Black Water Treatment

Graham Bell has lived in Scotland since 1988, having previously spent ten years in London.  His work has taken him around Europe, Africa, the Middle East and the USA. He has a Master's Degree in Old English & Linguistics from Oxford University.  It took him many years to actually make the connection that most of what he does is dependant on the use of language, and to revalue that educational start point. Graham teaches sustainable design, and has written two books on the subject The Permaculture Way and The Permaculture Garden.  He frequently contributes articles to local, national and international media. He is actively involved in the cultural scene of Scotland, including Scottish Traditional music, song, art and woodwork.  He enjoys his garden, which supports a historic collection of Scottish apple cultivars and a wonderful range of bird life.   "Family is the most sustaining thing in my life.  After that comes the valuable network of people that I draw on for creative progress, both for myself and the people I work with.  Home is where the heart is." For more about Graham and his work visit www.grahambell.org.

Questions and Answers

Q: We are planning to move an existing home onto a piece of property. The property I am interested in won't perk. Are there any green alternatives to a pumping station instead of a septic tank?

A: (Penny Livingston-Stark)The most ecologically sound alternatives for your situation would be an onsite waste water treatment system that is isolated from the ground water until it is treated. The options are a constructed wetland or a reed bed system. There are also other manufactured and engineered systems available. Also a composting toilet is great. You need to check your local environmental health problems.

Q: Is the chlorine that you can buy at a pool store be used in a septic system?

A: (Kelly) Pool chlorine is used to disinfect and kill any bacteria or fungus that might form. If you put this in a septic system it will do the same thing, which I think would be counter productive since septic systems rely on bacteria to decompose the wastes.

Q: What type of sewage system do you recommend?

A: (Kelly) Dealing with blackwater and graywater is often a tricky business, mainly because of the regulation imposed by health departments and other regulators. If municipal sewage is available, it is often obligatory to hook up to it. Where septic systems are commonly used, these are also required, even if you have little use for it because you have other methods of treatment. Compost toilets are a possibility, as is graywater and blackwater recycling systems...and these are generally more ecological because they conserve water use.

Q: I run a sanctuary for rescued bears in Southern Vietnam and have a major issue with the waste that is produced from cleaning night dens etc. There are very few options for dealing with waste in this country so we opted initially for a treatment plant similar to those used in local pig farms. The water flows to a holding tank to allow the sediment to accumulate, the effluent then flows off the top into a second chamber, here it is pushed up through a third container containing large diameter rocks, then smaller gravel, then a layer of charcoal before exiting to a sump. Does this sound like a good setup, and is there anyway that I could improve this system?

A: Sounds like a worthy project and a good approach. Essentially you want to separate solid waste from liquid. Solids are usable as fertilizer and liquids want cleaning to let back into the environment. The gradation of substrates creates the aeration which allows breakdown of the liquid waste. If it can be ponded once, twice, thrice in a sequence down hill then you have passive means of cleansing. Rushes or other wet water plants (native) will naturally trap and break down any pathogens. Then you just need a willing worker to shovel the shit somewhere useful. Perhaps you can train bears to do this?

Presently we separate our solids from liquids by manually removing the bear shit before it goes down the drain. We began to compost this, but I think the protein levels may be too high as it just seems to attract flies. I was considering installing a simple biogas digester and piling the bear poo into that, then filtering the rest through, as you say, two or three ponds. Do you have any tips on how to compost the shit more effectively so that I could avoid having to build a digester?

The effective composting of the waste depends on a good balance of materials rich in Nitrogen (N) which is what I guess what you mean by protein, Carbon (C) air, water and heat. Plenty of heat in Vietnam I’m guessing. No shortage of water. If you could pile the bear shit on some sort of grid that enables moisture to drain in to the ponds you’d end up with something lighter and easier to shift. It would then want to be piled (windrows i.e. up to 2m high raised beds should do the trick) and layered being N rich layered with C rich material. That would include old newspapers, straw, sawdust, small brashings – twigs etc, and leaves. The advantage of woody material is it helps create air pockets for aeration. If you can turn the heap at least once in its life that’ll help also. Hard work with a fork. Much easier if you can get the occasional use of a mechanical digger. Remember if you stick the stuff in a digester you’ve still got to get it out again and take it too where it’s useful. Cooling hose pipes in the rotting heaps gives you a free source of hot water, using gravity feed. Watch you don’t wreck them when clearing the heap though! Great stuff to grow potatoes, yams, tomatoes, sweet potatoes squashes etc. Sell them to pay for the labour! Or preach vegetarianism to the bears. Does give new meaning to ‘the bear necessities of life’ though.

Q: I have an alternative idea to black water / sewage treatment & I would really appreciate your feedback. 1a) the solids get separated almost at source. 1b) As the pan flushes, the solids are held in a poop-trap while the water falls into a septic water tank. 1c) The poop is pumped, with some water residue, (by electric sludge pump) into a separate septic poop-tank. 1d) After one year (for example) the poop is pumped from the poop-tank into a prepared composter bed/container and left for another year or until fully decomposed. 1e) As an extension to this idea, I thought of periodically pumping sawdust into the poop-tank from an overhead hopper to give the whole thing a head start. 2) I now have a tank full of black water which has little or no solids. Is it possible to do an initial treatment on this (cheaply and with nature) before entering it into the grey water system or do I have to treat it in a totally separate sewage bed system? 3) the end result of my grey water system (hopefully) would be a decorative pond full of fish for human consumption and for watering the garden. PS: I have looked into composter toilets and did not like what I saw there : ) So, just looking to see if I can do an alternative system. I am planning to buy land to set up an eco friendly homestead and just trying to find out as much as possible before hand.

A: Variations on the theme have been well proven. You don’t say where you are (and that may be significant as ambient temperatures have an effect on decomposition rates). The separation of wet effluent from solid remains is a good principle. The wet element is more easily treatable more quickly and its nutrient element is more quickly recovered. My experience suggests that a three stage reed bed/gravel filtration, ponding, final pond will probably leave you with water fit to drink- so not bad for fishes. Water falls between stages assist creating living water. This approach of using slope in the landscape also diminishes the need for energy inputs which creates a lighter impact system.

I think you are over complicating the solids treatment with the septic tank stage. Firstly pumps= energy usage (far better to use gravity/flow if you can) and secondly composting solids for a year will alone give you a smell free degraded and reusable compost. To be on the safe side this should be applied to interceptor crops (e.g. fruit trees) rather than say- salads- to ensure no risk of pathogen transmission.

If you want to go the septic tank route then I would have a tank with three baffle plates (two stalagmites ie upright from the floor, one stalactite ie down ward from the ceiling) with an outlet. Solids get trapped and can be cleared periodically from top inspection hatch. Fluids flow on through.

But this system is real easy to build and can create a pleasant comfort experience (not just a ‘bog’). One of the few pleasures in life that remain free:

Build a room at least one floor up. Separation from main building is good (e.g. on the end of a covered balcony). This prevents back pressure drawing up vapours from the pit. It has a bench delivery platform with two toilet seats and two holes into the underside. These holes vent into concrete block built chambers 2 cu metres. Come on US you can join the world and do metric! Each of these chambers has a mesh protected drain hole in a side wall to let excess fluid vent, and a removable front wall of wood slats sealed with tar or some such material.. Prime it with a small bale of straw (for the same reasons as your sawdust solution). Poop away. Ladies pee away. Gentlemen can prefer an outdoor discrete peeing option when weather allows. Like onto a compost heap or into a bucket for adding to compost heaps. One station is left open and the other is sealed. When a year later the first is full you swap over, sealing the first and leaving it to mature for a year.

When the second one is filling up you take out the wooden blocks and lo! You have a cubic metre or two of sweet smelling black rich compost. It’s less hard work if the bottom of the chambers is built at one meter height (easy to shovel). A bucket of wood ash in the bathroom with a handful added now and again helps balance the Ph and keeps any smells down. Beautifully decorate the bathroom. Add sink and washing water, mirror soap towel and all will be well.

Pumping the poop came from my friend the engineer. I wanted a gravity fall system to separate the solids asap to keep the water as 'clean' as possible, therefore reducing the process. I just can't think how to get solids to 'freeflow' from the trap into the poop container as they have the consistency of mud and are going to lead to some sticky issues. Solutions?? Basically, just want a simple system that separates water from solids almost at source so it's not sitting in black water.

It seems part of your plan is dominated by the idea that toilets need to be flushed with water. They don’t. And for an eco-house in a dry place water conservation is paramount. For free advice search in "settlement tanks, living water," www.cat.org.uk


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