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. There are two types of alternative systems on the market today. There are Level 4 treatment units approved under CAN/BNQ 3680-600, and there are BMEC approved systems. Level 4 treatment units are typically tanks which hold a type of media, some air pumps or both. Many of these treatment units are placed after a septic tank, but some have integrated pre-treatment tanks which can replace a septic tank if needed. The treatment which happens in the tanks breaks down the effluent to the point it looks like clean water. This can be done through through a combination of settling, aeration, and filtration; and many of the treatment units also have nitrogen reduction built in. Because the effluent is so clean coming out of the treatment units, the leaching beds can be much smaller. BMEC approved systems generally are leaching bed treatment units. The units are placed evenly throughout a specified sand area. The number of units needed in each bed is defined in their BMEC approval and is based on the Daily Design Flow of the building measured in Liters per Day.

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 Level 4 Treatment Systems work? 

Level 4 treatment systems are listed on the CAN/BNQ website. These technologies are approved by the Minister of Municipal Affairs & Housing through BNQ. Level 4 treatment units designed as “Treatment Units” other than septic tanks must meet the requirements of Section of the OBC and must produce level 4 treatment levels of suspended solids and CBOD5. The following treatment units are registered under CAN/BNQ 3680-600 and meet the level 4 treatment levels in Table of the OBC:

How does a BMEC Approved System work?

BMEC approved systems work through filtering the effluent through patented media placed under the pipe or wrapped around the septic pipes. These technologies are placed after a septic tank and used in a leaching bed. The size of the leaching bed and the number of units is determined in the BMEC approval. The following systems are approved for use in Ontario under BMEC:

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 sprayed 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 receive effluent from a Level 4 treatment unit. 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 a Type A Dispersal Bed?

The Type A Dispersal bed was added into the Ontario Building Code in 2012 under Division B Part 8.7.7. and contains an infiltrative zone similar to that of a filter bed. It generally consists of a clean stone layer 200 mm thick underlain by a sand layer 300 mm thick. The type A dispersal bed must only receive effluent from a level 4 treatment unit. Some of the level 4 treatment units are designed with an open bottom so the effluent can drain out the bottom of the unit to the stone area of the dispersal bed. Other level 4 treatment units are designed to discharge through a pipe or a pump. With these treatment units the dispersal bed would have 1 inch (min.) pressurized pipe or 3 inch (min.) gravity fed pipe laid within the stone layer. The Type A Dispersal bed contains a sand layer made of a specified sand which helps to distribute the effluent over a large area.

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 Level 4 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.

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

How long do 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 Level 4 treatment units and BMEC approved systems compare with conventional systems in terms of cost?

Generally speaking, Level 4 treatment units are the most expensive, followed by the BMEC approved systems, with the cheapest units being the conventional systems. Level 4 treatment units are the most expensive because they generally have many moving parts and require maintenance contracts to keep the parts operational.  Because there is much more treatment before the effluent reaches the leaching bed it is expected that the treatment units will last much longer than the conventional systems. BMEC approved systems are the middle ground for cost of a septic system. The technology doesn’t have any moving parts but needs a service contract for sampling and testing. Conventional systems are the cheapest systems of the bunch, but because there is no added technology it is expected that they will only last 20 years. See Cost for more details.