We're wasting our poo(p)

in some places you end up swimming in it.

Poo! 10 million litres of raw sewage dumped into lake Windermere in the UK, apart from being a crime against the biosphere it’s a ridiculous waste. It could have been converted into electricity, heat and farm fertiliser.

In 2023 English water companies released untreated sewage into rivers and coastal waters on average of 825 sewage times per day

The first big problem we face is that reducing energy use is not prioritised, nor is energy wastage.

Then we keep producing new electricity demands such as electric cars without first working out how to produce the extra energy needed, then we play catch up.

Finally we keep fixating on hi-tec solutions such as solar panels rather than on systems such as biogas reactors. Solar panels produce electricity but nothing else except a pile of waste at the end of their lives that is difficult to reuse or recycle. As shown below a biodigester sits in a waste stream that is currently mismanaged and polluting, it transforms this waste into useful products.

Let’s do some poo calculations :

Poole, Dorset, UK : population 151,500. Domestic food waste = 0.26 kg/person/day and faeces = 0.128 kg/person/day (that’s an average in case you got worried)

Approximately 556,418.926 MJ/day of useful energy (accounting for the 65% energy loss) can be generated from the biogas produced from the 58,588 kg of organic waste produced daily in Poole (including both food waste and faeces).

Approximately 12,785 people can be powered by the 556,418.926 MJ of electricity, assuming the people in Poole consume electricity at the same rate as the average person in the UK. Which may or may not be the case! Or this electricity production could reduce everyone in Poole’s bills by nearly 9%.

A part of the energy loss is heat and this can be captured and used. Another product is the digestate which is what remains after the fermentation, it’s been deodorised, pathogens have been killed and it lacks carbon but is an excellent fertiliser for farms. For Poole we could be looking at 1171.76 kg of Nitrogen, 585.88 kg of Phosphorus and 878.82 kg of Potassium, per day.

Yes, I’ve included domestic food waste as including this waste stream as biogas feedstock improves the productivity of the biogas plant. In the UK the cost to householders of purchasing food that was subsequently wasted in 2021/22 was £17 billion. This is ridiculous and needs to be addressed but that said there will always be domestic food waste, currently most of this goes to landfill which is ridiculous as well.

One of the most important aspects of Permaculture design is to manage flows and the interactions between the different elements of a system. We have some principles like:

1. Relative Location: Components placed in a system are viewed relatively, not in isolation.

2. Everything is connected to everything else: Recognize functional relationships between elements.

3. Every function is supported by many elements (redundancy): Good design ensures that all important functions can withstand the failure of one or more element.

Today we have the flow → toilet → sewage treatment → sewage sludge (biosolids) spread on farmland. Except when water companies empty their sewage directly into water bodies.

Improved flow → toilet → biogas plant → electricity/heat to homes → digestate to farmland

Biogas plants are not unknown in Europe, Germany (11,084 plants) and Italy (1,655 plants), France (837 plants), the United Kingdom (715 plants) and Switzerland (634 plants). The total amount of electricity generated from biogas in European countries is over 63,511 GWh.

Unfortunately more than 70% of the feedstocks used in biogas plants in Germany, Austria, Latvia, Hungary and Italy, come from energy crops and agricultural residues. Only in Sweden do we find sewage at wastewater treatment plants being used as the predominant feedstock for biogas production. So we don’t have nearly enough biogas plants and most of them aren’t using the abundant resource that is sewage sludge.

The discussions and debates about renewable energy production, in the media and by politicians, fixate on solar panels and wind turbines. In some countries politicians are talking up nuclear power as being the way forward despite the fact that we need the energy now and nuclear plants take years, decades even, before they come on stream. These plants produce quantities of nuclear waste which is highly toxic, long lived and we don’t really know how to deal with it. Biogas plants are orders of magnitude cheaper to build, come on stream in months and produce a useful by-product. Yes, we would need many more biogas plants than we would nuclear reactors but even so they are more cost effective, transform waste streams to useful products and don’t produce toxic waste. There are also good arguments in favour of decentralised electricity production units, each community having their own which are locally owned and run. Biogas plants fit nicely into this idea.

To wind up this article I feel it’s important to mention that biosolids, (sewage sludge), when spread on agricultural land often run off when it rains. In Paris, France the authorities are worried that it might rain before and during the Olympic games, this would return a lot of sewage sludge back to where it came from, Paris. No athlete would want to swim in the Seine if this happens. To avoid this in general agricultural practices need to change towards ones where the the land is continually covered in some form of vegetation. This can be the crop itself, ideally with an undercrop like clover or green manure crops. Hedgerows and agroforestry in general help reduce run-off. The same is true if we switch from sewage sludge to digestate, it mustn’t run off the land and contaminate water bodies.

The British, and not just them, have a choice to make. Continue the brown tides that flow into rivers, lakes and the sea and risk explosive diahorrea or send it to a biogas plant and get cheap electricity.