What goes down our toilet is commonly viewed as waste. This makes intuitive sense because separating people from their excreta – sanitation – is arguably the single most important public health objective, given the massive global disease burden of faecally-transmitted diseases.
Sadly 2.5 billion people still lack access to sanitation. Diarrhoeal disease is the biggest resultant travesty, killing 1.5 million children under the age of five every year. This equates to one in five children globally and accounts for more paediatric deaths than malaria, AIDS and measles combined.
Sanitation — in essence, the toilet — is an incredibly effective means of lessening the devastating impact of many faecally-transmitted diseases. The World Health Organization states that it reduces diarrhoeal morbidity by 38%.
But there is also an oft-forgotten secondary benefit arising from sanitation. Simply through providing an organised collection and distribution system, this nutrient-laden “waste” can also be seen as resource rather than a problematic substance to be disposed of.
Sanitation systems vary considerably, from simple pit latrines, to septic systems, through to large-scale reticulated sewerage systems servicing thousands of households. The types of “waste” are accordingly labelled: “sewage” for the waste being carried by a sewer and, equally imaginatively, “septage” for the contents of a septic tank.
At the end of the day though, there are just two fundamental types worth considering: a liquid component, wastewater (a broader term encompassing sewage, greywater and other sources) and a solid component, faecal sludge (more politely but misleadingly called “biosolids” in many of the more conservative Western societies).
There are various potential uses for faecal sludge and wastewater. But unquestionably the greatest potential and the largest current uses are in crop productivity improvement.
Human waste plays a vital role in providing food and sustaining livelihoods throughout the developing world. And it is becoming increasingly important in developed nations as well, particularly water-stressed countries like Australia, where wastewater irrigation schemes are now commonplace.
Faecal sludge can rejuvenate impoverished soils. Wastewater, while carrying some free fertiliser, is primarily just another irrigation source, and often the only option for the millions of poor urban and peri-urban vegetable farmers throughout Africa and Asia.
In Ghana, faecal sludge has been reported to lead to two- to three-fold increases in yield when applied to cereal crops and is highly sought after by farmers. It is also attractive to Ghanaian farmers because it is free (except for a tip of about US$2 to the truck driver per load). In contrast, a 50-kg bag of NPK fertiliser costs around US$17.
The preferred form of faecal sludge in Ghana is from septic tanks. In some instances it is “dewatered” in a drying bed: a shallow concrete basin designed to maximise evaporation. Such dewatered sludge is very high in organic matter, which means that it can be composted in conjunction with other solid organic waste to produce an excellent crop fertiliser.
Wastewater irrigation of crops is common throughout the world. But despite some very rough estimates (for example, 20 million ha), we really have no idea of its true extent.
In many African countries it is technically illegal, but authorities tend to turn a blind eye to it because they recognise its importance. Wastewater irrigation generally faces less official opposition in Asia.
The use of raw or partially-diluted wastewater is common in many developing countries, and treatment is the exception rather than the rule. This of course raises the question of disease risk, as with excreta.
These risks are real and need to be dealt with accordingly, and the WHO provides guidance on how this can be achieved. It is also crucial to consider the bigger picture of public health, and this includes the risks associated with using human waste as well as the benefits it has to offer in terms of supporting livelihoods and providing food.
There are also agricultural risks and benefits to consider. For example, the benefit of continuity of wastewater supply needs to be weighed against potential degradation of soil structure and decreased yield resulting from high salt concentrations.
Owing to its function of separating humans from their waste, the humble toilet has been rightly lauded as one of the most significant contributions to public health. But it is time for it to be viewed as a nutrient and water depository rather than a bin.
Graham Moore
University of Melbourne
I like the idea of promoting the closure of nutrient cycles, especially the P and K cycle where for much of agriculture mined non renewable sources of these elements are used. However, I think there are some misleading ideas in this article. It is well established that urine contains the majority of nutrients, so the statement "Wastewater, while carrying some free fertiliser, is primarily just another irrigation source" is only true after treatment processes remove nitrogen and phosphorous. If urine separation is practised at the point of production, recovery of these nutrients is very easy and we don't use large amounts of water just to transport our waste. Also, it is not really valid to compare a bag of biosolids with a bag of fertiliser. They have different purposes.
Andrew Hamilton
Senior Research Fellow and Science Director, Department of Agriculture and Food Systems at University of Melbourne
Graham,
Yes, I agree, but I could only go into so much detail here. This was mostly in a developing-world context, which is appropriate for World Toilet Day, and technologies such as urine-separating toilets are out of reach for most of the world's poor. It is without doubt true that the primary function of wastewater in the developing world, and the developed world for that matter, is as a source of irrigation water rarther than a fertiliser. That is not to say that significant yield increases cannot be obtained from the nutrients in wastewater. One must remain pragmatic.
Joe Ekman
Extension specialist
Recycling human waste for use in the food production system may also be the cause of disease proliferation. Here in Australia there is no nationally consistent treatment standard for 'biosolids', meaning all of the key food safety certification standards shy away from any use of human sewage/sludge in fresh food production.
This is an enormous waste of potential nutrients and soil improvement, plus added costs for farmers who are then reliant on chemical fertilisers. Farmers would use it if it was allowed but they cannot take the risk as customers exclude its use. We need a nationally standardised, validated and cost-effective treatment of solid/sludge human waste that ensures disease will not be transmitted in the final product.
Andrew Hamilton
Senior Research Fellow and Science Director, Department of Agriculture and Food Systems at University of Melbourne
Graham,
Yes, I agree, but I could only go into so much detail here. This was mostly in a developing-world context, which is appropriate for World Toilet Day, and technologies such as urine-separating are out of reach for most of the world's poor. It is without doubt true that the primary function of wastewater in the developing world, and the developed world for that matter, is as a source of irrigation water rarther than a fertiliser. That is not to say that significant yield increases can be obtained from the nutrients in wastewater. One must remain pragmatic.
Colin Bishop
Manager
I only have a question: What is in the shit that is then used to grow a consumable crop for human consumption?
Andrew Hamilton
Senior Research Fellow and Science Director, Department of Agriculture and Food Systems at University of Melbourne
Colin, there is lots of stuff in it: organic matter, nutrients, nasty pathogens ... the list goes on. As I said, "These risks are real and need to be dealt with accordingly, and the WHO provides guidance on how this can be achieved." Also note that many (most) don't have the luxury of choice that we have.
Andrew Hamilton
Senior Research Fellow and Science Director, Department of Agriculture and Food Systems at University of Melbourne
Note also that in Ghana, which I use as an example, one practical way of dealing with the risk of sludge us is that they use it on cereal crops only. wastewater, on the other hand, is also used on vegetables, as there is no other choice.
Colin Bishop
Manager
Andrew, I remember the debate when Anna Bligh proposed the introduction of "recycled effluent" into our drinking water supplies.
The major problem as I see it is that the "experts" can not agree on what is in the water after the treatments. I, personally can not see much harm in supplying industries or watering golf courses etc but firmly believe that using any sort of effluent for crop production is not without potential of harm.
Just as an aside - what happened to the GMO crops that could grow with minimum irrigation?
Andrew Hamilton
Senior Research Fellow and Science Director, Department of Agriculture and Food Systems at University of Melbourne
Colin, you keep switching from poo to water and you are confusing the real, developing world with profligate socities like Australia. Yes, drinking water is totally different and has nothing to do with what I was taking about here. In short, I was describing the reality of living in poverty. I am a risk modeller, and there are risks associated with everything, including not eating. I suggest you read on what is called the "income effect". Denying people income costs lives.
Andrew Hamilton
Senior Research Fellow and Science Director, Department of Agriculture and Food Systems at University of Melbourne
The treatments proposed for Toowoomba for were very high-tech and expensive. The urban poor are not so lucky.
bill parker
editor
Its good to see this subject being raised. I spent some eight years looking firstly at the health risks of septic tanks in the sands of Perth and then ways in which an industrial waste ( caustic bauxite residue) could be used to improve the nutrient and microbe retention of coarse sand. Now, as much more of Perth is sewered, the limited risk will have diminished.
However, the potential value of the components of sewage effluent are nowhere near fully exploited. We know how to generate potable…
Read moreDale Bloom
Analyst
I understand it is not the safest practice to apply excreta or sewage waste from any meat eating animal onto food crops. Many viruses can go through a sewage treatment plant, and even composting of solid sewage waste will not remove all viruses.
However a possible solution may be to use liquid waste from a sewage treatment plant as irrigation on timber plantations.
The timber plantations would also soak up some CO2, and help provide a more sustainable timber supply. If carried out well enough, the plantations may also provide a habitat for various animals.
Colin Bishop
Manager
Thank you Dale - this is the exact point that I am trying to make - once any "matter" goes into "sewage" it is "sewage". We have a couple of major problems with using any sewage and one is that no one in Australia is actually measuring what is in the "sewage" and secondly they have no real comprehension of what could be in the "sewage" and they have no idea what the combination of what is in the sewage is likely to produce.
Sewage: waste matter from domestic or industrial establishments that is carried away in sewers or drains for dumping or conversion into a form that is not toxic.
Andrew says that people in poor countries don't have much choice - is Australia any better off?
Colin Bishop
Manager
Andrew:
I am a risk modeler, and there are risks associated with everything, including not eating.
I totally agree, but how much "risk" is acceptable, and are we going to "model" on just the "known risks" or will we examine "all risks", will you take the time to research and to identify the "unknown risks"?
Personally I would rather die from starvation (no I am not advocating) than some "mysterious" illness/bug/disease etc that is caused by "something" in my food - something that "no one" knows anything about and something that is not treatable because there is no money to treat whatever ails me. I will die with a full belly and a full bladder - I will still die!
Leo Kerr
Consultant
"faecal sludge (more politely but misleadingly called “biosolids” in many of the more conservative Western societies)" I kinda think Andrew that faecal sludge is pretty polite but before I delve in to potty alternatives, aren't we and haven't we been using various forms of shit on our veggies for a long long time. Horse manure, sheep manure, chicken manure etc. We dump (no pun intended) this resource at great expense instead of recycling and realising its value. Perhaps we should mix all the variations together to make it more acceptable - Soil & Horticulture Improver Tonic (a rich blend of chicken, sheep and horse manure - see your crops thrive..... ***may contain peanut and human waste residues).
Colin Bishop
Manager
Leo, you are quite correct - BUT!
In my younger days in the UK the only danger in "manure" was the bit that landed on the road and caused one to loose control of ones bicycle/motor cycle or motor car.
Unfortunately the farmers were advised by "scientists" to inject their beasts with all sorts of nasty antibiotics and growth hormones (now instead of hormones they feed them small doses of arsenic) and unmentionable fluids/powders/treatments.
The other most notable process was to pile all of the basic ingredients - poo, pee and straw into a pile (manure heap) for a period of time to allow the microbes to do their work - before "muck spreading".
So: the answer does not lie in the soil, rather it lies in what is in the shit that is going to be spread on our soil.
Another thought - Australia is nearly 100% fluoridated - silicofluorides are growth retardants and 99.5% of the fluoridated water goes into the environment!
Tim Scanlon
Debunker
Biosolids (or whatever you want to call them) have been trialled in broadacre farming in WA and the numbers didn't add up. The main issue is transport and spreading. But not just that, you have to deal with the smell, the flies, the inconsistent nutrient content and the lack of quality control. When I say quality control, I mean that waste is not processed so as to remove heavy metals. This is a major issue for level five trophic consumers, where heavy metals are concentrated in our waste and thus returning this to the soil can cause contamination in a very short time period.
I would love to see a refined product from effluent that has been turned into a usable fertiliser product. We need to close the loop on nutrient removal from soils to make farming "sustainable" (sustainable being a nonsense term). This fertiliser has to be of consistent quality and in a high concentration form, preferably flowable through current machinery.