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2-1994 Wetlands: Mechanisms For Treating Acid Mine Drainage David C. Ditsch University of Kentucky, [email protected]

Anastasios D. Karathanasis University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits oy u.

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Repository Citation Ditsch, David C. and Karathanasis, Anastasios D., "Wetlands: Mechanisms For Treating Acid Mine Drainage" (1994). Agronomy Notes. 47. https://uknowledge.uky.edu/pss_notes/47

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Vol. 27, No.3, February 1994 . WETLANDS "Mechanisms For Treating Acid Mine Dra.inage" David C. Dilsch and A.D. Karathanasis

Introduction authorities to monitor discharge. current understanding ofthe chemical A great deal of attention has Currently, Kentucky requires a pHof and biological processes associated beengiven to wetlands in recent years. 6.0-9.0, and an averagedaily instrearn with AMD amelioration utilizing Research suggests that natural and/or iron and manganeseconcentrationnot wetlands technologies. constructed wetlands may play a to exceed 3.5 and 2 ppm, respectively. valuable role in flood flow moderation, Traditional treatment of Role ofWetland Plants and sediment retention and stabilization, AMD involves collecting drainage in Substrates and waste water treatment while ponds and adding alkaline reagents Early attempts to duplicate providing habitat for game and such as caustic soda or lime and natural wetlands receiving AMD nongame wildlife. Only within the aeration to neutralize acidity and simply involved planting cattails last 10 years have wetlands received precipitate metals. This treatment (Typha sp.) in existingsediment ponds serious attention in the treatment of method is costlyintermsofequipment, on mined sites. The hypothesis was acid mine drainage (AMD). chemicals, andmanpower. Inaddition, that the vegetation would spread and Large volumes of geologic this form ofAMD treatment must be the discharge would be treated. In in~finite material are exposed to the continued for an period. many cases, the vegetation either did environmentduringthe miningofcoal Estimates of this eost to the coal not proliferate ordied and the wetland and metal. Pyritic minerals (FeS,) industry exceed $1 million per day remainedineffectiveintreating AMD. commonly associated with coal and (K1einmann 1990). These failures prompted further metal deposits are subsequently Researchers at Wright State research to characterize more exposed to air and water (oxidized University and West Virginia thoroughly the substrates and and hydrolyzed) resulting in AMD. Un}versity (WVU) independently vegetation most effective in treating Thesedischargewaterstypically have notedthatAMDfrom abandonedmine AMD and to gain a better a low pH and high level s ofiron and lands was improved in quality after understanding of other important sulfate. Due to the elevated acidity, passing through natural moss parametersinthe biochemicalprocess. increased solubility of other metals (Sphagnum) wetlands in Ohio and suchas AI, Mn, Cu, and Zn associated WestVirginia(Huntsmanet.al.I978, Cattails (Typha sp.) have with AMD has increased concern Wieder and Lang 1982). Since then, been found tohave a greattoleranceto about possible toxic effects to plants, investigators have been able to adverse environments. One of the aquatic life, animals, andevenhumans observed and document this process reasons could be that the uptake and in the coal regions ofthe Appalachian in constructed wetlands and accumulationofmetals into their tissue states. Regulations have been greenhouse experiments. The does not become detrimental to the established by federal and state following discussion focuses on our plant. However, research indicates

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UNIVERSiTT OF KENTUCKY, KENTUCKY STATE UNiVERSiTY. U.S. DEPARTMENT OF AGRICULTURE, AND KENTUCKY CQU1"TIES, COOPERATING Agronomy Notes Page 2 that metal uptake by cattails may themine spoil mixture) showedsimilar pyrite weathering, can be reduced by account for less than I% ofthe irotl efficiencies for Fe removal, but all anaerobic iron reducing bacteria in removed by a volunteer wetland substrates were a source ratherthan a the wetland. treating AMD (Sencindiver and sink for Mn (Figures I and 2). For these processes to Bhumbia, 1988), Species such as Exchange reactions and the progress, the wetlands must be Sphagnum moss also have a well­ formation of organic complexes by constructed to enhance anaerobic documented capacity to accumulate substrates apparently are important conditions and contain a suitable iron, Algae and a few other processes for only a short time during populationofsulfateandiron reducing hydrophytic species havealso received the first stages ofoperation in a new bacteria. Preliminary results from a attention'dl,l't: to their increased metal wetland system when biological constructedwetlands studyatVirginia removal'affinity, Selection of activity is limited. After these Tech suggest that seasonal hydrophY,lic species should first be processes reach their stable level, fluctuations in biological activitymay based on the ability of the plant to precipitation processes dominate in reduce the effectiveness of wetlands survive local conditions. The use of forming hydroxide and secondarily in to treat AMD year round (Table I). exotic species for aesthetic reasons forming sulfate or sulfide forms. Significant fluctuations in sulfate should be cautiously considered, even reducing bacteria populations when they have been proven effective Chemical and Biological occurred between February and June elsewhere, OxidationlReduction with the highest numbers present Although the role ofwetland Reactions during the warmer months. Virginia plants is not completely understood, Tech researchers also found no Constructed wetlands utilize their most important role appears to difference in sulfate reducing bacteria bothchemicaland biological processes be their ability to stimulate both population size between areas with as a means of ameliorating AMD. aerobic and anaerobic microbial and without cattails. Microbial sulfate reduction is an processes. This is accomplished by If dissolved oxygen important process in treating AMD plants providing sites for microbial concentrations present in wetland which requires a source of sulfate, attachment, releasing oxygen from surfacewatersarefavorable forpyrite carbon (organicmatter)anda reducing their roots, and supplying organic minerals to oxidize, discharge waters environment. matter for heterotrophs may actually increase in acidity. Sulfate reducing bacteriaare (microorganisms requiring complex Therefore, by exposing the AMD in anacrobes that live in the absence of organic compounds of nitrogen and the open environment (prevalent free oxygen and utilize a small range carbon for metabolic synthesis), aerobic conditions) we initiate metal ofsimple carbon s,01Jrces provided by Wetland substrates also to oxidation/precipitation reactions. At plants andsubstrates. Sulfate, released vary in their ability to remove metals the same time, we induce metal into mine drainage as a resultofpyrite by exchange reactions, precipitation, hydrolysis reactions which generate (FeS,) oxidation, is subsequently and 'organic complexation, These more acidity. It is important then to reduced to sulfide. Two products of abiotic (do not require maintain the AMD anaerobic and sulfate reduction, hydrogen sulfide microorganisms) chemical and increase alkalinity before the AMD is (H,S) and bicarbonate (HCO,), are physical processes could account for exposed to the open environment. responsible in part for the mitigation over 90% of the metal retention in ofAMD within constructedwetlands. wetlands treating AMD. Results of Bicarbonate adds alkalinity and Constructed Wetlands Design greenhouse experiments at the increases the pH and H,S precipitates Limited research has lead to UniversityofKentucky, showedpine­ iron and other metals. In addition to considerabledebateconcerningproper needle and hay mixtures to be more its metal removal potential, sulfate design criteria for treatment ofAMD efficient than peat, sphagnum moss reduction consumes acidity (H+) and in constructed wetlands. However, and mine spoil mixtures in reducing raises water pH. Likewise, some iron there appears to be some agreement acidity and AI. Cu, and Zn compounds which form as a result of about the basic conditions that must concentrations. Thesubstrates (except be in place. A wetland should be Agronomy Notes Page 3 constructed to increase the residence where oxidation, hydrolysis and K1einmann, RL.P. 1990. Acid time and interaction ofthe AMD with precipitation reactions can occur. mine drainage in the United States. In: the substratematerial wheremicrobial Currentapproaches attempt to reduce Proceedings of the First Midwestern transformations and oxidation/ inherent Fe'+ and dissolved oxygen Region Reclamation Conference, reduction rcactions occur. This may levels in AMD by utilizing anaerobic Southern IlIinoisUniversity, Carbondale, IL. involve installing baffles, regulating lagoons before directing the AMD flow rates, and establishingsubsurface through the ALD. This approach Secindiver, J.C., and D.K. flow through the wetlands. appears promising as a water Bhumbia. 1988. Effects ofcattail (Typha) Alkalinity generation in a pretreatment, however, more research on metal removal from mine drainage. wetland is important for precipitating is needed to determine the long-term p. 359·366. In: Mine Drainage and metals and raising pH especially in effectiveness ofALDs. Surface Mine Reclamation, Vol. I Info: the early stages oftreatment so that Circular No. 9183 US Bureau ofMines, enough buffer is generated to Pittsburgh, PA. counteract the expected increase in Summary acidity resulting from the aerobic Acid mine drainage. is a Wieder, RK. and G.E. Lang. 1982. Modification ofacid mine drainage in a stages of treatment. One method of common problem where coal and other fresh water wetland. p. 43-53. In: generating alkalinity is by placing a minerals are mined. Treatment of AMD by chemical methods are Symposium on wetlands of the bed oflimestone beneath the layer of unglaciated appalachian region. West substrate with a perforated pipe effective but costly, whereas Virginia University, Morgantown, WV. serving as an underground drain. This constructed wetland systems offer a type of drainage system prevents low cost, natural approach alternative. channeling, increases the retention Several important factors should be time ofthe water and forces the water considered when treating AMD by through the anaerobic zone of the wetlands. They are:'(l) flow rate and wetland. However, efficientgeneration water chemistry;' (2) wetland of alkalinity from the dissolution of substrate; (3) wetland vegetation; and Extension Agronomy Specialist limestone is often reduced in an (4) microbial composition andactivity. • oxygenated envirorunent with time due Based on current knowledge, wetland to iron and manganese oxidation and technologies could provide sufficient precipitation reactions that coat or treatment for many AMD discharges. armor the limestone surface. More However, since the,. biochemical recent approaches utilize anoxic treatment processes involved in those limestone drains (ALD's) which add systems arenot well understood, long­ alkalinity to AMD by keeping term efficiency predictions need to be limestone and mine water anoxic cautiously evaluated by additional (containing low levels of dissolved research under field conditions. oxygen). These (ALDs) consist ofhigh References quality limestone buried in a trench, Huntsman, B.E., J.B. Solch, and underdrain, or cell. Anoxic drains M.D. Porter. 1978. Utilization of a intercept acid water while it is sphagnum species dominated bog for underground anddirect itinto a buried coal acid mine drainage abatement. trench of limestone. By keeping the Abstracts, 91 st Annual Meeting limestone and mine water anoxic, Geologic Society America, Ottawa, limestone can continue to dissolve Ontario, Canada. without becoming armored. The water can then be diverted into a wetland