Abstract: A mixed aerobic-anaerobic microbial treatment process was developed previously for acid mine drainage (AMD) using straw as a substrate. The process was effective only if AMD was supplemented with sucrose. The present study was conducted to determine which, if any, of three cellulosic materials could sustain the microbial treatment of AMD without the addition of a sucrose amendment and to determine the effect of the retention time on the performance of the reactors. The performance of small reactors that treated simulated AMD in the continuous mode was evaluated using alfalfa (Medicago sativa L.) hay, timothy (Phleum pratense L.) hay, and straw with a 5 d retention time. Parameters measured were pH, Fe, Al, sulfate, and ammonium. Timothy hay and straw sustained AMD mitigation for 3 wk, and thereafter all activity ceased. After the reactors ceased treating AMD, the mitigative activities were reinitiated by the addition of sucrose, but not by urea. Alfalfa sustained AMD mitigation for a longer time period than either straw or timothy. The effect of three retention times, 3.5, 7, and 35 d, was then investigated for reactors containing fresh alfalfa. Increasing the retention time resulted in better metal removal and a greater pH increase. With a 7-d retention time, 75 L of simulated AMD were neutralized from a pH of 3.5 to a pH value greater than 6.5. Reactors operating with a 3.5-d retention time treated only 58.3 L of simulated AMD before failing. Ammonium was detected in effluents of active reactors. The results of this study indicate that a low maintenance microbial treatment system can be developed with alfalfa as a substrate without the addition of a sucrose amendment.

Abstract: The water treatment performances of two anoxic limestone drains (ALDs) were evaluated. Anoxic limestone drains are buried beds of Limestone that are intended to add bicarbonate alkalinity to flow-through acid mine drainage. Both ALDs received mine water contaminated with Fe2+ (216-279 mg L(-1)) and Mn (41-51 mg L(- 1)). Flow through the Howe Bridge ALD increased alkalinity by an average 128 mg L(-1) (CaCO3 equivalent) and Ca by 52 mg L(- 1), while concentrations of Fe, K, Mg, Mn, Na, and SO42- were unchanged. The Morrison ALD increased alkalinity by an average 248 mg L(-1) and Ca by 111 mg L(-1). Concentrations of K, Mg, Mn, and SO42- all decreased by an average 17%, an effect attributed to dilution with uncontaminated water. Iron, which decreased by 30%, was partially retained within the Morrison ALD. Calcite dissolution was enhanced at both sites by high P- CO2. Untreated mine waters at the Howe Bridge and Morrison sites had average calculated P-CO2 values of 6.39 kPa (10(- 1.20) atm) and 9.24 kPa (10(-1.04) atm), respectively. At both sites, concentrations of bicarbonate alkalinity stabilized at undersaturated values (SICalcite = 10(-1.2) at Howe Bridge and 10(-0.8) at Morrison) after flowing through approximately half of the limestone beds. Flow through the second half of each ALD had little additional effect on mine water chemistry. At the current rates of calcite solubilization, 17.9 kg d(-1) CaCO3 at Howe Bridge and 2.7 kg d(-1) CaCO3 at Morrison, the ALDs have theoretical effective lifetimes in excess of 20 yr. By significantly increasing alkalinity concentrations in the mine waters; both ALDs increased metal removal in downstream constructed wetlands.