Several advanced sewage treatment technology introduction

First, the continuous circulation aeration system (CCAS)

A, CCAS process profile

The CCAS process, the Continuous Cycle Aeration System, is a continuous influent SBR aeration system. This process is based on SBR (Sequencing Batch Reactor, Sequencing Batch Processing). As early as 1914, SBR technology was successfully researched and developed, but it was difficult to popularize and apply it in large-scale sewage treatment plants because of the troublesome manual management, backward monitoring methods and easy aeration of aerators. SBR process has been generally considered suitable for small-scale wastewater treatment plant. Into the 60's, automatic control technology and monitoring technology has developed rapidly, the new non-clogging microporous aerator has also been successfully developed, for a wide range of intermittent treatment to create the conditions. In 1968, the University of New South Wales in Australia and the United States ABJ company to develop a "batch reactor system using continuous water, periodic drainage, delayed aeration aerobic activated sludge process." In 1986, the U.S. EPA formally acknowledged that CCAS is an innovative alternative technology (I / A), becoming the most advanced computer-controlled biological phosphorus and nitrogen removal process. CCAS process of sewage treatment less demanding, only the gap 15mm mechanical grille and grit chamber. The core of biological treatment is the CCAS reaction tank. The functions of phosphorus removal, denitrification, degradation of organic substances and suspended solids are all completed in this tank, and effluent can reach the standard discharge. The pretreated effluent continuously enters the pre-reaction cell at the front of the reaction cell, where most of the soluble BOD in the effluent is adsorbed by the activated sludge microorganisms and removed together from the perforations in the lower part of the main and pre-reaction zones Low flow rate (0.03-0.05m / min) into the reaction zone. In the main reaction zone, the wastewater is operated under the procedures of "Aeration, Idle, Settle, and Decant" to complete the carbon removal during the "aerobic-anoxic" Nitrogen, and in the "aerobic - anaerobic" repeated phosphorus removal completed. The duration of the process and the operation of the corresponding equipment are prepared in advance, and adjustable procedures, centralized control by the computer.

The unique structure and mode of operation of the CCAS process make it unique in its craftsmanship:

(1) aeration, sewage and sludge in a perfectly mixed state to ensure that the BOD, COD removal rate, the removal rate of up to 95%.

(2) The repeated operation mode of "aerobic-anoxic" and "aerobic-anaerobic" enhanced the phosphorus absorption and nitrification-denitrification, which made the nitrogen and phosphorus removal rate reach more than 80% .

(3) When the sedimentation, the entire CCAS reaction tank is in a completely ideal sedimentation state, making the water suspension (SS) extremely low and the low SS value also ensures the phosphorus removal effect. The disadvantage of CCAS technology is that each tank runs intermittently at the same time. It is almost impossible to control by hand. It is totally computer-controlled. It has high requirements on the quality of management staff in the treatment plant and stricter requirements on design, training, installation and commissioning.

B, domestic and international urban sewage treatment plant development overview

Water is an important factor in economic development and social sustainable development. With the continuous expansion of urban size and population growth, water pollution has become a major problem. Urban sewage is an important reason for the pollution of rivers and lakes and waters and is one of the main reasons that restrict the sustainable development of many cities. "Environmental Protection" is China's basic national policy, and its goal of sustainable development in 2000 formulated in its 2000 governance objectives requires centralized treatment of urban sewage by 20%. At present, our country is in a period of great development of urban sewage treatment. In particular, with the implementation of the national strategy of developing the western region, the protection of the environment and ecology in the central and western regions of China has been put on the top agenda. Urban domestic sewage treatment has drawn more and more attention since the Industrial Revolution 200 years ago. Urban sewage treatment rate has become an important symbol of regional civilization or not. For nearly 200 years, urban sewage treatment has evolved from primary natural treatment and simple primary treatment to using advanced technologies to deeply treat sewage and reuse it. From the traditional activated sludge process, oxidation ditch process development to A / O, A2 / O, AB, SBR (including CCAS process) and other processes, in order to achieve different effluent requirements. China's urban sewage treatment relative to the developed countries, started later, the current urban sewage treatment rate of only 6.7%. While we vigorously arouse advanced foreign technologies, equipment and experience, we must, in light of the development of our country, especially the actual conditions in the area, explore a suitable urban sewage treatment system suitable for our country.

Combined with the actual situation in our country, with reference to foreign advanced technology and experience, the construction of urban sewage treatment plant should meet the following development directions:

(1) Total investment province. As a developing country, China needs a very large capital for its economic development. Therefore, strict control of the total investment on the national economy is of great benefit.

(2) low operating costs. Operating costs is an important factor in the normal operation of sewage treatment plants, is to judge the merits of a set of one of the main indicators.

(3) covers the province. With a large population in our country, the per capita land resources are extremely scarce. Land resources are an important factor in the development and planning of many cities in our country.

(4) nitrogen and phosphorus removal effect. With the eutrophication of large-scale water environment in our country, the denitrification and dephosphorization of sewage has become an urgent problem. China's latest implementation of the "Integrated Wastewater Discharge Standard" (GB8978-1996) also clearly applicable to all sewage units, very strictly set the phosphate emission standards and ammonia emission standards. This means that the vast majority of urban sewage treatment plants in the future should consider the issue of nitrogen and phosphorus removal.

(5) modern combination of advanced technology and environmental engineering. The emergence and improvement of modern advanced technology, especially computer technology and automatic control system equipment, have provided strong support for the development of environmental engineering. At present, most advanced sewage treatment plants in developed countries adopt advanced computer management and automatic control systems to ensure the normal operation of sewage treatment plants and stable qualified effluent, while our country is still relatively backward in this respect. Computer control and management will also be the direction of the development of China's urban sewage treatment plants.

C, several processing system technology comparison

In order to select the most reliable and technically most cost-effective and most manageable urban sewage treatment system in our country, we have researched the mature experience and development trend of WWTPs at home and abroad based on the actual situation in our country and compared them with each other. At present, most of the domestic and foreign urban sewage treatment plant treatment process using a secondary treatment and secondary treatment. A treatment is the use of physical methods, mainly through the grid interception, precipitation and other means to remove large suspended solids in the waste water and sand and other substances. This treatment process has matured at home and abroad, little difference. Secondary treatment is the use of biochemical methods, mainly through microbial life movements and other means to remove suspended solids in wastewater, dissolved organic matter and nitrogen, phosphorus and other nutrients. At present, there are many ways to deal with this process. In summary, typical processes include traditional activated sludge, oxidation ditch, A / O or A2 / O processes, SBR and CCAS processes. At present, these several representative processes have practical applications both at home and abroad.