1 Hazards, sources and characteristics of wine wastewater
With the growth of China's economy and the increase in per capita income, the consumption level of China's wine market has rapidly improved, the wine industry has developed rapidly, and a large number of wineries have emerged. At the same time, the flourishing production of wine has generated a large amount of wastewater. As these enterprises are mostly located in remote suburban areas, lacking complete drainage facilities, the direct discharge of high-concentration organic pollutants containing sugars, alcohols and organic acid compounds seriously affects the environment.
The general process flow of wine production is roughly:
sorting and destemming → crushing → alcoholic fermentation → pressing → malolactic fermentation → blending → aging → stabilization → bottling → finished product. The discharged wastewater mainly comes from the crushing, pressing, fermentation, cleaning and other stages during processing. Wine production wastewater has the characteristics of high concentration, high chroma, high SS and difficulty in settling of suspended matter. Its water quality is usually acidic, and the water quality and quantity fluctuate greatly during the processing season, showing obvious seasonal changes between the pressing season and the non-pressing season.
2 Process flow design
2.1 Project background and influent water quality testing
A wine company located in Ningxia is a wine-making enterprise. The wastewater generated during production and operation mainly comes from workshop and wine tank cleaning drainage, containing a certain amount of wine, with no special industrial wastewater. The wastewater belongs to biodegradable high-concentration organic wastewater and domestic sewage. The water quality parameters tested are shown in Table 1.
| Table 1 Influent water quality parameters | |
| Parameter | Value |
| CODcr | ≤ 2400 mg/L |
| BOD5 | ≤ 900 mg/L |
| SS | ≤ 800 mg/L |
2.2 Design objectives
This project intends to adopt a relevant process. The design objective is that after treatment, the generated wastewater and domestic sewage will meet the "dry farming irrigation" water quality standard in the "Farmland Irrigation Water Quality Standard" (GB5084-2005), so that the enterprise can discharge pollutants according to law and meet the discharge standards.
2.3 Process selection
In view of the characteristics of wine wastewater, the "A²O biological contact oxidation" process was selected, with a scale of 5 m³/d and a floor area of 100 m². The wastewater flow direction of the sewage treatment facility is shown in Figure 1.
2.4 Process flow design
2.4.1 Process overview
The domestic wastewater of the project passes through a septic tank for sedimentation and filtration pretreatment, and then together with the production wastewater collected in the storage tank, passes through a bar screen for filtration. After filtration, it is sent by a lifting pump to the equalization tank. After homogenization and equalization in the equalization tank, it enters the A²O biological treatment unit. This unit mainly includes an anaerobic tank, an anoxic tank and an aerobic tank, where biological reactions such as organic matter degradation, nitrification and denitrification, and phosphorus release and uptake take place to purify the water quality of the sewage.
2.4.2 Process design
(1) Septic tank sedimentation and filtration: Domestic wastewater enters the septic tank through pipelines. The septic tank uses the principles of sedimentation and anaerobic fermentation to remove suspended organic matter from domestic sewage.
(2) Storage tank: Production wastewater enters the storage tank through pipelines for storage. The storage tank adopts a closed rectangular design, which can effectively avoid the emission of odorous gases.
(3) Bar screen: Mainly filters large suspended solids in the wastewater to ensure the smooth operation of the pump units and subsequent treatment structures and equipment.
(4) Equalization tank: In order to provide the best conditions for subsequent treatment, the flow rate and water quality of the wastewater need to be adjusted. Homogenization and equalization of flow rate and water quality can not only improve the treatability of the wastewater, reduce the impact load that may occur during the biochemical treatment stage, dilute toxic substances for microorganisms, but also cool down high-temperature water discharged in the short term. A liquid level controller is installed in the equalization tank, and then a signal is transmitted through the liquid level control instrument, and the wastewater is sent by the lifting pump to the anaerobic tank.
(5) Anaerobic tank: The anaerobic process uses a series of vertically installed baffles to make the treated wastewater flow up and down along the baffles in the reactor. With the help of the biogas generated in the reactor during the treatment process, the microbial solids in the reactor undergo expansion and sedimentation movements up and down in each compartment formed by the baffles. At this time, the water flow in the entire reactor moves horizontally at a relatively slow speed. Because the wastewater flows around the baffles under the action of the baffles, the total length of the flow path in the reactor increases. In addition, due to the blocking effect of the baffles and the sedimentation of sludge, the biological solids are effectively retained in the reactor. This process also requires circulating heating. The wastewater stays in this tank for 4 hours for treatment.
(6) Anoxic and aerobic tanks: This process uses biologically induced modified filler as the core. By changing the microenvironment, the bacterial strains are induced to mutate in a set direction, so that the anaerobic ammonia oxidizing bacteria continuously multiply, achieving stable anaerobic ammonia oxidation. This process does not require chemical addition, mainly inducing genetic variation of microorganisms. The aerobic biochemical tank is filled with hollow double-sphere biological packing, so that aerobic and anaerobic processes proceed simultaneously. The wastewater stays in the anoxic tank for 4 hours and then enters the aerobic tank for treatment, with a treatment time of about 8 hours.
(7) Secondary sedimentation tank: After anoxic and aerobic treatment, the wastewater flows into this tank by itself. A large amount of lost activated sludge and fallen-off bacterial film settle in this tank. The sediment is periodically pumped out by a return pump and returned to the anaerobic tank for further anaerobic digestion treatment, reducing the content of organic matter and suspended solids in the discharged wastewater. After sedimentation, the sludge is returned to the anoxic tank for reuse, and the wastewater then enters the clean water tank through pipelines. The wastewater stays in this tank for 2 hours.
(8) Clean water tank: After treatment, the wastewater enters the clean water tank for ultraviolet disinfection. This tank serves to store the treated wastewater that meets the standards. The达标 wastewater can be used for drip irrigation of forest trees.
The process flow and pollution generation points of the sewage treatment facility are shown in Figure 2.
3 Results and analysis
The scale of the project's sewage treatment facility is 5 m³/d, and the treatment process is the "A²O biological contact oxidation process". Through monitoring the operation results of the process, the main water quality parameters are shown in Table 2. The effluent water quality meets the dry farming standard in the "Farmland Irrigation Water Quality Standard" (GB5084-2005). The wastewater is used for drip irrigation of forest trees, ensuring that the enterprise discharges pollutants according to law and meets the discharge standards, with high economic benefits and prospects.
| Table 2 Effluent water quality parameters | |
| Parameter | Value |
| CODcr | < 200 mg/L |
| BOD5 | ≤ 100 mg/L |
| SS | ≤ 100 mg/L |
4 Conclusion
In this paper, according to the characteristics of wine wastewater, the A²O biological contact oxidation process was flexibly selected as the core process for relevant engineering design. Operation monitoring data show that the high-concentration organic wastewater containing wine can be effectively treated by this process, and the effluent water quality is greatly improved. The A²O biological contact oxidation process has the advantages of high removal efficiency for COD and ammonia nitrogen, stable operation, strong impact load resistance, convenient operation and management, and low operating costs. It is the development trend of wine production wastewater treatment technology. This paper provides a feasible solution and a stable and reliable process reference for the treatment of wine wastewater, and has certain application value and engineering guidance significance.