Mona Arnold

Development of on-line measurement techniques for siloxanes and other trace compounds in biogas

This paper focuses on the development of an on-line measurement method for siloxanes and other biogas trace compounds impeding the energy utilisation of biogas, as well as the main gas components, methane and carbon dioxide. The method is based on gas chromatography and FT-IR-analysis. The level of siloxane, hydrogen sulphide and halogens in biogas generated in a number of landfills and digesters in Finland is also presented and factors affecting the concentrations discussed. Generally, the level of biogas trace compounds hampering electricity production was lower than those measured at comparable sites in Central Europe and the US. Moreover, the paper discusses the significance of on-line monitoring of siloxane in connection to biogas-to-electricity applications and points out with activated carbon as an example the benefits of on-line siloxane measurement in the control of siloxane removal technology.

Wood ash for application in municipal biowaste composting.

This study aimed to clarify the impacts of pH control by wood ash amendment on biowaste composting processes. To achieve this, fresh source separated municipal biowaste was mixed with low doses (2-8% wt/vol) of wood ash and processed in a pilot and large-scale composting systems. The results indicated a correlation between a low initial pH and delay in the early rise of the process temperature. Wood ash elevated the composting temperatures and pH, and stimulated the mineralisation both in the pilot scale and the industrial large-scale processes. According to the results addition of amounts of 4-8% wood ash is sufficient for efficient biowaste composting process and yields a safe end product. However, to minimise the environmental risk for heavy metal contamination, and meet the criteria for the limit values of the impurities in wood ash, strict quality control of the applied wood ashes should be implemented.

Effect of light Sphagnum peat on odour formation in the early stages of biowaste composting

In the present study, we investigated the effects of two bulking materials, Sphagnum peat and pine wood chips, on the early stages of biowaste composting in two pilot-scale processes. Emphasis was placed on studying the formation conditions of malodorous compost gases in the initial phases of the processes. The results showed that gas emission leaving an open windrow and a closed drum composting system contained elevated concentrations of fermentative microbial metabolites when acid Sphagnum peat (pH 3.2) was used as a bulking material. Moreover, the gas emission of the peat amended drum composter contained a high concentration of odour (up to 450,000oum(-3) of air). The highest odour values in the outlet gas of peat amended composts coincided with the elevated concentrations of volatile organic compounds such as acetoin and buthanedion. We conclude that the acidifying qualities of composting substrates or bulking material may intensify odour emission from biowaste composts and prolong the early stages of the composting process.

Microbial Community Structure and Functions in Ethanol-Fed Sulfate Removal Bioreactors for Treatment of Mine Water

Sulfate-rich mine water must be treated before it is released into natural water bodies. We tested ethanol as substrate in bioreactors designed for biological sulfate removal from mine water containing up to 9 g L−1 sulfate, using granular sludge from an industrial waste water treatment plant as inoculum. The pH, redox potential, and sulfate and sulfide concentrations were measured twice a week over a maximum of 171 days. The microbial communities in the bioreactors were characterized by qPCR and high throughput amplicon sequencing. The pH in the bioreactors fluctuated between 5.0 and 7.7 with the highest amount of up to 50% sulfate removed measured around pH 6. Dissimilatory sulfate reducing bacteria (SRB) constituted only between 1% and 15% of the bacterial communities. Predicted bacterial metagenomes indicated a high prevalence of assimilatory sulfate reduction proceeding to formation of l-cystein and acetate, assimilatory and dissimilatory nitrate reduction, denitrification, and oxidation of ethanol to acetaldehyde with further conversion to ethanolamine, but not to acetate. Despite efforts to maintain optimal conditions for biological sulfate reduction in the bioreactors, only a small part of the microorganisms were SRB. The microbial communities were highly diverse, containing bacteria, archaea, and fungi, all of which affected the overall microbial processes in the bioreactors. While it is important to monitor specific physicochemical parameters in bioreactors, molecular assessment of the microbial communities may serve as a tool to identify biological factors affecting bioreactor functions and to optimize physicochemical attributes for ideal bioreactor performance.

Bioleaching of Phosphorus from Low Grade Ores and Concentrates with Acidophilic Iron- and Sulphur-Oxidizing Bacteria

Bioleaching experiments of phosphorus from low grade fluorapatite ore containing 8.2% P2O5 and from fluorapatite concentrate containing 29.8% P2O5 were carried out in shake flasks. Elemental sulphur was supplemented as an energy source for acid generation. Mixed and pure acidophilic bacterial cultures consisting of iron-and/or sulphur-oxidizing bacteria Acidithiobacillus ferrooxidans, A. thiooxidans and Leptospirillum ferrooxidans were used in the experiments. These acidophiles are commonly used in bioleaching of sulphide minerals, but their application on phosphorus bioleaching has been limited. Phosphorus leaching was shown to be a pH-dependant phenomenon. Phosphorus leaching yields of up to 97% and 28% were obtained in 3 weeks for low grade fluorapatite ore and concentrate, respectively. These results indicate a potential for applying bioleaching for phosphorus extraction from low grade materials.

Rare Earth Elements Recovery and Sulphate Removal from Phosphogypsum Waste Waters with Sulphate Reducing Bacteria

Phosphogypsum waste, originating from phosphoric acid production from apatite ores, is well known for its high production rate and possible release of sulphate-rich seepage waters. In addition to negative environmental impacts, phosphogypsum waste heaps are also remarkable secondary sources of Rare Earth Elements (REE); in the phosphoric acid production process a majority of REE, occurring in apatite, are precipitated to the phosphogypsum waste. Therefore, a method treating both sulphate-rich waters and recovering REE from phosphogypsum heaps and seepage waters would offer both economic and environmental benefits. In this ongoing study, seepage waters from a phosphogypsum heap are treated with Sulphate Reducing Bacteria (SRB) and ethanol as a substrate. Sulphate is first reduced to hydrogen sulphide, which then precipitates REE as sulphides. The main challenge, low concentration of REE in seepage waters (e.g. 2.87 μg/l La, 5.13 μg/l Ce, 0.67 μg/l Y and 3.32 μg/l Nd), is overcome by utilizing continuous mode, semi-passive and cost effective column apparatus, requiring no agitation and performing both sulphate reduction and REE recovery in a single reactor. The SRB method results in a sulphate reduction rate of 40-80 % (from app. 1400 mg/l to 276-844 mg/l sulphate in the effluent) and efficient REE recovery from seepage water. The concentrate obtained from the column consists of a mixture of anaerobic sludge and precipitated REE, with respective REE concentrations of 202 mg/kg La, 477 mg/kg Ce, 49 mg/kg Y and 295 mg/kg Nd.

Enrichment and Isolation of Phosphorus Solubilizing Bacteria

The aim of this study was to enrich phosphorus solubilizing microorganisms from high-phosphorus iron ores, apatite ores and phosphogypsum waste. Phosphorus solubilizing microorganisms can be utilized in dephosphorization of high-phosphorus iron ores and in phosphorus leaching from fluorapatite ores. Low grade fluorapatite ore (3.6% P, pH 6.8), fluorapatite concentrate (13% P, pH 8.3), phosphogypsum waste (0.7% P, pH 2.3), iron ore 1 (0.19% P, pH 7.6) and iron ore 2 (0.18% P, pH 7.6) were used as potential sources of phosphorus solubilizing microorganisms. The samples were cultured in NBRIP media at pH 5 and 8 with either glucose or sucrose as a carbon source, and in modified 9K media at pH 1.5 and 2.5 for 3 weeks. Phosphorus solubilizing bacteria were enriched only from the fluorapatite concentrate at the pH of 8. The four obtained heterotrophic isolates were identified by 16S rRNA gene sequencing, and were shown to be closest related to Burkholderia fungorum. These results indicate that the diversity of culturable phosphorus solubilizing bacteria present in apatite and iron ores is relatively low. The isolated Burkholderia strain showed phosphorus solubilizing potential.