1 treatment method of pharmaceutical wastewater
The treatment methods of pharmaceutical wastewater can be summarized as physical and chemical treatment, chemical treatment, biochemical treatment and the combination of various methods. Each treatment has its own advantages and disadvantages.
1. 1 physical and chemical treatment
According to the water quality characteristics of pharmaceutical wastewater, physicochemical treatment is needed as pretreatment or post-treatment process of biochemical treatment. At present, physical and chemical treatment methods mainly include coagulation, air flotation, adsorption, ammonia stripping, electrolysis, ion exchange, membrane separation and so on.
1. 1. 1 coagulation method
This technology is a widely used water quality treatment method at home and abroad. Widely used in pretreatment and post-treatment of pharmaceutical wastewater, such as aluminum sulfate and polymeric ferric sulfate used in traditional Chinese medicine wastewater. The key to efficient coagulation treatment lies in the selection and addition of coagulant with excellent performance. In recent years, the development direction of coagulant is from low molecular to high molecular polymer, from single component and function to compound development. Liu Minghua et al. used his high-efficient composite flocculant F- 1 to treat the wastewater from the production of fast syrup. When the pH is 6.5 and the dosage of flocculant is 300 mg/L, the removal rates of COD, SS and chromaticity of wastewater reach 69.7%, 96.4% and 87.5% respectively, and its performance is obviously better than that of single flocculant such as powdered activated carbon (PAC) and polyacrylamide (PAM).
1. 1.2 air flotation
Air flotation usually includes aerated flotation, dissolved air flotation, chemical flotation and electrolytic flotation. Xinchang Pharmaceutical Factory used CAF vortex-concave air flotation device to pretreat pharmaceutical wastewater, and added appropriate chemicals, the average removal rate of COD could reach about 25%.
1. 1.3 adsorption method
Commonly used adsorbents include activated carbon, activated coal, humic acid, adsorption resin, etc. Wuhan Jianmin Pharmaceutical Factory used fly ash adsorption-two-stage aerobic biological treatment process to treat its wastewater. The results showed that the removal rate of COD in wastewater by adsorption pretreatment reached 4 1. 1%, and the BOD5/COD value was improved.
1. 1.4 membrane separation method
Membrane technology includes reverse osmosis, nanofiltration membrane and fiber membrane, which can recover useful substances and reduce the total discharge of organic matter. The main characteristics of this technology are simple equipment, convenient operation, no phase change and chemical change, high treatment efficiency and energy saving. Juana et al. used nanofiltration membrane to separate lincomycin wastewater, and found that it not only reduced the inhibition of lincomycin on microorganisms in wastewater, but also recovered lincomycin.
1. 1.5 electrolytic method
This method has the advantages of high efficiency and easy operation, and people pay attention to it. At the same time, electrolysis has a good decoloration effect. Mars pretreated the supernatant of riboflavin by electrolysis, and the removal rates of COD, SS and chromaticity reached 765, 438+0%, 83% and 67% respectively.
When chemical methods are used in the chemical treatment of 1.2, excessive use of some reagents will easily lead to secondary pollution of water, so relevant experimental research work should be done well before design. Chemical methods include iron-carbon method, chemical oxidation-reduction method (Fenton reagent, H2O2, O3) and advanced oxidation technology.
1.2. 1 iron carbon method
The industrial operation shows that the biodegradability of the effluent can be greatly improved by using iron-carbon as the pretreatment step of pharmaceutical wastewater. Lou Maoxing et al. [9] used the combined treatment process of iron-carbon-micro-electrolysis-anaerobic-aerobic-air flotation to treat the wastewater from pharmaceutical intermediates such as erythromycin and ciprofloxacin hydrochloride. After iron-carbon treatment, the removal rate of COD reached 20%, and the final effluent reached the first-class standard of the national integrated wastewater discharge standard (GB 8978- 1996).
1.2.2 Fenton reagent treatment method
The combination of ferrous salt and H2O2 is called Fenton reagent, which can effectively remove refractory organic matter that traditional wastewater treatment technology can not remove. With the development of research, ultraviolet (UV) and oxalate (C2O42-) were introduced into Fenton reagent, which greatly enhanced its oxidation ability. Cheng Cangcang et al. [10] used Fenton reagent to treat pharmaceutical wastewater with TiO2 _ 2 as catalyst and 9 W low-pressure mercury lamp as light source, and achieved the effect of decolorization rate 100% and COD removal rate of 92.3%, and nitrobenzene compounds decreased from 8.05 mg/L to 0.41mg/L.
1.2.3 This method can improve the biodegradability of wastewater and has a good removal rate of COD. For example, Balcioglu used ozone oxidation to treat three kinds of antibiotic wastewater. The results show that not only the ratio of BOD5/COD is increased, but also the removal rate of COD is over 75%.
1.2.4 oxidation technology
Also known as advanced oxidation technology, it brings together the latest research results of modern optics, electricity, acoustics, magnetism, materials and other similar disciplines, mainly including electrochemical oxidation, wet oxidation, supercritical water oxidation, photocatalytic oxidation, ultrasonic degradation and so on. Among them, ultraviolet catalytic oxidation technology has the advantages of novelty, high efficiency and no selectivity to wastewater, and is especially suitable for the degradation of unsaturated hydrocarbons. The reaction conditions are mild and there is no secondary pollution, so it has a good application prospect. Compared with ultraviolet, heat and pressure treatment methods, ultrasonic treatment of organic matter is more direct and requires less equipment. As a new treatment, it is attracting more and more attention. Xiao Guangquan et al [13] used ultrasonic-aerobic biological contact method to treat pharmaceutical wastewater. Under the condition of ultrasonic treatment for 60 s and power of 200 w, the total COD removal rate of wastewater reached 96%.
1.3 biochemical treatment
At present, biochemical treatment technology is widely used in the treatment of pharmaceutical wastewater, including aerobic biological method, anaerobic biological method and aerobic-anaerobic combined method.
1.3. 1 aerobic biological treatment
Because pharmaceutical wastewater is mostly high-concentration organic wastewater, it is generally necessary to dilute the original solution when aerobic biological treatment is carried out, so it consumes a lot of electricity and has poor biodegradability, so it is difficult to discharge it directly after biochemical treatment. Therefore, aerobic treatment alone is not much, and pretreatment is generally needed. Commonly used aerobic biological treatment methods include activated sludge method, deep well aeration method, adsorption biodegradation method (AB method), contact oxidation method, sequencing batch batch batch activated sludge method (SBR method), circulating activated sludge method (CASS method) and so on.
1.3.2 anaerobic biological treatment
At present, anaerobic treatment is the main method to treat high-concentration organic wastewater at home and abroad, but the effluent COD after anaerobic treatment alone is still high, so post-treatment (such as aerobic biological treatment) is generally needed. At present, it is still necessary to strengthen the development and design of high-efficiency anaerobic reactors and conduct in-depth research on operating conditions. Upflow anaerobic sludge bed (UASB), anaerobic composite bed (UBF), anaerobic baffled reactor (ABR) and hydrolysis method have been successfully applied to the treatment of pharmaceutical wastewater.
(2) UBF Famaiwenning and others made a comparative experiment between UASB and UBF. The results show that UBF is a practical and efficient anaerobic bioreactor, which has the characteristics of good mass transfer and separation effect, large biomass, many kinds of organisms, high treatment efficiency and strong operation stability.
(3) Hydrolytic acidification method
Hydrolysis tank is called hydrolysis upflow sludge bed (HUSB), which is an improved UASB. Compared with the full-process anaerobic tank, the hydrolysis tank has the following advantages: it does not need to be sealed and stirred, and there is no three-phase separator, which reduces the cost and is beneficial to maintenance; It can degrade macromolecules and refractory organic substances in sewage into small molecules and biodegradable organic substances, and improve the biodegradability of raw water; Rapid reaction, small pool, less capital investment and less sludge. In recent years, hydrolysis-aerobic process has been widely used in pharmaceutical wastewater treatment. For example, a biopharmaceutical factory uses hydrolytic acidification-two-stage biological contact oxidation process to treat pharmaceutical wastewater, which runs stably and has obvious organic matter removal effect. The removal rates of COD, BOD5 and SS are 90.7%, 92.4% and 87.6% respectively.
1.3.3 anaerobic-aerobic combined treatment process
Because aerobic treatment or anaerobic treatment alone can not meet the requirements, anaerobic-aerobic, hydrolytic acidification-aerobic combined processes are obviously superior to single treatment methods in improving the biodegradability, impact resistance, investment cost and treatment effect of wastewater, so they have been widely used in engineering practice.
2 pharmaceutical wastewater treatment process and selection
The water quality characteristics of pharmaceutical wastewater make it impossible for most pharmaceutical wastewater to reach the standard by biochemical treatment alone, so it is necessary to carry out necessary pretreatment before biochemical treatment. Generally, regulating tanks should be set up to regulate water quality, water quantity and pH, and some physicochemical or chemical methods should be adopted as pretreatment processes according to the actual situation, so as to reduce ss, salinity and partial COD in the water, reduce biological inhibitory substances in the wastewater, improve the biodegradability of the wastewater, and be beneficial to the subsequent biochemical treatment of the wastewater.
The pretreated wastewater can be treated by anaerobic and aerobic processes according to its water quality characteristics. If the requirements for wastewater are high, post-treatment should be continued after aerobic treatment. The selection of specific process should comprehensively consider the nature of wastewater, treatment effect of process, capital construction investment, operation and maintenance and other factors, so as to make it technically feasible, economical and reasonable. The overall process route is pretreatment-anaerobic-aerobic-(post-treatment) combined process. For example, Chen Minghui et al. used the combined process of hydrolytic adsorption-contact oxidation-filtration to treat the comprehensive pharmaceutical wastewater containing artificial insulin, and the treated effluent quality was better than the first-class standard of GB 8978- 1996. Chemical pharmaceutical wastewater was treated by air flotation-hydrolysis-contact oxidation process, antibiotic wastewater was treated by composite micro-oxygen hydrolysis-composite aerobic-sand filtration process, and high-concentration Chinese medicine extraction wastewater was treated by air flotation-UBF-CASS process, all of which achieved good treatment results.
3. Recycling of useful substances in pharmaceutical wastewater
Promote cleaner production in the pharmaceutical industry, improve the utilization rate of raw materials and the comprehensive recovery rate of intermediate products and by-products, and reduce or eliminate pollution in the production process through technological transformation. Due to the particularity of some pharmaceutical production processes, their wastewater contains a lot of recyclable substances. To treat this kind of pharmaceutical wastewater, we must first strengthen the material recovery and comprehensive utilization. For example, Zhejiang Yiwu Huayi Pharmaceutical Co., Ltd. recovered about 30% of (NH4)2SO4 and NH4NO3 by fixed scraping film evaporation, concentration and crystallization as fertilizers or ammonium salts in its pharmaceutical intermediate wastewater, which had obvious economic benefits. A high-tech pharmaceutical enterprise uses stripping method to treat production wastewater with high formaldehyde content. Formaldehyde gas can be made into formalin reagent after recovery, and can also be used as boiler heat source for incineration. By recycling formaldehyde, resources can be continuously utilized, and the investment cost of the treatment station can be recovered within 4 ~ 5 years [33], realizing the unification of environmental benefits and economic benefits. But generally speaking, pharmaceutical wastewater has complex components, difficult recovery, complex recovery process and high cost. Therefore, advanced and efficient comprehensive treatment technology of pharmaceutical wastewater is the key to completely solve the sewage problem.