Septic Tank - Part 2

Articles Tagged with: Septic Tank

29 August, 2009

Human waste is where its at!!

By Rory
View original post on the Camps International Project Blog

Its true – human waste is where its at! Its the future you know – dont need any of this extracting gas and oil from the centre of the earth with all its associated detrimental environmental effects – just use what you flush away every day. This is the ultimate in recycling and minimising your impact – so sit back and learn about Bio Gas Collectors – even better sit back and learn whilst contributing to your bio gas collector, if you get my drift!

And now for the technical stuff, apologies if you are eating your dinner whilst reading this!! Basically any waste from animals, or any other bio waste, when it bio degrades gives off methane gas. And all a bio gas collector does is collect this gas and enable the user to burn this gas in a stove or even lighting. Apparently humans, chickens and pigs are best since we eat all sorts of rubbish and therefore give off good quality gas – I am sure you know someone, possibly within your own family who gives off good gas! Cows and other grass eaters are not so good since their bodies are designed (loads of stomachs you know) to break their food to such a degree that they actual fart methane – cows are one of the higher contributers to green house gases – so most of the useful gas has already escaped before the waste (cow pat) leaves the cows posterior – however it can still be used but not as a main stay of the collector.

And so why am I going on about this – well myself and my good mate Ian (the architect, featured on previous blog posts) got to talking about it (as you do across a bar, you often find the conversation turning to toilet humour) and we reckoned there was some scope for experimenting and seeing if perhaps this is a good way of reducing our carbon footprint and doing a little something to help the planet – it may be small be every little bit helps and as the saying goes, or at least my saying, “a lot of littles make a big!” – (first coined when teaching people what to pack (or not to pack) in their rucksack prior to a 3 week trek).

So I am going to do some posts on the bio gas collector we are building at our camp in Tinangol – we are hoping that we can get this prototype sorted and roll it out in other communities where it might work. And myself and Ian are not trying to convince people that Bio Gas Collectors are our idea – no way, they have been around for quite some time and are used to differing effect in Asia and I am sure beyond. However what we are trying to do (well Ian is doing most of this technical stuff) is make it “buildable” by a group of unskilled volunteers with little if any expertise whilst also trying to keep the cost down – but more on this and the design over the next few weeks.

So next time you are sat on your porcelain throne at home (which I hope is at least once a day – although I know someone who is on it at least 4 times – no names hey Stu, but at the other extreme I knew a girl once who only “dropped the kids off at school” once every 3 weeks – now surely that cant be healthy!) – anyway next time you’re sat on the throne, contemplate the potential energy of your “produce” and ask your family if they wouldnt mind helping dig a large hole in the backyard and building a bio gas collector. Watch this space for more amusing toilet tales as we watch the progress and get down and dirty on the build of our very own Bio Gas Collector.

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21 September, 2008

Biogas Collector

I find myself getting deeper into the shit. I’m not sure how it happened but I have become interested in biogas collectors. This is a device used to collect the biogas (mostly methane) which is emitted when biological waste is digested by bacteria.

The biogas once collected can be burned to provide cooking, lighting and carbon credits. The chemistry of burning methane in the presence of oxygen is that it produces water and CO2. Carbon dioxide is a less potent greenhouse gas than methane so that’s how we can earn carbon credits.

The waste I refer to is usually faecal but food and vegetable leftovers work too. In order of quantity of biogas per unit mass of waste; human and pig waste has the most potential, closely followed by chickens and with ruminant animals such as cows and horses bringing up the rear!

Large animals however, have the advantage of producing larger volumes of waste. The problem with this can be collecting it and putting it in the digester. I have heard of a cunning scheme where children earn pocket money by roaming the fields with a shovel looking for fuel for their village biogas collector.

Arkitrek is working with Camps International to build a demonstration biogas collector at a longhouse near Kudat in northern Sabah.

Camps International is a holiday company specialising in the gap year and ‘life experience’ market. The Kampung Tinangol Longhouse will be their first destination in Borneo and the beginning of a long term partnership which has been brokered by local NGO Partners of Community Organisations (PACOS).

The biogas demonstration project will be built by the first batch of guests to arrive in January 2009. The objective is to prove the viability of the idea, refine the design and build capacity with the hosts.

If the design is successful, future guests at the longhouse will find themselves building biogas collectors throughout the local community.

Update: 16th March 2011
Note that we have yet to get our digesters operational due to workmanship issues. They are leaking, first water and now gas. We are working on the problem and will update you as soon as we can. There is more detailed information on the problem here.

Drawings of our Mark II biogas digester are available to download here.
09 D130B
09 D131B
09 D132B
We will probably move over to a floating gas holder in our Mark III design. something similar to this

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26 March, 2008

Septic Tank Guide (archived)

Information on this page is out of date and has been kept as a record only.
The new updated Septic Tank Guide can be found here.

*****

A few people have asked me recently ‘what do I know about septic tanks?’, which made me realise that I know very little. To date my contribution to sustainable wastewater management has been a note on my drawing saying ‘pipe connected to new septic tank designed by contractor’ or even better ‘pipe connected to existing septic tank’.

Realising that I need to be a little more responsible than this, I have been googling all sorts of interesting subjects and this is a summary of what I have come up with.

Most septic tanks in Sabah look something like the above sketch. They are made of either plastic or concrete and usually discharge straight into a river or open drain. The effluent (discharge) pipe takes water from well below the scum layer and well above the sludge layer. Each time a new delivery arrives at the influent (inflow) pipe it will displace an equal volume of effluent.

There are two very important considerations:

Time is needed for bacteria to digest the waste. The tank needs to be large enough that fresh influent can sit for a while before being displaced as effluent. Obviously a higher volume of water flushing through the tank will need a larger tank.
Sludge will get deeper and eventually need to be removed. This is usually done by a ‘honey dipper’ as the Americans euphemistically call it. In reality it’s a tanker truck with a big dirty vacuum cleaner. In Sabah I have discovered that they don’t have this kind of truck so the sludge has to be removed by hand. Often immigrant labour will be used for this job which makes it more acceptable, apparently. On many of the sites I am working with there is no vehicular access anyway. In which case when the tank fills with sludge the only viable option is to seal it up and build another one.

Above is an illustration of what happens if the sludge is not cleaned out, but instead allowed to reach the outflow level of the effluent pipe. Any new delivery will cause sludge to be displaced as effluent. Clearly this is not good. In some cases the effluent pipe will become blocked and scum followed by sludge will come out through the inspection hatch or back up into the building. Clearly this is not good either. It is usually fairly obvious when this starts to happen because of the smell.

When correctly maintained this septic tank system works well. Plastic tanks are available cheaply off the shelf and concrete ones are easily built insitu. This system is apparently favoured by the Malaysian Ministry of Health.

A better system is to use dual tanks (or one tank with two compartments) which allows more control of the digestion process. The first tank has a mix of undigested and partially digested waste, whereas the second tank contains only partially digested and completely digested waste. Turbulence caused by fresh influent does not stir up the waste in the second tank.

Dual tanks will also give a better chance that wastewater will stay in the system long enough for waste to be fully digested. Dual tanks still need to be de-sludged, although perhaps at reduced frequency in the second tank.

In Sabah it seems acceptable to discharge effluent straight into the environment, even from a single tank system. In Western countries the standard practice is to use a ‘Leach Field’ or ‘Soakaway’. This is usually a series of perforated pipes connected to the effluent and buried in the soil. The wastewater is then slowly filtered and any remaining pathogens have time to be digested by bacteria in the soil. This probably makes more sense in a temperate climate where cold temperatures can inhibit bacteria growth.

My feeling is that in the humid tropics we probably get away without a leach field because as soon as the treated effluent is in the open, the bacteria have everything they need (oxygen, heat, water) to very quickly demolish any remaining pathogens. In the context of a rainforest camp I cautiously suggest that I am happy with this approach, as long as the effluent is downstream from the camp. The rainforest is very good at decomposing organic waste.

Where I am not comfortable with this approach is in slightly higher density projects such as a field station or jungle lodge. Although the environment may not be bothered by treated effluent, I have to consider the possibility of it coming into contact with people. In this case a good alternative is to use a reed bed or maturation pond for the final stage of effluent treatment. In extreme cases of a lot of people on a very small site – an island resort for example – I was interested to read that a hydroponicum can be used for this purpose.

After researching all of this I am still left with one very significant question. How do you deal with the sludge? Clearly I do not consider it acceptable to send someone down to dig it out.

One idea I have been thinking of is to try to using alternating septic tanks. Once one tank is full the influent is re-plumbed to an empty adjacent tank. Extra organic matter (rice husks, oil palm fibres etc) is then added to the full tank to soak up any remaining liquid and then it is sealed off and left for a year or more. By the time the second tank is full perhaps the first tank would have digested to something relatively harmless which could be more safely dug out?

The problem I have with this idea is that unlike a composting toilet, the sealed off tank would not be able to be dried out thoroughly. Unless it could be dried out I am not sure that the sludge could be composted to something non-hazardous.

Another idea I’m thinking of follows the ‘seal it up and forget about it’ philosophy. The catch with this is that plastic and concrete do not just go away. I am wondering therefore whether it is possible to make a septic tank out of a biodegradable material? Obviously it would need to last long enough for the tank to fill up (say 2-5 years) but then after that it could be allowed to degrade, say over a period of 10 years.

There are two other unfinished leads in this story. The first is how a composting toilet works and the second is what happens to the sludge once it has been ‘honey dipped’? Those stories are for another day. Meanwhile if anyone has any helpful advice on the above I’d be very happy to hear it.

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