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Frequent Backwashing Issues in Disc Filters: Fault Analysis
2026-06-15
Field Case: Fault Analysis of Frequent Backwashing in Disc Filters Caused by Incorrect Model Selection
In industrial fluid treatment systems, the stable operation of filtration equipment is critical to ensuring continuous production. Even mature disc filters can suffer a series of cascading failures in practical applications due to improper early-stage selection. Based on a real on-site case, this article deeply analyzes the technical causes of frequent backwashing in disc filters caused by wrong selection, and proposes corresponding solutions to provide a reference for procurement decisions in related fields.
Project Background & Fault Performance
This case occurred in the circulating water treatment system of a large-scale chemical enterprise.
- System design flow rate: 120 m³/h
- Raw water suspended solids concentration: approximately 80 mg/L
- Particle size distribution: more than 60% of particles smaller than 25 μm
To reduce initial investment costs, the enterprise selected a standard disc filter with a filtration precision set to 100 μm and a designed backwash trigger pressure difference of 0.05 MPa.
The system ran smoothly at the initial commissioning stage, but abnormalities appeared after two weeks. Operators found that the backwashing frequency of the filter gradually increased from the designed once every 8 hours to once every 2 hours, and eventually developed into almost continuous backwashing.
Frequent backwashing not only caused fluctuations in system water supply pressure and affected the stable operation of downstream reaction kettles, but also sharply increased the plant’s water treatment costs due to the surge in backwashing water consumption.
Fault Diagnosis & Root Cause Analysis
Technicians conducted detailed records and analysis of the fault symptoms:
- They first ruled out equipment quality issues, confirming that the filter discs were intact, seals were in good condition, and control valves operated normally.
- The focus then shifted to the matching between raw water quality and filter selection.
Laboratory particle size analysis of the raw water revealed a large number of colloidal particles ranging from 10 μm to 40 μm — much smaller than the nominal precision of the filter discs (100 μm).
The root cause lies in the filtration mechanism of disc filters: it is not simple "screening", but a combination of depth filtration and bridging effect. When water contains a large number of fine particles close to or below the filtration precision, these particles quickly penetrate the surface layer of the filter discs, enter internal pores, and form a dense filter cake through "bridging" in disc gaps. This layer rapidly increases flow resistance, causing pressure difference to surge in a short time and triggering the backwashing program.
Although backwashing can remove part of the surface filter cake, it cannot completely eliminate fine particles deep inside the discs. These residual particles become nuclei for the next round of bridging, accelerating filter cake formation, shortening backwashing cycles, and eventually leading to a vicious cycle.
Solution & System Retrofit
Based on the above analysis, the technical team adjusted the selection strategy:
- Replaced the original 100 μm disc filter with a 50 μm precision model
- Upgraded the backwash control system to adopt a dual-trigger mode of time + pressure difference
The 50 μm filtration precision better matches the particle size of main pollutants in the water, effectively intercepting particles and preventing them from entering the deep layers of the discs. Meanwhile, the dual-trigger mode avoids false backwashing caused by instantaneous pressure difference fluctuations.
Retrofit Effect & Conclusion
After the retrofit, the system returned to stable operation:
- Filter backwashing cycle stabilized at over 12 hours
- Backwashing water consumption reduced to 20% of the original level
- System pressure remained steady, effectively guaranteeing continuous production
This case highlights the critical importance of precision matching in filter selection. Procurement decisions should not only focus on initial costs or general parameters, but must be based on in-depth understanding of actual working conditions.
For fluids containing a large number of fine particles, selecting filtration precision matched to particle size is key to avoiding frequent backwashing failures. In addition, an intelligent control strategy combining time + pressure difference can effectively improve the operational stability of filtration systems. In future procurement lists, working condition analysis and precise model selection should be regarded as essential evaluation steps.