PEAT / FOAM & FABRIC FILTER Wastewater Treatment Plants

Summary

Peat, foam and fabric filter based wastewater treatment plants in France are frequently fundamentally flawed by an incomplete treatment process caused by insufficient aeration and temperamental operation.

Operation

In a filter type wastewater treatment plant typically the raw sewage flows to a septic tank which may or may not have a septic tank effluent filter. The septic tank effluent may flow by gravity or be pumped to be sprayed over the filter material. In the case where the effluent is gravity flowed over the filter material, the filter material then spreads the effluent through-out the surface area by means of a tipping tray. (This can be very noisy.) In the case where the effluent is pumped and sprayed over the filter media, there are spray nozzles that spray the septic tank effluent over the filter material. In either case in this type of wastewater treatment plant, the filter media allows the septic tank effluent to flow down and through permitting atmospheric air to penetrate the filter material. This may allow some conversion of the anaerobic septic effluent to some level of aerobic treatment. Once the liquid has passed through the filter media, it may be pumped around again for recycling back to the septic tank or be discharged into the disposal site by gravity or pump pressure.

Using the anaerobic septic tank effluent, the filter material becomes progressively clogged to the point where it needs to be replaced, and, the effluent being given to the drain field may still be anaerobic as there would be very low if any dissolved oxygen (DO) levels over time. As the drain field is designed to be aerobic, the lack of DO in the effluent from the peat or foam filter wastewater treatment systems does not assist the drain field to remain healthy or operational in the long term.

Service & Maintenance

The filter system that utilizes septic tank effluent being pumped and sprayed over the filter material typically requires that the spray nozzles be checked and serviced to ensure that they do not clog. The frequency of nozzle cleaning and/or replacement will vary given the behaviour patterns of the user. Each of the filter types rely on septic tank effluent and the septic tank requires the usual pumping out frequency of every two to three years. Both types of filter (peat moss or foam block) require that the filter material be removed and replaced as required which may be as long as every seven years or as short as three.

In summary, the serviceable parts would typically be:

• Filter material being replaced every 2-5 years
• Spray nozzles being checked, cleaned or replaced every 6 month
• The septic tank effluent pump and screen filter, cleaned and checked every 6 month
• The post filter pump checked every 6 month (which may also be used to discharge)
• Filter material replaced periodically and at “captive” costs.

Environmental Benefits

A filter type wastewater treatment plant may be marginally better than an anaerobic tank and drain or sand filter arrangement, but is unlikely to offer any significant, lasting ecological or environmental benefits.

Conclusion

With a peat filter type wastewater treatment plant, there is some question whether the natural peat moss material will be readily available in the future at a reasonable cost. This may be due to restricted or reduced access to the peat moss at the discretion of the peat moss supplier as approved by the peat moss technology supplier. This solution to your wastewater treatment does not offer any significant advantages over other wastewater treatment plants in France and it would be surprising to find one tested to EN 12566-3 and showing sustainably clean results.

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