R. Guy Riefler

Respirometric assay for biofilm kinetics estimation: Parameter identifiability and retrievability

Currently, no fast and accurate methods exist for measuring extant biokinetic parameters for biofilm systems. This article presents a new approach to measure extant biokinetic parameters of biofilms and examines the numerical feasibility of such a method. A completely mixed attached growth bioreactor is subjected to a pulse of substrate, and oxygen consumption is monitored by on-line measurement of dissolved oxygen concentration in the bulk liquid. The oxygen concentration profile is then fit with a mechanistic mathematical model for the biofilm to estimate biokinetic parameters. In this study a transient biofilm model is developed and solved to generate dissolved oxygen profiles in the bulk liquid. Sensitivity analysis of the model reveals that the dissolved oxygen profiles are sufficiently sensitive to the biokinetic parameters-the maximum specific growth rate coefficient (insertion markμ) and the half-saturation coefficient (Ks)-to support parameter estimation if accurate estimates of other model parameters can be obtained. Monte Carlo simulations are conducted with the model to add typical measurement error to the generated dissolved oxygen profiles. Even with measurement error in the dissolved oxygen profile, a pair of biokinetic parameters is always retrievable. The geometric mean of the parameter estimates from the Monte Carlo simulations prove to be an accurate estimator for the true biokinetic values. Higher precision is obtained for insertion markμ estimates than for Ks estimates. In summary, this theoretical analysis reveals that an on-line respirometric assay holds promise for measuring extant biofilm kinetic parameters. Copyright 1998 John Wiley & Sons, Inc.

NAD(P)H:Flavin Mononucleotide Oxidoreductase Inactivation during 2,4,6-Trinitrotoluene Reduction

ABSTRACT Bacteria readily transform 2,4,6-trinitrotoluene (TNT), a contaminant frequently found at military bases and munitions production facilities, by reduction of the nitro group substituents. In this work, the kinetics of nitroreduction were investigated by using a model nitroreductase, NAD(P)H:flavin mononucleotide (FMN) oxidoreductase. Under mediation by NAD(P)H:FMN oxidoreductase, TNT rapidly reacted with NADH to form 2-hydroxylamino-4,6-dinitrotoluene and 4-hydroxylamino-2,6-dinitrotoluene, whereas 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene were not produced. Progressive loss of activity was observed during TNT reduction, indicating inactivation of the enzyme during transformation. It is likely that a nitrosodinitrotoluene intermediate reacted with the NAD(P)H:FMN oxidoreductase, leading to enzyme inactivation. A half-maximum constant with respect to NADH, KN, of 394 μM was measured, indicating possible NADH limitation under typical cellular conditions. A mathematical model that describes the inactivation process and NADH limitation provided a good fit to TNT reduction profiles. This work represents the first step in developing a comprehensive enzyme level understanding of nitroarene biotransformation.

Kinetic analysis of simultaneous 2,4-dinitrotoluene (DNT) and 2, 6-DNT biodegradation in an aerobic fluidized-bed biofilm reactor.

We previously reported on the mineralization of 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) in an aerobic fluidized-bed bioreactor (FBBR) (Lendenmann et al. 1998 Environ Sci Technol 32:82-87). The current study examines the kinetics of 2, 4-DNT and 2,6-DNT mineralization at increasing loading rates in the FBBR with the goal of obtaining system-independent kinetic parameters. At each steady state, the FBBR was subjected to a set of transient load experiments in which substrate flux in the biofilm and bulk substrate concentrations were measured. The pseudo-steady-state data were used to estimate the biokinetic parameters for 2,4-DNT and 2,6-DNT removal using a mechanistic mathematical biofilm model and a routine that minimized the sum of the squared residuals (RSS). Estimated kinetic parameters varied slightly for each steady-state; retrieved parameters for qm were 0. 83 to 0.98 g DNT/g XCOD d for 2,4-DNT removal and 0.14 to 0.33 g DNT/g XCOD d for 2,6-DNT removal. Ks values for 2,4-DNT removal (0. 029 to 0.36 g DNT/m3) were consistently lower than Ks values for 2, 6-DNT removal (0.21 to 0.84 g DNT/m3). A new approach was introduced to estimate the fundamental biofilm kinetic parameter S*b,min from steady-state performance information. Values of S*b,min indicated that the FBBR performance was limited by growth potential. Adequate performance of the examined FBBR technology at higher loading rates will depend on an improvement in the growth potential. The obtained kinetic parameters, qm, Ks, and S*b,min, can be used to aid in the design of aerobic FBBRs treating waters containing DNT mixtures.

Growth optimization of algae for biodiesel production

Aims:  Algae are favourable as a biofuel source because of the potential high oil content and fast generation of biomass. However, one of the challenges for this technology is achieving high oil content while maintaining exponential or high growth of the organism. Introducing a two‐stage reactor to optimize both growth and oil content of the algae could be a solution to this hurdle. The aim of this study was to determine the reactor design parameters of the first‐stage reactor, which would optimize growth of two algal strains, Oocystis sp. and Amphora sp.

Role of sulfur-reducing bacteria in a wetland system treating acid mine drainage

This report describes a twenty month case study of a successive alkalinity producing system (SAPS) treating a strong acid mine drainage (AMD) source in Coshocton County, Ohio. Prior to the commencement of the project, a large volume of black amorphous sludge had accumulated in several of the constructed wetlands. The sludge was found to be 43% organic, with very high concentrations of sulfur, iron, aluminum, and acidity. Based on several biological, physical, and chemical analyses, the sludge was determined to be an anaerobic biofilm with a large population of sulfur-reducing bacteria and a high mineral content due to the formation of iron sulfide and aluminum precipitates. On average the system performed well, generating 26 kg CaCO3/d of alkalinity and capturing 5.0 kg/d of iron and 1.7 kg/d of aluminum. Several simple performance analysis tools were presented in this work. By comparing the pollutant influent and effluent loading, it was determined that the SAPS was performing at capacity and over the past year increased effluent concentrations were due to increased influent loadings and not system deterioration. Further, by performing a detailed cell-by-cell loading analysis of multiple chemical components, the alkalinity generated by limestone dissolution and by sulfate reduction was determined. Interestingly, 61% of the alkalinity generation in the vertical flow wetlands was due to sulfur-reducing bacteria activity, indicating that sulfur-reducing bacteria may play a more significant role in SAPS than expected.

Alkalinity production as an indicator of failure in steel slag leach beds treating acid mine drainage

Acid mine drainage is a serious environmental problem throughout mining regions of the US and around the world. In Appalachia, reuse of steel slag from steel production as a source of alkalinity for treatment of acid mine drainage has become a common practice. In these systems, dubbed steel slag leach beds, relatively clean surface water is percolated through a bed of steel slag to add large amounts of alkalinity to the water before mixing it with acidic, metalliferous mine water. These beds do not operate consistently and their failure mechanisms are poorly understood. Using the experience of Raccoon Creek watershed in southern Ohio, the alkalinity distribution of the discharge of six steel slag leach beds is compared. Two of these beds are still functional, one has been abandoned and three are operating poorly. The difference in alkalinity distribution between these beds suggests that a carbonate-dominated alkalinity system is an indicator of a poorly performing steel slag leach bed, while a more even distribution between hydroxide, carbonate and bicarbonate may point to more ideal operating conditions. In eight laboratory column experiments, this evidence was then expanded upon by testing different mixed media substrates (differing mixes of steel slag, wood chips and river gravel) to see which provided the most ideal alkalinity distributions. The columns that had steel slag mixed either with wood chips or wood chips and river gravel outperformed the column with slag only in terms of alkalinity distribution, perhaps due to microbial processes or increased hydraulic conductivity without significant added calcium or carbon that could drive calcium carbonate precipitation within the beds and causing them to fail.

Comparison of a type curve and a least-squared errors method to estimate biofilm kinetic parameters

Because of the kinetics of diffusion limitation and the difficulty of replicating biofilm structure in a test vessel, biokinetic parameters of substrate consumption (maximum specific substrate removal rate, qm and half-maximum removal coefficient, Ks) are particularly difficult to measure in biofilm reactors. In this research, a type curve method using load-shift experiments was compared to a method using a least-squared errors (LSE) routine. More accurate and precise estimates were obtained with the LSE routine than with the type curve method by removing subjectivity from the estimation process. In addition, the LSE estimation process allowed a more rigorous evaluation of the adequacy of the data fit, permitted estimation of approximate confidence intervals of parameters, and identified flaws in the data set. As a result, we advocate the use of the recently developed LSE based estimation routine to estimate parameters from such experiments.

Geochemistry of CO2 in Steel Slag Leach Beds

Performance data was previously collected from steel slag leach beds (SLBs) being used to treat AMD in southeastern Ohio. During initial analysis of the SLB performance, it was postulated that CO2 geochemistry significantly affected the performance through precipitation of carbonate minerals in the flow paths of the SLB. To verify this postulation, we conducted a further investigation of the CO2 geochemistry in the SLBs, including extended geochemical analyses and additional X-ray diffractometer analyses. Since the primary geochemical reaction of CO2 in SLBs is mineral carbonation with calcium, a simple model was used to calculate the Ca dissolution potentials in the SLBs. The molar values for Ca dissolution potential were then used along with each SLB’s influent chemical concentrations in PHREEQC geochemical analyses to verify effluent concentrations and calcite precipitation. Results showed good agreement between the modeled effluent concentrations and the actual data, indicating that this approach can be used to estimate calcite precipitation within SLB systems.ZusammenfassungIm Südosten Ohios werden zur Behandlung von sauren Grubenwässern Festbettreaktoren aus Stahlschlacke (SLBs) verwendet. Aus den Festbettreaktoren wurden zuvor Analysedaten gesammelt. Auf Grund der ersten Analysen des SLB-Verfahrens wurde davon ausgegangen, dass die CO2-Geochemie das Verfahren signifikant durch Karbonatfällung beeinflusst. Wir führten weitere Untersuchungen zur CO2-Geochemie in SLBs durch, um diese Annahme zu überprüfen. Diese Untersuchungen beinhalteten erweiterte geochemische Analysen und Röntgendiffraktometeranalysen (XRD). Da die Karbonatisierung mit Calcium die wesentliche geochemische Reaktion des CO2 in SLBs ist, wurde ein einfaches Modell zur Berechnung des Ca-Löslichkeitspotentials in den SLBs angewendet. Die molaren Werte des Ca-Löslichkeitspotentials wurden zusammen mit den chemischen Konzentrationen im Zulauf der SLBs in PHREEQC verwendet, um die Konzentration im Ablauf sowie die Calcitfällung zu prüfen. Die Ergebnisse zeigen eine gute Übereinstimmung zwischen den modellierten und den gemessenen Konzentrationen im Ablauf. Dies zeigt, dass diese Vorgehensweise genutzt werden kann, um die Calcitfällung in SLBs abzuschätzen.ResumenSe colectaron datos de comportamiento de lechos de lixiviación de escorias de acero (SLBs) que estaban siendo usadas para tratar AMD en el sudeste de Ohio. En un análisis inicial se propuso que la geoquímica de CO2 afectó significativamente el comportamiento a través de la precipitación de carbonato en los pasos del flujo de SLB. Para verificar esta hipótesis, se realizó una investigación posterior sobre la geoquímica del CO2 en los SLBs, incluyendo análisis geoquímicos extendidos y análisis de difracción de rayos X (XRD). Debido a que la reacción geoquímica primaria del CO2 en los SLBs es carbonatación con Ca, se desarrolló un modelo simple para calcular la potencial disolución de Ca en los SLBs. Los valores molares para la disolución de Ca fueron luego usados para cada concentración del influente dentro de los análisis geoquímicos PHREEQC para verificar las concentraciones del efluente y la precipitación de calcita. Los resultados mostraron buen acuerdo entre los datos reales y los predichos por el modelo, indicando que esta aproximación puede ser usada para estimar la precipitación de calcita dentro de los sistemas SLB.抽象本文收集了大量钢渣滤床(SLBs)行为特征的资料以指导俄亥俄东南地区酸性矿山废水(AMD)处理技术研究。在分析钢渣滤床(SLBs)地球化学行为特征的时候,通常假定二氧化碳(CO2)控制着钢渣滤床(SLBs)中水流通道内的碳酸盐矿物沉淀。为证明该假设,进一步试验研究了二氧化碳(CO2)在钢渣滤床(SLBs)中的地球化学特征,试验包括补充地球化学分析和X射线分析等。由于二氧化碳(CO2)在钢渣滤床(SLBs)中的主要地球化学反应是钙(Ca)的碳酸盐化,采用一种简便模型计算钙(Ca)在钢渣滤床(SLBs)的溶解势。钙(Ca)溶解势的摩尔值与每个钢渣滤床(SLBs)注入液的浓度一起用于PHREEQC模型计算,以验证SLB流出液体浓度和钙(Ca)沉淀数量。结果证明,模拟的SLB出流液浓度和实际观测值吻合较好,该方法能够用以评价SLB钙(Ca)沉淀特征。

Solution of the groundwater transport management problem by sequential relaxation

A heuristic algorithm is presented for problems which are formulated to find an optimal groundwater remediation strategy with constraints on confined groundwater flow and contaminant transport. The problem is simplified by decoupling the transport constraints from the hydraulic constraints to produce a linear hydraulic control optimization problem. The solution is obtained by an iterative process in which the constraints on hydraulic gradient are updated, using information from transport simulation, and the hydraulic control problem is solved repeatedly. In effect, the transport simulation is used to calibrate the head difference constraint values of the hydraulic control problem. The algorithm is described in detail and its convergence is demonstrated on several examples. The advantages and limitations of the algorithm are discussed.

Removal, by Vegetated Biofilter, of Medium and Low Concentrations of Pollutants from Simulated Highway Runoff

The removal of pollutants by a prototype of a vegetated biofilter was investigated at medium and low concentrations. The biofilter was 4 ft (1.2 m) wide by 14 ft (4.3 m) long and was tilted at slopes of 8:1, 4:1, and 2:1. Artificial runoff, formulated with metals, native soil, and oil at medium concentration, was delivered at a rate equivalent to a simulated 2-year storm event (medium flow) at each slope; an additional experiment using a 10-year storm event (high flow) was conducted at the 2:1 slope. The flow rates at the low concentration represented 10-year storm events. During each simulated storm event, samples were obtained from the inlet, surface runoff, and underdrain and analyzed for total and dissolved metals, total suspended solids (TSS), and oil and grease. Before and after all tests, specimens were extracted from the bed and analyzed for metal content in soil, roots, and grass. Results indicated that all constituents (seven total metals and TSS) were removed at levels above 75% (event mean concentration) for medium-concentration influent. Metals above background levels were found primarily in the first half [7 ft (2.1 m)] of the bed. Oil removal was also achieved. Removals at low concentration were lower and erratic, and residual metal concentrations in the bed were near background levels. Soil particles in the influent flow, tagged with lanthanum, were neither resuspended nor measured at any significant concentration in the outlet surface flow.