Essay on the sewage treatment aspects of chemical pharmaceutical

1, the necessity of sewage degreasing With the economic development and the improvement of people's living standards, the water quality of urban sewage is also changing, the sewage of animal and plant oils and mineral oils and other oily substances gradually increased. According to relevant information reports, by 2000, China has been built and put into operation about 180 urban sewage treatment plants, the design capacity of 1050 × 104m3 /d, of which the secondary biochemical treatment capacity of about 750 × 10 4m3 /d, most of these sewage treatment plants exist in the pollution of oily substances [1]; in particular, some of the small and medium-sized towns of sewage treatment plants, due to their water volume is relatively small, the water quality fluctuates greatly, and during the peak period of water consumption, a large amount of catering sewage enters the treatment plant, which has a serious impact on the normal operation of the sewage treatment plant. Southwest University of Science and Technology wastewater treatment plant, for example, the plant covers an area of 20 acres, the daily treatment capacity of 1 × 104m3 / d, serving a population of about 30,000 people, using an improved three-ditch oxidation ditch process. This wastewater treatment plant did not consider the oil substances in the influent water during the design process, but since its operation in May 2003, it has been found that the oil substances in the influent water have gradually increased, especially after the completion of the school teachers' apartments and the two students' canteens, and the situation has become even more serious. In the past three years, every winter, oil substances covered the whole surface of oxidation ditch, which seriously affected the oxygenation efficiency of oxidation ditch and the water quality condition of the effluent.Measurement of oil substances in the influent water found that the content was between 86mg/L and 420mg/L, in which the average content of oil in the influent water was 120mg/L in summer and 210mg/L in winter.2 Analysis of the oil removal methods of wastewaterAt present. domestic and foreign research methods for the treatment of oily wastewater are mainly the following three categories: chemical treatment method, physical treatment method and biochemical treatment method. Chemical treatment method mainly includes chemical coagulation, chemical precipitation, catalytic oxidation and the combined use of various methods; physical treatment method includes centrifugal separation, filtration and ultrafiltration, clarification and air flotation; biochemical method includes biological contact oxidation, biological rotary table method, activated sludge method and so on [2].2.1 Chemical treatment methodChemical treatment method mainly refers to the addition of a certain number of chemical substances, so that it is flocculation, precipitation, flocculation, precipitation, flocculation, precipitation, precipitation, etc., and the oil substances in the water. substances in the water to flocculation, precipitation or catalytic oxidation and other reactions, to achieve the purpose of removing the oil substances from the water. At present, in the process of oil removal from wastewater, the research of chemical method mainly focuses on the development of new flocculants [3-8]. Flocculants mainly include inorganic and organic flocculants, in terms of inorganic flocculants, Daqing Petrochemical General Plant Refinery has conducted a study on the application of iron salts in refinery wastewater treatment [3], which concluded that the addition of composite polymerization of ferro-aluminum in the flotation, in the flotation of the removal of oil at the same time, also has the role of sulfur removal. Organic flocculants mainly include nonionic, anionic, cationic, amphoteric organic polymers and other types, due to the large molecular weight, adsorption of suspended solids and colloidal ability, the formation of flocs with large dimensions, fast settling, low dosage, and produces a small amount of sludge, easy to dewater, and does not have a negative impact on the treated water, in recent years, is highly favored. In its application, has been mass-produced mainly polyacrylamide (PAM), polydimethyl diallylammonium chloride (PDMDAAC) and Mannian period reaction of cationic polyacrylamide. In the study of organic flocculants, Tang Shanfa et al. use propylene amide and dimethyldiallyl ammonium chloride, alkyl dimethyldiallyl ammonium chloride for poly***polymerization of polyacrylamide cationization and hydrophobicity modification and synthesized JH series of flocculants with good flocculation and turbidity removal, emulsion removal and removal of oil and the removal of organic matter [4]; Duan Hongwei et al. use of modified cyclohexyl cyclic propylene cationic polyether, etc. Duan Hongwei et al. utilized modified cyclic ethyl cyclopropyl cationic polyether and other RD-1 reversed-phase emulsion breaker synthesized by them to have better effect on the removal of oil from sewage [5]; in addition to this, there are also researches on the flocculants such as dithiocarbamates [6~8]. In recent years, wastewater oil removal methods have also been studied in the field of energy chemistry [9~12], such as the study of magnetochemical technology [9~11], and floating or dispersed oil in wastewater can be treated by using the method of magnetic particle in the oil film of the quilt and the method of magnetic particle filtration of the oil layer suspension. The former is to use some chemical substances on the surface treatment of magnetic particles, so that the surface is served with a layer of oleophilic and hydrophobic substances of the film, the magnetic species adsorption of oil, with a magnetic field to recover the magnetic species can be de-oiled; the latter is the use of adsorption of the oil film of the magnetic powder, or adsorption of oil in the magnetic species layer to filter the oil, through the magnetic field to fix the filtration layer, in order to increase the collision of the filtration layer and oil beads in the wastewater, the use of an alternating magnetic field. In addition, in electrochemistry [11,12], direct electrolysis, indirect electrolysis, electrochemical adsorption and desorption can be used to remove oil from the wastewater.2.2 Physical Treatment Physical treatment is the most widely used category of wastewater de-oiling system, and its core idea is to use physical methods to achieve the separation of oil and water. In the process of oil removal from sewage, the research of physical method mainly focuses on the research and development of oil-water separator, which includes flotation technology and flotation apparatus, cyclone technology and cyclone, membrane technology and membrane apparatus, etc.2.2.1 Flotation technology Flotation purification technology is a new technology of water treatment that is being intensively researched and continuously promoted at home and abroad [13~15]. Flotation oil removal is in the water through the air or other gases to produce fine bubbles, so that the water of some of the fine suspended oil beads and solid particles attached to the bubbles, with the bubbles together with the formation of slag floating to the surface of the water, so as to complete the solid-liquid separation of a new method of oil removal. According to the formation of bubbles in the water and bubble size differences, flotation treatment method can be broadly divided into four categories, namely, dissolved air flotation, induced flotation, electrolytic flotation and chemical flotation method, its detailed classification and the advantages and disadvantages of each method as shown in Table 1. Table 1 Classification of flotation treatment methods Method name Specific method Flotation causes Main advantages Main disadvantages Dissolved gas flotation method Pressurized dissolved gas flotation method Vacuum flotation method under pressure, so that the gas is dissolved in the sewage, but also under atmospheric pressure to release the gas, producing tiny bubbles. Under reduced pressure, the gas dissolved in the water is released to produce tiny bubbles. The size of the bubbles is small, uniform, stable operation, simple equipment, easy management and maintenance, high rate of oil removal stable upwelling, floc destroying the possibility of flocculent small, small energy consumption process is more complex, long residence time, equipment is huge, troublesome to operate the small amount of dissolved gas, the operation and the structure of the complexity of the induced flotation method of the mechanical drum flotation method of the impeller flotation method of the jet stream flotation method to allow the gas to pass through the myriad of tiny pore spaces or crevices to produce tiny bubbles. Impeller rotation generates negative pressure to inhale gas, and rely on its shear force to make the inhaled gas into small bubbles. Relying on the role of water jets to produce tiny bubbles in the sewage energy consumption is small, simple structure of the flotation chamber. Dissolved gas volume, short residence time, processing speed is higher than dissolved air flotation process, high oil removal efficiency, low cost of equipment, shock load resistance. Low noise, simple process, low overall energy consumption, small bubbles, oil removal efficiency is better than the impeller type need to add surfactant to form tiny bubbles, the scope of use is limited, easy to block the microporous. Flotation must be added flotation additives, bubble size is not uniform, may produce some invalid bubbles, manufacturing and maintenance trouble. Water injector requires high electrolytic flotation method electrolytic flotation method electroflocculation flotation method choose inert electrode, so that the sewage electrolysis produces tiny bubbles. Selection of soluble electrodes (Fe, Al, etc.) in the anode to produce tiny bubbles, in the cathode there is a coagulation effect of ions small bubbles, high oil removal rate. Small bubbles, flotation and flocculation at the same time, high oil removal rate high electrode loss, high operating costs. Ditto chemical flotation method Chemical flotation method relies on the chemical reaction between substances to produce tiny bubbles (generate CO2, O2). Low investment in equipment, the amount of bubbles is easy to control, especially for high suspended solids content of sewage sludge increased, labor-intensive. 2.2.2 Cyclone technology hydrocyclone is the use of oil and water density difference, in the liquid flow height of rotation by the unequal centrifugal force to achieve oil-water separation. The oily wastewater enters the cylinder vortex section tangentially and flows along the cyclone tube in axial spiral state. In the concentric reduction section, due to the contraction of the cone cross-section, so that the fluid speed up, and promote the formation of the spiral flow state forward, due to the difference in the density of oil and water, so that the water rotates along the pipe wall, while the oil beads move to the center. Fluid into the fine cone section, the cross-section continues to shrink, the flow rate continues to increase, small oil beads continue to move to the center of the oil core. Fluid into the parallel tail section, due to the constant velocity of the fluid flow, the upper section to produce a certain amount of back pressure, so that the low-pressure oil core to the overflow discharge, while the water is discharged from the outlet of the water purification. Its working principle is shown in Fig. 1. Fig. 1 Schematic diagram of the working principle of hydrocyclone Foreign hydrocyclone oil removal research began in 1967, after years of scientific research and engineering applications, has now entered a major technological development stage. At present, the U.S. Conoco, Krebs, Kvanemer, Mpe, Amoco, Australia BWN Vortoil Company, Sweden ALFALAVAL company have begun to produce oil-water cyclone separator. Many domestic research units and enterprises have also carried out the development of hydrocyclone, such as Xi'an Jiaotong University, Southwest Petroleum Institute, Sichuan University, Daqing Petroleum Institute, Dalian University of Science and Technology, Jianghan Petroleum Machinery Research Institute, Henan Petroleum Exploration Bureau Design Institute, Shengli Oilfield Design Institute, Dagang Oilfield Design Institute, Jiangdu Environmental Protection Equipment Factory, Shenyang Xinyang Machine Manufacturing Factory, etc. [16~22]. 2.2 .3 Membrane technology Membrane treatment technology is a recently emerged new technology for waste water degreasing [22,23], the core idea is to use semi-permeable membranes as a selective barrier layer, allowing some components to pass through while retaining other components in the mixture so as to achieve the purpose of separation of the general term for the technology. It has the advantages of simple equipment, convenient operation, no phase change, no chemical change, high treatment efficiency and energy saving, and has been increasingly emphasized as a unit operation in the process of wastewater degreasing. In the research and application of membrane technology, Tianjin Tian Membrane Technology Engineering Company has used hollow fiber ultrafiltration membrane treatment of oily wastewater research [23], indicating that the hollow fiber ultrafiltration membrane used for the treatment of pre-treated wastewater with low oil content is more desirable, while the untreated wastewater with a high oil content in addition to oil and turbidity effect is better; China Academy of Metrology and Research to deal with oily wastewater by using a kind of emulsification function of the membrane to achieve better results [24]. Achieved better results [24]. However, in the application of membrane technology, there are different degrees of membrane cleaning problems.2.3 Biochemical treatment method biochemical treatment is the use of microorganisms in the water to deal with organic pollutants in sewage, a process, the existing sewage treatment plant biological treatment unit, the oil in the sewage has a part of the removal efficiency, but the removal rate is low. The current application of biotechnology in wastewater degreasing mainly focuses on screening and optimization, cultivation and domestication of oleophilic microbial strains. Xinjiang environmental monitoring center through the use of catering services oily wastewater culture screening 28 strains of bacteria with strong oil removal capacity for research, found that it will be connected back to the sewage, the average oil removal rate of 68%, the preferred strains of bacteria connected back to the sewage 24h after the removal of 90%, while the same batch of sewage naturally stored for 10d after the removal of oil rate of only 29%. The use of selective cultivation of excellent strains of bacteria centralized rapid treatment can significantly improve the efficiency of such sewage treatment [25].3 Oil removal program for the exploration of the WKU sewage plant oil substances, in the winter of 2003 to 2005, we have used hydrodynamic scouring of the oxidation ditch surface and sand sedimentation tank before the lime throwing method for experiments. Although hydraulic flushing can temporarily make the oil on the surface of the oxidation ditch adsorbed on the surface of the sludge to precipitate down, but in the next operation stage the oil will be re-covered with the surface of the tank; sand sedimentation tank before the addition of lime can reduce the oil in the oxidation ditch, but lime at the same time will be part of the microorganisms will be inhibited, and the precipitated material produced by the sedimentation of the sand sedimentation tank is very difficult to precipitate down to the oxidation tank is easy to clog ditch micro-porous aerators, therefore the amount of injection is limited, while the dosage is limited. Therefore, the dosage is limited, and other flocculants have the problem of high price. In order to temporarily avoid the problem of anoxia in oxidation ditch, we remove the baffle plate of the weir of oxidation ditch, so that the floating oil pollution enters into the contact pool with the water, and it is salvaged at the beginning of the contact pool. It can be said that the above measures did not achieve the ideal oil removal purpose. When choosing the oil removal scheme, we also considered physical methods such as hydrocyclone, but failed to use it due to the space limitation between its fine grating and sand sedimentation tank as well as the troubles of expensive energy cost and the destination of the separated oil. Since the source of oil in the WKU wastewater plant is relatively single, we consider setting up a grease trap outside the two student cafeterias, and the separated oil and the driving rain from the cafeterias are treated together in a centralized manner; at the same time, we cultivate and domesticate oleophilic microorganisms in the oxidation ditch of the wastewater plant, and treat the rest of the oils through microbial technology, so as to achieve the purpose of saving costs and improving the efficiency of de-oiling.4 CONCLUSIONS4.1 De-oiling of the Wastewater Treatment Plant There are many methods, currently in the chemical, physical and biochemical treatment methods have been studied and applied. 4.2 Small and medium-sized towns of sewage treatment plants due to the existence of financial difficulties and other factors, in the design process is often not considered in the de-oiling facilities, and the operation of the oil pollution directly affects the treatment effect, so the implementation of its de-oiling measures must be combined with the specific circumstances of the plant. 4.3 For the source of the oil material is relatively single Urban wastewater treatment plant, the treatment from the source will play a simple, economical and practical effect.4.4 Microbial technology as an emerging technology, in the field of wastewater degreasing research and application is deepening, screening and optimization, cultivation and domestication of oleophilic microbial strains of small and medium-sized wastewater treatment plant degreasing has the advantages of energy saving, high efficiency and so on.