Michael H. Huesemann

The Inhibition of Marine Nitrification by Ocean Disposal of Carbon Dioxide

In an attempt to reduce the threat of global warming, it has been proposed that the rise of atmospheric carbon dioxide concentrations be reduced by the ocean disposal of CO2 from the flue gases of fossil fuel-fired power plants. The release of large amounts of CO2 into mid or deep ocean waters will result in large plumes of acidified seawater with pH values ranging from 6 to 8. In an effort to determine whether these CO2-induced pH changes have any effect on marine nitrification processes, surficial (euphotic zone) and deep (aphotic zone) seawater samples were sparged with CO2 for varying time durations to achieve a specified pH reduction, and the rate of microbial ammonia oxidation was measured spectrophotometrically as a function of pH using an inhibitor technique. For both seawater samples taken from either the euphotic or aphotic zone, the nitrification rates dropped drastically with decreasing pH. Relative to nitrification rates in the original seawater at pH 8, nitrification rates were reduced by ca. 50% at pH 7 and more than 90% at pH 6.5. Nitrification was essentially completely inhibited at pH 6. These findings suggest that the disposal of CO2 into mid or deep oceans will most likely result in a drastic reduction of ammonia oxidation rates within the pH plume and the concomitant accumulation of ammonia instead of nitrate. It is unlikely that ammonia will reach the high concentration levels at which marine aquatic organisms are known to be negatively affected. However, if the ammonia-rich seawater from inside the pH plume is upwelled into the euphotic zone, it is likely that changes in phytoplankton abundance and community structure will occur. Finally, the large-scale inhibition of nitrification and the subsequent reduction of nitrite and nitrate concentrations could also result in a decrease of denitrification rates which, in turn, could lead to the buildup of nitrogen and unpredictable eutrophication phenomena. Clearly, more research on the environmental effects of ocean disposal of CO2 is needed to determine whether the potential costs related to marine ecosystem disturbance and disruption can be justified in terms of the perceived benefits that may be achieved by temporarily delaying global warming.

Predictive model for estimating the extent of petroleum hydrocarbon biodegradation in contaminated soils

A series of solid- and slurry-phase soil bioremediation experiments involving different crude oils and refined petroleum products were performed in order to investigate the factors which affect the maximum extent of total petroleum hydrocarbon (TPH) biodegradation. Utilizing a comprehensive petroleum hydrocarbon characterization procedure involving group type separation analyses, boiling point distributions, and hydrocarbon typing by field desorption mass spectroscopy, initial and final concentrations of specified hydrocarbon classes were determined in each of the seven bioremediation treatments

Guidelines for land‐treating petroleum hydrocarbon‐contaminated soils

Abstract During land treatment, environmental parameters are optimized to achieve the fastest and most complete biodegradation of petroleum hydrocarbons present in contaminated soils. This article provides specific guidelines for optimization of the land treatment process at a field site. In particular, the necessary steps in the land treatment procedure are outlined in the time sequence expected under field conditions. Specific steps include sampling and site assessment, determination of contaminant levels and characteristics, estimation of biodegradation potential, estimation of bacterial numbers in soil, design of the land treatment unit, adjustment of the soil pH and moisture content, addition of nutrient fertilizers and bulking agents, operation of the land treatment unit involving tilling and irrigation, periodic monitoring of specific environmental parameters, and final closure of the site. In addition, a number of examples are used to familiarize the reader with the numerical calculations involved...

The role of oxygen diffusion in passive bioremediation of petroleum contaminated soils

Abstract In passive bioremediation of petroleum hydrocarbon contaminated soils, oxygen diffusion is the primary mechanism for supplying the oxygen which is required for microbial hydrocarbon biodegradation processes. It is the objective of this research to theoretically evaluate whether passive bioremediation can be a feasible treatment alternative for petroleum contaminated soils. In this paper we derive equations for the steady-state oxygen concentration profiles which are expected to develop as a result of simultaneous oxygen diffusion and consumption in hydrocarbon contaminated soils. These equations are used to estimate the maximum oxygen penetration distance and the total cleanup time for several environmental scenarios such as surface and subsurface soil contamination as well as contaminated soil piles. It was found that oxygen is expected to penetrate most contaminated soils for up to several meters if hydrocarbon biodegradation rates are similar to those measured during bioventing respiration tests, i.e. approximately 2.5–10 ppm TPH day −1 . Both the depth of oxygen penetration and the total passive bioremediation cleanup time were found to be strongly dependent on the magnitude of the diffusion coefficient for oxygen in soil ( D s ). As expected, increased oxygen penetration distances and decreased cleanup times are associated with increased D s values. Since the magnitude of D s is inversely related to the soil moisture content, it is imperative to maintain moderately low soil moisture levels in order to maximize the effectiveness of passive bioremediation treatment. Passive bioremediation is expected to be a feasible and cost-effective treatment alternative for TPH contaminated soils in cases where the minimization of cleanup times is not a major remediation objective.

A Screening Model to Predict Microalgae Biomass Growth in Photobioreactors and Raceway Ponds

A microalgae biomass growth model was developed for screening novel strains for their potential to exhibit high biomass productivities under nutrient‐replete conditions in photobioreactors or outdoor ponds. Growth is modeled by first estimating the light attenuation by biomass according to Beer‐Lamberts Law, and then calculating the specific growth rate in discretized culture volume slices that receive declining light intensities due to attenuation. The model uses only two physical and two species‐specific biological input parameters, all of which are relatively easy to determine: incident light intensity, culture depth, as well as the biomass light absorption coefficient and the specific growth rate as a function of light intensity. Roux bottle culture experiments were performed with Nannochloropsis salina at constant temperature (23°C) at six different incident light intensities (10, 25, 50, 100, 250, and 850 µmol/m2 s) to determine both the specific growth rate under non‐shading conditions and the biomass light absorption coefficient as a function of light intensity. The model was successful in predicting the biomass growth rate in these Roux bottle batch cultures during the light‐limited linear phase at different incident light intensities. Model predictions were moderately sensitive to minor variations in the values of input parameters. The model was also successful in predicting the growth performance of Chlorella sp. cultured in LED‐lighted 800 L raceway ponds operated in batch mode at constant temperature (30°C) and constant light intensity (1,650 µmol/m2 s). Measurements of oxygen concentrations as a function of time demonstrated that following exposure to darkness, it takes at least 5 s for cells to initiate dark respiration. As a result, biomass loss due to dark respiration in the aphotic zone of a culture is unlikely to occur in highly mixed small‐scale photobioreactors where cells move rapidly in and out of the light. By contrast, as supported also by the growth model, biomass loss due to dark respiration occurs in the dark zones of the relatively less well‐mixed pond cultures. In addition to screening novel microalgae strains for high biomass productivities, the model can also be used for optimizing the pond design and operation. Additional research is needed to validate the biomass growth model for other microalgae species and for the more realistic case of fluctuating temperatures and light intensities observed in outdoor pond cultures. Biotechnol. Bioeng. 2013; 110: 1583–1594.

Can pollution problems be effectively solved by environmental science and technology? An analysis of critical limitations

Abstract It is currently believed that science and technology can provide effective solutions to most, if not all, environmental problems facing western industrial societies. The validity of this optimistic assumption is highly questionable for at least three reasons: First, current mechanistic, reductionist science is inherently incapable of providing the complete and accurate information which is required to successfully address environmental problems. Second, both the conservation of mass principle and the second law of thermodynamics dictate that most remediation technologies — while successful in solving specific pollution problems — cause unavoidable negative environmental impacts elsewhere or in the future. Third, it is intrinsically impossible to design industrial processes that have no negative environmental impacts. This follows not only from the entropy law but also from the fact that any generation of energy is impossible without negative environmental consequences. It can therefore be concluded that science and technology have only very limited potential in solving current and future environmental problems. Consequently, it will be necessary to address the root cause of environmental deterioration, namely, the prevailing materialistic values that are the main driving force for both overpopulation and overconsumption. The long-term protection of the environment is, therefore, not primarily a technical problem but rather a social and moral problem that can only be solved by drastically reducing the strong influence of materialistic values.

Incomplete Hydrocarbon Biodegradation in Contaminated Soils: Limitations in Bioavailability or Inherent Recalcitrance?

Abstract Bioremediation has been used to treat soils contaminated with complex mixtures of organic compounds such as total petroleum hydrocarbons (TPH), oil and grease (O&G), or polycyclic aromatic hydrocarbons (PAHs). Despite the common use and cost-effectiveness of bioremediation for treating hydrocarbon-contaminated soils, it has been observed that a residual fraction remains undegraded in the soil even when optimal biodegradation conditions have been provided. This paper provides a brief review of the two major conceptual models that have been used to explain why a residual hydrocarbon fraction remains in the soil after bioremediation treatment. The contaminant sequestration model is based on the assumption that a certain fraction of hydrocarbons is “locked up” in small soil pores within soil particles or aggregates. These sorbed hydrocarbons are believed to be inaccessible to soil microorganisms. Consequently, limitations in bioavailability are thought to be the major reason for incomplete hydrocarbo...

Acetone-butanol fermentation of marine macroalgae.

The objective of this study was to subject mannitol, either as a sole carbon source or in combination with glucose, and aqueous extracts of the kelp Saccharina spp., containing mannitol and laminarin, to acetone-butanol fermentation by Clostridium acetobutylicum (ATCC 824). Both mannitol and glucose were readily fermented. Mixed substrate fermentations with glucose and mannitol resulted in diauxic growth of C. acetobutylicum with glucose depletion preceding mannitol utilization. Fermentation of kelp extract exhibited triauxic growth, with an order of utilization of free glucose, mannitol, and bound glucose, presumably laminarin. The lag in laminarin utilization reflected the need for enzymatic hydrolysis of this polysaccharide into fermentable sugars. The butanol and total solvent yields were 0.12 g/g and 0.16 g/g, respectively, indicating that significant improvements are still needed to make industrial-scale acetone-butanol fermentations of seaweed economically feasible.

A Comparison of Nannochloropsis salina Growth Performance in Two Outdoor Pond Designs: Conventional Raceways versus the ARID Pond with Superior Temperature Management

The present study examines how climatic conditions and pond design affect the growth performance of microalgae. From January to April of 2011, outdoor batch cultures of Nannochloropsis salina were grown in three replicate 780 L conventional raceways, as well as in an experimental 7500 L algae raceway integrated design (ARID) pond. The ARID culture system utilizes a series of 8–20 cm deep basins and a 1.5 m deep canal to enhance light exposure and mitigate temperature variations and extremes. The ARID culture reached the stationary phase 27 days earlier than the conventional raceways, which can be attributed to its superior temperature management and shallower basins. On a night when the air temperature dropped to −9°C, the water temperature was 18°C higher in the ARID pond than in the conventional raceways. Lipid and fatty acid content ranged from 16 to 25% and from 5 to15%, respectively, as a percentage of AFDW. Palmitic, palmitoleic, and eicosapentaenoic acids comprised the majority of fatty acids. While the ARID culture system achieved nearly double the volumetric productivity relative to the conventional raceways (0.023 versus 0.013 g L−1day−1), areal biomass productivities were of similar magnitude in both pond systems (3.47 versus 3.34 g m−2day−1), suggesting that the ARID pond design has to be further optimized, most likely by increasing the culture depth or operating at higher cell densities while maintaining adequate mixing.

Microbial Factors Rather Than Bioavailability Limit the Rate and Extent of PAH Biodegradation in Aged Crude Oil Contaminated Model Soils

The rate and extent of polynuclear aromatic hydrocarbons (PAH) biodegradation in a set of aged model soils that had been contaminated with crude oil at the high concentrations (i.e.,>20,000 mg/kg) normally found in the environment were measured in 90-week slurry bioremediation experiments. Soil properties such as organic matter content, mineral type, particle diameter, surface area, and porosity did not significantly influence the PAH biodegradation kinetics among the 10 different model soils. A comparison of aged and freshly spiked soils indicates that aging affects the biodegradation rate and extent only for higher-molecular-weight PAHs, while the effects of aging are insignificant for 4-ring PAHs and total PAHs. In all model soils with the exception of kaolinite clay, the rate of abiotic desorption was faster than the rate of biodegradation during the initial phase of bioremediation treatment, indicating that PAH biodegradation was limited by microbial factors. Similarly, any of the higher-molecular-weight PAHs that were still present after 90 weeks of treatment were released rapidly during abiotic desorption tests, which demonstrates that bioavailability limitations were not responsible for the recalcitrance of these hydrocarbons. Indeed, an analysis of microbial counts indicates that a severe reduction in hydrocarbon degrader populations may be responsible for the observed incomplete PAH biodegradation. Therefore, it can be concluded that the recalcitrance of PAHs during bioremediation is not necessarily due to bioavailability limitations and that these residual contaminants therefore might pose a greater risk to environmental receptors than previously thought.