PFA granules produce a large amount of highly polluted wastewater during processing and granulation. The wastewater has the characteristics of high concentration of organic matter, high content of SS, high content of petroleum, and large changes in water quality. In view of the pollution and discharge of the company's production wastewater, on the basis of comprehensive consideration of various sewage treatment technologies, in line with the principles of reasonable process flow, ensuring that the effluent index meets the national and local discharge standards, and on the premise of ensuring the sewage treatment effect, minimize project investment and daily operating costs, it is determined that the treatment process with slag separation coagulation sedimentation hydrolysis acidification contact oxidation as the main body is adopted, and the effluent quality can meet the first-class discharge standard of the Integrated Wastewater Discharge Standard (GB8978-1996).

 

wastewater characteristics

 

This type of wastewater entering the sewage treatment system has the following distinct characteristics:(1) large fluctuations in water quality and quantity (general day shift production);(2) large silt content and high suspended solids content;(3) containing petroleum (floating oil), emulsified oil and other oil substances;(4) recycling almost all PFA products except pesticide bottles, and the wastewater composition is complex;(5) in the process of using more detergent and salt;(6) containing dissolved organic matter.

 

Water quality and quantity

 

The main source of sewage in this sewage treatment station is PFA product processing wastewater, which contains mud and sand, SS, oil, detergent and organic pollutants, and the fluctuation range of water quality and quantity is large. Another part of the sewage comes from domestic sewage. The maximum daily flow of the two parts of sewage can reach 3000 m3/d after mixing. The designed water treatment capacity is 3000 m3/d.

 

The BOD5/CODCr of mixed wastewater is generally about 0.4, which has good biodegradability.

 

Process flow

 

This project adopts a physicochemical biochemical treatment process with slag separation coagulation sedimentation hydrolysis acidification contact oxidation as the main body.

 

The wastewater is collected through branch pipelines in the plant area. First, the larger impurities and floating substances in the wastewater are intercepted by the mechanical grid. Then, the small suspended substances in the wastewater are further removed by the lifting pump to the rotary solid-liquid separator, and the effluent is fed into the grit chamber. After sand sedimentation treatment, the sewage flows into the regulating tank, where the sewage is homogenized, then lifted to the coagulation tank, stirred and fully reacted, in order to further remove the coagulation sediment, the effluent from the primary sedimentation tank enters the hydrolysis acidification tank, and the role of the hydrolysis acidification tank is mainly to use the role of aerobic bacteria in the biofilm to decompose part of the organic matter while improving the biodegradability of the sewage. The effluent from the hydrolysis tank enters the contact oxidation tank for organic matter degradation through the metabolism of aerobic microorganisms, the effluent flows into the secondary sedimentation tank for mud-water separation, and the effluent from the secondary sedimentation tank is discharged up to the standard.

 

The grid slag raked out by the grid has low water content and can be directly transported to the outside for treatment; the mud and sand deposited in the grit chamber are periodically lifted by the slag paddle pump, and the extracted sand grains are naturally dried and transported to the outside.

 

The residual sludge produced by the primary sedimentation tank and the secondary sedimentation tank and the biofilm shed by the contact oxidation tank enter the sludge thickening tank, and the sludge cake (moisture content ≤ 80%) after concentration and pressing is transported out through the concentration dehydrator, and the filtrate of the dehydrator and the supernatant of the concentration tank enter the regulating tank for treatment.

 

Design and operation parameters of main structures

 

mechanical lattice

 

The purpose is to remove large particle size of solid waste garbage. Channel size: L×B×H = 5.0m × 1.5m × 5.0m (channel height), with a mechanical grid 500mm wide and 3mm gap.

 

Lift pump station

 

The main purpose is to upgrade the collected sewage in the plant to the next sewage treatment unit for further treatment. Three submersible sewage pumps (two for use and one for standby) are provided.

 

rotary solid-liquid separator

 

Placed at the rear end of the rotary grille, the purpose is to remove relatively small suspended solids in the sewage, so as to ensure that the water pump and process pipeline of the subsequent treatment process unit are not blocked. One rotary solid-liquid separator with a diameter of 800mm and a grid gap of 1mm is provided.

 

horizontal flow grit chamber

 

The horizontal flow structure is adopted; the sand settling area adopts the slurry pump to lift the sand, and the sand is lifted into the sand drying field and transported outward after drying. Size: L×B×H = 7.5m × 1.2m × 0.8m; Residence time: HRT = 130s; There are 2 slurry pumps and 1 fine grid.

 

regulating pool

 

Adjust the water quantity and mix the water quality. Due to the high SS concentration in the wastewater and the large difference in the concentration of each waste water discharged, an aeration stirring system is added. The effective volume of the regulating tank is 1000 m3,HRT is 8h, and 3 submersible sewage pumps (two for use and one for standby) and 2 submersible mixers are set.

 

Coagulation reaction tank

 

Coagulant and coagulant aid are added to the wastewater, and flocculation reaction occurs. HRT is 0.3h, with one fast and one slow mixer.

 

Primary sedimentation tank

 

Under the action of coagulant and coagulant aid, most of the suspended solids in the sewage settle, thereby reducing the indicators of SS, CODCr, BOD5 and chroma in the wastewater. In order to ensure the effect of subsequent anaerobic treatment, the surface load of the sedimentation tank is 0.6 m3/(m2?h), the diameter of the tank is 16m, the effective water depth is 4.5m, and there are 1 mud scraper, 1 sludge pump, 1 set of outlet weir and 1 set of scum weir respectively.

 

hydrolysis acidification tank

 

After being placed in the primary sedimentation tank, its function is to intercept suspended solids, colloids and other organic substances in the biofilm of the filler layer and convert macromolecular substances into small molecules, and solid substances into soluble substances, so as to improve the biodegradability of sewage while degrading some organic substances. Consider it in two squares. The effective volume is 750 m3,HRT is 6h, and the pool is filled with elastic filler of 600 m3.

 

contact oxidation tank

 

The reactor is the key facility for the effluent of this project to reach the standard. The biofilm grown on the surface of the filler and the activated sludge in the reactor are used to adsorb the organic pollutants dissolved in the sewage, and through biological metabolism, the organic substances in the water with high energy are used to release energy gradually through a series of biochemical reactions, and finally the organic substances with low energy are stabilized to meet the requirements of harmless treatment of sewage. The aeration adopts a variable microporous hose aerator, which basically does not have the problem of diaphragm tearing or blockage, and the utilization rate of oxygen is 15% ~ 18%. The effluent from the contact oxidation tank flows into the secondary sedimentation tank for mud-water separation. Designed as a four-format contact oxidation pool, push-flow structure. The effective volume is 1500 m3,HRT is 12h, the tank is filled with elastic filler of 1200 m3, and variable microporous aeration pipe φ65 is used for oxygenation and aeration.

 

secondary sedimentation tank

 

It is used for sludge-water separation of biochemical treatment effluent. radial flow structure. The surface load is 0.60 m3/(m2?h), the diameter of the pool is 16m, the effective water depth is 4.5m, and the HRT is 4h. One gas mud scraper, one sludge pump, and one outlet weir and one scum weir.

 

Project commissioning and results

 

Commissioning run

 

Access bacteria: discharge a small part of water from each pool, including anaerobic pool and aerobic pool.

 

Put in 100t of fresh dry sludge evenly according to the volume of each tank. Start the fan and run automatically for 1 ~ 2d without water intake to make the sludge evenly mixed.

 

If the water temperature is low, attention should be paid to circulating heating to keep the temperature in the biochemical system between 25 and 35 degrees Celsius.

 

Culture and domestication of strains: water should follow the principle of gradual and orderly progress.

 

Debugging results

 

　　PFA GranulesThe commissioning and operation results of each treatment unit of the processing plant sewage treatment project are as follows.

 

coagulation reaction sedimentation tank

 

The pH of the raw water in the regulating tank is between 9 and 10, and the CODCr is between 1100 and 2000mg/L, with an average of 1500mg/L. After adding OPAC (polyaluminium chloride) and PAM (polyacrylamide) coagulation and precipitation, COD is stable between 750 and 1300mg/L, with an average of 900mg/L, a removal rate of 20% to 40%, and an average removal rate of 30%.

 

hydrolysis acidification system

 

1# hydrolysis acidification tank effluent COD between 400~650mg/L, an average of 500mg/L, the average removal rate of 45%,2# anaerobic tank effluent COD between 420~570mg/L, an average of 500mg/L, the average removal rate of 45%.

 

aerobic system

 

The COD of contact oxidation effluent is between 31 and 90mg/L, with an average of 60mg/L, and the average removal rate is 90%.

 

Commissioning and acceptance monitoring

 

After the commissioning is completed, the system enters a stable operation state. The monitoring by the local environmental protection department shows that all effluent water quality meets the discharge standard, and the monitoring results are shown in Table 3.

 

During the acceptance period, the removal rates of CODCr, BOD5 and SS in the coagulation and sedimentation stage of sewage treatment were 30.0; 29.8; 60.0 respectively. The removal rates of CODCr, BOD5 and SS in the hydrolysis acidification stage were 45.0, 42.0 and 75.0, respectively. The removal rates of CODCr, BOD5 and SS were 88.0%, 93.5% and 40.0%, respectively.

 

Considering the PFA particles comprehensive utilization wastewater contains a large number of PFA particles suspended solids and other impurities, for the adverse effects of suspended solids on the subsequent treatment system, the use of rotating fine grid to remove most of the PFA particles and other impurities, the actual operation shows that this design is correct.

 

The depth of the hydrolysis reactor is increased, the effective water depth reaches 6.0m, and the anaerobic tank is covered to reduce the dissolved oxygen in the water, and at the same time, the odor generated by the reactor is avoided to produce secondary air pollution to the plant. The anaerobic tank is divided into two stages, the tank is filled with elastic filler, and the liquid agitator is used as the push flow power, the flow state of the sewage in the reactor is optimized, the full contact between the sewage and the filler is ensured, and the anaerobic tank becomes a new type of high-efficiency anaerobic reactor composed of multiple compartments. It has good hydraulic conditions, good microbial population division, simple structure, fast start-up, stable operation and other excellent characteristics. During the operation, each compartment of the anaerobic tank is fully mixed, and the whole is a push-flow reactor, which obtains a stable treatment effect, and the decomposition treatment effect of oxygen and anaerobic is good.

 

The contact oxidation tank is filled with a large amount of elastic filler, so the loss of sludge is relatively small. However, in order to ensure the index of suspended solids in the effluent, flocculant is added to the secondary sedimentation tank. As the flocculant is added to the secondary sedimentation tank and the amount of sludge is small, this part of sludge will not flow back and will be discharged into the sludge tank for treatment together with the physicochemical sludge.

 

The suspended solids such as PFA particles isolated from the physicochemical process can be returned to the recovery flotation process section for recovery treatment. After thickening and mechanical dewatering, other sludges with a moisture content of less than 80% shall be transported to qualified units for final treatment and disposal according to local environmental protection requirements. At the beginning of the design of this project, the problem of reuse of treated water was not considered. Under the situation of increasing shortage of water resources, the requirement of reuse of reclaimed water is becoming more and more urgent. In future similar projects, the reuse of reclaimed water after treatment must be considered.

This article comes from:www.tflpfa.com

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