High-salt and high-COD wastewater treatment process
Necessity of sewage classification and standard treatment
The company currently has a set of 350t/h (8400t/d) sewage treatment facilities, mainly using microfiltration-ultrafiltration-reverse osmosis-concentrated water secondary reverse osmosis-ion exchange treatment-pure water-recycling device, a small amount of concentrated water It is reused in the production process of polyvinyl chloride and acetylene to achieve nearly zero discharge of sewage.
At present, the sewage production of the whole company is 150t/h, which is less than the treatment capacity of the treatment facility. However, in the operation of the past year, it was found that the service life of the reverse osmosis membrane was greatly shortened, and the membrane had to be replaced in less than one year of operation (the original three years). once), and the power consumption increases.
The average effluent rate also decreased. Through the analysis and testing of the influent water quality, it was found that a small amount of high COD and high salt wastewater (13t/h) entered the system, resulting in membrane blockage and increased reverse osmosis pressure, thus greatly reducing the life of the reverse osmosis mold.
If this part of high-concentration pollutant wastewater is not treated in a targeted manner, the existing sewage treatment cost will be greatly increased, the energy consumption will be doubled, and the water output rate will be greatly reduced, which will seriously affect the stability of sewage treatment.
Through careful analysis and testing of the influent water quality, the high COD wastewater volume is 11t/h, and the COD is 5000-30000mg/L, which comes from the current production equipment of polyvinyl chloride, DHPPA, thiazole, etc.;
High salt and high COD wastewater is 2t/h, COD is 5000～30000mg/L, TDS is 6000～15000mg/L;
From caustic soda, DHPPA, thiazole.
At present, the wastewater volume that needs to be further upgraded and treated separately is 312t/d. Considering the redevelopment of the enterprise and the instability of wastewater discharge under special circumstances, it is therefore necessary.
Process technology flow plan
This project is divided into three parts: pretreatment, high brine evaporation and crystallization treatment and biochemical post-treatment.
Considering the high COD and poor biodegradability in high-concentration wastewater, it is proposed to adopt pH adjustment + micro-electrolysis + Fenton oxidation + pH adjustment + coagulation sedimentation process.
The wastewater is first adjusted to pH 3-4, and then enters the micro-electrolysis and Fenton oxidation towers, respectively, into steel carbon packing and hydrogen peroxide oxidation treatment, catalytic oxidation removes most of the organic matter in the wastewater and improves the biodegradability of the wastewater.
The B/C ratio of wastewater is improved; low-concentration wastewater adopts pH value adjustment + air flotation process to remove some organic matter and suspended particles.
(2) Evaporative crystallization treatment.
The high-salt wastewater is coagulated and precipitated to remove suspended solids and then enters the evaporative crystallizer to remove most of the inorganic salts and a small amount of organic matter in the wastewater.
(3) Biochemical post-processing.
The hydrolysis + anaerobic tower + AO process + Fenton oxidation + BAC filter biochemical treatment process is adopted. The process effect is good, and the effluent quality can reach the design standard.
The 4 strands of wastewater first enter the homogenizing adjustment tank and are stirred and mixed (tempering and tempering), and then lifted to the hydrolysis and acidification tank with a pump. 30 ~ 40 ℃) treatment, the anaerobic tower can degrade a large amount of organic matter to generate biogas, and further improve the B/C ratio.
The effluent flows to the AO biochemical tank for biochemical reaction, where most organic pollutants are degraded by biological oxidation, and the effluent flows to the secondary sedimentation tank for solid-liquid separation, and the supernatant of the sedimentation tank flows into the Fenton oxidation tank to remove the remaining refractory organic matter.
The effluent enters the coagulation and sedimentation tank for precipitation, and the supernatant liquid enters the intermediate tank and is pumped to the BAC carbon filter tank to further reduce the organic matter and reach the existing sewage plant influent standard.
The brine concentrate precipitated by the evaporator enters the centrifuge to separate the salt, and the saturated concentrate enters the adjustment tank to participate in the next evaporation. The sludge and sediment from the coagulation sedimentation tank, oxidation sedimentation tank, and secondary sedimentation tank enter the sludge tank.
Then, the pump is pumped into the centrifuge for solid-liquid separation, and the centrifugal dry mud is transported out. The water quality after treatment can reach the water inflow index required by the existing sewage treatment plant, and then enter the company’s existing sewage treatment system for reprocessing. Figure 1 shows the flow chart of the wastewater classification and upgrading treatment process.
See Table 1 and Table 2 for the influent and effluent indicators of the original 350t/h sewage treatment station reuse system; see Table 3 and Table 4 for the influent and effluent quality indicators of the high-salt and high-COD standard upgrading project after technical upgrading.
Economic and social impact analysis
The scale of the project is a 750t/d high-salt, high-COD organic sewage technical transformation treatment station. The upgrading and renovation project of Yuhua Company’s sewage treatment project (high-salt and high-COD wastewater treatment) is a water-saving and emission-reduction project. After water treatment, it is reused in various factories, which not only saves water resources once but also guarantees project finances. Evaluation is possible.
After the sewage treatment plant is put into operation, indirect social and economic benefits can be generated by improving the company’s environment.
Therefore the project is technically feasible and economically reasonable. The implementation of this project not only protects the local ecological environment, fully reflects the clean production level of the enterprise, but also improves the comprehensive utilization rate of energy;
The newly built 750t/d sewage treatment station can save 273,800 tons of fresh water every year, which can not only alleviate the problem of shortage of water supply for enterprises, but also control the pollution of enterprises, surrounding farmland, and the Haihe River Basin, and achieve enterprise benefits, environmental benefits and social benefits. unity.