In view of the problems of limited removal ability of dissolved organic matter by conventional treatment, high investment and operating costs for advanced treatment, and large area of land, this project integrates activated carbon adsorption, biodegradation, and coagulation precipitation functions into one process unit to develop a new type of activated carbon reflux Efficient precipitation process. The principle is to initially add a large amount of activated carbon in the coagulation and sedimentation unit to form high-concentration activated carbon in the mixed liquor. Through precipitation, concentration and sludge reflux, the residence time of the activated carbon in the system is extended, and the activated carbon adsorption and biological carrier are fully utilized., strengthen the removal of dissolved organic matter. Only the activated carbon lost due to sludge discharge is replenished every day, which is converted into raw water, with a low dosing amount. The main performance indicators reach the following levels.

1. The turbidity of precipitated effluent is stable below 1NTU;
2. When the carbon input amount is 12.8 mg/L, the CODMn removal rate is 48%~60%, close to the level of ozone activated carbon process, 26% higher than ordinary precipitation process, and 17% higher than traditional adding powdered carbon (no initial adding, evenly adding 20mg/L carbon every day);
3. The removal rate of semi-volatile small molecule organic compounds (GC-MS detection) reaches 95%.
4. If only the same CODMn removal rate of 31% is achieved as that of the traditional addition of powdered carbon (uniform addition of 20mg/L)~At 43%, the carbon input amount was 6.4mg/L, which was only 32% of the traditional carbon input amount, saving 68%.
5. This process only adds powder carbon adding and sludge reflux facilities on the basis of coagulation and precipitation. Based on a 100,000 m3/d water plant, the project cost is about 6.5 million yuan, the direct operation cost is about 0.15 yuan/m3, and the area is about 500m2. If the ozone-activated carbon advanced treatment process is adopted, the project cost is about 50 million yuan, the direct operation cost is about 0.22 yuan/m3, and the area is about 2600m2. The former occupies 80% less land and 85% less investment than the latter. Saving operating expenses by 30%.
   The creativity and advanced nature of this topic are reflected in:
6. Add more activated carbon initially to form a high-concentration activated carbon mixture, which is circulated in the pool to extend the residence time of activated carbon in the pool and enhance the removal effect of dissolved organic matters. This activated carbon utilization model is innovative.
7. The mathematical model of returning peat is deduced, and some important relationships such as carbon replenishment, mixed liquor activated carbon concentration, and carbon age are obtained, which has innovative and practical design and operation guidance significance.
8. Less land occupation, low operating costs, save investment, and advanced performance indicators and economic indicators.
9. The topic proposes an implementation model of this process combined with new construction projects and renovation projects, which has practical significance.
   This process occupies a small area, is low in cost, and can be started or stopped as needed. It is very suitable for new construction and renovation projects with tight land, and is highly targeted to raw water with high organic pollution and obvious seasonal changes. It has been used in many projects and achieved good economic and social benefits.
10. The first phase of the emergency standby water plant project in Shaoxing City has a design scale of 200,000 m3/d and adopts the process of "potassium permanganate pre-oxidation + new activated carbon reflux high-efficiency sedimentation tank + V-type filter + liquid chlorine disinfection." During the commissioning period, the removal rate of CODMn reached 50%, and the equivalent amount of powdered carbon was only 8mg/L.
11. The third phase project of Guhengqiao Water Plant in Pinghu City has a design scale of 50,000 m3/d. It adopts the process of "suspended filler biological pretreatment + new activated carbon reflux high-efficiency sedimentation tank + V-type filter + secondary ozone-activated carbon + liquid chlorine disinfection". The CODMn removal rate of the new activated carbon reflux high-efficiency sedimentation process reaches more than 50%, and has been in operation for 2 years.
12. The first phase of Qingpu No. 3 Water Plant has a design scale of 100,000 m3/d and adopts "pre-ozone + new activated carbon reflux high-efficiency precipitation + ozone activated carbon + submerged ultrafiltration membrane + sodium hypochlorite disinfection." When the CODMn of raw water is high, powdered carbon reflux can be started to reduce the removal load of the ozone activated carbon process unit.