6.2.5 Anaerobic biological treatment
Anaerobic biological treatment is suitable for high concentration organic wastewater (CODcr>2000mg/L, BOD5＞1000mg/L）。 It decomposes organic matter under anaerobic conditions through the action of anaerobic bacteria. During this process, 50% to 90% of the organic matrix involved in biodegradation is converted into biogas (methane), and the residue after fermentation can be used as high-quality fertilizer and feed. Therefore, anaerobic biological treatment of beer wastewater has received increasing attention.
Anaerobic biological treatment includes various methods, but the upflow anaerobic sludge blanket (UASB) technology is the most mature in the treatment of beer wastewater. The main component of UASB is the reactor, which is a sludge bed composed of anaerobic sludge with good flocculation and sedimentation performance at the bottom, and a dedicated gas-liquid solid separation system (three-phase separation chamber) is installed at the top. Wastewater is added from the bottom of the reactor and is degraded as it flows upward through a sludge bed composed of biological particles, generating biogas (bubbles). Gas, liquid, and solid (suspended sludge particles) are all lifted into the three-phase separation chamber, where the gas is collected in the gas hood. The sludge particles sink to the bottom of the reactor under heavy force, and the water is discharged through the outflow weir.
As of September 1990, 30 productive UASB reactors have been built worldwide for the treatment of beer wastewater, with a total volume of 60600m3. Domestic manufacturers such as Beijing Brewery and Shenyang Brewery have used UASB to treat beer wastewater. UASB reactors designed by some companies in the Netherlands and the United States have a CODcr removal rate of 80% to 86% for beer wastewater, and the pilot results of the UASB treatment device in Beijing Brewery have also maintained this level, with a biogas yield of 0.3 to 0.5 m3/kg (COD). The research results of Tsinghua University's anaerobic treatment of beer wastewater using UASB at room temperature showed that the removal rate was 85% to 90% when the influent CODcr concentration was 2000mg/L. Shenyang Brewery adopts a comprehensive treatment process of solid recovery and anaerobic digestion, implements clean and sewage separation, and centrally collects high concentration organic wastewater with CODcr greater than 5000mg/L and sends it to UASB for anaerobic treatment. The quality and energy utilization rate of CODcr in the wastewater can reach 91.93%.
Practice has proven that the key to successfully treating high concentration beer wastewater with UASB is to cultivate anaerobic granular sludge with good settling performance. The formation of granular sludge is the result of the continuous reproduction and accumulation of anaerobic bacterial communities. A higher sludge load is beneficial for bacteria to obtain sufficient nutrient matrix, thus playing a decisive role in promoting the formation and development of granular sludge; A moderately high hydraulic load will result in hydraulic screening of sludge, eliminating flocculent sludge with poor settling performance and leaving behind sludge with good settling performance. At the same time, shear force will be generated to continuously rotate the sludge, which is beneficial for filamentous bacteria to entangle with each other into balls. In addition, a certain alkalinity of the influent is also a necessary condition for the formation of granular sludge, because the growth of anaerobic organisms requires a relatively high alkalinity. For example, the optimal pH value for the growth of methanogenic bacteria is 6.8-7.2. A certain alkalinity can maintain the pH value required for bacterial growth and ensure sufficient balance buffering capacity. Due to the alkalinity of beer wastewater generally ranging from 500 to 800 mg/L (calculated as CaCO3), which is insufficient, it needs to be supplemented with sodium carbonate or calcium oxide in the processing industry.Research has shown that maintaining an influent alkalinity of no less than 1000 mg/L during the start-up phase of UASB is essential for the cultivation of granular sludge and the good operation of the reactor under high loads. It should be pointed out that ethanol in beer wastewater is an effective granulation promoter, which provides very favorable conditions for the successful operation of UASB. In summary, UASB has a series of advantages such as high efficiency, low treatment cost, low power consumption, low investment, and small footprint, making it fully suitable for the treatment of high concentration beer wastewater. Its disadvantage is that the CODcr concentration in the effluent still reaches about 500mg/L, and it needs to be reprocessed or combined with aerobic treatment to meet the discharge standards.
7. Utilization technology of beer wastewater
The use of natural ecological cycles to purify and utilize beer wastewater is also a direction for comprehensive treatment of beer wastewater, which is conducive to realizing the resource utilization of waste.
7.1 Beer wastewater land use
The land use of wastewater has a long history both domestically and internationally. The purpose is not simply to irrigate farmland with wastewater, but to scientifically utilize the purification function of the soil plant system based on ecological principles while fully utilizing water resources, so that the system can play a role in the secondary and tertiary treatment of wastewater. There are generally two methods for land use of wastewater: rapid infiltration and surface runoff. The characteristic of the former is that most of the added wastewater infiltrates through the soil to the lower layer, so it is limited to use on fast permeable soils such as sand and sandy clay. Plants have a relatively small purifying effect on wastewater, mainly through physical, chemical, and biological processes that occur in the soil to treat the wastewater. The latter is a fixed membrane biological treatment method, in which wastewater flows down the ditch from the upstream of the slope where plants grow, flows through the vegetation surface, and is discharged into the runoff collection channel. Wastewater purification is mainly achieved through the biofilm on the slope.
This method is most suitable for soils with slow infiltration. After passing through the land use system, the water quality of beer wastewater has significantly improved and can meet the requirements of the irrigation water quality standard for farmland (GB5084-85); At the same time, it can save water sources, increase the organic matter content of farmland soil, and improve crop yields. Its economic benefits are more reflected in arid areas. Of course, there are also certain issues with the land use of beer wastewater:
① During the treatment process, a foul odor may be generated, and the treatment site must be located far away from residential areas, which requires a longer water supply main pipe;
② When the salt content of wastewater is too high, it will harm plant growth and cause poor soil drainage and ventilation. Further research is needed to avoid these problems.
7.2 Plant purification of beer wastewater
Beer wastewater is rich in organic carbon content and has a certain level of nitrogen and phosphorus content, which can provide necessary nutrients for plant growth. In recent years, some scholars have conducted hydroponic experiments on plants such as luffacyclindrica, Lolium multiflorum, Ipomoea aquatica, and Hemerocallis fulva using beer wastewater. They have found that these plants grow well and can complete their life cycle, creating economic benefits while significantly reducing the concentration of various pollutants (except COD) in the wastewater. This has opened up a new idea for the resource utilization treatment of beer wastewater. According to reports, Wuxi Brewery has planted loofah in the oxidation pond to enhance the purification effect of the treatment system.
Post time: Aug-24-2024