Knowledge Center Filters Press

All About Filter Presses – Answering FAQs

Here you will find detailed answers to frequently asked questions related to filter presses for solid-liquid separation and sludge drying. From basic concepts to more specific technical queries, this section is designed to provide accurate, reliable, and up-to-date information on the operation, applications, and advantages of filter presses.

General aspects of a filter press
Technical questions
Operational questions
Troubleshooting
Comparative questions

General aspects of a filter press

1. What is a filter press?

A filter press is a solid-liquid separation device that operates by pressure filtration in discontinuous cycles. It is used to dewater suspended solids contained in sludge in order to increase its concentration. The filter assembly consists of a package made up of a series of plates covered with filter cloths, which when closed form chambers that will contain the dewatered sludge. This equipment is usually mounted on an elevated structure to facilitate the collection of separated sludge. Side transfer filter presses for sludge dewatering

2. How does a filter press work?

The slurry suspension is pumped into a filter press and conveyed to the filter pack under hydraulic pressure. The liquid passes through the cloth, while the solids are progressively retained until they form a cake with the degree of dryness specified in the equipment design. Once the cycle is complete, the equipment is opened and the cake is discharged, yielding a filtered liquid and a compact solid residue with a high dry matter content. Filter presses for mechanical sludge dewatering

3. What are the main applications of filter presses?

Sludge dewatering using filter presses is a widely used process in wastewater treatment and industrial processes. In wastewater, they are used to dewater primary sludge and biological sludge, usually for disposal in landfills or use in composting, while in industrial processes they are commonly used to purify and recover valuable products. Filter presses for mechanical sludge dewatering

4. Which industries use filter presses for wastewater treatment?

Press filters are used in numerous industries due to their ability to recover filtered water and valuable products, obtain a high dry matter content, and reduce the volume of waste to be managed. They are commonly used in the chemical, pharmaceutical, food (slaughterhouses, dairy, beverages), paper, textile, metallurgical, and mining industries. They are also used in tanning, ceramics, agriculture, and industrial waste treatment.

5. What are the benefits of using filter presses in sludge dewatering?

During the wastewater treatment process, suspended solids (TSS) are separated from the water through clarification processes (sedimentation and flotation) for subsequent management, which can be carried out as controlled discharge, as material for composting, or as a recoverable by-product. In any case, it is important to minimize their volume to facilitate transport, as well as to reduce their management cost, storage space, and environmental impact.

6. What types of filter presses are available?

There are several types of filter presses:

Plate and frame filter presses: This is the most traditional type. It consists of a series of alternating plates and frames, with a filter medium between them.
Filter presses with post-pressing membranes: In this type of filter press, elastic membranes are added to each plate which, when inflated, allow greater compression of the sludge cake.
Vertical or tower filter press: This type of filter press is similar to the plate and frame filter press, but instead of stacking the plates horizontally, they are arranged vertically in a tower. This allows for greater use of space.
Built-in chamber filters: This filter press uses filter packs that require the fabrics to be firmly attached to the plates. Sometimes a combination of membrane and built-in plates can be used.

7. Is a filter press expensive?

Considering the degree of dryness achieved by this equipment (≥30% DM), energy consumption, and space occupied, it is an economical system. There are technologies that have a lower acquisition cost, but they do not achieve the dryness values required by landfills, or they have higher operating costs. In addition, this equipment is very robust, has a long service life, and experiences few breakdowns.

8. How much space does a filter press take up?

Obviously, filter presses can vary greatly in size. That said, the space required for the installation of a filter press is generally moderate, considering its drying performance and the reduction in volume of the dehydrated sludge obtained, compared to alternative processes. The filter assembly itself is limited in size, although it requires additional space for auxiliary elements such as: the cake opening and discharge area, feed pumping, electrical panel, and, in some cases, hoppers or evacuation belts.

9. Does a filter press have any environmental impact?

The environmental impact of a filter press is low, as it is a mechanical device with no atmospheric emissions and low energy consumption. The filtered water is usually of sufficient quality to be reused as process water or in the treatment itself, thus reducing the volume of waste. The pumps used are usually pneumatic, which means there is some noise impact, but this can be minimized with the right design and operation. The filter cloths are washed sporadically and can be done on site.

10. Is it complicated to assemble and start up a filter press?

The equipment is usually supplied pre-assembled, which means that installation is limited to mechanical installation at the site, hydraulic and electrical connections to pumps, pipes, and auxiliary systems.

Start-up is simple and basically involves checking the plates for leaks and adjusting the design parameters and automatic controls (times, flow rates, and, where applicable, reagent dosing). After a brief testing phase and operator training, the system is ready to go.

11. What materials are filter presses usually made of?

Filter presses are robust pieces of equipment that are constructed from materials resistant to the type of sludge to be treated. In general, the materials are as follows:

Structure and frame: painted or galvanized carbon steel. Stainless steel is used in aggressive environments.
Filter plates: Polypropylene is the most common material due to its chemical resistance and light weight. Coated metal plates can be used in special applications.
Filter fabrics: polypropylene, polyester, or polyamide, depending on particle size and operating pH.
Hydraulic components: stainless steel, carbon steel, or plastic materials (PP/PE/PVC).

12. What is the service life of a filter press?

Press filters are robust, reliable, and durable pieces of equipment. The filter elements (plates and hydraulic elements) can have a lifespan of 10 to 20 years, while the metal structures and connections can last for more than 20 years. Filter cloths have a variable lifespan (from months to years) depending on the nature of the sludge to be treated.

Technical questions

1. How does a plate and frame filter press work?

The operating stages of a filter press of this type can be summarized as follows:

Filter closure. The plates and frames are aligned and closed using a hydraulic system.
Sludge feeding. The sludge in suspension, already conditioned (with chemical reagents if necessary), is pumped into the chambers.
Filtration. The liquid passes through the filter cloths and is discharged as filtrate, while the solids gradually form the cake.
Opening of the filter chambers. When filtration is complete, the pressure is released and the plates and frames are separated.
Cake discharge. The dewatered sludge falls by gravity or is removed mechanically.
Preparation for new operation. Inspection and cleaning of fabrics before starting a new cycle.

2 . What is the role of filter cloths in a filter press?

Filter cloths are the main filtration component in a filter press, as they retain the pumped sludge until the design dry matter concentration is reached. These fabrics determine the degree of filtration, the sludge concentration that can be obtained, the tolerance to fouling and washing, as well as the resistance to abrasion and aggressiveness of the medium. Therefore, their proper selection (material, porosity, and weave) is essential for the proper operation and performance of the equipment.

3. What is the optimal cycle time for a filter press?

The optimal drying time for a filter press varies, as it depends on the type and filterability of the sludge, the working pressure, the type of cloth, and the characteristics of the dehydrated sludge cakes.

The approximate time for complete drying ranges from 60 to 120 minutes, divided into:

Filter closure: 2–5 minutes
Filtration: 60–120 minutes
Drained: 10–15 minutes
Opening and unloading of cakes: 10–20 minutes

4. How is a filter press sized?

The design calculation for a filter press is relatively simple, but it depends on some basic data and the results of laboratory tests:

The kg/h of sludge to be filtered (CF) is obtained from the flow rate (Q) and the sludge concentration (C): Q(^m³/h) * C(kg^DM/m³) = CF (kg/h of sludge to be filtered)
Based on a cycle time in hours (t) and expected dryness (S), obtained in previous tests, the kilograms of dehydrated sludge per cycle are calculated based on the flow rate and final dry matter (DM). (DMf) (K) Kg. sludge per cycle = (CF (Kg/h) x t (h)) x (C/DMf)
With a sludge density (D) determined in laboratory tests, the cake volume per cycle is obtained. V (l) = K/D liters of cake.

The filter package for the cycle is sized according to the surface area and volume of the chambers and plates available on the market.

5. What are the optimal operating pressures for a filter press?

This depends on the type of sludge and its filterability, so it is common to perform laboratory tests to determine the basic design parameters. As a general rule, the optimum pressure is that which allows the chambers to be filled within the expected cycle time to achieve the required dryness. As a guide, depending on the type of sludge, the expected filtration times are usually:

Biological sludge: 6–8 bar.
Physicochemical sludge: 7–10 bar.
Industrial sludge: 8–10 bar.
Mining sludge: up to 15 bar.

Beyond a certain point, increasing the pressure no longer improves filtration, but only has a negative impact on energy consumption and causes deterioration of the filter fabrics.

When the degree of dryness is increased by using post-pressing membranes, pressures of 16 bar can be achieved.

Press filters are typically constructed for PN10, PN16, and, in special cases, PN25.

6. How is the end of a drying cycle detected in a filter press?

To detect the end of a filter press cycle, a combined criterion is usually used, which requires the provision of certain instruments and automatic devices.

Reaching the predetermined design pressure in tests, at which point the process is no longer cost-effective (pressure transmitter with alarm at the inlet of the filter pack).
Reduction of permeate flow rate to ≤ 5-10% of initial value (flow transmitter with minimum alarm at permeate outlet).

Of the two control parameters, pressure control prevails in order to prevent damage to the assembly.

7. What additives are used to improve the performance of filter presses?

To improve sludge dryness and accelerate filtration in a filter press, conditioning reagents are mainly used, the application of which is optimized through laboratory testing. The typical dose is usually 2–10 kg/ton of dry matter (DM).

The most commonly used are:

Flocculants (the most common), with organic polymers that can be cationic, anionic, and nonionic.
Coagulants (_FeCl₃,_Al₂(_SO₄)_₃, PAC, and_FeSO₄) that neutralize polarity and improve the performance of flocculants.
Lime (CaO, or Ca(OH)₂). It increases the concentration and filterability of the sludge, stabilizes it, and increases the pH, but it has the disadvantages of increasing sludge production and having an abrasive effect.

Special materials: Cellulose, diatoms, perlite. These types are specific to the chemical industry.

8 . What are the typical plate sizes and how many plates does a filter press require?

The most common sizes of plates available on the market are:

470 x 470 mm (low flow rates)
630 x 630 mm (small WWTPs)
800 x 800 mm (medium-sized WWTPs)
1000 x 1000 mm (Industries and WWTPs)
1200 x 1200 mm (Large size)
1500 x 1500 mm (Large installations)
2000 x 2000 mm (Heavy industry)

The most common cake thicknesses are: 25, 30, 40, and 50 mm.

The number of plates will depend on the total volume of the cycles and are sized to ensure that the filter pack is viable. This number typically ranges from 10 to 100 units, with larger plates requiring more plates.

9 How are cakes discharged from a filter press?

Once the pressing cycle is complete, the dehydrated sludge is discharged in the following sequence:

Power outage.
Depressurization. The electrohydraulic or mechanical closure opens.
Manual plate separation (small equipment), or with an automatic top or side displacer (the most common).
Fall of cakes detached by gravity.
Sludge collection in a hopper, using a conveyor belt, screw conveyor, or directly into a container.

To improve discharge, systems such as shaking or vibrating the open filter pack, or blowing with compressed air, are used. Before closing the filter press plates again, it is necessary to inspect and clean them if necessary.

10. Can the dryness of the sludge be increased after pressing?

It is possible to increase the dryness of sludge cakes dehydrated in a filter press using the following internal or external systems.

Internal systems (in the same filter):

Membrane plates installed in the system, which can reach 16 bar of pressure and increase sludge dryness by 3–8%.
Air blowing with moderate improvement in sludge dryness (1–3%).
By adding coagulants, flocculants, or lime, dryness can be increased by 2–5%.

External systems (outside the filter):

Repressing (uncommon)
Thermal drying, in drum or disc dryers, achieves high degrees of dryness (70–90%) at the expense of high energy consumption.
Maturation and draining in container systems or on draining surfaces (approx. 70%).
Sun exposure, with ample surface area, favorable weather and climate (60–70%)

Operational questions

1. How are filter press fabrics cleaned?

Filter cloths must be cleaned frequently, either by simple dragging or chemically, to remove deposits and clogging, the composition of which depends on the types of sludge and the additives used to optimize mechanical drying.

Cleaning of filter fabrics:

Cleaning of fabrics with pressurized water after each cycle, if required by the type of sludge. In automatic filters, washing is performed with mobile systems.
Periodically, and when necessary, chemical cleaning will be carried out using alkaline reagents (NaOH and specific detergents) to remove grease and polymer deposits, or acids (citric, formic, or phosphoric) to remove scale and salts. During this cleaning process, the filter cloths must be removed and cleaned externally.

2. What is the usual maintenance for a filter press?

Filter presses require systematic maintenance to ensure proper dewatering, prevent excessive pressure drops, and extend the service life of fabrics, plates, and mechanical components.

After each filtration cycle, a visual inspection must be carried out to detect tears, obstructions, or traces of cake not detached from the filter cloths in the discharge. Any necessary repairs must be made.
Inspection and cleaning of support plates and filter channels, checking for damaged areas and possible cracks. If necessary, damaged plates must be replaced.
Check the hydraulic system (pressures and possible leaks) and check the level and condition of the hydraulic oil.
Lubrication of moving parts, such as rails, rollers, or clamping and locking systems.

3. How often should filter fabrics be replaced?

Replacing the plates should be considered in the following cases:

The filtration time increases.
More pressure is required for the same flow rate.
The dryness of the cakes is reduced.
Fabrics do not recover well after dry cleaning.
Cracks are visible.

The filter cloths in a filter press do not have a fixed service life. Their replacement depends on the type of sludge, operating conditions, and maintenance performed. However, replacement periods of 6 months to 2 years can be expected. Some of the most common factors for changing the cloths are:

Type, dosage, and quality of flocculant reagents.
Operating pressure.
Operating frequency
Frequency and method of cleaning.
Characteristics (material, filtration grade) of the fabric.
Type of plates (chamber, membrane).

4. What best practices are recommended for operating a filter press?

In addition to strictly following operating recommendations and maintenance schedules, there are a number of best practices that help extend the service life and performance of a filter press:

Adjust the flocculant dosage correctly (excessive dosage accelerates deterioration or clogging) and check that the sludge is properly thickened.
Avoid working with low-concentration or poorly flocculated sludge.
Avoid forcing high filtration pressures if the flow rate no longer increases.
Monitor cycle times, cake dryness, and pressure to detect deviations.
Smooth start and progressive pressure.
Stable flow, without pulsations.
Continuous control of pressure and filter flow.
Ensure that the cakes have been properly separated from the plates and that no residue remains on the cloths.

5. How should sludge be loaded into a filter press?

After proper pretreatment of the sludge through flocculation and thickening, an adequate concentration (3–6% DM) is obtained to proceed with pumping it to the filter pack. Rapid filling (5–6 minutes) is recommended to ensure the correct formation of sludge cakes. For this purpose, it is common to use high-flow, low-pressure booster pumps, which operate before pressurization begins with the main pumps, which are usually pneumatic.

For a uniform and effective sludge loading process, a series of points to observe are proposed:

Monitoring of the gradual increase in pressure, the progressive reduction in flow rate, and the filtration quality.
The filter must stop when the design pressure and flow values are reached and remain stable.

6. What is the energy consumption of filter presses?

The costs associated with the energy consumption of a filter press are generally low compared to other dewatering technologies. They are best expressed in kWh per ton of dry matter (t DM), as they depend on the volume treated and the dryness achieved. The usual consumption range is between 5 and 15 kW/t DM. This consumption occurs in the following processes:

Slurry feed pumping. Continuous consumption of 50–70% of the total.
Hydraulic locking system. Short-term consumption (≤10%)
Compressor/inflation pump membranes. Consumption 10–20% (if applicable).
Auxiliary systems. Consumption ≤10% (washing, flushing, automatic devices).

7. Can a filter press be automated?

The operations of a filter press can be automated using a programmable logic controller (PLC) located in the control and power panel. The entire mechanical drying sequence can be automated:

Plate closure by hydraulic group action.
Start-up and shutdown of the air compressor that feeds the pneumatic feed pump, with pressure and filtered flow control.
Plate opening by means of lateral or front displacement with electric motor.
Unloading plates by vibration or shakers.
Inflation of post-pressing membranes.
Automatic fabric washing or blowing.
Activation of the cake transport system (belt, screw).

The filter press must be checked to remove any cake residue before preparing it for the next drying operation.

High and low pressure alarms are also included, as well as alarms for minimum flow, plate limit switches, and safety sensors.

There are also semi-automatic filters, in which only some functions are automated (automatic opening, assisted cleaning, etc.).

8. What safety measures are taken in a filter press?

Filter presses require safety measures, as they are devices that operate at high pressures and with chemicals, posing risks of entrapment and projection.

The regulations require the implementation of:

Technical safeguards (fairings and barriers, lifelines, emergency stop buttons, instruments with safety interlocks, and electrical safeguards).
Use of PPE, operating procedures, and staff training.
Signaling of hazards and work areas.
Safe design (spaces and accesses, walkways, protections, lighting, etc.)

9. How can the volume occupied by sludge cakes be reduced?

The processes commonly used to reduce the space occupied by dry cakes produced by a filter press are:

Conveyor belts, screw conveyors, and compactors.
Vibrators and plate shakers that facilitate the breaking of cakes.
Hoppers for collecting and accumulating sludge.
Breaking ropes or chains that fragment the cake as it falls.
Rain shelters and container liquid drainage systems.

The most practical combination is to discharge and break up the cakes into a screw hopper that feeds a container.

9 . What are the operating parameters that must be monitored during filter press operation?

The basic parameters for controlling the operation of a filter press are:

Determine the concentration and conditions of the sludge to be filtered. It is essential that it is well conditioned and has adequate dryness (3–6% DM).
The feed pressure allows the cake formation to be monitored and the correct closure of the plates to be verified.
Cycle time, which depends on the type of sludge, the desired dryness, and the size and type of filter.
Filter flow rate to monitor the progress of dehydration.
Dryness of the resulting cake. This is determined through laboratory tests to ascertain the DM concentration obtained, in order to optimize equipment performance.

Troubleshooting

1. Why is my filter press producing wet sludge cakes?

When a filter press produces wet sludge cakes, it is usually due to poor physicochemical stabilization of the sludge. The most common reasons are:

La concentración del fango es baja (< 2–3 % MS).
Incorrect flocculation due to lack or excess of polyelectrolyte.
Poorly adjusted cycles (pressure, pressing time).
Clogged or inadequate filter fabrics.
Heterogeneous distribution of sludge.
Cameras not closed properly.
Organic sludge that is difficult to dry.

2. What causes clogging of the filter fabric in filter presses?

The clogging of the pores in the fabric of filter cloths is caused by the blockage of fines, polymers, or fats contained in the sludge. This reduces the permeability and performance of the filter. The main causes are:

Poor flocculation or excess flocculant.
Highly diluted sludge.
Fats, oils, and proteins, which adhere to the fibers.
Mineral deposits.
Incorrect cleaning of fabrics.
Incorrect pressures.

3. Why do leaks occur in a filter press?

Leaks occur when the filter plate pack is not watertight. The main causes are usually:

Misaligned or deformed plates.
Improperly fitted or worn fabrics.
Residue on sealing surfaces.
Excessive or insufficient filtration pressure.
Hydraulic system failures.

4. How can uneven sludge distribution in a filter press be resolved?

The uneven distribution of sludge can be resolved with the following measures:

Flocculation. Adjust the dosage and injection point of the polymer to improve flocculation.
Progressive pressure and flow. Gradually increase the sludge supply by controlling the pressure and flow.
Fabric inspection. Check that they are properly positioned, clean, and free of debris on the plates.
Cleaning of supply and collection systems. Remove deposits at plate inlets and outlets.
Check that the plates are closed correctly. Check closure, plate balance, guides, and hydraulic pressure.
Pump check. Adjust pumps to prevent pulsations, check that the flow rate is sufficient for rapid initial filling.

5. Why does a filter press operate at reduced capacity?

A filter press loses capacity when the permeability of the system decreases and the drying cycle is disrupted. The most common causes are:

Poorly flocculated sludge due to a defect or excess polymer.
Clogged or damaged filter fabrics.
Poorly adjusted cycle design parameters (pressure, time).
Irregularity in filling the chambers.
Problems caused by misaligned plates or leaks due to poor sealing.

6. Why is the drying cycle longer in a filter press?

The cycle is prolonged when water drains poorly through the cake and the fabrics, mainly for the following reasons:

Inlet slurry too diluted. More time is needed to form the cake and, in many cases, it does not form properly.
Incorrect flocculation. Permeability is reduced by the presence of fine or gelatinous flocs.
Excess polymer. Sticky cake that sticks to fabrics and retains water.
Clogged filter cloths. The flow rate drained through the cloths is reduced.
Incorrect pressure. Insufficient or pulsating pressure.
Pressure maintained at the end of the cycle. Unnecessary energy is consumed without improving performance.

7. Why won't the filter press start?

A filter press can become blocked for various reasons, which are usually related to hydraulics, process control, or safety systems. The most common causes are:

Safety guards: poorly closed plates, limit switches, open safety guards or shields, system alarms, or emergency stop activation.
Problems in the hydraulic system: insufficient feed pressure, hydraulic valve failure, low oil level in the sump, or leaks in the circuit.
Electrical or control failures: lack of power supply, PLC failures, flow and pressure or level sensors.
Problems in the sludge feed circuit: feed pumping, closed valves, sludge blockage, circuit obstructions.
Incorrect startup sequence: a previous cycle has not been completed.

8 What are the most common problems that arise in a filter press?

The most common problems with a filter press are usually:

Electrical and control problems in the electrical panel (circuit breakers, etc.).
Errors in the PLC (signals or programming).
Manufacturing materials unsuitable for the physicochemical characteristics of the sludge.
Leaks between plates due to wear on filter cloths, or breakage or poor sealing between plates. The problem is solved by replacing damaged cloths and plates and checking the hydraulic system to ensure proper sealing.
Obstruction of filter cloths due to accumulation of solids. This can be solved by cleaning the cloths properly.
Hydraulic system failures due to leaks in the system or low oil level.
Very wet sludge cakes, due to incorrect sludge conditioning or incorrect operating parameters.

Comparative questions

1. What mechanical sludge drying alternatives are commonly used in wastewater treatment?

The selection of the most efficient technology depends on the type of sludge to be treated (biological or physicochemical), the required dryness of the sludge (between 15 and 40%), the flow rate to be treated, and the space available for installing the equipment. Other points to consider are the cost of installation and operation, as well as the environmental impact.

The most commonly used technologies are as follows:

Band filters in medium-sized WWTPs for mixed and biological urban sludge.
Centrifugal decanters are commonly used in medium-sized and large wastewater treatment plants, in facilities with space limitations, and for thickened and digested sludge.
Press filters for industrial sludge, WWTPs with high transport or disposal costs, and for obtaining high dryness. Commonly used for aerobic and physicochemical biological sludge.
Other options include rotary drums and screw presses for small and medium-sized WWTPs with low sludge dewatering requirements. These are typically used as pre-dewatering systems.

2 . What are the differences between a plate filter press and a belt filter?

The plate filter press compresses the sludge by pumping it into a set of watertight chambers, while in a belt filter the sludge is dragged between two belts that compress it by tension. These are some of the main differences between the two types of filter presses:

The degree of dryness of the sludge obtained in a filter press is 30–40%, while in a belt filter it is 15–25%.
A filter press operates in cycles (discontinuous mode), while a belt filter operates continuously.
The investment and maintenance costs and operational complexity are higher for a filter press than for a belt filter.
The band filter requires more floor space, while a plate filter press is much more compact, although it needs some height and auxiliary space for opening the plates and removing the sludge.

3. What are the advantages of a filter press over a centrifuge?

A plate filter press has a number of advantages over a centrifugal decanter , including:

Achieve greater sludge dryness (30–40% vs. 20–25%), which translates into lower transportation costs and a reduction in the amount of sludge produced.
Better filtration quality is obtained, so it can sometimes be reused.
It has lower energy and reagent costs.
The filter press is a more robust piece of equipment and requires less maintenance.
It is more suitable for dewatering complex sludge.

4 . Is a filter press a good option for treating small sludge flows?

A plate filter press is suitable for small sludge flows, especially industrial or physicochemical sludge, for the following basic reasons:

Its intermittent operation is suitable for low or intermittent production.
Allows high levels of dryness in dehydrated sludge (30–40% DM).
Low energy consumption and simple operation.
Robust and compact equipment with minimal space requirements.

5. In addition to filter presses, what other sludge drying techniques are available?

There are other alternatives for sludge dewatering, such as:

Draining tables. These are filtering surfaces commonly used in pre-dehydration processes.
Greenhouse-type beds and drying yards, which are mainly used in WWTPs located in areas with low rainfall and which have a large surface area for environmental dewatering, where the sludge is spread over gravel or sand-type surfaces.
Thermal dryers. These are systems that allow water to evaporate through contact with hot surfaces or hot air. The most commonly used types are thermal belt dryers, rotary dryers, disc and plate dryers, and fluidized bed dryers. The expected drying rate is around 80–90%, but at the expense of high energy consumption.

6. What are the cost differences between filter presses and other dewatering technologies?

The filter press is the technology with the highest acquisition cost among mechanical sludge drying processes, but it is often the most economical option in the long term, especially when the cost of transporting or disposing of the sludge is a determining factor.

The following comparative table shows the OPEX and CAPEX costs of the most common alternatives:

SYSTEM	capital expenditure	OPEX	SUMMARY
Filter Press	High	Medium-low	High dryness and low space requirements
Centrifuge	Medium to high	Medium to high	Medium dryness and high energy and polymer consumption
Band filter	Medium	Medium-low	Medium dryness and high polymer consumption
Screw press	Under	Medium-low	Medium-low dryness and high polymer consumption
Rotary drum	Medium-low	Under	Low dryness. Pre-dehydration