Biooxidation Rates Research Articles

Polyurethane foam as biomass support for removal of thiosalts from flotation process water

Water recycling is a common practice in sulphide ore processing plants by flotation. Inherent thiosalts accumulation in process water often causes efficiency drop and environmental issues for wastewater discharging. Passive and active depuration methods have been applied for thiosalts removal and bio-oxidation in packed bed bioreactors can be considered the most promising option.In this work, polyurethane foam is for first time used as biomass support material in continuous bio-oxidation of thiosalts. Two columns, 15 and 197 cm in height and 8.4 cm in diameter, packed with 1 cm in edge length cubic particles were trialled. A new and fast start-up procedure was performed allowing to effectively operate them in less than seven days. Complete removal of thiosalts in real liquors were achieved with bio-oxidation rates close to 0.45 kg/hm3 and residence time lower than 7 h. Stability, robustness and versatility showed by the bioreactors allows to affirm that polyurethane foam is a suitable material as biomass support in continuous packed bed bioreactors for thiosalts bio-oxidation.

A new thiosalt depuration bioprocess for water- recycling in metallic sulphide mineral processing

Economic and environmental imperatives force the metallic sulphide processing industry to re-use liquors that normally contain thiosalts; this processing entails difficulties in operation control and losses in metal-extraction performance. Bio-oxidation presents a promising option for thiosalt removal. Hitherto, this method has been tested to treat synthetic liquors containing only one thiosalt, either tetrathionate or thiosulphate, usually at low concentration (<1 g/L). In this article, bio-oxidation is studied of synthetic and real liquors containing mixtures of these thiosalts at concentrations close to 4.5 g/L. Coexistence of thiosulphate and tetrathionate in an acidic medium leads to strong and irreversible inhibition phenomena (performance losses close to 80%). In order to solve this problem, a previous treatment is proposed consisting of the 8-hour aeration of inlet solution after adding up to 20 mg/L and pH 1.5 of Cu2+ and sulphuric acid, respectively, resulting in the complete removal of thiosulphate and sulphite. Pre-treated real liquors were fed into a 1 L discontinuous stirred tank bioreactor and a 1 L continuous flooded packed-bed bioreactor, which were successfully started up and operated, thereby obtaining bio-oxidation rates close to the highest rates found in the literature with synthetic liquors.

Kinetics of arsenite oxidation by Sinorhizobium sp. M14 under changing environmental conditions

Many arsenite oxidizing bacteria show potential for application in bioremediation of arsenic-contaminated waters, but most can be used effectively only under conditions similar to those prevailing at their isolation site. This problem may be overcome by the use of the plasmid pSinA, which provides its hosts arsenite oxidation ability. However, the application potential of the natural host strain, Sinorhizobium sp. M14, has not been assessed under environmental conditions, which may readily affect the efficiency of the oxidation process. Thus, the aim of this study was to investigate the impact of several factors (e.g. pH, temperature, arsenic concentration) on the growth kinetics and arsenite oxidation abilities of Sinorhizobium sp. M14. Batch experiments were carried out to determine the adaptability of the strain. Subsequently, growth kinetics were tested and verified in continuous cultures, under environment-like conditions. The obtained results indicate that the strain is capable of intensive growth (doubling time = 9.2 h) and efficient biooxidation in a wide range of conditions, including low temperatures (As(III) oxidation rate = 0.533 mg L−1 h−1 at 10 °C). It was shown that aeration of the cultures may increase both growth and biooxidation rates, when appropriate supplementation with organic nutrients is provided. The obtained qualitative indicators allow for the comparison of arsenite-oxidizing abilities of M14 with other strains, proving its potential for application in arsenic-contaminated water treatment technologies.

Biosurfactant-enhanced immobilization of hydrocarbon-oxidizing Rhodococcus ruber on sawdust

Immobilization of microorganisms on/in insoluble carriers is widely used to stabilize functional activity of microbial cells in industrial biotechnology. We immobilized Rhodococcus ruber, an important hydrocarbon degrader, on biosurfactant-coated sawdust. A biosurfactant produced by R. ruber in the presence of liquid hydrocarbons was found to enhance rhodococcal adhesion to solid surfaces, and thus, it was used as a hydrophobizing agent to improve bacterial attachment to a sawdust carrier. Compared to previously used hydrophobizers (drying oil and n-hexadecane) and emulsifiers (methyl- and carboxymethyl cellulose, poly(vinyl alcohol), and Tween 80), Rhodococcus biosurfactant produced more stable and homogenous coatings on wood surfaces, thus resulting in higher sawdust affinity to hydrocarbons, uniform monolayer distribution of immobilized R. ruber cells (immobilization yield 29-30mg dry cells/g), and twofold increase in hydrocarbon biooxidation rates compared to free rhodococcal cells. Two physical methods, i.e., high-resolution profilometry and infrared thermography, were applied to examine wood surface characteristics and distribution of immobilized R. ruber cells. Sawdust-immobilized R. ruber can be used as an efficient biocatalyst for hydrocarbon transformation and degradation.

Effects of dissolved oxygen on the biooxidation process of refractory gold ores

While multiple theories exist regarding the effect of dissolved oxygen (DO) on the biooxidation of minerals, few studies have been performed the cellular or molecular scale (e.g., genetics) and the mechanism remains unclear. In this paper, the effects of DO concentration on the biooxidation process of refractory sulfide gold ores by Acidithiobacillus ferrooxidans were investigated in the experimental stirred tank bioreactors (STRs). The results indicated that higher biooxidation and cell growth rates were correlated with higher DO concentration. The biooxidation process was restricted at 1.2 ppm DO due to oxygen limitation. Furthermore, the effects of DO on cellular and molecular scale were studied for the first time. The results demonstrated that the oxygen uptake rate (OUR), the Fe(2+) oxidation activity and the rus gene expression of A. ferrooxidans all increased with the DO concentration, which might be responsible for the increase of the biooxidation rates with the DO concentration. This study provides insight into the potential impact of molecular-level mechanisms of DO in the biooxidation process of minerals.

Effect of agitation intensity on the biooxidation process of refractory gold ores by Acidithiobacillus ferrooxidans

Various views persist about the effect of the agitation intensity on the mineral biooxidation process, but the mechanism remains unclear. In this study, the effects of the agitation intensity on the biooxidation process of refractory gold ores by Acidithiobacillus ferrooxidans were investigated in experimental stirred tank bioreactors (STRs). The results demonstrated that both the biooxidation rates and the concentration of cells decreased with the agitation intensity. The higher agitation intensity not only damaged the suspended cells but also prevented the adsorption of cells onto the mineral surface. The oxygen uptake rate (OUR), the Fe2+ oxidation activity and the rus gene expression of A. ferrooxidans decreased with the agitation intensity during the biooxidation process, which might be responsible for the decrease of the biooxidation rates with the agitation intensity.

Diel carbon monoxide cycling in the upper Sargasso Sea near Bermuda at the onset of spring and in midsummer

Rapid bio‐oxidation of carbon monoxide (CO), a photoproduct of dissolved organic matter, results in diel cycles reflecting photochemical‐biogeochemical‐physical interactions. These cycles were characterized by time‐series studies of hydrography, meteorology, insolation, optics, and CO concentration ([CO]). Diel patterns of near‐surface [CO] generally varied little seasonally, despite different forcings. In summer 30% of CO was below the mixed layer (ML); ML depths and optics indicate that two‐layer photochemistry is common elsewhere. [CO] decayed at similar rates in both isolated layers. In spring CO extended to 150 m, reflecting nocturnal mixing. Cruise‐average profiles indicated a shallower ML defined by CO than that defined by density, illustrating short‐lived CO’s sensitivity to recent mixing. Below the ML, [CO] dropped exponentially with depth on scales controlled by photoproduction in summer but mixing in spring. Mass‐balance modeling of diurnal variations in CO column burden (CB) gave similar production rates in summer and spring (~50 µmol m−2 d−1 CO), but different biooxidation rates, 1.5 ± 0.2 d−1 (summer, 0‐50 m) and 0.52‐0.66 d−1 (spring, 0‐200 m). Outgassing averaged 4% of bio‐oxidation in summer and 14% in spring. Similar production and differing sinks resulted in different CBs: 39.3 µmol m−2 (summer) versus 94.9 µmol m−2 (spring). Insolation‐normalized CO productions were 1.8 times those in the oligotrophic equatorial Pacific. Improved, well‐blanked analyses found [CO] at 200 m always &lt;0.1 nmol L−1 in summer, and usually in spring. Prior reports of [CO] systematically ≥0.2 nmol L−1 at depth in well‐stratified, oxic blue waters may be high because of method artifacts.

BOD sensors using multi-species living or thermally killed cells of a BODSEED microbial culture

A biochemical oxygen demand (BOD) biosensor installed with a biofilm containing immobilized thermally killed cells of a BODSEED (Cole-Palmer E-05466-00) microbial culture gave BOD sensing sensitivity comparable with that of a biosensor using the same population of the immobilized living cells of the same culture. The thermally killed cell sensor showed better response and storage stability but slightly longer response and recovery times than the living cell sensor. Both the living and thermally killed cell sensors generally underestimated the BOD 5 of wastewater differing by about −21–28.4% from the values obtained by the conventional APHA method of 5-day BOD measurement using the same BODSEED for seeding. The poor response of both the BOD biosensors to dairy wastewater and industrial organic waste and zero response to lactose compared with the conventional APHA method of 5-day BOD measurement could be attributed to the mass transfer resistance of the membranes in the sensor but more significantly to the slow assimilation and bio-oxidation rates of these components by the BODSEED microbial system. Unlike the living cell BOD sensor which requires periodic additions of nutrients and minerals to keep the microorganisms alive and viable, the thermally killed cell BOD sensor can be stored in phosphate buffer at room temperature over long idling period without such periodic additions. More significantly with respect to commercialization of these biosensors, the thermally killed cells can be prepared in bulk and stored in dry sealed container over long period.

Biooxidation capacity of the extremely thermoacidophilic archaeon metallosphaera sedula under bioenergetic challenge

The biooxidation capacity of an extremely thermoacidophilic archaeon Metallosphaera sedula (DSMZ 5348) was examined under bioenergetic challenges imparted by thermal or chemical stress in regard to its potential use in microbial bioleaching processes. Within the normal growth temperature range of M. sedula (70-79 degrees C) at pH 2.0, upward temperature shifts resulted in bioleaching rates that followed an Arrhenius-like dependence. When the cells were subjected to supraoptimal temperatures through gradual thermal acclimation at 81 degrees C (Han et al., 1997), cell densities were reduced but 3 to 5 times faster specific leaching rates (Fe3+ released from iron pyrite/cell/h) could be achieved by the stressed cells compared to cells at 79 degrees C and 73 degrees C, respectively. The respiration capacity of M. sedula growing at 74 degrees C was challenged by poisoning the cells with uncouplers to generate chemical stress. When the protonophore 2,4-dinitrophenol (5-10 μM) was added to a growing culture of M. sedula on iron pyrite, there was little effect on specific leaching rates compared to a culture with no protonophore at 74 degrees C; 25 μM levels proved to be toxic to M. sedula. However, a significant stimulation in specific rate was observed when the cells were subjected to 1 μM nigericin (+135%) and 2 μM (+63%); 5 μM levels of the ionophore completely arrested cell growth. The ionophore effect was further investigated in continuous culture growing on ferrous sulfate at 74 degrees C. When 1 μM nigericin was added as a pulse to a continuous culture, a 30% increase in specific iron oxidation rate was observed for short intervals, indicating a potential positive impact on leaching when periodic chemical stress is applied. This study suggests that biooxidation rates can be increased by strategic exposure of extreme thermoacidophiles to chemical or thermal stress, and this approach should be considered for improving process performance. Copyright 1998 John Wiley & Sons, Inc.

Oxygen mass transfer limitation of batch bio-oxidation at high solids concentration

In contrast to the cyanide leaching of gold and acid leaching of uranium, performed at solids concentrations of 40 to 50 per cent, the concentrations used in the bio-oxidation of refractory gold-bearing sulphide concentrates have been limited to 18 to 20 per cent solids. Oxygen availability has been identified as a key factor limiting bio-oxidation at high solids concentration. Mass transfer correlations for agitated, aerated slurries have been used to predict the maximum oxygen transfer potential in typical industrial stirred tank reactors. Previously reported bio-oxidation rates have been used to predict the oxygen demand for typical operating conditions. In the region at lower solids concentrations, where the oxygen supply is not limiting, the bio-oxidation rate increases linearly with solids concentration. In the region where oxygen demand exceeds oxygen supply, the bio-oxidation rate is defined by the oxygen transfer potential of the system and the rate declines with increasing solids concentration. Predicted rates and limiting solids concentrations have been compared with data from the literature and found to be in agreement. A series of laboratory batch stirred tank reactor tests have been conducted to investigate the effect of sulphide grade and solids concentration on the specific bio-oxidation rate. The highest solids concentration for bio-oxidation of a particular sulphide, at the maximum specific bio-oxidation rate, is determined by the oxygen demand in relation to the oxygen transfer potential of the system. Low grade sulphides, with a low oxygen demand per unit mass, can be oxidised at far higher solids concentrations than high grade material.

In vitro synthesis of nitroxide free radicals by hog liver microsomes

The in vitro biooxidation of 4-hydroxy-2,2,6,60tetramethylpiperidine (TEMP), 4-hydroxy-2,2,4,4-tetyramethyl-1,3-oxazolidine (TEMO) and diphenylamine (DPA)_by hog liver microsomes to their respective nitroxide free radicals, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 2,2,4,4-tetramethyl-1,3-oxazolidine-1-oxyl (TEMOO), and diphenylnitroxide (DPNO) has been investigated. For extending the life span of the liver microsomes, a calcium alginate immobilization procedure was used. The biooxidation rates of the above amines to their respective nitroxide metabolites were measured by means of oxygen uptake at 37°C and pH 7.4. N-octylamine was found to be an activator in the biooxidation of the amines. The formation of the nitroxide radicals was identified by E.S.R. spectroscopy.

Inhibition of respiration of activated sludge: Variability and reproducibility of results

AbstractAssessment of the toxicity of chemicals to the respiration of activated sludge microorganisms is a relatively simple and reproducible method when applied to a standard population of bacteria. However, activated sludge is, by nature, a variable commodity, and varying results are often reported. Within‐plant variations can occur from day to day as a result of shifts in the bacterial population, probably caused by changes in the strength of components of the sewage feed. Between‐plant variations can be considerably greater. Factors such as differing operating conditions and presence of industrial waste waters in the sewage can result in differing species composition of the sludge, which, in turn, may account for differing biooxidation rates of components of the waste water and thus different respiration rates. Sludge from different sources, and/or grown under different conditions, may also vary in response to inhibitors, because of varying degrees of reaction of some inhibitors with non‐living sludge components. Therefore, in practice, it has been usual to consider EC50 values from the inhibition of respiration of activated sludge test in terms of order of magnitude. Variations in EC50 results of the ‘ISO’ inhibition of respiration test have been quantified for a number of chemicals, both within and between batches of sludge, and with sludges from different sources. The coefficient of variation of EC50 results within batches of sludge was found to be approximately 9%. Between batch and between source variations were 28–76% depending on the test chemical.

Occurrence and Rates of Chemical Biodegradation in Superior Harbor Water

Microbial degradation of ten industrial chemicals was measured in coarse-filtered Superior harbor water using the standard biochemical oxygen demand technique. The first-order biodegradation rate constants of seven chemicals were between 0.023/day for hexadecane and 0.247/day for phenol. Similarly, chemical half-lives were between 3 days for phenol and 30 days for hexadecane. Chemicals including benzene, N-methylaniline, and naphthalene were not measurably degraded by the native aquatic microbes. All biodegradable chemicals were tested to assess the effect of a reduced level of suspended matter on their bio-oxidation rates. Chemicals were incubated in fine-filtered harbor water containing 2.5 mg/L suspended solids. The rate constants of several soluble chemicals increased by an average of 74% in this filtered water from those in the coarse-filtered water containing 5.6 mg/L particulate matter. Four selected chemicals with half-lives greater than 9 days were tested to evaluate the effect of added nutrients and acclimated microorganisms on their biodegradation rates. Chemicals were incubated in coarse-filtered harbor water amended with 1) a source of nitrogen and phosphorus and/or 2) adapted microbial seeds of wastewater origin. Biodegradation rates of all test chemicals were greater in the water enriched with both supplements than in other test systems.

Biological treatment of wastewater from urea plants of Kuwait

A qualitative and quantitative study of the pollutants in the hydrolyzer effluent of the Petrochemical Industries Company (PIC) was undertaken.This task involved flow measurements coupled with a routine and intensive collection of wastewater samples, a comprehensive analysis for the determination of a set of 6–11 parameters and 10 heavy metals, and statistical analysis of the results.The results showed that despite process optimization of the hydrolyzer plant, the average concentration of ammonia and urea in the hydrolyzer effluent were 100 and 130 mg/l, respectively. The biological treatment studies were aimed at removing urea and ammonia in batch and continuous systems.Biological treatment in the batch system indicated that hydrolyzer effluent was a nutritionally deficient medium to sustain microbial growth, hence supplementation with optimum levels of nutrients was a prerequisite for high treatment efficiency. Kinetic studies were undertaken to optimize nitrification — denitrification and urea biodegradation. The observed rates of nitrification, denitrification, urea and combined nitrogen bio-oxidation rates were comparable to or sometimes better than the corresponding rates reported in the literature.In a continuous biological treatment system urea and ammonia could be completely removed from the hydrolyzer effluent at a hydraulic retention time of 20–24 hours and a solids retention time in excess of 30 days.The average concentrations of ammonia, nitrite, nitrate and urea in the final effluent were 0.3, 0.21, 0.4 and 0.0 mg/l, respectively; the total dissolved solids were 450 mg/l.

Phenol and free ammonia inhibition to Nitrosomonas activity

Laboratory evaluations were conducted of the rate of ammonia bio-oxidation to nitrite by an autotrophic culture of strict nitrifiers. Ammonia oxidation biokinetics was found to follow Michaelis-Menten type relationships. Experiments were conducted to quantify the influence of phenol, and the influence of un-ionized (free) ammonia on biokinetic parameters. Results show that the Michaelis-Menten constant varies with the square root of ambient phenol concentration, and that the influence of un-ionized ammonia on ammonia oxidation may be best described by a “substrate-inhibition” model which follows from classical Monod kinetics. This model explains, to a large degree, observed differences in ammonia bio-oxidation rates as functions of pH. Conclusions based on engineering calculations are presented to illustrate design and operational considerations for the biological removal of wastewater ammonia.

BIODISPOSAL FARMING OF REFINERY OILY WASTES

ABSTRACT Oily waste materials, whether they are derived from oil spill cleanup operations or generated during petroleum processing, present somewhat similar disposal problems which are of major concern. With oily waste disposal in sanitary landfills increasingly unacceptable and with the many problems and high costs associated with incineration, landspreading (landfarming) is becoming more and more important as a disposal method. Although simple in principle, it is somewhat complex in application with little experimental data available. The API has undertaken a study to define the requirements and limitations for an environmentally acceptable landspreading method. Suntech selected three sites in the United States for the study, one of which is discussed in this paper, namely, Toledo, Ohio. Typical refinery oily wastes were spread on test plots in multiple, controlled applications and tilled into the top eight inches of soil, and the fate of these wastes and their components in the soil environment was monitored for a two year period. Bio-oxidation rates were determined for the oil fractions. Microflora population counts served to monitor the microbial response and determine overall soil viability. Leachate and groundwater quality and surface runoff contamination were studied to assess any tendency toward waste constituent migration. Heavy metals, phenolics, and cyanides were also examined. Biodegradation rates were found to be substantial, with controlled applications in excess of 1,000 barrels of oil per acre per year.