Cui Chengwu 1, * Gert Peterson 1, 2
(1. Data transmission unit of Lindby Institute of Environment and Resources, Denmark, 2800; 2. Envidan, kastrup, Denmark, 2770)
This paper briefly introduces the present situation of urban sewage treatment in Denmark, including the number, types and treatment load of urban sewage treatment plants, as well as the relevant requirements of EU and Danish environmental protection departments. In addition, for large-scale urban sewage treatment plants, this paper takes Lynetten, Damhusen, Lundtofte and Avedre as examples to introduce their experience in operation, maintenance and management. Finally, this paper also introduces the sewage and sludge treatment costs of sewage plants in Denmark and the above four cities.
Key words: Denmark, sewage treatment, sludge treatment, gas treatment, urban sewage treatment plant, operation management, operation cost.
China Library Classification Number: X703. 1 Document Identification Number: A.
Operation, maintenance and management of large domestic sewage treatment plants in Denmark
Cui Chengwu 1, * Gert Peterson 1, 2
(1. Institute of Environment and Science. Resources, data transfer unit, Limby, Denmark, 2800 2. Envidan, kastrup, Denmark, 2770)
Abstract: This paper briefly introduces the situation of domestic sewage treatment in Denmark, including the number, types and treatment capacity of domestic sewage treatment plants, as well as the discharge requirements of EU and Danish Environmental Protection Agency. Mainly according to the United States, Lennton, Dahus? Well, Lund tofte and Arbide? About WWTP in Denmark. Finally, this paper also introduces the average sewage treatment cost in Denmark and the operating cost of sewage treatment and sludge treatment in these four sewage treatment plants.
Key words: Denmark, wastewater treatment, sludge treatment, gas treatment, domestic sewage treatment plant, operation management, operation fee.
1. Introduction
Denmark is located in the northern part of Europe, with developed economy, and its per capita GNP ranks among the top in the world. At the same time, the Danish government attaches great importance to environmental protection, especially urban sewage treatment. In the third and fourth summary reports of the European Commission on the implementation of 9 1/27 1/EEC (Urban Sewage Treatment Act), Denmark, Germany, Austria and other countries are among the countries with better urban sewage treatment in the European Union. Since the implementation of EU Act 9 1/27 1/EEC, the effluent quality of municipal wastewater treatment plants and industrial wastewater treatment plants in Denmark has been significantly improved. From 1989 to 2004, the development of urban sewage treatment in Denmark can be divided into two stages, namely, the rapid effect stage of 1989 ~ 1996 and the steady decline stage of 1996 ~ 2004. For example, in 1989, the total output of BOD5 from Danish municipal sewage treatment plants was 35,000 tons. By 1996, this figure dropped rapidly to 5,000 tons, and by 2004, it dropped steadily to 2,500 tons.
The Danish government stipulates that when the population equivalent is more than 30PE 1, it is necessary to build corresponding sewage treatment equipment. According to the statistical results in 2004. See Table 2 for the treatment load and influent load of the sewage treatment plant in 2004.
Lynetten is the largest municipal sewage treatment plant in Denmark, with a designed treatment capacity of 654.38+500,000 tons/day. In 2004, the actual inflow load was nearly 200,000 tons/day. Damhus? En is the third largest urban sewage treatment plant in Denmark, with a designed treatment capacity of 70,000 tons/day. Damhus? En and Lynette belong to Lynettenf? The management of Llesskabet Company (Lynetten United Company). Aved？ Re is the fifth largest sewage treatment plant in Denmark, with a designed treatment capacity of 64,000 tons/day, which belongs to Denmark's Spildevandscenter Aved? re (Aved？ Re sewage center) management. Lundtofte is relatively small with a design capacity of 22,000 tons/day.
See Table 3 and Table 4 for the influent quality characteristics and effluent conditions of the above four sewage plants.
After analyzing the influent quality, it is found that the influent COD/BOD5 values of the four sewage plants all belong to the middle and low value range in reference [6], which may be related to the inflow of industrial wastewater. Through summary, it is found that the COD/TN and COD/TP of urban sewage in Denmark are within the range of medium and high values specified in reference [6].
It was found that the effluent indexes of the main pollutants in the four municipal sewage plants were lower than the relevant requirements of EU 9 1/27 1/EEC Act and Danish environmental protection department.
2.2 process flow
The process of Danish urban sewage treatment plant can be generally divided into three parts: sewage treatment unit, sludge and waste treatment unit and waste gas treatment unit. Lund tofte Sewage Treatment Plant is a typical Danish municipal sewage plant. The following parts are discussed according to the technological process of Lundtofte Sewage Plant. The specific process flow of Lundtofte Sewage Treatment Plant is shown in Figure 2.
2.3 sewage treatment plant
2.3. 1 mechanical treatment
For municipal sewage plants, the mechanical treatment of sewage usually includes coarse grid, aerated grit chamber, fine grid, primary sedimentation tank and secondary sedimentation tank. Because the design of various mechanical treatment processes is very mature, it is not necessary to discuss them in detail. However, the treatment of waste and waste gas produced in the process of mechanical treatment is worth learning and using for reference.
Before entering the aeration tank, a series of mechanical treatment processes will produce a lot of waste. The practice of large-scale urban sewage plants in Denmark is that the solid waste does not enter the anaerobic digester with the surplus sludge, but directly enters the sludge incinerator for incineration after dehydration. This is because the inorganic matter content in this kind of solid is relatively high, and directly entering the digester will affect the anaerobic digestion effect. In addition, this kind of waste has not been used for building recycling, mainly because this kind of sand contains heavy metals and persistent organic compounds, which is potentially harmful to human health.
Large-scale urban sewage treatment plants in Denmark attach great importance to the collection and treatment of waste gas produced by aeration or stirring during mechanical treatment. Generally speaking, all aerated grit chambers are covered with aluminum. The primary sedimentation tanks of some sewage treatment plants will also be capped. Gases generated in the treatment process, such as H2S, will also enter the incinerator for treatment along with specific gas pipelines.
biological treatment
As mentioned above, the biological treatment process of sewage in large-scale urban sewage plants in Denmark is very close. The above four sewage treatment plants all adopt biological denitrification or biological denitrification process. Let's briefly introduce these two processes.
1 process introduction
Biological nitrogen removal and biological nitrogen removal process are patented technologies of Krüger Company in Denmark. This technology has the characteristics of high degree of automatic control, small floor space and good removal effect of organic matter and nitrogen and phosphorus. Different from the biological nitrogen removal process, Biodenipho realizes the function of biological phosphorus removal by adding an anaerobic tank in front. However, biological nitrogen removal can not carry out biological phosphorus removal, but only chemical phosphorus removal.
Taking the biological denitrification process as an example, this paper focuses on the operation and control of this process.
The operation of biological nitrogen removal process is based on oxidation ditch technology (most urban sewage plants in Denmark adopt oxidation ditch technology based on surface exposure). Usually, two oxidation ditches are divided into one group and operated by alternating aeration to achieve the purpose of nitrification and denitrification. The biological denitrification process is divided into four stages, as shown in Figure 3. Among them, it is worth noting that there are two main purposes for setting Grade B and Grade D: one is to remove the residual ammonia nitrogen in the first-stage anoxic pool; Second, because nitrification takes a relatively long time, in order to achieve better effluent standards.
Generally speaking, although the Biodenipho process has a strong biological phosphorus removal function, the sewage treatment plant will still assist in using chemical phosphorus removal methods to achieve a better TP concentration in the effluent. This is especially true for sewage treatment plants that use biological denitrification process. Generally, FeCl3 _ 3 _ 3 or AlCl3 _ 3 _ 3 is put into the aeration tank. An online phosphorus monitoring device is installed behind the aeration tank, which will automatically add and remove phosphorus when the TP concentration exceeds the standard.
2.3.2.2 control system
The above four large-scale urban sewage treatment plants all adopt SCADA and STAR systems to control the normal operation of sewage plants. SCADA technology is based on 3C+S (computer, communication, control and sensor). The system is mainly used to control the pumping station, flow and sludge dewatering process. STAR system (patented technology of Krüger Company) is based on SCADA system and is an application software system for controlling the operation of aeration tank. On-line measuring instruments will be installed in the oxidation ditch to send the parameter information of main pollutants such as ammonia nitrogen, nitrate nitrogen, total phosphorus and dissolved oxygen concentration to the central PLC. The operation time and aeration mode of each aeration tank are controlled by microcomputer program. Therefore, the specific running time of the four stages shown in Figure 3 is controlled by the STAR system through the data of specific pollutant concentration in the aeration tank, but there will be a longest running time. The longest running time of each stage of Lundtofte Sewage Treatment Plant is 90 minutes.
In addition, if there is a problem with the equipment, the program will automatically send a short message to the technician's mobile phone to inform the specific location of the technical fault. At the same time, the microcomputer program will automatically send an email to the technician to inform the specific problem, and the technician can judge whether the fault problem should be dealt with immediately.
2.4 Sludge treatment unit
2.4. 1 Brief Introduction of Sludge Treatment in Denmark
The European Union and the Danish government attach great importance to the sludge produced by municipal sewage treatment plants and its treatment and discharge, and have formulated relevant bills, such as 86/278/EEC Bill, 9 1/27 1/EEC Bill, etc. The contents of heavy metals and persistent organic compounds in sludge discharged from municipal sewage treatment plants are specified.
According to statistics, from 1999 to 2005, the sludge treatment and discharge of Danish urban sewage plants have changed to some extent, as shown in Table 5. It can be seen that the most obvious change is that the proportion of sludge incineration has increased significantly and the proportion of landfill has decreased significantly. The proportion of sludge incineration increased from 6% in 1999 to 25% in 2005. Sludge from the above four large-scale urban sewage plants in Denmark has been burned. In addition, although the total sludge output has increased, the per capita sludge output has remained basically unchanged.
sludge disposal
The residual sludge discharged from the primary sedimentation tank and the secondary sedimentation tank is firstly dewatered and flocculated, and then subjected to anaerobic digestion. Most urban sewage plants in Denmark adopt mesophilic anaerobic digestion process, with the temperature controlled at 32 ~ 37℃ and SRT controlled at 25 ~ 30 days. Generally speaking, after anaerobic digestion, the solid content of sludge is about 1.55 ~ 3%.
After anaerobic digestion, the sludge enters a centrifuge for dehydration, and the solid content of the sludge is increased to 20% ~ 32%. The residual sludge after centrifugal dehydration will be mixed with the sludge in the grit chamber and then enter the incinerator. After incineration, the sludge is collected and transported to the landfill.
2.4.3 Biogas
Generally speaking, the methane content in the biogas produced by the anaerobic digester of the Danish municipal sewage plant is about 65%, and each biogas produced is 1. 1.5 kg of dry sludge will decrease. Biogas can be effectively collected and reused. There are two main ways of recycling: one is to generate heat energy and electric energy for internal use in the factory; The other part is sold to nearby factories or natural gas companies.
2.5 Waste gas treatment device
In the process of sludge incineration, Danish municipal sewage plants attach great importance to potential air pollution. The waste gas produced by the incinerator must be deeply treated before it can be discharged into the atmosphere. Taking Lundetov Sewage Plant as an example, this paper briefly introduces the advanced gas treatment equipment and device after sludge incineration.
After cooling, the waste gas discharged from the incinerator first enters the cyclone separator, during which 85% ~ 90% of ash will be separated from the gas. Subsequently, the gas enters the annihilation furnace for advanced treatment. In the annihilation furnace, water is sprayed first to further cool the gas. There is dissolved sodium bicarbonate and a small amount of activated carbon in the water. The main purpose is to absorb sulfur dioxide, hydrogen chloride and hydrogen fluoride with sodium bicarbonate and convert them into sodium sulfate, sodium chloride and sodium fluoride. Activated carbon is used to adsorb heavy metals such as mercury. Finally, the treated gas enters the bag separator for solid-gas separation, and all the solids and sludge are transported to the landfill, and the treated gas is discharged into the atmosphere through the chimney.
3. Energy consumption, chemical consumption and operation cost of sewage plant
Because the technology, operation mode and management structure adopted by large-scale urban sewage plants in Denmark are similar, the statistical data of energy consumption and operation cost of sewage plants are also consistent. Statistical accounting of these data is of certain value and significance to the design, operation, management and evaluation of urban sewage plants that intend to adopt or have adopted similar processes in China in the future.
However, in view of different national conditions and different ways of environmental and sewage management, it is unreasonable to describe the operating cost of sewage treatment plants in a single currency (such as euro). Therefore, in the specific accounting of operating expenses, it is discussed from the following aspects. Chemicals are measured by the amount of drugs; Energy is measured in kWh.
3. 1 energy consumption of sewage treatment plant
The power consumption of large-scale urban sewage plants in Denmark is 35 ~ 45 kWh/(PE year) and 0.5 ~ 0.6 kWh/m3 sewage. The power consumption of biological sewage treatment is about 0.20 ~ 0.25 kWh/m3 sewage, accounting for 30% ~ 50% of the total power consumption; The power consumption of sludge treatment accounts for about 30% ~ 40% of the total power consumption; Electricity consumption for sewage lifting, mechanical treatment and management accounts for about 15% ~ 35% of the total electricity consumption. Sludge treatment, it takes 0.02~0.06 kWh to treat 1kg dry sludge.
3.2 chemical dose
Chemicals in sewage plants are mainly used for chemical phosphorus removal and sludge dehydration. For chemical phosphorus removal, different sewage treatment plants use different substances. For example: Lynetten Sewage Plant adopts FeCl 3；; While the Lundtofte Sewage Plant adopts AlCl3. The dosage of chemical substances is directly related to wastewater quality, process and effluent index. See Table 6 for chemical phosphorus removal in Lynetten and Lundtofte sewage treatment plants.
From the data in Table 6, it can be seen that the Biodenipho process with biological phosphorus removal function can save the quality of chemical phosphorus removal and obtain better TP effect in the effluent under the condition of basically the same TP concentration.
3.3 Operating cost of sewage treatment plant
The main operating expenses of Danish urban sewage plants are four parts: personnel salaries, taxes, energy consumption and chemicals, and operation and maintenance expenses. With Lynetten and Damhus? En, for example, in 2005, the operating expenses of two sewage plants were 654.38+86 billion DKK, and the specific proportion distribution is shown in Figure 4.
In general, the biggest expenditure of Danish sewage treatment plants is the salary of employees. At the same time, a considerable part of the operation and maintenance is used for venue leasing. In addition, Danish sewage treatment plants need to pay taxes and fees for sewage and sludge treatment to the government. Sludge incineration and transportation to landfills are also taxed. In Denmark, there is no need to pay taxes to the government only when the sludge is reused. Generally speaking, the sludge treatment cost of Danish urban sewage treatment plants accounts for 40% ~ 50% of the total operating cost (excluding labor costs and taxes).
See Table 7 below for the statistics of operating costs of the above four sewage plants.
It is worth mentioning that the average sewage treatment cost in Denmark is 15 DKK/m3, which is quite different from the sewage treatment cost of urban sewage treatment plants after accounting. The main reason is that the total cost of sewage treatment in Denmark includes not only the operation cost of sewage treatment plants, but also the construction and maintenance cost of sewage pipelines. The maintenance and management of municipal sewage pipelines belong to all administrative regions.
4. Conclusion
Great changes have taken place in urban sewage treatment in Denmark since 1990s. This change is due to the Danish government's active implementation of the EU 9 1/27 1/EEC Act, and the formulation of stricter relevant emission standards. Large-scale urban sewage plants in Denmark are similar in operation technology and management mode. Summarizing its development experience and management system, making statistics and absorbing and digesting effective data are very beneficial to sewage treatment in developing countries.
References:
[1] The third report submitted by the Committee to the Council, the European Parliament, european economic and social committee and the regional committees-2 1/271/EEC's implementation of Council Directive 21May/20091on municipal wastewater treatment. Access via Internet (20/08/2007):
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