Papers by Author: Anna H. Kaksonen

Abstract: The amenability of sulfate reduction at low temperature for the treatment of acid mine drainage in arctic areas was investigated with three reactor experiments. The aim of these studies was to assess the potential and determine rates of sulfate reduction at 9oC with formic acid and hydrogen as electron donors. Three different bench-scale reactor configurations were tested: fluidized-bed reactor, membrane bioreactor and gas-lift bioreactor. The reactors were inoculated with a low temperature enrichment culture of sulfate-reducing bacteria. The temperature range of sulfate reduction was studied with a temperature gradient assay. The microbial community structure of the reactors was analyzed using polymerase chain reaction - denaturating gel gradient electrophoresis (PCR-DGGE) with universal 16S rRNA gene primers and SRB specific dsrB primers. The stable sulfate reduction rates at 9oC in all the reactors ranged from 0.6 to 1.4 g SO42- L-1 d-1. The temperature gradient assay supported also by the PCR-DGGE sequence profiling indicated that the low temperature enrichment was dominated by a psychrotolerant mesophilic Desulfomicrobium sp. having their maximal sulfide production rate at 31oC.

Abstract: The aim of the present work was to study the feasibility of using bioleaching for the solubilisation of metals from solid waste streams and by-products of copper, steel and recycling industries. Optimal process conditions were tested using iron and sulphur oxidising acidophiles in shake flasks at 25°C. The effects of inoculum, ferrous iron, sulphur, chloride ion, pH, and the type of waste material on metal solubilisation were evaluated. Solubilisation of metals was mainly achieved through acid attack due to the formation of sulphuric acid by sulphur oxidising bacteria. Addition of ferrous iron and chloride ion did not enhance solubilisation.

Abstract: In this study, ferrous iron oxidation rates of a Leptospirillum ferriphilum dominated culture were determined over the temperature range of 2-50oC at pH below one. The results show that at pH 0.9 the culture oxidizes iron within the temperature range of 10°C to 45°C. Using the Arrhenius equation, an Ea value of 89.9 ± 6.75 kJ/mol was calculated. From the data fitted to Ratkowsky Equation, the optimum, minimum and maximum temperatures were 35 ± 1.5, 9.96 ± 1.72 and 42.93 ± 0.64 °C for this culture, respectively. The redox potential of the solution becomes more positive, which was the maximum (650-700 mV) at temperatures between 19-40 oC due to completing biological oxidation and increasing in ferric iron concentration.

Abstract: The amenability of hydrolysed cellulose material to low cost sulfate reduction electron donor was examined with fluidized bed reactor (FBR) treating synthetic mine waste water. The studied cellulose material was dried Phalaris arundinacea reed, which was acid hydrolysed (1.5 w/w % H2SO4, 7 w/w % solids) at 120oC to hydrolyse polymeric materials to biodegradable monomers. The FBR was operated at 35oC, and ethanol has previously been used as the electron donor. FBR was fed with synthetic waste water (pH 4.5) containing soluble fraction of Phalaris arundinacea hydrolysate, metals (Fe and Zn) and sulfate. The switch of the electron donor from ethanol to hydrolysate was successful. The acidic influent was neutralized in the FBR by the alkalinity produced in the oxidation of Phalaris arundinacea hydrolysate. The main oxidation product of the soluble hydrolysate was acetate, which accumulated in the FBR during overloading. The percent sulfate reduction remained in the range of 40-95 %. The highest obtained hydrogen sulfide production was 0.91 g L-1d-1 at a hydraulic retention time (HRT) of 9 h, while highest sulfate reduction was 8.4 g L-1d-1 (HRT 8 h). Iron and zinc precipitated in the FBR, and highest metal precipitation rates were 1.14 g Fe L-1 d-1 and 30 mg Zn L-1d-1 (HRT 8 h). The electron donor load was measured as soluble chemical oxygen demand (CODs), and highest CODs removal rate was 2.13 g L-1d-1 (HRT 9 h) and CODs percent oxidation 92 % (HRT 10 h). Soluble Phalaris arundinacea hydrolysate was found to be a suitable electron donor for sulfate reducing FBR and mine waste water treatment. The soluble fraction of Phalaris arundinacea hydrolysate was used very efficiently by sulfate-reducing bacteria (SRB). Additionally, batch bottle assays showed that SRB-enrichment also used solid, dried Phalaris arundinacea as electron donor for sulfate reduction (total sulfide yield 340 mg L-1 in 14 days). The results of sulfate reduction and iron precipitation are shown in figures 1 A-B.

Abstract: An overview is presented of a multi-year research effort on developing high-rate fluidized-bed bioprocesses for ferric sulfate production to be used as a unit process in various hydrometallurgical applications including indirect tank leaching of ore concentrates, regeneration of heap leach liquors and control of iron containing acidic mine wastewater. Iron oxidation rates of over 26 kg m-3 h-1 were achieved at hydraulic retention times of less than 1 h at 37 °C. Oxygen supply became the rate-limiting factor even with 99.5% dioxygen aeration. Fe2+ oxidation proceeded at pH below 1 even in the presence of 60 g Fe3+ L-1 allowing the regeneration of concentrated ferric sulphate solutions required in indirect tank leaching of sulfidic ore concentrate applications. Of several tested FBR carrier materials activated carbon was the most suitable based on its availability, long-term durability and the achieved high iron oxidation rates. Jarosite precipitates accumulating to the top of the inert carrier materials played an important role in the FBR biomass retainment. For regeneration of synthetic and actual sulfidic ore heap leaching liquors, a gravity settler was installed in the recycle line of the FBR. The system produced iron precipitates with good settling characteristics and settling tank effluent with low turbidity and suspended solids concentrations. These results revealed the potential of FBR process in both heap leach liquor regeneration and controlling the iron containing waste streams. The PCR-DGGE-partial seguencing of the 16S rRNA gene protocol revealed that the FBR culture at 25-37 °C remained dominated by Leptospirillum ferriphilum over a range of operational conditions studied over the years. A modeling approach for managing Fe3+ production by FBR in combination with heap leaching was based on an artificial neural network-back propagation algorithm (ANN-HEAP) and resulted in excellent match between the measured and the predicted concentrations. High-rate fluidized-bed iron oxidation is amenable to regeneration of tank and heap leaching solutions as well as controlling iron containing waste streams.