5）The filling rate of the filler affects the water treatment capacity of the biological filter.S2（75%filling rate）and S3（100%filling rate）are thicker,which retains more particles,and can discharge more particles during self-cleaning.,So that the total suspended solids in the system is smaller than the S1（50%filling rate）treatment group,the chemical oxygen demand concentration of the S1 treatment group is higher than the S2 and S3 treatment groups,and the difference between the S2 and S3 treatment groups is not obvious.The concentration of ammonia nitrogen and nitrite nitrogen in the S1treatment group was significantly higher than that of S2 and S3,but the difference in the concentration of ammonia nitrogen and nitrite nitrogen in the S2 and S3 treatment groups was not significant.In combination with the above,selecting a filling rate of 75%is a better filling rate parameter.The results of this experiment will promote the development of industrialized circulating aquaculture to conform to the needs of the development of the times,and also provide a theoretical basis for the formation of a more water-saving and efficient circulating water system.