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The TRAISELECT System in an Urban Context

Towards Sustainable Sanitation

The principle of selectively treating grey water apart from black water opens up new perspectives on bringing about cities that no longer pollute water. Those who regard the « all-to-the-sewer » concept as inescapable will doubtless find my reasoning utopian. I will however attempt to demonstrate that the solutions proposed herein constitute a set of technical applications that have already proven themselves, and as such, generate possibilities that are far from utopian.

Various experiments and attempts have been carried out to create city neighbourhoods that would apply more rational water management practices than those proposed by conventional sanitation proponents. Attempts to treat water by the use of plants have sometimes given surprising results: you can now find apartment buildings having walls covered with water purifying plants. Others have tried in-soil water purification that goes short of actually replenishing the water table. It involves installing a planted layer of earth and gravel overtop a watertight membrane. Water then percolates down through the planted root zone. This has given mixed results: the set-up requires lots of space and is relatively expensive.

The common ground to all these attempts is the will to purify water as best as can be done, so as to return the cleanest water possible back to nature. It’s on this level that we feel current approaches to be incomplete. When you consider the overall environmental impact of city wastewater production and treatment, water pollution actually only represents one aspect of the problem. To our knowledge, there exists another, probably greater aspect that remains shamefully neglected: biomass destruction for purposes of water treatment.

We suggest that the notion of purification efficiency be replaced by a more comprehensive one, that of environmental performance. From that point on, you come to realize that water purification cannot remain the ultimate goal, but that reducing environmental damage is a more fundamental target. Another neglected aspect of the problem is the breakdown of nature’s great natural cycles (i.e. carbon, nitrogen, phosphorous, and even water) due to urban activities.

The main objective of sustainable sanitation must be to renew domestic activities within nature’s great cycles. To take heed of these cycles, we must intervene on two fronts:

Separate Grey Water and Black Water Collection

In a perspective of ecological sanitation, we must abandon the « all-to-the-sewer » concept, just as absurd as the « all-to-the-bin » philosophy. The key to this approach is to collect and treat grey and black wastewater separately.

The transition to such a concept is undeniably problematic in existing built city neighbourhoods. The main impediment comes from the lack of separate storm-water and sewage (black water) conveyance networks. Sanitation in today’s cities obeys to the « all-to-the-sewer » principle. Nevertheless, many cities are currently implementing separate water conveyance networks, although not for ecological sanitation purposes. Their aim is to avoid diluting sewage with storm-water. By collecting and conveying storm-water separately, sanitation plants will not have their sewage treatment processes disrupted by major rainfalls. Thus, implementing separate sewer systems currently has the seal of approval from sanitation engineers.

We suggest somewhat the same thing, although not for sewage and storm-water, but rather for sewage and grey water. As for storm-water, we recommend that it be totally retrieved and stored in cisterns to be located near or under buildings [2]. Street and road storm-water – not containing faecal matter – can be conveyed in the grey water conveyance network. In already built urban communities, the existing sewerage network will serve this purpose, as it will no longer receive any black water. The new type of black water proposed herein will therefore need to be conveyed in a new generation of sewerage network.

Finally, important modifications will also be needed within existing buildings. This will consist in disconnecting conventional WC’s from the sanitary building drain. A new but smaller-sized drainage piping network will need to be installed to convey the black water discharged from a new generation of WC’s, and bring it to the new generation of sewerage network, as described below.

Selective Treatment of Black Water

Turbo-Toilets (or TT’s) and the BLT Principle

Current WC’s could be replaced by turbo-toilets (TT’s). These would combine the advantages of a standard WC with those of the BLT, while minimizing any inconvenience. From the outside, a TT would resemble toilets used on airplanes. After use, the stainless steel or porcelain toilet bowl would be rinsed out with a high-pressure jet (from 20 to 30 bars or 300 to 450 psi). Thanks to this high pressure, each toilet use would only consume between 100 and 200 ml (3½ to 7 oz) of water.   

The TT’s proper mode of operation would rely on diluting excreta as little as possible: in other words, of maintaining excreta as concentrated as possible. This is a pre-condition for appropriate black water treatment. The next condition is to be able to easily convey this concentrated black water to its treatment centre. For this, effluent must be liquefied to be transportable inside small-section pipes. Therefore, the TT would be equipped with a grinder to liquefy the toilet’s effluent into an acceptable slurry.

Such toilets (with grinders) already exist (although they are not called « turbo-toilets »), but they come with a standard volume flush, which represents much too much water. It’s to reduce this water volume that the water flush must be pressurized. Pressure pumps that can do this job already exist in domestic pressure washers (e.g. manufactured by « Kärcher »). A TT would therefore use two existing and proven technologies.

Integrated Biomass Treatment Centre

As previously mentioned, the TT would be connected to a smaller-sized sanitary piping network within the building. The sanitary building drain would itself be connected to a new generation of sewerage network. Therefore, the concentrated TT effluent would be conveyed to an integrated biomass treatment centre via the sewerage network. This network would require smaller-section conduits (when compared to conduits used for grey water conveyance)[3]. To improve the wastewater’s passage in these conduits [4], it may be advisable that they be slightly pressurized (about one hundred millibars or 1.5 psi) with appropriate booster pumps. When the distance between the home and the treatment centre is excessive, sewage pumping stations would become necessary.

The wastewater conveyed to the treatment centre would be used to impregnate a cellulose litter for aerobic composting. This is the only part of the concept that needs to be technically perfected. Given the principle of cellulose impregnation before composting, we need now to perfect the dispersion system itself, on or within the litter. Then, we must also provide for an automated conveyance system to hoard the impregnated litter to the treatment centre’s designated composting area.

Impregnated litter (having an appropriate carbon/nitrogen ratio of about 60) barely diffuses any odour. When treating large quantities, the centre can resort to accelerated composting by periodically turning and aerating the compost heaps with the use of heavy machinery. Such installations already exist.

The biomass treatment centre’s importance relies on an integrated management of many types of waste that combine concentrated black water with cellulose and organic waste from many sources: for example, the fermentable part of domestic waste, and also its cellulose component (cardboard, paper waste) [5]. The treatment centre can also include other waste in the recycling process: organic plant waste from city park and tree maintenance, seasonal leaf and yard waste collection, etc. – and to a certain extent –rural, agricultural and forestry waste [6] and agro-food industry waste.

The treatment centre’s end product will be fully cured compost, an ideal organic soil amendment for fertilizing and especially regenerating agricultural land that has been destroyed by a century of intensive (chemical dependant) farming. Integrated biomass treatment centres will become the sustainable management hub of our environment [7].

Selective Treatment of Grey Water

Technical solutions differ for different urban contexts, between already built and not yet built urban communities, and single family housing neighbourhoods.

To uphold the water cycle, it is best to avoid resorting to grey water sewerage networks if there is sufficient land for grey water infiltration into the soil. For roadway storm-water collection, there could be a system of drainage gutters and/or covered chases (e.g. topped with perforated concrete covers, grates, etc.). These should not be watertight, just as the grey water conveyance network itself need not be watertight. From there, roadway storm-water should be conveyed through densely vegetated humid areas before re-entering a watercourse.

In Already-built Urban Communities

Grey water collection is really only necessary in already built urban communities. For simple grey water (black water being collected separately), we can resort to already existing sewers. However, the sanitation plants to which these sewers are connected are inappropriate for grey water treatment – at least not any better than they are for mixed grey and black wastewater. Even when considering the purification aspect, the main shortcoming of such plants is the discharge of treated wastewater directly into rivers. This must be avoided at all cost. Another shortcoming is the insufficient length of stay of wastewater (a few hours at most) for proper treatment. In such conditions, a not insignificant quantity of detergent is discharged with the wastewater. Even a weak concentration of such substances gravely disrupts aquatic life.

To avoid such harm, we must work out a way to avoid discharging grey water into watercourses– even when treated. There are a few options for this. One would consist in subdividing a city into many collection zones or sub-networks. Each sub-network would discharge its grey water load into a primary treatment system (grease removal, screening). Once its grease content is removed, the water should end up in an appropriately planted humid zone somewhere in the urban periphery. These wetlands could become migratory stations for birds. The water’s discharge back into the river can only occur after it has passed through these filtering humid zones. Experience has shown that daylight is the key vector in clarifying the water in such wetlands. Soap and detergent micelles tend to coagulate and settle on the bottom. The resulting sludge is then transformed by bacterial fauna, which decomposes it into water and carbon dioxide.

In Not-yet-built Urban Communities

Not yet built communities have two possibilities, depending on their local climate conditions.

In Dry or Desert Regions

For proper grey water treatment, it will first be stored in grey water batch reactors located near or under buildings. These should have a capacity of about 1 m³ per inhabitant. In these conditions, grease will be « digested » in the reactor, and about 60 to 80 % of the pollutant load will disappear. Water discharged from these reactors can easily be infiltrated into the soil without risk of clogging. When designing a community, it is therefore necessary to provide an infiltration field [8] with enough space (about 1 m² per inhabitant) for the wastewater’s dispersion and infiltration in the soil. This will obviously be in planted areas. In this way, all water used by households eventually returns back to the groundwater reserves. The water cycle remains thus undisrupted. This option is particularly useful in dry regions.

Total water produced by inhabitants living in dry or arid regions could even be used for irrigation of food crops, without the least health risk. To reduce unavoidable odour problems, grey water will have to go through an aeration pit where air is to be injected into the water.

In this way, you get comprehensive grey water reuse. By also using turbo-toilets or TT’s (± 0.2 litres of water per use), you can hope to reduce water consumption by about 25 to 30%.

In Temperate Regions (With Sufficient Regular Rainfall)

Another option is to treat grey water right nearby dwellings. This will be done with the complete TRAISELECT system. Water issuing from the grey water batch reactor is discharged into a planted trench filter having a capacity of 0.5 m² per inhabitant. The trench’s overflow spills into a decorative wetland of about 1 m² per inhabitant. In this pond, water becomes crystal-clear and odourless. Its quality gets close to that of potable water. Planted trench and wetland finish filtering systems also become beneficial landscape elements close by apartment buildings. However, this system is only appropriate in moister regions where saving water is not an issue. This is due to the fact that in spite of its efficiency, the complete system is characterized by greater evaporative water loss, especially in summer.

For a building that houses 100 people for example (about thirty families), the planted filter bed would measure about 5 x10 m and the wetland would measure 10 x10 m. Consider that in new neighbourhoods, there are substantially more green spaces usually planned around buildings.

In Suburbs and Single Family Housing Neighbourhoods

The situation is much simpler in urban and suburban neighbourhoods where single-family houses having a yard (or garden). In such houses, it would be better to promote dry toilet use like the BLT. From that point, selective grey water treatment can be done as per the TRAISELECT system guidelines. Families who absolutely insist on the convenience of a WC will then opt for the turbo-toilet or TT, which’s effluent would have to be sent conveyed to plant-based litter bed somewhere in a corner of the yard.

Let us now visit the pages dedicated to dry toilets.

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[1] Water consumed by a city’s inhabitants, and discharged – after treatment – back into the closest river is equivalent to drawing from our water reserves a quantity of water equal to that of a small river.

[2] By conforming to PLUVALOR standards, i.e. 15 m³ storage capacity for each 100 m² of horizontally measured roof catchment area, a city’s cisterns would represent the equivalent of an enormous storm-water tank. Instead of rushing into the sewerage network and flushing its pollutant load towards the river, storm-water would be held in the cisterns to be gradually released to the grey water conveyance network, in proportion to domestic grey water production.

[3] In reality, existing sewers would be redefined as the new grey water and storm-water conveyance networks. The old sewers would not even have to be rendered watertight, as the soil underground is their logical destination. Instead of disrupting the quality of rivers and their soil moisture regimes, grey water (representing about 75% of current wastewater) should be infiltrated into the soil, where its purification is completed without the least detrimental effect on groundwater. In a way, grey water conveyance networks would ideally be suited as underground dispersion systems.

[4] This is necessary to respect the BLT principle. The delay between actual faecal sludge (black water) production and its treatment must be as short as possible. This is absolutely necessary in order to prevent natural enzymes having sufficient time to decompose organic matter. Early contact with a cellulose substrate inhibits these enzymatic reactions, thus setting the stage for the process of humus formation. Otherwise, the longer faecal sludge sits in the absence of cellulose, the greater the likelihood of ammonia production and its oxidation into nitrate ions, which leads to a concentrated solution of ammonium nitrate, totally inappropriate for humus formation. Black water (or simple urine) stored without cellulose produces a liquid that is chemically alike to extremely polluting industrial pig manure.

[5] Many municipalities already collect city waste selectively, specifically for recycling or composting. Most collection covers glass, paper and plastics. We feel that the most important waste that should be collected is fermentable domestic waste (about 45% of garbage) and cellulose-based domestic waste. These are without a doubt the most precious components of urban waste. Besides cardboard, cellulose also includes soiled paper that is impossible to recycle as paper.

[6] Resorting to forestry waste combustion (in the form of compressed wood fibre pellets) for furnaces and boilers is an unforgivable waste that undermines the biosphere. This cellulose waste is an important component of the natural carbon cycle. It is an innate and indispensable complement to industrial pig manure production – in so much as we insist on maintaining such an aberration. A biomass treatment centre should not only integrate dejecta from livestock farming, but also wood and cardboard waste from packaging and construction industries. After shredding, these are ideal cellulose substrates for animal and human manure. The most logical use for forestry by-products such as wood fibre pellets is heat production not by combustion, but by composting using the Jean Pain method. In this way, wood pellets would produce almost as much energy as combustion, but instead of being reduced to ashes (with the inherent CO2 emissions), they would produce highly valuable compost for agriculture.

[7] The resulting compost will rapidly become a vector of farmland soil regeneration and fertilization. Synthetic fertilizing needs will drop. Remember that it takes 2.5 kg of petroleum to manufacture 1 kg of chemical fertilizer, plus the pollution involved not only in its production but also by its use. A progressive increase in soil’s humus content will also entail a reduction in the need for synthetic pesticides and herbicides.

[8] An infiltration field is quite unlike conventional leach-fields or drain-fields, which address an altogether different reality from that of the TRAISELECT system, notably by their treatment of black water. Water’s chemical composition is modified by the elimination of nitrates and phosphates. On the other hand, in a simple infiltration field, no water treatment is involved or even necessary, and plants have nothing to do with clarifying the water. Lab tests have shown that the water discharged from a grey water batch reactor becomes clear – and often potable – after having gone through a few centimetres of earth (arable or not). The water’s chemical composition remains unchanged. Floating impurities (soaps, detergents, fats, bacterial micelle) are eliminated by simple adsorption, and than taken in charge by bacterial fauna.

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