Effect of High Strength Food Wastes on Anaerobic Codigestion of Sewage Sludge.

Anaerobic codigestion has been practiced at water resource recovery facilities to increase methane production, but the impact of many variables is still not well understood. In this study, the feasibility of codigesting fats, oils, and grease (FOG), and other high strength wastes (HSWs) with municipal sewage sludge was investigated. Four laboratory-scale digesters were operated at a working volume of 9.75 L, 15 days solids retention time (SRT), and at a temperature of 37 °C. Wastes including whey (cheese), juice, grease trap waste (GTW), and dissolved air flotation waste (DAF), along with municipal sewage sludge, were fed to the digesters in varying amounts. The addition of HSWs led to higher methane production at lower organic loadings. However, at higher organic loadings, the GTW appeared to be toxic to methanogens, leading to a decrease in digester pH and biogas production, and an accumulation of volatile fatty acids within the digester.

Evaluation of an Industrial Byproduct Glycol Mixture for Denitrification.

In this study, the effectiveness of an industrial byproduct that contained ethylene and propylene glycols to serve as a denitrification carbon source was investigated. Use of the byproduct was compared to methanol on the basis of denitrification rate and yield. Three sequencing batch reactors (SBR) were studied; one was fed methanol, the other two were fed with low and high dosages of the byproduct separately. The low dosage reactor (GLYL) exhibited the highest denitrification rate of 11.55 mg NOx-N/g MLVSS•h and the lowest yield of 0.21 mg VSS/mg COD, while the high dosage reactor (GLYH) had the lowest denitrification rate of 8.56 mg NOx-N/g MLVSS•h and the highest yield of 0.55 mg VSS/mg COD. The results of this study showed that the industrial byproduct can be used to effect efficient nitrogen removal, but excess dosage can cause poor performance.

Evaluation of gasoline-denatured ethanol as a carbon source for denitrification.

In this study concerning denitrification, the performance of three carbon sources, methanol (MeOH), ethanol (EtOH) and gasoline-denatured ethanol (dEtOH), was compared and evaluated on the basis of treatment efficiency, inhibition potential and cost. The gasoline denaturant considered here contained mostly aliphatic compounds and little of the components that typically boost the octane rating, such as benzene, toluene, ethylbenzene and xylenes. Results were obtained using three lab-scale SBRs operated at SRT of 12.0 +/- 0.9 days. After biomass was acclimated, denitrification rates with dEtOH were similar to those of EtOH (201 +/- 50 and 197 +/- 28 NO3-N/g MLVSS x d, respectively), and higher than those of MeOH (165 +/- 49 mg NO3-N/g MLVSS x d). The denaturant did not affect biomass production, nitrification or denitrification. Effluent soluble COD concentrations were always less than the analytical detection limit. Although the cost of dEtOH ($2.00/kg nitrate removed) was somewhat higher than that of methanol ($1.63/kg nitrate removed), the use of dEtOH is very promising and utilities will have to decide if it is worth paying a little extra to take advantage of its benefits.

Dose of UV light required to inactivate Listeria monocytogenes in distilled water, fresh brine, and spent brine.

The purpose of this research was to establish the dose of UV light (253.7 nm) needed to inactivate Listeria monocytogenes in distilled water, fresh brine (9% NaCl), spent brine, and diluted (5, 35, and 55%) spent brine, using uridine as a chemical actinometer. Strains N1-227 (isolated from hot dog batter), N3-031 (isolated from turkey franks), and R2-499 (isolated from meat) were mixed in equal proportions and suspended in each solution prepared so as to contain 10(-4) M uridine. Samples were irradiated in sterile quartz cells for 0, 5, 10, 15, 20, 25, or 30 min. Inactivation was evaluated by serially diluting samples in 0.1% peptone, by surface plating in duplicate onto modified Oxford agar and Trypticase soy agar with yeast extract, and by enrichment in brain heart infusion broth, followed by incubation at 37 degrees C for 24 to 48 h. For dose measurements, the absorbance (262 nm) was measured before and after irradiation. Differences were observed in population estimates depending on the solution (P < or = 0.05). Reductions were as follows from greatest to least: water > fresh brine > 5% spent brine > 35% spent brine > 55% spent brine > undiluted spent brine. UV light did not significantly reduce populations suspended in spent brine solutions. L. monocytogenes decreased to below the detection limit (1 log CFU/ml) at doses greater than 33.2 mJ/cm(2) in water and at doses greater than 10.3 mJ/cm(2) in fresh brine. Knowledge of UV dosing required to control L. monocytogenes in brines similar to those used for ready-to-eat meat processing will aid manufacturers in establishing appropriate food safety interventions for these products.

Effect of acid stress, antibiotic resistance, and heat shock on the resistance of Listeria monocytogenes to UV light when suspended in distilled water and fresh brine.

Exposure to sublethal processing treatments can stimulate bacterial stress responses. The purpose of this research was to determine whether adaptation to common food processing stresses encountered during the preparation of ready-to-eat foods affects the dose of UV light required to significantly reduce Listeria monocytogenes populations in sterile distilled water and a 9% NaCl solution, using uridine as a chemical actinometer. L. monocytogenes strains N1-227 (from hot dog batter), N3-031 (from turkey franks), and R2-499 (from ready-to-eat meat) were acid stressed for 3 h at 35 degrees C in Trypticase soy broth with yeast extract acidified to pH 5.0, heat shocked for 1 h at 48 degrees C in brain heart infusion broth (BHIB), and selected for sulfanilamide resistance (512 microg/ml). These strains were then mixed in equal proportions and suspended in water and 9% NaCl solution, each containing 10(-4) M uridine. Samples were exposed to UV light (253.7 nm) for 0, 5, 10, 15, 20, 25, or 30 min. Inactivation was evaluated by surface plating onto modified Oxford agar and Trypticase soy agar with yeast extract and by enrichment in BHIB followed by incubation at 37 degrees C for 24 h. The absorbance of each sample was measured before and after irradiation to calculate the dose of UV light. There were no significant differences between population estimates based on medium or suspension solution. There were no population differences between acid-stressed and antibiotic-resistant or unstressed and heat-shocked L. monocytogenes strains. However, acid-stressed and antibiotic-resistant strains were significantly more resistant to UV light than were unstressed and heat-shocked strains (P < or = 0.05).

Effect of high hydrostatic pressure processing on freely suspended and bivalve-associated T7 bacteriophage.

The effectiveness of hydrostatic pressure processing (HPP) for inactivating viruses has been evaluated in only a limited number of studies, and most of the work has been performed with viruses freely suspended in distilled water. In this work, HPP inactivation of freely suspended and shellfish-associated bacteriophage T7 was studied. T7 was selected in hopes that it could serve as a model for animal virus behavior. Clams (Mercenaria mercenaria) and oysters (Crassostrea virginica) were homogeneously blended separately and inoculated with bacteriophage T7. The inoculated bivalve meat and the freely suspended virus samples were subjected to HPP under the following conditions: 2, 4, and 6 min at 241.3, 275.8, and 344.7 MPa pressure and temperatures of 29.4 to 35, 37.8 to 43.3, and 46.1 to 51.7 degrees C. Reductions of 7.8 log PFU (100% inactivation) were achieved for freely suspended T7 at 344.7 MPa for 2 min at 37.8 to 43.3 degrees C. At 46.1 to 51.7 degrees C, T7 associated with either clams or oysters was inactivated at nearly 100% (>4 log PFU) at all pressure levels and durations tested. These results indicate that T7 is readily inactivated by HPP under the proper conditions, may be made more susceptible to HPP by mixing with shellfish meat, and may serve as a viable model for the response of several animal viruses to HPP.

Toxicity of ammonia to three marine fish and three marine invertebrates.

Laboratory toxicity tests were performed to obtain more data on the toxicity of ammonia to saltwater organisms. The standards for in-stream ammonia limits in marine environments presently are based on toxicity tests involving both freshwater and saltwater organisms. Acute tests (48 and 96 h) were performed at 20 degrees C, and chronic tests (7 days) were performed at 25 degrees C. Synthetic seawater and natural seawater from the Chesapeake Bay were used and compared. Included among the organisms tested were sheepshead minnow (14 days old), summer flounder (2 months old), Atlantic silverside (14 days old), mysid shrimp (less than 2 days old), ghost shrimp (10 days old), and quahog clam (9 months old). Based on these results, it seems the chronic criterion for ammonia in marine environments could be increased from 0.035 to 0.081 mg/L un-ionized ammonia, which would, of course, increase the chronic limit for total ammonia under typical saltwater conditions by a factor of 2.31. No difference was observed in the toxicity of ammonia in natural water compared to synthetic water for both the summer flounder and Atlantic silverside. Furthermore, the Atlantic silverside became more sensitive to ammonia as the salinity was increased from 14 to 22 ppt, but exhibited no change in toxicity response from 22 to 30 ppt.