CO2 capture by means of an enzyme-based reactor.

We report a means for efficient and selective extraction of carbon dioxide (CO(2)) at low to medium concentration from mixed gas streams. CO(2) capture was accomplished by use of a novel enzyme-based, facilitated transport contained liquid membrane (EBCLM) reactor. The parametric studies we report explore both structural and operational parameters of this design. The structural parameters include carbonic anhydrase (CA) concentration, buffer concentration and pH, and liquid membrane thickness. The operational parameters are temperature, humidity of the inlet gas stream, and CO(2) concentration in the feed stream. The data show that this system effectively captures CO(2) over the range 400 ppm to at least 100,000 ppm, at or around ambient temperature and pressure. In a single pass across this homogeneous catalyst design, given a feed of 0.1% CO(2), the selectivity of CO(2) versus N(2) is 1,090 : 1 and CO(2) versus O(2) is 790 :1. CO(2) permeance is 4.71 x 10(-8) molm(-2) Pa(-1) sec(-1). The CLM design results in a system that is very stable even in the presence of dry feed and sweep gases.

Evaluation of autotrophic denitrification, heterotrophic nitrification, and PAOs in full scale simultaneous biological nutrient removal sysyems.

Anoxic and aerobic batch reactor assays using a two-by-two factorial design were developed to determine the potential activity of autotrophic denitrification and heterotrophic nitrification in biological nutrient removal (BNR) activated sludge systems, especially those accomplishing simultaneous BNR (SBNR). Results from the application of these assays to three full scale closed loop bioreactors previously documented to be accomplishing SBNR demonstrated that these activities were minimal in comparison with the conventionally recognized activities of heterotrophic denitrification and autotrophic nitrification. Activity within the mixed liquor consistent with current theories for phosphorus accumulating organisms (PAOs) was also observed. Along with other observations, this suggests the presence of PAOs in the facilities studied.

Biokinetic models for representing the complete inhibition of microbial activity at high substrate concentrations.

This paper reintroduces the Wayman and Tseng model for representing substrate inhibition effects on specific growth rate by further documenting its potential predictive capabilities. It also introduces a modification to this model in which an Andrews inhibition function is used in place of the Monod noninhibitory substrate function. This modification better represents the relationship between specific growth rate and substrate concentration for those substrates that show Andrews type inhibition at lower substrate concentrations, rather than the Monod type noninhibitory behavior described in the model of Wayman and Tseng. Results from nonlinear, least squares regression analysis are used to evaluate the ability of these models to empirically represent experimental data (both new and from the literature). The statistical goodness of fit is evaluated by comparing the regression results against those obtained using other empirical models. Finally, possible mechanisms of toxicity responsible for the observed inhibition trends are used to further justify use of these empirical models. The dominant mechanism considered to be relevant for conceptually explaining complete inhibition at high concentrations of solvents is the deterioration of cell membrane integrity. Literature citations are used to support this argument. This work should lead to improvements in the mathematical modeling of contaminant fate and transport in the environment and in the simulation of microbial growth and organic compound biodegradation in engineered systems.

Measurement of iron(III) bioavailability in pure iron oxide minerals and soils using anthraquinone-2,6-disulfonate oxidation.

The quinol form (AHDS) of 9,10-anthraquinone-2,6-disulfonate (AQDS) was used as a titrant to determine bioavailability of Fe(III) in pure iron minerals and several soils. AHDS oxidation to AQDS was coupled to Fe(III) reduction to Fe(ll) in biological media consisting of trace salts and vitamins, providing estimates of bioavailability consistentwith the biogeochemical mechanisms and conditions that control Fe(III) availability to iron-reducing bacteria. Iron(III) oxide sources were synthetic oxides (amorphous and crystalline) and three soils separated into two size fractions each (0-500 and 500-1000 microm). This titration gave a measurement of the amount of Fe(III) available to dissimilatory iron-reducing bacteria and was compared to hydroxylamine reduction, oxalate extraction, and biological reduction by Shewanella alga BrY. The advantage of AHDS titration over existing chemical techniques is that it can be performed at normal soil pH and ionic strength, and it allows for distinction of iron(III) oxides rendered unavailable by sorption of Fe(II) or by other pH-dependent geochemical processes. This approach also allows distinction of Fe(III) present in micropores that is not directly available to bacteria but bioavailable in the presence of an electron shuttle capable of transporting electrons into the micropores.

Biological removal of gaseous ammonia in biofilters: space travel and earth-based applications.

Gaseous NH3 removal was studied in laboratory-scale biofilters (14-L reactor volume) containing perlite inoculated with a nitrifying enrichment culture. These biofilters received 6 L/min of airflow with inlet NH3 concentrations of 20 or 50 ppm, and removed more than 99.99% of the NH3 for the period of operation (101, 102 days). Comparison between an active reactor and an autoclaved control indicated that NH3 removal resulted from nitrification directly, as well as from enhanced absorption resulting from acidity produced by nitrification. Spatial distribution studies (20 ppm only) after 8 days of operation showed that nearly 95% of the NH3 could be accounted for in the lower 25% of the biofilter matrix, proximate to the port of entry. Periodic analysis of the biofilter material (20 and 50 ppm) showed accumulation of the nitrification product NO3- early in the operation, but later both NO2- and NO3- accumulated. Additionally, the N-mass balance accountability dropped from near 100% early in the experiments to approximately 95 and 75% for the 20- and 50-ppm biofilters, respectively. A partial contributing factor to this drop in mass balance accountability was the production of NO and N2O, which were detected in the biofilter exhaust.

Composting on Mars or the Moon: II. Temperature feedback control with top-wise introduction of waste material and air.

Whereas Earth-based composting reactors that effectively control the process are batch operations with bottom-to-top airflow, in extraterrestrial application both the fresh waste and the air need to be introduced from above. Stabilized compost and used air would exit below. This materials flow pattern permits the addition of waste whenever generated, obviating the need for multiple reactors, and the incorporation of a commode in the lid. Top loading in turn dictates top-down aeration, so that the most actively decomposing material (greatest need for heat removal and O2 replenishment) is first encountered. This novel material and aeration pattern was tested in conjunction with temperature feedback process control. Reactor characteristics were: working, volume, 0.15 m3; charge, 2 kg dry biomass per day (comparable to a 3-4 person self-sufficient bioregenerative habitat); retention time, 7 days. Judging from temperature profile, O2 level, air usage, pressure head loss, moisture, and odor, the system was effectively controlled over a 35-day period. Dry matter disappearance averaged 25% (10-42%). The compost product was substantially, though not completely, stabilized. This demonstrates the compatibility of top-wise introduction of waste and air with temperature feedback process control.

Composting on Mars or the Moon: I. Comparative evaluation of process design alternatives.

As a candidate technology for treating solid wastes and recovering resources in bioregenerative Advanced Life Support, composting potentially offers such advantages as compactness, low mass, near ambient reactor temperatures and pressures, reliability, flexibility, simplicity, and forgiveness of operational error or neglect. Importantly, the interactions among the physical, chemical, and biological factors that govern composting system behavior are well understood. This article comparatively evaluates five Generic Systems that describe the basic alternatives to composting facility design and control. These are: 1) passive aeration; 2) passive aeration abetted by mechanical agitation; 3) forced aeration--O2 feedback control; 4) forced aeration--temperature feedback control; 5) forced aeration--integrated O2 and temperature feedback control. Each of the five has a distinctive pattern of behavior and process performance characteristics. Only Systems 4 and 5 are judged to be viable candidates for ALS on alien worlds, though which is better suited in this application is yet to be determined.

Evaluation of respirometric data: identification of features that preclude data fitting with existing kinetic expressions.

The use of respirometric for from the evaluation of intrinsic biodegradation kinetic parameters for single organic compounds is discussed. Emphasis is placed on the preliminary assessment of the data set to determine whether it is suitable for kinetic parameter estimation. Careful preliminary examination of the data avoids attempting parameter estimation with unacceptable data. Furthermore, the use of unbiased respirometric data helps ensure that the estimated parameters truly reflect the intrinsic kinetics for biodegradation of a single substrate by the culture tested. Both experimental and theoretical oxygen uptake curves are used to illustrate how various conditions can limit the utility of a given data set. The effect of substrate inhibition, dual or multiple substrate limited growth, inaccuracies in the initial conditions assumed for curve fitting, and the use of poorly acclimated cultures are discussed. Techniques are presented which allow identification of whether a data set is unsuitable and should not be used for parameter estimation. In addition, experimental procedures which can help avoid the collection of aberrant data are discussed.

Obstetric complications with GDM. Effects of maternal weight.

Obstetric complications recorded prospectively were assessed retrospectively in 150 women with gestational diabetes mellitus (GDM) and 305 control subjects matched for age, parity, and ethnicity. Intensive diet therapy and self-monitoring of capillary blood glucose were used to obtain postprandial euglycemia; 22% of GDM subjects required insulin. GDM and control subjects were grouped by body mass index to detect any influence of maternal prepregnancy weight on outcome. Polyhydramnios, preterm labor, and pyelonephritis were not more frequent in GDM, but hypertension without proteinuria (7.3 vs. 3.3%) and preeclampsia (8 vs. 3.9%) were more frequent in GDM. The frequency of hypertensive complications in GDM was not totally attributable to being overweight. Abnormalities of labor, birth trauma, and fetal macrosomia were not more common in GDM; 6.7% of the infants of mothers with GDM weighed greater than 4200 g at birth compared with 3.6% of control infants (NS), and 10% were large for gestational age and sex compared with 6.6% of control infants (NS). Despite this, cesarean delivery was more common in GDM (35.3 vs. 22%, P less than 0.01), mostly due to significantly more cesarean births without labor.

Outcome of very-low-birth-weight infants exposed to beta-sympathomimetics in utero.

In this study we examined neonatal and early childhood outcomes after intrauterine exposure to beta-sympathomimetic agents on infants with birth weights less than or equal to 1500 gm. The hospital courses and anthropomorphic, developmental, and neurologic development of 201 infants exposed to one or more beta-sympathomimetic agents (isoxsuprine, 33; ritodrine, 70; terbutaline, 43; combination, 55) were analyzed and compared with those of 130 control infants of similar birth weight. One hundred and seventy-seven infants had follow-up to 1 year of age, 101 to age 3, and 58 to age 4. When treatments consisting of a single beta-sympathomimetic or no treatment were compared, there were no statistically significant overall differences found in growth and development or in most of the short-term measures of infant well-being. However, significant overall differences with no evidence of confounding by time-related effects were found for the following; mortality, none greater than terbutaline; maximum positive inspiratory pressure when respiratory distress syndrome was present, none greater than terbutaline; neonatal trauma, terbutaline greater than ritodrine. Other differences were found in conjunction with evidence of time-related confounding, or within specific time intervals. It should be noted that these differences are not necessarily due to effects of the different treatments, as the data are observational.

Prognostic value of ambulatory blood pressure measurements: further analyses.

The value of ambulatory systolic blood pressure as a predictor of the development of cardiovascular complications was investigated in a sample of 761 hypertensive patients who had undergone ambulatory blood pressure monitoring and who were followed for an average of 5.5 years. Of the 695 patients without prior cardiovascular events at entry into the study, 11% subsequently experienced an event during the follow-up period (up to 10 years) compared to 48% of the 102 patients with a prior cardiovascular event. For each patient, a 'predicted' ambulatory systolic blood pressure was calculated, using the patient's office systolic blood pressure and the equation derived from regressing ambulatory on office blood pressure for the entire sample. By subtracting the predicted from the observed ambulatory pressure, a 'residual' ambulatory systolic blood pressure was derived for each patient, as a measure of that portion of the ambulatory pressure that could not be predicted from the office pressure. We used a Cox proportional hazards model to analyse the independent effect of each of the following patient characteristics at entry on the occurrence of subsequent cardiovascular events: sex, age, ECG evidence of left ventricular hypertrophy, hypertensive retinopathy, ambulatory systolic blood pressure, office systolic blood pressure, residual ambulatory systolic blood pressure and subsequent drug therapy. In both groups, with and without a prior cardiovascular event, women, younger patients and those with lower residual ambulatory systolic blood pressure tended to have longer periods of survival without new cardiovascular events. In the group without prior cardiovascular events, a lower office systolic blood pressure and the absence of advanced ECG evidence of left ventricular hypertrophy were also independently predictive of longer event-free survival.(ABSTRACT TRUNCATED AT 250 WORDS)