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            Wastewater treatment technology and typical process flow

            Release:jstmhj Browse:614

            1Pharmaceutical wastewater


            Pharmaceutical wastewater has the characteristics of large difference in composition, complex composition, large amount of pollutants, high COD, low BOD5/CODCr ratio and great fluctuation, poor biodegradability, more refractory substances, strong toxicity, intermittent discharge, large fluctuation of water quantity, water quality and pollutants.



            3、Processing technology

            ①Preprocessing:Coagulation, flotation, microelectrolysis, Fenton reagent, catalytic oxidation, etc.

            ②Anaerobic process:UASB, two-phase anaerobic digestion, EGSB, etc.

            ③Aerobic process:Biological contact oxidation method, CASS, SBR, activated sludge method, etc.



            2Wastewater from papermaking industry


            Papermaking wastewater is very harmful. Black water is the most harmful. It contains more than 90% of the total pollutant discharged from the papermaking industry. Because black water is alkaline, dark, smelly, and foam, it consumes large quantities of dissolved oxygen in water. It seriously pollute the water source and brings harm to the environment and human health.

            The most serious environmental pollution of intermediate water is chlorine-containing wastewater produced in bleaching process, such as chlorinated bleaching wastewater, hypochlorite bleaching wastewater and so on. In addition, bleaching effluent contains dioxins, a highly toxic carcinogen, which also poses a serious threat to the ecological environment and human health.


            Pulping and papermaking wastewater is mainly divided into:Black liquor, intermediate wastewater and white water are three kinds.

            Black liquor:Plant fibers are boiled with NaOH or NaOH + sodium sulfate alkaline reagents to dissolve lignin. The discharged cooking liquor is "black liquor" (alkali boiled as black liquor, acid boiled as red liquor, most of which are boiled by alkali). Black liquor contains lignin, pentosan and total alkali, and is a high concentration and refractory wastewater.

            Middle stage wastewater:The COD load per ton of pulp is about 310 kg in the wastewater produced during washing, screening and bleaching of alkali-boiled pulp. BOD/COD ranged from 0.20 to 0.35, and its biodegradability was poor. The main pollutants are soluble COD such as lignin, cellulose and organic acid. The most serious pollution is chlorine-containing wastewater from bleaching.

            Plain water:Water content is large, mainly contains fine fibers, fillers, coatings and dissolved wood components, mainly insoluble COD, poor biodegradability, added preservative toxicity.

            3、Processing technology

            Black liquor and intermediate wastewater:Alkali recovery, acidification, LB-1 alkali precipitation, membrane separation, flocculation and sedimentation, biofilm, anaerobic biological treatment, screen microfiltration, air flotation, advanced oxidation.

            Plain water:Filtration, air flotation, precipitation and screening.





            3Tannery wastewater


            Tannery wastewater is the waste water discharged from the tannery process. Usually animal skins are salted or soaked in water to make them swell, add lime, demeat and dealkali, then tanned and softened with tannin or chromium, and finally dyed and processed into leather. Tannery wastewater mainly comes from preparation, tanning and dyeing sections, which contains a large number of toxic and harmful substances such as protein, fat, inorganic salts, suspended solids, sulfides, chromium and vegetable tanning agents. It has high biochemical oxygen demand and high toxicity.


            Sulphur containing wastewater:It refers to the lime-alkali dehairing process, which is the waste liquor of leaching and the corresponding wastewater of washing process.

            Defatted wastewater:It refers to the waste liquid formed by the treatment of raw leather grease with surfactants and the corresponding wastewater from washing process in the process of leather and fur degreasing.

            Chromium containing wastewater:It refers to the waste chrome liquor produced in the chrome tanning and chrome retanning processes and the corresponding wastewater from the washing process.

            Comprehensive wastewater:It refers to all kinds of wastewater produced by tannery and fur processing enterprises or centralized processing zones that are directly or indirectly discharged into integrated wastewater treatment projects (e.g. production process wastewater, factory domestic wastewater, etc.).

            3、Processing technology

            Single Processing Technology

            a、Defatted wastewater

            Oil content, CODcr and BOD5 in degreasing effluent are very high. The treatment methods include acid extraction, centrifugal separation or solvent extraction. The acid extraction method is widely used, adding H2SO4 to adjust the pH value to 3-4 for demulsification, stirring with steam and salt, and standing for 2-3 hours at 40-60 t, the oil gradually floats to form an oil layer. The recovered oil can reach 95% and CODcr can be removed more than 90%. Generally, the mass concentration of influent oil is 8-10 g/L, and that of effluent oil is less than 0.1 g/L. The recovered oil can be further processed into mixed fatty acids for soap production.

            b、Lime-soaking and depilation wastewater

            The wastewater from lixiviation and depilation contains protein, lime, sodium sulfide and solid suspension, 28% of total CODcr, 93% of total S2-and 70% of total SS. The treatment methods include acidification, chemical precipitation and oxidation.

            In production, acidification method is often used. Under negative pressure, H2SO4 is added to adjust the pH value to 4-4.5 to produce H2S gas, which is absorbed by NaOH solution to produce alkali sulfide for reuse. The soluble protein precipitated from wastewater is filtered, washed and dried into products. The removal rate of sulphide can reach more than 90%, and CODcr and SS can be reduced by 85% and 95%, respectively. Its cost is low, production operation is simple, easy to control, and shorten the production cycle.

            c、Chrome tanning wastewater

            The main pollutant of chrome tanning wastewater is heavy metal Ce3+, the mass concentration is about 3-4 g/L, and the pH value is weak acidic. The treatment methods include alkali precipitation and direct recycling. Ninety percent of domestic tanneries adopt alkali precipitation method. Lime, sodium hydroxide and magnesium oxide are added into waste chromium liquor to react and dehydrate to get chromium-containing sludge. After being dissolved in sulfuric acid, it can be reused in tanning section.

            The pH value is 8.2-8.5, the temperature is 40 (?) C, and magnesium oxide is the best alkali precipitator. The recovery rate of chromium is 99%. The mass concentration of chromium in effluent is less than 1 mg/L. However, this method is suitable for large tanneries, and the recovery of soluble oils, proteins and other impurities in chrome sludge will affect the tanning effect.

            Integrated Processing Technology

            a、Pretreatment system

            It mainly includes grille, regulating tank, sedimentation tank, air floatation tank and other treatment facilities. Tannery wastewater has high concentration of organic matter and suspended solids. The pretreatment system is used to regulate water quantity and quality, remove SS and suspended solids, and reduce part of pollution load to create good conditions for subsequent biological treatment.

            b、Biological Processing System

            The CODcr of tannery wastewater is generally 3000-4000 mg/L, and the BOD5 is 1000-2000mg/L. It belongs to high concentration organic wastewater. The m(BOD5)/m(CODcr) value is 0.3-0.6. It is suitable for biological treatment. At present, oxidation ditch, SBR and biological contact oxidation are widely used in China, while jet aeration, batch biofilm reactor (SBBR), fluidized bed and upflow anaerobic sludge bed (UASB) are seldom used.

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