Angela R. Bielefeldt

Modeling competitive inhibition effects during biodegradation of BTEX mixtures

Abstract A quantitative evaluation of the biodegradation rates of mixtures of volatile aromatic compounds (benzene, toluene, ethylbenzene, xylenes [BTEX]) was conducted. Three different mixed bacterial cultures grown on BTEX or benzene were used in batch biodegradation tests with individual and mixed BTEX compounds. The bacteria degraded each compound faster when it was present alone than when it was a component of a BTEX mixture. The biodegradation rates in the mixtures were predicted using a basic competitive inhibition model to account for the effects of up to five BTEX compounds. Under the limiting assumptions of similar individual half-saturation coefficients ( K s ) for the multiple compounds and substrate concentrations significantly greater than K s , the competitive inhibition model could be simplified to demonstrate that the biodegradation rate of any individual compound in the multi-component mixture should be proportional to its individual maximum specific degradation rate and the concentration of the compound relative to the total mixture concentration. Comparison of measured BTEX mixture degradation to predictions from this simplified model showed this model yielded estimates of similar accuracy to the more rigorous competitive inhibition equation. This is the first report of a quantitative evaluation of the biodegradation of five-compound mixtures.

Bacterial treatment effectiveness of point-of-use ceramic water filters.

Laboratory experiments were conducted on six point-of-use (POU) ceramic water filters that were manufactured in Nicaragua; two filters were used by families for ca. 4 years and the other filters had limited prior use in our lab. Water spiked with ca. 10(6)CFU/mL of Escherichia coli was dosed to the filters. Initial disinfection efficiencies ranged from 3 - 4.5 log, but the treatment efficiency decreased with subsequent batches of spiked water. Silver concentrations in the effluent water ranged from 0.04 - 1.75 ppb. Subsequent experiments that utilized feed water without a bacterial spike yielded 10(3)-10(5)CFU/mL bacteria in the effluent. Immediately after recoating four of the filters with a colloidal silver solution, the effluent silver concentrations increased to 36 - 45 ppb and bacterial disinfection efficiencies were 3.8-4.5 log. The treatment effectiveness decreased to 0.2 - 2.5 log after loading multiple batches of highly contaminated water. In subsequent loading of clean water, the effluent water contained <20-41 CFU/mL in two of the filters. This indicates that the silver had some benefit to reducing bacterial contamination by the filter. In general these POU filters were found to be effective, but showed loss of effectiveness with time and indicated a release of microbes into subsequent volumes of water passed through the system.

Evaluation of biodegradation kinetic testing methods and longterm variability in biokinetics for BTEX metabolism

Abstract Two methods were investigated for measuring the substrate utilization Monod biodegradation kinetics of benzene, toluene, ethylbenzene, o -xylene, and p -xylene (BTEX) by mixed bacterial cultures grown under three different conditions. The mixed cultures were grown in completely mixed reactors that were batch fed every two hours with either BTEX or benzene and operated at a 5-day solids retention time (SRT); a BTEX-fed culture was also grown at a 20-day SRT. Only maximum specific substrate degradation rates ( k ) could be determined in batch tests where BTEX concentrations were measured at discrete time points, since not enough data could be acquired at low substrate concentrations near the half-saturation concentration ( K s ) of the compounds. Both k and K s could be determined in batch tests using an indirect method where dissolved oxygen depletion was continuously measured. The measured biokinetics of each of the cultures varied over time (coefficient of variation of the k and K s values of 27–44% and 43–100%, respectively), despite constant growth conditions. This biokinetic variability should be incorporated into design uncertainty to develop safety factors for reliable bioreactor performance. Results also showed that the operating solids retention time of the reactor and the combination of growth substrates affected the biokinetic coefficient values of the individual BTEX compounds.

Nonionic surfactant effects on pentachlorophenol biodegradation.

Several potential mechanisms of surfactant-induced inhibition of pentachlorophenol (PCP) biodegradation were tested using a pure bacterial culture of Sphingomonas chlorophenolicum sp. Strain RA2. PCP degradation, glucose degradation, and oxygen uptake during endogenous conditions and during glucose degradation were measured for batch systems in the presence of the nonionic surfactant Tergitol NP-10 (TNP10). TNP10 did not exert toxicity on RA2 as measured by dissolved oxygen uptake rates under endogenous conditions and glucose biodegradation rates. TNPIO reduced the substrate inhibition effect of PCP at high PCP concentrations, resulting in faster PCP degradation rates at higher concentrations of TNP10. Calculations of a micelle partition coefficient (Kmic) show that PCP degradation rates in the presence of surfactant can be explained by accounting for the amount of PCP available to the cell in the aqueous solution. A model is discussed based on these results where PCP is sequestered into micelles at high TNP10 concentrations to become less available to the bacterial cell and resulting in observed inhibition. Under substrate toxicity conditions, the same mechanism serves to increase the rate of PCP biodegradation by reducing aqueous PCP concentrations to less toxic levels.

Removal of virus to protozoan sized particles in point-of-use ceramic water filters

The particle removal performance of point-of-use ceramic water filters (CWFs) was characterized in the size range of 0.02-100 microm using carboxylate-coated polystyrene fluorescent microspheres, natural particles and clay. Particles were spiked into dechlorinated tap water, and three successive water batches treated in each of six different CWFs. Particle removal generally increased with increasing size. The removal of virus-sized 0.02 and 0.1 microm spheres were highly variable between the six filters, ranging from 63 to 99.6%. For the 0.5 microm spheres removal was less variable and in the range of 95.1-99.6%, while for the 1, 2, 4.5, and 10 microm spheres removal was >99.6%. Recoating four of the CWFs with colloidal silver solution improved removal of the 0.02 microm spheres, but had no significant effects on the other particle sizes. Log removals of 1.8-3.2 were found for natural turbidity and spiked kaolin clay particles; however, particles as large as 95 microm were detected in filtered water.

Incorporating a Sustainability Module into First-Year Courses for Civil and Environmental Engineering Students

As articulated in the Bodies of Knowledge for Civil Engineering and Environmental Engineering, all civil and environmental engineering students should be introduced to the concept of sustainability. A sustainability module was added into two required first-year, 1-credit introductory courses, one for civil engineering and one for environmental engineering. Data from approximately 150 students were collected. Student attitudes about sustainability were evaluated using a written survey. There was greater initial knowledge of sustainability and positive attitudes toward sustainability among students enrolled in the environmental engineering course compared with those in the civil engineering course, but this did not translate into better performance on the related homework assignment. There was strong evidence that the inclusion of the sustainability module encouraged the students to consider sustainability in subsequent course assignments, even when not explicitly prompted to do so. This indicates that earl...

Bacterial Kinetics of Sulfur Oxidizing Bacteria and Their Biodeterioration Rates of Concrete Sewer Pipe Samples

The importance of bacteria in catalyzing microbially induced concrete corrosion was evaluated. Experiments were conducted to determine the optimum pH and growth kinetics of four selected bacterial strains (Thiobacillus neapolitanus C2, Thiobacillus thioparus H1, Acidithiobacillus thiooxidans, and Acidiphilium cryptum LHET2). Combinations of these strains were inoculated into flasks containing ∼42 g concrete blocks half-submerged in 600 mL of synthetic wastewater with hydrogen sulfide in the headspace air. Controls not inoculated with bacteria lost 0–3 mg/g concrete over 227 days; in the aqueous phase the minimum pH was 6–6.7 and 19–23 mg of calcium/g concrete was released. Systems inoculated with two species of neutrophilic sulfur oxidizing microorganisms (SOM) lost 8 mg/g concrete; in the aqueous phase the minimum pH was 4.5 and 25 mg of calcium/g concrete was released. The concrete samples incubated with neutrophilic and acidophilic SOM and an acidophilic heterotroph experienced the greatest deteriorati...

Biodegradation of propylene glycol and associated hydrodynamic effects in sand

At airports around the world, propylene glycol (PG) based fluids are used to de-ice aircraft for safe operation. PG removal was investigated in 15-cm deep saturated sand columns. Greater than 99% PG biodegradation was achieved for all flow rates and loading conditions tested, which decreased the hydraulic conductivity of the sand by 1-3 orders of magnitude until a steady-state minimum was reached. Under constant loading at 120 mg PG/d for 15-30 d, the hydraulic conductivity (K) decreased by 2-2.5 orders of magnitude when the average linear velocity of the water was 4.9-1.4 cm/h. Variable PG loading in recirculation tests resulted in slower conductivity declines and lower final steady-state conductivity than constant PG feeding. After significant sand plugging, endogenous periods of time without PG resulted in significant but partial recovery of the original conductivity. Biomass growth also increased the dispersivity of the sand.

Equilibrium partitioning of a non-ionic surfactant and pentachlorophenol between water and a non-aqueous phase liquid.

The partitioning of the non-ionic surfactant Tergitol NP-10 (TNP10) and pentachlorophenol (PCP) into a mineral oil light non-aqueous phase liquid (NAPL) were quantified in batch tests. Due to the ionizable nature of PCP, the effects of pH and ionic strength (micro) on the equilibrium partitioning were evaluated. NAPL:water partition coefficients (K(n:w)) of TNP10 ranged from 3 to 7 l(water)/l(NAPL). Enhanced PCP dissolution into water from the NAPL was achieved at aqueous TNP10 concentrations > or =200mg/l. Surfactant addition of 1200 mg/l TNP10 increased the aqueous PCP concentrations by 14-fold at pH 5 versus 2 to 3-fold at pH 7 as compared to PCP aqueous solubility. The more significant response at the lower pH is likely due to the greater hydrophobicity of PCP at the lower pH, which is approaching PCPs pK(a) of 4.7. Higher ionic strength (micro 0.11 versus 0.001 M) increased K(n:w) of PCP by 10-33% without surfactant, compared to a more than 150% increase with a dose of 4000 mg/l TNP10. This work contributes information relevant to the application of surfactants to remediate sites contaminated with NAPLs.

Biodegradation of aromatic compounds and TCE by a filamentous bacteria-dominated consortium.

The Michaelis-Menten biodegradation kinetics (k and Ks) of aromatic compounds and trichloroethene (TCE) by an aerobic enrichment culture grown on phenol and dominated by a unique filamentous bacterium were measured. The average k and Ks values for phenol, benzene (B), toluene (T), ethylbenzene (E), o-xylene (oX), p-xylene (pX), naphthalene and TCE in g per g VSS-d and mg L-1 were 5.72 and 0.34, 1.20 and 0.51, 2.09 and 0.47, 0.77 and 0.23, 0.61 and 0.16, 0.73 and 0.23, 0.17 and 0.18, and 0.16 and 0.18, respectively. Significant variability in these measured kinetics was noted between tests conducted over the 5-month period during which the fed-batch culture with a 5-day solids retention time was maintained; the coefficient of variation of the k and Ks values ranged from 11–43% and 4–50%, respectively. This variation was significantly greater than the method measurement error on a given date. Degradation of BTEoXpX mixtures could be described by a basic competitive inhibition model.Batch tests during which the culture was fed individual BTEX compounds showed the culture grew poorly on the xylenes and had poor subsequent xylene degradation rates. This work indicates the potential to simultaneously treat a mixture of volatile organic compounds using this consortium, and the ability to predict the mixture biodegradation rates on the basis of the individual compound biodegradation kinetics.