Having spent a number of years assisting in the design of medium sized sewerage works, I was amazed to find here that my installation was inspected and initially rejected by a well dressed office worker, with clean shoes who had not the slightest idea what he was talking about. So I thought I would write a basic article on the subject.

Thousands of households throughout the Republique rely on their own mini-sewage treatment plant - their fosse septique. This on-site treatment system when properly designed, installed, operated and maintained, will treat sewage to protect the family, community and water supply from diseases and contamination for many years. If it works do not touch it. Do not lift covers, do not pass go, do not collect 200 euros.

There is a myth about septic tanks - they are basically 2 or 3 stage holding tanks with the first stage collecting solids, the second collecting those that got away and the third tries, if bacterially correct to break down the liquor into a less contaminated fluid which passes into the filter bed. This bed is more important than the tank - for it is this which treats strains and cleans the fluid and passes clean often sterile fluid into the stream or ditch. To qualify this, find the outfall of a sewage works and you will see that very little grows for a distance. Better still, find the filter bed and see tomatoes growing well - the seeds are almost impossible to break down and they grow anywhere. Only if you suspect problems with the tank lift the cover of the first chamber, and you will see a crust formed by the anaerobic action - if it appears solid and has a warmth about it, (dont touch it to find out - guess) put the cover back as most 3000 litre tanks serving a family of 4 will work for years without any emptying. It should not smell much. They generate heat whilst they work. Lift the second cover and if it smells over much, remove the clinker and clean it - nowhere near the tank as it is septic - wear protective gloves and masks - then replace. If it does not smell much, leave it and replace the cover. It could be that the vents at the front or rear of the tank are obstructed or broken, in which case, replace. The vent at the inlet draws air in and that at the outlet pushes it out. But all tanks puff occasionally so do not worry. Worry if the outlet fluid is discoloured. A septic tank will operate successfully for years with only occasional interruption for pumping. However, bleaches, oil, petrol and other spirit based fluids, washing powders, some medicines, and high water flows will cause a tank to fail. Petrol and oil will kill it stone dead. Additives may not be effective in serious cases, in which case pump it and start again. Odours, blockages and ponding in the drain field occur and can be serious problems at worst or unhealthy nuisances at least.

Following last month’s article I have received calls about problems with tanks and emptying periods so this month I thought it useful to write a little about that subject BUT if a system is working do not touch it. The instruction to empty a system regularly even yearly is very wrong. Why? Because a good system relies upon anaerobic action and aerobic action to work and these actions stop once the system is interfered with. Today’s living means more water going through the system, which can be useful in a town system where pipes need flushing, but a home system does not thrive on copious amounts of water. The more water you put through your fosse, the more water it must treat and, by consequence, the quicker it will stop working, so the best advice for prolonging the life of your fosse is to conserve water. Organise laundry, dish washing and bathing to use your water wisely and efficiently.

Men in this country still believe they must widdle outside - preferably in view of passers by - rather than use a loo. That is a bit extreme nowadays but the concept is correct though unnecessary. There are certain things that you pour down your kitchen sink that over a period of time will harm the performance of your fosse septique. Items such as grease or coffee grounds (put them on the soil) and similar materials fall into this category. Paints, cleaners, solvents and any caustics are also particularly destructive and should NEVER EVER be poured down any drain. Some people toss cigarette ends, sanitary products, wads of hair and paper and other solid materials into the toilet - this is a serious mistake, as these block the pipes and cause big problems for the flow of sewage. Sanitary towels rarely break down, neither do rubber or latex products, flavoured or not. The main thing to remember is not to use your toilet and septic system as a dustbin at all. Throwing anything in it apart from normal human waste will add to the sludge build-up and overload the bacteria and they will be unhappy and go ‘en greve’. If you have a kitchen sink waste disposal, you may need to pump out the solids more often than normal but count the time in tens of years for a modern 4000 litre tank serving a family of four. Therefore, try to limit the amount of food waste you put through the disposal system.

You will know when a problem occurs as apart from the obvious stink created by overflowing sewage, there are many different indicators which will alert you to the fact that your septic tank is full and needs to be cleared. Typical danger alerts are as follows:
· a strong smell of sewage
· slow drainage in the house
· The tank covers move
· surface flooding before or after the fosse
.
Only then take action, but do so carefully as septic waste is toxic and harmful except when treated. Treated and dried sludge is disposed of on barren fields - look out for the tomatoes - they still survive!

Septic Tanks - The filter

In the previous two articles we discussed the workings of a fosse septique - septic tank. There was some confusion over the difference between a cesspit and a septic tank. It is easy - a cesspit collects waste and does nothing except smell and overflow when it gets full - a septic tank partially treats the waste provided it does not get killed by petrol, oil or bleach based products. The next step on from a tank is the sand/gravel filter. This is where the aerobic action starts. Micro-organisms, snails and worms break down and digest the liquor from the tank in the presence of air thus cleaning the water. No different from a municipal works really, where you can see the rotating arms of the filter beds trailing water over black clinker on which is growing the digesters. (In the sun you can almost see them glistening). The arms rotate to provide an even distribution of raw water over the clinker. In the same way herringbone pipes from the septic tank will distribute raw water over the sand/gravel filer - the more distribution pipes, the better the spread.- with limits! A good 7x5x1 metre sand gravel filter will effectively filter raw water from a very large house. The secret is - not too fine sand and gravel and they must be inlayers. Gravel at the bottom, sand in the middle and gravel at the top, sandwiched between distribution pipes at the top and collector pipes at the bottom. These bottom pipes collect the strained water and discharge it into a vented manhole then into the soil or into a ditch. Unlike clinker beds, domestic sand /gravel filters do not tolerate excessive rain water, which is why it is useful to cover the filter bed with a porous, not waterproof, membrane material. Ideally the sides and bottom of the filter should be wrapped in polythene, but this is only when the filter is near a dwelling.

Now if the water from the filter outlet smells excessively - panic a bit as it could mean the sand is too fine or saturated - possibly with rain water. It works the same as the sea shore, water will go down and the sand will dry, but water will also come up and back flush the sand which is what happens in floods. In some countries - Italy for example - specially prepared reed beds have the capability to transfer oxygen from the stems to the rhizomes (roots) where biological action purifies the water from the tank. The resulting effluent which will be almost clean, can be discharged to a land drain or watercourse (subject to consent.) But they can be stagnant & smell. Interestingly modern municipal works have methane collectors which I will detail next time. Lastly, look for the outfall from a works - the water supports little growth - it is virtually sterile - well for about a metre downstream! The engineer I worked for maintained he had his own limited water supply when fresh water ran out and he lived to an old age!.............Ed