Technology of constructed wetland for sewage treatment and water environment protection
Wetlands store water, regulate the climate, and provide habitats for plants and animals. In addition to natural wetlands, constructed wetlands are mostly irrigation land, water storage area, pond, and can also effectively play a role in sewage treatment and water environment protection. In the 1950s, constructed wetland technology was developed to provide ideas and methods for sewage treatment. In the recent development, the research of constructed wetland technology has been paid attention to and achieved remarkable results.
1. Constructed wetland
Artificial wetland can create wetland environment by artificial means, or use artificial control technology to control wetland ecological environment efficiently. Constructed wetlands ensure the treatment effect of sewage and sludge through microorganisms, soil and plants, and can also increase the oxygen content of water bodies. The technology of constructed wetland involves the principle of material circulation and regeneration, including adsorption, filtration and oxidation precipitation. The application of this technology can significantly reduce the cost of expenditure. Constructed wetlands are mostly used in areas with small population and low pollution. Compared with sewage treatment plants, constructed wetlands mainly apply microbial technology to treat sewage problems, so as to comprehensively improve the cleaning effect and reduce the cost of human and material resources.
2. Decontamination principle of constructed wetland
2.1 Nitrogen Removal
There are a lot of pollutants in sewage, including inorganic nitrogen, organic nitrogen, organic nitrogen involves purine, pyrimidine, urea, etc. Inorganic nitrogen includes ammonia nitrogen, nitrite, nitrate. In constructed wetlands, the application of microbial technology can effectively adsorb pollutants, filter and precipitate at the same time. In the absorption of nitrogen, plants can play a significant role in promoting nitrogen volatilization.
2.2 Phosphorus Removal
Sewage phosphorus includes active phosphorus and inactive phosphorus. In constructed wetlands, there are many ways to remove phosphorus from wastewater, such as aquatic plant absorption, matrix absorption and biological assimilation to accumulate microorganisms. A large number of experiments show that the phosphorus removal effect of reed and water stem is remarkable, and the phosphorus removal rate is 55% ~ 66% after the combination of the two.
2.3 Removing Heavy Metals
In the sewage structure, the proportion of industrial sewage is large, and the content of heavy metal ions is large. In the treatment of heavy metal ions, through the absorption and enrichment of plants, soil colloid, particle adsorption and other ways, the effective adsorption and collection of heavy metals in sewage. In the treatment of constructed wetlands, plant planting can also be used to deal with heavy metal pollution.
2.4 Removing organic pollutants
Constructed wetlands promote the degradation of organic pollutants. The composition of sewage organic matter is complex, involving granular, soluble and insoluble substances. Organic pollutants in sewage are absorbed by microorganisms and plant roots, insoluble organic matter is filtered and treated by nitrification and denitrification mechanisms, and is decomposed by microorganisms. Organic matter is absorbed and utilized by microorganisms and plants and converted into water and carbon dioxide.
2.5 Remove germs and suspended matter
The sewage contains a large number of suspended solids, which has a great pollution effect and more bacteria. The constructed wetland can effectively remove suspended matter and bacteria by filtration, precipitation and adsorption.
3. Application fields of constructed wetland technology
Constructed wetland technology is an important technology in sewage treatment, which can effectively act on domestic sewage and municipal sewage. It is worth mentioning that constructed wetlands can efficiently treat low-concentration sewage, but can not play a significant role in the treatment of active sewage. In urban sewage treatment, constructed wetland purification treatment can be used for secondary and tertiary sewage treatment. In the treatment of industrial wastewater, constructed wetland technology can also be applied. Due to the high concentration of pollutants in the wastewater, preliminary treatment is required before it enters the wetland.
4. Application of constructed wetland technology
4.1 Sewage Treatment
There are abundant land resources in rural areas, and the utilization rate is relatively high, which provides high value application conditions for wetland technology. Common domestic sewage treatment methods include anaerobic tank, septic tank, sedimentation tank, biological filter and so on. In the treatment of domestic sewage, the application advantage of subsurface flow wetland is greater than that of runoff constructed wetland. Subsurface flow wetland can improve the treatment capacity of sewage phosphorus, suspended matter and nitrogen, so it is widely used in rural sewage treatment.
4.2 Water pollution control
The pollution of urban water bodies is relatively large, and there is obvious pollution in rivers and lakes. The technology of constructed wetland can treat polluted water efficiently. The construction of small constructed wetlands in urban residential buildings to treat and store rainwater and realize the secondary use of rainwater, for example, it can be applied to green irrigation to reduce water waste. Constructed wetland technology can be applied in the treatment of tail water of sewage plant, which can ensure the treatment effect of low concentration pollutants and promote the improvement of water environment.
4.3 Restoring polluted water
Constructed wetland has many functions, which can not only degrade water pollutants, but also restore polluted water. The sewage discharged into the constructed wetland can play a purifying effect. The subsurface flow constructed wetland is built near the polluted water source to improve the treatment effect of nitrogen and phosphorus removal and eliminate organic matter in the water body. Reasonable application of constructed wetland technology can restore sewage, and has a remarkable effect on the treatment of sewage in urban parks, lakes and rivers.
4.4 Regulation of urban climate
Reasonable application of constructed wetland technology can purify air and regulate local climate. According to the relevant research, the evaporation capacity of wetland is relatively large, and the use of artificial technology to plant vegetation can expand the heat capacity of wetland. Constructed wetland technology can not only regulate the ambient temperature, but also regulate the surrounding wetlands, effectively alleviate the heat island effect, and improve air quality. Wetland plants absorb atmospheric carbon dioxide through photosynthesis, achieve dynamic balance of carbon dioxide and water, and reduce the total amount of carbon dioxide.
4.5 Purify water resources and improve water resource utilization
Water eutrophication is a serious problem in most areas, and the sewage contains a lot of phosphorus and nitrogen. According to relevant studies, conventional sewage treatment methods can not only deal with nitrogen and phosphorus efficiently, but also aggravate the eutrophication of surface water. The investment cost and use cost of traditional nitrogen and phosphorus removal technology are relatively high, and the secondary pollution is obvious. The use of wetland plants can effectively remove nitrogen and phosphorus in sewage, and then provide high-quality water for local residents. Constructed wetland technology can also replenish groundwater. At present, the underground development space is gradually expanding, leading to the reduction of groundwater resources, and the problem of water level decline in some areas is serious. The technology of constructed wetland can effectively recharge groundwater and prevent ground subsidence.
The constructed wetland system can provide water for the urban aquifer, and the water source of the wetland integrated into the aquifer can be pooled into groundwater, effectively replenishing the shallow groundwater system, while maintaining the surrounding water level. The development of underground space reduces the groundwater level, which easily leads to the subsidence of the area, and the groundwater recharge through the constructed wetland system can avoid geological disasters. Wetlands are large water storage systems with a large capacity that can regulate the natural amount of water by storing rainwater during heavy rains. Artificial channels can recharge urban groundwater, which can be used for urban green space and ground sprinkling, etc., to alleviate the pressure of urban water supply and reduce water waste.
5. Application prospect of constructed wetland technology
Constructed wetland technology can effectively remove organic pollutants, nitrogen and phosphorus substances, fully demonstrate the potential of resource production, and realize the treatment effect of sewage resources, which is an efficient way to treat sewage. Constructed wetland sewage treatment technology integrates environmental benefits, economic benefits, social benefits, low investment cost, high efficiency, low operating costs and maintenance costs, and small power consumption, which is an important supplement for secondary sewage treatment plants. The treatment of sewage by constructed wetland technology can meet the requirements of harmonious development between man and nature and build a benign ecological environment. This method has broad application prospects and can be applied to small and medium-sized cities and rural areas. Since constructed wetlands cover a large area and have a large impact on restoration and restoration, the waste of land resources should be reduced in the application of constructed wetland technology, reasonable selection of sites, wetland systems and plants should be combined with the actual situation of the region, and cooperation with other countries to ensure that wetland systems are better applied to sewage treatment.
6. Conclusion
The secondary activated sludge treatment technology is used in sewage treatment plants in most areas, which has high engineering investment and high investment benefit. The constructed wetland treatment system can combine many benefits and has low operation and maintenance cost. However, because the treatment technology of constructed wetland is in the initial stage, the process data and examples are few, it is necessary to deeply analyze the actual situation of the region, obtain the relevant environmental and climatic conditions, and fundamentally promote the application of the treatment technology of constructed wetland in the region.
