1. The initial investment and operating costs are higher, economical
Municipal water supply, as a livelihood project, has extremely high requirements for "long-term low-cost operation", but the cost characteristics of fiber bundle filters are inconsistent with this requirement:
High initial equipment investment : While the core filter media of fiber bundle filters (such as polypropylene or polyester fiber bundles) is inexpensive per strand, it requires high-density packing (up to tens of kilograms per filter unit). Furthermore, the filter media requires specialized "fiber bundle fixing devices" (such as porous plates, hooks, and pressure plates) to prevent fiber bundle loss or entanglement during backwashing. Furthermore, to precisely control the compaction level of the filter media (which affects filtration accuracy), an electric or pneumatic adjustment system is required. These components are significantly more expensive than traditional quartz sand filters (the cost of a quartz sand filter + ordinary porous plates combination is only 1/3-1/2 that of a fiber bundle system). For example, if a 100,000-ton/day municipal water plant were to utilize fiber bundle filters exclusively, the initial equipment investment would be 40%-60% higher than that of traditional quartz sand filters, placing significant pressure on the plant's construction budget.
High operating and replacement costs : The service life of fiber bundle filter media is about 2-3 years (shorter than 3-5 years of quartz sand), and when replacing, the old fiber bundles need to be completely removed and new filter media need to be re-fixed, and the labor cost and consumables cost are added (the replacement cost of filter media for a single filter is about tens of thousands of yuan); in addition, the backwash requirements of fiber bundle filters are higher - to avoid entanglement of fiber bundles, backwashing requires "air-water combined backwashing" (first pass compressed air to loosen the fiber bundles, and then flush with water), and an additional air compressor system is required. The backwash energy consumption is 20%-30% higher than that of traditional quartz sand filters (traditional filters only require water backwashing), and the energy consumption cost of long-term operation accumulates significantly.
2. High complexity of operation and maintenance, with strict requirements on operation and management
Municipal water plant operations and maintenance teams typically need to balance multiple processes (coagulation, sedimentation, filtration, and disinfection), placing high demands on the equipment's operability. The O&M complexity of fiber bundle filters far exceeds that of traditional equipment:
Controlling the filter media's state is difficult : The filtration effectiveness of fiber bundle filter media depends on its "compaction" (the tightness of the filter media layer). Excessive compaction will result in overly large filter media pores, allowing fine suspended matter to penetrate; excessive compaction will increase water flow resistance, leading to a sudden increase in the inlet and outlet pressure differential. In actual operation, the compaction level must be adjusted in real time based on the turbidity of the influent (for example, when turbidity rises during the rainy season, the compaction level must be appropriately reduced to increase the space for sewage interception). This relies on the linkage between online monitoring instruments (such as differential pressure sensors and turbidity meters) and the automatic control system. System failures or improper parameter settings can easily lead to fluctuations in filtration accuracy or filter media clogging. In contrast, traditional quartz sand filter media has a fixed gradation and does not require frequent adjustment. Operations and maintenance personnel only need to perform regular backwashing, making the operation threshold low.
Difficulty in troubleshooting and repairing : The internal structure of fiber bundle filters is more complex (densely distributed fiber bundles and numerous fixtures). If problems such as filter media entanglement (caused by incomplete backwashing) or uneven local compaction (adjustment system failure) occur, the filter manhole cover must be opened and the fiber bundles manually combed or replaced. Troubleshooting and repairs can take several hours (if filter media loss occurs in traditional quartz sand filters, only quartz sand needs to be replenished, which can be completed in 1-2 hours). In addition, fiber bundles easily absorb organic matter in the water (such as humus). Long-term operation will breed biological slime, requiring regular soaking and cleaning with chemical agents (such as sodium hypochlorite solution). If cleaning is not timely, the filter media's adsorption capacity will decrease, requiring increased cleaning frequency, further increasing the workload of operation and maintenance.
3. Weak scale adaptability and limited impact resistance
Municipal water supply needs to meet the requirements of "large treatment capacity and strong adaptability to water quality fluctuations", but the design characteristics of fiber bundle filters limit their large-scale application:
Low single-unit processing capacity and poor modular combination efficiency : The processing capacity of a single fiber bundle filter is usually ≤1000m³/h (the processing capacity of a single traditional quartz sand filter can reach 5000m³/h). To meet the processing scale of 100,000 tons/day, more than 100 fiber bundle filters are required, which is far more than the 20-30 groups of traditional filter tanks. This not only takes up more water plant land (the equipment footprint is 30%-50% higher than that of traditional filter tanks), but also increases the complexity of pipeline connections (multiple devices in parallel require precise flow distribution to avoid biased flow), and reduces system stability (although the impact of a single device failure on the overall water supply is small, the total maintenance frequency is higher after the failure probability is accumulated).
Poor resistance to high turbidity shocks : Municipal raw water is prone to sudden increases in turbidity during the rainy season (e.g., from 20 NTU to over 100 NTU). Traditional quartz sand filters can maintain basic filtration effectiveness by extending backwash cycles and reducing flow rates. While fiber bundle filter media has a large interception capacity, the large amount of suspended matter in high-turbidity water can quickly clog the fiber bundle pores, causing the pressure differential to rise to over 0.1 MPa (far exceeding the design threshold of 0.08 MPa) in a short period of time. This necessitates frequent backwashing (shortening the backwash cycle from 12 hours to 3-4 hours). This not only increases energy consumption but can also lead to excessive effluent turbidity due to incomplete backwashing. In contrast, traditional quartz sand filters are more tolerant of high turbidity water and are better suited to the fluctuating nature of municipal raw water quality.
4. Insufficient technical compatibility and difficulty in integrating with existing processes
Low compatibility with pre-sedimentation process : In traditional processes, the turbidity of the effluent from the sedimentation tank is usually controlled at 5-10NTU, which is just suitable for the inlet water requirements of the quartz sand filter (quartz sand has the highest filtration efficiency for water of 5-10NTU); the advantage of the fiber bundle filter is that it can process low turbidity water (for example, when the turbidity of the effluent from the sedimentation tank is ≤5NTU, it can give full play to its high-precision filtration advantage). If it is directly connected to the existing sedimentation tank, its high-precision characteristics cannot be fully utilized. On the contrary, due to the relatively high turbidity of the inlet water, the filter material will be quickly saturated, and the cost-effectiveness is low. If it is to adapt to the fiber bundle filter, it is necessary to upgrade the sedimentation tank (such as adding an inclined tube sedimentation tank, adding more flocculants), reduce the effluent turbidity to ≤3NTU, and add additional sedimentation tank modifications.
Poor synergy with subsequent disinfection processes : Traditional quartz sand filters maintain an effluent turbidity of ≤1 NTU, which is sufficient for subsequent chlorine disinfection (disinfectant utilization is highest when turbidity is ≤1 NTU). While fiber bundle filters can reduce turbidity to ≤0.5 NTU, further reductions in turbidity only improve disinfection effectiveness (from 99% to 99.5%), requiring higher equipment and operating costs and a low return on investment. Furthermore, if excessive organic matter is adsorbed by the fiber bundle filter media, it may react with chlorine during the disinfection process to produce more disinfection byproducts (such as trihalomethanes), increasing water quality risks and requiring the addition of an activated carbon filtration unit, further increasing process complexity and cost.
Summarize
In municipal water supply scenarios, the fundamental disadvantage of fiber bundle filters lies in the contradiction between their high cost and complexity and the need for low-cost, easy-to-operate, and scalable municipal water supply . Their high-precision filtration advantage is not cost-effective given the municipal water supply's focus on simply meeting basic safety standards. Furthermore, issues such as high initial investment, complex operation and maintenance, and poor adaptability further limit their large-scale adoption. Therefore, unless municipal water supply demands exceptionally high standards (such as a drinking water turbidity requirement of ≤0.5 NTU in some regions), traditional quartz sand filters remain the preferred choice. Fiber bundle filters are only suitable for small-scale applications in localized deep treatment processes (such as supplemental filtration units in drinking water quality improvement projects), and are unlikely to replace traditional processes and become mainstream equipment.
