Pharmaceutical wastewater

1. Characteristics

 

Pharmaceutical wastewater is characterized by large differences in composition, complex components, high pollutant load, high COD, low and fluctuating BOD5/CODcr ratio, poor biodegradability, many refractory substances, strong toxicity, intermittent discharge, and large fluctuations in water volume, water quality, and pollutant types.

 

2. Composition

 

Type	Source	Composition
Antibiotic production wastewater	Fermentation filtrate, extraction residue, distillation pot residue, adsorption wastewater, and pipeline wastewater, etc.	Mainly contains mycelium, residual nutrients, metabolites, and organic solvents. The concentration of organic matter is very high, with COD reaching 5000～20000mg/L, BOD reaching 2000～10000mg/L, SS concentration reaching 5000～23000mg/L, and TN reaching 600～1000mg/L.
Synthetic drug wastewater	Raw material loss, by-products, and organic solvents caused by multiple steps in the synthesis process and low product conversion rate.	Contains a wide variety of toxic and harmful chemicals, such as steroid compounds, nitro compounds, aniline compounds, piperazine compounds, fluorine, mercury, chromium, copper, and organic solvents such as ethanol, benzene, chloroform, petroleum ether, organic matter, metals, and waste acids and alkalis.
Traditional Chinese medicine production wastewater	Wastewater discharged from washing, decoction, purification and separation, evaporation and concentration, and preparation processes, including washing wastewater, separation water, evaporation condensate, and drug solution loss water.	Natural biological organic matter, such as organic acids, anthraquinones, lignin, alkaloids, tannins, proteins, sugars, and starch.

 

3. Treatment technologies

① Pretreatment: coagulation, flotation, micro-electrolysis, Fenton reagent, catalytic oxidation, etc.;

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

③ Aerobic process: biological contact oxidation, CASS, SBR, activated sludge, etc.;

 

4. Typical process flow

Flotation treatment of pharmaceutical wastewater

Membrane separation treatment of pharmaceutical wastewater

Combination process treatment of pharmaceutical wastewater

 

 

Papermaking wastewater

1. Characteristics

Papermaking wastewater is very harmful, with black liquor being the most harmful, accounting for more than 90% of the total pollution discharge from the papermaking industry. Due to its high alkalinity, dark color, strong odor, and abundant foam, black liquor consumes a large amount of dissolved oxygen in the water, seriously polluting water sources and posing a threat to the environment and human health.

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

 

2. Composition

Pulp and paper wastewater is mainly divided into three types: black liquor, intermediate wastewater, and white water.

Black liquor: The cooking liquor discharged after cooking plant fibers with alkaline agents such as NaOH or NaOH+sodium sulfate to dissolve lignin is called "black liquor" (alkaline cooking produces black liquor, acid cooking produces red liquor, and most use alkaline cooking). Black liquor contains lignin, pentosans, and total alkali, and is a high-concentration, refractory wastewater.

Intermediate wastewater: Wastewater produced during the washing, screening, and bleaching of pulp produced by alkaline cooking, with a COD load of about 310 kg per ton of pulp. BOD/COD is between 0.20 and 0.35, with poor biodegradability. Pollutants are mainly soluble COD such as lignin, cellulose, and organic acids, and the most serious pollution is chlorine-containing wastewater produced during bleaching.

White water: Large water volume, mainly containing fine fibers, fillers, coatings, and dissolved wood components, mainly insoluble COD, poor biodegradability, and toxic preservatives.

3. Treatment technologies

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

White water: filtration, flotation, sedimentation, screening.

4. Typical process flow

 

Extraction of lignin from papermaking black liquor to produce water coal slurry

 

 

Shallow flotation-oxidation pond

 

 

Coagulation flotation-A/O process

 

 

Oxidation ditch process for treating alkaline kraft pulp wastewater

 

 

Hydrolysis acidification-anaerobic-biological contact-coagulation sedimentation

 

 

 

Flotation treatment of paper machine white water

 

 

Leather industry wastewater

1. Characteristics

Leather wastewater is wastewater discharged during leather production. Animal skins are usually salted or soaked in water to make them swell, then limed, fleshed, delimed, and then tanned with tannins or chromium, fatliquored and softened, and finally dyed and processed into leather. Leather wastewater mainly comes from the preparation, tanning, and dyeing sections, containing large amounts of proteins, fats, inorganic salts, suspended solids, sulfides, chromium, and plant tannins, which are toxic and harmful substances with high biochemical oxygen demand and high toxicity.

2. Composition

Sulfide-containing wastewater: This refers to the lime wastewater and the corresponding wastewater from washing processes generated during the liming and unhairing process in leather making.

Degreasing wastewater: This refers to the wastewater and the corresponding wastewater from washing processes generated during the degreasing process of leather and fur processing, where surfactants are used to treat the grease of rawhide.

Chromium-containing wastewater: This refers to the waste chromium solution and the corresponding wastewater from washing processes generated during the chrome tanning and chrome retanning processes.

Combined wastewater: This is a general term for various types of wastewater generated by leather and fur processing enterprises or concentrated processing areas that are directly or indirectly discharged into a comprehensive wastewater treatment facility (such as production process wastewater, factory area domestic sewage, etc.).

3. Treatment technologies

  Single-item treatment technology

a. Degreasing wastewater

The degreasing wastewater has very high levels of pollutants such as oil content, CODcr, and BOD5. Treatment methods include acid extraction, centrifugal separation, or solvent extraction. Acid extraction is widely used, adjusting the pH value to 3-4 with H2SO4 to break the emulsion, adding salt and stirring with steam, and allowing it to stand for 2-3 hours at 40-60 ℃, with the oil gradually rising to form an oil layer. Up to 95% of the oil can be recovered, removing more than 90% of CODcr. The general influent oil concentration is 8-10 g/L, and the effluent oil concentration is less than 0.1 g/L. The recovered oil can be further processed into mixed fatty acids for soap making.

b. Lime unhairing wastewater

Lime unhairing wastewater contains protein, lime, sodium sulfide, and solid suspended matter, accounting for 28% of total CODcr, 93% of total S2-, and 70% of total SS. Treatment methods include acidification, chemical precipitation, and oxidation.

Acidification is mostly used in production. Under negative pressure, H2SO4 is added to adjust the pH value to 4-4.5, generating H2S gas, which is absorbed by NaOH solution to generate reusable alkali sulfide. The soluble protein precipitated from the wastewater is filtered, washed, and dried to become a product. The sulfide removal rate can reach more than 90%, and CODcr and SS are reduced by 85% and 95%, respectively. This method is low-cost, simple to operate, easy to control, and shortens the production cycle.

c. Chrome tanning wastewater

The main pollutant in chrome tanning wastewater is the heavy metal Ce3+, with a concentration of about 3-4 g/L, and a weakly acidic pH value. Treatment methods include alkali precipitation and direct recycling. 90% of tanneries in China use alkali precipitation, adding lime, sodium hydroxide, magnesium oxide, etc., to the waste chromium solution, reacting and dehydrating to obtain chromium-containing sludge, which can be redissolved with sulfuric acid and reused in the tanning process.

The best precipitation occurs at a pH of 8.2-8.5 and a temperature of 40℃, with magnesium oxide being the best alkali precipitant. The chromium recovery rate is 99%, and the chromium concentration in the effluent is less than 1 mg/L. However, this method is suitable for large tanneries, and soluble oils, proteins, and other impurities in the recovered chromium sludge will affect the tanning effect.

   Comprehensive treatment technology

a. Pretreatment system: This mainly includes treatment facilities such as screens, equalization tanks, sedimentation tanks, and flotation tanks. Leather wastewater has high concentrations of organic matter and suspended solids. The pretreatment system is used to adjust the water volume and quality; remove SS and suspended matter; reduce some of the pollution load; and create good conditions for subsequent biological treatment.

b. Biological treatment system The ρ(CODcr) of leather wastewater is generally 3000-4000 mg/L, and the ρ(BOD5) is 1000-2000 mg/L, which is high-concentration organic wastewater, with an m(BOD5)/m(CODcr) value of 0.3-0.6, suitable for biological treatment. Currently, the more commonly used methods in China include oxidation ditches, SBR, and biological contact oxidation. Less commonly used methods include jet aeration, intermittent biofilm reactors (SBBR), fluidized beds, and upflow anaerobic sludge beds (UASB).

4. Typical process flow

 

Leather wastewater treatment process

 

Leather wastewater treatment process

 

Leather chromium-containing wastewater treatment process

 

 

Coke wastewater

1. Characteristics

Coke wastewater is one of the main types of wastewater discharged by steel enterprises. Coke wastewater has a complex composition and contains a large number of toxic and harmful substances. It is a typical refractory organic wastewater. Conventional treatment methods have a low removal rate for refractory compounds, resulting in high COD and chroma in the effluent, which cannot meet the standards.

2. Composition

Coke wastewater is high-concentration organic wastewater produced during the coking of coal, coal gas purification, and the recovery of coking products. Coke wastewater mainly includes coal gas condensate water from the initial cooling stage, coal gas final cooling water, coal gas washing water, coal gas washing water from the coal gas generation station, benzene separation water, gas holder wastewater, coke oven water seal water, and other wastewater from various sources.

3. Treatment technologies

Physical treatment methods: Adsorption, coagulation and flocculation sedimentation, Fenton reagent method

Biochemical treatment methods: A/O and A2/O methods, SBR method, oxidation ditch technology

Chemical treatment methods: Catalytic wet oxidation technology, ozone oxidation method, photocatalytic oxidation method

4. Typical process flow

 

Coke wastewater treatment process

 

Nitrification and denitrification treatment of coke wastewater

 

Coke wastewater treatment process

 

 

Electroplating wastewater

1. Characteristics

Electroplating wastewater is highly toxic and harmful to soil and plant growth. Therefore, it is necessary to strictly treat the wastewater to meet the discharge standards. In water-scarce areas, the treatment of wastewater to meet the standards and its recycling should be promoted. From a technical production perspective, since the electroplating production process and wastewater treatment process require the addition of a certain amount of various chemicals, after the electroplating wastewater is treated to achieve recycling, the recycled water must be desalted before it can be reused in the production line. The total salt content in the environment will not be reduced, and the concentrated liquid from the resin exchange and reverse osmosis processes will still return to the ground.

2. Composition Classification

Classification is based on the heavy metal elements contained in heavy metal wastewater. Generally, it can be divided into chromium (Cr)-containing wastewater, nickel (Ni)-containing wastewater, cadmium (Cd)-containing wastewater, copper (Cu)-containing wastewater, zinc (Zn)-containing wastewater, gold (Au)-containing wastewater, silver (Ag)-containing wastewater, etc.

3. Treatment technologies

Flotation method: The principle of using the flotation method to treat chromium-plating wastewater is that ferrous sulfate and hexavalent chromium undergo a redox reaction under acidic conditions, and then flocculants are produced under alkaline conditions. Under the action of countless fine bubbles, the flocculants float to the surface, making the water clear.

Ion exchange method: One of the effective methods for treating electroplating wastewater and recovering certain metals, and also an important link for certain plating types of electroplating wastewater to achieve closed-loop circulation. However, the investment cost of using the ion exchange method is very high, and the system design and operation management are relatively complex, which is difficult for general small and medium-sized enterprises to adapt to. Often due to poor maintenance and management, the expected results cannot be achieved. Therefore, its promotion and application are subject to certain limitations.

Currently, the ion exchange method is more commonly used in China to treat chromium-containing and nickel-containing electroplating wastewater, and there is relatively mature experience in design, operation, and management. After treatment, the water can meet the discharge standards, and the effluent quality is good, and it can generally be recycled. After the resin exchange adsorption is saturated, the regeneration eluent can be reused in the plating tank after adjustment and purification of the electroplating process components, basically realizing closed-loop circulation. In addition, the ion exchange method can also be used to treat copper-containing, zinc-containing, and gold-containing wastewater.

Electrolysis method: The electrolysis method for treating electroplating wastewater is generally used in medium and small-sized factories. Its main characteristics are that no treatment agents need to be added, the process is simple, the operation is convenient, and the production site is small. At the same time, because the recovered metal has high purity, it has good economic benefits for recovering precious metals. However, when the amount of water to be treated is large, the electrolysis method consumes a lot of electricity and a large amount of iron plates. At the same time, the separated sludge is difficult to dispose of, just like the chemical treatment method, so it is rarely used.

Extraction method: The extraction method uses a solvent that is insoluble in water but can dissolve a certain substance (called solute or extractant) in water, added to wastewater, so that the solute is fully dissolved in the solvent, thereby separating and removing or recovering a certain substance from the wastewater. The extraction process includes three main steps: mixing, separation, and recovery.

4. Typical Treatment Processes

 

Ion exchange method for treating electroplating wastewater

Treatment process for plastic electroplating wastewater

Treatment process for chromium-containing wastewater

Treatment process for electroplating wastewater

Treatment process for electroplating wastewater

 

 

Metallurgical wastewater

1. Characteristics

The waste acid wastewater is very strong in acidity. After neutralization and removal of fluoride, the salt content of the wastewater increases, the hardness is high, and the pH value rises to 9-11. The wastewater contains metal ions such as zinc, copper, lead, cadmium, arsenic, and nickel, as well as pollutants such as fluoride, nitrate, organic matter, and colloidal particles. If the raw water directly enters the membrane system, it will cause less membrane water production and easy blockage. It must be softened first, and then the heavy metal ions and COD in the wastewater must be removed. After the deep treatment system of the membrane, the produced water is reused.

2. Composition

Classified by wastewater source and characteristics, it mainly includes cooling water, pickling wastewater, washing wastewater (dust removal, coal gas or flue gas), slag flushing wastewater, coking wastewater, and wastewater condensed, separated, or overflowed during production.

3. Treatment Technology

Treatment of pickling wastewater: A small amount of pickling wastewater can be neutralized and iron salts recovered; a larger amount can be used to recover acid and iron salts or separate and recover iron oxide by methods such as freezing, spray combustion, and diaphragm dialysis. If a neutral electrolysis process is used to remove iron oxide scale, pickling wastewater will not be produced. However, the electrolyte must be treated by filtration or magnetic separation before it can be recycled.

Treatment of cooling water: The treatment method is to first remove particles larger than 100 micrometers through a coarse particle sedimentation tank or hydrocyclone, and then send the wastewater to sedimentation to remove suspended particles; to improve the sedimentation effect, flocculants and coagulant aids polyacrylamide can be added; floating oil in the water can be removed by scraping. After purification and cooling, the wastewater can be recycled. The direct cooling water in the cold rolling workshop contains emulsified oil, and the emulsified oil must first be broken down by chemical coagulation, heating, or pH adjustment, and then subjected to flotation separation, or directly separated by ultrafiltration. The collected waste oil can be regenerated and used as fuel.

Treatment of washing water: Cyanide in wastewater can be oxidized to cyanate by chlorine, bleaching powder, or ozone, or ferrous sulfate can be added to convert cyanide into non-toxic ferrous cyanide. It can also be biologically treated using a tower-type biofilter or aeration tank. The amount of blast furnace gas washing water is large, and it is uneconomical to treat cyanide with the above methods. Therefore, most of the wastewater is clarified in a sedimentation tank and then recycled.

Treatment of non-ferrous metallurgical wastewater: The control measures are: strengthen production management, reduce wastewater volume, and recover useful metals. The commonly used treatment method is the lime neutralization method , mainly to control the pH value of the wastewater, so that the heavy metal ions precipitate as hydroxides; or the sulfidation method , hydrogen sulfide is introduced into the wastewater to convert heavy metal ions into heavy metal sulfides before extraction; arsenic and fluoride and other harmful substances can be precipitated and separated by forming insoluble compounds with calcium ions. In addition, ion exchange method, flotation method, reverse osmosis method, diaphragm electrolysis method, etc. can also be used to recover useful metals and purify wastewater.

4. Typical Treatment Processes

 

Fluidized precipitation method

 

Coagulation/membrane Method

 

 

Dyeing wastewater

1. Characteristics

Dyeing wastewater is wastewater discharged from dyeing plants that mainly process cotton, linen, chemical fibers, and their blended products. Dyeing wastewater has a large volume; for every ton of textile processed, 100-200 tons of water are consumed, 80-90% of which becomes wastewater.

Textile dyeing wastewater is characterized by large water volume, high content of organic pollutants, high alkalinity, and large variations in water quality, making it one of the difficult industrial wastewaters to treat. The wastewater contains dyes, sizing materials, auxiliaries, oils, acids, alkalis, fiber impurities, sandy substances, and inorganic salts.

2. Treatment technology

Common treatment methods for dyeing wastewater can be divided into three categories: physical, chemical, and biological methods. Physical methods mainly include screens and sieves, adjustment, sedimentation, flotation, filtration, membrane technology, etc.; chemical methods include neutralization, coagulation, electrolysis, oxidation, adsorption, disinfection, etc.; biological methods include anaerobic biological methods, aerobic biological methods, and facultative anaerobic biological methods.

3 Typical treatment processes

 

Dyeing wastewater treatment process

Dyeing wastewater treatment process

Dyeing wastewater treatment process

 

 

Food processing wastewater

1. Characteristics

• Production varies with the seasons, and the water quality and quantity of wastewater also vary with the seasons;

• The amount of wastewater varies greatly. Food industries range from small-scale household industries to various large factories, with a wide variety of products. The raw materials, processes, and scales vary greatly, and the wastewater volume ranges from several m3/d to several thousand m3/d;

• Food industry wastewater contains many biodegradable components. For general food industries, because the raw materials come from natural organic substances, the components in their wastewater are also mainly natural organic substances, and do not contain toxic substances, so they are highly biodegradable, with BOD5/COD as high as 0.84;

• High-concentration wastewater is common;

• The wastewater contains various microorganisms, including pathogenic microorganisms, and the wastewater is easily putrefied and odorous;

• The wastewater has a high nitrogen and phosphorus content.

2. Treatment technology

Physical treatment methods: Physical treatment methods used in food industry wastewater treatment include screening, skimming, adjustment, sedimentation, flotation, centrifugal separation, filtration, and microfiltration. The first five processes are mostly used for pretreatment or primary treatment, while the last three are mainly used for advanced treatment.

Chemical treatment methods: Chemical treatment methods used for food industry wastewater include neutralization, coagulation, electrolysis, oxidation-reduction, ion exchange, and membrane separation.

Biological treatment methods: In food processing wastewater treatment, biological treatment processes can be divided into aerobic processes, anaerobic processes, stabilization ponds, land treatment, and various combined processes formed by the combination of the above processes. Food wastewater is organic wastewater, and biological methods are the main secondary treatment processes, aiming to degrade COD and BOD5.

Aerobic biological treatment processes are divided into activated sludge processes and membrane processes according to the growth form of the microorganisms used. The former includes traditional activated sludge method, step aeration method, biosorption method, complete mixing method, delayed aeration method, oxidation ditch, intermittent activated sludge method (SBR), etc. The latter includes biofilters, tower biofilters, bio-rotating discs, activated biofilters, biological contact oxidation method, aerobic fluidized bed, etc. Generally, aerobic treatment is more effective for low-concentration wastewater.

Anaerobic biological treatment processes are suitable for food processing wastewater treatment, mainly because the wastewater contains easily biodegradable high-concentration organic matter and is non-toxic. In addition, anaerobic treatment has low energy consumption, the produced biogas can be used as energy, the amount of sludge produced is small, the anaerobic treatment system is completely closed, which is conducive to improving environmental sanitation, and it can operate seasonally or intermittently, and the sludge can be stored for a long time.

3. Typical treatment processes

 

CASS process for treating food processing wastewater

 

Biological treatment of food processing wastewater

 

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