Investigation of acid mine drainage remediation by
co-treatment with municipal wastewater using the activated
sludge process
Background: Since mining operations ceased in 1982, acid mine drainage (AMD) has been emanating
from the abandoned copper and sulphate mines and tailings piles near Avoca, Co. Wicklow, SE Ireland.
The main area impacted by mining is divided by the Avoca River into East and West Avoca, and is
comprised of spoils heaps, open pits, and numerous shaft openings. Two major adits, the “Deep” and
“Ballymurtagh” Adits, discharge acid mine drainage (AMD), characterized by elevated concentrations of
heavy metals, acidity, and sulphate, directly into the Avoca River. Other adits (with seasonal flows),
surface runoff from spoil, groundwater discharge and bank intrusion also pollute the river, resulting in
severe contamination (Gaynor and Gray, 2004; Gray, 1998). Ecosystem destruction, caused primarily by
ochre deposition and an associated thick layer of precipitated metals, is obvious in the reaches of the
river immediately downstream of the mines, and the extremely poor river quality caused by AMD has
resulted in significant losses of macroinvertebrate species, fish, and other native biota, with impacts
evident in the entire river downstream of the mine site (Gray and Delaney, 2010). No remediative
measures are in place at the Avoca mine site. A sustainable, reliable, and long-term treatment system for
Avoca AMD is needed.  

Project: The purpose of this project was to examine the feasibility of acid mine drainage (AMD)
remediation by co-treatment with municipal wastewater using the activated sludge process. This
innovative approach to AMD remediation is based on the premise that combining AMD with wastewater,
activated sludge, or digested sewage sludge can effectively neutralize acidity and remove metals. This
investigation focused on the three key aspects of co-treatment: (i) the treatability of AMD by activated
sludge, (ii) the metal removal and neutralization capacity of wastewaters, activated sludges, and other
waste organic materials such as digested sewage sludge and cattle slurry, and (iii) the impacts of AMD
loading on wastewater treatment performance.

Results from treatability studies, metal removal and neutralization studies, and extended co-treatment
process evaluation studies confirmed that co-treatment is a feasible approach to AMD remediation.
Unacclimatized activated sludge tolerated large volumes of AMD, and adaptation of activated sludge was
evident after extended periods of AMD loading. Significant removal of Al, Cu, Fe, Mn, Pb, and Zn from
AMD occurred on mixing with activated sludge, return activated sludge, and wastewaters, and
neutralization of extremely acidic AMD occurred readily after mixing with wastewaters. Extended process
evaluation studies demonstrated that wastewater treatment (in terms of removal of chemical oxygen
demand and biochemical oxygen demand) can remain efficient in reactors continuously loaded with high-
strength AMD, and that total phosphorus (TP) removal is significantly enhanced where AMD contains Fe
and/or Al. Based on these findings, co-treatment of AMD and municipal wastewater is a promising
remediation strategy with the potential to save material, energy, and financial resources while exploiting
synergies in treatment. Especially in situations where there is a long-term need for continuous, reliable
AMD treatment, it will be of enormous benefit if the treatment system can be incorporated into a pre-
existing WWTP, thus creating a long-term active AMD treatment system with minimal construction
requirements, which can operate continuously without the need for additional staff or energy inputs.

Book Chapter:
  • Hughes, T.A. and  Gray, N.F. (2010) Effectiveness and Sustainability of Active and Passive Systems for the
    Treatment of Acid Mine Drainage and the Recovery of Metals: A Review. In Robinson, B.C. (Ed.), Mine Drainage
    and Related Problems (In press). New York: Nova Science Publishers.

Peer-reviewed publications:
  • Hughes, T.A., and Gray, N.F. (2012). Acute and Chronic Toxicity of Acid Mine Drainage to the Activated Sludge
    Process. Mine Water and the Environment, 31(1), 40-52.
  • Hughes, T.A.., Gray, N.F. and Guillamón, S. Removal of metals from acid mine drainage using liquid and dried
    digested sewage sludge and cattle slurry. Mine Water and Environment (in press)

  • Co-treatment of acid mine drainage with municipal wastewater using the activated sludge process: Preliminary
    treatability studies”, oral presentation, 2011 Meeting of the American Society of Mining and Reclamation,
    Bismarck, North Dakota, US. (Received Best Oral Presentation Award)

Other publications:
  • Hughes, T.A., & Gray, N.F. (in preparation). Co-treatment of acid mine drainage with municipal wastewater using
    the activated sludge process: Impacts on wastewater treatment performance and sludge characteristics.
  • Hughes, T.A., & Gray, N.F. (in preparation). Co-treatment of acid mine drainage with municipal wastewater using
    the activated sludge process: Metal removal and alkalinity budget.
  • Hughes, T.A., & Gray, N.F. (in review). Removing metals from acid mine drainage using municipal wastewater and
    activated sludge.

Further reading:
  • Gaynor, A., & Gray, N.F. (2004). Trends in sediment metal concentrations in the River Avoca, South-east Ireland.
    Environmental Geochemistry and Health, 26(411-419).
  • Gray, N.F. (1998). Acid mine drainage composition and the implications for its impact on lotic systems. Water
    Research, 32(7), 2122-2134.
  • Gray, N.F., & Delaney, E. (2010). Measuring community response of bentic macroinvertebrates in an erosional
    river impacted by acid mine drainage by use of a simple model. Ecological Indicators, 10, 668-675.
Theresa Hughes
Centre for the Environment, TCD


Funded: IRCSET Embark Initiative.
Acid mine drainage entering the River Avoca
via the deep adit which drains the East side
of the abandoned mining complex.
Small lake of acid mine drainage within
one of the open cast mining areas on the
Avoca site.
Theresa was awarded her PhD
in 2012 and is currently based in
the US.
 Water Technology Research Group
 Trinity College Dublin
   1980-2010 thirty years of research, training and consultancy