SBR Air Flotation Process for food production wastewater treatment

SBR Air Flotation Process for food production wastewater treatment

A certain amount of wastewater was produced during the production process of one food company in Indonesia. The amount of wastewater discharge reaches 80m3/d during the peak season (September-February) and about 40m3/d during the off-season (March-August). It is discharged into the ancient canal across the urban area, which has brought some pollution to the water body of the ancient canal. According to the information provided by the manufacturer and combined with the laboratory measurement data, the wastewater quality is shown in Table 1.

Table 1 Wastewater  Quality

1. Wastewater treatment process

1.1 Engineering Features

1.1.1 Wastewater mainly comes from food raw material cleaning wastewater in semi-finished product processing workshops. The main components of wastewater are sugar, starch, cellulose, animal and vegetable oils, etc., which are biodegradable organic matter and have no poisonous or inhibitory effect on microorganisms.

1.1.2 The usable land area is small. The project is located in the northeast corner of the factory area, in a long and narrow area behind the warehouse, with a usable land area of about 300m2.

1.1.3 The company was listed by the Municipal Environmental Protection Bureau as a discharge unit in the Yangtze River Basin within a time limit. The required construction period was tight, and the investment was low.

1.2 Process flow

The BOD5/CODcr of wastewater is about 0.4, and the biodegradability is good. The traditional activated sludge method generally needs to set up secondary settling tanks and sludge return facilities, and its land use and investment are higher than those of the SBR method. Considering the non-uniformity of wastewater quality, large seasonal differences in water volume, and small usable land area, this project chooses the SBR process with a simple process and flexible operation. The treatment process flow is shown in Figure 1.

2. Main processing structures and their process parameters

2.1 Grille

Set up a thick grid and a thin grid. The plane size is 1000mm×600mm, the gap between the coarse grid and the grid is 30mm, and the gap between the fine grid and the secret grid is 5mm.

2.2 Conditioning pool

The company’s wastewater discharge varies greatly, and the regulating tank must have sufficient water storage volume. The hydraulic retention time of the regulating pool is 10h, the total volume is 70.0m3, the effective water storage volume is 50.0m3, the plane size is 5.5m×4.0m, and the effective water depth is 2.3m. Choose a WQ40-15-4 submersible pump to lift the wastewater to the SBR pool.

2.3 SBR pool

The SBR pool adopts two groups of pools, with a total volume of 70.0m3 and an effective volume of 600m3. The plane size of each pool is 3.5mx4.0m, and the effective height is 4.5m. Drainage is done with a hose decanter. There are 2 Roots blowers; the model is SSR100, one for use and one for standby. The air enters the water through the diaphragm microporous aeration head, and the air-to-water ratio is 15:1. There is a sludge pipe at the bottom to discharge excess sludge to the sludge field. SBR pool operation cycle: 24h in low season, water inflow for 1.0h, aeration for 5.0h, sedimentation for 2h, drainage for 0.5h, idle for 15.5h; peak season for 12h, water intake for 1.0h, aeration for 5.0h, sedimentation for 2h, drainage for 0.5h, idle for 3.5h.

2.4 Storage tank

The total volume of the storage tank is 60.0m3, storing the effluent of SBR, the plane size is 4.0m×5.3m, and the depth is 2.8m.

2.5 Air flotation device

The air flotation device (DAF) adopts the pressurized reflux air flotation method, and the reflux ratio is 30%, the hydraulic retention time is 40min, the effective water storage volume is 4.3m3, the effective water depth is 2.0m, and the total volume is 5.5m3.

2.6 Sludge Disposal

The SBR tank and the scum of the air flotation device are discharged to the sludge tank together, and the effective volume of the sludge tank is 18.0m3. The sludge in the sludge tank is lifted by the sludge pump to the filter press to be pressed into a mud cake, and the mud cake is transported outside for incineration, building materials, landfill, and soil cultivation.

3. Engineering debugging

3.1 SBR pool debugging

The engineering commissioning starts with the SBR pool. The aeration time is 8 hours, the sludge concentration is controlled at 4000-6000mg/L, and the sludge load is  0.1-0.2kg[BOD]/(kg[MLSS]·d). After a week of trial operation, the sludge in the SBR tank increased, the sedimentation was good, and the mud-water interface was clear. Through microscopic examination, it was found that the dominant bacteria had formed .

The SBR tank can maintain a high sludge concentration, so the reaction time is relatively short. Since the mud-water separation is carried out through static settling, it can avoid short-circuiting and differential density flow affecting the mud-water separation effect, and the effluent water quality is better than that of ordinary secondary sedimentation tanks . Each cycle of the SBR process goes through different stages, such as the water intake period, reaction period, and precipitation period, which accelerates the selection and evolution of biological species. The alternate operation of water intake (anaerobic)-aeration (aerobic)-quiet (anaerobic) can inhibit the proliferation of filamentous bacteria and prevent sludge bulking.

3.2 Air flotation debugging

First, fill the air flotation tank with clean water, wait for the dissolved air and reflux system to be normal, then enter the wastewater, the air compressor is always in the state of automatic start and stop, and the pressure in the dissolved air tank is stable at 0.3MPa. Adjust the dosing amount according to the influent water quality and effluent water quality. The selected medicament is polyaluminium, and the dosage is 40-60mg/L.

4. Treatment effect and technical and economic indicators

4.1 Processing effect

The project was completed and put into trial operation in June 2000, and the operation has been efficient and stable so far.

The Yangzhou City Environmental Monitoring Center Station monitored the wastewater discharged from food production, and the results showed that the average values of CODCr, BOD5, SS, animal and vegetable oils in the wastewater were all in line with the relevant regulations in the “Comprehensive Wastewater Discharge Standard” (GB9878-1996). The monitoring results are shown in Table 2.

Table 2 Wastewater monitoring results and evaluation

4.2 Technical and economic indicators

See Table 3 for the main technical and economic indicators of the wastewater treatment project.

Table 3 Main technical and economic indicators

5. Some experiences

1. The main body of the treatment system of this project is the SBR tank and the air flotation device, which is simple to treat structures and convenient to operate and manage.
2. The SBR pool has the advantages of less land occupation, less infrastructure investment, lower operating costs, and better treatment effect.
3. Oil exists in the form of dissolved oil and non-dissolved oil in sewage. This project adopts biological and air flotation methods, which have a good removal effect on oil.