What is a Septic Tank?
Septic Tank Sewage Treatment Systems (or septic tank systems as they are called in some parts of the world,) treat sewage at its location, rather than transporting the sewage to a sewer system or larger treatment system nearby. A septic tank is basically a vessel buried underground, the purpose of which is the collection, storage, and to some limited extent treatment of sewage. On a simple hierarchy of sewage facilities the septic tank falls between the “long drop” and a piped connection to a fully functioning sewage treatment works, the function of which is to convert human waste products into mostly harmless end products.
A typical septic tank system normally operates by gravity and consists of a tank and a soak away drain. Untreated waste water from a property flows into the septic tank where the solids separate from the liquids. Some solids, such as soap scum or fat, will float to the top of the tank to form a scum layer. Heavier solids such as human and kitchen wastes settle to the bottom of the tank as sludge.
Self forming bacteria in the tank help the system digest these solids or sludge where a natural process of anaerobic decomposition occurs in the tank which reduces the amount of solid matter and provides some treatment of the waste. The remaining liquids flow out of the tank to a percolate into the soil (soak away or French drain) and eventually taken up through the root system of plants or added to the underground water. Baffles built into the tank hold back the floating scum from moving past the outlet of the tank.
But what you may not know is that an improperly sited, Designed, installed or operated septic tank system can pollute drinking and surface water, and cause many problems, especially environmental. Because septic tank systems are underground, they are often ignored by people who own or use them. However because septic tank systems are generally out of sight they should not be out of mind. The effluent from a septic tank still contains about 70%of the polluted matter in the sewage, and hence there is a need for further treatment of liquid from the tank.
Septic tank care is crucial to maintain a healthy septic system. The septic tank is a passive system. There is nothing electrical or mechanical involved. Although the septic system is actually quite self-sufficient, there are things you can help the system to work efficiently. Microbes in your septic system will naturally break down the organic material that drains into your septic tank. The broken down material and water will naturally drain out of the septic tank and into the ground underneath it.
Some solids cannot drain out of the septic tank. Regular septic tank care requires you to pump out these solids every three to five years. The size of your septic tank, the amount of use, and the kind of products you flush down your drain will determine how often you need to pump your septic tank.
Several Acts or Regulations, in different parts of the world set requirements for minimum treatment standards, new construction and replacement of systems. Some local jurisdictions require disclosure of system status and location upon property transfer, and may have stricter requirements. Therefore if you're not sure your system is in compliance with the law, check with your local government office.
How does a Septic Tank Work?
Untreated waste water from a property flows into the septic tank, where the solids separate from the liquids. Some solids, such as soap scum or fat, will float to the top of the tank to form a scum layer. Heavier solids, such as human and kitchen wastes, settle to the bottom of the tank as sludge. Self forming bacteria in the tank help the system "digest" these solids or sludge. The remaining liquids flow out of the tank to a land drainage system or drain field. Baffles built into the tank hold back the floating scum from moving past the outlet of the tank. It is generally recommended that septic tanks be pumped out annually, or the sludge and scum layers be measured at least every year so that solids don't wash out into the soil treatment system. Solids can clog the soil and limit its ability to properly treat the septic-tank effluent.
There should also be a vent pipe from the first stage chamber and preferably the second stage as well to vent any gasses, that rise from the sludge, to atmosphere. Suitable covers should always be placed completely over a septic tank capable of withstanding an adult’s weight, and to avoid children /animals falling into the tank. (Sometimes it pays to have light duty covers over the tank and to place a lockable strap over the covers.)
The effluent from a septic tank, still contains about 70% of the polluted matter in the sewage, and hence there is a need for further treatment of theliquid from the tank.
- In order to recycle as much as possible water, Bluetec will advise that the grey and black water be separated.
- The black water will be treated in the septic tank.
- The grey water will be treated in a grey water treatment system; this water can then be recycled for flushing, irrigation and non-portableuses.
- Bluetec can be contacted if you require this option.
PROCESS & FLOW DIAGRAM OF A TYPICAL SEPTIC TANK
GENERAL INFORMATION ON THE USE OF SEPTIC TANKS.
Combined and separate systems
Two types of disposal systems are general use, namely the one-pipe system whereby all the liquid household wastes are put into the septic tank, and separate or two-pipe system whereby the kitchen and bathroom wastes bypass the septic tank and are diverted to the soil percolation ( soak away) system directly. Although a grease trap is generally provided for the waste from the kitchen, it certainly would not be amiss if provided for the combined system as well. Of the two systems, combined treatment of all wastes in the septic tank is to be preferred.
In order to protect the soil percolation system, grease traps are commonly used in the separate or two-pipe system of disposal on the waste pipe from the kitchen with the object of removing as much grease trap usually falls away since the septic tank fulfils this function. Nevertheless it would be advantageous not to leave it out.
Small grease traps are prefabricated from salt-glazed earthenware or plastic, but lager ones should be built from concrete, fiberglass, plastered masonry or approved industrial plastic molded systems. The fatty material and solid matter removed from the grease traps must be removed with the garbage.
Synthetic detergents, soaps, disinfectants, chemicals and non-biodegradable matter
Provided that these substances are used sparingly in households, they should have no significant adverse effect on a septic tank system, but uncontrolled use of disinfectants or chemical cleansers especially as is often the case at institutions such as hospitals, schools and hotels may inhibit the natural bacterial activity. Industrial or other potentially toxic effluent should not be allowed into septic tanks.
Coarse, non-degradable, solids such as coffee grounds, cigarette butts, facial tissues, plastic bags, bottle tops, sanitary towels and nappies, must not be deposited into the septic tank.
Starters and cleaners
A new septic tank should be filled with water prior to use. It will however, still take a few weeks before normal operational condition are established, during which malodorous smells may be produced. After stabilization the functioning of a septic tank is almost odorless. The only starter which is likely to bring stabilization of the digestion process is a few buckets of sludge from an already operational septic tank.
Inspection and maintenance
Contrary to the normal practice of leaving septic tank systems well alone, it is important that these systems receive proper attention. When the sludge and scum have accumulated to a level where they might, start discharging with the effluent, the septic tank should be emptied and the sludge and scum removed, to avoid possible permanent damage to the percolation system.
When septic tanks are cleaned, they should not be washed or disinfected. In order that the digesting process can continue when the tank is put into use again a small quantity of sludge must be retained to serve as the starter. Although very little can be done to a soil percolation system once it starts clogging, usually seen by sogginess on the surface around the trenches, it should nevertheless be inspected regularly to assess it possible life.
The septic tank must be watertight at all times. Septic tanks should be constructed of materials such as plastic, fiberglass & concrete substances, which are not subject to excessive corrosion. The interior of brick tanks should be plastered with a waterproof mortar. Prefabricated tanks are available from commercial firms. Their design should be based on sound principles and the tanks should be sturdy enough to withstand handling. If the tanks are delivered in several components the joints should be sound enough to ensure that the tank remains watertight.
LEGISLATION CONSIDERATIONS WHEN INSTALLING A SEPTIC TANK
The following conditions are a collection of all the laws and regulations that needs to be adhered to when considering the physical installation of a septic system :
- A Septic tank must discharge to a soak away (SABS 0400-1990 pp10.3).
- The soil and subsoil must be suitable and the size of the plot adequate. 900m2 is considered to be the minimum size acceptable.
- The septic tank system must have adequate water supply at all times.
- Combined drainage may be permitted where absorptive capacity is adequate and subject to detailed approval of a septic tanks and a soak away by the executive director of city health No buildings will be permitted on the site of the septic tank and soak away.
- The tank shall be designed and constructed in accordance with the information contained within SABS 0400 – 1990, PP10.4 and must also be in accordance with the Council’s specifications, it is essential that Septic tanks are water tight.
- Where the tank is to serve any building other than a dwelling house/unit it shall be of a designed capacity to receive not less than three (3) times the daily flow from such building.
- The depth in a septic tank below the outlet invert must not be less than 1m and there must be an airspace of not less than 200mm between the surface of the liquid contained therein and the underside of the top cover.
- No industrial effluent must be allowed to flow into a septic tank.
- If the septic tank and soak away fail to operate, thereby causing nuisance, the owner will be held responsible for abating the nuisance forthwith or for closing down the system.
INSTALLATION INSTRUCTIONS FOR THE SEPTIC TANK
- FOUNDATION AND SEPTIC TANK INSTALLATION - Excavate the correct size hole in which to insert the manhole A 1:6 river and cement mix is required to cover at least 300mm across the base of the excavated hole. Make sure no solid objects are protruding from cement sand mix. Insert the manhole into the excavated hole and bed the manhole properly, by gently rocking the manhole backwards and forwards in the cement mix, making sure the manhole is accurately leveled.
- JOINING - When joining pipes to the septic tank manhole, it is easily done by using a water soap mix and ramming the required pipes home.
- BACKFILLING - 1:6 concrete sand mix should be carried out in 300mm thick layers from the base up to 100mm below the top of the septic tank manhole with the concrete filled lid in place on the manhole. The backfill material should preferably be sandy and slightly moist each 300mm layer should be densely compacted to achieve 90% of modified A S H TO maximum dry density. For manholes deeper than 2.150mm or where a high water table is anticipated, backfill material must consist of a soil Crete mix of 5% cement and 95% selected granular material.
- HOW DO I CONNECT THE TANK - Connect the toilet outlet to the septic tank inlet with a 110mm PVC pipe. Connect the overflow or outlet to the French drain, making sure that it is not too close to household underground water supplies, e.g.: borehole.
WHAT IS A SOAK AWAY
The soak away or percolation trench is an underground soil treatment system, which receives partially treated sewage from the septic tank. The soil on a site must be suitable for a soak away to work properly. IT is noted here that the effluent from a septic tank is by no means fit (in terms of health) for discharge into a water course (e.g. a river, vlei or an aquifer) or onto the ground where it could be accessible to animals, humans included.
Not all sites are suitable for septic tank and soak away systems. Of primary concern is the type and porosity of the soil at the site. Soils that are too coarse or too fine can limit the effectiveness of the treatment system. Also the depth of seasonally high water table or bedrock can also cause problems. Some of these problems may possibly be overcome by altering the design of the septic system. It is good practice to carry out percolation tests on the ground soil to ascertain its suitability for a soak away and generally you cannot improve a suitable site to the point where a soil treatment system will work.
In some areas in South Africa, the seasonally high water table is within a 600mm of the ground surface. Therefore a soak away may be typically installed close to the surface of the ground, but care must be exercised as it is possible that the polluted water may break through the ground surface. In other areas there may be clay ground present close to the ground level, and where this occurs then it is very unlikely that the use of a soak away will be prove satisfactory.
The size of your septic tank soak away is determined by the size of not only your septic tank but the size of your dwelling as well. You cannot simply construct a soak away to the specifications that you wish. There are other considerations including where the soak away is built. It cannot be built near any open water such as a river or a vlei because of the possibility of seepage from the soil into the water. This would result in contamination of the water source which could lead to many problems including health concerns.
CONDITIONS FOR A SOAK AWAY
The standard of a soak away constructed in South Africa leaves much to be desired and the haphazard system of digging a hole and filling it with stone or various kinds of builder’s rubble is not permitted anymore.
The following are now laid down as the types of soak away that is accepted by the government of South Africa and no other type of soak away will be considered unless the type and manner of construction has been approved by EIA for the area.
NO SOAK AWAY SHALL BE CONSTRUCTED IN ANY GROUND WHERE:
- Such ground has a percolation rate exceeding 30 minutes.
- Any effluent may flow out due to the contours of or the strata forming such ground.
- The site to be affected by such effluent is of insufficient size to accommodate the soaking away of the effluent.
- The level of the water table is or may be such as to prevent adequate percolation.
- Any site may be affected by the presence of such soak away.
- Only drainpipes of approved material may be used in conjunction with septic tank installations.
- Inspection chambers must be installed at all bends and junctions.
- The soil drain shall be properly vented and the vent pipe shall be carried up above eaves level.
WHAT IS A CONSERVANCY TANK?
Conservancy tank is any covered tank without an overflow which is used for the reception and temporary retention of sewage and do require routine emptying with a honey sucker.
CONDITIONS FOR A CONSERVANCY TANK
1. A conservancy tank SHALL NOT BE USED FOR THE COLLECTION OF SEWAGE UNLESS:
• In the opinion of the city engineer, it is impractical to connect the premises concerned to a public sewer
- It is impossible for the city engineer to arrange for the clearance of such tank having regard to:
- The accessibility of the premises concerned by road
- The level of such premises in relation to the level of the abutting road
- The quantity of sewage discharged or to be discharged from such premises
- The availability of vehicles for the clearance of such tank
2. Every conservancy tank shall comply with the FOLLOWING REQUIREMENTS:
- The tank shall have a capacity of not less than:
- 5400 litres
- The maximum amount of sewage likely to be discharged into it over a period of 2 days
The owner of the property served by such tank shall provide and maintain at his own expense a suitable road or other means of access to enable the vehicle used by the municipal to reach and empty such tank, and any person contravening the provisions of this sub-regulation shall be guilty of an offence.