Operation Cost Composition and Cost Control of Sewage Treatment Plant

In recent years, with the state's attention to environmental protection and the enhancement of people's environmental awareness, the sewage treatment industry in China has developed vigorously. The development speed is also in the forefront in the world history, and the sewage treatment process has evolved from a single traditional activated sludge process to a combination of various processes or processes. Different treatment processes will produce different operation effects and operation costs will also vary. Traditional activated sludge process and its deformation process are mostly used in large-scale sewage treatment plants, while oxidation ditch process is mostly used in small-scale sewage treatment plants. The capital construction cost of oxidation ditch process is lower than that of traditional activated sludge process, but its operation cost is higher than that of the latter. The smaller the scale of sewage treatment plant, the more obvious the advantages of using oxidation ditch process. Municipal sewage treatment plant is a major energy consumer. By describing and analyzing its various costs, this paper illustrates the importance of energy saving and consumption reduction for sewage treatment plant, and gives detailed cost control measures.

Cost Composition of Sewage Treatment Plant

1. Direct costs

(1) Energy costs: including electricity and water, of which electricity is the main cost, accounting for 40-50% of the total cost.

(2) Material costs: including flocculant fees, laboratory fees, low-value consumables, etc.

(3) Direct labor and welfare: wages and welfare for all production personnel.

2. Manufacturing costs

Including maintenance fee, raw material fee, spare parts fee, etc.

3. Periodic expenses

Various expenses incurred by management departments for organizing and managing production include administrative management, various administrative expenses, financial expenses, depreciation of equipment and other indirect expenses.

4. Cost Composition Analysis of Sewage Treatment

(1) The consumption of electricity and chemicals in production costs is a necessary cost in the production process, which accounts for a large proportion, and must be strictly controlled in the production process in order to effectively reduce costs.

(2) The wages and benefits of employees in production costs are the motive force to improve the enthusiasm of employees, enhance the vitality and cohesion of enterprises, and further improve energy conservation and consumption reduction. They are also the symbols of the development level of enterprises and society. Under normal production and operation conditions, the higher the proportion, the better the development of enterprises.

(3) On the basis of sustainable development of enterprises, manufacturing costs should minimize maintenance, overhaul and investment in fixed assets, so as to maximize the profits of enterprises.

(4) The management fee is an integral part of the operation cost of an enterprise. It should be controlled to minimize unnecessary expenditure and reduce costs.

5. Cost calculation of sewage treatment plant

(1) Electricity cost: The most energy-consuming equipment in sewage treatment enterprises includes various types of pumps, oxygen supply equipment, such as blowers and sludge concentration and dewatering equipment, etc. The unit consumption of sewage treatment can be calculated. On the one hand, the unit consumption of sewage treatment can be analyzed according to the number and power of equipment used, on the other hand, the unit consumption of sewage treatment in previous years can be combined with the unit consumption of sewage treatment in this enterprise. At the same time, according to the relevant local standards, the reasonable unit consumption of sewage treatment suitable for the enterprise is formulated.

For example, the unit consumption of sewage treatment in a provincial municipal wastewater treatment plant operation management assessment standard has clear requirements. The unit consumption of sewage treatment in the first A standard can be divided into four levels, <0.34 degrees/cubic metre, 0.34 degrees/cubic metre-0.37 degrees/cubic metre, 0.37 degrees/cubic metre-0.42 degrees/cubic metre and (>0.42 degrees/cubic metre), and the first B standard. Assessment is carried out according to 70% of the unit consumption of the first A standard and 50% of the unit consumption of the first A standard, which is lower than the first B standard. Therefore, within the range of 0.17-0.42 kWh/cubic sewage, according to the current electricity price of 0.852 yuan/kWh (taking Nanjing as an example), the calculated power consumption cost of secondary sewage treatment enterprises is 0.145-0.358 yuan/cubic sewage.

(2) Pharmaceutical cost: Most of the pharmaceuticals used in sewage treatment plant are polyacrylamide used in sludge dewatering machine or ferric chloride and calcium oxide used in sludge plate and frame filter press dewatering. According to statistics, the sludge output of sewage treatment enterprises is 1 to 1.2 tons of dry sludge per 10,000 tons of sewage. The cost of different sludge treatment equipment is as follows:

The agent used in sludge dewatering machine is cationic polyacrylamide, which contains 0.6% polyacrylamide per ton of dry sludge. The price is 25,000-35,000 yuan/ton. The cost of flocculant is 0.018-0.0216 yuan/cubic sewage calculated by 30,000 yuan/ton.

The dosage of ferric trichloride used in plate and frame filter press is 10% of absolute dry mud, and the unit price is 750 yuan/ton of market price (40% of ferric trichloride). The cost of ferric trichloride is 0.0075-0.009 yuan/cubic sewage. The dosage of calcium oxide used in plate and frame filter press is 30% of absolute dry mud, and the unit price of calcium oxide is 450 yuan/ton (purity 70-80%, granular specification 90-100 mesh). The cost of adding calcium oxide is 0.0135-0.0162 yuan/cubic sewage. Therefore, the cost of dewatering agent for plate and frame filter press sludge is 0.021-0.0252 yuan/cubic sewage.

(3) Cost of overhaul of facilities and equipment: mainly refers to the special fund for overhaul of fixed assets such as facilities and equipment of sewage treatment plants. According to the built sewage treatment plant, the cost of each ton of water is generally 1500-2000 yuan, calculated according to the conventional fixed assets formation rate of 85%, combined with the actual overhaul cost in the past and referring to relevant information, the annual overhaul cost is extracted from 1.7% to 2.0% of the fixed assets, and the fixed assets repair cost of the sewage treatment enterprise is 0.0594.~ 0.0931 yuan per cubic meter of sewage.

(4) Maintenance cost of facilities and equipment: Mainly used for spare parts of fixed assets, low-value consumable and regular maintenance and repair costs of fixed assets, including maintenance of automatic control systems, strong inspection of measuring instruments, preventive testing of electrical equipment and materials used for daily maintenance, etc. According to established