The selection of core equipment for the reclaimed water reuse system is directly related to the system's operational efficiency, effluent quality, and economic benefits. As key components of the system, the selection of pumps, membrane components, and disinfection devices requires comprehensive consideration of various factors such as treatment scale, water quality characteristics, operating costs, and maintenance requirements.
1、 Selection criteria for pumps
1. Flow and head calculation
Flow determination: The flow rate of the pump should be determined according to the system processing scale, usually taking 1.1-1.2 times the maximum flow rate as the selection basis. The calculation formula is: Q=P × η/(2.73H), where Q is the flow rate (m3/h), P is the shaft power (kW), η is the pump efficiency (%), and H is the head (m).
Head calculation: The total head is composed of static head, dynamic head, and pressure loss. Static head refers to the height difference between the centerline of the pump outlet and the water surface of the suction tank; Dynamic head refers to the pressure converted from the kinetic energy obtained by a liquid passing through a pump; Pressure loss includes pipeline friction loss and local resistance loss. The formula for calculating the total head is: H=H suction+H pressure - h loss, where h loss is the energy loss caused by pipeline friction and valve resistance.
2. Selection principle
-Flow matching: The rated flow of the selected pump should match the system design flow to avoid the phenomenon of 'big horse pulling small car'
-Head margin: The calculated total head needs to be increased by a safety margin of 10% -20% to cope with the maximum resistance increase during system operation
-Efficiency optimization: When selecting a water pump, it should be ensured that the operating point falls near the high-efficiency area of the pump to ensure stable and economical operation
-Medium adaptability: Select the corresponding pump material (cast iron, stainless steel, fluoroplastic, etc.) based on the characteristics of the conveying medium (such as clean water, sewage, corrosive liquids)
3. Power Calculation
The formula for calculating shaft power is P=ρ× g × Q × H/1000 η, where ρ is the liquid density (kg/m3), g is the gravitational acceleration (9.81m/s?), Q is the flow rate (m3/s), H is the head (m), and η is the pump efficiency (%).
2、 Selection criteria for membrane components
1. Membrane type selection
Ultrafiltration membrane: suitable for the pretreatment stage, with a filtration accuracy of 0.002-0.1 μ m, it can effectively remove large molecular organic matter, colloids, bacteria, etc. PVDF material has the characteristics of good hydrophilicity, resistance to organic pollution, acid and alkali resistance, and the operating pressure is generally 1-7 bar.
Reverse osmosis membrane: used for deep desalination, with a filtration accuracy of 0.0001 μ m and a desalination rate of over 99%. The main material is aromatic polyamide, with high operating pressure, usually used for pure water preparation.
Nanofiltration membrane: Between ultrafiltration and reverse osmosis, with a pore size of 1-2nm, it can selectively remove divalent and trivalent ions and organic matter with a molecular weight of 200-800, with a desalination rate of 20% -98%.
2. Selection parameters
-Membrane flux: The design flux of ultrafiltration membrane is usually 8-15L/(m? · h), while the flux of reverse osmosis membrane is selected according to water quality, generally around 17.8 LMH
-Membrane size: 4040 membrane element is selected for water production less than 4T/H, and 8040 membrane element is selected for water production greater than 4T/H
-Recovery rate: The ultrafiltration system can achieve a recovery rate of 88% -90%, while the reverse osmosis system is determined based on the inlet water quality
-Anti pollution performance: Choose anti pollution film or standard film according to the inlet water quality
3. Membrane arrangement method
Reverse osmosis systems typically adopt a multi-stage series arrangement, such as a 28 × 14 arrangement (28 membrane tubes in the first section and 14 membrane tubes in the second section). By arranging suitable membrane tubes in parallel and series, a scientific flow rate and pressure are formed to ensure low power consumption and component water balance.
3、 Selection criteria for disinfection equipment
1. Comparison of disinfection methods
| Disinfection method | Dosage used | contact time | advantage | shortcoming |
| UV disinfection
| 10-40mJ/cm² | 10-15second
| No by-products, fast disinfection speed, small footprint | Highly affected by water quality, requiring regular replacement of light tubes, and lacking continuous disinfection capability |
| chlorine dioxide disinfection
| 0.5-2mg/L | 10-20minute
| Good disinfection effect, minimal by-products, and not affected by ammonia nitrogen | Complex equipment, high operating costs, and easy explosion require on-site preparation |
| Ozone disinfection
| 2-5mg/L | 5-10minute
| Very strong disinfection effect, simultaneous degradation of organic matter, and no residual chlorine | Expensive equipment, high operating costs, and exhaust gas treatment required |
| Chlorine disinfection
| 10mg/L | 10-30minute
| Cheap price, strong sterilization ability, and continuous disinfection capability | Generate disinfection by-products and be ineffective against certain viruses |
2. Selection principle
UV disinfection: suitable for reuse of wastewater and strict discharge standards scenarios, ensuring that the water quality SS is below 30mg/L and turbidity meets penetration requirements. The power of the ultraviolet lamp tube is selected based on the amount of water processed, such as a 200W/cm UV lamp tube to ensure disinfection efficiency.
Chlorine dioxide disinfection: suitable for medium to large-scale water plants and scenes sensitive to by-products. Automatic dosing equipment is required, with the dosing point set on the main pipeline that is more than 15 minutes away from the main user's water intake point.
Chlorine disinfection: suitable for large water plants, with low operating costs and simple operation. A leak alarm device is required, which will sound an alarm when the chlorine concentration is ≥ 0.5ppm.
3. Joint disinfection plan
For the reclaimed water reuse system, it is recommended to use a combination of ultraviolet light and chlorine dioxide for remote disinfection. Installing ultraviolet sterilizers at the beginning of the pipeline network for one-time disinfection (irradiation dose 40-80mJ/cm2), and adding chlorine dioxide (dosage 0.5-2mg/L) at key water transmission nodes can not only improve sterilization ability but also reduce the amount of chemical agents added.
4、 Comprehensive selection suggestions
1. Selection process
-Water quality analysis: Clarify the characteristics of raw water quality and the requirements for recycled water quality
-Determination of processing scale: Determine equipment processing capacity based on daily processing volume and peak coefficient
-Process selection: Choose membrane separation technology and disinfection method based on water quality characteristics and reuse purposes
-Equipment configuration: Configure corresponding pumps, membrane components, and disinfection devices according to the processing technology
-Performance verification: Verify the rationality of equipment selection through performance curves to ensure that the operating points fall within the high-efficiency zone
2. Economic considerations
-Equipment investment: Prioritize selecting equipment with mature technology and stable operation to avoid excessive configuration
-Operating costs: Consider factors such as energy consumption, medication consumption, and consumable replacement cycles
-Maintenance cost: Choose equipment that is easy to maintain and has sufficient spare parts supply to reduce maintenance difficulty
-Service life: The service life of membrane components should be ≥ 5 years, and pump equipment should have good corrosion resistance
3. Safety and Environmental Protection
-Safety protection: Disinfection equipment should be equipped with safety protection devices, such as explosion-proof design for chlorine dioxide generators
-Environmental requirements: Choose low-energy, low-noise equipment that meets environmental standards
-Automated control: using an automated control system to achieve real-time monitoring and automatic adjustment of equipment operating status
Through scientific and rational equipment selection, the reclaimed water reuse system can achieve efficient and stable operation, with effluent quality meeting reuse standards, while reducing operating costs and improving economic and environmental benefits.