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  Main page | Summary | Table of contents | Rainwater | Wastewater purification | Dry toilets | Ecological sanitation

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 hygienic concepts. Conventional sanitation limits itself to sanitizing the home, preventing disease and promoting 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 (chlorine) 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, water purification), which are undeniably favoured over decentralized techniques. In additional fact, while although not explicitly stated, repair or corrective techniques (e.g. water purification) are preferred over preventive techniques (e.g. use of rainwater, dry toilets).

Purification is the technique par excellence for conventional sanitation. Treated effluent is preferably discharged in watercourses. Environmental impact is minimized by the elimination of the treated sludge. 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.

Water purification using plants 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:

The options that drastically reduce the strain on our hydrous resources are not taken into account, or very little. Such as to:

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 key to ecological sanitation lies in a generalized use of dry toilets (or an adapted biolitter technique), the effluent of which is to be treated jointly and concurrently with cellulose waste. Ecological sanitation is impossible without appropriate dry toilets.

It also concerns the influence of sanitation installations on land’s soil moisture regime.

One of the fundamentals 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

Sanitation mainly concerns water for domestic use in homes. 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 storm-water are collected in separate water conveying systems. The first enters the sanitation plant, whereas the second ends up in a storm-water 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 WC’s is even discouraged!

Conventional sanitation proponents regard rainwater as a sort of calamity that must be channelled to the river as soon as possible. To limit its domestic use (which would be «unfair» competition to the mains supply company), 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.

For a city, such water influx in a river from a combined or split sewer system represents the equivalent volume of an average sized river. This discharge rate, added to the receiving body’s own discharge rate could aggravate a flood risks.

Soil Moisture Regime in Ecological Sanitation

In ecological sanitation, all efforts tend to:

From this point of view, in an ecological home, water used by the household will come exclusively (or in great part) from rooftop water. After filtering, it will serve all domestic uses. By using an appropriate dry toilet, water needs are reduced by 25 to 35 % and the only wastewater produced is grey water (soapy waters without fecal content). Once through a grey water batch reactor, this water is infiltrated into the grounds of the yard or garden.

The organic matter contained in dejecta is then composted and transformed into non-leaching nitrogen-containing soil improvement: thus, no pollution by 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 whole, as if it simply wasn’t there.

Often, such a house needs not be connected to the water distribution network. The wastewater conveyance system (previously called a sewer) that passes close to the house need not be a closed watertight system: therefore it is less expensive. It will drain roadway storm-waters 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 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, black water 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 cases of water treatment, it is important to consider the great volumes of water that must be conveyed rapidly within a sewer system. In a centralized system, this volume constitutes water initially drawn from the mains water supply reserves, used by the population and after being conveyed to the sanitation plant, is treated and discharged back into the rivers. In an ecological sanitation system, much of the water that is initially taken out is rainwater, which after being used by the population and treated, is infiltrated back into the ground.

An array of correctly dimensioned cisterns in a city (150 litres per m² of roof area) constitutes a greatly efficient storm-water retention system.

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.

Purification Efficiency vs. Environmental Performance

Purification Efficiency

This figure characterizes the degree of elimination of wastewater’s pollutant load after having gone through a treatment system. 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.

For example, for a wastewater treatment system, besides taking into account the purification efficiency, one will consider other factors, such as:

Only a few of these factors are taken into account via impact studies that precede the implementation of a public sanitation plant.

To evaluate the environmental performance of different toilet types, another series of factors are to be considered:

 Household Wastewater

Black Water and Grey Water

Domestically produced wastewater is a mixture of grey water and black water. The conventional view of sanitation is that these waters must be mixed and treated together. The concept of ecological sanitation is in stark contrast to the « all-to-the-sewer » logic of a water-borne sewage system, which is also consistent with a « throw-away » philosophy. The composition of both water types being different, their selective treatment presents advantages.

Wastewater Composition

Black water

Grey water

Water from WC’s 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. 9 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 fecal contaminated bacteria.

Little fecal 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.

Black Water Treatment

Selective Black Water Treatment

With current technology, there is not much advantage to selective biological treatment of black water. The bio-oxidation of organic matter constitutes degradation, indeed a destruction of organic matter, of potential humus. When excreta are discharged in water, even considering efficient purification and treatment, the environmental wastage is irreversible. In a perspective of sustainable development, our excreta must be treated out of the water as a solid waste, and most especially, this must be done jointly and concurrently with our other organic wastes. In this sense, the conventional treatment methods are incompatible with the concept of sustainable development.

Black Water Infiltration in Soil

Before treatment, 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, the soil’s fauna decomposes them, progressively freeing organic nitrogen in form of nitrates. The process is relatively slow, and the so-formed nitrates thus have a chance to be absorbed by plants. It’s at this point that a fundamental rule must apply:

Conventional isolated water treatment by the process of bio-oxidation speeds up the formation of nitrates. When infiltrating treated water, plants will not have time enough to absorb these nitrates, which thus seep down to the water table. In this case - and that is the case of most set-ups imposed by legislation – the better a conventional sanitation system works, the more it pollutes the environment. Thus, another fundamental rule must apply:

Black water discharge in a river or stream, even when adequately treated/purified, will tend to asphyxiate the river by eutrophication.

Black water infiltration in the soil without treatment obviously represents a lesser evil when compared to conventional sanitation (more expensive, polluting and energy consuming). Black water infiltration is not a recognized component of ecological sanitation because, thanks to dry toilets, black water is simply not produced.

Wastewater Purification Using Plants

When taking a closer look at the objectives and evaluation criteria of the water purification using plants (commonly called wetland methods), in fact, one will find that this is a conventional sanitation technique.

Some consider that wastewater purification (combined black and grey) with plants is an ecological sanitation technique. Others deem that purification using plants can only be justified by maintaining flushable WC’s. Yet, the use of a WC is incompatible with the notion of ecological sanitation. The debate is still open on this subject.

The production of sewage (from WC’s and urinals) involves the implementation of a treatment system that is adapted to water containing high levels of nitrogen and organic phosphorus. Purification using plants represents an elimination technique for nitrogen and phosphorus – like conventional tertiary treatment. This type of treatment is, in a way, a corrective technique. The reinsertion of our dejecta’s nitrogen and phosphorus into nature’s cycles - by way of plant purification - involves much loss for the biosphere, as it requires an additional solar cycle (i.e. an extra year) for their integration into the environment, when compared to direct composting of dry toilet effluent.

For further reading on this matter, go to page on Water Purification Using Plants.

Grey Water Treatment

Selective Grey Water Purification

When black water is not produced (by eliminating the use of water-closets), selective biological grey water treatment becomes the natural option. However, in spite of its exceptional performance with respect to the protection of the environment, selective grey water treatment is generally forbidden by law in areas serviced by collective sewage treatment.

Selective grey water treatment using a small-scale electromechanical treatment unit (bio-oxidation) has little use. Plus, this type of set-up is pretty expensive. Considering the treated effluent discharge techniques, infiltration in the soil is the more rational solution.

Soaps and detergents are composed of electrically polarized organic macromolecules that easily adsorb (stick) to soil particles. They are taken in charge by a bacterial fauna that transforms them in water and carbon dioxide. The organic sulphur is transformed into sulphates. With the laundry phosphates, the sulphates precipitate in the soil due to calcium ions, which are almost ever present as insoluble (or as not very soluble) salts.

A dispersion system appears to be the simplest solution to treat grey water. However, the presence of grease presents a risk of system blockage. To avoid this, it is preferable to treat the grey water in anaerobia (in absence of air) before dispersion, in a buried tank that we will call a grey water batch reactor. After a stay of about 3 weeks in this tank, the water presents no risk of blockage to the system. After that, the simplest and cheapest solution appears to be its discharge in an absorption pit.

In the urban periphery or residential suburbs, grey water, after going through a batch reactor, would have to be conveyed through a planted trench filter system to end up in an artificial decorative wetland or a natural wetland. City cores equipped with turbo-toilets (or TT’s) would also need only to treat grey water, either in small decentralized installations, or in larger set-ups that would eventually drain to natural wetlands.

For further reading, go to the page on Selective Grey Water Treatment.

Grey Water Infiltration in Soil

To avoid system blockage, the grey water must initially hold about 2 weeks in a grey water batch reactor. Then, it can either be discharged in an absorption pit or in a dispersal drain (i.e. underground French drains used to distribute wastewater effluent in soil). Once treated this way, the polluting potential of grey water ceases to exist.

Comment: when used for grey water only, biological treatment with plants is expensive, generates evaporative water loss, and is completely useless for the environment’s protection.

In flood zones (water table near ground level) or on fractured rock grade, infiltration into the soil is impossible. In such a case, the treatment of water emanating from a grey water batch reactor must be done in accordance with the TRAISELECT purification system: it must pass through a planted trench filter system (0.5 m² per person) and an artificial wetland (1 m² per person).

Absorption Pit

This pit (commonly called a drainage well or « soakaway ») is usually a few meters deep and receives discharged water, which infiltrates in the soil. The depth of a proper pit never goes down to the water table (underground water level). In light of the pollution danger to underground waters, legislation in most countries forbids the use of absorption pits.

In a perspective of ecological sanitation, under certain conditions, an absorption pit constitutes an efficient and economical solution for the discharge of treated grey water. Considering that an absorption pit does not go down to the water table, the only true menace to underground water comes from the eventual presence of black water. Such water, especially after treatment, contains large quantities of nitrates. These small-sized ions will penetrate all geological formations to infiltrate underground water. On the other hand, grey water contains no nitrogen (especially after anaerobic treatment in a grey water batch reactor), and even when discharged in an absorption pit will not generate any pollution.

Eutrophication

The process of eutrophication is the excessive multiplication of algae in river, lake 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.

Natural water that is eutrophied 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 public sanitation 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 WC’s.

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 an auto-purification process for rivers. At a certain distance downstream from a public sanitation plant’s outlet, eutrophication can disappear. More often than not, a successive of sanitation plants along a river will exceed a river’s auto-purification capacity. An important part of the nitrates and phosphates that are of metabolic origin (resulting from excreta) ends up in the sea, provoking an excessive growth of algae there also. If we continue to use flushable water closets, the suppression of phosphates in laundry detergents will have very little effect on reducing eutrophication.

Generalized use of dry toilets and the simple infiltration of grey water into the soil would restore the natural purity to all rivers that are polluted by industry or agriculture.

Dry Toilet Use

So-called dry toilets are installations that evacuate human excreta without its being discharged in 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 WC flush tanks;

  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 WC’s. In addition, the spreading of stored urine on the ground is akin to the valorization of agricultural liquid manure reuse. 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

Ecological Sanitation in an Urban Context

Conventional vs. Ecological Neighbourhoods

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

Conventional option

Installation of sewers and construction of a sanitation plant here represents enormous costs for a dubious result. 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.

Ecological option

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 storm-waters would simply be conveyed to covered chases, 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.

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 page on TRAISELECT in an urban context.

Sustainable Management of Soils

Ecological sanitation is impossible without sustainable soil management practices.

Pedogenesis

Pedogenesis is the process of soil formation, which goes through two steps: first, the fracturing and breaking-up of stone, followed by plant and bacterial actions on the stone. 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 stones.

Importance of Humus

At the base of all terrestrial life, we find humus, which’s formation 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 fauna. 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), sulphates (gypsum or plaster) and phosphates. 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 sources. 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.

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

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 ration or C/N of 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, whereby 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 interstitial water (that 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. Using 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.

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.

In contrast, restoring humus content to desert regions is likely of restoring 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 complete the natural cycle loop. This process does not occur when animal or human excreta are discharged in water: such shameful wastage becomes absolute, and irreversible. All excreta (animal or human) discharged in water remove precious organic nitrogenous matter from humus formation and produce, in fine, water pollution by nitrates.

In addition, it is important to know that each kilogram of plant matter (cellulose, including paper and cardboard) has a much greater biological value as potential humus than it does as energy obtained from its combustion. The burning of wood pellets in furnaces and boilers and the manufacturing of bio-fuels are gravely undermining the biosphere. Actually, mobilizing farmland for bio-fuel production instead of food production is really 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.

For further reading on this matter, go to page On Bioenergy Development

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