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Process Methods and Characteristics of Wastewater Treatment in the Pharmaceutical Industry

2022-04-06

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Marya

The treatment methods of antibiotic wastewater can be summarized as the following: physicochemical  treatment methods, aerobic biological treatment methods, anaerobic biological treatment methods and a combination of various methods.

Physical and chemical methods mainly include precipitation, coagulation, filtration and other methods. Due to the complex composition of antibiotic production wastewater, high organic content and a small amount of residual antibiotics, when biochemical treatment is used, the strong inhibitory effect of residual antibiotics on microorganisms results in complex wastewater treatment processes, high costs and unstable effects.

Aerobic biological treatment mainly includes SBR,oxidation ditch, deep well aeration and contact oxidation. However, since antibiotic wastewater is a high-concentration organic wastewater, the conventional aerobic process activated sludge method cannot withstand wastewater with a COD concentration of more than 10g/L, and the original wastewater needs to be heavily diluted. Therefore, the consumption of clean water and power is large, resulting in high treatment costs, and the actual wastewater treatment rate of application manufacturer is also low.

Anaerobic biological treatment mainly includes anaerobic digester,anaerobic filter, up-flow anaerobic sludge bed ,anaerobic expanded granular sludge bed, internal circulation,etc. Compared with aerobic treatment, anaerobic treatment usually has high organic load in antibiotic wastewater treatment, low sludge yield, easy dehydration of biological sludge, less nutrient requirement, no need for aeration, and low energy consumption. It can generate biogas, recover energy, has a wide range of suitable water temperature, and has the advantages of long storage time of activated anaerobic sludge, which has been used more and more widely.

  • Source and Characteristics of Antibiotic Wastewater

Antibiotic production includes microbial fermentation, filtration, extraction crystallization, refining and other processes. The wastewater used for producing antibiotics with grain or molasses as the main raw material mainly comes from high-concentration organic wastewater from separation, extraction, refining and purification processes, such as crystallization liquid, waste mother liquor, and washing wastewater from seed tanks and fermentation tanks, and cooling water for fermentation tanks. Therefore, wastewater has the following characteristics:

1. High content of COD

The COD of antibiotic wastewater is generally between 5000 and 80000mg/L. Mainly include fermentation residual matrix and extraction process, distillation kettle residual liquid discharge after solvent recovery,adsorption waste liquid discharged from ion exchange process, fermentation filtrate of insoluble antibiotics in water, and contamination tank waste liquid, etc. The concentration of these components is high, such as the CODCr concentration of penicillin wastewater is 15000-80000mg/L, and the CODCr concentration of oxytetracycline wastewater is 8000-35000mg/L.

2. High SS concentration in wastewater(500～25000mg/L）

The SS in the antibiotic wastewater is mainly the residual culture substrate of fermentation and the microbial mycelium produced by the fermentation.For example, SS of gentamicin wastewater is about 8000mg/L,and penicillin wastewater is 5000-23000mg/L.

3. Complex ingredients.

Antibiotic wastewater contains raw materials such as intermediate metabolites, surfactants,and high concentrations of acids, alkalis and organic solvents remaining in extraction and separation, with complex components.It is easy to cause PH fluctuation and affect the biochemical effect.

4. Presence of biotoxic substances.

Wastewater contains substances that are difficult to degrade by microorganisms and even have inhibitory effects on microorganisms. In the process of fermentation or extraction, the organic or inorganic substances that need to be added for production, as well as the residual solvents and residual antibiotics and their degradation products discharged during the production process,etc, when these substances reach a certain concentration, they will inhibit microorganisms.

5. The concentration of sulfate is high.

For example, streptomycin wastewater sulfate content is about 3000mg/L, up to 5500mg/L, penicillin is more than 5000mg/L.

In addition, antibiotic wastewater has the characteristics of high chroma, large PH fluctuation, and intermittent discharge. It is one of the toxic organic wastewater with high treatment costs and difficult treatment.

  • Physical Treatment Method of the Antibiotic Wastewater

Because antibiotic production wastewater is refractory organic wastewater, the strong inhibitory effect of residual antibiotics on microorganisms can lead to complex wastewater treatment processes, high costs and unstable effects. Therefore, in the treatment process of antibiotic wastewater, physical treatment method can bu used as a pretreatment method for subsequent biochemical treatment to reduce suspended solids in water and reduce bioinhibitory substances in wastewater. The physical treatment methods currently used mainly include coagulation, sedimentation, air flotation, adsorption, reverse osmosis and filtration.

The coagulation method is that after adding a coagulant, the particles that have lost their charge are contacted with each other by stirring to form flocs, which are convenient for their precipitation or filtration to achieve the purpose of separation. After coagulation treatment, not only the concentration of pollutants can be effectively reduced, but also the biodegradation performance of wastewater is improved.Coagulants commonly used in the treatment of wastewater in the antibiotic pharmaceutical industry include:polymeric ferric sulfate,ferric chloride,ferrous salts,polyaluminum chloride sulfate,polyaluminum chloride, polyaluminum chloride ferric sulfate,polyacrylamide(PAM),etc, Sedimentation is the separation or removal of suspend particles that are denser than water from water by gravity precipitation separation.

Air flotation is a process in which highly dispersed tiny air bubbles are used as carriers to adsorb pollutants in wastewater, so that the density is lower than that of water and float up to achieve solid-liquid or liquid-liquid separation. It usually includes various forms such as inflatable air flotation, dissolved air flotation, chemical air flotation and electrolytic air flotation. A domestic pharmaceutical factory uses a CAF vortex concave air flotation device to pretreat pharmaceutical wastewater. With appropriate pharmaceutical coordination, the average removal rate of CODcr can be around 25%.

Adsorption method refers to the use of porous solids to adsorb certain or several pollutants in wastewater to recover or remove pollutants, thereby purifying wastewater.Commonly used adsorbents are activated carbon, activated coal, humic acids,adsorption resins,etc.The method has the advantages of small investment,simple process, convenient operation and easy treatment, and is more suitable for process improvement of the original sewage treatment plant.

The reverse osmosis method uses a semi-permeable membrane to separate the concentrated and dilute solutions, and uses the pressure difference as a driving force to apply a pressure exceeding the osmotic pressure of the solution to change the natural permeation direction, and infiltrate the water pressure in the concentrated solution to the dilute solution side, the purpose of wastewater concentration and purification can be achieved.

  • Chemical Treatment Method of Antibiotic Wastewater

1. Photocatalytic oxidation.

This technology can effectively degrade the concentration of organic matter in pharmaceutical wastewater, and has the advantages of stable performance, no selectivity for wastewater, warm reaction conditions, and no secondary pollution, which has a good application prospect.Using Ti02 as a catalyst, a fluidized bed photocatalytic reactor was used to treat pharmaceutical wastewater, and the photocatalytic effect under different process conditions was investigated. After 150 min, the COD of the effluent in the photocatalytic oxidation stage was 113 and 124mg/L, the removal rates were 81.0% and 85.6% and the BODs/COD value could also be increased from 0.2 to 0.5, which improved the biodegradability of the wastewater.However,there are still shortcomings in the photocatalytic oxidation method, and the most widely used Ti02 catalyst has high selectivity and is difficult to separate and recycle. Therefore, the preparation of efficient photocatalysts is the premise for this method to be widely used in the field of environmental protection.

2. Fe-C method.

Fe-C is a wastewater treatment technology that has been widely studied and applied.The electrolyte solution is filled with wastewater with a PH value of 3 to6 Iron filings and carbon particles form numerous tiny primary batteries, releasing highly active[H]. The new ecological [H] can interact with many components in the solution. A redox reaction occurs, and a new ecological Fe3 is produced at the same time.The new ecological Fe3 has a high activity and generates Fe3. With the progress of the hydrolysis reaction, a gel with Fe3 as the center is formed, so as to achieve the degradation effect of organic wastewater.

Under normal temperature and pressure, the activated carbon-iron filings were installed in the leaching column with tube length ratio indine as the filter layer, and Mn2 and the Cu2 were used as catalysts to treat the comprehensive wastewater of the tetracycline pharmaceutical factory, the results show that activated carbon has a larger adsorption effect.At the same time, the Fe-c micro-battery formed in the tube oxidizes iron into ferric hydroxide flocculant, which separates solid and liquid and reduces turbidity. In the actual application of chemical treatment methods, excessive use of reagents can easily lead to secondary pollution of water bodies, so relevant research work should be done before design.

3. Antibiotic and aerobic treatment of wastewater.

Aerobic biological methods commonly used in pharmaceutical wastewater mainly include: ordinary activated sludge method, pressurized biochemical method, deep well aeration method, biological contact oxidation method, biological fluidized bed method, sequencing batch activated sludge process,etc.

At present, the more mature method for treating antibiotic wastewater at home and abroad is the activated sludge method.Due to the strengthened pretreatment,improved aeration method and stable operation of the device, it has become a method commonly used by pharmaceutical factories in some industrialized countries in the 1970s.However, the disadvantage of the common activated sludge method is that the wastewater needs a lot of dilution, there is a lot of foam during operation, sludge expansion is prone to occur, the amount of excess sludge is large, and the removal rate is not high.In this case, two or more stages of processing must be employed.Therefore, in recent years, improving the aeration method and microbial immobilization technology to improve the treatment effect of wastewater has become an important part of the research and development of activated sludge process.

Compared with the ordinary activated sludge method, the pressurized biochemical method increases the concentration of dissolved oxygen, and the oxygen supply is sufficient, which is not only conducive to accelerating biodegradation,but also improving the biological shock load resistance.

The deep well aeration method is a high-speed activated sludge system. Compared with ordinary activated sludge method, deep well aeration method has the following advantages: high oxygen utilization rate, equivalent to 10 times that of ordinary aeration;high sludge load, 2.5 to 4 times higher than ordinary activated sludge method;Small,low investment, low operating cost, high efficiency, the average removal rate of COD can reach more than 70%; strong resistance to hydraulic and organic load impact;no sludge bulking problem; good thermal insulation effect.

The biological contact oxidation method has the characteristics of both the activated sludge method and the biofilm method, and has a high processing load, which can treat organic wastewater that easily causes sludge bulking. In the treatment of production wastewater in the pharmaceutical industry, biological contact oxidation is often used directly, or anaerobic digestion and acidification are used as pretreatment procedures to treat pharmaceutical production wastewater. However, when the contact oxidation method is used to treat pharmaceutical wastewater, if the concentration of the influent water is high, a large amount of foam is likely to appear in the pool,and preventive and countermeasures should be taken during operation.

The biological fluidized bed combines the advantages of the ordinary activated sludge method and the biological filter method, so it has the advantages of high volume load, fast reaction speed and small footprint.

   Sequencing batch activated sludge process(SBR)has the advantages of homogenized water quality, no need for sludge return, impact resistance, high sludge activity,simple structure, flexible operation, less land occupation,low investment, stable operation,and a matrix removal rate higher than common activated sludge method.It is more suitable for treating wastewater with intermittent discharge and large fluctuations in water quality and quantity.However, the SBR method has the disadvantages of sludge settling and long sludge-water separation time. When treating high-concentration wastewater, is is required to maintain a high sludge concentration, and at the same time, high-viscosity swelling is prone to occur.

  Therefore, it is often considered to add powdered activated carbon to reduce the foam in the aeration tank, improve the sludge settling performance, liquid-solid separation performance and sludge dewatering preformance,etc, so as to obtain a higher removal rate.The direct application of aerobic method to treat antibiotic wastewater still needs to consider the toxicity of residual antibiotics in wastewater to aerobic bacteria, so pretreatment of wastewater is generally required.