The percolator filter treatment plants, along with activated sludge treatment plants, represent one of the most common methods for the biological treatment of domestic and urban wastewater and are used for the purification of both small and medium/large users.

Percolator filter treatment plants operate by reproducing the phenomena of natural biological purification in a limited space. This allows for the treatment of larger quantities of wastewater in smaller spaces and in shorter times.

The biological percolation treatment plant is one of the oldest systems used by humans, as it operates through the regular distribution of wastewater from top to bottom over a so-called “percolation bed” made up of multiple layers of draining material (gravel, plastic material, etc.), which allows for the complete reproduction of the same microbiological environment found in nature.

Percolator filter treatment plants can be constructed from concrete, plastic, or fiberglass and must be sized according to the number of equivalent inhabitants they serve.
Percolator filters are built in two types:

Aerobic percolator filters with electric power
Anaerobic percolator filters

In addition to these two types, there is another unique type that provides internal aeration without the use of electric power, called biorock® (link to biorock video).
In anaerobic percolator filters, it is necessary to install an additional sedimentation unit (Imhoff tank) downstream for the treatment of the adhered sludge that detaches from the internal anaerobic section of the filter and exits towards the receiving body.

In the initial phase, which can last from a few weeks to a few months, purification in percolator filter treatment plants may not occur at its maximum efficiency, as the biological film has not yet formed on the filtering material.

After the initial phase of operation, however, the characteristics of this system allow for optimal purification even of wastewater coming from facilities characterized by highly discontinuous water loads, such as restaurants, second homes, agritourisms, etc.

Bacterial colonies adhere to the internal draining filling of the percolation treatment plant, managing to remain alive and operational without being washed away by the wastewater from the facilities, thus continuing their biodegradation action.

Before being directed to the percolator filter treatment plant, wastewater must undergo a pre-treatment through appropriate primary wastewater treatment systems such as Imhoff tanks, biological tanks, septic tanks for black water treatment, grease traps for gray/soapy water treatment, or otherwise regulated systems under d.lgs 152/06 environmental code part iii on environmental protection to remove those parts that would obstruct certain areas of the draining bed.

Percolator filter treatment plants can be constructed from concrete, plastic, or fiberglass and must be sized according to the number of equivalent inhabitants they serve.
As with activated sludge treatment plants, percolator filter treatment plants can also be part of condominium services, and the cost of their maintenance/management can be shared among those who benefit from them according to criteria established by law or condominium regulations.

Good Usage Practices

The percolator filter treatment plant is widely used for domestic and/or similar users, even with characteristics of load discontinuity.

While for small users the purification yield is not very high, especially for direct flow systems, it is still one of the treatment systems defined as appropriate that has become common and is therefore widely used for all users.

It is good practice to plan the sizing of the entire system, including pre-treatments, as the overall pollutant load can undergo more effective reduction.

In aerobic percolators with air blowers, the need for constant electric power and frequent monitoring of operating conditions requires installation near energy sources.

It is important to remember that rainwater must absolutely not be directed into the percolator filter treatment plant.

Fields of Application

Through the percolator filter treatment plant, all types of domestic and/or similar wastewater can be treated, coming from small facilities for 4 inhabitants up to much larger users serving even small municipalities (ideal up to an indicative threshold of 500 equivalent inhabitants or with high load discontinuity). It is also possible to treat:

wastewater from hotels, campsites, tourist villages, agritourisms, and other accommodation activities.
wastewater from fish farms and kennels
wastewater from agricultural enterprises in general
wastewater from dairies and wineries, as well as mushroom farms and road wash

It can be used with excellent purification yields and integrated with primary and tertiary treatment systems.

Regulatory References

The percolator filter treatment plant is indicated as a secondary plant element according to d.lgs 152/06 and is mentioned in various regional regulations, to be used together with other systems, both primary and possibly tertiary, necessary to reduce the pollutant load of wastewater and to return it to the environment as purified as possible.

IMPORTANT

European Regulation No. 305/11 has stipulated that this type of plant must also be certified according to directive CE EN 12566:3 for both structural and functional parameters, the latter mandatory since July 1, 2013, through the mandatory purification performance test lasting at least 38 weeks.

Links:

Maintenance

To optimize the operation of this plant element, periodic maintenance is necessary to remove the sediment or biological sludge that settles inside. Moreover, poor functioning of the primary treatment system can cause anomalies in any downstream wastewater treatment system installed, such as phytodepuration, a percolator filter treatment plant, an activated sludge treatment plant, etc. Periodic maintenance operations must be carried out by vacuum truck companies that will then dispose of the waste either at a landfill or at a public treatment plant. More specific technical interventions must be carried out by specialized personnel.

Indicative List of Advantages

decent purification yields of aerated percolators even for small users
constant but not excellent purification yields for anaerobic percolators even for small users
good resistance to short load discontinuities
cost-effectiveness of purchase for plants serving small users (up to 100 equivalent inhabitants)
ease of installation for monoblock plants serving small users (up to 100 equivalent inhabitants)
reduced installation costs for plants serving small users (up to 100 equivalent inhabitants)
possibility of underground installations
the aerobic percolator filter treatment plant with electric power is an active system with modifiable operating parameters
the Biorock® natural aerobic percolator filter treatment plant does not require electric power for operation and guarantees very high and certified wastewater purification standards CE EN 12566:3 2005

Indicative List of Disadvantages

costly extraordinary maintenance and restoration operations, due to the need for the removal of internal draining plastic fillings.
necessity of installing Imhoff tanks downstream of anaerobic percolators.
high operating costs due to the need for constant electric power for aerobic percolator filter treatment plants that operate on electric power.
management and maintenance operations to be carried out by specialized personnel.

Aerobic Percolator Filter Treatment Plant