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Peat has been used for wastewater treatment since 1891. In Italy a professor of hygiene and the director of public health in Rome described using an early septic tank in combination with a “peat filter” to treat wastewater.
Peat is partially decayed organic matter mainly of plant origin. It consists of partly decomposed remains of roots, stems, leaves, flowers, fruits and seeds. In peat bogs the soil and the peat that forms on it, are saturated with water for much or all of the year. The partially decayed organic matter cannot complete its decomposition process because of the saturated conditions that exist in the peat bogs. Most of the living roots in the bog are situated in the semi-aquatic layer where the plant heads are just above water. Below this layer, there is an anaerobic zone where the pace of decomposition in the waterlogged soil is very slow. In the depths of the anaerobic layer decomposition has almost stopped. In these conditions peat or partly decomposed plant remains, accumulates in layers. In its natural state, peat may consist of as much as 98 percent water. One of its features is the capacity to bind or retain water. This natural water binding ability of peat accounts for its widespread use in horticultural applications and it also allows for a very long residence time when used to filter wastewater.
Peat bio-filters performance is consistent for intermittent or year round use and they have low operation and maintenance requirements. The bio-filter module(s) can be placed at grade to meet vertical separation requirements or can be place in the ground up to the lid for aesthetics. The design footprint for a peat bio-filter can be considerably smaller than a mound or sand filter.
Just like the sand filter, peat bio-filters are used as the second step in wastewater treatment after solids in raw wastewater have been separated in a septic tank, aerobic unit or other sedimentation tank.
The treatment technology is based on simple, passive bio-filtration principles. The treatment of the wastewater within the system is achieved by a combination of unique physical, chemical and biological interactions between the wastewater and the fibrous media. A complex chemical structure permits a number of separate treatment and attenuation processes to occur simultaneously.
Peat Bio-filter System (Pura-Flo Peat System)
In a mature peat bio-filter the biological transformation processes are crucial in maintaining the treatment efficiency. The bulk of the treatment and assimilation processes are achieved by diverse micro-flora that adhere to the surface of the peat media. This micro-flora is largely composed of aerobic and facultative aerobic heterotrophic bacterial from a large number of genera.
A wide variety of “higher life” forms such as protozoan, rotifers, worms, insects and larvae also live in the media matrix. These organisms play an important role in keeping the bacterial population in check thereby maintaining a balanced and stable ecosystem. The larger numbers of heterotrophic bacteria are found in the upper portions of the filter media and nitrifiers become more prevalent deeper into the filter. Therefore, the assimilation of waste is affected within the upper portions of the filter and nitrification occurs deeper in the filter.
The effluent from the septic tank can go directly to the peat module(s) by gravity or can be collected in a pump chamber and pumped to the peat module(s). If a pump is used the system is usually activated by a programmable timer.
The partially clarified effluent is evenly distributed over a specialized fibrous peat media that is contained in a number of molded polyethylene modules. The effluent percolates through the unit and emerges as a clear innocuous liquid from the base of the system. The long residence time allows the wastewater a much greater contact time with the treatment media that results in a very efficient single pass or recirculating treatment system.
The module(s) are placed on a gravel bed at grade and then covered with topsoil or a hole can be dug and the module(s) can be placed on the gravel base and buried to their lids. The lids allow air into the module and therefore should not be covered.
Once distributed evenly over the peat media the effluent moves laterally and vertically within the module(s). There are two methods for the effluent to exit the module(s). The treated effluent either weeps through holes drilled in the base of the module and disperses directly into the gravel pad or the effluent can be collected into a separate pump basin and pressure dosed to a typical leach field.
The septic tank should be checked for sludge and scum buildup and pumped as needed. A effluent filter is recommended and should be maintained as needed.
If a pump chamber or pump basin is used the pump(s) and floats should be checked annually and replaced or repaired as necessary. All electrical parts and conduits should be checked for proper operation and corrosion. Follow all of the manufacturer’s operation and maintenance instructions. All equipment must be tested and calibrated according to the manufacturers specifications.
The treatment technology is based on simple bio-filtration principles. There is no requirement for moving parts or forced aeration mechanisms. The peat module(s) are low-maintenance and require no annual pumping or backwashing. They should be racked annually to break up any biomat that may be forming and to level the media.
Some Advantages and Disadvantages are listed below.
Advantages:
· High effluent quality.
· Due to the modular design installation is simple.
· The treatment capacity can be expanded through modular design.
· Nitrogen reduction is often times possible.
· Peat bio-filters are stable and work well for intermittent usage.
· Depending on design peat bio-filters have little to no energy requirements
· Little land area is required.
· Easily accessible for monitoring and does not require a lot of skill to maintain.
Disadvantages:
· Annual inspections must be completed by a trained operator.
· Treatment media has a limited useful life and has to be replaced with new media depending on the use.