A Fixed Bed Pervious Concrete Anaerobic Bioreactor for Biological Sulphate Remediation of Acid Mine Drainage Using Simple Organic Matter

Abstract

The development of low-operational-cost and low-operational-complexity active sulphate (SO4) reducing bioremediation for Acid Mine Drainage (AMD) is an ongoing pursuit towards sustainable mining. This study introduces a fixed bed pervious concrete anaerobic bioreactor as a second stage AMD remediation process. The study investigated the pH self-regulation capabilities, SO4 remediation capabilities and the rate limiting parameters of the bioreactor using glucose as an organic matter source. The AMD was pre-treated using a permeable reactive barrier. A 21-day trial comprised of an increase in the SO4 loading rate while reducing the organic loading rate was undertaken to identify performance limiting conditions. A daily average SO4 concentration reduction rate of 55.2% was achieved over the initial 13 days of the experiments. The study found that a COD to SO4 ratio and VFA to alkalinity ratio below 5:1 and 0.5:1 respectively were performance limiting. The bioreactor was capable of self-regulating pH within the neutral range of 6.5 and 7.5. The study findings indicate that the bioreactor design can reduce operational costs and operational complexity of active AMD bioremediation.

Effects of Contact Time and Flow Configuration on the Acid Mine Drainage Remediation Capabilities of Pervious Concrete

“…Pozzolanic CEM IV A and 9.5 mm granite stone were selected as the cement and aggregate for the PRB due to the proven AMD treatment capabilities of siliceous cement from existing literature [16,17,20,23] and the chemical resisting properties of silica-based concrete [24]. The CEM IV A mix design comprised Portland CEM I with 4% silica fume CSF-90 TM and 8% siliceous fly ash.…”

“…The CEM IV A mix design comprised Portland CEM I with 4% silica fume CSF-90 TM and 8% siliceous fly ash. Both extenders contain high amounts of reactive SiO 2 (exceeding 80% in silica fume and exceeding 50% in siliceous fly ash), which improves the strength of concrete through a pozzolanic reaction with the Ca(OH) 2 produced during the cement hydration process, forming the cementing compound Calcium Silicate Hydrate (CSH) [23,24]. Silica Fume was incorporated to the mix design to enhance the chemical resisting properties of the concrete against sulphates, improve cementing of the aggregates and improve the overall concrete strength.…”

Review of Remediation Solutions for Acid Mine Drainage Using the Modified Hill Framework

“…The resulting H 2 S reacts with the dissolved metals and precipitates the metals from the solution as insoluble metal sulphides, as indicated in Equation ( 2) [40,94]. The bicarbonate ion from Equation ( 1) reacts with the protons (H + ) to form CO 2 and water, thereby removing acidity from the solution, as indicated in Equation (3) [59,95].…”

“…Active biological treatment using SRP is a promising AMD remediation method with the advantage of combining SO 4 , metals and acidity removal into a single Anaerobic Digestor (AD) process with minimal sludge generation [59]. Influential design and operational factors for successful AD biological sulphate reduction include consistency in SO 4 loading rates, pH stability, minimal temperature variance, maintaining a balance between alkalinity and volatile fatty acids, hydraulic retention time, the availability of nutrients nitrogen, phosphorus and potassium (N, P, K), the reactor design, the organic source available for SO 4 reduction and the ability of the SRP to outcompete methanogens for the available organic substrates [43,62,95,96]. Active AD treatment processes typically comprise of automated temperature regulation at mesophilic temperatures of between 35-39 • C, automated flow regulation and automated alkaline dosing to neutralise the acidity generated by the acidogenic microorganisms [30,32].…”

“…The challenges associated with the implementation of active biological treatment for AMD remediation include the high operational complexity, the costs and logistics for a stable supply of a suitable organic matter source, the high process sensitivity to change and the toxicity of high concentrations of heavy metals and high acidity to the biology that necessitates pre-treating [62,[94][95][96].…”