Environment Technology

Summary of Domestic Sewage Treatment Technology in Constructed Wetlands

2019-1-31

Source:Publication

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1. Basic concepts
Constructed wetland is essentially a comprehensive ecosystem, which mainly uses the regeneration of energy and material cycle of each symbiotic species in the ecosystem. On the premise of promoting the benign cycle of pollutants in wastewater, it gives full play to the potential of resource production, achieves the best benefits of sewage treatment and resource utilization, and prevents secondary pollution caused by sewage to the environment.

2. Technical Principles
The principle of wastewater treatment technology in constructed wetlands is to construct and control the ground similar to that in marshes, and distribute sewage to wetlands in a controlled way. In the process of sewage flowing along certain directions in the soil crevices and surfaces of wetlands, wastewater is treated by the three synergistic effects of soil, artificial medium, plant and microorganism, which are physical, chemical and biological. Technology. The mechanisms of the ecosystem include adsorption, retention, filtration, precipitation, microbial decomposition, transformation, redox, plant shelter, residue accumulation, transpiration water and nutrient absorption, and other functions of various animals.

3. Systematic classification
Constructed wetland treatment system can be divided into the following types: free surface constructed wetland treatment system, subsurface constructed wetland treatment system, vertical flow constructed wetland treatment system, etc.

The pollutants removed by the system include N, P, SS, organic matter, pathogens and so on. Under the condition of low influent concentration, the removal rate of BOD5 and COD in constructed wetland can reach 85%-95% and 80% respectively. The concentration of BOD5 in effluent is 10 mg/L and SS is less than 20 mg/L. Most of the organic matter in wastewater is the nutrient of heteromorphic microorganisms, which are eventually converted into microbial organisms, CO2 and H2.

4. Technical characteristics
Constructed wetland treatment system has the advantages of large buffer capacity, good treatment effect, simple process, less investment and low operation cost, which is very suitable for centralized treatment of domestic sewage in small and medium-sized villages.

5. Scope of application
(1) Constructed wetland wastewater treatment technology is susceptible to climate conditions, and there are great differences between the north and the south. Winter temperature in most areas of the north is low, which makes it difficult to maintain the normal operation of ecosystems or ensure the sewage treatment effect. Therefore, when choosing this technology, we should select suitable plants, and fully consider the problem of wintering plants in the project site.

(2) The treatment technology is suitable for centralized and decentralized wastewater treatment in rural areas, depending on the land abundant situation, residential mode and economic conditions. For villages with dispersed residence and abundant land, decentralized treatment mode can be chosen, taking households as units, making full use of scattered open land in rural areas, and constructing small-scale wetland treatment system, which can meet the effect of purifying sewage and beautifying the environment at the same time. Centralized treatment system is more suitable for rural areas with concentrated living and limited land, especially in villages, towns and newly-built rural communities. Every household discharges sewage through pipelines or ditches into the treatment system for centralized treatment.

(3) The requirement of the technology for the terrain conditions of the project is relatively loose, and the design can be adapted to local conditions.

6. Notes
Using constructed wetland treatment technology, the following points should be paid attention to:

(1) The seepage control system of constructed wetland treatment technology must be done well. For the seepage control of wetland in rural areas, simple and practical methods such as geomembrane or tamping of lime-flyash soil can be used.

(2) Selection of plants in constructed wetlands. Wetland plants are the most obvious biological characteristics of wetland treatment system. They are the main components of constructed wetlands and play an important role in the sewage treatment process. Wetland plants should be selected according to local conditions, taking into account the following characteristics of plants: water tolerance, well-developed root system, perennial, cold tolerance, large amount of nitrogen and phosphorus uptake, both ornamental and economic, and the selection of indigenous species as far as possible. At present, commonly used are reed, cattail, calamus, banana, windmill grass, rainbow bird, water bamboo, onion, rice grass, iris, fern, rush and so on.

(3) The survival rate of constructed wetland plants is mainly guaranteed by the management in the initial stage of plant planting. Wetland plants are best planted in spring, and plants are easy to survive. If it is not planted in spring but in winter, we should do a good job of anti-freezing measures, in summer, we should do a good job of sunshade and sunscreen. In short, measures should be taken according to the actual situation to ensure the survival rate of planted plants.

(4) In the early stage of plant planting, in order to make the roots of plants deeper, it is necessary to control the water level of wetlands to promote the downward growth of plant roots.

(5) Do a good job of daily care to prevent other weeds from breeding and timely removal of dead branches and leaves to prevent decay and pollution.

(6) Frost-proof measures or timely harvesting of cold-resistant plants should be taken before winter comes.

Next paper:Brief Analysis of Ammonia Nitrogen Wastewater Treatment Technology

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