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Guidance on Septic Systems

Some Notes for your guidance on Septic Systems


Concept: When it is managed properly, a Septic Tank System is the ideal rural sewage digestor. [It has been since Napoleonic times]. The system is anaerobic and, apart from around the influent pipe, where fresh effluent containing dissolved oxygen enters; the microorganisms degrade feacal impurities in the absence of dissolved oxygen. There is no in-put energy; electricity, so there is virtually no operating cost with a dedicated septic system. The tank is vented up the sewer to the house, and the stack pokes through the eave in the roof, where breezes carry any odour away..


What Makes it Work: However, a septic system is only as good as the quality and efficacy of the microbial ‘biomass’ [regenerating population of sewage degrading microbes] it contains. Your use of Bio-Systems products ensures optimum performance.


Size: Make sure that the septic system you have is capable of handling the organic ‘load’ [sewage] that you are imposing upon it. Tanks are often too small for the volume of effluent they receive. Then they give trouble. A septic tank will only function if sufficient ‘residence’ time is allowed. This is typically a minimum of 18-21 days. The longer the residence time; the greater the degradation and the better the discharge quality.  On average, one person will flush a residential toilet 6 times a day. Each flush is around 10lt. So one person flushes 60lt /day. So a family of 4 flushes 200lt / day. So their tank needs to be at least 4,000lt [4m3] capacity. [rule of thumb: allow 1,000lt capacity per resident;, plus 1,000lt for friends]


Soak-away Size: In suitable [sandy/loam] soil, you need an average of 2m length of soak-away per person Clay soils may demand double or treble this amount – because the clay resists seepage.


Warning: Allowing ‘grey’ [bath, laundry &c] water into the septic tank will cause ‘hydraulic overload’ and result in the tank being ‘washed-out’. The soak-away then suffers from an abnormal quantity of semi-degraded feacal impurities, gets blocked and packs-up


Construction:  Septic Tanks usually have two chambers.

1.    The Primary receives and breaks down the incoming faeces and there should be a thin, soft surface scum crust [not more than 50mm thick] floating on the surface. The thickness is regulated by the microbes which are continually breaking it down from the underside. The microbes may dislodge fragments which are further degraded as they descend very slowly through the body of microbe rich effluent. Any inorganic or heavy material ends up on the tank floor where a thin silt layer builds-up

2.    The Secondary, where maturation occurs, should have ‘black’ water-free of any scum- with a myriad of tiny bubbles [methane gas] constantly re-forming on the surface – like the sky on a crisp clear, winter’s night.

3.    The  Baffle, is a common dividing wall between the chambers and is perforated near the bottom to act as an underpass baffle that permits the egress of partially treated effluent whilst retaining the scum and solids and the attendant majority of ‘break-down’ bacterial biomass.

4.    Connections: For proper operation it is essential for both the inlet and outlet to be fitted with ‘t’ junctions which are at exactly the same level. Made sure all inspection covers are airtight, or odour may be apparent. Keep frames and airtight grooves free of soil and grass. Use heavy grease. Replace ‘cracked‘ covers; often responsible for odours. Covers should be above ‘T’s to facilitate cleaning if blockages [paper, usually] occur

5.    The Inspection Covers – there should be one over each ‘t’ junction, at each end of the tank – They must be airtight, [grease the frames], to prevent the escape of sulphide gasses which are generated in the sewer-line and the outfall to soak-away.  These gasses cause odour. Keep frames and airtight grooves free of soil and grass. Use heavy grease. Replace ‘cracked‘ covers; often responsible for odours. Covers should be above ‘T’s to facilitate cleaning if blockages [paper, usually] occur

6.    A tank that is out of biological balance may give rise to bad odours, especially early morning and evening.


How your System Works: When you press the flush lever of the toilet, water from the cistern washes the feacal ‘soldiers’ and paper into the sewer, and along to the Primary chamber of the tank.‘Soldiers’ and paper float to the surface and form a crust 25-75mm thick. Sewage bacteria in the chamber, such as concentrated in our product STR, gnaw away at this crust from the underside, regulating the thickness and dropping a fine mist of COD that descends slowly as it is progressively degraded by the self regulating varieties of microbes. Bio-degradation of human wastes occurs in layers [clines] from crust to floor. Freshly entered effluent is richer in floating solids than the previous days’ so it rises to under the crust where

the majority of microbes live – where their ‘food’ is most plentiful. Partially treated effluent [free of optically discernable solids] is displaced under the baffle into the Secondary chamber by the incoming toilet flush; volume for volume. A healthy Secondary has a surface similar to a starlit sky on a cold winter’s night; a myriad of tiny silver gas bubbles on jet-black water. Further degradation – known as ‘maturation’ now

takes place and processed effluent is thus periodically welled into the pipe that runs down to the soak-away. Here,the waste water is further refined by slowly passing through the slimes that grow on the ‘media’.


The soak-away should be a perforated brick strip trench, surrounded by small non-calcareous aggregate [crushed granite or old car tyres] are idea encased in a geo-textile [like Bidim] and must be level on a

contour, to allow even seepage along its length – with a bifurcated entry-splitting the soakaway into 3 x equal lengths. Trenches can be ‘herringbone’ on plan, but soak pits have reduced vertical area. A common mistake is to make the soakaway too deep. We often hear of 1.5m and even over 2m deep . Remember the soil gets harder as you descend. A domestic soakaway should be about 600mm – 800mm deep! Rather go longer!  Both tank and soak-away should remain at a constant water [effluent] level. If the [average poorly constructed] soak-away dries out, the walls are liable to collapse inwards, blocking the flow and causing surface subsidence. The septic tank may then overflow. However, a properly constructed facility will not be affected by level variations. Final bio-degradation by the naturally occurring soil bacteria, in the ‘leach field’ called ‘polishing’, takes place where the effluent seeps from the soak-away into the surrounding soil – leach field. Here also, live the essential bacteria that reduce ammonia through nitrite to harmless nitrate.  And so, being progressively further refined the effluent filters down to the underlying water table where it should be ‘clean’ and potable after its journey – when it finally arrives. If not you, and your neighbours, have trouble with a capital ‘T’ with your/their borehole/s


NB: If the soak-away becomes fat lined and the water cannot ‘seep’ into the surrounding soil, it is usually because the tank is too small for the number of residents; this also will cause the septic tank to overflow - see above. This can be largely prevented with our Soak-Away Cleaner


Pumping Out: ‘Having the tank pumped’ is not the solution one supposes.

  1. All one is doing is alleviating the immediate problem, - the flooding, - and removing a large percentage of the [already depleted] essential microbes upon which the successful operation of the system relies.  Had there been sufficient microbes, the malfunction would probably not have occurred.
  2. The built-up fat in the soak-away remains. 
  3. Very few pumps have the capacity to ‘suck-out’ the sludge crust which settles on the inside of the tank. This sludge traps the fine silt that should be removed periodically [every 7-10 yrs]. Treated this way, a tank will rapidly ‘die’


Prevent Problems: Invariably a Septic System fails because the soak-away becomes inoperative. We supply ‘trans-fat’ digesting Soak-Away Cleaner and Septic Tank Reviver. These natural organic products are targeted to break-down the complex composition of modern foodstuffs, you are advised to use these them regularly. You have your car serviced. Treat your friend in the garden if only once a year !


Technical Support: We sell [sized] construction drawings of approved designs that comply with National Building Regulations with for both septic tanks and soak-aways if you need them, at R125 each [or R225 +Vat for a pair in email] format SA. Per eft Ask


Plastic Septic Tanks: These units, usually roto-moulded, appear cheaper than brick tanks. However, they should be buried on a concrete base within a 115mm r/f wall, and back-filled with dry sand, to stop them collapsing or moving - causing leaks after a few years. This makes them more expensive. They’re also very difficult to access and clean. Most hdpp actually attracts sewage grease


Soak-Away Replacements: DWAF and many local municipalities frown on soak-aways these days because they are so often the cause of ground water pollution following over-population and owner neglect. If this is the case in your area, we can offer a selection of small ‘package plants’ or a SOG Filter that will process septic tank effluent to DWAF Standard [COD100 / BOD10ppm].


Grey Water: This can go to the soak-away, but must never go via the septic tank [except the kitchen drainage]. However, grey water –from bath, & laundry etc - can be a valuable resource that should not be wasted as it is costly  &  good for the garden, to where it will return via the soil to the water table anyway, so there is no ‘loss’. You save money by re-using your grey water on the garden. To ‘clean’ and refresh it is simple and inexpensive. We supply both the technology:


Health & Safety: All biological products offered by Bio-Systems SA are accredited for compliance with international health and environmental authorities, and are quite safe to all forms of life; used as directed..

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