Kinetics of Oxygen Release from ORC

Oxygen release compounds (ORC) are one possibility to enhance aerobic degradation in contaminated aquifers. However, some applications have been reported where oxygen concentrations did not meet expectations, this was attributed to ground water composition, e.g., high pH. Column experiments have been performed and the measurements were interpreted using a numerical model to investigate oxygen release kinetics from ORC in more detail. Because the zero-order rate law recommended by the manufacturer did not reflect the measurements, a more complex kinetic scheme was developed. The simulations show a minor influence of inorganic ground water constituents on oxygen release from ORC in the columns due to buffering by mineral precipitation, but an enhanced oxygen release if aerobic degradation takes place. If ORC is applied as socks, the impact of inorganic ground water composition increases compared to the application in column experiments. A simple quadratic equation is provided to estimate oxygen release rate from the buffer capacity of the ground water versus increasing pH—a parameter easily determinable in the laboratory. For slightly mineralized waters with high pH, this equation forecasts decreased oxygen release, but no total inhibition of oxygen release.     

Mixed aerobic and anaerobic microbial communities in benzene-contaminated groundwater

Aims:  To investigate the factors affecting benzene biodegradation and microbial community composition in a contaminated aquifer.
Methods and Results:  We identified the microbial community in groundwater samples from a benzene-contaminated aquifer situated below a petrochemical plant. Eleven out of twelve groundwater samples with in situ dissolved oxygen concentrations between 0 and 2·57 mg l⁻¹ showed benzene degradation in aerobic microcosm experiments, whereas no degradation in anaerobic microcosms was observed. The lack of aerobic degradation in the remaining microcosm could be attributed to a pH of 12·1. Three groundwaters, examined by 16S rRNA gene clone libraries, with low in situ oxygen concentrations and high benzene levels, each had a different dominant aerobic (or denitrifying) population, either Pseudomonas , Polaromonas or Acidovorax species. These groundwaters also had syntrophic organisms, and aceticlastic methanogens were detected in two samples. The alkaline groundwater was dominated by organisms closely related to Hydrogenophaga .
Conclusions:  Results show that pH 12·1 is inimical to benzene biodegradation, and that oxygen concentrations below 0·03 mg l⁻¹ can support aerobic benzene-degrading communities.
Significance and Impact of the Study:  These findings will help to guide the treatment of contaminated groundwaters, and raise questions about the extent to which aerobes and anaerobes may interact to effect benzene degradation.     

Lough Ennell: laboratory studies on sediment phosphorus release under varying mixing, aerobic and anaerobic conditions

SUMMARY. 1. The exchange of phosphorus between the epilimnetic (shallow zone) sediment and water column in Lough Ennell was investigated in laboratory experiments using five intact cores.
2. Variations in water mixing, sediment suspension and aerobic–anaerobic oxygen status in the water column and its effects on sediment phosphorus release rates were determined.
3. Experimental results indicated that phosphorus release is possible under both aerobic and anaerobic conditions. Aerobic release (0.025 mg P l⁻¹ over 5 days) was possible up to the point when mass resuspension of sediment occurred. Anaerobic release for the same period and mixing conditions was 0.183 mg Pl⁻¹.
4. The release rate under aerobic conditions at 10°C equates to an internal areal loading of 0.134 g P m⁻² yr^−1, which is approximately 17% and 30% of the average total phosphorus and orthophosphate loadings respectively for the period 1974–79.
5. The results clearly implicate aerobic inorganic phosphorus release from the epilimnetic sediments as a significant source of this nutrient to the overlying water column and is likely a major factor in the continuing eutrophic status in the lake.     

Aerobic Biodegradation of Mononitrotoluenes in Batch and Continuous Reactor Systems

Degradations of nitrotoluenes, individually and in a mixture, were carried out in batch and continuous aerobic reactors by a defined mixed microbial culture. The degradation rates and efficiencies of the isomers were evaluated in batch and continuous reactors. The results demonstrated that all the three-mononitrotoluene isomers were degraded simultaneously and completely in presence of excess oxygen. The nitro group position on the benzene ring influenced the degradation rates of the individual MNT isomers in batch systems. In the continuous biofilm reactor with a sufficient biocatalyst quantity, quality and excessive oxygen supply rate, the degradation rates of the mononitrotoluenes were almost identical as long as the compounds were present individually and their loading did not exceed the capacity of the catabolic master reaction. The microbial composition of the biofilm changed qualitatively and quantitatively during long-term continuous operation under aerobic non-aseptic conditions. This complex investigation resulted in data that can be applied for the scale-up procedure for field experiments.     

Modeling aerobic carbon source degradation processes using titrimetric data and combined respirometric-titrimetric data: experimental data and model structure

Experimental data are presented that resulted from aerobic batch degradation experiments in activated sludge with simple carbon sources (acetate and dextrose) as substrates. Data collection was done using combined respirometric-titrimetric measurements. The respirometer consists of an open aerated vessel and a closed non-aerated respiration chamber for monitoring the oxygen uptake rate related to substrate degradation. The respirometer is combined with a titrimetric unit that keeps the pH of the activated sludge sample at a constant value by addition of acid and/or base. The experimental data clearly showed that the activated sludge bacteria react with consumption or production of protons during aerobic degradation of the two carbon sources under study. Thus, the cumulative amount of added acid and/or base could serve as a complementary information source on the degradation processes. For acetate, protons were consumed during aerobic degradation, whereas for dextrose protons were produced. For both carbon sources, a linear relationship was found between the amount of carbon source added and the amount of protons consumed (in case of acetate: 0.38 meq/mmol) or produced (in case of dextrose: 1.33 meq/mmol) during substrate degradation. A model taking into account substrate uptake, CO(2) production, and NH(3) uptake for biomass growth is proposed to describe the aerobic degradation of a C(x)H(y)O(z)-type carbon source. Theoretical evaluation of this model for reference parameters showed that the proton effect due to aerobic substrate degradation is a function of the pH of the liquid phase. The proposed model could describe the experimental observations with both carbon sources.     

A method for controlling hydrogen sulfide in water by adding solid phase oxygen

This work evaluates the addition of solid phase oxygen, a magnesium peroxide (MgO(2)) formulation manufactured by Regenesis (oxygen-releasing compounds, ORC), to inhibit the production of hydrogen sulfide (H(2)S) in an SRB-enriched environment. The initial rate of release of oxygen by the ORC was determined over a short period by adding sodium sulfite (Na(2)SO(3)), which was a novel approach developed for this study. The ability of ORCs to control H(2)S by releasing oxygen was evaluated in a bench-scale column containing cultured sulfate reducing bacteria (SRB). After a series of batch tests, 0.4% ORC was found to be able to inhibit the formation of H(2)S for more than 40 days. In comparison, the concentration of H(2)S dropped from 20 mg S/L to 0.05 mg S/L immediately after 0.1% hydrogen peroxide (H(2)O(2)) was added, but began to recover just four days later. Thus, H(2)O(2) does not seem to be able to inhibit the production of sulfide for an extended period of time. By providing long-term inhibition of the SRB population, ORC provides a good alternative means of controlling the production of H(2)S in water.     

The role of external and matrix pH in mitochondrial reactive oxygen species generation

Reactive oxygen species (ROS) generation in mitochondria as a side product of electron and proton transport through the inner membrane is important for normal cell operation as well as development of pathology. Matrix and cytosol alkalization stabilizes semiquinone radical, a potential superoxide producer, and we hypothesized that proton deficiency under the excess of electron donors enhances reactive oxygen species generation. We tested this hypothesis by measuring pH dependence of reactive oxygen species released by mitochondria. The experiments were performed in the media with pH varying from 6 to 8 in the presence of complex II substrate succinate or under more physiological conditions with complex I substrates glutamate and malate. Matrix pH was manipulated by inorganic phosphate, nigericine, and low concentrations of uncoupler or valinomycin. We found that high pH strongly increased the rate of free radical generation in all of the conditions studied, even when DeltapH=0 in the presence of nigericin. In the absence of inorganic phosphate, when the matrix was the most alkaline, pH shift in the medium above 7 induced permeability transition accompanied by the decrease of ROS production. ROS production increase induced by the alkalization of medium was observed with intact respiring mitochondria as well as in the presence of complex I inhibitor rotenone, which enhanced reactive oxygen species release. The phenomena revealed in this report are important for understanding mechanisms governing mitochondrial production of reactive oxygen species, in particular that related with uncoupling proteins.     

Aerobic phosphorus release linked to acetate uptake in bio-P sludge: process modeling using oxygen uptake rate

The main processes involved in enhanced biological phosphorus removal (EBPR) under anaerobic and subsequently aerobic conditions are widely described in the literature. Polyphosphate accumulating organisms (PAO) are the organisms responsible for this process. However, the mechanisms of PAO are not fully established yet under conditions that differ from the classical anaerobic/aerobic conditions. In this work, we made a comparison between the behavior of PAO under classical EBPR conditions and its behavior when consuming substrate under only aerobic conditions. In addition, oxygen uptake rate (OUR) was measured in the set of experiments under aerobic conditions to improve the characterization of the process. A kinetic and stoichiometric model based on Activated Sludge Model No.2 (ASM2) and including glycogen economy (AnOx model), calibrated for classical anaerobic/aerobic conditions, was not able to describe the experimental data since it underestimated the acetate consumption, the PHB storage, and the OUR. Two different hypotheses for describing the experimental measurements were proposed and modeled. Both hypotheses considered that PAO, under aerobic conditions, uptake acetate coupled to PHB storage, glycogen degradation, and phosphorus release as in anaerobic conditions. Moreover, the first hypothesis (PAO-hypothesis) considered that PAO were able to store acetate as PHB linked to oxygen consumption and the second one (OHO hypothesis) considered that this storage was due to ordinary heterotrophic organisms (OHO). Both hypotheses were evaluated by simulation extending the AnOx model with additional equations. The main differences observed were the predictions for PHB degradation during the famine phase and the OUR profile during both feast and famine phases. The OHO hypothesis described the experimental profiles more accurately than the PAO hypothesis.     

Carbon System Measurements and Potential Climatic Drivers at a Site of Rapidly Declining Ocean pH

We explored changes in ocean pH in coastal Washington state, USA, by extending a decadal-scale pH data series, by reporting independent measures of dissolved inorganic carbon (DIC), spectrophotometric pH, and total alkalinity (TA), by exploring pH patterns over larger spatial scales, and by probing for long-term trends in environmental variables reflecting potentially important drivers of pH. We found that pH continued to decline in this area at a rapid rate, that pH exhibited high natural variability within years, that our measurements of pH corresponded well to spectrophotometric pH measures and expected pH calculated from DIC/TA, and that TA estimates based on salinity predicted well actual alkalinity. Multiple datasets reflecting upwelling, including water temperature, nutrient levels, phytoplankton abundance, the NOAA upwelling index, and data on local wind patterns showed no consistent trends over the period of our study. Multiple datasets reflecting precipitation change and freshwater runoff, including precipitation records, local and regional river discharge, salinity, nitrate and sulfate in rainwater, and dissolved organic carbon (DOC) in rivers also showed no consistent trends over time. Dissolved oxygen did not decline over time, indicating that long-term changes did not result from shifts in contributions of respiration to pH levels. These tests of multiple potential drivers of the observed rapid rate of pH decline indicate a primary role for inorganic carbon and suggest that geochemical models of coastal ocean carbon fluxes need increased investigation.     

Fate and biodegradability of sulfonated aromatic amines

Ten sulfonated aromatic amines were tested for their aerobic and anaerobic biodegradability and toxicity potential in a variety of environmental inocula. Of all the compounds tested, only two aminobenzenesulfonic acid (ABS) isomers, 2- and 4-ABS, were degraded. The observed degradation occurred only under aerobic conditions with inocula sources that were historically polluted with sulfonated aromatic amines. Bioreactor experiments, with non-sterile synthetic wastewater, confirmed the results from the aerobic batch degradation experiments. Both ABS isomers were degraded in long-term continuous experiment by abioaugmented enrichment culture. The maximum degradation rate in the aerobic bioreactor was 1.6–1.8 gl^–1 d^–1 for 2-ABS and a somewhat lower value for 4-ABS at hydraulic retention times (HRT) of 2.8–3.3h. Evidence for extensive mineralization of 2- and 4-ABS was based on oxygen uptake and carbon dioxide production during the batch experiments and the high levels of chemical oxygen demand (COD) removal in the bioreactor. Furthermore, mineralization of the sulfonate group was demonstrated by high recovery of sulfate. The sulfonated aromatic amines did not show any toxic effects on the aerobic and anaerobic bacterial populations tested. The poor biodegradability of sulfonated aromatic amines indicated under the laboratory conditions of this study suggests that these compounds may not be adequately removed during biological wastewater treatment.     

Synthesis of Polygalacturonate Trans-eliminase and Polygalacturonase by a Strain of Enterobacter cloacae Isolated from Ponded Sitka Spruce

During the ponding of Sitka spruce in lake water there was a change from a diverse, aerobic flora (16 species) to a restricted, facultatively anaerobic flora (1 or 2 species). This change corresponded with a marked increase in the degradation of pectin and a concomitant increase in the permeability of the wood to preservatives. A strain of Enterobacter cloacae (NCPPB 2909) isolated during ponding, synthesized an extracellular and intracellular polygalacturonase (PG) and an intracellular polygalacturonate trans-eliminase (PGTE). Both PG and PGTE were growth–linked; extracellular PG was produced initially and then replaced by intracellular PG and PGTE. A change in the pH value of the medium did not alter the relative synthesis of enzyme. Reduced oxygen tension retarded growth but had no effect on enzyme activities. PG and PGTE of E. cloacae were shown to have specific ion requirements and when tap-water was used in the preparation of a medium growth did not occur. The results are discussed in relation to an artificial system of sprinkling water, seeded with known species of bacteria, on to spruce wood in order to control the rate of pectin degradation and thus the permeability of the wood to preservatives.     

The effect of a protein on the radiolysis of DNA studied by HPLC and pulse radiolysis

Double-stranded DNA from calf thymus was irradiated in the presence of bovine serum albumin (BSA) with a ratio of 1:10 in weight, at pH7 and pH5, under aerobic and under anaerobic conditions. The irradiated biomolecules were separated by high-performance liquid-gel permeation chromatography. At pH 7, in the presence of the protein, degradation of DNA was enhanced by oxygen, while under anaerobic conditions formation of protein-DNA crosslinks was observed. At pH5, crosslinking of BSA to DNA occurred under anaerobic as well as under aerobic conditions, while fragmentation of DNA could not be detected with this method with doses up to 1600 Gy. Under nitrogen, the degradation of BSA was not altered by the addition of DNA, but in the presence of oxygen less BSA was lost for a given dose when DNA was present.     

Stimulation of hybrid poplar growth in petroleum-contaminated soils through oxygen addition and soil nutrient amendments

Hybrid poplar trees (Populus deltoides x nigra DN34) were grown in a green-house using hydrocarbon-contaminated soil from a phytoremediation demonstration site in Health, Ohio. Two independent experiments investigated the effect of nutrient addition on poplar growth and the importance of oxygen addition to root development and plant growth. Biomass measurements, poplar height, and leaf color were used as indicators of plant health in the selection of a 10/5/5 NPK fertilizer applied at 1121 kg/ha (112 kg-N, 24.4 kg-P, 46.5 kg-K per ha) to enhance hybrid poplar growth at the Health site. Five passive methods of oxygen delivery were examined, including aeration tubes, gravel addition, and an Oxygen Release Compound (ORC). When ORC was placed in coffee filters above hydrocarbon-contaminated soil, a statistically significant increase of 145% was observed in poplar biomass growth, relative to unamended controls. The ORC in filters also stimulated significant increases in root density. A 15.2-cm interval of soil directly below ORC addition exhibited an increase from 2.6 +/- 1.0 mg/cm3 to 4.8 +/- 1.0 mg/cm3, showing stimulation of root growth in hydrocarbon-stained soil. The positive response of hybrid poplars to oxygen amendments suggests that overcoming oxygen limitation to plants should be considered in phytoremediation projects when soil contamination exerts a high biochemical oxygen demand, such as in former refinery sites.     

Nutrients and oxygen alter reservoir biochemical characters and enhance oil recovery during biostimulation

Biostimulation of petroleum reservoir to improve oil recovery has been conducted in a large number of oilfields. However, the roles and linkages of organic nutrients, inorganic salts and oxygen content during biostimulation have not been effectively elucidated. Therefore, we investigated the relationships between carbon source, nitrogen source, phosphorus source, oxygen content, and microbial stimulation, oil emulsification, and oil degradation. The organic nutrients (molasses) accelerated microbial growth, and promoted oil emulsification under aerobic conditions. The added molasses also promoted metabolites production (CO₂, CH₄ and acetic acid) and microbial anaerobic hydrocarbon degradation under anaerobic conditions. (NH₄)₂HPO₄ improved gases production by neutralizing the acidic production and molasses. NaNO₃ could also improve gases production by inhibiting sulfate-reducing bacteria to adjust pH value. Oxygen supply was necessary for oil emulsification, but bountiful supply of oxygen aggravated oil degradation, leading the entire ranges of alkanes and some aromatic hydrocarbons were degraded. Core-flooding experiments showed an oil displacement efficiency of 13.81 % in test with air package injected, 8.56 % without air package injection, and 4.77 % in control test with air package injection and 3.61 % without air package injection. The results suggest that the combined effect of organic nutrients, inorganic salts and oxygen content determines microbial growth, while production of metabolites, oil emulsification and biodegradation alter the reservoir biochemical characters and influence oil recovery during stimulation.     

Studies on the physiology of microbial degradation of pentachlorophenol

Summary The requirements and conditions for pentachlorophenol (PCP) biodegradation by a mixed bacterial culture was studied. The effects of oxygen, nutrients, additional carbon sources, pH and temperature are described. Up to 90% of PCP was degraded into CO₂ and inorganic chloride in 1 week at an input concentration of <600 M. Degradation continued when pO₂ was lowered to 0.0002 atm but ceased when pO₂ was further decreased to 0.00002 atm. Supplementary carbon sources, such as phenol, hydroxybenzoic acids or complex nutrients did not affect the biodegradation, but the presence of ammonium salts enhanced the rate of PCP degradation without affecting the yield of CO₂. The degrading organisms were shown to be procaryotic mesophiles; no degradation was shown at temperatures below +8° and above +50°C. The optimum pH for degradation was from 6.4 to 7.2 and at higher pH value (8.4) degradation was inhibited more than at lower pH (5.6).     

Effect of aeration rate and waste load on evolution of volatile fatty acids and waste stabilization during thermophilic aerobic digestion of a model high strength agricultural waste

Thermophilic aerobic digestion (TAD) is a relatively new, dynamic and versatile low technology for the economic processing of high strength waste slurries. Waste so treated may be safely disposed of or reused. In this work a model high strength agricultural waste, potato peel, was subjected to TAD to study the effects of oxygen supply at 0.1, 0.25, 0.5 and 1.0 vvm (volume air per volume slurry per minute) under batch conditions at 55 degrees C for 156 h on the process. Process pH was controlled at 7.0 or left unregulated. Effects of waste load, as soluble chemical oxygen demand (COD), on TAD were studied at 4.0, 8.0, 12.0 and 16.0 gl(-1) (soluble COD) at pH 7.0, 0.5 vvm and 55 degrees C. Efficiency of treatment, as degradation of total solids, total suspended solids and soluble solid, as well as soluble COD significantly increased with aeration rate, while acetate production increased as the aeration rate decreased or waste load increased, signifying deterioration in treatment. Negligible acetate, and no other acids were produced at 1.0 vvm. Production of propionate and other acids increased after acetate concentration had started to decrease and, during unregulated reactions coincided with the drop in the pH of the slurry. Acetate production was more closely associated with periods of oxygen limitation than were other acids. Reduction in oxygen availability led to deterioration in treatment efficiency as did increase in waste load. These variables may be manipulated to control treated waste quality.     

Bio-drying of municipal solid waste with high water content by aeration procedures regulation and inoculation

To improve the water content reduction of municipal solid waste with high water content, the operations of supplementing a hydrolytic stage prior to aerobic degradation and inoculating the bio-drying products were conducted. A 'bio-drying index' was used to evaluate the bio-drying performance. For the aerobic processes, the inoculation accelerated organics degradation, enhanced the lignocelluloses degradation rate by 10.4%, and lowered water content by 7.0%. For the combined hydrolytic-aerobic processes, the inoculum addition had almost no positive effect on the bio-drying efficiency, but it enhanced the lignocelluloses degradation rate by 9.6% and strengthened the acidogenesis in the hydrolytic stage. Compared with the aerobic processes, the combined processes had a higher bio-drying index (4.20 for non-inoculated and 3.67 for the inoculated trials). Moreover, the lowest final water content occurred in the combined process without inoculation (50.5% decreased from an initial 72.0%).     

The Kill Date as a Management Tool for Cover Cropping Success

Integrating cover crops (CC) in rotations provides multiple ecological services, but it must be ensured that management does not increase pre-emptive competition with the subsequent crop. This experiment was conducted to study the effect of kill date on: (i) CC growth and N content; (ii) the chemical composition of residues; (iii) soil inorganic N and potentially mineralizable N; and (iv) soil water content. Treatments were fallow and a CC mixture of barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) sown in October and killed on two different dates in spring. Above-ground biomass and chemical composition of CC were determined at harvest, and ground cover was monitored based on digital image analysis. Soil mineral N was determined before sowing and after killing the CC, and potentially mineralizable N was measured by aerobic incubation at the end of the experiment. Soil water content was monitored daily to a depth of 1.1 m using capacitance sensors. Under the present conditions of high N availability, delaying kill date increased barley above-ground biomass and N uptake from deep soil layers; little differences were observed in vetch. Postponing kill date increased the C/N ratio and the fiber content of plant residues. Ground cover reached >80% by the first kill date (∼1250°C days). Kill date was a means to control soil inorganic N by balancing the N retained in the residue and soil, and showed promise for mitigating N losses. The early kill date decreased the risk of water and N pre-emptive competition by reducing soil depletion, preserving rain harvested between kill dates and allowing more time for N release in spring. The soil potentially mineralizable N was enhanced by the CC and kill date delay. Therefore kill date is a crucial management variable for maximizing the CC benefits in agricultural systems.     

Effect of γ Irradiation on the Fatty Acid Composition of Soybean and Soybean Oil

Food irradiation is a form of food processing to extend the shelf life and reduce spoilage of food. We examined the effects of γ radiation on the fatty acid composition, lipid peroxidation level, and antioxidative activity of soybean and soybean oil which both contain a large amount of unsaturated fatty acids. Irradiation at 10 to 80 kGy under aerobic conditions did not markedly change the fatty acid composition of soybean. While 10-kGy irradiation did not markedly affect the fatty acid composition of soybean oil under either aerobic or anaerobic conditions, 40-kGy irradiation considerably altered the fatty acid composition of soybean oil under aerobic conditions, but not under anaerobic conditions. Moreover, 40-kGy irradiation produced a significant amount of trans fatty acids under aerobic conditions, but not under anaerobic conditions. Irradiating soybean oil induced lipid peroxidation and reduced the radical scavenging activity under aerobic conditions, but had no effect under anaerobic conditions. These results indicate that the fatty acid composition of soybean was not markedly affected by radiation at 10 kGy, and that anaerobic conditions reduced the degradation of soybean oil that occurred with high doses of γ radiation.     

Mineralization of N and P along a trophic gradient in a freshwater mire

Release of inorganic nitrogen and phosphorus in the soil of a peatland (fen) in The Netherlands was measured by means of an in situ incubation technique. Three sampling stations were chosen along a gradient in the plant productivity and water chemistry of the fen. The station with the highest biomass production was located near the ditch that supplied the fen with water in amounts matching water losses through evaporation and downward percolation to the groundwater. Water chemistry at this station strongly resembled that of the ditch water. The two stations remote from the ditch had much lower plant biomass, and significantly lower pH, conductivity, and calcium and bicarbonate concentrations. The vegetation at these two stations was characterized by a thick Sphagnum carpet.The release of inorganic N and P was much faster at the two stations remote from the ditch than at that located near the ditch. The differences in mineralization rate are probably due to the differences in water chemistry; phosphates are more soluble at low than at high pH. The fast N mineralization at stations with a thick Sphagnum carpet may be related to the chemical composition of Sphagnum litter. The difference in productivity is not explained by the N and P mineralization rates. Direct supply of N and P from the ditch are probably the main cause of the high productivity at the station bordering the ditch.