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Pressure Filter

Overview

Category / type: tertiary treatment.
Application: industrial, wastewater recycling, pollutant removal, car wash, laudry.
Flow: from 0,5 m3/h up to 10 m3/h standard solution and more than 10 m3/h tailor-made.
Material: steel, glass-reinforced plastic (GRP), composed.
High efficiency treatment.

The filtration, using sand or activated carbon, is a commonly used technology that exploits the passage of water within a media for the removal of some pollutants through both mechanical and chemical effects carried out by the filter material.
Filtration process consists on passing water through material to remove particulate and impurities as suspended particles (fine silt and clay), biological matter (bacteria, plankton, spores, cysts or other matter) and sludge flocs.
There are two main kinds of filter media defined by their action on wastewater: mechanical and chemical (adsorption and reaction). Filter media can be inserted in two different filters or incorporated in the same filter to improve the result.
The material to be used must be selected depending on the characteristics of the water to be treated. Consequently a careful chemical analysis is needed for design and size the correct material to fill filters.
The efficiency of these removal mechanisms will depend on the nature of the water being treated, on the choice of filtration system, on the degree of pre-treatment, and on filter characteristics.

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How It Works

Filters can be supplied in an open-top gravity system or, more commonly, in pressure vessels loaded by pumps.
Filters are sized according to the contact time required for removal pollutants and the desired frequency for media replacement.
Pressure filters are designed and manufactured with different filtering media such as sand or activated carbon. These filters can be used as polishing units for industrial water treatment always follow physical chemical plant, as pretreatment (for drinking water) and tertiary treatment of domestic wastewater. These filters made by steel, glass-reinforced plastic (GRP) or plastic are provided externally with valves and piping to direct and control water flow during treatment and cleaning. Filters can be both stand-alone or skid-mounted systems. In either case, system piping, valves, controls, and instrumentation are needed to manage all units. Filters often can have a remote electronic control to increase durability.
Filters always follow physical-chemical plants in industrial wastewater treatment, because it needs to remove residual sludge flocs dragged by effluent.
Optimum filtration depends also on quantity and flocs size and composition of particles which have to be removed by gravity. Also pollutants settlement characteristics are important.
When a proper floc is hard to establish, a greater amount of of flocculant must be dosed in the previous physical-chemical plant.
The main sizing parameters are: operating flow (m3 per day or L per second) and type and concentration of pollutants (depending water analysis).
Filters work usually with a constant flow, so an equalization (load) chamber upstream is always installed to avoid peak flows.
Medium flow is calculated on effective working hour, net of maintenance and backwash operations. A storage tank downstream to the filters is needed, especially in water recycle plants or in industrial wastewater treatment for outflow equalization and homogenization.
Usually sand filters are used to remove suspended solids and organic matters and activated carbon for pollutants that can be removed by chemical adsorption.

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Operation and maintenance

Most important cleaning operation is filter backwash. The backwash reverses water flow, lifts up and flushes the media expelling dirty water via a dedicated waste line upstream to the system.
To assist in cleaning the bed, the backwash operation is sometimes preceded by scouring by way of agitation trough the under drain system. The air scouring agitates sand with a scrubbing action, which loses intercepted particles. After this operation the filter is ready to put back into services.
Filter plant is easy to install and manage, but it requires skilled personnel, authorised company for exhaust filter media disposal.
Activated carbon must be periodically replaced because of their saturation.
Back wash operations are often automated; particular attention should be paid in backwash water and its recirculation in wastewater plant. Valves, PLC, pipes, pumps, etc. require normal maintenance.
A by-pass system is provided for extraordinary maintenance operations and malfunctions.

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Features and benefits

Pressure filtration systems are designed for both municipal and industrial water treatment, where is the removal of suspended solids such as particulates, iron, manganese, free oils, mill scale and other precipitates in ground or surface water is required. Pressure filters are commonly placed after clarification, flocculation or physical-chemical plants.
There is no pathogens removal, therefore a sterilisation section is often necessary, especially for water recycling.
Flushing times are strongly dependent on inlet water pollution. Filters can operate manually as well as automatically. Automatic control is usually done by a programmable logic controller (PLC) or microprocessor in combination with pressure meter.

Advantages (benefits)