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How about taking Willem Van Cotthem’s idea (“Diaper Farmer”) a step further and scattering a million or so used baby diapers over a desert? The hydrogel would absorb dew that settles overnight, and the diaper contents would provide nutrients. The remainder of the diaper should disintegrate rapidly in the hot sun, and our dumps would be relieved of tons of waste.
West Hartford, Conn.”
My sincere thanks go to Jack Bass for commenting on Bruce GRIERSON’s article, published in Popular Science, under the title “Diaper Farmer” – Willem van Cotthem’s super-soil harnesses the power of Pampers to turn dirt into lush gardens“.
I fully understand Jack Bass’ hypothesis that it might be possible to use diapers as such, but I am afraid that things are not that simple.
In order to react constructively upon Jack Bass’ hypothesis that we could make a desert area fertile by scattering used baby diapers over its surface, I want first to highlight the following elements of Grierson’s text :
- But water alone won’t make gardens flourish in sand.
- So van Cotthem invented a ‘soil conditioner’ called TerraCottem. It’s an 8- to 12-inch layer of dirt impregnated with hydrogels, along with organic agents that nourish the natural bacteria in the soil.
- Until only recently, though, hydrogels were toxic, and skeptics doubted that they could ever be made safe for consumption.
1. The importance of water
According to our actual knowledge, plant life is totally impossible without water, every living plant cell containing a high percentage of it. Seeds can only germinate if sufficient water is present to start up the cell divisions within the embryo in the seed. Newly formed cells in the root(s), the stem and the leaflets need water to expand to their adult volume. A growing seedling, before breaking out of the seed, is therefore full of water. Once the primary root leaves the seed coat to enter in contact with the soil, it needs to find some moisture in the small cavities of that soil or at the surface of the moistened soil particles. If that minimal quantity of water is not available, the primary root will not continue its growth and die off rather quickly. So, water is absolutely necessary to get plants growing, particularly in sand.
But water alone won’t make gardens flourish in sand.
Seedlings, and later on young plants and even adult plants, need to absorb through their roots not only water, but a solution of mineral elements (nutrients) in water. Therefore, if one wants to “make gardens flourish in sand“, a number of nutrients have to be dissolved in the soil moisture to enable their uptake by the roots and their incorporation in some synthesis processes of the biomass, the plant body.
For this reason, it is interesting to know that the different hydro-absorbent hydrogels, that we have chosen to be components of the TerraCottem soil conditioner, not only absorb water but also the solution of nutrients in water. Inside the hydrogels, swollen into gel lumps when absorbing that solution, one will not only find a considerable amount of water, but also different major nutritive elements for the plants, e.g. Ca, Fe, N, P, K, S, …
This indicates clearly that the soil conditioner TerraCottem offers all the major elements for the plant’s growth, a lot of water and the major nutrients, to the absorbing roots.
Therefore, TerraCottem makes the gardens flourish in sand, water alone doesn’t.
2. The effect of TerraCottem on soil and plant
Grierson called TerraCottem: an 8- to 12-inch layer of dirt impregnated with hydrogels, along with organic agents that nourish the natural bacteria in the soil.
I want to precise that TerraCottem is NOT a layer of dirt impregnated with hydrogels, but a granular soil conditioner, a compound of more than 20 different substances (hydroaborbent polymers or hydrogels, mineral fertilizers, organic substances, rootgrowth activators and volcanic rock – for its exact composition see www.terracottem.com).
This compound of mineral and organic substances has to be mixed with an 8- to 12-inch layer of dirt in order to condition that “dirt” (the local soil), i.e. to give it a higher water retention capacity (with its hydrogels), a higher fertility (with its mineral NPK-fertilizers), a higher organic content (with its organic substances), a higher root activating property (with its organic root activators) and a higher air retention capacity (with its volcanic rock granules).
Mixing a certain dosage of TerraCottem soil conditioner with a given volume of dirt or soil creates all the different improvements mentioned above, resulting not only in the nourishment of the natural bacteria and other organisms in the soil, but principally in a better plant growth, in particular a maximal biomass production with a minimal of water. Yes, TerraCottem stimulates also the development of benign natural bacteria in the soil, and this in turn will activate the mineralisation process, setting free a lot of beneficial elements.
3. Toxicity and usefulness of hydrogels
A general description of hydrogel properties can be found at gz.e:
To understand clearly the nature, composition and significance of hydrogel applications, one can find a lot of information on Wikipedia (search “Hydrogels”).
A clear view on the history of super-absorbent polymers is given in http://en.wikipedia.org/wiki/Superabsorbent_polymer
“Until the 1980’s, water absorbing materials were cellulosic or fiber-based products. Choices were tissue paper, cotton, sponge, and fluff pulp. The water retention capacity of these types of materials is only 20 times their weight – at most.
In the early 1960s, the United States Department of Agriculture (USDA) was conducting work on materials to improve water conservation in soils. They developed a resin based on the grafting of acrylonitrile polymer onto the backbone of starch molecules (i.e. starch-grafting). The hydrolyzed product of the hydrolysis of this starch-acrylonitrile co-polymer gave water absorption greater than 400 times its weight. Also, the gel did not release liquid water the way that fiber-based absorbents do.
The polymer came to be known as “Super Slurper”. The USDA gave the technical know how to several USA companies for further development of the basic technology. A wide range of grating combinations were attempted including work with acrylic acid, acrylamide and polyvinyl alcohol (PVA).”
Polyacrylate/polyacrylamide copolymers were originally designed for use in conditions with high electrolyte/mineral content and a need for long term stability including numerous wet/dry cycles. Uses include agricultural and horticultural. With the added strength of the acrylamide monomer, used as medical spill control, wire & cable waterblocking”
From the Wikipedia-data above can be deduced that not all the highly water absorbent hydrogels are safe to be used in nature.
One of the parameters of our screening tests when developing the soil conditioner TerraCottem was precisely this possible toxicity of the hydrogels. At the end of the day we had to be sure that none of the TerraCottem hydrogels were toxic.
The TerraCottem website (www.terracottem.com) offers a lot of interesting information on the hydrogels, particularly in the section of
“Frequently asked questions about the TerraCottem soil conditioning technology” :
Once for 100% sure about the non-toxicity of the water absorbing hydrogels, we were able to add to them substances belonging to different chemical groups without any danger of creating problems with soil treatment.
Hossein OMIDIAN and Kinam PARK in the
“Biomedical Applications of Hydrogels Handbook”
express their concern about application of hydrogels in diapers as follows:
“Although the absorbent hydrogels can keep the skin area dry, there is a serious concern that these synthetic materials can increase the incidence of diaper dermatitis. Their non-biodegradability, toxicity, and environmental pollution are also of concern.”
Recently, descriptions of some alternatives for these “toxic” diapers have been published, e.g. the gDiapers, and the diapers from Seventh Generation.
The gDiapers description mentions two parts: a washable cloth part and a disposable, flushable liner, breaking down in the toilet. The Seventh Generation disposable diapers are said to be chemical free.
Here is the Handbook’s interesting summary:
“Crosslinked hydrophylic polymers provide superior physical, chemical, and environmental properties in their wet state. These features have made hydrogels invaluable in numerous disciplines including: hygiene, agriculture, biomedical, and pharmaceutical. Successful design of a hydrogel for a specific application requires careful understanding of the application and the environment that the hydrogel is intended to serve. Although challenging, a hydrogel can be tailored to address some special need in almost any discipline due to the wide spectrum of synthetic and natural hydrogel structures and processing technologies available.”
Several times, the hope has been expressed that the producers of disposable diapers would be willing to change the production process of their diapers to make them more environmentally friendly. However, websites of many disposable diaper manufacturers show only poor information on MSDS (Material Safety Data Sheets).
4. Properties of disposable diapers
Let me first list a number of interesting quotes from Wikipedia’s diaper description:
- The decision to use cloth or disposable diapers is a controversial one, owing to issues ranging from convenience, health, cost, and their effect on the environment.
- In the 20th century, the disposable diaper gradually evolved through the inventions of several different people.
- Disposable diapers were introduced to the US in 1949 by Johnson & Johnson.
- In 1956, Procter & Gamble began researching disposable diapers. Victor Mills, along with his project group including William Dehaas, both men who worked for the company, invented what would be trademarked “Pampers”.
- Over the next few decades, the disposable diaper industry boomed and the competition between Procter & Gamble’s Pampers and Kimberly Clark‘s Huggies resulted in lower prices and drastic changes to diaper design. Several improvements were made, such as the introduction of refastenable tapes, the “hourglass shape” so as to reduce bulk at the crotch area, and the 1984 introduction of super-absorbent material from polymers known as sodium polyacrylate that were originally developed in 1966.
Nowadays, and all over the world, every child wares diapers from its birth until it is potty trained (some 8000 diapers in 2 to 4 years). Due to their chemical composition, disposable diapers do not biodegrade easily, so that landfills contain a high percentage of these diapers.
Scientists studied the complete life cycle of different types of diapers (cloth ones and disposable ones): materials used, chemicals included, and energy consumed during production, usage and disposal. Their possible environmental impact on toxicity, acidification and eutrophication was analysed. A number of these studies showed that most of today’s diapers contain some toxic chemicals, which makes them useless to improve the soil qualities.
For a better understanding of this problem, one can read the Wikipedia-description of diapers:
An interesting study on the “USE OF DIAPER POLYMERS AS SOIL CONDITIONER” was published by a Portugese team:
Shahidian S., Serralheiro R.P., Serrano J., Machado R., Toureiro C. and Rebocho J.
In their introduction, the authors describe the properties and use of super absorbent polymers (SAP). They confirm that “Over the past years there has been a continuous reduction in their price and a generalized use of disposable diapers in the developed and some parts of the developing world. Although there are no global statistics, each child uses approximately 30 kg of polymers in his first two years of life, filling the landfills with around 400 kg of waste. However, diapers are not necessarily un-reusable waste, and SAPs have been successfully used as soil amendments to improve the physical properties of soil in view of increasing their water-holding capacity and/or nutrient retention, especially in sandy soils. SAP hydrogels potentially influence soil permeability, density, evaporation, and infiltration rates of water through the soils. Potentially, the hydrogels can reduce irrigation frequency and compaction tendency, stop erosion and water run off, and increase the soil aeration and microbial activity.
The objective of their study was “to evaluate the viability of recycling used diaper filling in agriculture, as a soil amendment. To achieve this goal, the effect of diaper filling on soil available water, crop water stress and production had to be studied, since diapers contain varying amounts of bleached cellulose fiber and other additives besides SAPs, which influence the overall effect of diaper addition to the soil.”
The study indicates that a diaper may contain as much as 10 g of SAP and that the polymer must be able to absorb liquids even when it is being pressed.
Concerning the use of polymers in agriculture, it was said that “over the past three decades both soluble and insoluble polymers have been used. Watersoluble polymers, such as polyacrylamides (PAM) have been used extensively to stabilize the soil structure and to increase infiltration and reduce runoff and erosion. Insoluble water-absorbing polymers can be divided into three main groups: the starch-graft co-polymers, the polyacrylate type widely used in disposable diapers, and the acrylamide-acrylate co-polymers, used in agriculture because of their great capacity to expand and absorb water under pressure, thus not only providing plants with water, but also helping to aerate the soil.”
The following beneficial effects of the hydrogels were listed:
- reduce irrigation frequency;
- reduce compaction tendency;
- stop erosion and water run off;
- increase the soil aeration;
- increase the microbial activity.
A study of the effect of an amendment of sandy soil with highly cross-linked polyacrylamide on Aleppo pine seedlings during water stress showed that the survival rates in 0.4% hydrogel were doubled, allowing the seedlings to tolerate drought for 19 days.
Another study showed that water retention capacity of a sandy soil was significantly increased by 23 and 95% with addition of 0.03 and 0.07% polymer, respectively, and water use efficiency increased by 12 and 19% with the application of 0.03 and 0.07% w/w polymer, respectively.
Addition of an hydrogel to saline soil improved seedling growth of a salt tolerant poplar species during a period of 2 years. Root length and surface area of treated poplars was 3.5 fold more than those grown in untreated soil. Hydrogel treatment enhanced the Ca2+ uptake and increased the capacity of that salt-tolerant poplar to exclude salt (i.e. reduces contact with Na+ and Cl-). This is another interesting aspect of hydrogel amendment, improving plant growth on somewhat saline soils.
The SAPs used in agriculture are polyelectrolyte co-polymers, often composed of acrylamide and potassium acrylate. This makes them swell much less in the presence of monovalent salts and collapse in the presence of multivalent ions, present in the soil or in fertilizers.
Most SAPs are moderately bio-degradable in the soil, converting finally to water, carbon dioxide and organic matter, leaving no undesirable chemicals in the soil or in the environment. No adverse effect has been shown on microbial populations and their toxicity for mammals is almost nonexistent.
In its experiments, the Portugese team used only new diapers in order to isolate the influence of the diaper SAP and fiber from that of the urea and other organic compound present in used diapers. The treatment plots received 100g per square meter of dry diaper content (the equivalent of 10 diapers), which was mixed in the 0.2 m topsoil prior to planting. This is roughly equivalent to 0.2 g per kg of soil. Thus, diaper filling (cellulose and SAPs) were added to soil at the lower limits recommended by literature. Where other researchers found that SAPs enhance available water in the soil, the Portugese team reported that the adding of diaper filling had a negative effect on both available soil water and crop production. Thus, their data are not in line with the general findings: SAPs increase crop survival and biomass production. It was therefore decided to carry out further experiments, especially with different concentrations of diaper fillings and different crops in order to encounter the right balance for using diaper fillings as a soil ameliorant.
5. Components of a typical disposable diaper
The basic components of a typical disposable diaper are already described in detail by Richer Investment Diaper Consulting Services (2007):
- A back sheet, preventing liquids from leaking out of the diaper, made of plastics (polyethylene) or breathable cloth-like material.
- A special tissue paper with high elasticity and wet strength, used as a carrier for the pad.
- Hot melts (resins, oils, tackifiers) to glue the different components of the diapers (pad and elastics).
- Hydrophobic Non-woven: top sheet for the leg cuffs to prevent leakage, made of polypropylene resin.
- Hydrophylic Non-woven: top surface that is in contact with the skin, with surface surfactants allowing the liquids to flow into the diaper core.
- Elastics in cuffs for waist and legs, made of polyurethane of polyester foam.
- Lateral tapes for mechanical grip, made of velcro or polypropylene adhesive tabs.
- Frontal tapes to facilitate multiple repositioning of the lateral tape, made of polypropylene film.
- Cellulose pulp from pine trees in the pad for absorbing liquids in the void capillaries between the fibers.
- Acquisition and distribution layer between the top sheet and the absorbent core to provide a sense of dryness by additional separation between the pad and the skin, made of non-wovens or fibers.
- Sodium polyacrylate (super-absorbent polymer or SAP): fine granules to improve liquid retention and keep the pad thinner (less pulp). In contact with water, the sodium detaches itself and the polymer absorbs water, solidifying into a gel.
- Top Sheet surface add-on lotions, like Aloe vera, vitamin D or E, almond oil, oat extract, jojoba, etc.
- Decorated films (different inks) and wetness indicators.
6. Disposable diapers and the environment in the past
The American Real Diaper Association described a number of diaper facts (health, environment, dryness and rash, cost):
Here are some facts about the environment:
- Based on their calculations, they estimated that 27.4 billion disposable diapers are consumed every year in the U.S. and 92% of all single-use diapers end up in a landfill.
- In 1988, nearly $300 million dollars were spent annually just to discard disposable diapers, whereas cotton diapers are reused 50 to 200 times before being turned into rags. No one knows how long it takes for a disposable diaper to decompose, but it is estimated to be about 250-500 years.
- Disposable diapers are the third largest single consumer item in landfills, and represent about 4% of solid waste.
- Disposable diapers generate sixty times more solid waste and use twenty times more raw materials, like crude oil and wood pulp.
- The manufacture and use of disposable diapers amounts to 2.3 times more water wasted than cloth.
- Over 300 pounds of wood, 50 pounds of petroleum feedstocks and 20 pounds of chlorine are used to produce disposable diapers for one baby EACH YEAR.
- In 1991, an attempt towards recycling disposable diapers was made in the city of Seattle, involving 800 families, 30 day care centers, a hospital and a Seattle-based recycler for a period of one year. The conclusion made by Procter & Gamble was that recycling disposable diapers was not an economically feasible task on any scale.
7. Disposable diapers and the environment in the future
It goes without saying that the discarding of disposable diapers is one of the major problems for the environment (see figures above).
Taking into account :
- That the global landfills contain billions of tons of used disposable diapers (4 % of all solid waste);
- That the disposable diapers are still made of synthetic materials that biodegrade extremely slowly in landfills;
- That the presence of some toxic synthetic materials in today’s diapers may create a number of health problems;
- That the presence of water absorbing sodium acrylate
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