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ENVIRONMENTALLY-FAVORABLE EROSION CONTROL
WITH A POLYVINYL ACETATE-BASED FORMULATION

Jennie Crowley
Technical Marketing Specialist
Cognis Corporation
Cincinnati, Ohio

Dr. Doris Bell
Soil Ecologist
Cognis Deutschland GmbH
Duesseldorf, Germany

Dr. Bettina Kopp-Holtwiesche
Microbiologist
Cognis Deutschland GmbH
Duesseldorf, Germany

ABSTRACT

A polyvinyl acetate-based formulation is a biodegradable, liquid soil stabilizer for soil and seed protection from wind and water erosion. It is currently used for erosion control solutions in the United States and around the world.

This polyvinyl acetate dispersion forms a three-dimensional membrane structure that holds seeds and soil in place, yet, allows water and oxygen to penetrate. This formulation can be applied using hydroseeding equipment and other conventional spray equipment, minimizing labor requirements.

Due to its excellent eco-toxicological profile, it is ideal for all soil and seed stabilization applications especially in environmentally sensitive areas. Furthermore, polyvinyl acetate exceeds the minimum standards for slope protection and performs as well as other slope protection products. In addition, it is biodegradable and non-phytotoxic. Results from performance tests indicate that polyvinyl acetate reduces the water demand of plants in both dry and moist soil conditions.

This paper presents the detailed results of the testing performed on a polyvinyl acetate-based formulation including slope protection, water savings, dust suppression, biodegradability, and eco-toxicity.

Key words: polymer, erosion control, slope protection, chemical soil stabilizer, heavy-duty soil binder

BIOGRAPHICAL SKETCHES

Jennie Crowley
Jennie Crowley earned a Bachelor of Science in Chemical Engineering from the University of Cincinnati. She is currently working for Cognis Corporation as a Technical Marketing Specialist. In this role, she is responsible for new product introduction in the United States. Jennie is also a member of the IECA.

Doris Bell, Ph.D.
Doris Bell, Ph.D., soil ecologist, has been working in the landscaping and reclamation industries for 16 years. Since 1998, she has been working for Cognis Deutschland as a Technical Marketing Specialist. In this role, she is responsible for managing the research and development of Cognis’s Soil Cure line, a product line for soil and plant protection.

Bettina Kopp-Holtwiesche, Ph.D.
Bettina Kopp-Holtwiesche, Ph.D., microbiologist, has been working on multiple international biotechnology projects for more than 25 years. During the last ten years she was responsible for diverse product and technological developments especially on soil problems and was honored in 1994 with the European invention award. Most recently, she has lead the development of Cognis’s Soil Cure line, including products for erosion control, plant health, and soil conditioning.

I. INTRODUCTION

Exposed soil layers, in all climatic zones, are subject to constant erosion by wind and water. Fertile layers of humus are carried away, and seeds — whose root systems would normally stabilize the subsoil layers — cannot take a firm hold. As a result, the surfaces of slopes and embankments are subjected to erosion. Remediating these landslides is a costly and time-consuming procedure involving a great deal of labor. To prevent unnecessary and expensive damage, efficient and economic solutions are required. Polyvinyl acetate offers a long-term (12-18 months) and cost efficient solution to all revegetation projects.

Increasing environmental consciousness, and the growing recognition that labor reduction is a key for business survival, have led to the development of a soil stabilizing polymer dispersion based on polyvinyl acetate, known as Land-GrabÒ Soil Stabilizer. This polyvinyl acetate dispersion provides protection of the seed and soil from erosion by wind and water. This aqueous homopolymer dispersion contains raw materials that are used as cosmetic and food additives. On a long-term scale, the product is completely biodegradable. This formulation has an excellent eco-toxicological profile. No toxic side effects on the ecosystem, including plants, soil bacteria, and fungi, have ever been observed.

The product can be added directly to the hydroseeding equipment or applied via sprayer after dilution. Other applications are possible including dust suppression. The product is not only characterized in comprehensive lab and pilot testing but also has proven its effectiveness in multiple commercial applications. Using polyvinyl acetate dispersions as a soil stabilizer in mining revegetation projects or in golf course construction is quite common in Germany, and increasingly in other European countries, the Middle East, Northern Africa, and Asia.

II. BENEFITS

Polyvinyl acetate is a "liquid crust" that strengthens the surface of the soil. It forms a three-dimensional network structure in the upper 1-2 centimeters of the soil resulting in several beneficial effects. It fixes valuable seed material to the soil grains and promotes germination. Rain and oxygen are able to permeate through the "crust." This polyvinyl acetate dispersion holds water in the soil longer and protects the soil and plants from rapid dehydration.

Benefits proven through extensive testing of a polyvinyl acetate dispersion include:

• 2-5 days earlier germination
• more than a 20% higher germination rate of grasses
• higher degree of coverage
• water retention in the range of up to 40 %
• reduction in soil losses due to strong precipitation
• prevention of sediment losses due to wind erosion

III. EFFECTS ON SEDIMENT LOSS

With the polyvinyl acetate-based formulation, slope protection was highly efficient under simulated high precipitation, e.g., for a 1:3 slope (loamy soil) less than 30 percent of soil loss was observed compared to the untreated plots. After a field trial conducted at Texas Transportation Institute, the product successfully passed all currently adopted performance standards for Class 1 applications. In this survey, the density of the vegetative cover was 24 percent higher than the untreated control (clay) and 67 percent higher than the sand plot.

Observations from field trials in France, as well as from wind tunnel measurements indicate a secure protection against soil losses caused by strong winds. Depending on the soil type, a dosage of 10 g/m2 (for silt) and 45 g/m2 (for sand) will resist wind speeds up to 140 km/hr.

IV. EFFECTS ON SOIL MOISTURE AND SEED GERMINATION

As the polyvinyl acetate dispersion builds up a three-dimensional network in the topsoil — comparable to a "liquid crust" — it does not affect soil’s permeability to rain or oxygen, but retains moisture longer in the soil. On turfgrass consisting of Kentucky bluegrass (Poa pratensis), polyvinyl acetate treated plots showed a ten percent higher water content in the soil. In irrigation trials, a water savings potential of about 30 percent has been proven.

Field trials in Algeria confirmed a significant water retention effect with a polyvinyl acetate dispersion, while untreated plots lost 30 to 40 percent of its moisture content. With polyvinyl acetate, turfgrass species germinated two to five days earlier than in the control. Furthermore, the germination rate of polyvinyl acetate-treated turfgrass plots was 20 percent higher. These advantages were significant for at least 6 weeks after treatment and seeding, which is the whole vegetation period until complete turf establishment. Due to the seed fixing and water retaining properties, the product offers an economic solution to vegetation projects, especially in arid or water-restricted areas.

V. EFFECTS ON GERMINATION

Polyvinyl acetate was tested under controlled conditions at the University of Guelph for effects on germination of turfgrass species. Plots consisted of sandy soil, with high stone content and were maintained with low-medium maintenance. A noticeable acceleration (of 2-5 days to 50%) in germination and establishment was noted in three of the four species treated with the commercially available polyvinyl acetate dispersion versus the control plots.

Thus, it is clear that the product has no detrimental effects on seedling germination and establishment. In fact, it can enhance germination in many instances.

VI. LABORATORY TESTING

Several studies were conducted on the polyvinyl acetate dispersion including a series of tests performed by LUFA in Speyer, Germany, and at the Agricultural Research Institute at the University of Bonn, Germany. The test results were as follows:

These results demonstrate the improvement in soil structure that this polyvinyl acetate-based formulation provides over an untreated plot.

In addition, tests were conducted on lettuce seedlings to determine water savings. The results clearly indicate the ability of the product to reduce water demand. The biomass was compared to control plants under the same conditions. The results were as follows:

Soil moisture is defined as the percentage of maximum water carrying capacity. Water demand reduction is the percentage reduction in water required to yield an identical plant biomass.

VII. FIELD TRIALS

Soil Moisture Retention

At a field trial in Algeria, polyvinyl acetate dispersion was tested to determine the water savings. In sandy soil vegetated with grass and at temperatures of 35-40^° C, the following soil saturation was observed:

Soil Stabilization

AUSTRALIA

A field test, conducted in Victoria, Australia, demonstrated the soil stabilization performance of the polyvinyl acetate dispersion. The test site was an embankment along a freeway extension. The slope of the site was approximately 60° . The soil was a loose clay and topsoil mixture with a heavy solid clay base. Temperatures averaged 18 to 25° C. Rainfall was intermittent and approximately 10-15 mm each time.

Two plots were treated with the polyvinyl acetate dispersion using a hand-held spray gun. A third plot was left untreated to act as the control.

Photograph 1. Immediately following application in Victoria, Australia. Untreated plot is on the left.

After two weeks, noticeable differences between the treated and control plots were observed. The untreated plot developed rilling as pictured in Photograph 2. In addition, sediment was collected against the silt fence placed at the base of the plots that had run-off of the untreated plot. See Photograph 3.

Photograph 2. Two weeks following application in Victoria, Australia. Sediment build-up at base of untreated plot.

Photograph 3. Two weeks after application in Victoria, Australia. Notice rilling in untreated plot on the left.

At the end of five weeks, grass germination was greater on the treated plots as shown. See Photograph 4.

Photograph 4. Five weeks following application in Victoria, Australia. Untreated plot is on the left.

MALAYSIA

Polyvinyl acetate was applied on slopes in Malaysia along the Puchong — Shah Highway Interchange to demonstrate the stabilization and germination characteristics of polyvinyl acetate. This trial covered an area of 2500 m². The dispersion was applied using hydroseeding equipment and the typical constituents including seed, mulch, fertilizer, binder, and water.

One slope was divided into three sections to apply the dispersion at varying rates. See Photograph 5. A second slope was used to demonstrate the ability of a polyvinyl acetate dispersion to germinate seeds on rocky, barren soil on severe slopes. See Photograph 8. Two weeks after application of the product, grass was germinating on the first slope. See Photographs 6 and 7. Less than two months after application, the rocky slope was vegetated. See Photograph 9. The results of the trial demonstrate that polyvinyl acetate can be applied as a soil consolidator as well as a binder in the hydroseeding process.

Photograph 5. Application of polyvinyl acetate-based formulation in Malaysia.

Photograph 6. One week following application.

Photograph 7. Two weeks following application.

Photograph 8. Product application in Malaysia on steep slope comprised of rock and sandy soil.

Photograph 9. Rocky slope 54 days following product application.

Long and Short-term Dust Suppression

BULGARIA

Two studies were conducted by the Geological Institute at University of Mining and Geology in Bulgaria on two fine-particle, waste stockpiles using polyvinyl acetate. Both studies indicate the stabilization and germination properties of polyvinyl acetate under extreme wind erosion. The Kremikovtzi ShH waste stockpile proves the long-term dust suppression capabilities of a polyvinyl acetate dispersion using tolerant grass species. The TPP Maritza-Iztok 2 study demonstrates short-term dust suppression using only the polymer dispersion.

Photograph 10. Application of product via helicopter.

Study 1 — Kremikovtzi ShH

The polyvinyl acetate dispersion was diluted to 10% with water and applied at 15 g/m² via helicopter, type Kamov 26, onto the tailings pond surface of Kremikovtzi ShH. See Photograph 10. The pond is subjected to continuous wind and water erosion. Conditions of the test site were as follows:

• 0.8 km² total surface area
• Moisture content of only
• 2.5% at 0-10 mm
• 16% at 10-100 mm
• Chemical Analysis
• 73% Fe₂O₃
• 5% SiO₂
• 6% CaO
• 1.4% MgO
• 1.3% Al₂O₃
• Ambient temperature 31-35° C
• Rainfall for July was 25 mm
• Wind speeds averaging 9-12 m/s, up to 20 m/s
• Particle sizes of wastes were below 1 mm and could be eroded by wind at 5 m/s.

A full vegetative cover was observed 40 days following the treatment, despite low moisture content in the soil, low rainfall, and high temperatures.

In addition, dust levels reduced to background levels immediately following the product application. The waste stockpile has remained as such and fully vegetated since the application.

Study 2 — TPP Maritza-Iztok 2

Two fly-ash waste piles from a thermoelectric power plant (TPP) at Maritza-Iztok 2 were treated with a polyvinyl acetate dispersion to prevent dust generation. Conditions of the test site were as follows:

• 1 km² total surface area
• Particle sizes of wastes were below 1 mm and could be eroded by wind at 5 m/s.

The product was applied via helicopter at a rate of 30 g/m2 and a 1:10 dilution rate.

The dust was completely suppressed for over one year immediately following product application.

VIII. BIODEGRADABILITY

The polyvinyl acetate dispersion slowly degrades over 12 to 18 months. The rate of degradation will be accelerated in moist soil conditions and those with a high organic content. The primary degradation product of the polymer is classified as "inherently biodegradable" according to the modified Zahn Wellens Test (OECD 302B.) The proprietary additives in the commercially-available product have been classified as "readily biodegradable," in accordance with stringent closed bottle test (OECD 301D) and screening test for evaluation of ultimate biodegradability; BOD28/COD>60%.

IX. ECO-TOXICOLOGICAL PROFILE

No toxic effects of the commercially available polyvinyl acetate dispersion against plants, soil bacteria, and fungi are known. Acute toxicity of the primary degradation products of the ingredients is accordingly very low. Please see table.

X. APPLICATION

The commercially available polyvinyl acetate formulation is a liquid product that can be added directly into the tank of the hydroseeder along with the seed, mulch, fertilizer, and water. It requires minimal labor for application. The product may also be applied via traditional spray equipment. After use, the equipment can be cleaned with just water.

XI. OTHER PRODUCTS FOR SOIL STABILIZATION

Other products used for erosion control and revegetation on steep slopes include:

• Other liquid soil stabilizers such as polyacrylamides and polybutadienes
• Physical soil stabilizers including geosynthetic mats, polymer resin mats, coir blankets, and straw blankets

Due to the high cost and labor intensive characteristics of physical and mechanical methods for erosion control, the polyvinyl acetate formulation is ideal for stabilizing soil on both steep slopes and flat surfaces. The polyvinyl acetate-based formulation is less expensive and requires minimal labor during application.

Another liquid soil stabilizer is polyacrylamide. Its mode of action is completely different from a polyvinyl acetate formulation. Polyacrylamide precipitates fine soil grains and thus reduces erosion. However, PAM does not "glue" the particles like polyvinyl acetate. Thus, polyacrylamide is not suitable for steep slopes. In addition, polyacrylamide is not biodegradable.

Polybutadiene is currently seldom used for erosion control. The raw materials used for polybutadiene emulsions are used in painting products and are not biodegradable. In addition, solvents are necessary to keep the product liquid.

XII. SUMMARY

This polyvinyl acetate-based formulation provides an environmentally friendly and labor-minimizing solution to water and wind erosion control problems and revegetation requirements. In addition, this formulation can provide water savings and increased germination. The formulation and its attributes have been proven around the world in field trials and laboratory tests.

REFERENCES

Carey, Ken. 1998. "Effects of Land-Grab soil amendment on soil stability of seeded Kentucky bluegrass, perennial ryegrass, fine fescue, and tall fescue."

Hadjiev, A., and P. Hadjiev, 1998. "Protective Covering Layers on Waste Stockpiles."

Northcutt, Paul and Jett McFalls. 1999. "Final Performance Analysis through the 1998 evaluation cycle."

Weller, H. And Gillman. 1998. "Pot Tests on Water Saving by Soil Treatment with ‘Land-Grab SC-823’."