In the field of sludge treatment, plate and frame filter presses are widely used due to their advantages such as high dewatering efficiency and controllable solid content in the mud cake. However, in actual operation, two major problems, namely "the persistently high moisture content of the mud cake" and "the 'runny core' phenomenon of being dry on the outside but wet on the inside", have always plagued the enterprise. These problems not only increase the disposal cost, but also restrict the resource utilization of sludge. This article deeply analyzes the causes of pain points and provides systematic solutions from the perspectives of technological innovation and process optimization.
I. Problem Manifestations: The dual challenges of moisture content and "runny core"
The moisture content of the mud cake exceeds the standard
Industry standards require that the moisture content of sludge be reduced to below 60% before it can enter resource utilization processes such as incineration and building material utilization. However, after dehydration of most plates and frames, the moisture content of the mud cakes still remains at 70%-80%, resulting in:
Transportation costs have soared: For every 1% increase in moisture content, the volume of sludge increases by 3% to 5%.
High disposal costs: Landfills refuse to accept sludge with high moisture content, and incineration requires additional auxiliary fuel.
The phenomenon of "runny heart" occurs frequently
The surface of the mud cake is dry, while the interior is in a flowing or viscous state, which is manifested as:
Turbid filtrate: In the later stage of pressure filtration, the filtrate still carries a large amount of suspended solids.
Intensified equipment wear and tear: Frequent flushing of the filter cloth still fails to thoroughly remove the residual sludge.
Ii. Pain Point Tracing: From Sludge Characteristics to Process Defects
One. The nature of sludge is "inherently deficient"
High proportion of organic matter: The proportion of microbial cells in the excess sludge exceeds 60%, and the cell walls hinder the release of water.
High viscosity: Extracellular polymers (EPS) make the sludge gel-like and clog the pores of the filter cloth.
The bound water is difficult to remove: Traditional agents can only remove interstitial water and have no effect on the bound water within cells.
Two. "Acquired imbalance" of process parameters
Improper dosing of chemicals: Excessive PAC leads to calcification of the filter cloth, and unreasonable dosing points of PAM cause local flocculation failure.
The filtration pressure curve is rough: The segmented pressure increase strategy was not designed based on the characteristics of the sludge. The initial high pressure causes the surface of the filter cake to seal rapidly.
Poor equipment compatibility: The pore size of the filter cloth does not match the particle size of the sludge, and the feeding speed is too fast, which aggravates the uneven density.
Iii. Technological Breakthroughs: An Innovative Path from "Treating Symptoms" to "Treating Root Causes"
Sludge modification technology - Solving the problem of bound water
Adding sludge enhancer is a modified polymer product with multiple functions.
Persulfate oxidizes EPS, reduces sludge viscosity and improves filtration performance.
Experimental data: The sludge specific resistance (SRF) decreased by 55%, and the bound water content decreased by 28%.
Two. Process optimization strategy - Precisely control the pressure filtration curve
Segmented boost control
The initial pressure is 0.5MPa and maintained for 5 minutes to ensure that the sludge fills the filter chamber evenly.
Increase the pressure to 1.0MPa in the medium term to promote water migration;
At the end, maintain the pressure at 1.5MPa for 10 minutes to completely remove the internal moisture.
Optimization of feeding speed
Reduce the feed flow rate (from 5L/min to 3L/min) to avoid the density gradient caused by local overload.
Three. Equipment adaptation and upgrade - Reducing the risk of "runny core" from the source
Customized filter cloth
The pore size is selected based on the particle size distribution of the sludge (usually 20-50μm), and a double-layer composite filter cloth (surface polyester + bottom polypropylene) is adopted, which takes into account both filtration accuracy and wear resistance.
Add a pretreatment device:
Install a static mixer to ensure that the chemicals are thoroughly mixed with the sludge.
Configure an online pH adjustment system to maintain a weakly acidic environment for sludge (pH 6-7) and enhance the activity of oxidants.
Iv. Case Evidence: See Practical Results from Data
Case 1: A certain printing and dyeing wastewater treatment plant
The moisture content of the sludge is 83%, and the incidence of "runny core" is 40%.
Plan: Add sludge enhancer (8kg/t dry sludge) and optimize the filtration pressure curve;
Effect:
The moisture content was reduced to 62%, and the volume of the mud cake decreased by 45%.
The incidence of "runny core" has dropped to 5%, and the frequency of filter cloth cleaning has decreased from 5 times per week to 1 time per week.
Case 2: A municipal sewage treatment plant
Question: The dosage of PAC is 10kg/t of dry sludge, and the dosage of PAM is 2.5kg/t.
Solution: Pretreatment with enhancers + Synergistic optimization of chemicals;
Effect:
The dosage of PAC was reduced to 5kg/t, and the dosage of PAM was reduced to 1.5kg/t.
The comprehensive treatment cost decreased by 28%, and the COD of the filtrate dropped by 18%.
V. Future Outlook: Intelligence and Resource Utilization Advancing in Parallel
With the integration of AIoT technology into the sludge treatment field, the intelligent filter press system can monitor the filter chamber pressure and filtrate turbidity in real time through sensors and dynamically adjust the process parameters. Meanwhile, the increase in calorific value of low-moisture mud cakes (10%-15%) provides a new path for co-incineration power generation, further reducing the treatment cost.
Conclusion
The "moisture content problem" and "runny core pain" of plate and frame sludge dewatering essentially stem from a systematic contradiction among sludge properties, chemical technology, process control and equipment compatibility. Innovative technologies such as sludge efficiency enhancers and modified polymer products with multiple functions, combined with refined process management, enable enterprises not only to achieve standard discharge but also to open a new chapter in the resource utilization of sludge, finding the best balance between environmental protection and benefits.