Peter F. Strom

Phenanthrene binding and sorption to dissolved and to mineral-associated humic acid

Abstract Phenanthrene, a three ring aromatic hydrocarbon, was used as a model substrate to distinguish between binding and sorption to dissolved and to mineral-associated humic acid (HA), with an emphasis on its implication to bioavailability. Binding was analyzed by a fluorescence quenching technique using Aldrich HA and HAs derived from compost, loamy and clay loamy soils. Measurements were made both in buffered water and in a mineral medium to be used later in a bioavailability study. Sorption of phenanthrene to mineral-associated HA was analyzed in batch experiments. Mineral–HA complexes were prepared with goethite, hematite, and Ca2+- and Cu2+-montmorillonite. Interaction of HA with clay minerals was greater at low pH and was dependent on the mineral type. Sorption of phenanthrene to these complexes was substantially higher at lower pH and higher when the HA was associated with montmorillonite rather than goethite or hematite. Binding coefficients (Kb(oc)) obtained for dissolved HA were at least an order of magnitude higher than sorption coefficients (Kp(oc)) obtained for mineral-associated HA. Both binding and sorption coefficient values were substantially higher for Aldrich HA. This work emphasizes the need for a detailed sorption study before conducting well controlled bioavailability experiments.

Bioavailability of phenanthrene sorbed to mineral-associated humic acid

Abstract Phenanthrene, a 3-ring aromatic hydrocarbon, was used as a model substrate to analyze the effect of sorption on the bioavailability of polycyclic aromatic hydrocarbons (PAHs). This study focused on sorption to mineral-associated humic acid (HA). Batch sorption analyses of phenanthrene to mineral-HA complexes were performed as integral part of the bioavailability experiments to account for the sorbed fraction under the various experimental conditions. A mixed culture that was enriched from a coal tar contaminated soil dominated by Pseudomonas sp . served as an inoculum. Phenanthrene mineralization was substantially enhanced upon sorption to mineral-HA complexes and the degree of enhancement was positively correlated with the fraction of sorbed phenanthrene. This stimulation is thought to be related to sorption of both the microorganisms and phenanthrene to the colloidal surfaces. This study suggests that when sorbed contaminants are still bioavailable, the presence of surfaces may stimulate mineralization.

Spatial Distribution of Total, Ammonia-Oxidizing, and Denitrifying Bacteria in Biological Wastewater Treatment Reactors for Bioregenerative Life Support

ABSTRACT Bioregenerative life support systems may be necessary for long-term space missions due to the high cost of lifting supplies and equipment into orbit. In this study, we investigated two biological wastewater treatment reactors designed to recover potable water for a spacefaring crew being tested at Johnson Space Center. The experiment (Lunar-Mars Life Support Test Project—Phase III) consisted of four crew members confined in a test chamber for 91 days. In order to recycle all water during the experiment, an immobilized cell bioreactor (ICB) was employed for organic carbon removal and a trickling filter bioreactor (TFB) was utilized for ammonia removal, followed by physical-chemical treatment. In this study, the spatial distribution of various microorganisms within each bioreactor was analyzed by using biofilm samples taken from four locations in the ICB and three locations in the TFB. Three target genes were used for characterization of bacteria: the 16S rRNA gene for the total bacterial community, the ammonia monooxygenase (amoA) gene for ammonia-oxidizing bacteria, and the nitrous oxide reductase (nosZ) gene for denitrifying bacteria. A combination of terminal restriction fragment length polymorphism (T-RFLP), sequence, and phylogenetic analyses indicated that the microbial community composition in the ICB and the TFB consisted mainly of Proteobacteria, low-G+C gram-positive bacteria, and a Cytophaga-Flexibacter-Bacteroides group. Fifty-seven novel 16S rRNA genes, 8 novel amoA genes, and 12 new nosZ genes were identified in this study. Temporal shifts in the species composition of total bacteria in both the ICB and the TFB and ammonia-oxidizing and denitrifying bacteria in the TFB were also detected when the biofilms were compared with the inocula after 91 days. This result suggests that specific microbial populations were either brought in by the crew or enriched in the reactors during the course of operation.

The effect of sorption on phenanthrene bioavailability

Abstract Critical parameters that need to be considered in a bioavailability study are reviewed and applied to a study on the sorption (binding) of phenanthrene to dissolved humic acid (HA). Sorption coefficients values ( K ∞ ) of phenanthrene to HA were measured for HA from several sources. These values were used to calculate the amount of HA that was needed to bind different fractions of solution-phase phenanthrene. Sorption linearity and complete reversibility were assumed. A mixed culture of phenanthrene degraders, dominated by Pseudomonas sp. was sensitive to changes in dissolved phenanthrene concentrations in the range that was used in this study. Therefore, it was expected that if bound phenanthrene was not available, as is commonly stated in the literature, sorption would affect mineralization rate by reducing the concentration of free phenanthrene. However, it was found that mineralization of phenanthrene was not affected by sorption even when 90% of the phenanthrene was in the bound phase. It was concluded that the organisms were able to use the phenanthrene directly from the bound phase and at the same rate as from the free phase.

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

ABSTRACT 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 ~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.

The question of nitrification in the Passaic River, New Jersey: Analysis of historical data and experimental investigation

Abstract Historical NH 4 + and NO 3 − data from six stations on the Passaic River, New Jersey, were analyzed. The data for five of the stations span 1963 to 1976, and for the sixth station 1947 to 1976. Some of the conclusions reached are as follows: 1. (1) The concentration of NH 4 + fluctuated widely, but the trend was towards an increase with time. 2. (2) The concentration of NH 4 + was elevated during a period of extreme drought (1963 to 1966). 3. (3) The concentration of NO 3 − tended to increase smoothly with time. 4. (4) The concentration of NH 4 + increases longitudinally (with downstream travel). 5. (5) The loads (concentration × stream-flow) of both nitrogen species tended to increase with time. 6. (6) Substantial NO 3 − enters the stream from non-point sources. 7. (7) The potential for instream nitrification is not fully realized, as represented by elevated levels of NH 4 + . Item (7) was puzzling because conditions in the Passaic, especially in the summer, appear to be favorable for nitrification. The point was clarified, in part through an experimental investigation. River water samples, with and without added NH 4 Cl, were incubated, and the course of the first step of nitrification was followed through the appearance of NO 2 − . (The second step of nitrification was inactive during the experimental period.) The added NH 4 Cl enhanced nitrification in samples from the uppermost stations (native NH 4 + -N approximately 0.1 mg l −1 , but had little or no effect in samples from the middle and lower reaches (native NH 4 + -N > 0.5 mg l −1 ). Consequently, it was inferred that over most of the rivers mainstem the growth of NH 4 + -oxidizing bacteria was not substrate limited. There was also no indication of other nutrient limitations or of the presence of any inhibitors. This led to a projection of a 60-fold increase in the population density of planktonic NH 4 + -oxidizers over a certain stretch of the river. However, no increase in the most-probable-number (MPN) of NH 4 + -oxidizing bacteria was observed, which is consistent with item (7). In fact, at the end of a quiescent segment of the river the MPNs were anomalously low. This is attributed to the removal of cells from the water column through settling. This reasoning is extended to suggest that, throughout the river, settling may be the mechanism preventing a response of planktonic nitrifiers to the enrichment with NH 4 + from pollution sources. In turn, this could prevent a full expression of the potential for nitrification. The analyses are discussed from a regulatory perspective. It is concluded that the nitrification component of the Passaics self-purification capacity is overburdened, and first became so in 1953.

Application of computational fluid dynamics to closed-loop bioreactors: I. Characterization and simulation of fluid-flow pattern and oxygen transfer

A full-scale, closed-loop bioreactor (Orbal oxidation ditch, Envirex brand technologies, Siemens, Waukesha, Wisconsin), previously examined for simultaneous biological nutrient removal (SBNR), was further evaluated using computational fluid dynamics (CFD). A CFD model was developed first by imparting the known momentum (calculated by tank fluid velocity and mass flowrate) to the fluid at the aeration disc region. Oxygen source (aeration) and sink (consumption) terms were introduced, and statistical analysis was applied to the CFD simulation results. The CFD model was validated with field data obtained from a test tank and a full-scale tank. The results indicated that CFD could predict the mixing pattern in closed-loop bioreactors. This enables visualization of the flow pattern, both with regard to flow velocity and dissolved-oxygen-distribution profiles. The velocity and oxygen-distribution gradients suggested that the flow patterns produced by directional aeration in closed-loop bioreactors created a heterogeneous environment that can result in dissolved oxygen variations throughout the bioreactor. Distinct anaerobic zones on a macroenvironment scale were not observed, but it is clear that, when flow passed around curves, a secondary spiral flow was generated. This second current, along with the main recirculation flow, could create alternating anaerobic and aerobic conditions vertically and horizontally, which would allow SBNR to occur. Reliable SBNR performance in Orbal oxidation ditches may be a result, at least in part, of such a spatially varying environment.

Pesticides in Yard Waste Compost

Samples from six yard waste composting facilities in New Jersey were analyzed for a wide range of pesticide residues. Chlordane was found at low levels (0.3-3.2 mg/kg) in all samples; no other pesticide was detected. It appears likely that the source of the chlordane is the residential soil incorporated with the raw yard waste during collection. Based on these findings, routine analysis of yard waste compost for pesticide residues does not appear warranted.

Application of computational fluid dynamics to closed-loop bioreactors. II. Simulation of biological phosphorus removal using computational fluid dynamics

Based on the International Water Associations (London) Activated Sludge Model No. 2 (ASM2), biochemistry rate expressions for general heterotrophs and phosphorus-accumulating organisms (PAOs) were introduced to a previously developed, three-dimensional computational fluid dynamics (CFD) activated sludge model that characterized the mixing pattern within the outer channel of a full-scale, closed-loop bioreactor. Using acetate as the sole carbon and energy source, CFD simulations for general heterotrophs or PAOs individually agreed well with those of ASM2 for a chemostat with the same operating conditions. Competition between and selection of heterotrophs and PAOs was verified using conventional completely mixed and tanks-in-series models. Then, competition was studied in the CFD model. These results demonstrated that PAOs and heterotrophs can theoretically coexist in a single bioreactor when the oxygen input is appropriate to allow sufficient low-dissolved-oxygen zones to develop.

Small-scale composting of horse manure mixed with wood shavings

There is an increased interest in composting manure on small horse farms (1-5 horses). It is known that simple backyard, food waste composters do not efficiently reduce pathogens due to their small scale. However, it was not clear if small-scale manure composting on horse farms could ensure pathogen reduction during all seasons. Furthermore, because of potential human health concerns, the release of Aspergillus fumigatus on small horse farms was of interest. The objective of this study was to evaluate pathogen reduction in a simple shed composter and the release of Aspergillus fumigatus emissions from fall to spring under typical farm operational conditions. Horse manure mixed with wood shavings (bedding) was composted for 4-8 weeks in the fall, winter, early spring and late spring. Fecal streptococci and eggs of strongyles, which are a major recognized health concern for horses, were used as pathogen indicator organisms. Temperatures increased in all composting piles during all seasons, but tended to be higher in warmer weather. After 4 weeks, the fecal streptococci reduction was about 10- to 100-fold and, after 8 weeks, about 100- to 1000-fold. There was some effect of season on fecal streptococci levels, with the higher composting temperatures appearing to provide greater reductions. Strongyle eggs in this study were very low and were reduced over time. Levels of viable A. fumigatus spores during turning ranged from 12-2084 CFU m−3, while background levels ranged between 6 - 300 CFU m−3. Overall, this study indicates that composting horse manure mixed with wood shavings reduces pathogens. A. fumigatus levels are elevated during turning, but the levels are lower than those found at sewage sludge/municipal solid waste composting facilities or inside barns.