Fundamental source of modern standards of public health• Water supply: – Public mains – Private boreholes – Private reservoirs• Drainage: – Domestic drainage – Public sewerage and waste treatment – Private sewage treatment
Drains• The basis of Western health and longevity is efficient drainage and effective waste treatment. All other medical advances are fairly peripheral.• UK drainage systems are amongst the oldest in the world• Some parts of the London sewerage system are Roman!
Basics of drainage• Drains are a network of ventilated pipes• Waste is moved in water by gravity whenever possible• Small pipes flow into equal sized or larger pipes, never the other way• Drains must be accessible• Shared drains are called sewers
Drain types• Surface water drainage – Removes clean rain water from roofs and clean areas (not car parking areas or roads)• Grey water drainage – Removes water from baths and basins (not food preparation areas or WC) Where collected it is used for flushing WC• Foul water drainage – WC, kitchen sinks, roads and car parks• Surface and foul should be kept separate, but not always possible
Surface water drainage Rain is collected in gutters and flows out through down pipes Down pipe exits into a gully. Surface water drains do not need to be trappedSurface water fromdriveways should not run intorainwater gullies because ofthe risk of oil contamination.But they often do.
Rain water disposal• Rainwater can be discharged into – A soakaway, if the soil is permeable and there is room to build it some distance from the property – A nearby water course, but only if it is totally separate from the foul drainage – Into the foul drainage sewerage, but only if there is no alternative. This is often the case with old properties. Heavy rain can flood the sewage farm
Practical examples: rain waterDown pipe beinginstalled Building a large soakawayGully. Downpipeenter tops,discharges intodrain through sideUnderground pipegoing to a soakawaySoakawaydischarges intopermeable subsoil
Foul drainage• Waste water is collected by a continuous network of airtight, but ventilated pipes• Conveyed underground to a point of disposal – Public sewer – Septic tank (which needs emptying regularly) – Cess pit (which needs emptying frequently. Not a disposal point)
Schematic drain layout Top of pipe open for ventilation Foul Foul down connections. pipe also All trapped at called a soil sanitary unit vent pipe to exclude (SVP) smells Underground drainsWater trap,replaced by Large radiusflowing water curved transition
Above ground drainageNon-return • Typical componentsvalve can be of an above groundused instead of drainage systemabove-roof • Basin drains approxventilation 40mm Ø • WC drains and SVP approx 100mm Ø
Underground drainage• Underground drains – Water tight and gently sloping – Protected from crushing – Access needed at all junctions, bends and change of slope for inspection and maintenance
Drain pipe in a trench • Trench excavated • Base partially filled with gravel • Pipe laid andDrain below soil surrounded by gravel • Care taken to establish and maintain correct slope on drain • Trench carefully back filled andDrain below floor consolidated
Access pointsRodding point: push blockage downstream to inspection chamberInspection chambers give direct access to drain
Materials for drain pipes (domestic)• Above ground drainage – PVCu and polypropylene with gasket sealed joints – Typically 40mm Ø but can be larger – WC drains 100mm Ø• Below ground drainage – PVCu, jointed with integral gaskets – Vitrified clay, jointed with PVCu collars and gaskets or socketed
Sewer connections Shared sewer Private drains Sewer inspection chambers • Discharge into public sewer is disposal as far as private property owner is concerned • Water company willDrain inspection treat sewage andchambers, close discharge into waterto but not directly course or the sea.on sewer
Building regulations• Maintenance of drains is a public health issue• Drains must comply with Building Regulations• Building inspector will test drains during construction – Smoke test – Pressure test – Rolling ball test
Local sewage treatmentControlled biological digestion of wastes
Local sewage plants• If it is not possible to connect a building’s drainage system to a public sewer, waste will have to be treated on site or pumped to a distant sewer.• Treatment is needed to reduce the volume of waste and to render it harmless to people and the environment.
Sewage storage• Sewage can be stored and then removed in bulk. This requires use of a cess pit or cess tank. This must be completely water tight but vented and must never be allowed to overflow.• Cess pits must be emptied regularly• Cess pits should only be used on new developments for holding waste that cannot be discharged into a sewer, e.g. grease, oil, fat or heavy metals
Sewage treatment• Sewage treatment is a four stage process: – Biological digestion of the raw waste – Aeration of the effluent from the bio- digester to kill bacteria – Dissipation of the final liquid effluent – Removal of build up of solid waste left over from the bio-digester• This treatment is either carried out in a septic tank system or in a modern bio-disc unit
Anaerobic digestionWaste in Effluent rich in anaerobic bacteria flows out Anaerobic digestion under air• Two chamber septic tight crust tanks • Modern, bottle• Waste is digested by style septic bacteria in anaerobic tanks moulded (oxygen free) conditions in GRP • Tanks buried in• This reduces the volume concrete to but leaves a ensure they do contaminated effluent not float in ground water
Aeration to kill bacteria• Bacteria-rich effluent is trickled over an aeration media (often broken rock with a large surface area)• Air passes up through this media and kills off anaerobic bacteria• Treated effluent then runs into land drain system or local water course.
Self contained bio-disc treatment systems• Modern bio-disc units consist of a septic tank topped by a rotating series of discs, which dip into the effluent and lift it up into the air.• This repeated anaerobic digestion/aeration cycle speeds the digestion and reduction of the waste
Effluent removal• Waste effluent from both septic tanks and bio-disk units should be safe and can be dissipated into the environment• In practice, effluent would normally be directed to a soak away in permeable ground rather than direct to a water course in case of accidental sewage leakage. Aerated effluentBuried, perforated pipes
Solid waste removal• Solid waste must be periodically removed from the tank• This sludge cannot be dumped at sea, as was common practice until recently.• Now much sludge is heat treated to make it sterile and used as a fertilizer/soil conditioner, but build up of heavy metal contamination is a problem.
Pumped sewage; single WC systems• Macerator behind WC liquidises waste and pumps up 5m vertically or 50m horizontally through small diameter pipe (22mm) Pump, valve and macerator unit. Works each time water flows in waste pipe.
Pumped sewage, large capacity stored systems High pressure pipe High level sewerChain for pumpretrieval Float switch starts pump periodically Storage tank Flexible, pressure hose Submersible pump