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1. Purification of biogas digesters
Purification of biogas digesters is based on the development of septic tanks, and it was also the earliest technology used to treat dispersed domestic wastewater. Since the 1990s, Sichuan, Zhejiang, and Jiangsu provinces have successively compiled a standard atlas of pool-shaped structures suitable for the application of purified biogas digesters in the region. Purification biogas digesters are generally composed of secondary anaerobic tanks and follow-up biofilters. The secondary anaerobic tanks are filled with soft fillers; biofilters have two types of facultative filters and aerobic filters, generally divided into multiple compartments. In the room, the front compartment is filled with soft fillers, and the rear compartment is filled with hard fillers such as gravel and pebbles. Domestic sewage is removed from the sand trap to remove coarse contaminants and then fermented in an anaerobic tank to produce valuable biogas. After the anaerobic filtration in the secondary anaerobic tank, a large amount of sludge is retained, and organic pollutants are further fermented and decomposed at this point. After that, the sewage is purified and filled with soft and hard fillers. The effluent COD, NH4+-N, TN, and TP indicators generally meet the secondary standards required by the GB18918-2002 "Urban Wastewater Pollutant Discharge Standard". .
The method of purifying the biogas digesters can be combined or diverted according to the amount of treatment. Because the hydraulic retention time is longer (2~4 days), it is generally applicable to the treatment of domestic sewage with a size of less than 200m3/d. The confluent purification of biogas digesters should be suitable for the treatment of domestic sewage with a size of less than 100m3/d, and it has been widely used because of the low investment cost. When the scale is relatively large, it is advisable to use split-flow purification biogas tanks.
According to the survey, the biogas production rate of the purified biogas digesters is approximately 0.02 to 0.15 m3/(m2.d), and the removal rate of COD is 80% to 90%, which is 5% to 10% higher than the conventional anaerobic digestion technology. However, the nitrogen and phosphorus content in the effluent is still relatively high, and it is generally difficult to meet the Class I B standard required by GB18918-2002. With the continuous improvement of the discharge requirements of national and local sewage discharge standards, the issue of water standards has become a difficult problem. To this end, purification biogas digesters can be combined with land infiltration, constructed wetlands, ponds, and other technologies, and after nitrogen and phosphorus are further treated, they can be discharged into natural water bodies or used as green water for irrigation.
2. Eco Filter and High Algae Pond
The Eco Filter is a technology developed from France and Chile to treat municipal solid waste and sewage. In general, suspended matter, biological sludge, and some microorganisms are used as food. In the process of degradation of pollutants, earthworm excrement and small organic matter produced by earthworms can create conditions for the growth of microorganisms. Therefore, the earthworms and microorganisms in the earthworm ecological filter can form a good synergy, on the one hand, it extends the food chain of the organism and enriches the types of microorganisms, thereby strengthening the removal of organic pollutants and nitrogen and phosphorus; Due to the activity of helium, the filter material in the filter tank has good permeability, which can significantly increase the hydraulic load of the helium eco filter. In addition, the bio-filter is stable, the capillary water absorption time is about 30~50s, and the sludge dewatering performance is good. Compared with the conventional activated sludge treatment technology, the sludge treatment cost can be greatly reduced.
Domestic Tongji University, Nanjing University and other organizations first conducted research on the treatment of domestic sewage by a helium ecofilter, and developed technologies such as a multi-level helium ecofilter and a tower helium ecofilter, and have been applied to the treatment of rural domestic sewage. Engineering practice.
Because of the relatively high requirements of environmental humidity, long-term survival in a stagnant environment, it may lead to its death, thus limiting the hydraulic load of the earthworm ecological filter, and its hydraulic load is generally not higher than the traditional secondary treatment process. At the same time, an excessively high COD load (generally no more than 200 mg/L) tends to destroy the synergistic relationship between earthworms and microorganisms, which leads to a decrease in the treatment efficiency of the system. In addition, the technology is not mature enough in filter selection. High-efficiency algal ponds are an artificially-enhanced natural ecosystem based on traditional stable ponds. Through sunlight, algae and bacteria in the pond form a good synergy, and then effectively remove pollutants.
Compared with traditional stable ponds, the characteristics of high-efficiency algae ponds are good for removal of nitrogen and phosphorus, shallow depth of ponds, generally not more than 0.5m, compared to the importance of HRT in the design of stable ponds, pool depth is a design of high-efficiency algae ponds. The most important parameters are: simple treatment process; short HRT, suitable for large-scale sewage treatment, and a large application prospect in scattered rural areas, and can also be used as a viewing pond with a landscape effect. This technology has been applied abroad, and it is still at the stage of applied research. In addition, further research is needed on the content of algae in the outflow and the algae resources.
3. Membrane bioreactor process
Membrane bioreactor is a sewage treatment system integrating activated sludge and membrane separation technology. Generally based on the size of the membrane pore size can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane; according to the different components of the membrane, can be divided into hollow fiber type, plate type, round tube type; according to the membrane module and Bioreactor locations can be divided into one-piece and split-type.
The separation method is to separate the membrane module from the bioreactor. This method is beneficial to the replacement and backwash of the membrane module, and it is widely used in wastewaters that are prone to membrane fouling such as refractory industrial wastewater, toxic wastewater, and high-concentration wastewater. The integrated membrane bioreactor is widely used in the treatment of domestic sewage and micro-polluted source water because of its small footprint and low energy consumption.
Membrane bioreactors can achieve complete separation of hydraulic retention time and sludge residence time, which can increase the sludge concentration in the reactor and increase its volumetric load. In general, the sludge age in the reactor is longer, which is conducive to the growth of nitrifying bacteria. Therefore, the nitrogen removal effect of the system is good, and the removal rate can reach more than 90%. Due to the efficient separation of the membrane, the effluent quality of the system is stable, and the traditional secondary sedimentation tank can be omitted and the floor area can be reduced. However, the inevitable membrane fouling during the operation makes membrane modules need to be flushed or replaced regularly, thereby increasing the operation and maintenance costs of the system.
At present, this technology has many applications and can be used for the treatment of large, medium, and small-scale water volumes. The practice shows that the effluent COD and SS concentration can be stably below 50 and 10 mg/L respectively. Other major pollutants can meet the water reuse standards and can be used for flushing toilets, greening irrigation, firefighting, etc. to achieve a better economy. benefit. Since this system does not have an anaerobic tank, the removal effect of phosphorus is not good. Phosphorus may be further removed by a chemical method, and may also be combined with a nitrogen and phosphorus removal process.
4. Constructed wetland technology
Constructed wetland is an artificially enhanced natural ecological treatment system, which removes pollutants under the action of fillers such as pebbles, gravel, zeolites, reeds, calamus, canna and other microorganisms. The types can be divided into surface flow constructed wetlands, subsurface flow constructed wetlands and tidal flow constructed wetlands, and subsurface flow constructed wetlands are divided into vertical and horizontal subsurface flows. The subsurface flow constructed wetland is less affected by the ambient temperature than the surface flow constructed wetland, it is not easy to breed worms, the sanitary conditions are good, and the effect of nitrogen and phosphorus removal can be well achieved. It has been widely used in the treatment of domestic sewage.
The removal of nitrogen by constructed wetlands is mainly achieved by the nitrification-denitrification of microorganisms, while the removal of phosphorus is mainly through the adsorption and deposition mineralization of wetland fillers. Some fillers rich in calcium, magnesium, and iron ions, such as ceramic particles, steel slag, etc., have a good adsorption effect on phosphorus. Plants with long and well-developed plant roots, such as reeds that are used more often at this stage, have a good anaerobic-anaerobic-aerobic environment due to their root system, and have a good removal effect on nitrogen.
Constructed wetlands require high concentration of suspended solids in the influent, so the influent generally passes through the grid to remove coarse particles and then undergoes pretreatment before entering the artificial wetland system to further remove organic pollutants, nitrogen and phosphorus and other substances. Pretreatment facilities include septic tanks, biofilters, and contact oxidation tanks, among which septic tanks are the most commonly used. Due to the effective removal of contaminants, low investment, convenient management and beautification of the environment, constructed wetlands are now widely used in rural areas and scenic spots in the south. Song Xiaokang et al used ABR (anaerobic baffled reactor) and composite subsurface flow constructed wetland to process disperse rural sewage. The results show that this system has good impact resistance. When the constructed wetland operates stably under a hydraulic load of 24.6 cm/d, the main pollutants such as COD, SS, NH4+-N, TN and TP can be reached. The first-class A standard required by GB18918-2002.
At the same time, the artificial wetland has a large area, the processing efficiency in the winter declines, and the design hydraulic load is small (the hydraulic load is not more than 10cm/d for the secondary treatment, and is less than 20~50cm/d for the tertiary treatment) . At this stage, it is difficult to formulate uniform design specifications in different regions. How to ensure that the nitrogen and phosphorus in the water can stably reach the standards in some areas where the requirements for nitrogen and phosphorus in the effluent are relatively high, how to combine the sewage treatment with the recycling of sewage, and how to treat the sewage and landscape The integration of construction is an issue that needs to be resolved in the future. In addition, in terms of the operation and maintenance of constructed wetlands, there is no mature experience in preventing plugging of constructed wetlands, and the long-term operation of constructed wetlands is not yet mature. Under low temperature conditions, the application of some artificial strengthening measures is not mature.
5. Integrated processing device
The integrated treatment device refers to an anaerobic tank, a biological filter, a contact oxidation tank, an oxidation ditch, an SBR, or other technologies or a single or combined transformation into a small integrated sewage treatment system. The integrated A/O biomembrane reactor, integrated biofilter, integrated sbr pool, integrated oxidation ditch, etc. have been applied.
According to the specific situation, the integrated treatment device can be constructed as a buried type, basically reaching the goal of not occupying land. It is applicable to the treatment of domestic sewage in highway service stations, living quarters, and tourist landscape areas, and can also be applied to colder northern regions in winter in order to reduce the influence of temperature on the system operation effect. The investment and operating costs of the integrated treatment system are generally higher than those of the natural ecological treatment system, but the quality of the effluent is better, and it can meet the Class I B standard required by GB18918-2002.
These five major processes will be the mainstream of the environmental protection industry
In recent years, with the rapid development of China's economy and the deteriorating ecological environment, ecological and environmental protection has become an important issue facing the entire society and the country. In the construction of ecological civilization, water pollution is the most serious and thorny issue, and it is closely related to people's lives. The whole society has begun to pay attention to wastewater ecological treatment technologies. Eco-environmental wastewater treatment technology is an important measure to change the status of water pollution, and will also be the development direction of future wastewater treatment technologies. The ecological treatment of sewage has the characteristics of simple operation, low cost, and good effect, and can achieve a healthy development of human living environment. The following five technologies will be the mainstream of the future environmental protection industry.