What are the methods of wastewater treatment

sewage treatment, wastewater treatment in order to make the sewage after a certain method of treatment, to meet certain standards set, discharged into a body of water, discharged into a body of water, or re-use of some of the measures taken by or methods.

Modern wastewater treatment technology, according to the degree of treatment, can be divided into primary, secondary and tertiary treatment.

Primary treatment, the main removal of sewage in a suspended state of solid pollutants, most of the physical treatment method can only complete the requirements of primary treatment. After primary treatment of sewage, BOD can generally remove about 30%, not up to discharge standards. Primary treatment belongs to the pretreatment of secondary treatment.

Secondary treatment, the main removal of sewage in the colloidal and dissolved organic pollutants (BOD, COD substances), the removal rate of up to 90% or more, so that organic pollutants to meet the discharge standards.

Tertiary treatment, further treatment of difficult to degrade organic matter, nitrogen and phosphorus can lead to eutrophication of the water body, such as soluble inorganic substances. The main methods are biological denitrification and phosphorus removal, coagulation and precipitation, sand rate method, activated carbon adsorption, ion exchange and electro-osmosis analysis.

The whole process is through the coarse grid deletion of raw sewage through the sewage lifting pump, after lifting, through the grid deletion or sieve rate, and then into the sand sedimentation tank, after the sand and water separation of sewage into the initial sedimentation tank, the above for the first level of treatment (i.e., physical treatment), the primary sedimentation tank of the effluent into the biological treatment equipment, there are activated sludge and biofilm method, (which activated sludge method of the reactor has aeration tank, oxidation ditch, etc.), biofilm method includes biological filter tanks, and biofilm method includes biological filter tanks. (The reactors of activated sludge method are aeration tank, oxidation ditch, etc.), biofilm method includes biofilter, bio-turntable, bio-contact oxidation and bio-fluidized bed), the effluent of the biological treatment equipment enters into the secondary sedimentation tank, and the effluent of the secondary sedimentation tank is disinfected and discharged or enters into the tertiary treatment, which is the end of the primary treatment to the secondary treatment, and the tertiary treatment includes the biological denitrification and removal of phosphorus, coagulation and sedimentation, sand filtration, activated carbon adsorption, ion exchange and electro-dialysis method. Part of the sludge from the secondary sedimentation tank is returned to the primary sedimentation tank or biological treatment equipment, part of it goes into the sludge thickening tank, and after that it goes into the sludge digesting tank, and after the dewatering and drying equipment, the sludge is finally utilized.

Analysis of the energy consumption of each treatment structure

1. Sewage lifting pumping station

The sewage entering the sewage treatment plant enters the sewage lifting pumping station through the coarse grids and is lifted by the sewage pumps to the front pond of the sand sedimentation tank. Pump operation to consume a lot of energy, accounting for a considerable proportion of the total energy consumption of sewage plant operation, which is related to the sewage flow and to lift the head.

2. sand sink

Sand sink function is to remove the specific gravity of inorganic particles. Sand sedimentation tank is generally set up in front of the pumping station, inverted siphon before, in order to reduce the inorganic particles on the pump, pipeline wear and tear; can also be set up in front of the primary sedimentation tank, in order to reduce the load on the sedimentation tank and improve the sludge treatment conditions of the treatment structure. Commonly used sedimentation tanks are advection sedimentation tank, aeration sedimentation tank, Dore sedimentation tank and bell-type sedimentation tank.

Sedimentation tanks require energy supply is mainly sand and water separator and sand suction machine, as well as the aeration system of the aeration tank, Dore sedimentation tank and bell-type sedimentation tank power system.

3. Initial sedimentation tank

First sedimentation tank is the theme of the primary sewage treatment plant treatment structures, or as a secondary sewage treatment plant pretreatment structures located in front of the biological treatment structures. The object of treatment is SS and part of the BOD5, can improve the operating conditions of the biological treatment structure and reduce its BOD5 load. Primary sedimentation tanks include stratospheric sedimentation tanks, radial flow sedimentation tanks and vertical flow sedimentation tanks.

The main energy-consuming equipment of the primary sedimentation tank is the mud-discharging device, such as chain belt scraper, mud-scraper and skimmer, suction mud pump and so on, but due to the influence of mud-discharging cycle, the energy consumption of the primary sedimentation tank is relatively low.

4. Biological treatment structures

Sewage biological treatment unit process energy consumption to account for a considerable proportion of the direct energy consumption of sewage plants, it and sludge treatment unit process energy consumption and accounted for more than 60% of the direct energy consumption of sewage plants. Activated sludge method of aeration system of aeration to consume a lot of electricity, which is basically linked to the operation, and the power is larger, otherwise it can not achieve a better aeration effect, the treatment effect is not good. Oxidation ditch treatment process installed aeration machine is also a great energy consumption equipment. Biofilm method of treatment equipment and activated sludge method compared to lower energy consumption, but the current application is less, is the future need to vigorously promote the treatment process.

5. Secondary sedimentation tank

Secondary sedimentation tank capacity consumption is mainly in the sludge pumping and sewage indicating the removal of floating materials, energy consumption is relatively low.

6. Sludge treatment

Sludge treatment process in the thickening tank, sludge dewatering, drying are to consume a lot of electricity, sludge treatment unit of energy consumption is quite large, the power consumption of these devices are very large.

Aiming at the energy-saving ways of each treatment structure

1. Sewage lifting pumping station

Sewage lifting pumping station to save energy, the main consideration of the sewage lifting pumps how to save electricity, the correct and scientific selection of pumps, so that the pumps work in the high-efficiency section is an effective means of rational use of the topography, reduce the height of the sewage lifting to reduce the pump shaft power N is also an effective method, regular maintenance of the pumps, regular maintenance of the pumps, the pumps, the pumps and the pumps, the pumps and the pumps, the pumps and the pumps. The regular maintenance of the pump to reduce friction can also reduce power consumption.

2. Sedimentation tank

The use of advection sedimentation, avoid the use of sedimentation tanks that require power equipment, such as advection sedimentation tank. The use of gravity sand removal, avoid the use of mechanical sand removal, these measures can greatly save energy.

3. Initial sedimentation tank

First sedimentation tank energy consumption is low, the main energy consumption in the sludge removal equipment, the use of hydrostatic pressure will undoubtedly significantly reduce the consumption of energy.

4. Biological treatment structures

Foreign scholars through the energy and cost-effective analysis of the biological treatment process, they believe that most of the energy consumption of the treatment facilities is occurring in the motor of a single piece of equipment, and thus energy saving should be improved from the whole plant power factor, selecting high-efficiency electromechanical equipment and to reduce the peak of the power requirements and so on. They proposed energy-saving measures to improve the electrical performance of the motor, including the solution of the operation of the process, including sewage plant products in the energy recovery (Energy

Recovery).

The energy consumption of the aeration system is quite large, the study of the energy efficiency of the aeration system always involves the renovation and innovation of aeration equipment. New aeration equipment, although endless, but still can be divided into two categories: the first is the use of submerged porous diffusion head or air nozzles to produce air bubbles will be passed into the aqueous solution of oxygen, the second is the use of mechanical methods of stirring the sewage to promote the dissolution of atmospheric oxygen in the water method. Microporous aeration, aeration diffuser head layout and aeration system adjustment are effective measures for energy saving. In the traditional activated sludge treatment plant aeration tank to create a front-end anaerobic zone, with submerged mixer mixing energy-saving, biological phosphorus removal program. This simple transformation can save nearly 20% of the aeration energy consumption, if counted in the mixing energy, energy saving also reached 12%. The application of automatic control system for energy saving in sewage treatment, aeration system for stage aeration, dissolved oxygen concentration gradient exists, which not only reduces energy consumption, but also improves the treatment effect and reduces the amount of sludge.

Biofilm treatment process using anaerobic treatment can significantly reduce energy consumption.

5. Secondary sedimentation tank

Secondary sedimentation tank in the study of the sludge discharge equipment and sludge discharge mode improvement is an effective way to reduce energy consumption.

6. Sludge treatment

Sludge treatment system energy saving research is mainly focused on the energy recovery of sludge treatment. Recovery of energy from organic pollutants in sewage sludge for the treatment process has been put into practice as early as the beginning of the last century, but has not been emphasized before the energy crisis. Currently, there are two ways of recovery: one is the utilization of sludge anaerobic digestion gas, and the other is the utilization of sludge incineration heat.

Digested gas is stable and easy to store, it can be converted into mechanical or electrical energy by internal combustion engine or fuel cell, and the waste heat can be recycled for heating of digested sludge. Therefore, the use of digested gas can solve the problem of energy self-sufficiency of sewage plants to varying degrees. Lin Rongchen et al. compared the two forms of utilization of biogas generator and fuel cell, and concluded that the fuel cell has high energy utilization and has a good development prospect. Maximizing the utilization of digested gas is the main way to improve energy efficiency. The research and application of grid-connected biogas generator sets have been applied in China, which is a feasible way to comprehensively utilize biogas in large-scale sewage treatment plants.

Another way of energy recovery is to build municipal solid waste incinerator next to the sewage treatment plant, the solid waste and sewage sludge together with the incineration, the electricity obtained for the operation of the treatment plant.

Municipal wastewater treatment of energy consumption analysis and energy-saving technology and means of development is often not synchronized. Due to the lack of energy balance analysis of sewage treatment methodology, the development and implementation of energy-saving measures are often ahead of schedule. And most of the energy-saving ways and means are often combined with the actual situation of the treatment plant operators and managers of the treatment facilities proposed, empirical and individual, not necessarily applicable to other sewage plants and even sewage plants with similar processes; on the other hand, in a broad sense, the field of sewage treatment discipline of technological innovation, the use of new materials and new equipment are embedded in energy-saving efficiency potential, and thus energy-saving ways and means often is very broad.

Conclusion

Wastewater treatment is energy intensive (energy intensity) type of integrated technology. For a period of time, large energy consumption and high operating costs have hindered the construction of urban sewage treatment plants in China to a certain extent, and some of the completed plants have been in a state of shutdown and semi-suspension due to energy consumption. In the future for a long period of time, energy consumption will become the bottleneck of urban sewage treatment. Whether we can solve the problem of energy consumption of sewage consumption plant, rational energy allocation, has become a key factor in determining the operating efficiency of sewage treatment plants. Whether the energy consumption is low, but also the future of the new sewage treatment plant feasibility analysis of the decisive factor, the development of energy-efficient sewage treatment technology, rational design and operation of sewage treatment plants will be the future of sewage treatment plant design and operation of the road.