Bacterial Oxidation Process Research Articles

Промышленное использование бактериального окисления железа в технологиях подземного выщелачивания урана

A technology for bacterial iron oxidation in the process of in-situ leaching of uranium has been developed and proposed for industrial use. The technology was validated by the results of pilot tests conducted at a uranium deposit in Kazakhstan over a period of 12 months. The aim of the study was to develop a technology for bacterial iron oxidation in the process of in-situ uranium leaching using a new type of flow bioreactor. Two biotechnological installations with bioreactors of 20 m³ volume were created and installed in 40-foot containers. The bioreactors, equipped with piping, air compressors, a pumping station, and control and measuring instruments, were installed at the geotechnical site and connected to the main in-situ uranium leaching system through wells. The installations had a productivity of over 150,000 m³/year for the leaching solution. After passing through the bioreactors, the redox potential of the solution increased from 360 mV to 430-450 mV in flow mode. The concentration of ferric iron increased from 0.1 g/L to 1.5 g/L and higher. The bacterial iron oxidation process was carried out at a solution temperature of 10 to 12°C (optimal temperature — 25-35°C), which allowed eliminating the costs of heating the solution. The test results showed an increase in uranium content in the productive solution by 10-20% after the leaching solution passed through the ore-bearing layer for 1 month. This confirmed the prospects for using this technology for in-situ well uranium leaching. The economic costs of using the technology are 6-8 times lower compared to using chemical oxidants such as hydrogen peroxide. The obtained industrial results open new prospects for the application of biotechnological methods for in-situ well leaching of uranium and other metals for the first time.

Stimuli-Responsive Dendritic Macromolecules for Optical Detection of Metal Ions and Acidic Vapors by the Photoinduced Electron Transfer Mechanism: Paper-Based Indicator for Food Spoilage Sensing.

Visual detection of analytes has been a significant challenge in the design and development of optical chemosensors. Sensing of analytes in aqueous solution by organic molecules has encountered some issues, such as poor water solubility and quenching of optical properties. In this study, a new category of smart dendritic macromolecules was designed and synthesized by functionalization of the poly(amidoamine) (PAMAM) dendrimer with spiropyran molecules to afford a photoluminescent dendritic structure (SP-PAMAM). Smart optical sensors were prepared by physical incorporation of four different oxazolidine derivatives containing hydroxyl and nitro substituted groups into the SP-PAMAM structure. Investigation of optical properties demonstrated photoinduced electron transfer (PET) between the spiropyran end group of SP-PAMAM and oxazolidine derivatives (in a concentration of about 0.0002 M), which can result in quenching of fluorescence emission of spiropyran photoswitch in the form of merocyanine (MC). Treatment of the oxazolidine-doped SP-PAMAM samples with metal ions resulted in changes in the PET mechanism (switching on or off), as observed in the case of Fe3+, Pb2+, Cu2+, Zn2+, Cd2+, Co2+, and Ni2+ by different oxazolidine derivatives through various mechanisms (increase or decrease of fluorescence emission). These smart photoluminescent dendritic macromolecules have potential applications for photodetection of metal ions in aqueous media as optical chemosensors. In addition, the smart macromolecules displayed disconnection of PET between MC and oxazolidine and also showed red fluorescence emission under acidic conditions (pH 1-5). It is due to the protonation of the MC to MCH form and demonstrates a remarkable red shift in fluorescence spectra. The pH-responsivity of smart macromolecules was used for designing a paper-based pH indicator for visual detection of spoilage in the food industry, especially in the case of milk. The prepared papers applied on cap of the milk bottles did not show any fluorescence emission in the case of fresh milk; however, a red fluorescence emission was observed after milk spoilage as a result of adsorption of acidic volatile components generated by bacterial degradation and oxidation process on the paper surface. The reported smart papers can serve as optical portable pH indicators for timely detection of spoilage in food materials, which are usable in food packaging as smart indicator tags.

Моделирование нечеткой логики для управления процессом бактериального окисления концентратов в реакторах с мешалкой

Множественность химических, биологических, технологических параметров и нелинейная зависимость при извлечении металлов в средах бактериального окисления усложняют математическое моделирование этих систем. Данное исследование было проведено с целью обеспечить управление извлечением золота и железа из флотоконцентрата в биореакторе с мешалкой с использованием модели нечеткой логики. Опыты проводились в присутствии смешанной культуры ацидофильных бактерий (Lactobacillus acidophilus) при 42°С и смешанной культуры умеренно термофильных бактерий при 48°С. Входными переменными были: метод операции, тип бактерий и время. Извлеченное золото и железо являлись выходными данными. Связь между указанными входными данными и выходными данными была обеспечена с помощью разработанных правил «ЕСЛИ-ТО». Полученная нечеткая модель показала удовлетворительный прогноз извлечения золота и железа и имела хорошую корреляцию экспериментальных данных с R-квадратом (более 0,97). Результаты исследования показали, что нечеткая логика представляет собой мощный и надежный инструмент для прогнозирования нелинейных и изменяющихся во времени процессов бактериального окисления.

Extraction and encapsulation of Laurus nobilis leaf extract with nano-liposome and its effect on oxidative, microbial, bacterial and sensory properties of minced beef

The aim of this study was the effect of nanoliposome-encapsulated extract and free extract of bay leaf (Laurus nobilis) on shelf-life of minced beef during 16 days storage in refrigerator (4 ± 1 °C). First, the leaf extract was extracted using ultrasound and various solvents (aqueous, alcoholic and hydroalcoholic) and the amounts of phenolic and flavonoid compounds, antioxidant and antimicrobial activity were determined. The results showed that the highest values of phenolic and flavonoid compounds, antioxidant and antimicrobial activity were observed in hydroalcoholic solvent extract (p < 0.05). The hydroalcoholic extract was nanoencapsulated with liposome, the particle size was 99.05 ± 2.98 nm and the encapsulation efficiency was 73.76 ± 1.10%. Then, it was used for investigate the effect of bay leaf extract on shelf life of minced beef. Five treatments including control, 1000 ppm extract, 1500 ppm extract, 1000 ppm nano-extract and 1500 ppm nano-extract. Chemical and microbial parameters were detected periodically, as well as the effect of different treatments on minced beef inoculated with Escherichia coli and Staphylococcus aureus were examined. The results showed that the extract has an antimicrobial and antioxidant properties and the nanoencapsulation process enhances the attributes mentioned, so that bacterial spoilage and oxidation process delayed in the minced meet contains 1500 ppm of the nano-extract (p < 0.05). This treatment also inhibited the growth of E. coli and Staph.aureus and had sensory ratings approved by the evaluators. Therefore, it seems that nano-extract of bay leaf can be used as a natural preservative with appropriate antioxidant and antimicrobial properties in meat and meat products.

Bacterially-mediated supergene alteration and redistribution of copper in mineralised rocks at the Salobo IOCG deposit, Brazil

The primary ore at the giant Salobo iron oxide copper-gold (IOCG) deposit in Brazil is dominated by magnetite and Fe-rich silicates, with minor (~1%) disseminated Cu-Fe sulphides and a distinctive absence of pyrite. Supergene Fe-silicate and sulphide oxidation has been mediated by bacteria, commonly within micrometre-scale acidic environments, but silicate-dominated acid neutralisation has maintained ambient circumneutral pH. Supergene Cu mobility has been controlled by the highly localised Fe-dominated biogeochemical processes, with Cu redistribution on the micrometre to metre scales and negligible supergene Cu enrichment. Silicates, especially the phyllosilicates biotite and chlorite, have variably altered to the clay minerals vermiculite and/or smectite, and ultimately to kaolinite. Leaching of Mn, Fe, Mg and Si accompanied silicate alteration, with minor addition of Cu to clay mineral structures and along cleavage planes. Iron mobilised by bacterial oxidation processes initially precipitated as ferrihydrite (with up to ~10 wt% Cu). Most Cu and Mn, mobilised in localised acidic environments, were precipitated nearby (metre scale) at circumneutral pH and reflect the immediate supergene biogeochemical environments: Cu-carbonates, pseudomalachite, chrysocolla, and Cu-Mn oxides (= “copper wad”). The early stages of these natural supergene processes were simulated in laboratory leaching studies using a range of fresh rocks inoculated with an endemic iron-oxidising strain of Acidithiobacillus ferrooxidans previously cultured from the Salobo site. Bacterially-mediated precipitation of ferrihydrite, commonly Cu-bearing, in these experiments strongly resembles that seen in the natural outcrops. These leaching experiments confirmed the effectiveness of silicate-dominated acid neutralisation, especially when accompanied by bornite oxidation, which is also acid-consuming. In contrast, chalcopyrite oxidation is acid-producing and leads to more effective localised Cu mobility in solution. Our combination of field and laboratory observations at the Salobo IOCG deposit shows that the biogeochemical environment dominated by Fe-silicates with little sulphides, typical for these systems, has led to an entirely different style of supergene Cu redistribution from that seen at many other Cu deposits, such as chalcopyrite and pyrite-rich porphyry copper deposits, where substantial supergene Cu enrichment has occurred.

Geochemical features of bitumen shows in the Lower-Middle Devonian deposits of the Northern-Western part of Kotelny Island (Novosibirsk Island Archipelago) v

The work presents the results of organic matter (OM) study of rocks, the composition, chemical structure of chloroform bitumen (CB), their fractions and the nature of the hydrocarbon biomarkers distribution in samples taken from outcrops. The obtained results confirmed the existing idea of ​​the domanicoid nature of OM and the high oil and gas potential of the studied deposits. According to our data, the aquagenic type of OM is indicated by a high content of Corg, a high yield of CB, a high content of oils in the composition of synbitumoids, and the predominance of relatively low molecular weight n-alkanes with a maximum at nС15-18. A sufficient maturity of bitumen can be judged by CPI coefficients close to unity and low absorption coefficients of oxygen-containing groups and bonds in the CB, thus deposits entered the main oil generation zone and generated liquid hydrocarbons that could migrate and form clusters. According to the data of Chromato Mass Spectrometry, it is shown that a feature of the composition of CB from the Lower Devonian sediments is the presence of high concentrations of dibenzothiophenes, in contrast to the Middle Devonian, which may be associated with the formation of the initial OM in an environment with higher hydrogen sulfide contamination of sediments. It has been suggested that naphthides generated by aquagenic OM of the Lower Devonian deposits can be enriched with dibenzothiophenes. The studied bitumen shows are mainly syngenetic in nature and have been influenced by hypergenic oxidation (judging by the nature of the IR spectra of resinous components) and contact metamorphism. According to the characteristics of the distribution of saturated hydrocarbons, it was shown that, in the Middle Devonian, bitumen occurrences along with chemical oxidation were affected to a different degree of bacterial oxidation processes, in contrast to the Lower Devonian bitumen shows. The results can be used to assess the generation potential of oil source strata and to forecast the prospects of oil and gas potential in the shelf of the eastern sector of the Russian part of the Arctic.

Photochromic Paper Indicators for Acidic Food Spoilage Detection.

A photoresponsive microstructured composite is fabricated through the impregnation of cellulosic filter paper (FP) with a spiropyran-modified acrylic polymer. The polymer enwraps uniformly each individual cellulose fiber, increases the thermal stability of cellulose, and ensures the preservation of the composite functionalities even upon removal of the surface layers through mechanical scratching. The photochromic spiropyran moieties of the polymer, even while embedded in the cellulosic sheet, can reversibly interconvert between the colorless spiropyran and the pink merocyanine isomeric states upon irradiation with UV and visible light, respectively. Moreover, the photochromic polymer presents a faster photochromic response and a higher resistance to photodegradation, with an outstanding reusability for more than 100 switching cycles when it is incorporated in the cellulose network. Most importantly, the acidochromism of the modified FP, attributed to the spiropyran molecules after UV activation, allows the real-time optical and visual detection of acidity changes and spoilage in food products, such as wine and milk. Spoilage due to bacterial degradation and oxidation processes generates acidic vapors that induce the protonation of the merocyanine. This results in a visually detectable chromic transition from pink to white of the treated cellulose fibers, corresponding to a blue shift in the absorption spectrum. The developed photoresponsive cellulose composite can serve as cost-effective robust optical component in integrated functional platforms and consumer-friendly indicators for smart food packaging, as well as portable on demand acidoresponsive interfaces for gas monitoring in industrial and environmental applications.

Study on the Gold Recovery of Double Refractory Gold Ore Concentrate by Biological Oxidation Pretreatment

In this paper, Bacterial oxidation-cyanide leaching experiments were carried out and the carbonaceous substances composition of carbonaceous gold concentrate was been studied. The elemental composition was 9.73 % iron, 9.66 % sulfur, 4.84 % arsenic and 13.23 % carbon which element carbon and organic carbon was 12.11wt.% and 0.06 wt.% respectively. The main carbonaceous substances were elemental carbon which the morphology was dense and similar to graphite. The removal rates of iron, arsenic and sulfur were achieved to 93.78%, 97.02% and 95.54% respectively by bioleaching, and the gold recovery of oxidation residue reached 92.34% by carbon inhibited cyanide leaching process. The sulfide minerals packing problem could be effectively solved by bacterial oxidation process and greatly increased the gold recovery. So the bacteria oxidation and carbon inhibited leaching process is applicable to the carbonaceous gold ore.

Bacterial Oxidation and Cyanide Leaching Process for Carbonaceous CarlinType Gold Deposit

Bacterial Oxidation and Cyanide Leaching Process for Carbonaceous CarlinType Gold Deposit

Application of Anaerobic Digestion Model No. 1 to describe the syntrophic acetate oxidation of poultry litter in thermophilic anaerobic digestion

A molecular analysis found that poultry litter anaerobic digestion was dominated by hydrogenotrophic methanogens which suggests that bacterial acetate oxidation is the primary pathway in the thermophilic digestion of poultry litter. IWA Anaerobic Digestion Model No. 1 (ADM1) was modified to include the bacterial acetate oxidation process in the thermophilic anaerobic digestion (TAD). Two methods for ADM1 parameter estimation were applied: manual calibration with non-linear least squares (MC-NLLS) and an automatic calibration using differential evolution algorithms (DEA). In terms of kinetic parameters for acetate oxidizing bacteria, estimation by MC-NLLS and DEA were, respectively, km 1.12 and 3.25±0.56kgCODkgCOD−1d−1, KS 0.20 and 0.29±0.018kgCODm−3 and Yac-st 0.14 and 0.10±0.016kgCODkgCOD−1. Experimental and predicted volatile fatty acids and biogas composition were in good agreement. Values of BIAS, MSE or INDEX demonstrate that both methods (MC-NLLS and DEA) increased ADM1 accuracy.

Modelling and optimization of processes for removal of dissolved heavy-metal compounds from drinking water by microbiological methods

The results of laboratory modelling of microbiological removal of soluble compounds of Fe, Mn, and other heavy metals (Al, Cr, Zn, Co, Cu, Pb, Cd) with the use of a laboratory bioreactor. The results have shown that the main method of optimization of conditions facilitating the removal of dissolved metal compounds from drinking water consisted in creating and maintaining an oxygen aeration regime favorable for bacterial oxidation processes and, which is especially important, in preventing stagnancy in the sand filter of bioreactor during its shutoff. The latter was accompanied by an acceleration of bacterial reduction processes of precipitated heavy metals, resulting in their dissolution, hence secondary water pollution.

A proposed mechanism for nitrogen acquisition by grass seedlings through oxidation of symbiotic bacteria

In this paper we propose and provide evidence for a mechanism, oxidative nitrogen scavenging (ONS), whereby seedlings of some grass species may extract nitrogen from symbiotic diazotrophic bacteria through oxidation by plant-secreted reactive oxygen species (ROS). Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism. We employed 15N2 gas assimilation experiments to demonstrate nitrogen fixation, direct microscopic visualization of bacteria on seedling surfaces to visualize the bacterial oxidation process, reactive oxygen probes to test for the presence of H2O2 and cultural experiments to assess conditions under which H2O2 is secreted by seedlings. We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae. Key elements of the proposed mechanism for nitrogen acquisition in seedlings include: 1) diazotrophic bacteria are vectored on or within seeds; 2) at seed germination bacteria colonize seedling roots and shoots; 3) seedling tissues secrete ROS onto bacteria; 4) bacterial cell walls, membranes, nucleic acids, proteins and other biological molecules are oxidized; 5) nitrates and/or smaller fragments of organic nitrogen-containing molecules resulting from oxidation may be absorbed by seedling tissues and larger peptide fragments may be further processed by secreted or cell wall plant proteases until they are small enough for transport into cells. Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.

AFM & EFM study on attachment of acidophilic leaching organisms

Bioleaching is the dissolution of metal sulfides by bacterial oxidation processes such as pyrite (FeS 2) and chalcopyrite (CuFeS 2). It is well known that attachment of leaching bacteria to the mineral surface enhances the metal sulfide dissolution. On one hand, leaching organisms oxidize different sulfidic ores, resulting in a type of water pollution called acid mine drainage (AMD). On the other hand, bioleaching processes are used in biotechnology due to their significant economic impact on heavy metal recovery such as gold, copper or zinc winning from sulfide ores. To prevent AMD or to optimize bioleaching processes for industrial use, attachment and the accompanying leaching efficiency of microorganisms have to be positively or negatively controlled. Therefore, not only the physiology of pure cultures has to be understood, but also the ecology and interactions of mixed cultures has to be studied. In this study a combination of Atomic Force Microscope (AFM) with Epifluorescence Microscope (EFM) are used to get “new insights” for a better understanding of attachment of leaching microorganisms to metal sulfides. The combination of AFM with EFM demonstrated by the use of DAPI staining and FISH probes that attached cells on pyrite coupons can be identified and assigned to a particular organism. During this study it was shown that L. ferriphilum causes aggregate formation and increased attachment of cells to pyrite coupons. Furthermore, it became obvious that mixed cultures of L. ferriphilum and A. caldus attach better than pure cultures. Moreover, A. caldus cannot attach to pyrite grains on its own, but needs a precolonization by L. ferriphilum for attachment. In such mixed cultures L. ferriphilum is the pivotal organism for biofilm formation.

Visualization of initial attachment of bioleaching bacteria using combined atomic force and epifluorescence microscopy

Bioleaching is the dissolution of metal sulfides, such as pyrite and chalcopyrite, by bacterial oxidation processes. It has been found that attachment of leaching bacteria to the mineral surface enhances the metal sulfide dissolution. The interaction of mixed cultures with respect to initial attachment processes has not been investigated. Therefore in this study we quantified and visualized initial colonization on pyrite by pure and mixed cultures. Strains of the genera Acidithiobacillus and Leptospirillum were tested. Sessile and planktonic cells were visualized by fluorescence microscopy using DAPI, FISH, Syto™ 9, lectin- and calcofluor-staining. Additionally, atomic force microscopy (AFM) was used for the investigations on cell morphology, spatial arrangement of cells on pyrite and mineral surface topography. The morphology of planktonic and sessile cells is different. Moreover, planktonic cells show differences in morphology due to the use of different substrata. By using different visualization methods it could be proven that colonization and biofilm formation on pyrite in mixed cultures is mostly dominated by Leptospirillum spp. Interactions of different species resulted in increased production of extracellular polymeric substances (EPS) or caused bacteria showing little tendency to attach when in monoculture to be incorporated into a biofilm by those that attach preferentially. Consequently, biofilm formation and metabolic diversity were furthered. One of the most important results is the finding that not all bioleaching bacteria are involved to the same extent in biofilm formation. Thus, further work shall allow us elucidate the important bacteria for biotechnological use, thereby leaching processes can be faster, more efficient and costs can be reduced.

Process mineralogy of bacterial oxidized gold ore in São Bento Mine (Brasil)

The São Bento deposit (Santa Bárbara, MG) occurs in the middle portion of the Quadrilátero Ferrífero (latu sensu), hosted by the São Bento iron formation. The most important minerals in the deposit are arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, electrum, magnetite, ilmenite, siderite, ankerite, calcite, quartz, chlorite, stilpnomelane and muscovite. A mineralogical characterization of samples from the bacterial oxidation process at the São Bento gold mine (MG) was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), Mössbauer spectroscopy and electron probe microanalysis (EPMA). Samples were collected in four different dates: one sample from the flotation concentrate and four from the bacterial oxidation system (BIOX) (TK2, TK4/TK68 bioreactors and TK28 thickener). Pyrrhotite was completely oxidized and arsenopyrite, pyrite and chalcopyrite were only slightly oxidized in the BIOX. Siderite occurs in small concentration in BIOX. Quartz, chlorite, and muscovite were slightly affected along the process. In BIOX, amoniumjarosite and hydroniumjarosite in lower abundance are the main phases formed. Native sulfur was detected in significant concentrations. Goethite and hematite are the main oxyhydroxides and an unidentified hydroxide containing up to 10 wt.% MgO was observed. Subordinate phases in BIOX samples are fibroferrite, zykaite, bukovskyite, sarmientite, tooeleite, alunite and gypsum. Chemistry of the iron sulfates shows that there are two amoniumjarosites in the BIOX, high and low-As jarosites. Low-As amoniumjarosite contains 10 wt.% As 2O 5 in average; while the high-As one contains 20 wt.% As 2O 5 in average. As-to-S substitution ratio is 1:1 suggesting a solid solution series toward an “As jarosite”. Their crystallization seems to be controlled by a solvus.

Optimization of Bacterial Oxidation Process Parameters for Selective Leaching of Nickel by Thiobacillus Ferrooxidans

Nickel bioleaching from copper flotation concentrate assumes greater significance because of its value and not many studies are carried out in these lines. Hence, nickel leaching was attempted and several process parameters of bacterial oxidation for copper flotation concentrate were examined for optimization. The parameters considered for shake flask leaching experiments were temperature, pulp density, particle size, agitation, residence time and inoculum size. The effect of variable proportions of each parameter on nickel leachability was studied. Optimum values of pulp density (10%) and agitation (140 rpm) played an important role in controlling the mass transfer resistance during leaching process. Increase in temperature from 27oC to 30oC has accelerated the bacterial oxidation process while initial concentration of inoculum (1-10%) has not shown considerable variation in nickel leachability. A particle size of ±60#size was found to be essential for bacterial attack. Maintenance of optimum conditions of leaching has yielded considerable nickel recovery (55%) compared to low recovery under unoptimal conditions.

Seeping hydrocarbons and related carbonate mineralisations in sediments south of Lihir Island (New Ireland fore arc basin, Papua New Guinea)

Hydrocarbon gases have been sampled from both cold-seeping and heat-venting areas in the New Ireland fore arc basin in the vicinity of Lihir Island. Highest concentrations of up to 10 μl/l CH 4 with a δ 13C CH 4 value of −54.9‰ PDB have been measured in the deep ocean water within a long and narrow deep sea basin located between Edison Seamount and an uplifted structure named “Mussel Cliff.” Surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as Calyptogena species and tube worms. Large authigenic calcite concretions occur in the sediments between 50- and 200-cm sediment depth. The carbon isotopes of the carbonates in the concretions range from −15‰ to −40‰ PDB indicating a mixture of two CO 2 sources: normal marine-inorganic carbon fixed in biogenic shells and CO 2 from anaerobe bacterial oxidation processes of methane. Accordingly, 14C-AMS dating suggests that authigenic calcite mineralisation incorporated relatively “young” carbon from methane oxidation. In contrast, the C1/C2 ratio of 234 and the δ 13C CH 4 value of −24.1‰ PDB in the hot hydrothermal vent of Lihir Harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with Lihir Volcano. The observed variable fluid characteristics within only 20-km distance between hot hydrothermal-venting and the methane-seeping deep sea area indicates highly variable heat flow situations and/or sediment distributions which control the gas geochemical characteristics in the New Ireland fore arc basin.

Potential for reduction of odorous compounds in swine manure through diet modification.

Recent public concern about air pollution from pork production units has prompted more research to develop methods to reduce and control odors. Masking agents, enzymes and bacterial preparations, feed additives, chemicals, oxidation processes, air scrubbers, biofilters, and new ventilation systems have been studied. Research relating the effects of the swine diet on manure odors has been scarce. Introducing feed additives to bind ammonia, change digesta pH, affect specific enzyme activity, and mask odors has been either costly or not consistently successful. Recent research emphasis has focused on manipulating the diet 1) to increase the nutrient utilization of the diet to reduce excretion products, 2) to enhance microbial metabolism in the lower digestive tract to reduce excretion of odor-causing compounds, and 3) to change the physical characteristics of urine and feces to reduce odor emissions. Primary odor-causing compounds evolve from excess degradable proteins and lack of specific fermentable carbohydrates during microbial fermentation. Reductions in ammonia emissions by 28 to 79% through diet modifications have been reported. Limited research on reduction of other odorous volatile organic compounds through diet modifications is promising. Use of synthetic amino acids with reduced intact protein levels in diets significantly reduces nitrogen excretions and odor production. Addition of nonstarch polysaccharides and specific oligosaccharides further alters the pathway of nitrogen excretion and reduces odor emission. Continued nutritional and microbial research to incorporate protein degradation products, especially sulfur-containing organics, with fermentable carbohydrates in the lower gastrointestinal tract of pigs will further control odors from manure.

The oxidation kinetics of zinc sulphide with Thiobacillus ferrooxidans

The kinetics and rate limiting sub-processes in the bacterial oxidation of zinc sulphide with Thiobacillus ferrooxidans were examined. The oxidation rate of synthetic ZnS in the presence and absence of bacteria at equal ferrous and ferric iron concentration and pH, was measured in parallel batch experiments. Bacteria oxidize Fe 2+ produced in the chemical oxidation of ZnS with Fe 3+. In the fermenter without bacteria hydrogen peroxide was added to regenerate ferric iron and maintain the Fe 2+ concentration equal to that in the fermenter with bacteria. No significant differences in the oxidation rates of zinc sulphide were found between the slurry with and without bacteria at equal Fe 2+ and Fe 3+ concentrations. Consequently, an indirect mechanism (i.e. chemical oxidation of ZnS with Fe 3+ to Zn 2+, S 0 and Fe 2+, and bacterial oxidation of S 0 to SO 4 2− and Fe 2+ to Fe 3+) determines the oxidation rate of ZnS in the bacterial oxidation process. From the experiments it was shown that T. ferrooxidans prefers S 0 as a substrate and the regeneration of Fe 3+ can even become terminated. From the experimental data several suggestions for improved process design and experimental research are given.

The Machanism of Bacterial Oxidation of Sulphides

Abstract The bacteria used in the experiment are Thiobacillus Ferrooxidans separated from acidic mine water in sulphide deposits. The chemoautotrophic bacteria can act directly on sulphides and accelerate the oxidation of sulphides. The experiment shows that the bacteria, as an important microbial factor of gold's supergenous enrichment within the oxidized zones of sulphide deposits, are helpful to dissolve gold and silver in ferric sulphate. In the bacterial oxidation process, the precipitation of goethite is concerned both with the lower activity of ferric ions and with the existence of carbonates in solution. Meanwhile, the acid‐resisting and oxidizing ability of the bacteria will certainly lead up to a microbial way of treating the acidic mine water.