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Type: Thesis
Title: Investigation of algal-microbial biofilms for acid mine drainage treatment.
Author: Orandi, Sanaz
Issue Date: 2013
School/Discipline: School of Chemical Engineering
Abstract: Mining wastewaters, typically acid mine drainage (AMD) have been listed as one of the most severe types of contaminated surface waters containing heavy metals (e.g. Cu, Zn, Cr, Pb) and toxic metalloids (e.g. As, Cd, Sb). AMD convey these elements into water bodies and threaten aquatic life and human health, consequently. AMD is required to be treated before discharge to the environment, particularly in arid areas with scarce water resources. To date, neutralisation and evaporation have been commonly used at mine sites to decrease the elemental contents of contaminated surface waters. However, these techniques are expensive or ineffective for removing recalcitrant elements e.g. Mn; and produce large volumes of contaminated sludge. In recent decades, the exploitation of microorganisms for treating wastewaters, particularly municipal wastewaters, has significantly improved water treatment technologies, and are referred to as biotreatment/bioremediation. High efficiency, cost effectiveness and sustainability are associated with biotreatment. The application of biotreatment has been investigated for AMD treatment and documented extensively. However, the results are limited and not comprehensive enough for an applicable system to be deployed in mine sites. The main objective of my PhD research was to establish and develop an effective and sustainable AMD biotreatment system for removing metals/metalloids, applicable for mine sites. The indigenous mine microorganisms were used as biosorbents in a biotreatment system, obtained from AMD resources at Sarcheshmeh copper mine, Iran. The microbial sample contained mainly filamentous and unicellular green micro-algae, Klebsomidium sp. and Chlamydomonsae sp.; bacteria, Acidithiobacillus ferroxidance, Leptospirillum ferroxidans and Pseudomonas sp.; and fungi, Aspergillus sp. and Penicillium sp. The AMD, from which the indigenous microbial consortium was collected, was analysed to quantify its cation and anion (including nutrients PO₄⁻³ and NO₃⁻) contents. The analysis data was used to synthesise a multi-ion AMD composed of 25 components (cations and anions at concentrations 0.005-100 mg/L), high sulphate (>1000 mg/L) and low pH (~3). The indigenous microbial assembly was maintained in synthetic AMD (Syn-AMD) in vitro. For the biotreatment investigations, a laboratory-scale photo-rotating biological contactor (PRBC) was designed and used to immobilise the microbial consortium as an algal-microbial biofilm. The PRBC was initially operated in batch mode, using Syn-AMD and indigenous microbes as PRBC solution and inoculum, respectively. An algal-microbial biofilm (60g dry weight) was successfully grown on the discs’ surfaces in the PRBC after 12 weeks. The PRBC was then operated at both batch and continous modes to investigate the efficiency of the system for removing different elements from the Syn-AMD. Batch systems were conducted in 7-day periods under pH 3 and 5. The batch results showed that the algal-microbial biofilm system was able to reduce the concentration of major elements from 10 to 60 % at pH 3 in the order of Na > Cu > Ca > Mg > Mn > Ni > Zn, whereas higher results (40-70 %) were recorded for these elements at pH 5 in the order of Cu > Mn > Mg > Ca > Ni > Zn > Na. The removal trend for each element contained maximum and minimum removal values that occurred during the experiment. The removal efficiency of the system for trace elements varied extensively between 3 and 80 % under both pH conditions. The efficiency of the system was also evaluated in continous condition, by introducing Syn-AMD (pH~3) into the PRBC at the flow rate of 10 ml/min and hydraulic retention time of 24 h. The operation of PRBC within a 28-day period showed similar removal efficiency (10-60%) compared with the batch operation, for most of elements. The chemical composition of treated water was examined daily within 28 days and the results revealed absorption (7 days) and desorption periods occurring alternatively. The increase and decrease of pH by 0.5 and 0.2 were recorded at the same time of absorption and desorption periods, which was attributed to mobilisation and immobilisation mechanisms occurring in the algal-microbial biofilm. The system was operated for a further 10 weeks continuously and the results demonstrated the average weekly removal for major elements from 20 to 50% in the order of Cu> Mg> Ni> Na> Mn> Ca> Zn whereas for trace elements varied broadly between 10 and 80 %. Scanning electron microscopy (SEM) analysis illustrated the accumulation of heavy metals in/on the biofilm. Biofilm analysis also revealed the presence of different elements up to 10% of the dried biomass. The results demonstrated the effectiveness and sustainability of indigenous environmental friendly algal-microbial biofilm to be exploited for removing most of elements from AMD. The results offer a potentially sustainable approach for the primary treatment of AMD at mine sites.
Advisor: Lewis, David Milton
Moheimani, Navid R.
Ashman, Peter John
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2013
Keywords: AMD; biotreatment; mining; algae; wastewater
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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