This is a cross section of an AES (Advanced Enviro-Septic™) pipe installed in a sand bed with an expanded section of the edge of the pipe superimposed: –
Stage 1: Effluent enters the pipe and is cooled to ground temperature. Suspended solids separate from the liquid effluent.
Stage 2: Skimmers further capture the grease and suspended solids from the effluent.
Stage 3: Pipe ridges allow the effluent to flow without interruption around the circumference of the pipe
Stage 4: Bio-Accelerator™ fabric facilitates the development of a biofilm of self-colonising micro-organisms that process the organic material.
Stage 5: A mat of coarse, random fibres provides additional surface area for microorganisms.
Stage 6: Geo-textile fabric, where biofilm reduces the permeability of the pipes, allows effluent to spread evenly along the pipes before seeping into the surrounding sand.
Stage 7: Air space is maintained in the top of the pipes and passive ventilation enhances aerobic activity.
Stage 8: Sand wicks liquid from the geo-textile fabric and evenly distributes high quality treated effluent over the base of the bed.
NOTE: System Sand is installed to a depth of 300mm below the AES pipes and 150mm above and between individual AES pipes. In less permeable soils the lower 150mm of the sand bed is extended horizontally to provide the required infiltration surface area. This is called a ‘Bed Extension’
Raw effluent flows from a building or ablution block to a standard, locally-sourced septic tank which is sized with a working capacity as a minimum of 3x the daily expected inflow. Anaerobic (without air) micro-organisms within the effluent use some of the suspended organic material as a food source and provide some treatment. Inorganic material settles to the base of the tank and a scum layer floats on the surface sealing the majority of the effluent from air on the top of the tank. If the overflow from this tank is then sent to some form of final disposal into the ground this is termed Primary Effluent Treatment.
Secondary Treatment is often a council requirement and anyway a worthwhile investment. This can be due to small area of land available for a disposal field, the proximity to surface water and concern about groundwater contamination. This level of treatment involves aerobic (in the presence of air) micro-organism or aerobic bacterial processes which results in the almost complete further removal of dissolved and suspended organic matter from the effluent stream. AES provides this environment without the ongoing use of any technology. That is the AES pipe and sand bed under where the ball game is starting.
So after Primary, Secondary or Tertiary treatment, where any remaining coliform bacteria are reduced, the effluent is usually required to be disposed of ‘to ground’ where soil bacteria and microbes in general in the soil are able to consume whatever nutrients are left after the treatment.
In order to achieve secondary wastewater treatment, an oxygenated environment is required. AES system pipes achieve this in the simplest possible manner by chimney effect ‘venting’ also called differential venting. Air is drawn into a low level inlet vent at the end of a line of AES pipes to an outlet high vent of at least 80mm in diameter positioned at least 3m above the low vent from the other end of the AES pipe system. You can see the sequence of this process in the diagram above.
When it is possible and with the septic tank access lids sealed, the terminal vent at the building end of the waste line can be the high level vent. When this is impractical the high level vent can be attached to an adjacent building or some other dedicated support.
The fabrics and fibres provide a large surface to support the microbial life breaking down solids and digesting potential organic pollutants. An ample air supply through the pipe system using a passive chimney effect and fluctuating liquid levels as the usage fluctuates during the day increases aerobic bacterial respiration
The key to the success of the AES system without any mechanical intervention is the passive airflow through AES pipes which are hosting the micro-organisms. Careful attention to the integrity of this air passage is an essential aspect of any AES design and installation.
For the high vent to draw airflow from the low vent, via the septic tank:
• The septic tank access lids and inspections need to be airtight
• The septic tank must not include an air vent
• The high vent at the house must be a minimum of 80mm in diameter
AES systems work best when one row is filled to overflowing rather than 2-3 rows partially filled. (The last row will only receive effluent when there is peak occupancy in the home.) Thus when rows are connected in series, the first row is likely to receive more effluent than the last row. While this initially appears counter-intuitive to standard primary treated effluent dispersal to soil, we need to consider the benefits of the rising and falling of liquid in each row of AES pipe. This is referred to as the ‘lung effect’ and provides optimal conditions for aerobic microbes as the liquid level rises and falls within the pipe system.
After around 21 days the aerobic micro-organisms have completely colonised the pipes and a stable community established. A biomat is created which allows the effluent to extend the entire length of the pipe. Treated effluent, stripped of the majority of its food values by these organisms, then slowly seeps out into the System Sand. The grain size of this sand allows effluent to travel slowly throughout the sand bed where further habitat for microbes is provided. In this way the base of the AES is bed receives an even amount of effluent stripped of BOD and TSS to ≤ 2mg/100mls – 10x less than Secondary Standards confirmed by test results.
Because of the structure of the AES system pipe, it does not suffer from Progressive Failure. In 15 or 20 years if you were to open up an AES system, the system sand will still be clean which will facilitate the working of water out of the AES system pipes and the introduction of oxygen into the micro- biological processes that also occurs in the sand. Homeowners are not confronted with costs of maintaining their aerated wastewater systems and will not have to address the problems of failing and non-maintained septic systems.