Comparison of advantages and disadvantages of various biological treatment methods for sewage treatment

     Aerobic treatment: activated sludge and biofilm method
Activated sludge:
The Activated Sludge Process (Activated Sludge Process) first appeared in the UK in the early 20th century. It has a history of nearly a hundred years and is currently one of the most widely used sewage treatment technologies. The method has been established in Manchester, England since 1914 Since the sweat test plant, it has a history of more than 80 years. At present, it has become the main body of organic wastewater biological treatment, but there are still some shortcomings that cannot be ignored: poor adaptability to shock loads, sludge expansion is prone to occur, and treatment structures occupy land Large area, high capital investment and operating costs, complicated management, etc. The following are the new processes of activated sludge treatment methods:
Oxidation Ditch (Oxidation Ditch)
The oxidation ditch was first researched and developed by Pasveer in the Netherlands in the early 1960s. The first oxidation ditch sewage treatment plant was built by Pasveer in Voorshoten, the Netherlands in 1954. The oxidation ditch is a process of aeration, sedimentation and sludge stabilization. Integrated and intermittent operation is a modification of the activated sludge method. After 50 years of development, various types of treatment systems have been formed, which have been widely used in urban sweat and industrial sweat treatment projects.
The oxidation ditch has the characteristics of both a completely mixed type and a plug flow type.Under appropriate control conditions, there are both aerobic and anoxic zones in the ditch, which can carry out nitrification and denitrification reactions, and achieve denitrification effects, while making active pollution Mud has good settling properties.

Oxidation ditch is being used in many engineering projects in China due to its simple process, convenient management and good treatment effect. In recent decades, with the continuous development of technology, oxidation ditch has been a breakthrough that is only suitable for small sewage treatment plants. Limitations. Generally speaking, the oxidation ditch has multiple layouts such as single trench, double trench, three trench, multi-ditch concentric and multi-ditch series connection; there are separate or joint construction of the secondary sedimentation tank and the oxidation ditch; there is continuous progress Water or alternating water intake; there are rotary brush aerators, rotary table aerators or pump types, inverted umbrella-type surface aerators for oxygenation and stirring, etc.
Sequencing batch activated sludge process (SBR)
The SBR process is the Sequencing Batch Reactor Activated Sludge Process (SBR), also known as the batch activated sludge process. Due to the indirect operation in operation, each reaction tank is a batch Batch treatment of wastewater, hence the name.
In the late 1970s, the American professor RLlrvine and others first proposed to solve some of the problems in the continuous sewage treatment method, and published the first article in 1979 on the use of SBR process for sweat treatment. Subsequently, Japan, the United States, Australia and other countries The technicians have successively conducted a lot of research.

With the in-depth research, people have a new understanding of the mechanism and advantages of the process. In 1980, with the funding of the U.S. Environmental Protection Agency, Culver City, Indiana, invested in the construction of the world’s first sewage treatment plant with SBR process. .China’s leading sewage treatment facility using the SBR process-the SBR treatment system designed by the Shanghai Municipal Engineering Design Institute was put into use in 1985, and has since been promoted and used in the field of urban sewage and industrial wastewater, and at the same time, it has also set off throughout the country. The upsurge of studying SBR has become a hot spot for scholars at home and abroad in recent years.
At present, SBR is mainly used in the following fields: urban sewage, industrial sewage (mainly industrial sewage treatment such as petroleum, chemical, food, pharmaceutical, etc.), toxic and harmful wastewater and wastewater with nutrients.
SBR is a modification of the activated sludge method. Its reaction mechanism and pollutant removal mechanism are the same as the traditional activated sludge method, but the operation is different. SBR is in a single reactor and performs various purposes in time Therefore, it is called the waste water treatment process on the time series.
A complete operation cycle of the SBR process has five stages: the water inlet period, the reaction period, the precipitation period, the drainage period and the idle period.
One of the more significant features of the SBR method is that the two processes of reaction and precipitation are carried out in the same reactor, which expands the function of the reactor. SBR is an intermittently operating sweat treatment process. The orderly nature of the operation period makes it have Some characteristics different from traditional continuous flow activated sludge process.
1 The process is simple and the operating cost is low;
2 The solid-liquid separation effect is good, and the effluent water quality is good;
3 Flexible operation and stable effect;
4 Good effect of nitrogen and phosphorus removal;
5 Effectively prevent sludge expansion;
6 Impact load resistance;
Traditional SBR has certain limitations in its application.For example, when the inlet water flow is large, the reaction system needs to be adjusted, which will increase the investment.
Biofilm method:
Anaerobic treatment: anaerobic contact method, anaerobic biological filter
Anaerobic biological filter:
Natural purification treatment: stable pond, wastewater land treatment system
Stabilization pond: The oxidation pond is a sewage treatment pond that has been designed and constructed with a dike and an impermeable layer. It is also called a stabilization pond and a biological pond. The oxidation pond has simple structure, easy maintenance and management, good sewage purification effect, and energy saving.
The source of oxygen-mainly provided by the algae through photosynthesis, the pond reoxygenation plays an auxiliary role.　

The oxidation pond can be used as primary, secondary or tertiary treatment.
The main advantage
1. It can make full use of the terrain (old rivers, swamps, canyons), the project is simple, and the infrastructure investment is low;
2. It can realize the recycling of sewage and combine sewage treatment and utilization: ①Agricultural irrigation②The formation of algae, aquatic plants, plankton, benthic animals, fish, shrimp, waterfowl and other multi-level food chains in the oxidation pond forms a composite ecosystem, Convert organic matter in sewage into fish, shrimp, and waterfowl for food.
3. The sewage treatment has low energy consumption, convenient maintenance and low treatment cost.
Shortcomings
1. Long stay time and large area; 　
2. The treatment effect is unstable, and it is greatly affected by natural factors such as season, temperature and light;
3. Improper anti-seepage treatment may pollute groundwater; 　
Wastewater land treatment system:
1. The concept of land processing system
Under artificially controlled conditions, the sewage is put on the land, and a series of chemical, physical, physical, chemical and biochemical purification processes are carried out through the soil-plant system to purify the sewage.
2. The composition of the land processing system
Sewage pretreatment, sewage conditioning and storage equipment
Sewage transportation, distribution and control system
Land purification field, purification water collection and utilization system
3. The principle of action of sewage land treatment　
1. Physical filtration
　The ability of the pores between soil particles to intercept and filter out suspended particles in water.
　Pay attention to the problem: blockage (too many suspended particles, too coarse, too much microbial metabolites)
2. Physical adsorption and physical and chemical adsorption
Van der Waals attraction-mineral particles adsorb neutral molecules
Wastewater land treatment system
1. Slow infiltration system
It is suitable for areas with good water permeability, low evaporation, and humid climate, and uses microorganisms and plants to purify-farmland irrigation.
Water distribution method: surface water distribution, spray water distribution
Low sewage dosing rate and long residence time
2. Rapid infiltration system
It is suitable for soils with excellent water permeability, for the purpose of replenishing groundwater or sewage recycling, and is effective for removing suspended solids, organic matter, phosphorus and metals. Mainly distribute water on the surface, and circulate irrigation and rest irrigation, and set up underground water collection pipes or well groups to collect reclaimed water. If the groundwater is recharged, there is no water collection system, which requires higher pre-treatment.
3. Surface flooding system
It is suitable for clay and loam with poor water permeability. The ground is required to have a slope of 2~8%. The sewage is dosed to the above ground of perennial grass in a controlled manner. The dosing method is sprinkler irrigation or immersion irrigation to control uniform flooding. . Sewage flows slowly along the surface in a thin layer. The vegetation on the ground prevents soil loss and is used for microorganisms to inhabit. The sewage is purified during the flow process. A collection channel is set downstream to collect the treated wastewater.
4. Wetland System
The wetland treatment system is to put sewage into the swamp where the soil is often saturated with water and grow reeds, cattails and other water-resistant plants. The sewage flows in a certain direction. During the flow, under the combined action of soil and water-resistant plants, the sewage is purified A kind of land treatment system. Including natural wetland systems and constructed wetland systems.

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