Styrene, isoprene, dicyclopentadiene, n-pentane, isopentane, cyclopentane, piperylene, mixed xylene, mixed trimethyl benzene, mixed tetramethyl benzene, industrial cracked carbon 9, mixed recombination Oil separation, mixed methyl naphthalene, petroleum naphthalene, heavy aromatics, etc. Therefore, there are many types of wastewater, which change from time to time, and contain a large number of pollutants such as neutral oil, organic acid, volatile phenol, and sulfide.
Alkali residue wastewater is one of them. It has high concentration, strong alkalinity, and is difficult to degrade by microorganisms. It also contains a lot of harmful substances that affect the normal operation of the biochemical treatment system. If it enters the sewage treatment system directly, it will have an impact on the sewage treatment plant. Water quality.
Introduction to the process flow
The process of the sewage field is wedge wire grid collecting tank → regulating tank (accident tank) → oil separator → neutralization tank → concave aeration tank → dissolved air flotation tank → adsorption sedimentation tank → A2O tank → secondary sedimentation tank → intermediate tank → Efflux.
Problems in operation
In the early stage of operation, the alkali residue wastewater was not paid attention to. When the pH of the incoming water is alkaline, it is only considered that the wastewater in the petrochemical industry is generally alkaline, and it is conceptually ignored. But when the alkali residue wastewater accumulates and flows into the biochemical system, it is too late. A large number of microorganisms were poisoned and died, floating sludge continued to rise in the secondary sedimentation tank, and the effluent did not meet the standard. The average COD was 65mg/L, and the ammonia nitrogen also continued to rise, with an average of 13mg/L. Therefore, a large amount of sewage has to be returned, and a small amount of effluent is diluted and discharged.
When the seriousness of the problem is recognized, process improvements must be made since these were not considered when designing the process. It was found that changing the adsorption sedimentation tank into a high-load adsorption regeneration tank is very feasible and meets the operational requirements. The removal of pollutants by the high-load biosorption regeneration process includes the following four functions:
①The flocculation effect of sludge and microbial flocculation substances in the adsorption tank on fine particle pollutants;
②The adsorption of dissolved pollutants by biological sludge in the adsorption tank;
③ The natural sedimentation of large suspended solids in the sedimentation tank;
④ The biological metabolism of microorganisms in the regeneration tank to the adsorbed dissolved organic pollutants.
Among them, the flocculation and adsorption of the adsorption tank and the biological metabolism of the regeneration tank have an effect on the alkali residue sewage. However, in the regeneration tank, the biological metabolism is mainly to restore the activity of the sludge, the biological metabolism time and biological metabolism are small, and the removal of pollutants is small. Therefore, the treatment of pollutants by the high-load biological adsorption regeneration method is mainly the adsorption of biological sludge.
Therefore, the process flow is changed to: on the basis of the existing adsorption sedimentation tank, add a sludge return line at the bottom of the sedimentation tank to the adsorption tank, lead an excess sludge line to the adsorption tank, and add an industrial wind line to the adsorption tank at the same time. Pool blast aeration.
The body operation is to inoculate some targeted high-efficiency microbial colonies in the adsorption tank after the manual screening. It can economically treat the high-concentration and toxic wastewater that is difficult to treat by traditional microorganisms into low-concentration, easy-to-biochemical wastewater, greatly reducing the high-concentration organic wastewater. processing costs. High load and low sludge age should be maintained in the adsorption tank.
This can quickly flocculate and adsorb a large number of pollutants through the adsorption tank to form sludge flocs. Due to the short hydraulic retention time, the adsorbed organic matter basically does not undergo a biochemical reaction, and then enters the sedimentation tank. After the separation of mud and water, it passes through the sedimentation tank. The sludge discharge line discharges the precipitated alkali residue.
In order to restore the biological adsorption activity of the sludge in the sedimentation tank, part of the sludge in the sedimentation tank is returned to the adsorption tank for aeration activation to restore the sludge activity. If the return flow is small or there is an abnormal situation, it can be supplemented with excess sludge to form a cycle to continuously remove the alkali residue in the wastewater to ensure that it does not enter the biochemical system.
Effect and discussion after process improvement
The average value of COD in upstream incoming water is 1600mg/L, ammonia nitrogen is 65mg/L, and oil in water is 30mg/L. After the improvement of the process, the COD is reduced to 480mg/L, the ammonia nitrogen is reduced to 18mg/L, and the oil in the water is reduced to 17mg/L after being treated by the adsorption regeneration tank. (Other indicators can be qualified by the original process, no explanation is given)
The above results show that it is correct to improve the adsorption sedimentation tank into an adsorption regeneration tank. It can not only efficiently treat the alkali residue wastewater in time but also reduce the subsequent biochemical treatment load. By observing the water quality in the past year, it is found that the discharge water is stable and the indicators have dropped significantly. Contribute to the green development of the country. It also provides a reference for the treatment of alkali residue wastewater.
At present, the domestic treatment of petrochemical alkali residue wastewater is mainly a chemical method, but its cost is high, reaction conditions are strict, energy consumption is high, investment is large, the catalyst is required, chemical sludge is produced, covers a large area, and the treatment efficiency is average, The operation is unstable and there are potential safety hazards.
Therefore, the biological treatment of petrochemical alkali residue wastewater has a bright future. It converts alkali residue organic matter in wastewater into inorganic matter through microbial metabolism. It can overcome the shortcomings of the chemical treatment of alkali residue wastewater, such as QBR technology. The most important thing is to comply with the national development concept, that is, green development.
However, there are still many problems in biological treatment, such as the screening of high-efficiency strains, which requires a lot of manpower and material resources, and the degradation mechanism of microorganisms to pollutants needs to be further improved. Although there are many problems, the general trend will not change. I believe that in the next few years, scientists and the sewage treatment workers around them will overcome these difficulties. At that time our production and environment will be greatly improved.