Passive treatment of acid mine drainage through permeable concrete and organic filtration
Date
2016
Authors
Zaal, Steven Michael
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Abstract
The aim of this research was to reduce heavy metal and sulfate content of acid mine drainage
(AMD) through the methods of passive filtration by combining permeable concrete and
organic materials. This was to achieve a low cost, yet effective temporary treatment method
for rural/poor communities who are affected by AMD. The acids are filtered through layers of
alternating pervious concrete and biological composting layers. The concrete layers target
removal of heavy metals such as iron, manganese, potassium, and magnesium, etc. through
precipitation as well as reduce sulfate content to a small degree along with total dissolved
solids. The concrete layers also aid in raising the pH of the AMD to more acceptable levels.
The biological layers achieve sulfate remediation through the metabolism of sulfatereducing-
bacteria (SRB). This process however required time and the organic layers were thus
thicker and less permeable than the concrete layers in order to allow seepage to take place
at a reduced rate. A wide variation of composting layers were tested, including cow manure,
chicken manure, sawdust, straw, zoo manure, and leaf compost to find an optimum mix of
materials which allows for the greatest sulfate reduction through sulfate reducing bacteria in
the shortest possible time. Short as well as Long-term testing of rigs was undertaken to
establish effectiveness, limitations and lifespan of the filtration systems. AMD from a mine in
the Mpumalanga coal fields with exceptionally high sulfate content was used to test
effectiveness of the organic materials over a short period of time. With long term testing
conducted with a synthetic AMD, due to limited supply from the mine. The short term testing
yielded removal of sulfates in the order of 56% when using kraal manure as the biological
reagent mixed with sawdust for added organic carbon. The mix percentages by volume were
80%Sawdust to 20%manure and this setup was able to achieve the 56% removal of sulfates
within 14 days. The filter also successfully raised the pH to 8 while removing a significant
portion of heavy metals. The long term tests showed complete (100%) remediation of sulfates
after a period of approximately sixty days. The tests are continuing to determine their finite
lifespan and limitations. The results show promise for using the technology as a low cost,
temporary measure to protect locally impacted groundwater, especially for isolated and/or
rural communities while a permanent long term solution is sought.
Description
A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2016
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Citation
Zaal, Steven Michael (2016) Passive treatment of acid mine drainage through permeable concrete and organic filtration, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/20998>