UASB—TF Treatment of wastewater from food industry

Generally, physicochemical methods (air flotation, coagulation sedimentation, adsorption, etc.) are used to treat food processing wastewater, but the removal efficiency is unstable, the operation cost is high, and the management and operation are inconvenient. In recent years, there are also treatment technologies based on aerobic process. Although the removal of organic matter is better, its operation cost is higher. The UASB TF technology, which combines the upflow anaerobic sludge bed (UASB) with the basic non power consumption drop filter bed (TF), has been applied in many food production wastewater treatment of many manufacturers, which shows that the process has high efficiency, low operation cost, less investment and simple operation and management, and the secondary start-up is very convenient. The effluent can meet the comprehensive discharge standard of sewage (GB) The first level standard in 8978-1996) and some manufacturers have used their effluent back to the non direct cooling system in production.

1、 Wastewater quality

The water quality of soybean products (soybean milk powder, soybean milk beverage), dairy products (yoghurt, fresh milk, etc.), beer production wastewater is shown in Table 1, and the treatment water volume is 800, 400 and 600m3 / D respectively.

2、 Selection of treatment process

1. air flotation treatment process

In view of the large amount of colloidal substances in wastewater, the conventional air flotation method can be used to remove them. The effluent is clear after air flotation treatment, but it can not meet the discharge standard because it can not remove the dissolved organic matter, the CODcr content in the effluent is high and the operation is unstable. At the same time, because of the air floatation, there will be more sludge, and the sludge moisture content is very high, so the operating cost is also high. At present, it is not used for the treatment of such wastewater alone.

2. aerobic treatment process

For organic wastewater with high organic content and good biochemical properties, the most used aerobic processes in the previous years are contact oxidation, SBR, activated sludge method, etc. the treatment effect of food wastewater is also good, the removal rate of CODCr can reach more than 90% [1], and the operation is stable. The disadvantages are that it needs air blast aeration, high power consumption and high operating cost, and it takes a long time to start after shutdown and maintenance (generally about one month).

3. UASB TF processing process

For the manufacturers of wastewater treatment, it is urgent to use a treatment technology with less investment, low operating cost, stable operation, good treatment effect and simple operation and management. Based on the long-term pilot study, a new treatment technology, UASB TF, is proposed, which is suitable for the treatment of medium and low concentration food processing wastewater (UASB TF process is adopted for anaerobic treatment (UASB with mature technology and wide use is adopted for anaerobic treatment, and micro power consumption trickling filter bed is used for aerobic treatment). The process has been applied in many food processing plants and has achieved very good operation results.

The treatment process of UASB TF process (see Fig. 1) refers to the wastewater from the workshop entering the regulating tank for water quality and water quantity regulation. If the water temperature is low in winter, the temperature is added to meet the requirements of UASB water inflow. UASB was digested by anaerobic digestion at medium temperature. Because the anaerobic effluent can not meet the discharge requirements, it is necessary to use aerobic for further treatment. Aerobic use the technology of trickle filter bed, fill in the trickle filter bed with inorganic solid bioactive filler, through the automatic rotating water distributor without power, evenly distribute anaerobic water on the surface of the filler of the trickle filter bed, and supply oxygen by natural ventilation. The effluent of trickle filter bed is partially reflux to ensure the hydraulic load and the water distributor speed.

3、 System operation

1. system processing efficiency

Each UASB TF process has been running for several years, during which, it has experienced various adverse conditions such as water shortage, maintenance, secondary start-up, influent concentration and hydraulic conditions, but its operation has been very normal and the water quality of effluent is very stable (see Table 2).

2. anaerobic operation

Because the water quality and water quantity of the incoming water of each plant fluctuate greatly, a regulating tank is set up and a heating system is installed in the tank. When the water temperature is low, the wastewater is properly heated to reduce the impact load of the influent water on anaerobic bacteria in UASB. See Table 3 for operating parameters of UASB.

The bacteria in UASB are the anaerobic sludge (water content is 75%) of the sewage treatment plant of Haibohe, Qingdao. The sludge concentration in the sludge layer 1.0m from the bottom of the measured reactor is 100 gtss/l (MLVSS is 70 gvss/l), and the UASB is controlled to operate at medium temperature (35-37 ℃).

The sludge granulation degree in anaerobic reactor is good. After 2 years operation, the results of sampling and measuring sludge concentration from each sampling pipe of the reactor are shown in Figure 2.

3. aerobic operation

Aerobic is a kind of trickle bed reactor which is rarely used in China. The automatic rotary water distributor is adopted to distribute water evenly. The height difference of anaerobic effluent is fully utilized without mechanical aeration. At the same time, partial reflux is carried out to reduce the influent concentration of the trickle filter bed and increase the hydraulic load. The effective height of trickle filter bed is 4 m, the particle size of the inorganic solid active biological filler is 80-100 mm, the porosity is more than 90%, and the specific surface area is more than 250m2 / m

3.In the long-term operation of trickle filter bed, no packing blockage and large biofilm on the surface of the filler were found to fall off at the same time, and no odor and filter flies were produced. The effluent from the trickle filter bed enters the inclined pipe sedimentation tank. The biofilm in the water can be removed in the inclined pipe sedimentation tank well [2], and the aerobic "micro power consumption" operation is achieved. See Table 4 for operation parameters of trickle filter.

4. operating expenses

The whole treatment system has stable operation effect, and its direct operation cost is the power consumption cost and personnel salary of 3 pumps. Each shift only needs one person to operate simply, and there is no other equipment to be maintained except the water pump.

All sludge produced by the trickle filter bed will be returned to the regulating tank and then into UASB for digestion. The UASB granular sludge is sold for external sale, and there is no residual sludge in the whole system to be treated.

4、 Conclusion

① UASB trickle filter bed technology is a new treatment technology for the treatment of medium and low concentration organic wastewater with advanced process.

② The process has low investment, low direct operation cost, high CODcr removal rate (up to 95%), stable operation and simple operation.

③ The sludge production of the system is low, and it can not be discharged. After a period of operation, UASB can grow better granular sludge (which can be sold directly), without sludge treatment.

④ The operation practice shows that UASB TF process has good impact load resistance, and the effluent is still stable under certain fluctuation conditions, and is also suitable for seasonal manufacturers.

⑤ The new packing of trickle filter bed is used to solve the problems that are easy to appear in the trickle filter bed.

⑥ The development of UASB TF process is suitable for the needs of many manufacturers, and has a broad application prospect.