1、 Overview
Biological filter has always been the main process for secondary sewage treatment. According to materials from the Science and Technology Development Department of the Ministry of Construction, in the United States, where sewage treatment is advanced, there were approximately 4300 biological filter sewage treatment plants in 1975. The widespread adoption of biofilters is mainly due to their low cost and operating expenses, stable operation, and simple management. But with the improvement of effluent quality standards, simple biological filters can no longer adapt to the new effluent quality standards. After research by American health engineers, the addition of a contact aeration tank after a biofilter has significantly improved the effect and fully ensured the quality of the effluent. After more than 20 years of promotion and application since the 1980s, a mature TF/scT art has been formed. There are over fifty sewage treatment plants designed and renovated using this process in the United States, both in the South and North. The large-scale Salt Lake City sewage treatment plant has a designed water capacity of 237000 meters per day. The "ATs" process is a new technology developed by Shandong Linqu Oasis Environmental Protection Equipment Co., Ltd. in cooperation with relevant design institutes, drawing on TF/SC technology from the United States, and summarizing the operation of a 50000 ton daily sewage treatment plant in Linqu County. This process comprehensively utilizes the biological treatment mechanisms of anaerobic adsorption, aerobic attachment growth, and suspended growth, and is currently the most economical and practical new technology in the field of urban sewage treatment in China. Its advantages can be summarized as follows:
l、 The effluent quality is stable and reliable.
2. Low engineering cost and low power consumption.
3. Easy to operate and manage, with a wide range of applications.

2、 Process flow

Processing effect of each unit

3、 Process Description
1. Pre treatment: The sewage is treated with coarse and fine grids to remove floating debris and suspended solid particles, and large particles of mud and sand are removed in the sedimentation tank to avoid system blockage and equipment wear.
2. Hydrolysis tank: It is a new type of upflow sludge bed with a hydraulic retention time of 2.4-4.0 hours, and its biochemical reaction is stable in the hydrolysis and acid production stages. This section does not require energy consumption, which significantly removes pollution load and decomposes insoluble organic matter into soluble organic matter, greatly improving the biodegradability of sewage and making it more suitable for subsequent aerobic treatment.
3. High load biofilter: It is a non submerged biofilm process, in which a rotating water distributor is driven by the water pressure difference at the outlet of the hydrolysis tank, using pebbles as the biological carrier. Microorganisms attach and grow on pebbles to form biofilms, which are constantly updated and metabolized under the erosion of water flow. In this section, the goal of degrading most of the dissolved organic matter can be achieved without consuming electricity.
4. Aerated solid contact tank: Mix the returned sludge from the secondary sedimentation tank with the effluent from the biological filter tank for aeration. Utilize the biological activity of the returned sludge to perform biological flocculation and adsorption under aerobic conditions. The biofilm with poor cohesiveness of small particles and colloids in the wastewater is flocculated into easily sedimentable substances, which further degrade organic pollutants in the wastewater while exerting adsorption flocculation effect.
5. Secondary sedimentation tank: It is an efficient flocculation and clarification tank, with a flocculation well at the center of the tank to further flocculate dispersed particles and broken flocs, ensuring the effluent effect of the secondary sedimentation tank.
6. Sludge treatment: Sludge is anaerobically discharged in the hydrolysis tank, and then transported to the dewatering room for dewatering through the sludge concentration tank, greatly reducing the investment and cost of sludge treatment.

4、 Economic analysis (taking daily processing of 50000 tons as an example)
Investment per ton of water: approximately 550 yuan
Ton of water occupies an area of approximately 0.7 square meters
Direct operating cost per ton of water: approximately 0.22 yuan
Among them:
Electricity fee: approximately 0.13 yuan
Pharmaceutical cost: approximately 0.049 yuan
Labor cost: approximately 0.015 yuan
Maintenance fee: approximately 0.01 yuan
Management fee: approximately 0.016 yuan

5、 Engineering Examples
l、 The Linqu County Sewage Treatment Plant, with a daily processing capacity of 50000 tons, started construction in July 1997 and was completed and put into operation in September 1998.
2. Yishui County Sewage Treatment Plant, with a daily processing capacity of 50000 tons, started construction in August 2000 and was completed and put into operation in December 2001.
3. Yiyuan County Sewage Treatment Plant, with a daily processing capacity of 40000 tons, started construction in October 2000 and was completed and put into operation in December 2001.