According to monitoring, groundwater in most cities in the country has been polluted to a certain extent by punctate and surface pollution and has been increasing year by year. The increasingly serious water pollution has not only reduced the use of water bodies, further exacerbated the contradiction of water resources shortage, and had a serious impact on the sustainable development strategy being implemented in China. It has also seriously threatened the drinking water safety of urban residents and the people. Health.
Taking Xi'an as an example, in 2000, the built-up area of â€‹â€‹Xi'an City has reached 187k with a population of 3.26 million. According to Xi'an Drainage Planning (1995-2010), Xi'an downtown area is divided into six sewerage systems. The current total discharge volume is about 800,000/d, and the sewage treatment rate is about 34%.
The current drainage service area in Xiâ€™an City is approximately 152.2 kilograms. Apart from the confluence of the old urban area and the northeastern suburbs, the rest of the drainage pipeline is dominated by the diversion system. The total length of the drainage network is about 835.4km. Of these, the sewage pipeline is 490km (including the current confluence), the penetration rate is 67%, the rainwater drainage canal is 345.4km, the penetration rate is 45%, and the canal density is about 5.5km/k. The current sewage pipeline network accepts urban sewage. With a volume of about 800,000/d, two municipal sewage treatment plants have been built, with a total treatment capacity of 270,000/d, and a sewage treatment rate of 34%, of which the Shishiqiao WWTP is 150,000/d, and the Dengjiacun WWTP is 120,000/d. d.
At the same time, Xiâ€™an is a city lacking water resources. The per capita possession of surface water resources in the city is less than 350, which is only 1/6 and 1/20 of the national and world per capita possession, which is much lower than the internationally recognized maintenance of a regionâ€™s socio-economic environment. The critical value of environmental demand of 1000, with the acceleration of urban modernization in the future, water shortages will affect urban water supply. Sewage is a kind of stable and reliable water resource that can be recycled and reused. It is an important way to solve urban water shortage. After advanced treatment, the sewage can be used for industrial and mining enterprises, municipal sanitation, landscaping and urban river landscapes.
Second, the status of sewage treatment technology
The current sewage treatment generally adopts the traditional sewage treatment process, adopts the flocculation sedimentation and sand filtration system, and designs and adds the ferric chloride agent to the A2/O system final sedimentation tank and the water well, strengthens the biological phosphorus removal, and reduces the final sedimentation pool. Phosphorus concentration in water. After the sedimentation, the effluent passes through the lift pump station to the sand filter tank, and the air-water backwash filter tank is used. After filtering, the water is sent to the clear water tank, and the pressure is added to the reuse water pipe network. Such wastewater treatment plants as Dengjia Village in Xiâ€™an, Xishi Bridge Wastewater Purification Center, Xiâ€™an Textile City Wastewater Treatment Plant, Xiâ€™an Dianzicun Wastewater Treatment Plant, etc. basically all use this wastewater treatment system.
In a conventional sewage treatment system, a sedimentation tank is used for the coagulation of the sewage, which does not form a good condition for particle agglomeration, and does not generate agglomerated floc, resulting in a low solid-liquid separation efficiency.
Third, new sewage treatment technology - granulation fluidized bed sewage treatment technology
1, the basic concept of fluidized bed
When a fluid passes up through the particle bed at different speeds, the following conditions may occur. Fixed bed - When the velocity of the fluid is low, the fluid flows only through the gap between the stationary particles. This bed is called a fixed bed. Initial or critical fluidized bed - When the flow rate of the fluid increases to a certain degree, the particles begin to loosen, the position of the particles is also adjusted within a certain interval, the bed is slightly expanded, but the particles are still not free to move. The layer is in an initial or critical fluidized state; the fluidized bedâ€”if the flow rate of the fluid rises until all the particles are just suspended in the upward flowing gas or liquid and can perform random motion, the friction between the particles and the fluid Just balanced with its net gravity.
After this, the bed height L will increase with increasing flow rate. This bed is called a fluidized bed; a rare-phase transport bedâ€”if the flow rate rises to a certain limit value, the interface on the fluidized bed disappears, and the particles are dispersed and suspended in the air flow, which is carried away by the air flow. The seed bed is called a rare-phase transport bed.
2, the characteristics of fluidized bed
The gas-solid motion in the fluidized bed is much like a boiling liquid and in many ways exhibits liquid-like properties. The fluidized bed has a liquid-like flow behavior, and solid particles can be ejected from the orifices of the vessel wall. And like a liquid, flows from one container to another; for example, objects less dense than the bed can be easily pushed into the bed, and when released, it springs up and floats on the surface of the bed; When the vessel is tilted, the upper surface of the bed remains horizontal, and when the two beds are in communication, their bed surfaces self-adjust to the same level; the pressure change between any two sections in the bed is approximately equal to the area between the two sections. Gravity of layers.
3, granulation type fluidized bed sewage treatment technology
The self-granulation fluidized bed is a new type of water treatment technology brought forward by applying quasi-steady state operation principle and reaction engineering theory of chemical engineering and combining the practical experience of the coagulation project. The main technical specifications of this technology are as follows:
Â§ Chemical coagulation in the first stage is completed in the hydraulic mixer, and the hydraulic retention time is less than 1min;
Â§ The self-granulation reaction is completed in an upward flow mechanical stirring device, the mechanical stirring strength (G value) is about 30s-1, and the hydraulic retention time is 10-20min;
Â§ The solid-liquid separation is completed in the solid-liquid separation zone on the fluidized bed of the self-granulation fluid, and the hydraulic retention time is 5-10 min;
Â§ Sludge is automatically concentrated at the same time as the separation process. Inorganic suspended particulates dominate the system, the water content of the separated sludge can reach 80% to 85%, and the organic components and inorganic suspended matter coexist in the system. The water content of the separated sludge is 90. ~95%;
Â§ The concentration of SS in the separated water is usually less than 5mg/L, and the concentration of SS in the separated water is usually less than 1mg/L.
Â§ Scope of application: Raw water (sewage, waste water) SS concentration 1,000-20,000mg/L, COD not more than 1,000mg/L.
The technology is implemented in specially designed integrated devices. Its main features are short hydraulic retention time, small size, small footprint, wide applicability, flexible use, high treatment efficiency, and simultaneous solid-liquid separation and sludge concentration.
The technology can be widely used for high turbidity water treatment, high suspended solids wastewater treatment and reuse, sludge concentration in water plants and municipal wastewater plants, wastewater treatment in construction sites, and disaster relief water treatment.
4. Industrialization prospect of granulation type fluidized bed sewage treatment technology
In the process of actively implementing the â€œNational Ecological Environment Construction Planâ€, comprehensive utilization of water resources, water resources regeneration, and water pollution control are particularly important links. Therefore, the market capacity of water treatment equipment will greatly increase, and market competition will be the competition of technology level, applicability and price. The series of equipment adopting this technology has the characteristics of advanced technology, small size and low cost, and can be produced in accordance with the requirements of users. It will be highly competitive in the environmental protection equipment market. The main users of the equipment will be the industrial water treatment, wastewater treatment, industrial water recycling, small and medium-sized water supply and wastewater treatment plant sludge treatment of small and medium-sized industrial enterprises.
The technology has successively been in the Garden of Yellow River Garden in Zhengzhou (high turbidity water treatment), Dengjiacun sewage treatment plant in Xi'an (digestion sludge dewatering), Shaanxi Lueyang Iron and Steel Plant (gas scrubber wastewater and beneficiation wastewater treatment), Shenzhen Water Company (precipitation The semi-productive experiment was conducted on the pool mud treatment. On this basis, the equipment was repeatedly improved, and the invention patent for the High-Efficiency Solid-Liquid Separator was applied. At present, it has successfully passed the actual examination of the invention patent, and the technology has been recognized by the State Patent Office. protection.
The patented technology has so far been used in Xi'an Xijiao Thermal Power Plant for the recovery and reuse of ash-washing wastewater. The Beishiqiao Wastewater Treatment Center in Xiâ€™an City is used for the separation of activated sludge mixture and sludge concentration in Qujiang Water in Xiâ€™an City. The plant, the Zaozhuang City Water Supply Company of Shandong Province and the Binzhou City Water Supply Company of Shandong Province were used for the regeneration and reuse treatment of production wastewater, and achieved good practical application results. Therefore, this technology has a huge market and industrialization prospects.
IV. Research status of granulation fluidized bed technology for sewage treatment
In recent years, the granulation type fluidized bed has been developed and applied in the water treatment process, and in particular, the research on the granulation fluidized bed for the purpose of solid-liquid separation of sludge dewatering, high turbidity raw water, and high-concentration waste liquid has caused domestic The concern of the external water treatment industry. Many experts and scholars abroad have begun to conduct in-depth research on this technology, and there have been many research results. However, the technology started late in the country and still needs to be improved!
There are mainly two aspects of the research on granulation fluidized bed technology. One is to study from experiment or practice, mainly on the application of granulation fluidized bed technology in practice. For example, Prof. Wang Xiaochang's â€œTest Measurement of Particle Flow in Self-Pelletizing Fluidized Bedsâ€ and Pan Yongzhangâ€™s â€œExperimental Study on the Treatment of Car Washing Wastewater in the Process of Granulating Fluidized Bed Technologyâ€, etc.; the other is theoretical research. This is mainly to study the mechanism of particle flocculation in fluidized bed and simulate the solid-liquid flow in fluidized bed. For example, Prof. Huang Tinglin's "Balanced Fluidized Bed Movement Balance" and Professor Wang Xiaochang's "Kinetic study of fluidized pellet bed process. Development of amathe matical model". However, in general, at present, China's research on this technology mainly remains in experimental research.
Fifth, application of granulation fluidized bed technology for sewage treatment
Since the granulation fluidized bed technology is capable of efficient solid-liquid separation, it is widely used for high turbidity water treatment, high suspended solids wastewater treatment and reuse, sludge concentration in water plants and municipal wastewater plants, and wastewater treatment at construction sites. Disaster rescue water treatment.
The use of granulation-type high-efficiency solid-liquid separation technology to treat industrial wastewater with high suspended solids concentration is superior to traditional treatment processes in the following aspects:
(1) The treatment efficiency is high and the effect is good. The hydraulic retention time of the main equipment of the high-efficiency solid-liquid separation device is about 9 minutes. With the mixing of the front water pump and the pipeline, the total hydraulic retention time is within 10 minutes, which is much longer than that required by the traditional treatment process. The time is short. After such a short treatment time, the effluent turbidity of the device has met the industrial reuse water quality requirements, and the required amount of inorganic coagulant is lower than the traditional coagulation sedimentation process.
(2) The separation sludge has a low moisture content and does not require special concentration treatment. The separation sludge of the high-efficiency solid-liquid separation device has very good dewatering performance. After it stays in the mud storage area for more than 1 hour, the moisture content of the sludge is reduced to less than 85% without specialization. Concentrate for final sludge treatment.
(3) Operational flexibility, can meet different processing needs, high-efficiency solid-liquid separation device can not only carry out continuous treatment of wastewater, but also can perform intermittent treatment, and has strong anti-impact load capacity, and it is also basic if the rated load exceeds 50%. Can guarantee the treatment of water quality.
The following describes the application of fluidized bed in the treatment of industrial wastewater by taking the application of granulation fluidized bed technology in the treatment of car wash wastewater as an example:
With the continuous improvement of people's living standards, the number of cars is also rising, so the car wash industry has a huge market demand. Now, car wash yards of different sizes are scattered all over the country. However, most of the car wash sites do not have wastewater treatment and recycling facilities. The car wash water is discharged directly into municipal pipelines after simple sedimentation. This not only wastes water resources, but also Urban water environment caused a certain amount of pollution.
In view of the current status of water pollution and water waste in the car wash industry, various types of car wash wastewater reuse equipment have emerged on the market in recent years. Some based on multi-media filters, ceramic adsorption filter, ultrafiltration system retention, adsorption, screening principle to achieve the reuse of car wash wastewater treatment; some use conventional oil precipitation, filtration, disinfection methods. Although the effluent treated by these equipments can meet the requirements for the quality of car wash wastewater, its common shortcomings are large floor space, high construction and operating costs, and many difficulties in launching the market.
However, when the granulation fluidized bed technology is used to treat the car wash wastewater, after the car wash wastewater is treated by the fluidized bed device, the quality of the effluent water can reach the discharge standard of the car wash back water. The moisture content of the sludge produced by the granulation fluidized bed method is significantly lower than that produced by the conventional coagulation sedimentation method, and no sludge concentration equipment is required. In addition, the granulation fluidized bed method has the advantages of small occupied area, simple equipment structure, and low investment and operating costs compared with the traditional treatment process, so it is used in the reuse treatment of car wash wastewater, and has a broad market prospect. .
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