Mine Soil Remediation Using Compost and Coal Ash Mixtures A Project in Progress Donald L. Cawthon and John J. Sloan

Department of Agricultural Sciences,
        Texas A&M University-Commerce

Texas A&M University Agricultural Research and Extension Center-Dallas,
        The Texas A&M University System

Central and Southwest Services

Southwestern Electric Power Company

HIE Consulting
 
 

 To document the effects of utilizing coal ash products in conjunction with composted agricultural wastes and biosolids to produce an environmentally safe/effective soil amendment.
 
 

The production of some coal combustion by-products continues to exceed the rate of use, and development of beneficial/value added utilization strategies is advantageous.  In several studies, fly ash amendments have improved the physical properties of both heavy clay and sandy soils, and to a lesser extent, improved chemical soil properties depending upon the qualities of the fly ash amendment.  Less information is available on the use of bottom ash and flue gas desulfurization ash (FGD) for similar purposes.  Agricultural concerns associated with the utilization of coal ash products are basically limited to salinity and heavy metal content.

Re-vegetation of any tract of land suffering from topsoil depletion due to wind/water erosion, highway construction, mining activities, etc., would benefit from addition of a topsoil layer or incorporation of an appropriate amendment.  An effective soil amendment should contain essential plant nutrients and organic material; foster the re-establishment of soil microbiology; reduce the environmental and food-chain risks associated with heavy metals, and provide suitable physical qualities to soil and overburden material for promotion of rapid root establishment and shoot growth.
 
 

• Identify blends of fly/bottom ash/FGD and composted agricultural wastes/biosolids suitable for supporting plant growth when used as a soil amendment mixed with overburden material from a coal-mining site.
• Document the physical (water holding capacity, bulk density, porosity) and chemical (macro/micro plant nutrients, pH, salinity, heavy metals) properties of the amended soils.
• Evaluate the ability of composted waste products to reduce water leaching and/or plant uptake of heavy metals when incorporated as soil amendments in overburden material.

This project will include greenhouse evaluations of plant growth in prepared growth media, laboratory analysis of the physical and chemical growth media properties and plant tissues, and laboratory analysis of leachate collected from the growth media.  Experiments will be adequately replicated to generate reliable statistical analysis of data.  Annual ryegrass will be used as a model plant species in the greenhouse.
 
 

• Identification of appropriate blends of composted organic materials/coal ash to support plant growth when use as a soil amendment.
• Documentation of the ability of composted agricultural wastes and biosolids to reduce heavy metal plant uptake.
• Estimation of the ability of composted agricultural wastes and biosolids to reduce heavy metal NPS loading of watersheds.
• Necessary insight to develop on-site field-scale studies at coal mining facilities and/or highway ROW's.

Growth media will be blended using a greenhouse soil mixer and samples will be collected, dried and stored for later nutrient and heavy metal analysis.  Additional growth media samples will be placed in 5.1 cm diameter by 15.2 cm long leachate collection cylinders and leached with 1.0 liter of distilled water.  The collected leachate will be analyzed for heavy metal content.  Physical properties of additional samples will be tested using soil porometers.

Ryegrass seeds will be direct seeded into 6 inch azalea pots containing experimental media blends in early November.  Plants will be watered as needed.  Plant height and visual evaluations will be determined prior to harvest.  Above-ground plant parts will be harvested, oven-dried to determine dry weight accumulation, and tissue samples will be analyzed for nutrient and heavy metal content.

 Data will be analyzed by Analysis of Variance and LSD will be used for means separation.
 
 

Collection of materials:

Coal combustion by-products including bottom ash and scrubber sludge (a combination of fly ash and FGD material) was collected from the Pirkey Power Generating Plant in September, 1998.  The Pirkey generating facility is located near Hallsville, Texas and burns lignite coal.  Bottom ash was also shipped by Central and Southwest Services from their Northeastern 3 and 4 power generating plants located in northeastern Oklahoma.  These generating facilities burn western coal.

Overburden material and topsoil was collected from Sabine Mining Company located near Hallsville, Texas.  All products were transported to Texas A&M University-Commerce.

Composted dairy manure was collected in Como, Texas from a 400-cow freestall dairy facility using in-vessel composting procedures.  Poultry litter was supplied by Pilgrim's Pride Corporation and was composted using in-vessel composters on the TAMU-Commerce campus.  Composted biosolids was collected after the completion of an in-vessel composting demonstration conducted for the City of Hot Springs, Arkansas.

Material preparation and blending:

All ash and soil materials were allowed to air-dry and were passed through a hammermill to make particle sizes more uniform.  Composted organic materials were screened to remove any large particles. Bottom ash and scrubber sludge from the Pirkey Generating Plant were individually blended with composted dairy cattle manure, poultry litter, or biosolids at the rates of 0, 33, 66 and 100%.  These blends were then further blended with overburden material using 55, 70, 85 or 100% of the overburden in the total mix.

Bottom ash from Northeastern 3 and 4 generating facilities was blended with composted poultry litter at the rates of 0, 33, 66 and 100%.  These blends were then further blended with topsoil using 55, 70, 85 or 100% of the topsoil in the total mix.

All blended materials were transported to the Texas A&M University Agricultural Research and Extension Center in Dallas.  The blended soils were placed in 6-inch azalea pots, labeled and randomly positioned inside the greenhouse for later seeding.
 
 

Dr. Don Cawthon, Texas A&M University-Commerce
Mr. Todd Freeman, Texas A&M University-Commerce
Dr. John Sloan, Texas A&M University Agricultural Research & Extension Center-Dallas
Mr. Howard Selman, HIE Consulting
Mr. Walt Kletzker, Central and Southwest Services
Mr. Mike Tatterson, Central and Southwest Services
Mr. Neal Baremore, Southwestern Electric Power Company
Mr. Bobby Welch, Pirkey Power Generating Plant