(iii) Soakaways

A soakaway is the safest and most convenient way of disposing of greywater, as long as soil conditions permit this. Groundwater pollution is still a possibility and care should be taken to prevent it. The design of the soakaway must comply with the guidelines given in the National Building Regulations SANS 10400. 72 Where simple maintenance tasks are possible, the use of grease traps should be considered for kitchen wastewater.

(iv) Piped systems

The disposal of greywater in piped systems is a viable option when dealing with communal washing points that generate large amounts of greywater.

K.4.7 Design of sludge disposal infrastructure

 

K.4.7.1 Disposal of sludge from on-site sanitation systems

On-site sanitation results in an accumulation of sludge that should be removed from the pit or tank and conveyed to some treatment or disposal facility. If the pit or tank contains fresh sewage, the sludge should be treated or disposed of in a way that will not be harmful to the environment or a threat to health. If the waste matter has been allowed to decompose to the extent that no pathogens are present any longer, the sludge can be spread on the land as compost. Pit toilet sludge can be disposed of by burial in trenches. Figure K.29 illustrates how such a burial trench should be constructed and subsequently maintained on a day-to-day basis.

Figure K.29: Disposal of pit toilet sludge in a trench

Dehydrated faecal matter from urine-diversion toilets may be safely reused as soil conditioner, or disposed of by burial, if preferred. It may also be co-composted with other organic waste.

Sludge from septic tanks, aqua privies, etc. should be disposed of in accordance with the Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 3: Requirements for the on-site and off-site disposal of sludge. 74

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An effective refuse collection system should be in operation in high-density residential areas (see Section M). The absence of a functioning solid waste management system often leads to toilets being used for refuse disposal. This causes problems when emptying pits with a vacuum tanker. It is advisable to construct permanent pits with lined walls to prevent damage during emptying, as this could lead to the collapse of the pit walls. Note that the pit linings should make allowance for percolation of effluent into the surrounding soil (e.g. by leaving the vertical joints of a brick lining unfilled).

K.4.7.2 Composition of pit or vault contents

In a sealed tank or vault, human excreta usually separate into three distinct layers, namely a layer of floating scum, a liquid layer and a layer of sediment. Well-drained pits may have no distinct liquid layer, and therefore no floatingscum layer. The scum layer is usually caused by the presence of paper, oil and grease in the tank and generally more prominent in tanks with a large number of users. The water content of pits can vary between 50% and 97%, depending on the type of sanitation system, the personal habits of the users, the permeability of the soil, and the height of the groundwater table. Cognisance should be taken of the fact that different materials used for anal cleansing will have different breakdown periods, i.e. newspaper require more time to break down than ordinary toilet paper, and in some cases will not break down at all, which could cause the pit to fill up more quickly.

K.4.7.3 Methods of emptying pits

The most suitable method of emptying a pit mechanically involves the use of a vacuum tanker, where a partial vacuum is created inside a tank and atmospheric pressure is used to force the pit contents along a hose and into the tank. Thin sludge with a low viscosity can be conveyed by immersing the nozzle below the surface of the sludge and drawing a constant flow into the tank.

The use of VIDP toilets allow the excreta to decompose into a pathogen-free, humus-rich soil, after having been stored in the sealed pit for about two years. These pits could be emptied manually, using scoops, buckets and spades to dig out the thicker sludge. Manual emptying could pose health risks and workers should wear protective gloves and clothing.

K.4.7.4 Methods of emptying pits

Unless the sludge has been allowed to decompose until no more pathogens are present, it may pose a threat to the environment, particularly where the emptying of pits and septic tanks is practised on a large scale. The design of facilities for the disposal of sludge needs careful consideration, as the area is subject to continuous wet conditions and heavy vehicle loads. Discharge speed and sludge volume dictate the equipment to be used for disposal of sludge. Cognisance should be taken of the immediate environment, as accidental discharge errors may cause serious pollution and health hazards.

Pond systems can be very effective in treating sludge from on-site sanitation systems. If the ponds treat only sludge from pit toilets, it may be necessary to add water to prevent the ponds from drying out before digestion has taken place. Sludge from on-site sanitation systems can also be treated by composting at a licensed central treatment works, using forced aeration.

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K.4.8 Materials

 

K.4.8.1 Pipes and joints

When selecting a pipe type to use in the design of sanitation and wastewater systems, the following aspects need to be considered:

  • The type of wastewater
  • Corrosion, abrasion or scour conditions
  • Installation and handling requirements
  • The depth of the sewer
  • Product specifications (smoothness, length, fittings and connections)
  • Cost effectiveness (materials, installation, maintenance, and life expectancy)
  • Physical characteristics (soil conditions, pipe stiffness, loading strengths, etc.)
  • Municipal specifications and preferences

Pipe materials that are acceptable for sewers are listed in Table K.26.

Table K.26: Pipe materials for sewers
Diameter Generally accepted material type
<400 mm uPVC Heavy Duty Class 34 complying with SANS 791 Un-plasticised poly(vinyl chloride) (PVC-U) Sewer and Drain Pipes and Pipe Fittings75 and fittings that comply with SANS 1601 Structured wall pipes and fittings of un-plasticised poly(vinyl chloride) (PVC-U) for buried drainage and sewerage systems76 for stiffness class 400 pipes.
>400 mm Reinforced concrete pipes containing dolomitic aggregates can be used for sewers larger than 400 mm. The pipes should have an approved sacrificial lining inside as per SANS 677 Concrete nonpressure pipes77. Other specifications are as contained in SANS 1200 LD Sewers, Standardized Specification for Civil Engineering Construction.78

Only Polyethylene (HDPE) pipes should be used in areas underlain by dolomite. Minimum allowable class PE pipe: PE80, PN6, SDR21.

All joints for rigid pipes should be of a flexible type, and rigid joints should only be used where the pipes themselves are flexible. For pipe material other than uPVC, see Table K.27.

Table K.27: Pipe material and specifications
Material Specifications
Un-plasticised poly(vinyl chloride) structured wall pipes and fittings (PVC-U) PVC pipes should comply with the relevant requirements of SANS 1601 Structured wall pipes and fittings of un-plasticised poly(vinyl chloride) (PVC-U) for buried drainage and sewerage systems79 for stiffness Class 400 pipes and they should be fitted with approved spigot and socket joints with rubber seal rings. PVC products should be stored out of the sun and should be backfilled as soon as practicable after being laid.

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Table K.27: Pipe material and specifications
Material Specifications
Vitrified clay pipes and fittings Vitrified clay pipes and fittings should comply with the requirements of SANS 559 Vitrified clay sewer pipes and fittings. 80

All pipes with a diameter of 200 mm and smaller should be plain-ended and joined with polypropylene.

Pipes exceeding 200 mm in diameter should have spigot-and-socket ends with factory-applied polyurethane joints, or should be plain-ended with an approved fibreglass-type of coupling.
Reinforced concrete pipes Reinforced concrete pipes should comply with the relevant requirements of SANS 677 Concrete non-pressure pipes81 for SI type spigot-and-socket D-load pipes and should have been manufactured from the dolomitic aggregate.

During the manufacturing process, each pipe should be provided with a sacrificial layer of concrete to increase the minimum cover to the reinforcement as specified in SANS 67782, with the following additional thicknesses:

(a) Pipes with a nominal diameter up to and including 1 500 mm – at least 15 mm;

(b) Pipes with a nominal diameter of 1 800 mm and over – at least 20 mm.
Fibre-cement (FC) pipes and fittings FC sewer pipes should comply with the relevant requirements of SANS 819 Fibrecement pipes, couplings and fittings for sewerage, drainage and low-pressure irrigation83 and should have suitable approved flexible joints. FC fittings should have a crushing strength equal to or better than that of the pipes to which they are coupled and should otherwise comply with the relevant requirements of SANS 819.

Fibre-cement pipes and fittings should be factory-coated internally, and externally they should be covered with an approved bitumen or epoxy.
Cast-iron (CI) pipes and fittings Cast-iron pipes and fittings should comply with the requirements of BS 78 Specifications for Cast-iron Pipes and Special Castings for Water, Gas and Sewage84 and BS 2035 Specification for cast iron flanged pipes and flanged fittings85 respectively. Pipes and fittings should be class A and should be factorycoated internally and externally with an approved bitumen or epoxy.

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Table K.27: Pipe material and specifications
Material Specifications
Steel pipes and fittings Steel pipes and fittings should be both lined and coated with a protective layer. Steel pipes should comply with the requirements of SANS 719 Electric welded low carbon steel pipes for aqueous fluids (large bore)86 for grade A or B pipes, as scheduled, whereas steel fittings should comply with BS EN 10224 Non-alloy Steel Tubes for the Conveyance of Aqueous Liquids Including Water for Human Consumption. Technical Delivery Conditions.87

Steel pipes should be joined by using flanges, by welding or by using flexible couplings. Gaskets for flanges should be of the full-face type, with the appropriate diameter, provided with bolt holes, and should be made of virgin rubber. They should also comply with the requirements of BS EN 681 Elastomeric seals - Materials requirements for pipe joint seals used in water and drainage applications. Thermoplastic elastomers88, Class WC.
Polyethylene (PE) pipes and fittings PE pipes should comply with the relevant requirements of SANS 4427 Plastics piping systems - Polyethylene (PE) pipes and fittings for water supply89 and should be one of the following: PE80 PN16 SDR9, or PE63 PN12.5 SDR9.

Pipes should be joined together and to fittings by using thermos fusion carried out in accordance with the requirements of SANS 10268-1 Welding of thermoplastics - Welding processes Part 1: Heated-tool welding. 90
Rubber joint rings Rubber joint rings should comply with the relevant requirements of Part I of SANS 974-1 Joint rings for use in water, sewer and drainage systems91 and should not have more than one joint. This joint should be positioned at the soffit of the pipeline.
 

K.4.8.2 Manholes

Manholes and chambers should be constructed as specified in SANS 1294 Precast concrete manhole sections and components.92 General guidelines are as follows:

  • Manhole channels should be made of precast fibre cement, even if uPVC pipes are used in reticulation.
  • Manholes should be precast concrete with dolomitic aggregate or fibre-cement rings (min. 1.05 m nominal diameter).
  • Manholes should be provided with access shafts and/or step irons.
  • Benching in manholes should be concrete of minimum strength of 20 MPa at 28 days.
  • Cast-iron manhole covers and frames should comply with the relevant requirements of SANS 558 Cast iron surface boxes and manhole and inspection covers and frame.93 All surfaces not embedded in concrete should receive two coats of epoxy-tar paint.
  • Precast concrete manhole covers and frames can also be used, but should be of approved manufacture and capable of carrying the same load as their cast-iron counterparts.
  • Manhole frames should be bedded in a 1:3 cement: sand mortar and finished off with a reinforced concrete surround.

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K.4.8.3 Bedding and backfill

Specifications, as set out in relevant industry standards, should be followed for the bedding and backfill of sewer pipes. Bedding, backfill and pipe strength should be sufficient to ensure that pipelines are not overstressed by all superimposed loading.

  • All bedding material should be of selected granular material with a PI less than 6, and free from organic matter, clay or stones larger than 20 mm.
  • Subsoil drains should be provided where groundwater is a problem. The designer should ensure that the design is sufficient to meet the requirements.
  • Backfill material should be homogeneous and should be compacted in 150 mm layers.
  • Density tests should be conducted on the backfill during installation.

K.4.8.4 Pump stations

All materials used in pump stations should be durable and suitable for use under the conditions of varying degrees of corrosion to which they will be exposed.

K.4.8.5 Concrete

Structural reinforced concrete and plain concrete below ground level and/or in contact with sewage should be designed and constructed in accordance with relevant industry design standards.94 It is advisable to use only dolomitic aggregates for in-situ concrete. The dolomitic sand, however, may be blended with up to a maximum of 40% by mass of an approved pit sand. In-situ concrete used for the construction of pipe beddings and the concrete encasing of pipes must also conform to the relevant requirements, except that dolomitic aggregates need not be used.

K.4.8.6 Structural steelwork

All exposed steelwork should be adequately protected against corrosion.

K.4.8.7 Electrical installations

All electrical installations employed for sanitation services should comply with the Machinery and OccupationalSafety Act, 1983 and with the relevant municipal electricity supply by-laws/regulations.

K.4.9 Upgrading of existing sanitation systems

The upgrading of existing sanitation systems refers to the following:

  • The upgrading of existing sewerage infrastructure (to meet current and future requirements)
  • The extension of the network (provide a higher level of service to users)
  • Maintenance of the existing network (ensure adequate rehabilitation and maintenance)
  • The upgrade of sanitation facilities (VIPs, chemical toilets, etc.)

The upgrade of existing infrastructure should be planned in terms of the priorities outlined in the relevant infrastructure and spatial development plans. It is important to implement the necessary upgrading, refurbishment and maintenance of the infrastructure at the same rate as the demand for new infrastructure.

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K.4.9.1 Upgrading chemical toilets

Chemical toilets are sometimes used as a temporary solution. They are regarded as not desirable as a permanent sanitation option in a residential development. Upgrading to a more permanent system would take the form of total replacement with any improved sanitation system. The chemical toilet would be removed from the site as a unit; thus there would not be any reuse of materials.

K.4.9.2 Upgrading unventilated pit toilets

The first and most important step in upgrading ordinary pit toilets is to install a vent pipe to convert the toilet into a VIP toilet. This upgrading should be undertaken at the earliest possible opportunity. After the addition of a vent pipe, further upgrading would follow the same route as a VIP toilet (see below).

K.4.9.3 Upgrading VIP toilets

The VIP toilet provides several opportunities for upgrading. A major improvement can be attained by introducing a water seal between the user and the excreta, thus providing a level of convenience that is more acceptable to users. It may be necessary to consider the removal of liquids from the site only if problems arise with the drainage of excessive quantities of water. This can be expected when individual water connections are provided to each site. Since the pit of a VIP toilet is not watertight, it will be necessary to construct a new tank on the site for solids retention if upgrading to a settled-sewage system is required. The pit of the VIP toilet will thus become redundant. If, at the outset, the final stage of the upgrading route is known to be a conservancy tank or settled sewage system, it is preferable to begin with a sealed-tank system (such as a vault toilet, aqua privy, or on-site digester), to avoid having to construct a new tank when the upgrading takes place.

The installation of a urine-diversion pedestal is another significant improvement to a VIP toilet. The contents of the existing pit should be covered with a layer of earth. The structure may subsequently be operated as a normal urinediversion toilet, where urine is diverted to a soakaway or collection container, and faeces are covered with ash or dry soil while drying out.

K.4.9.4 Upgrading ventilated vault toilets

The Ventilated Vault (VV) toilet is a VIP toilet that has a waterproof/sealed pit or vault. The comments on upgrading for VIP toilets also apply to this system. The upgrade option of removal of liquids from site will be different from that of the normal VIP toilet, because the VV toilet has a lined, waterproof vault that can be used. Because the VV toilet already has a waterproof tank, this system is ideal for upgrading to a settled sewage system.

K.9.4.5 Upgrading ventilated improved double pit toilets

The Ventilated Improved Double Pit (VIDP) toilet is a VIP toilet that has a double pit. The comments for the VIP also apply to the VIDP toilet.

K.4.9.6 Upgrading conservancy tank systems

A conservancy tank can be upgraded to a settled sewage system. The tank can be used to retain solids on the site.

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K.4.9.7 Upgrading septic tank systems

A septic tank can be upgraded to a settled sewage system, since the outlet from the septic tank can be connected to a settled sewage system without any further alterations being necessary. Solids would be retained on the site and digested in the septic tank.

K.4.9.8 Upgrading aqua privies

The aqua privy has a rough water seal that can be greatly improved by removing the pedestal and chute and replacing them with a device such as a tipping-tray, pour-flush or low-flush pan. An aqua privy can also be upgraded to a settled sewage system, since the outlet from the aqua privy can be connected to the sewer system without any further alterations. Solids would then be retained on the site and digested in the aqua privy tank.

K.4.9.9 Upgrading settled sewage systems

No upgrading of this system is necessary, but the stand owner can implement aesthetic improvements to the superstructure. Upgrading to a conventional waterborne sewer system is not recommended due to the fact that the settled sewage system only complies with relaxed design standards, which would cause settling problems in the pipes if settling tanks are removed from the system.

K.93

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The Neighbourhood Planning and Design Guide
Creating Sustainable Human Settlements

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