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The aquaculture mode in the mainland is changing from extensive aquaculture mode to high-density intensive aquaculture mode, but in high-density intensive aquaculture, the accumulation of aquatic animal excreta has caused the concentration of nitrogenous pollutants such as ammonia nitrogen and nitrogen in the aquaculture water to increase, making farmed animals prone to disease and even death.
This paper will focus on the application of biological flocculation technology in aquaculture wastewater treatment and its effect on water quality improvement.
Through the research and practice of this field, we can provide useful references and references for the sustainable development of the aquaculture industry.
The water quality parameters of various analysis methods are applied in environmental monitoring
DOC adopts combustion oxidation-non-dispersive infrared absorption method; PH, DO, T and other parameters were determined by YSI multi-parameter water quality measuring instrument; Ammonia nitrogen was spectrophotometrically used by Knott's reagent; N-(1-naphthyl)-ultraviolet spectrophotometry for nitrate nitrogen; Nitrite nitrogen is colorimetric method of naphthalene ethylenediamine hydrochloride.
Xanthine oxidase kit for the determination of superoxide dismutase (T-SOD) activity; Alkaline phosphatase (ALP) was determined by AMP buffer; Determination of lysozyme (LSZ) activity by self-turbidimetric method; TP was determined by the double uretal method.
The definition of T-SOD activity unit is that the amount of SOD corresponding to the SOD inhibition rate in 1ml reaction solution reaches 50% per mg of tissue protein is one SOD activity unit (U); Lyophilized powder with micrococcus lysolatis was used as substrate.
The experimental results were expressed as mean ± standard deviation, and SPSS17.0 software was used for data analysis and statistics, and one-way analysis of variance (ANOVA) and Duncan method were used for analysis and comparison, and the significance level was P<0.05.
The changes of ammonia nitrogen, nitrate nitrogen and nitroso nitrogen in the two aquaculture systems were shown in the results, and the concentrations of ammonia nitrogen and nitrate nitrogen in system A increased from 1.74mg/L to 17.62mg/L during the experiment. The concentration of nitrate increased from 73.03 mg/L to 313.07 mg/L.
Nitrous nitrogen has been kept at a low level of 0-3mg/L, and the ammonia nitrogen and nitrosagen of system B have shown a trend of first rising and then decreasing, and the concentration of ammonia nitrogen has risen to 60.98mg/L. The concentration of nitrogen rose to 117.34mg/L; Nitrate concentrations have been kept at a low level of 1-15mg/L.
Using the method of inoculating and cultured flocs, after the system operation entered the normal, the flocs were scanned by electron microscopy, and the particle size of the flocs was measured at 0.1-1.0mm, and the flocs were observed with an optical microscope, and it was found that the flocs contained a large number of protozoa such as actinomycetes, branchworms, paramecium, rotifers, bell worms, etc., and the dominant species in the flocs were different at different times.
Feed, bait feces, flocs and other nutrient content
The crude protein content in the floc was 30.90% and the crude fat content was 1.27%, which were significantly lower than the crude protein content of 43.57% and crude fat 16.51% of the feed, and the crude protein content in the residual feces was significantly lower than that of the floc crude protein content of 12.07%, but the crude fat content was 0.99%, which was not significantly different from the crude fat content in the floc.
After the determination of this experiment, it was found that after 30 days of experimentation, the activities of alkaline phosphatase (ALP), lysozyme (LSZ) and total superoxide dismutase (T-SOD) in the liver and pancreas of fish body of group A were slightly higher than those in group B. The activities of alkaline phosphatase (ALP), lysozyme (LSZ) and total superoxide dismutase (T-SOD) in group A were slightly lower than those in group B.
The serum activity of alkaline phosphatase (ALP) and lysozyme (LSZ) was not much different between the two groups (P>0.05), but group A was significantly higher than group B in terms of total superoxide dismutase activity.
At 60 days of experimentation, it was found that the activity of alkaline phosphatase (ALP) in the liver and pancreas of group A was slightly lower than that of group B, the activity of lysozyme (LSZ) was slightly higher than that of group B, and the activity of total superoxide dismutase (T-SOD) was slightly higher than that of group B.
Alkaline phosphatase (ALP) activity in head and kidney was slightly lower in group A than group B, lysozyme (LSZ) activity group A was slightly lower than group B (P>0.05), and total superoxide dismutase activity (T-SOD) also showed that group A was slightly lower than group B.
Alkaline phosphatase (ALP) activity in serum was slightly higher in group A than in group B, lysozyme (LSZ) activity group A was slightly lower than group B, and total superoxide dismutase activity (T-SOD) showed that group A was significantly higher than group B.
After 90 days of experimentation, the activity of alkaline phosphatase (ALP) in the liver and pancreas of fish in group A was less than that of group B, and the activity of lysozyme (LSZ) and total superoxide dismutase (T-SOD) were greater than that of group B.
The alkaline phosphatase (ALP) activity, liver and pancreatic lysozyme (LSZ) activity and total superoxide dismutase (T-SOD) activity in the head and kidney were all smaller than group B in group A, especially the total superoxide dismutase (T-SOD) activity, and group A was significantly smaller than group B.
Alkaline phosphatase (ALP) activity, hepatopancreatic lysozyme (LSZ) activity, and total superoxide dismutase (T-SOD) activity in serum were slightly higher in group A than in group B.
Water quality and effects on non-fish immunoenzyme activity under different culture modes
In the recirculating aquaculture mode, ammonia nitrogen rises slowly, which may be due to the fact that as the fish grow, the amount of food feeding also increases, and the fish excretion exceeds the maximum load of the system. Nitrate is slowly enriched, while nitroso is kept at a very low level.
This is in line with the benign operation law of the circulating water system. Under the culture mode of biological flocculation technology, ammonia nitrogen and nitroso nitrogen increased to very high levels in the early stage of aquaculture, reaching 60.98mg/L and 117.34mg/L, respectively.
However, after aquaculture entered the normal state, ammonia nitrogen and nitroso nitrogen were maintained at a relatively stable concentration, while nitrate nitrogen was maintained at a very low concentration during the whole breeding process, and the nitrate content also showed a slow growth trend before the first water change.
The reason may be that the aquaculture water body of this experiment is small, the breeding density is large, and the utilization rate of nitrogen in the water body by bioflocculates is much smaller than the rate of bait and feces production of fish under the normal conditions of intensive culture.
After the experiment entered the normal state, the measured particle size of the biological floc was 0.1~1.0mm, and the floc contained a large number of protozoa such as actinomycetes, branchworms, paramecium, rotifers, bell worms, etc., and the dominant species of protozoa in the flocs were different at different times. Therefore, protozoa can be studied as indicator organisms to determine whether the floc has matured and entered a homeostatic state.
After analyzing the nutrient composition of the flocs after entering the normal state, it was found that the crude protein content was 30.90%, the crude fat content was 1.27%, while the crude protein content of the feed was 43.57% and the crude fat content was 16.51%.
The crude protein content in feces was 12.07%, and the crude fat content was 0.99%, which indicated that the floc did reuse the nitrogen source in the water body and converted it into crude protein.
The crude protein content in the floc can meet the protein needs of geifelafia. However, experiments have also shown that bioflocculation technology has a limited ability to convert crude fat. The suitable amount of fat in the feed of ONI tilapia is 4%, the suitable content of fat in tilapia feed is 6.2%, and in general, it is more appropriate to control the fat content in tilapia feed at 4%~6%.
Therefore, species with slightly higher crude fat content should be selected when selecting feed, so that the average proportion of crude fat in the actual feeding of tilapia cultured in the biological flocculation mode can reach an appropriate standard.
For fish, specific immunity is less dominant than non-specific immune system. Alkaline phosphatase (ALP), lysozyme (LSZ), and total superoxide dismutase (T-SOD) are important immune-related factors, and their activity is a direct response of fish to its environment, feeding conditions, and its own growth stage.
The study found that after the use of biological flocculation technology, the concentration of ammonia nitrogen and nitrogen in the aquaculture water body was effectively controlled, thereby alleviating the pollution problem. The study also analyzed the nutrients in the flocs and found that it is rich in crude protein, which can meet the protein needs of fish, but has limited conversion capacity for crude fat.
In addition, we discussed studies of non-fish immunoenzyme activity and found no significant differences in fish immunoenzyme activity between the two culture modes, including combining circulating water and sequencing batch reactors to culture and utilize flocs to address the problem of mismatched nitrogen source utilization rates.
Overall, this study provides a useful reference for the sustainable development of aquaculture, especially in the treatment of aquaculture wastewater and improving water quality, and bioflocculation technology may have potential applications.