Ecological treatment and restoration of river water pollution
Water pollution in rivers, lakes, reservoirs, ponds, weirs and canals mainly includes nitrogen, phosphorus and other nutrients and organic pollution. From the integration of physical methods and biological ecological methods, mainly from external source control + internal source control, combined with environmental protection advantage microbial treatment, as we all know, the water body Pollution ecological restoration is the use of the principles of ecosystems to take various biological groups and structures to restore damaged water ecosystems, rebuild healthy aquatic ecosystems, repair and strengthen the main functions of water ecosystems, and enable the ecosystem to achieve overall coordination , A virtuous circle of self-sustainment and self-success-therefore, the biological-ecological approach appears to be the key to ecological treatment and restoration of pollution of rivers, lakes, reservoirs, ponds, weirs, and canals.
Water pollution control technologies mainly include:
1. Physical methods: through engineering measures, mechanical algae removal, sediment dredging, water diversion, etc.
2. Chemical method: adding chemical agents to kill algae, adding iron salt to promote the precipitation of phosphorus, adding lime to remove nitrogen, etc.
3. Biological-ecological methods: stocking algae-controlling organisms, constructing artificial wetlands and aquatic vegetation.
Generally, comprehensive treatment is mainly adopted. Biological-ecological method + physical method is a suitable ecological treatment plan for water pollution in rivers, lakes, reservoirs, ponds, weirs and canals. There are three methods for natural remediation analysis: empirical analysis, one-dimensional settlement analysis; two-dimensional pollutant migration analysis. It is also possible to qualitatively simulate the impact of pollutants on water bodies to deepen people's in-depth understanding of processes such as photosynthesis, respiration and material circulation, thereby contributing to ecological self-repair. The deterioration of water quality is mainly caused by the accumulation of a large number of nutrients imported from the outside in the water body. Effective control of the input of exogenous nutrients is an important prerequisite for the ecological restoration of water pollution, and the endogenous load is also the main source of nutrients.
4. Comprehensive governance
One, Control methods of exogenous pollutants
1. Centralized treatment of sewage and wastewater in the basin: to achieve the discharge of sewage and wastewater in the basin, fundamentally cut off the external input source, and make the water body lose the possibility of enrichment of nutrients. Compared with the source, non-source pollution is not only large in quantity but also difficult to control. You can control the amount of nitrogen fertilizer, balance the ratio of nitrogen, phosphorus, and potassium, return organic fertilizer to the field, develop "microbial fertilizer" and save water in agricultural farmland irrigation. And so on.
2. Restoration and reconstruction of the coastal ecosystem: One is to establish a wetland protection zone around the lake. This is a line of defense to control the flow of nutrients from land surface runoff into the lake from the way of migration and transformation. The second is to restore and rebuild the aquatic vegetation on the shores of lakes, and promote the deposition of pollutants and the absorption of large amounts of nutrients through physical blocking. The third is to transform the ecology and environment of the estuary into the lake and give full play to the natural purification effect of the river into the lake.
Two, Control methods of endogenous pollutants
1. Engineering measures
(1) Dilution and flushing
The use of outflow diversion for dilution and scouring can effectively reduce the concentration and load of pollutants in a short time, improve the self-purification capacity of water bodies, and can also affect the deposition rate of pollutants to sediments. However, diversion of water leads to changes in the ecosystem of the exchange water body, which will also have certain negative effects.
(2) Sediment dredging
Sediment dredging is an effective technology for the restoration of lakes and reservoirs, which can completely remove the toxic and harmful substances accumulated in it, but attention must be paid to prevent sediments from blooming and reasonable disposal of sediments to avoid secondary pollution.
(3) The bottom mud is covered by laying a plastic film or pebbles with low permeability on the bottom mud surface
Reduce the tumbling of the bottom mud during wave disturbance, effectively inhibit the release of nutrients in the bottom mud, improve the transparency of the lake water, and promote the growth of submerged plants. However, there are shortcomings such as treating the symptoms but not the root cause, high cost, and difficulty in large-scale use, and it also affects the inherent ecology and environment of the lake.
(4) Hydraulic dispatching technology
According to different water conditions, organisms can behave in three states in the water: free state, growth state and inhibited state. Hydraulic dispatching technology is based on the ecological and hydraulic characteristics of living organisms to create a specific water flow environment and the environment required by aquatic organisms, inhibit the proliferation of algae, and adopt methods such as water system connection. in principle. However, attention should be paid to flood prevention, waterlogging prevention, sand prevention, snail prevention, pollution migration and prevention of internal source release.
(5) Gas extraction technology
Vacuum pumps and wells are used to induce airflow in the contaminated area to convert organic pollutant vapors or adsorbed, dissolved or free-phase pollutants into gas phases, pump them to the ground, and then collect and process them. In the United States, extraction technology has almost become a "legal" technology to repair groundwater and soil contaminated by gas stations.
(6) Air blowing off technology
Under certain pressure conditions, compressed air is injected into the contaminated area to drive out volatile compounds dissolved in groundwater, compounds adsorbed on the surface of soil particles, and compounds blocked in soil voids. In practical applications, it can be combined with extraction technology to get good results.
2. Bio-ecological approach
(1) Hydrophyte restoration technology
Under suitable growth conditions, aquatic plants that interact with microorganisms, algae and other organisms in the water, according to their own characteristics, absorb the eutrophication substances in the water, such as N, P, heavy metal pollutants, etc. in the roots, stems, leaves, etc. It can not only provide its own nutritional needs, but also purify water quality. Moreover, the biodegradation of organic pollutants can be accelerated by promoting the activities of rhizosphere microorganisms.
At present, the following technologies are researched and widely used at home and abroad:
① Constructed wetland technology
Wetland soil is a loose and porous system composed of solid and liquid phases. It contains a large number of colloidal particles. They have a large surface area and surface energy, and play an important role in removing organic matter and heavy metals. In the wetland treatment system, as long as the physical function is precipitation, filtration and adsorption, solid suspended particles can be removed: the chemical effect is mainly to remove heavy metals and fillers: the biological effect is more complicated, mainly the synergistic effect of aquatic plants and various microorganisms. The shortcoming of constructed wetland technology is that when the influent suspended pollutants (fss) and the concentration of organic matter are too high, it is easy to cause blockage and severe anaerobic oxidation, causing plant roots to rot and die.
②Front library technology
The upstream tributaries of protected lakes use natural or artificial reservoirs (ponds) to intercept storm runoff. The process flow is as follows: runoff sewage-grit tank-water distribution system-plant pond-lake. Aquatic plants are an indispensable main component of the pre-reservoir. They absorb a large amount of nitrogen and phosphorus from the water body and sediment to meet the growth needs, and are removed from the pre-reservoir to be used after maturity. Surface aquatic vegetation restoration technology The so-called "aquatic vegetation restoration technology" does not intend to rebuild the original vegetation, but is based on the actual lake ecology and environmental needs, combined with the remaining aquatic vegetation foundation. To redesign and construct a benign lake ecology based on the destroyed lake environment, the technology must be based on reducing the nutrient load of the water body, otherwise the artificially restored aquatic vegetation cannot maintain a stable state.
③ Hydroponics technology
Use eutrophic water to cultivate economic crops in the planting tank without soil. With the help of the plant's developed root system, the suspended solids flowing into the shallow water are filtered. The suspended organics and nutrients, microorganisms, protozoa and metazoa constructs Create a relatively rich ecosystem. This technology has conducted a lot of research in the United States, Japan and other countries, and can produce edible or ornamental plants with economic value, and achieve resource recycling through composting. The advantage of this technology is to isolate soil pathogens and pests from infecting crops to a certain extent, so there is no obstacle to continuous cropping, and labor is saved.
④ Ecological floating island technology
A type of plant water purification project is a combination of greening technology and floating technology. The floating body for plant growth is generally made of expanded polystyrene, which is light and durable. The plants on the island can be used for rest for birds, and the roots of the lower plants form a habitat for fish and aquatic insects, and can absorb nitrogen and phosphorus that cause eutrophication. Compared with the constructed wetland technology, the ecological floating island technology has the advantage of not occupying additional land, and it is more suitable for the characteristics of the space utilization of most rivers in my country without tidal flats.
In summary, phytoremediation technology has the following advantages: low investment, low energy consumption, the treatment process has a great compatibility with the natural ecosystem, no secondary pollution, can achieve the nutritional balance of the water body, improve the self-purification ability of the water body, All major pollutants in the water body have good treatment effects. Among them, the advantage of dealing with organic pollution is that plants can assimilate most of the compounds into CO, or as cytoskeleton, even if some environmental pollutants accumulate in plants, they can be removed by transferring plants. The limitation lies in the high operating conditions, long processing time, large floor area and severe weather effects. Phytoremediation is considered to be one of the promising environmental remediation technologies, but there are many problems such as how to select, cultivate and rationally match high-efficiency plant varieties to meet the remediation needs of different environments, especially the improvement of phytoremediation efficiency in the low temperature season. Further Discussion. To give full play to the advantages of this technology, the key lies in the basic research on the good removal of different pollutants by different types of plants, so as to realize the optimal aquatic plants according to local conditions and form a good remediation system.
(2) Biological control technology
Biological control technology to restore aquatic ecosystems is to use the trophic chain effect to invest in selected fish in the reservoir to swallow another type of small fish, thereby protecting certain zooplankton from being eaten by small fish, and these zooplankton food It is the algae that people hate. This technology has the following advantages: good treatment effect, low engineering cost, and low operating cost. No secondary pollution will be formed, and the economic benefits of the reservoir can be appropriately improved.
(3) Biofilm technology
According to the filtering and purification effects of the biofilm attached to the natural river bed, the filter material and carrier are artificially filled, the filter material and the carrier have a large specific surface area, and the characteristics of a large number and variety of attached organisms have doubled the self-purification ability of the river. Biomembrane technology has been developed and applied by leaps and bounds due to its strong degradation ability, short contact time, small footprint and low investment. Some developed countries have used a variety of biofilm technologies in engineering practice to purify severely polluted small and medium-sized rivers with good results. Our country is still in the experimental stage in this regard, and there is no real engineering practice. The currently available methods mainly include artificial filler contact oxidation method, thin laminar flow method, floating flow purification method, gravel contact oxidation method, biological activated carbon purification method and so on.
(4) Microbial remediation technology
Microorganisms can degrade organic matter in polluted waters into inorganic matter, and reduce and remove some inorganic pollutants such as ammonia nitrogen. In order to give full play to the role of microorganisms in the degradation and transformation of pollutants, there are currently two ways: one is to supplement pollution Biodegrading microorganisms can use bacteria with a specific function, or they can be isolated and screened from contaminated water and sediments and enriched. When returning to contaminated waters, the conjugative transfer of genetically engineered bacteria can also be used. The second is to provide suitable nutrition and environmental conditions for indigenous microorganisms: Proper nutrition and environmental conditions can activate indigenous microorganisms with slow growth and metabolism or in a stagnant state, so that they can regain the ability to decompose pollutants at a high speed.
(5) Biomimetic plant purification technology
Based on the reconstruction of a healthy river ecosystem, it is designed with materials with strong elasticity, toughness and flexibility to imitate the submerged plant chara in the river ecosystem. The bionic plant uses the original natural biological flora in the river as the source, and forms a biofilm through the natural enrichment of organisms on the surface of the filler silk, and removes pollutants in the water through the life activities of microorganisms. This technology effectively purifies the polluted water body and also has the following characteristics: it does not affect the river's navigation and flood discharge functions, does not damage the river ecosystem, and is suitable for the complex and changeable flow conditions of the river. It has a large specific surface area and a high porosity. It is chemical and biological. It has strong stability, does not dissolve harmful substances, is cheap and easy to install.
(6) Land treatment technology
Sewage, especially domestic sewage, contains a large amount of nutrients such as nitrogen and phosphorus. The use of sewage for agricultural irrigation through slow percolation can meet the nutrients necessary for the growth of crops and other plants. At the same time, pollutants are also removed, which can alleviate the shortage of water resources in my country to a large extent. The process flow chart is as follows: raw sewage-sewage storage tank-anaerobic adjustment tank-land treatment system-drainage well. This method has a good removal effect on nitrogen, phosphorus and other pollutants, but the hydraulic load is generally low and the seepage speed is slow.
(7) Deep water aeration technology
The deep-seated water is extracted by mechanical means for aeration and then refilled into the deep-seated layer, or pure oxygen and air are injected into the water surface and then released. Increase the concentration of dissolved oxygen in the water body, improve the growth environment of cold water fish and increase food supply, and reduce the load of endogenous phosphorus by improving the anaerobic environment of the sediment interface to aerobic conditions. This technology has a profound impact on the restoration of water ecology and environment.
Article link: China Environmental Protection Online http://www.hbzhan.com/Tech_news/Detail/310141.html