Text: Bread Clip Knowledge
Edit|Bread Clip Knowledge
«——【Preamble】】 ——»
China's ornamental fish farming industry has shown a rapid development trend in recent years. According to the data of 2022, the output value of the national ornamental fish industry reached 11.092 billion yuan, a year-on-year increase of 16.93%, of which the output value of freshwater ornamental fish reached 9.643 billion yuan.
As a typical water-dependent industry, the development of ornamental fish aquaculture industry is directly affected by the quality of aquaculture water, in order to ensure the safety of ornamental fish aquaculture production, it is very important to effectively treat the water quality of ornamental fish farming.
At present, the biological method is the most common water treatment method for ornamental aquariums, but this method has some shortcomings, such as large footprint, slow start-up speed, and lack of disinfection and sterilization functions, so ornamental aquaculture needs to explore more efficient water treatment technologies.
Ozone (O3) and ultraviolet (UV) are widely used in aquaculture water treatment, O3 is a strong oxidizing agent, which can remove inorganic pollutants and organic pollutants in water, but also has a strong bactericidal ability, and has little impact on water quality conditions.
UV can effectively kill microorganisms, but it cannot remove ammonia nitrogen and organic matter in aquaculture water, and is easily affected by water turbidity.
A single water treatment technology often has certain limitations in practical applications, but coupling technology can effectively combine different technologies to improve water treatment efficiency.
Previous studies have shown that under UV irradiation, O3 in water can produce more oxidizing hydroxyl radicals (•OH), with a redox potential of 2.80V, and the chemical reaction rate constant of •OH is nearly 7 orders of magnitude higher than that of O3, which can significantly improve the mineralization efficiency of refractory organic pollutants.
•OH can not only effectively remove inorganic and organic pollutants such as iron and manganese ions, sulfides, humus and other inorganic pollutants in water, but also effectively kill viruses and bacteria, and the reaction process is not affected by water quality conditions.
Moreover, the life of OH is very short, and the water treatment process will not produce secondary chemical pollution, so in the water treatment of freshwater ornamental fish farming, the O3 and UV water treatment technologies are coupled, and the O3/UV water treatment system constructed is constructed, how to remove inorganic pollutants, organic pollutants and pathogenic bacteria in the ornamental fish breeding water?
«——【· Construction of O3/UV water treatment system·]——»
As shown in Figure 1, the O3/UV water treatment system is mainly composed of a cylindrical FRP sink (volume 300L), a pipeline booster pump (power 370W, maximum head 38m), an air source O3 generator (power 80W, ozone output 3g/h), a pipeline UV device (power 40W, the main wavelength of 254nm, and a UV lamp length of 80cm), an activated carbon tank (108cm high, a diameter of 22cm) and a PP cotton filter (pore size 5μm).
The outlet at the bottom of the FRP sink is connected with the pipeline booster pump, the O3 generator is connected with the main pipeline through the jet mixer, and the generated O3 is mixed with the water to be treated in the main pipeline, and then flows through the pipeline UV device, and then flows through the activated carbon tank and PP cotton filter, and then flows back to the FRP tank.
During the test, the amount of water to be treated in the FRP sink is 200L, and the flow rate of water in the system is controlled at 950L/h.
Referring to the water quality conditions in the process of koi fish breeding, a certain amount of pure ammonium chloride, sodium nitrite and glucose were prepared into mother liquor and added to the FRP water tank, so that the initial concentrations of total ammonia nitrogen (TAN) in the prepared water were 0.51, 0.96 and 1.97 mg/L, the initial concentrations of nitrite nitrogen (NO2--N) were 0.34, 0.62 and 1.08 mg/L, and the initial concentrations of chemical oxygen demand (COD) were 2.05, 5.30 and 11.37 mg/L, respectively. L。
After the O3/UV system is put into operation, water samples in the FRP sink are taken regularly, and each sample is repeated in three copies.
The concentrations of TAN, NO2--N and COD in water were determined by hypobromate oxidation, naphthalene ethylenediamine hydrochloride spectrophotometry and alkaline potassium permanganate (GB17378.4-2007), respectively.
O3/UV系统对水中污染物的去除率RA(%)和去除效率RE(mg/(L·h))可分别用如下公式计算：
In order to investigate the killing effect of O3/UV on Escherichiacoli, a single colony of E. coli taken from the Disease Laboratory of Dalian Ocean University was added to the sterilized LB broth medium and cultured overnight (37°C, 150r/h, 12h) at constant temperature shaking overnight.
The cultured E. coli bacterial solution was added to the FRP water tank, and 100.0mL of water samples were taken at 7.5, 15.0, 22.5 and 30.0min after the O3/UV coupling system was started, and the water samples were filtered by a 0.22μm filter membrane, and the retentate on the filter membrane was flushed into a 15mL centrifuge tube with normal saline to form a suspension, and the OD600 value was adjusted and determined to be 0.3 with normal saline as a reference.
Take 1.0mL of the adjusted bacterial solution as the stock solution, and gradually dilute the original solution into 10-1, 10-2, 10-3, 10-4, 10-5, 10-6, 10-7, and 10-8 bacterial solutions with sterile water, and set up 3 parallels.
Take 200.0 μL of the stock solution and 200.0 μL of the dilution solution and evenly coat it on the surface of LB agar medium, and invert the seeded plate and place it in a 37°C constant temperature incubator for 12 hours.
Take out the cultured plate, count with a dilution of 30~200 single colonies, calculate the average number of colonies of 3 plates of the same dilution according to the number of colonies, and the amount of E. coli in the water sample (cfu/mL) = the average number of colonies ×dilution factor of 3 replicates of the same dilution ×5.
The koi carp (body length (13.1±0.4) cm, body weight (64.8±8.0) g) used in the experiment were purchased from the Xianglujiao Flower and Bird Fish Market in Dalian City, Liaoning Province, and the daily bait amount was 3%~5% of the average body weight of the fish during the temporary breeding period.
200L koi fish breeding water was placed in the glass fiber reinforced plastic water tank of the O3/UV water treatment system, the initial concentrations of TAN, NO2--N and COD in the water were 2.21, 0.59 and 4.61mg/L, respectively, after the start of the O3/UV water treatment system, the water samples in the FRP water tank were taken on the 3rd, 6th, 9th and 12th h, and each sample was three parallel to determine the concentration of TAN, NO2--N and COD in the water.
«——【Treatment Effect of Aquaculture Water Quality·】——»
Figure 2 shows the removal effect of the O3/UV water treatment system on TAN in the prepared water.
As can be seen from Figure 2, the concentrations of TAN at different initial concentrations in water showed a decreasing trend during O3/UV treatment. When the initial concentration of TAN in water was 0.51 mg/L, the concentration of TAN decreased to 0.21 mg/L after 12 h of treatment, and the removal rate reached 58.8%.
When the initial concentration of TAN was 0.96 mg/L, the concentration of TAN in water decreased to 0.53 mg/L after 12 h, and the removal rate was 44.8%.
When the initial concentration of TAN in water was 1.97 mg/L, after 12 h of treatment, the concentration of TAN in water decreased to 1.30 mg/L, and the removal rate was 34.0%.
The results showed that the O3/UV water treatment system could achieve TAN removal in water, but the removal rate of TAN in water decreased with the increase of the initial concentration of TAN in water.
Fig. 3 shows the removal of NO2--N in the prepared water by the O3/UV water treatment system, and it can be seen that the concentration of NO2--N in the prepared water decreases rapidly with the increase of treatment time.
When the initial concentration of NO2--N in the prepared water was 0.34mg/L, after 1 h of treatment, the concentration of NO2--N in the water decreased to 0.030mg/L, and the removal rate of NO2--N reached 91.1%.
当水中NO2--N的初始浓度为0.62mg/L时,1h后水中NO2--N浓度降至0.19mg/L,NO2--N去除率为69.3%;
When the initial concentration of NO2--N was 1.08mg/L, the concentration of NO2--N in the water decreased to 0.64mg/L after 1h of O3/UV treatment, and the removal rate of NO2--N was 40.7%.
The results showed that the O3/UV water treatment system could effectively remove NO2--N in water, but the removal rate of NO2--N in water decreased with the increase of the initial concentration of NO2--N in water.
Figure 4 shows the treatment effect of the O3/UV water treatment system on COD in the prepared water.
As can be seen from Figure 4, the COD concentration in the water decreases with the increase of treatment time. When the initial concentration of COD in the prepared water was 2.05 mg/L, after 12 hours of treatment, the concentration of COD in the water decreased to 1.18 mg/L, and the removal rate of COD was 42.4%.
When the initial concentration of COD in water was 5.30 mg/L, the concentration of COD in water decreased to 1.54 mg/L after 12 hours, and the removal rate of COD reached 70.9%.
When the initial concentration of COD in the prepared water was increased to 11.37 mg/L, after 12 hours of treatment, the concentration of COD in the water decreased to 7.22 mg/L, and the removal rate of COD was only 36.5%.
The results showed that when the initial concentrations of COD in water were 2.05, 5.30 and 11.37 mg/L, respectively, the O3/UV water treatment system had the highest removal rate of COD at the initial concentration of 5.30 mg/L within 12 h.
O3/UV水处理系统对配制水中TAN、NO2--N和COD的去除效率如表1所示。
As can be seen from Table 1, the removal efficiency of TAN, NO2--N and COD in the prepared water by the O3/UV water treatment system increases with the increase of initial concentration.
当配制水中TAN的初始浓度从0.51mg/L升高至1.97mg/L时，O3/UV水处理系统对TAN的去除效率从0.025mg/(L·h)提高至0.056mg/(L·h)。
When the initial concentration of NO2--N in the prepared water is 1.08mg/L, the removal efficiency of the O3/UV water treatment system can reach 0.440mg/(L·h).
When the COD concentration in water increased from 2.05 mg/L to 11.37 mg/L, the removal efficiency of COD in water by O3/UV water treatment system increased from 0.037 mg/(L·h) to 0.346 mg/(L·h).
Figure 5 shows the treatment effect of O3/UV water treatment system on E. coli in water.
As shown in Figure 5, the initial concentration of E. coli in water was 1.575×108 cfu/mL, and after 0.125 h treatment with O3/UV water treatment system, the concentration of E. coli in water decreased to 6.45×107 cfu/mL. With the extension of water treatment time, the concentration of E. coli in water continued to decrease, and the concentration of E. coli in water decreased to 1.525×107cfu/mL after 0.5 h, and the killing rate of E. coli reached more than 90%.
The koi culture water was selected as the actual water treatment object, and Fig. 6 shows the removal effect of O3/UV water treatment system on TAN, NO2--N and COD in koi culture water.
Fig. 6(a) shows the effect of O3/UV on the removal of TAN in koi aquaculture water, it can be seen that the initial concentration of TAN in water was 2.21mg/L, and with the extension of treatment time, the concentration of TAN in water gradually decreased, and the concentration of TAN in water decreased to 1.57mg/L after 12 h, and the removal rate was 29.0%.
Fig. 6 (b) shows the removal of NO2--N with an initial concentration of 0.59mg/L by O3/UV in koi fish breeding water, and it can be seen that the concentration of NO2--N in the water has decreased to 0.08mg/L after 3 hours, and the removal rate has reached 86.4%, and the concentration of NO2--N in the water has been lower than the lower detection limit at 6 h, indicating that the O3/UV system can quickly remove NO2--N in koi culture water.
Fig. 6(c) shows the treatment effect of O3/UV on COD in koi aquaculture water, when the initial concentration of COD in koi aquaculture water was 4.61mg/L, the concentration of COD in the water decreased to 2.36mg/L after 6 h, and the concentration of COD in the water decreased to 1.37mg/L after 12 h, and the removal rate was 70.3% after 12 h.
«——【Discussion·】——»
In the traditional process of koi fish farming, water consumption is large, and pollutants such as organic matter, nitrogen and phosphorus in the effluent tail water will cause potential eutrophication of the receiving water.
Water shortage and increasing pressure on environmental protection have affected the sustainable development of freshwater ornamental fish farming represented by koi fish farming.
Therefore, the water quality control equipment that can realize the rapid removal of pollutants in water and the recycling of water resources has broad application prospects.
The results show that the system can effectively purify the water quality of ornamental fish aquaculture, and the TAN concentration in the water can be maintained in the range of 0.011~0.028mg/L, and the concentration of NO2--N can be maintained in the range of 0.001~0.002mg/L under suitable breeding density and appropriate feeding conditions.
The application of biofloc technology to koi fish breeding showed that biofloc (C/N ratio of 20:1) could effectively purify the water quality of aquaculture, improve feed use efficiency and reduce water pollution.
Some scholars have studied the purification ability of 16 ornamental plants to purify nitrogen and phosphorus in the water body, and the results show that Acorus astragalus, Phyllostachys mosaica and Celandine can be used as water purification plants in ecological floating beds.
Although the biological method can remove pollutants in aquaculture water, the treatment process of ornamental aquaculture water using biological method is very susceptible to the influence of changes in external climate and environmental conditions, and the application of new materials and new processes has promoted the development of water quality control technology for koi culture.
The researchers investigated the purification effect of carbon fiber on koi breeding water, and found that carbon fiber has good biocompatibility, and the removal rates of COD and TAN reached 71.96% and 58.11% respectively within 21 days of breeding when the carbon fiber density was 0.3kg/m3.
When volcanic stone is selected as the biological filter material of koi fish breeding pond, due to the high specific surface area of volcanic stone, it is conducive to the growth of biofilm, and can effectively remove COD and TAN in koi breeding water.
The results show that the killing rate of E. coli in water after 0.5 h has reached more than 90%, indicating that the O3/UV water treatment system has the function of disinfection and sterilization, which is consistent with the sterilization effect of E. coli in drinking water by relevant researchers.
The O3/UV coupled koi aquaculture water treatment system can realize the removal of pollutants and pathogenic microorganisms in the water, which can not only form a separate water treatment unit, but also can be combined with different breeding systems, with a wide range of applications.
«——【·Conclusion·】——»
The O3/UV water treatment system can realize the removal of TAN, NO2--N and COD in water, and the removal efficiency increases with the increase of initial concentration, but the removal rate of TAN and NO2--N in water decreases with the increase of initial concentration.
When the initial concentrations of TAN, NO2--N and COD in the actual breeding water of koi were 2.21, 0.59 and 4.61 mg/L, respectively, the removal rates of TAN, NO2--N and COD in the water were 29.0%, 100% and 70.3%, respectively, and the removal efficiency was 0.053, 0.170 and 0.270 mg/(L·h), respectively.
It can be seen that the O3/UV water treatment system constructed by coupling the two water treatment technologies of O3 and UV can play a good role in removing inorganic pollutants, organic pollutants and pathogenic bacteria in ornamental fish breeding water.