关于环境污水处理Cyclic Activated Sludge System（CASS）的英语文献

关于环境污水处理Cyclic Activated Sludge System（CASS）的英语文献

给你些很不错的英语文献和网站吧
http://web.deu.edu.tr/atiksu/ana58/cass.html
CASS™ (Cyclic Activated Sludge System)...
Brief History of Sequencing Batch Reactors...
Activated sludge is the most widely used biological wastewater treatment process in the developed world, treating both sewage and a variety of industrial wastewaters. Batch operation of the activated sludge process is nothing new. During the early development of the activated sludge process in the United Kingdom by Adern and Lockett around 1914, plants were operated using fill-and-draw or interrupted batch feed methods. These researchers firmly established the concept of operating a single reactor basin using repetitive cycles of aeration, settlement and discharge of treated effluent. Around 1956, during the development of oxidation ditch technology, Pasveer incorporated interrupted and continuously fed batch treatment principles. Further advancements to the oxidation ditch fed-batch treatment then too place by incorporating a rectangular basin configuration. By the late 1970's, the generic sequencing batch reactor (SBR) was well established and many small plants were in operation. A major development took place in 1978 with the incorporation of a pre-react zone within the SBR to control filamentous sludge bulking. Further refinements of SBR processes took place mainly in Australia and the United States and has led to the wide scale application of the technology worldwide. The shortfalls of the original design have led to the development of the present state-of-the-art CASS™ Sequencing Batch Reactor. While SBRs have generally been classified by the water industry for small or medium scale applications, CASS™ has found application in large scale municipalities ( 50 MGD or 400,000 + population equivalent ) and the modular expansion, retrofit or upgrading of existing wastewater treatment facilities.
CASS™ Process Components...
CASS™ is a combination of a biological selector and variable volume process reactor. The process operates with a single sludge in a single reactor basin to accomplish both biological treatment and solids-liquid separation. CASS™ is by design and operation with municipal wastewaters, a biological nutrient removal process, configured to function with filamentous sludge bulking control. A simple repeated sequence of aeration and non-aeration is used to provide aerobic, anoxic and anaerobic process conditions, which in combination with the aeration intensity, favor nitrification, denitrification and biological phosphorus removal.
The essential features of the CASS™ technology are the plug-flow initial reaction conditions and the complete-mix reactor basin. Each CASS™ reactor basin is divided by baffle walls into three sections (Zone 1: Selector, Zone 2: Secondary Aeration, Zone 3: Main Aeration). For typical domestic wastewater treatment applications, these sections are in the approximate proportions of 5%, 10%, and 85%. Sludge biomass is continuously recycled from Zone 3 to the Zone 1 selector to remove the readily degradable soluble substrate and favor the growth of floc-forming microorganisms. System design is such that the sludge return rate causes an approximate daily cycling of biomass in the main aeration zone through the selector zone. The mechanisms of Zone 1 and the internal sludge recycle eliminate the requirement for separate fill-ratio selectivity, anoxic, and anaerobic mixing periods. The selector is self-regulating for any load condition and operates under anoxic and anaerobic reaction conditions during non-aerated periods. Polishing denitrification and enzymatic transfer of available substrate during enhanced biological phosphorus removal is also achieved in the selector zone. The complete-mix nature of the main reactor provides flow and load balancing and a tolerance to shock or toxic loadings, and the process prevents solids washout during peak or wet weather hydraulic surges.
Process Cyclic Operation...
CASS™ utilizes a simple repeated time-based sequence which incorporates :
FILL-AERATION (for biological reactions)
FILL-SETTLE (for solids-liquid separation)
DECANT (to remove treated effluent)
Completion of these three operations constitute a cycle which is then repeated. The sequence above can also include a FILL, FILL-MIX, FILL-REACT, and REACT if required.
During the period of a cycle, the liquid level inside the reactor basin rises from a set bottom water level in response to a varying wastewater flow rate. Aeration ceases at a predetermined period of the cycle to allow the biomass to flocculate and settle under quiescent conditions. After a specific settling period, the treated effluent supernatant is removed (decanted), using a moving weir decanter. This operation returns the liquid level in the reactor basin to the bottom water level. Surplus solids are wasted as required to maintain the biomass MLSS at the required level. Solids wasting after settling enables waste sludge concentrations in excess of 10,000 mg/L to be removed.
Fill - Aeration...
The FILL-AERATION (react) operation refers to the air-on time of the process cycle. During this period, influent is received into the basin through the selector zone where it contacts with the biomass recycled from the main aeration zone. Complete-mix reaction conditions occur in Zone 3 during this variable volume operational period.
Fill - Settle...
This refers to the first part of the air-off time period when quiescent settling conditions are created in Zone 3 for solids-liquid separation. The activated sludge solids form a sludge-level interface which progressively falls toward the floor of the basin. The flocs adhere together and the mass settles as a blanket leaving a clear supernatant. At the end of the aeration period, the sludge is at a uniform concentration. During the initial settling period, the sludge undergoes internal flocculation due to the residual mixing energy within the basin. As this energy dissipates the sludge interface forms and settles as a blanket. Dense solids fall through the formed mass to settle on the basin floor. There is an initial slow settling velocity which increases and then gradually falls off due to the compressive accumulation of solids on the basin floor. Zone settling velocity is a function of the initial solids concentration, basin depth, total area of the basin and nature of the biological solids. A top water level solids concentration of around 3,500 mg/L will typically settle to form a layer of sludge having a mean concentration of around 10,000 mg/L. CASS™ facilities are sized and configured to operate with inflow into the basin during the settle phase of the cycle. Biomass is returned from the main aeration zone to the selector zone to promote selectivity and create anoxic/anaerobic conditions.
Decant ( Effluent Removal )...
Inflow to the basin undergoing decanting (effluent withdrawal) is interrupted and directed to an alternate basin in a multi-basin facility or stored in a pump well in a single basin facility. The weir trough of the decanter is situated above top water level for both aeration and settling phases to prevent the accidental discharge of mixed liquor suspended solids. When operated during the decant phase of the cycle, the decanter travels down at an initial fast speed. Interaction with the liquid level is detected by a level indicator float switch which causes the skimmer to proceed at its design rate of travel producing a constant rate of discharge of treated effluent from the basin. On reaching designated bottom water level, the decanter is reversed to its rest position at the initial fast speed.
Idle...
In practice, decanting will always be less than the allocated time available. This residual time is designated as IDLE and can be used as a period of inflow without aeration or reaction. The IDLE sequence begins 4 minutes after the skimmer has traveled in the reverse up direction and finishes at the end of the designated decant period. Biomass is recycled from Zone 3 to the selector zone to promote selectivity and create anoxic/anaerobic conditions.
Respiration Rate Control (RRC™)...
Dissolved oxygen is a necessary requirement for the biological oxidation reactions which take place with the CASS™ process. Residual dissolved oxygen occurs as a result of oxygen which is not used by the microorganisms in the biomass. Too much dissolved oxygen in the CASS™ process is wasteful of energy and may inhibit biological nutrient removal mechanisms. A simple control method has been developed to ensure optimum biological reaction conditions take place and valuable energy is not wasted. Advantage is taken of the fact that the CASS™ process conforms to a complete-mix reaction model. This also means that CASS™ provides a very stable reaction environment when compared to other conventional plug-flow activated sludge, extended aeration, contact stabilization, or sequencing batch reactor systems. A dissolved oxygen sensor is used to measure changes in biomass oxygen demand. For example, a reduction in the oxygen load demand to a CASS™ basin will automatically cause a lowering of the aeration intensity (air supply) so that the excessive dissolved oxygen concentrations are prevented. Conversely, an increase in load demand will cause an increase in aeration intensity so that the metabolic activity of the biomass, as registered by its propensity to use oxygen, is matched with the corresponding aeration intensity rate of air feed into the reaction basin.
RRC™ directly interacts with the best sensor which is available for the control of air into the process. The system is an in-basin respirometer. Simply stated, low oxygen demand caused by low loadings during diurnal, or other variations can now be directly matched to energy use. The biomass senses the oxygen requirements which are needed for the process. The dissolved oxygen sensor interprets that message and causes interaction with the rate of introduction of air into the reaction basin.
The CASS™ RRC™ is simple and direct. RRC™ has direct benefits :
- Saves operating costs.
- Reduction of waste activated sludge.
- Improved nutrient removal performance.
http://www.energymanagertraining.com/textiles/pdf/Cyclic%20Activated%20Sludge%20Technology.pdf
http://www.sbrcass.com/process.htm
http://www.freepatentsonline.com/7083324.html
http://books.google.com.sg/books?id=lyM6SgHXimEC&pg=PA657&lpg=PA657&dq=cyclic+activated+sludge+system&source=web&ots=RZhwp9iKY3&sig=wpKRxcRFOj0qWKz5pJSqZApCgBU&hl=en
http://www.sawea.org/Workshops/Presentation2005/MainSession/Nov30/LUCAS%20ACTIVATED%20SLUDGE%20TECH.%20-%20WATERLEAU.pdf
http://books.google.com.sg/books?id=Cnic0Co2V2QC&pg=PA351&lpg=PA351&dq=cyclic+activated+sludge+system&source=web&ots=wTkt1_5Rji&sig=lv5pGQArXqqESB7M1wr2AoE3zfI&hl=en