Open Cut » Environment
This project is further development of technology from an earlier ACARP project (C28074) which involved sulphate reduction based bioremediation for in situ treatment of acidic pit lakes arising from open cut coal mining operations.
In this previous study, encouraging responses of using green waste and sewage sludge in laboratory microcosms for acidity and heavy metal removal were taken to field scale studies in which the Garrick East pit lake at the Collinsville coal project (CCP) area was partitioned into two lakes (treated Garrick East West - GEW and untreated Garrick East - GEE). Bioremediation was initiated in GEW by adding sewage sludge and green waste. Water quality in this field scale trial was monitored for up to 15 months afterwards in the treated lake and two untreated lakes.
Following addition of organic waste materials bioremediation quickly began with an increase in pH at the lake bottom. However, after 12 months the pH rise stopped and treated lake started to return to pre-treatment levels for pH.
In order to determine why this pH rise stopped, the current ACARP research project broadly investigated environmental factors that influenced bioremediation success probability and rate of treatment for acidic pit lakes for removal of acidity and heavy metals in Collinsville, Queensland.
A major component of this project was also to continue field monitoring at monthly intervals to collect data on physico-chemical characteristics (pH, oxidation reduction potential - ORP, electrical conductivity - EC, metals/metalloids and nutrients) in order to ascertain how bioremediation effects on water quality progressed over more sustained periods of treatment.
Another component of the project was to specifically evaluate environmental factors that influenced and possibly hindered bioremediation in the field experiment. The major environmental factors evaluated were: effect of cyclonic events on lake mixing (stratification), the importance of the form of carbon dosed and its quality and quantity on sulphate reducing bacteria (SRB) activity and the pit lake's acid-base budget to determine the role of ongoing acidity inputs from lake catchment and groundwater in decreasing bioremediation treatment efficacy.
In situ bulk remediation technology this and previous ACARP projects have studied has shown strong potential to treat acidic pit lakes. However, many factors must be considered in the efficacy and relevance of its application to pit lakes; time of treatment available being the most prominent one. We therefore recommend that any proposal to relinquish acid pit lakes with this technology begin the remediation process as early upon pit lake dewatering as possible.
Based on the results and experiences of the ACARP grants we have outlined further broad guidelines for application of this technology that can be trialed in other acid pit lakes.