General food wastewater is biodegradable wastewater, which can directly degrade organic matter through biological methods, while general food wastewater contains substances that inhibit microorganisms, such as salt. When the salt concentration exceeds a certain limit, it will inhibit anaerobic bacteria, nitrifying bacteria, denitrifying bacteria and polyphosphate bacteria, resulting in low biological treatment efficiency.
Food enterprises with high-salt wastewater mainly come from vegetable pickling industry and fish processing industry. Salt pollution mainly comes from the pickling and pickling of brine cans, and brine loss and wastewater discharge come from the salt washing process; The fish with seawater unloaded will also produce wastewater rich in protein, nitrogen, organic matter and salt in the subsequent process.
The salt in high-salt food wastewater is generally chloride ion, and the chloride ion concentration is too high, which leads to increased cell osmotic pressure, resulting in cell wall separation due to dehydration. At the same time, high salt will also destroy the cell membrane and enzymes in the bacteria, inhibiting the growth of microorganisms, and the general biological treatment process is not effective.
(1) Reduction of high-salt wastewater
Reform the production process to reduce the discharge of high-salt wastewater, so as to reduce a lot of salt pollutants entering the wastewater, and achieve clean production, emission reduction and efficiency improvement.
According to the data, in the production process of mustard tuber, we can reuse the third pickling liquid for the second pickling, and reuse the second pickling liquid for the production of mustard tuber soy sauce, so as to reduce the pollutant discharge of the pickling liquid.
(2) Mix with other low-concentration wastewater to dilute high-salt wastewater
Food enterprises not only discharge high-salt wastewater, but also other low-concentration wastewater. By mixing low-concentration wastewater with high-salt wastewater, its salinity can be adjusted so that it can reach the range of biological treatment, thereby reducing the impact of salt pollutants on microorganisms.
(3) Use "special" microorganisms
Cultivate its salt tolerance by inoculating activated sludge, so that it can achieve high effluent quality under a certain salinity, that is, salt-tolerant bacteria.
If the salinity exceeds a certain limit, we need halophilic bacteria. Many projects use halophilic bacteria to maintain a high degradation rate of organic matter in wastewater under high-salt conditions, while keeping the types and numbers of domesticated microorganisms relatively stable in the biochemical system. Building a halophilic microbial treatment system under high-salt conditions has become the key to efficient and low-cost treatment of high-salt food wastewater.
At present, biological methods are difficult to use alone to treat organic high-salt wastewater. There are still huge challenges in terms of how to improve the biological denitrification and phosphorus removal effects in high-salt environments and the stable operation of the system when the salt content fluctuates.
(4) Combining other wastewater treatment technologies with biological methods
There are many ways to solve high-salt wastewater. We can solve most of the salt problems in the pretreatment stage and then enter biological treatment. This method is generally used to treat high-salt wastewater alone when the salt concentration is extremely high.
Evaporation is mainly used to remove salt from organic high-salt wastewater. By heating, water and volatile or semi-volatile organic matter are evaporated and converted into wastewater with a lower salt content, while achieving salt concentration and crystallization.
The membrane separation method uses natural or synthetic membranes, relies on the selective permeability of the membrane, and uses external energy or chemical potential difference as a driving force to selectively separate and purify inorganic ions or organic matter in wastewater, so that the wastewater can be purified.
The actual treatment of high-salt food wastewater adopts "physical and chemical + biological + deep treatment". First, physical and chemical pretreatment is carried out to solve the factors affecting biological treatment, and then microorganisms that can operate under high salt concentrations are selected. Finally, in the deep treatment stage, it is ensured that each pollutant can meet the discharge standards.
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