Maintaining stable water quality has long been a top priority in aquaculture.
To this end, farmers have opted for more advanced farming systems or advanced water treatment technologies. For example, the Circulating Aquaculture System (RAS), which has a strong ability to treat water bodies and high yields, is deeply loved by farmers. However, total suspended solids (TSS) is the dry weight of suspended particles in water bodies and is the main cause of water quality deterioration in circulating aquaculture systems (RAS).
1. Water treatment technology for circulating aquaculture systems
In most cases, the wastewater from aquaculture ponds is pretreated with a solid-liquid separator, a process that helps to reduce the power load on the equipment at a later stage, and the microfilter (MDF) is one of the most efficient and widely used solid-liquid separators in the RAS system.
The equipment has a small footprint, high processing efficiency and simple operation, but the filtration efficiency of MDF depends on the size of the filter mesh, which is not possible if the mesh size of the filter is reduced. Instead, increasing the particle size of TSS is another way to improve MDF's filters.
Nowadays, the use of chemical flocculants is a universal method that can increase the size of suspended particles. These particles usually include ingredients such as shrimp shells, residual bait and shrimp manure. However, electrocoagulation (EC) has more prominent advantages, such as: reduced additional waste generated during treatment, less pollution, ease of use and easy control.
Electrocoagulation (EC) is performed on an electrolyte battery with two positive and negative electrodes, both of which are immersed in the electrolyte. First, bubbles are created during electrocoagulation, after which flocs form and float on the surface of the water in relatively small sizes and increase over time until they reach a certain size.
Second, the application of electrocoagulation (EC) in the circulating aquaculture of Penaeus vannamei in South America
The aim is to increase the size of the particles suspended in the water, thereby increasing the waste disposal capacity of the MDF. Professor Xu Jianping's research group proposed the idea of combining electrocoagulation technology with microfiltration technology (EDIR-MDF). Furthermore, the first trial was conducted in the circulatory system (RAS) of Penaeus vannamei.
In aquaculture systems, the TSS composition and water quality of water bodies usually vary with the cultured species, the frequency of feeding and the environmental factors of the pond. Therefore, the research team used the current intensity of the EDIR system to make appropriate changes according to the water quality in the pond, which can not only ensure good waste disposal capacity, but also save electricity. To do this, the authors use a sensing device (TMDF) to adjust the appropriate current intensity.
System diagram
Figure A: EDIR-MDF system, including equipment, such as: power supply (DC power supply), programmable time (programmable time replay), electrode plate (Electrode plate), liquid flowmeter (Lipid flowmeter), pump (Air pump), heat accumulator, microfilter.
Figure B: The RAS system in the experiment: breeding pond, ultraviolet lamp, foam separator, mobile bed biological filter, liquid flow meter (lipid flow meter), electrocoagulation diameter increase reactor, electrode plate, buffer tank, level switch, microfilter, water collection tank, circulation pump.
Third, the design and main purpose of the study
1. The two systems used in this study are laboratory-scale EDIR-MDF systems. That is, electrocoagulation (EC) systems that increase particle size, combined with filter systems, are used in circulating aquaculture systems.
2. Water samples in circulating aquaculture systems (RAS) ponds to assess the effect of E on TSS size. The salinity of the experimental water body is about 15‰, the pH value is 6.92, the dissolved oxygen is 6.93-7.25 mg/L, and the temperature is 26.8 degrees Celsius. Prior to evaluation, culture water filtered by mesh-sized sieves of 300 μm is used to collect suspended particles in the water, such as shrimp shells and residual bait. The current intensity of the EDIR is 50 A/m².
Figure A: Uneected pool on day 7, the water is light yellow with foam on the surface. However, in Figure B, under the influence of the DIR-MDF system, the cultured water body becomes clearer and foam-free (Day 11).
3. The experiment was carried out for 21 days. In the first 7 days (no EC treatment phase), the aquatic products did not use the EDIR-MDF system to treat the water body at all, and from day 8 to day 21, the EDIR-MDF system was put into use (also known as the EC stage). Details of water quality parameters between water bodies cultured during use and between unused systems are then assessed.
4. Measure the concentrations of TSS, COD, ammonia and nitrite in the breeding pond, MDF and imported wastewater every day. The length and weight of shrimp before and after the end of the experiment were 6 cm, 3.23 g and 9.0 cm, and 8.43 g, respectively. The culture density is 1100 fish per cubic meter.
5. Automatic feeding machine is adopted, the feeding frequency is 1-4 times / hour, and the feeding intake is 15.2-27.5 kg / day.
6. The waste removal performance (RE,%) of the equipment is calculated as: RE= (C1-C2)/C1×100%. where C1 (mg/L) is the initial concentration of the waste and C2 (mg/L) is the treated waste concentration.
4. Conclusions of the study
The experimental results show that the average RE values of TSS, COD, ammonia, nitrite and RAS systems in the water body without EC treatment are 61.24%, 50.87%, 27.27% and 33.33%, respectively. In the ec stage, the RE values of these indicators were 85.31%, 75.17%, 8.94% and 1.39%, respectively.
therefore