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Ecological sanitation or ECOSAN
Ecological Sanitation and EAUTARCIE

Failings of Sanitary Engineering

Six Principles of Ecological Sanitation

Components of Ecological Sanitation

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EAUTARCIE's strongpoint is the integration of mutually dependent relations that involve water management, plant and animal biomass and their influences on climate change. Once these interdependences are acknowledged, it becomes immediately possible to propose a global program to get humanity out of its food and water shortage problems by means of reclaiming damaged ecosystems. Such a program, much less expensive than current proposals that only address global drinking water issues, would have an impact that could slow or even end climate changes, if done concurrently to a reduction program of global energy consumption.

The text within this page was first published in French on : in November 2007

The original text has since been adapted and first published in English on this page at : 2009-06-15

Last update : 2017-01-30

Components of Ecological Sanitation

Conventional vs. Ecological Sanitation

Conventional sanitation

Sanitize = to make clean. The basic philosophy behind conventional sanitation has much to do with an anthropocentric view and the hygienics ideology. Conventional sanitation only aims to sanitize the home, prevent disease and promote human health, by preventing the population's contact with pathogenic germs. This is at the core of its concerns. For these purposes, the means of disinfection are usually chemical (chlorination) and physical (irradiation).

In the process, conventional sanitation insists on discharging extensively treated water in the receiving milieu, our environment. Thus, water treatment and purification are put forth before any other technique. This involves collective centralized installations (water distribution, wastewater purification), which are undeniably favoured over decentralized techniques. In addition, while although not explicitly stated, corrective techniques (e.g. wastewater purification) are preferred over preventive techniques (e.g. use of rainwater, dry toilets, thermogenic composting, etc.).

Purification is the technique par excellence of conventional sanitation. Treated effluent is preferably discharged in watercourses. The environmental impact of eliminating treated sewage sludge is belittled. In fact, sanitation engineers don’t like to talk about it. Purification efficiency is honoured whereas the notion of environmental performance is not even considered. In the best case, an environmental impact study may be required.

Phytopurification (or phytoremediation) is also part of conventional sanitation. It answers to the same objectives and requirements: purify as best as can be done, without other considerations or concerns.

In conventional water management, household water conservation is the main argument put forth to the public. The insistence is on savings that are relatively insubstantial:

• Reduce the water volume of tank flushes;
• Repair plumbing water leaks;
• Use low-flow shower heads and faucets;
• Shut the faucet while brushing teeth;
• Do laundry with full loads only;
• Irrigate garden with drip or soak systems;
• Etc.

Unofficially, conventional sanitation aims to avoid depriving mains water suppliers of inherent revenues (profits for private corporations, and tax revenues for public corporations). A reduction in revenues would have an impact on funding of water policies. For sustainable sanitation, water legislation needs to be totally revisited: instead of taxing the water consumer, you must tax the water polluter. The options that drastically reduce the strain on our hydrous resources are not taken into account, or very little. Such as to:

• Use dry toilets (25 to 35 % reduction in water consumption);
• Use rainwater for all domestic uses (water that falls on residential roofs could cover 60 to 80 % of total household consumption);

Ecological sanitation

Ecological sanitation is a new vision of sanitation, which differs in some aspects from the conventional view. It integrates concerns about sustainable water management but also about biomass in cities and homes. The joint management of water and biomass (i.e. the organic component of sewage effluent, plant waste and fermentable city garbage) is indispensable.

Ecological sanitation broadens the scope not only to wastewater treatment, but also to household water supply and to environmental impacts upstream and downstream of actual water treatment and/or purification. To assess an ecological sanitation technology, the notion of environmental performance must be defined. This is the main difference between the two visions of sanitation.

The first principle of ecological sanitation is the selective treatment of black water (containing human dejecta), separate from greywater (containing soaps and detergents). Black water needs to be combined with plant-based cellulosic waste to make compost. In rural and peri-urban areas, households will have the choice between dry toilets and a septic tank reserved exclusively for black water (with regular emptying). Greywater would be directly infiltrated into the soil of a home’s garden. In cities, greywater would be collected in existing sewers whereas the toilet effluent from ultra-low-flush toilets would be conveyed in a separate sewerage network towards an impregnation centre for composting.

Ecological sanitation is also concerned with the influence of sanitation installations on land's soil moisture regime.

One of the underlying principles of ecological sanitation lies in the integration of domestic activities into Nature's great natural cycles (carbon, nitrogen, phosphorous and water). Conventional treatment breaks from nature's cycles. It removes domestic activities from the biosphere while at the same time generating nitrate pollution. On the other hand, observance of these cycles has an effect on climate change, but also on global water management and the functioning of ecosystems.

Soil Moisture Regime

The soil moisture regime is the manner by which precipitation is distributed on land, between surface run-off, infiltration in soil and evaporation. In this sense, the moisture regime is an integral part of the water cycle.

Soil moisture regime in conventional sanitation

Conventional sanitation is mainly concerned with domestically-produced wastewater. By conventional view, supply water will be drawn from water reserves (underground water, surface water). After use, this water is recovered, channelled to treatment plants and discharged into the receiving milieu (i.e. rivers, in the vast majority of cases).

City ground surfaces that are made impervious incite water runoff rather than replenishing the water table (i.e. underground water reserves). In conventional sanitation, rainwater catchment from roof surfaces must be channelled to a recovery system. In practice however, this water ends up in the sewage system. Thus, precipitation dilutes the waters that need to be treated and disrupts the treatment plant's operations. The length of stay of water at the treatment plant is only a few hours, and a major rainfall is likely to purge the entire plant, discharging the entire pollutant load in the river. Dilution of wastewater with rainwater reduces the treatment's efficiency.

To mitigate this problem, sanitation plants incorporate bypass circuits to channel rainfall water directly to the river (including the pollutant load of non treated water that was in the sewers during the rainfall). Another solution involves doubling the systems. Wastewater and stormwater are collected in separate water conveying systems. The first enters the sanitation plant, whereas the second ends up in a stormwater basin, before being discharged into the river.

Conventional sanitation engineers are doubtful about, even hostile to extended rainwater reuse within the home. For example, a new law in France that legislates on matters of rainwater reuse states that such water can only be used to water the yard and for exterior cleaning. Its reuse for WCs is even discouraged!

Proponents of conventional sanitation regard rainwater as a sort of calamity that must be conveyed to a water course as soon as possible. To limit its domestic use (considered « unfair » competition to the mains water supplier, be it in terms of profits [for private corporations] or tax revenues [for public corporations]), they go so far as to recommend small-sized cisterns only. Fear is instilled in the population by invoking pathogenic bacteria.

Result: almost all rooftop rain is quickly channelled to the closest river.

In an urban context, the water outfall represents the equivalent volume of an average sized river, either when combined or split sewer systems are present. This discharge rate, added to the receiving body's own discharge rate could aggravate flood risks.

Soil moisture regime in ecological sanitation

In ecological sanitation, all efforts for our water resources attempt to:

Water supply

Under EAUTARCIE’s ECOSAN (SAINECO), water used by the household will come exclusively from rooftop water. After proper treatment and filtration, it will be used for food, drink, and personal hygiene, and whatever water remains can be used for all other domestic uses.

In order to reduce the cost of water as well as the health risks, another option is to distribute to the population a non-potable water that we call « safe water » (of inoffensive quality). Such water would be used in the household for all non-food uses (personal hygiene, laundry, dishes, etc.). All one person actually needs is 5 litres per day of truly potable drinking water. This can be produced in each household using a relatively inexpensive reverse osmosis system. This water will be reserved for drinking and cooking, for washing vegetables and for brushing teeth.

Wastewater management

In rural and peri-urban areas, when using an appropriate dry toilet, water needs are reduced by 25 to 35 % and the only wastewater produced is greywater (soapy water without faecal content). After transiting through a greywater batch reactor, this water is infiltrated or dispersed into the soil. In the summer, greywater can safely be used for watering plants without any prior treatment.

Those who wish to keep using a flush toilet will need to install a septic tank reserved exclusively for black water (toilet effluent) and needing to be periodically emptied. The removed septic waste is then to be conveyed to impregnation and composting centres, similarly to what we recommend for cities. Through these measures, the organic matter contained in dejecta will be composted and transformed into a soil amendment that contains non-leaching nitrogen: thus, no pollution from nitrates, phosphates, or detergents.

From a soil moisture regime perspective, an ecological house has little or no impact on our water reserves, and it no longer pollutes our water: in short, as if it simply wasn't there.

Provided that the roof is large enough, such a home often does not need to be connected to water mains. The wastewater conveyance system (previously called a sewer) that passes near the house need not be a closed watertight system: therefore it is less expensive. It would drain roadway stormwaters and channel them to a natural wetland. A sanitation plant no longer becomes necessary. Because such infrastructure is simplified, ecological sanitation would be inherently less expensive than conventional sanitation, ensuring at the same time a much greater degree of protection for the environment.

Corrective vs. Preventive Techniques

Unlike what goes on in conventional sanitation, ecological sanitation gives priority to techniques that seek to prevent the source of pollution and other nuisances, before consideration for corrective techniques. For example, wastewater purification and treatment is a corrective technique whereas the use of dry toilets is a preventive technique. Complete rainwater reuse, naturally soft, reduces the use of detergents. Thus, it is also a technique for reducing pollution at the source. Drinking filtered rainwater reduces the wastage of plastic water bottles and represents a not-insignificant factor of good health.

In conventional sanitation, all wastewater is treated. This results in the rapid drainage of large masses of water from the sewers into rivers. Mains water distribution draws an equivalent mass of water from the water reserves, which is then discharged, after use and treatment, back into water courses. Under EAUTARCIE’s ECOSAN (SAINECO), much of the water that would have been drawn form water reserves is replaced by rainwater. After use, such water (treated or untreated, as deemed appropriate) would be infiltrated into the ground instead of being discharged into drains.

An array of correctly dimensioned cisterns in a city (160 litres of storage capacity per m² of roof area) constitutes a greatly efficient stormwater retention system.

Purification Efficiency vs. Environmental Performance

Purification efficiency

This value characterizes the degree of elimination of wastewater's pollutant load after having gone through a conventional sanitation plant. It is the ratio between the pollutant load that enters a facility (as untreated water) and that which exits the same facility (as treated water), expressed as a percentage.

P = (1 - Xs/Xe).100

Where P = purification efficiency

Xs = pollutant load at outlet of treatment facility

Xe = pollutant load at point of entry of treatment facility

A facility that works improperly will have a purification efficiency of zero because the pollutant load which exits the system will be identical to that which enters: Xs = Xe, thus P = 0.

A facility that works perfectly will have a purification efficiency of 100 %. In this case, Xs = 0, total pollutant load is eliminated from the water, and P = 100.

Environmental performance

Environmental performance embodies a set of factors that help define the environmental impact of an activity, in general, or of a sanitation system in particular.

In ecological sanitation, purification efficiency is only applicable to urban greywater that is selectively treated, and only when greywater is to be discharged into a river. In all other situations, purification efficiency is senseless, as water purification is averted under EAUTARCIE’s version of ECOSAN (SAINECO).

As long as ecological sanitation and conventional sanitation co-exist in our world, conventional sanitation would be more appropriately evaluated for its environmental performance. Such an exercise would be provisional, as wastewater purification systems that do not comply with SAINECO’s five first principles would be gradually phased out. To assess the environmental performance of conventional sanitation, you need to consider the following factors :

The last factor is the most important. Only a few of these factors are taken into account via impact studies that currently precede the implementation of a public sanitation plant.

To evaluate the environmental performance of different types of dry toilets (source-separating dry toilets, composting dry toilets, BioLitter dry toilets), another series of factors are to be considered:

Household Wastewater

Black water and greywater

Domestically produced wastewater is a mixture of greywater and black water. The conventional view of sanitation is that these waters must be mixed and treated together. In EAUTARCIE’s version of ECOSAN, they are treated separately. The composition of both water types being different, their selective treatment presents advantages.

Domestic wastewater composition

Black water Grey water
Water from WCs and urinals Water from bathing, dishwashing, laundry, and cleaning.

Organic matter containing phosphorus and nitrogen
About 98% of nitrogen in wastewater is found in black water, completely organic.

Organic nitrogen: approx. 5 kg per person annually.

Organic matter containing sulphur and phosphorus, but no nitrogen

Surface-active substances: soaps, detergents.

Organic phosphorus of metabolic origin,

Approx. 1 kg per person annually.
Mineral phosphorus from laundry in the form of mineral phosphates.
Very large number of faecal contaminated bacteria. Little faecal contaminated bacteria.
Micro-pollutants: medicinal residues, antibiotics, hormonal molecules (oestrogen), biocides used in WC maintenance.

Micro-pollutants: additives to laundry, dishwashing and cleaning products.

Softeners, lens cleaners, enzymes, etc.
Always cold Hot or warm (important pour treatment)
Represents about half the global domestic wastewater pollutant load, expressed in COD (chemical oxygen demand) Represents about half the global domestic wastewater pollutant load, expressed in COD (chemical oxygen demand)

Product of conventional sanitation:
The organic nitrogen and phosphorus are oxidized into nitrates and phosphates.

These end up in the sewage sludge and in the treated water.

Product of conventional sanitation:

Water, carbon dioxide, sulphates, phosphates, detergent residue.
The organic matter from our excreta is an integral part of the biosphere. In a perspective of sustainable management, it must be recycled into the formation of humus for the soil. The macromolecules of the grey water pollutant load are a threat to rivers and lakes when discharged after treatment.

Treated Effluent Discharge Techniques

Treated effluent discharge techniques (downstream of the process) often have a greater impact on the receiving environment than do treatment and purification techniques (upstream of the process). In a perspective of ecological sanitation, one must avoid as best one can to discharge treated water in rivers or other natural surface waters.

Even with effective purification, the residual pollutant load constitutes a threat to aquatic life, to varying degrees. The situation is completely different when infiltrating water directly in the ground.

Black Water and Greywater Treatment

Selective black water treatment

In ecological sanitation, the selective treatment of black water is senseless and must altogether be avoided. The bio-oxidation of organic matter constitutes a degradation, indeed a destruction of organic matter, of potential humus. Human excreta - preferably concentrated or pure – must never be purified: they must be recycled. Our excreta must be treated as a solid waste, and most especially, this must be done jointly and concurrently (second principle) with our other organic waste. In this sense, conventional sanitation is incompatible with the concept of sustainable development.

Black water infiltration in soil

Under EAUTARCIE’s ECOSAN, you do not purify black water, nor do you infiltrate it into the soil. Yet something must be said on this last matter. At a flush toilet’s outfall, the pollutant load of black water is composed of organic nitrogenous macromolecules and urea (a nitrogenous organic matter). Due to their dipole moment, these molecules have a great affinity for soil particles. When fixed on these, everpresent soil microorganisms decompose the molecules, progressively freeing organic nitrogen in the form of nitrates, sometimes ammonia. The process is relatively slow, so the so-formed nitrates have a greater chance of being absorbed by plants. It's at this point that a fundamental rule must apply:

This approach has the advantage of being less polluting than conventional sanitation. Even if phytoremediation is relatively simple and inexpensive, it remains nevertheless true that infiltrating black water into wetlands destroys our human dejecta’s precious organic matter.

Standard domestic individual on-site sewage treatment systems speed up the production of nitrates through the process of bio-oxidation. If the treated wastewater were to be infiltrated into the soil, plants would not have time enough to absorb these nitrates, which would thus seep down to the water table. In this case - and that is the case of most set-ups imposed by legislation – the more efficiently conventional wastewater treatment systems work, the more they pollute the environment. Thus, another fundamental rule must apply:

In rural areas, the traditional solution was to dump untreated wastewater in an open pit or a marsh. This basic and inexpensive solution was less environmentally harmful than some of the sophisticated and expensive electro-mechanical systems imposed by authorities in some countries (like in France). On the other hand, the discharge of treated or untreated black water into a water course will tend to asphyxiate the water course by eutrophication (besides other nuisances).

Dispersion of untreated black water in the soil represents at best a lesser evil, when compared to conventional sanitation (which is more expensive, more polluting and more energy consuming). Black water infiltration is not a recognized component of ecological sanitation.

Phytopurification and greywater treatment

When taking a closer look at the objectives and evaluation criteria of water purification using plants (also commonly called phytoremediation), you will come to find that this is a conventional sanitation technique. This approach can only be justified when the « all-to-the-sewer » system is upheld. Once you stop producing black water by using a proper dry toilet (whereby the toilet effluent is treated by composting), phytopurification becomes totally unnecessary.

As for greywater, when it has been « digested » in a greywater batch reactor , it can either be dispersed into the soil [1] or conveyed through a planted trench filter [2] to an artificial wetland: this is what we call the TRAISELECT system.

When the absorption pit (also called a soakaway) does not reach groundwater levels, the only threat to groundwater would arise from the presence of black water, which contains large amounts of nitrates and/or ammonium ions. These small-sized ions would seep through all geological formations to reach groundwater. As greywater contains almost no nitrogen, it is non polluting, even when discharged into an absorption pit.
This is by no means a purification process using plants. Greywater coming out of a batch reactor contains little nitrate, even much less than a household’s mains water supply. If no phosphate-containing detergent is used, there is also much less phosphorus. There is no « food » for plants to absorb. Their rhizosphere (plant root area) serves only as a mechanical filter to clarify the water, by retaining bacterial micellae and soiled micellae from soaps and detergents. Aerobic bacteria then operate on the filtered particles.

In the summer, greywater can also be recycled for irrigating plants in the garden. Indeed, this is the most rational and environmentally friendly solution.

Phytopurification is a technique that seeks to remove nitrogen and phosphorus – just like conventional tertiary sewage treatment. Again, this is a corrective technique. The plants used in the phytopurification process can be composted, yet this will only provide partial recovery of the nitrogen and phosphorus derived from human dejecta. There is much loss and an added solar cycle (an extra year’s delay). Direct composting of dejecta derived from a proper dry toilet (on-site) or of that conveyed to a black water impregnation centre is much more efficient and simple. [3]

Composting of cellulosic plant material impregnated with black water can produce a lot of low-temperature heat that is usable for heating greenhouses and even homes. This is no longer possible when black water is subjected to a phytoremediation process. Also, it is not known if and how efficiently medicinal and drug residues are removed during phytoremediation. Chances are that these substances are no more removed then in conventional wastewater treatment.

For further reading on this matter, go to page on The Problem with Phytopurification.


The process of eutrophication is the excessive multiplication of algae in rivers, lakes or seawaters. It is the result of too high nitrate content in the water. The presence of small quantities of phosphates is equally necessary for eutrophication. Even without phosphate detergents, eutrophication appears when black water is purified. Indeed, we produce about 1 kg of phosphorus (P) per person per year in our excreta, which represents 3 kg total phosphate after purification (equivalent to the release of 5.3 kg trisodium phosphate used in detergents).

A natural water body that is eutrophic can still be clear. In extreme cases, the water becomes greenish and its surface gets covered with duckweed. In all cases, the rocks in the water will get covered with a slimy, slippery biofilm, and potentially also with filamentous algae. Downstream from a wastewater treatment plant's outlet, the river water always presents this eutrophication phenomenon. Nitrates and phosphates are the result of bio-oxidation during purification of the pollutant load discharged from flush toilets.

This phenomenon's effect is that the oxygen dissolved in the water by the algae is consumed (mostly at night), leading to asphyxia of the aquatic environment and making it hard for fish to survive.

To grow, algae consume dissolved nitrates and phosphates. This is a river’s self-purification process. At a certain distance downstream from a wastewater treatment plant's outfall, eutrophication can disappear. More often than not, successive sanitation plants along a river will exceed a river's self-purifying capacity. An important part of the nitrates and phosphates of metabolic origin (resulting from excreta) end up in the sea, provoking an excessive growth of algae there also. As long as we continue to apply the « all-to-the-sewer » system, suppressing phosphates in our laundry detergents will have very little effect on reducing eutrophication.

The invasion of algae on NorthWestern Europe’s sea beaches is of special concern as it is becoming costly to the community. Evidently, the pollution discharged with treated wastewater has exceeded the self-purifying capacity of those rivers flowing into the sea. Advocates of centralized wastewater treatment and the agricultural sector mutually accuse each other of being responsible for this pollution. It is more likely that the algae on our beaches are due to wastewater treatment, not agriculture. Indeed, the onset of algae occurred after the implementation of a pharaonic wastewater treatment program, whereas « agricultural pollution » has been ongoing for nearly a century. Indeed, agricultural pollution is mostly a concern for groundwaters. Surface waters are rather polluted by sewage treatment plants.

The large-scale application of EAUTARCIE’s ECOSAN principles would restore the natural purity to all rivers that are polluted by industry. Algae would also progressively disappear from our beaches.

Dry Toilet Use

So-called dry toilets are set-ups that evacuate human excreta without excreta being discharged into water. Contrary to standard views, all dry toilets do not have the same impact on the environment. Dry toilets can be classified along different criteria. Some are defined as internal vs. external composting toilets. They can also be classified by their method of operation, which leads us to define three generations of dry toilets.

As a preventive technique, dry toilets are an inherent part of ecological sanitation…in principle. The use of dry toilets has three objectives:

1. To prevent pollution of surface water by black water discharge;
2. To conserve water by suppressing flush toilets;
3. To restore nitrogenous organic matter from excreta back into the great natural cycles and in the process of soil formation.

These goals are achieved in varying degrees by the dry toilets in use. The first goal is achieved by all toilets that don't involve a water flush. The second goal is only partially attained, and the third one is not at all achieved by Scandinavian-type dry toilets that function by separating urine from the faeces, and the subsequent spreading of urine on the ground. In effect, the obligation to dilute urine before its agricultural use partially cancels out the water conservation realized by suppressing WCs. In addition, the spreading of stored urine on the ground is akin to promoting the inadequate reuse of agricultural liquid manure on farmland. As a result, there is practically no reintroduction of organic matter in the natural nitrogen cycle. To attain this goal, the totality of excreta (urine + faeces) must enter the process of humus formation. In light of current scientific knowledge, only by applying the principles of a BioLitter Toilet (BLT) can the third goal also be achieved.

For further reading on this matter, go to page on Why Use a Dry Toilet

EAUTARCIE’s ECOSAN in an Urban Setting

Imagine a small river watershed, transformed into an open-air sewer by the sewage that comes from many residential neighbourhoods.

A conventional neighbourhood

Installation of sewers and construction of a sanitation plant here represents enormous costs for quite dubious results. In spite of treatment, the river water quality will remain mediocre (eutrophication). About 90% of the nitrogen and a large part of the phosphorus will remain in the sewage sludge. Agricultural reuse of this sludge will generously feed surface waters and infiltrated ground waters with nitrates. Maintenance and operations costs of this sanitation system will remain high and recurrent for years to come.

An ecological sanitation neighbourhood

Total rainwater reuse combined with the use of dry toilets and selective treatment of grey water would have an environmental impact exceeding the most optimistic visions, at a ridiculous fraction of the cost.

In this option, roadway stormwaters would simply be conveyed to permeable chases or street gutters, etc. The non-installation of closed sewers and the non-construction of sanitation plants would largely cover the cost of a selective grey water treatment system, and even cover that of rainwater recovery cisterns. Maintenance and operations costs for this type of system would be comparatively negligible with respect to a conventional system.

Thus, a river would quickly recover its original purity, with the bonus of offering fishing possibilities! Thanks to the water retention capacity of humus, the use of composted human excreta in gardens would diminish watering needs. It would also eliminate the use of chemical fertilizers and greatly lessen the need for phytosanitary products (i.e. pest and weed control), thus also reducing pollution. Total rainwater reuse would diminish the use of detergents and eliminate the need to purchase bottled mineral or spring water and the consequent bottle wastage. In dry regions, EAUTARCIE’s ECOSAN is an urgent priority: it is the first necessary step to eliminating water problems. It is interesting to read a testimonial from Andalusia (Spain) on this matter.

Contrary to conventionally-expressed views (and skilfully encouraged), the concept of ecological sanitation is perfectly transposable to a city environment.

For further reading on this matter, go to the page on EAUTARCIE's ECOSAN in an urban setting.

Sustainable Management of Soils

Ecological sanitation is impossible without sustainable soil management practices.


Pedogenesis is the process of soil formation, which goes through two steps: first, the fracturing and breaking-up of rock, followed by plant and bacterial actions on the rock. It takes centuries, even millennia to obtain a few centimetres of fertile earth capable of sustaining plant life. Without plant cover, wind and rain can quickly erode the earth to form a desert of rock.

The importance of humus

At the base of all terrestrial life, we find humus, the formation of which is an integral part of pedogenesis. Humus is a brown organic matter of great complexity that is always present in arable land. It is often called « brown gold of the earth », because it is the basis of soil's natural fertility. In fact, desertification is nothing less than the disappearance of humus from soil.

Humus is itself formed from organic matter, at the end of a long transformation process that calls upon bacteria, fungi, earthworms and other soil organisms. Humus is composed of reticulated macromolecules that are related to protein substances (containing amino acids). These macromolecules are chemically adsorbed to soil particles, especially to clay (aluminosilicates). But humus can also adsorb itself to silica (pure silica sand) or sulphates (gypsum or plaster). On carbonates like limestone, adsorption is less stable. Humus that is adsorbed to aluminosilicates constitutes a clay-humus complex that is particularly stable and important in maintaining soil's natural fertility.

Humus formation is a complex process that can be studied in detail in the soil of deciduous forests. It is formed naturally within forests, from dead leaves, branches and other plants, but also from wildlife's excreta.

With sufficient humus present, sandy soil acquires a certain consistency as it compacts and stabilizes, protecting it against wind and water erosion. Likewise, naturally compact clay soil becomes friable and easier to till. In all cases, humus works as an enormous sponge. Soil containing lots of humus has a great water holding capacity: one gram of humus is capable of holding and fixing 10 to 50 times its mass in water. Water that infiltrates in a humus-bearing soil is held there, being progressively absorbed by plants as needed, or slowly seeping down deep layers to replenish the water table, wells and springs. Crops then need less irrigation, meaning less surface water and less erosion.

Plant and animal biomass in humus

In nature, the quantity of plant-sourced biomass – rich in carbon – dominates over that of animal-sourced biomass (also including decaying dead animals) – rich in nitrogen. Both types of biomass together form humus, at the end of a process that can take many years.

Putting organic matter directly into soil gives very little humus. Plant matter is too poor in nitrogen, and it will tend to mobilize the soil's humus reserves, giving rise to nitrogen deficiency. Putting in animal-sourced biomass (fresh manure) brings too much nitrogen, which will quickly show up in an ammonia or nitric state (this explains its fertilizing ability). The excess nitrogen becomes a source of nitrate pollution for the water table. This is why even biological agricultural practices can become polluting, if not properly done. Therefore, truly sustainable agriculture cannot exist without composting.

Humus formation needs the combined simultaneous presence of cellulose, plant lignin, and animal protein substances (dejecta + urea contained in urine). Important: these three (or four) components must be present, in aerobic conditions (in presence of air) right from the start of the process. Otherwise, when urine is stored separately, its urea content is removed by enzymatic hydrolysis (due to the ever present urease content of urine). The carbon structure of cellulose fixes the urea molecules and in so doing, prevents the hydrolysis phenomenon that would otherwise produce smelly ammonia. Once urea is fixed by cellulose, it goes through a series of chemical processes that generate peptide linkages, giving rise to macromolecules related to amino acids. This is the first precursor to actual humus, and is commonly called humic acid. (When urine or liquid manure is stored separately, this process does not occur: urea decomposes spontaneously into ammonia and carbon dioxide, which inevitably leads to water pollution.)


Composting that is done correctly is none other than the artificial reconstitution of natural humus formation. This is the reason that well-balanced compost requires the combined presence of plant and animal biomass. The gardener builds his humus by piling up his garden residues (dead leaves, weeds, grass clippings, hedge trimmings, etc.) and kitchen scraps (meal leftovers, peels, spoiled food, etc.). Next to these plant residues, it is best to introduce animal and/or human manure to the composting process.

The carbon/nitrogen or C/N ratio of a balanced compost (before curing) is around 60 (therefore rich in plant cellulose and poor in animal-sourced nitrogen). At the end of the composting process (about one year), the C/N ratio is down to about 14. At this point, the brown matter obtained is not quite yet humus. The process needs to finish directly in the soil by interactions with the soil's natural fauna (bacteria, worms, etc.). What we call stable humus is the brown matter that is fixed to soil particles with a true chemical link. We speak then of clay-humus complexes. That is what gives a brown colour to rich soils with a high water-holding capacity. With clay-humus complexes (or silico-humus complexes), heavy clay soils become crumbly, sand becomes « sticky ». Clay-humus complexes can be generated during composting by adding finely sifted clay powder to the compost.

For further reading on this matter, go to page on Composting Human Dejecta.

Humus degradation

Humus contained in soil progressively disappears through a natural process that is called « combustion » or slow oxidation. In well-maintained farmland, humus' natural elimination is offset by regular input of organic fertilizing.

Soil's humus spontaneously decomposes, thereby feeding plants. Its decomposition rate increases quickly with temperature rises. Moreover, this rate increases exponentially with respect to the square root of the ionic strength of retained water (interstitial water contained between soil particles). This ionic strength is proportional to the concentration of soluble salts (soluble fertilizers, lime, wood ashes, certain mineral additives, etc.). The greater the salt concentration, the quicker humus decomposes, and in the process, the more nourishment plants receive. This is what explains impressive crop yields after addition of lime, wood ashes, biomethane residues, urine, liquid manure, etc., which increase the ionic strength. The use of synthetic chemical fertilizers also accelerates the natural process of humus decomposition.

The first (ephemeral) impact of intensive agricultural practices is a spectacular increase in agricultural yields. Such yields are however obtained at the expense of the soil's humus reserves. With little or no humus in the soil, as soon as these inorganic fertilizers are withheld from the system, agricultural yields collapse. Ultimately, one enters into the infernal spiral of having to use synthetic chemical fertilizers to maintain desired yields.

Plants that are « force-fed » with inorganic nutrients take up much water, by which they only show increased weight yields. Like force-fed geese, such plants are fragile and prone to disease. The need for pesticides becomes inevitable, the logical outcome of using inorganic amendments. The end-product is food that is of lesser nutrient value, and can sometimes even be harmful for one’s health.

Whatever humus was left disappears. Erosion sets in. Clay soils become more and more compact, cracking as they dry, and requiring bigger and more powerful machinery to till the soil. This machinery in turn compresses the soil further. Without humus, precipitation will tend to run off, causing flooding. Sand comes loose in sandy soils, and thus is more likely to blow away. During dry spells, without the water normally stored in humus, rivers tend to settle at their low level. Water holding capacities go down, river discharge rates become irregular, springs dry up, flash floods alternate with extended dry spells each year. Vegetation becomes sparse, agricultural yields collapse. Without humus and with sparser vegetation, the soil becomes lighter coloured (its albedo increases), thus generating ascending air currents that push clouds further and further away. Rainfall becomes sparse. In short, desert conditions progressively set in.

All this is the expected outcome of industrial agriculture that is currently burning up farmland's last remaining humus reserves. Intensive chemically-based agriculture gravely compromises soil's natural fertility, indeed compromising our future.

Producing « green energy » is self-destructive

Another consequence of this unsustainable agriculture is the excessive consumption of fossil fuels. Land without humus requires much more energy and power (e.g. tractors) for tillage. The manufacture of fertilizers and other products also consumes energy. For example, to produce 1 kg of nitrogen as fertilizer, it takes 2.5 kg of crude oil. Currently, « modern » agriculture consumes more energy then it produces.

Fortunately, this process can still be reversed, however late it is. For that, we must mobilize all plant and animal (human) biomass available to increase the humus content of farmland. It will take about 50 years of intensive management to save our arable lands.

We can now understand why the emphasis on « renewable energy » techniques that involve the combustion of biomass is not only a wastage, but also self-destructive for humanity and harmful to the biosphere. In our world of energy over-consumption, biomass-derived « green energy » has a much lesser value then the biological value of the biomass that is being destroyed by combustion and prevented from contributing to pedogenesis.

Thus, burning wood pellets in boilers and producing biogas and other biofuels are irrational activities. Harnessing farmland for energy-production crops instead of food is only a minor aspect of the problem. Rather, with the burning of our biomass, we are actively setting the ground for the deserts of tomorrow, and worldwide famine.

In contrast, restoring humus content to desert regions is likely to restore the soil's moisture regime: springs coming back to life and river flows stabilizing. Plants that eventually cover the soil will help modify the climate by increasing annual rainfall. As more and more flood problems crop up around the world, it is safe to say the problem is directly related to humus depletion in the soil, either from excessive deforestation or poor agricultural practices.

Sustainable Management of Biomass

To halt and reverse this process, it is essential to put in place a worldwide sustainable biomass management program.

To start, we must acknowledge that animal and human dejecta are not waste to be eliminated. They are part of the ecosystems that produce our food. As food comes from the earth, our excreta must inevitably return to the earth in form of stabilized humus to maintain the Natural cycle.

The main obstacle to the implementation of such a program is the irrational and obstinate stand to maintaining the « all-to-the-sewer » system. The other obstacle is the financial speculation system that controls worldwide agriculture.

For further reading on this subject, go to chapter on Bioenergy valorization


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