The trapzene field trial was performed at Robinson Phillips Coal Company refuse site near Marianna, in Wyoming County, West Virginia. This site historically experienced acid mine drainage problems for fifteen (15) to twenty (20) years. The site has refuse from the Sewell, Gilbert, and Red Ash coal seams mined in Wyoming County. The Red Ash coal seam refuse is believed to be the source of acid mine drainage, which was the first refuse material to be disposed at the site. Total sulfur on the Red Ash coal seam ranges from 0.7 to 1.3 percent, with the pyritic sulfur being approximately 0.6 to 0.9 percent.
Water emanating from the pile ranges from 3.2 to 3.8 in pH, acidity 99.6 to 170.6 mg/L, iron 21.1 to 29.4 mg/L, manganese 12.5 to 14.3 mg/L, aluminum 3.2 to 4.1 mg/L, sulfates 680 to 2,054 mg/L, conductivity 1,845 to 1,996 u/cm, dissolved solids 1,145 to 1,378 mg/L, calcium 171 to 209 mg/L, and magnesium 90 to 120 mg/L.
Two (2) sumps were selected for monitoring the treatment with trapzene. The water from these sumps discharged into two (2) ponds where more treatment could be performed utilizing caustic, if needed, to insure compliance with the NPDES program. The sumps were chosen for primarily three (3) reasons.
- To see if trapzene could effectively remove metals,
- To see if trapzene alone could neutralize the acid mine drainage, and
- To compare sludge generation to sodium hydroxide treatment.
A ten (10) percent slurry of trapzene was used to obtain a 0.25 g/liter dosage proportional to flow in order to duplicate lab tests performed by West Virginia University. A skid was set up at the site which contained a mixer to constantly mix the trapzene slurry, and an air pump was used to feed the trapzene into the acid mine drainage. An existing small mixing box was utilized to give the slurry contact more time and better mixing with the acid mine drainage. The treatment was started on May 29, 1991, and the sumps were sampled on May 30, 1991; eighteen (18) hours after the slurry of trapzene was introduced in the raw water entering Sump 1. The pH of the water going into the sump was regulated at 6.0 to see if oxidation of manganese could be achieved at a lower pH than normally used for manganese removal.
The pH of the Sump 1 discharge was 7.0, with no measurable acidity. Iron was 4.2 mg/L, manganese 2.6 mg/L, aluminum 2.0 mg/L, and alkalinity 53.0 mg/L. The Sump 2 discharge has a pH of 7.2, with no measurable acidity, iron 1.0 mg/L, manganese 1.6 mg/L, aluminum 1.2 mg/L, and alkalinity 48.0 mg/L. Data similar to this was collected on June 4 and 5, 1991, as shown on the data sheet.
On June 6, 1991, the trapzene flow was cut back to see at what point the manganese level would rise out of compliance according to the NPDES standard of 2.0 mg/L. The pH at the point of treatment was near 5.0. Sump I at the discharge point, proved to have a 6.2 pH, with no measurable acidity, iron 3.5 mg/L, manganese 4.9 mg/L, alkalinity 52.2 mg/L, and aluminum 1.7 mg/L. Sump 2 discharge proved to have a 6.3 pH, with no measurable acidity, iron 0.8 mg/L, manganese 3.8 mg/L, alkalinity 37.4 mg/L, and aluminum 1.1 mg/L. The treatment rate was maintained, and samples were collected from the sumps, which again almost duplicated the data on June 7, 1991.
After reviewing the analytical data and observing the sludge generation, it was concluded that:
- Metals did precipitate, and at a lower pH manganese was removed,
- Acid neutralization was achieved, and
- Sump 1 was approximately one-third full of sludge after a ten (10) day trial. (These sumps had to be cleaned every two (2) weeks when sodium hydroxide was used.) Sludge production was reduced substantially (60 - 70 percent), and a more stable and compact sludge was produced.
The site consists of a small, heated shed located between two (2) retention ponds located at the base of an old coal strip mined hill side. The upstream pond acts as a reservoir for a seep of acid runoff from the immediate hillside as well as a control point for several upstream ponds acting as similar collection points. The downstream pond acts as a reaction vessel and sludge settling basin for treated water. The shed has been historically used as a metering and mixing point for caustic treatment of the water as well as a testing area for briquet treatment. Within the shed is a concrete channel running down the middle of the floor with a removable weir and a small sump pit at the downstream end of the shed. The sump is drained by a twelve (12) inch PVC elbow with the end pointing to the bottom of the sump. The sump volume was approximately eight (8) cubic feet, and had flow rates of five (5), twenty (20), and fifty (50) gallons per minute.
The raw water had a pH of 4.2, with an average metals content of 102.0 mg/L manganese, 0.7 mg/L iron, and 28.0 mg/L aluminum. The acidity averaged 411.0 mg/L. A feed rate of 0.63 grams/liter proved adequate to reduce the metals to an average of 2.66 mg/L manganese, 0.1 mg/L iron, 0.34 mg/L aluminum, and acidity was less than 1.0 mg/L. The pH at the pond discharge averaged 7.94. On one (1) day of the trial, the pH was dropped to 5.5 at the outfall of the pond, and the manganese content rose to 28.4 mg/L. Trapzene was then mixed with water and sprayed on the pond which proved successful in reducing an out of compliance manganese level to meet standard limits within a very short time.
Presently, a trial is being performed at Omega Mining Company near Morgantown, West Virginia. A dry feed system is being utilized instead of the slurry mixture. An in-line aeration system designed by Techni-Flow, Inc. will also be utilized to see if oxidation is enhanced, and chemical use reduced.
Also, another trial is planned at Shrewsbury Coal Company near Belle, West Virginia, to utilize briquettes for low flow sites. This trial will determine if oxidation of manganese can be achieved especially with sediment ditches of on-bench drainage design. Trapzene briquettes will be available for this trial in approximately two (2) weeks.
