Conventional vs. Alternative Systems


What is an alternative treatment system?

The connotation generally refers to an on-site system that provides enhanced treatment beyond the level of treatment provided by a conventional septic system. An alternative treatment system usually provides better quality effluent prior to entering the soil absorption system or leaching bed. Generally, the system provides better treatment by adding components to the system beyond the septic tank. Most of the additional components achieve higher levels of treatment by providing an aerobic environment, which will ensure the faster working aerobic bacteria are present to break down wastewater. Alternative treatment systems may consist of multiple components. One component may reduce waste strength or remove pathogens, while another may remove nitrate-nitrogen, others, working in combination, do all three. The type of advanced treatment system that you install will depend upon the water resource you are interested in protecting.

Are there certain areas where Alternative Treatments should be used?
Yes, in sensitive resource areas, like around drinking water supplies, advanced treatment systems are necessary to remove pathogens and nutrients such as nitrate-nitrogen from your household wastewater. Conventional systems do not provide the this level of treatment even when working properly. Also, enhanced treatment systems should be used at existing home sites requiring repairs or replacement where the site cannot accommodate a conventional system.

How do Ontario Authorized Alternative Treatment Systems work? 

Approved alternative treatment systems are listed in the Ontario Building Code, Division C, Supplementary Standard SB-5. These technologies are approved by the Minister of Municipal Affairs & Housing. Alternative treatment systems designed as “Treatment Units” other than septic tanks must meet the requirements of Section of the OBC and must produce either secondary or tertiary quality effluent (also described in the same Section). All of the authorized alternative treatment systems described in the following section of our FAQ’s meet tertiary effluent criteria as specified in the Ontario Building Code.

How does the Waterloo Biofilter work?

The Waterloo Biofilter is an aerobic trickling filter that uses an absorbent synthetic filter material developed by researchers at the University of Waterloo and first installed in Ontario in 1991. At this time is was a case-by-case approval system. In August of 1996 the OMOEE approved it, and the MMAH incorporated this approval into the OBC in 1998. Septic tank effluent is applied intermittently to the top of the filter media. The synthetic media is a support for microbiological growth, and these microorganisms are responsible for the aerobic breakdown of the wastewater. Effluent from the biofilter is suitable for discharge into shallow buried trenches, or a conventional leaching bed or filter bed (although the footprint of the bed may be reduced). The Waterloo Biofilter also has a BMEC authorization to use an area bed dispersal system (see FAQ 10),and this is used in the majority of their installation. This system is often used on sites that have a limited area available (not enough for a conventional on-site system) and has a very small footprint. Installation of a waterloo Biofilter system requires the property owner to enter into a contract for regular maintenance and site visits by an authorized service provider every 6 to 12 months.
What is an Ecoflo Biofilter and how does it work?

The Ecoflo Biofilter is a trickling filter that uses peat to treat wastewater. The Ecoflo Biofilter consists of an open-bottomed fibreglass shell full of harvested peat. Effluent from a septic tank is delivered by pump or by gravity (depending on relative elevations) to the top of the peat media. Wastewater percolates downward through the peat and then through the infiltration zone, which consists of 200 mm of clear stone & 300 mm of clean sand. After moving through this infitrative zone, wastewater infiltrates into the native soils. The peat acts both as a place for aerobic bacteria to anchor and treat wastewater as it passes through the filter and as a physical filter. Some limited chemical reactions are also achieved. Aeration of the unit is passive, i.e. there are no blowers or fans to enhance air movement through the peat. This system is often used on sites that have a limited area available (not enough for a conventional system) or that do not have appropriate soil for a conventional system. Effluent from the Ecoflo biofilter is most often discharged to an area bed as they have the BMEC authorization for this type of dispersal system (see FAQ 10), but can be collected and directed to shallow buried trenches, or a smaller conventional leaching bed or filter bed. The Ecoflo system requires the property owner to enter into a yearly maintenance contract, which must be completed by an authorized representative of the manufacturer. The peat must be replaced approximately every 8 years.

What soil absorption systems are most commonly used with alternative treatment?

When using an alternative treatment system, there are more options for soil absorption systems. These absorption systems typically require less space than conventional leaching beds. Options are a reduced size conventional leaching bed, an area bed (if the approval for the unit exists) a shallow buried trench system or a reduced size filter bed.

What are Shallow Buried Trenches?

A shallow buried trench is an alternative to a conventional leaching bed. It consists of a pressure distribution system which delivers doses of effluent to a leaching bed which consists of 25 mm PVC laterals laid inside a plastic chamber. The laterals are perforated at regular intervals on the top of the pipe. When the dosing pump is activated, wastewater is forced along the entire length of the lateral and prayed upwards where it hits the chamber and trickles down into the soil. By sizing the pump correctly, the entire footprint of the system is dosed at the same time, ensuring much more efficient distribution and use of the soil absorption system. Shallow buried trenches may only be used when the wastewater has been treated to tertiary standards. The footprint of a shallow buried trench system is much smaller than a conventional system, because the soil is not relied upon to complete very much treatment. In addition, shallow buried trenches may be installed in native soils with a T-time up to 125 min/cm. This system is appropriate for sites with a high water table, shallow depth to bedrock or tight soils

What is a Filter Bed? 

A filter bed is a soil absorption similar to a sand filter. It must be preceded by a septic tank. Wastewater flows from a septic tank to network of distribution laterals that distribute the flow evenly over the surface of the filter. The laterals are placed on a continuous bed of gravel approximately 300 mm thick. The gravel layer is underlain by a 750 mm depth of filter sand. Filter sand is very coarse grained, uniformly distributed sand which must meet the requirements of Section of the OBC. This filter sand is underlain by another 250 mm mantle sand. Wastewater percolates downward through the gravel and filter sand and eventually infiltrates the native soils. Filter beds can be raised, partially raised or fully in-ground. Use of an ATU instead of a septic tank will allow some reduction in the size of the filter bed.

What is an area bed?

An area bed is an infiltrative zone similar to that of a filter bed. It generally consists of a clean stone layer 250 mm thick underlain by a sand layer 200 – 300 mm thick. The area bed may or may not have a distribution network of PVC laterals, depending on the technology. Some area beds are located directly beneath the treatment units themselves, which helps to save space. Area bed authorizations are not contained in the building code, rather they are granted by the Building Materials Evaluation Commission (BMEC). Area bed authorizations are technology specific and cannot be used with every alternative technology. Minute differences in area bed authorizations are present from one technology to the next, so you must consult the authorization for the technology you wish to install for specific area bed requirements for that technology. Area beds have very small footprints, are are only allowed in conjunction with alternative treatment units providing tertiary level treatment.

When should an alternative treatment unit be installed instead of a conventional one? 

When enhanced treatment is desired, either greater nutrient or pathogen reduction. Also when a site cannot accommodate a conventional technology or if in new construction you want to avoid fill or retaining wall costs, or extensive mounding.

How does an alternative treatment unit improve water quality?

By putting the effluent through either aerobic or a combination of aerobic and anaerobic treatment before effluent is released to the leaching bed, or by using existing upper-level soil to encourage additional treatment through a shallow, narrow trench design.

What kind of site constraints can be overcome with an alternative treatment unit? 
Sloping sites, high groundwater, fast or slow percolating soils, proximity to wetland or other resource area.

How long do alternative treatment units last? 

When properly engineered, installed, and maintained, the overall system (i.e. tank and treatment zone) should last indefinitely. Individual components such as pumps, electrical components, and filter media may require eventual replacement.

How do alternative systems compare with conventional systems in terms of cost?

Generally speaking, alternative systems will be more costly than conventional stone and pipe systems, especially in aggregate rich areas of the province. However, alternative systems become more economically attractive in areas with a high ground water table or unsuitable soils, especially if gravel and sand are difficult to obtain. Large filled based conventional systems can cost as much, if not more than alternative treatment systems in areas of the province where sand and gravel are not readily available.