The anaerobic co-digestion of fruit and vegetable waste and horse manure mixtures in a bench-scale, two-phase anaerobic digestion system.

In this study, the anaerobic digestion of mixtures of food waste (FW) and horse manure was investigated using a bench-scale two-phase reactor system. Both phases were maintained at 35 degrees C for the duration of the 30-day study period. The first phase reactors were prepared with biomass mixtures in deionized water such that each mixture had an initial total solids (TS) concentration of 6 wt%. The second phase reactors were inoculated with cow manure in water two weeks prior to the study period at 3 wt% TS. The biogas from all second phase reactors contained greater than 60 vol% methane in the biogas before they were used in the study, thus indicating the presence of active methanogens. Filtrate (5 mL) from the first phase was used as feed to the second phase reactor. The chemical oxygen demand (COD), total organic carbon, and volatile solids (VS) of the feed from Phase 1 increased with FW content in the biomass mixture, and so the organic loading rates (OLRs) to the Phase 2 reactors also increased. Accordingly, the volume ofbiogas and methane generated from Phase 2 also increased with FW content. The low OLR (<0.2 g VS/L/day), the use of a two-phase system, and the use of filtrate from Phase las feed to Phase 2 allowed for high utilization of the feed; the observed specific methane yields (mL/g COD) were greater than 80% of the theoretical yields for all mixtures. The methane yields were statistically similar to within a 95% confidence interval.

A dual grafted fluorinated hydrocarbon amine weak anion exchange resin polymer for adsorption of perfluorooctanoic acid from water.

Perfluorooctanoic acid (PFOA) is a persistent and recalcitrant organic contaminant of exceptional environmental concern, and its removal from water has increasingly attracted global attention due to its wide distribution and strong bioaccumulation. Adsorption is considered an effective technique for PFOA removal and more efficient PFOA sorbents are still of interest. This study developed a dual grafted fluorinated hydrocarbon amine weak anion exchange (WAX) polymeric resin (Sepra-WAX-KelF-PEI) for PFOA removal from water. This polymer was synthesized by a two-step amine grafting reaction procedure involving first the reaction of the Sepra-WAX hydrocarbon polymer with poly(vinylidinefluoride-chlorotrifluoroethylene) (Kel-F 800) and then a second reaction with polyethyleneimine (PEI). Characterization of the synthesized polymers was performed using scanning electron microscopy and elemental analysis (F and Cl) by energy dispersive X-ray spectroscopy. The PFOA adsorption performance evaluations were conducted by packed column flow analyses with on-line detection. The results show the breakthrough of the Sepra-WAX-KelF-PEI synthesized with optimum stoichiometry was two times better than the starting anion exchange polymer Sepra-WAX, and six times better than powdered activated carbon, when using the same column size. The adsorption mechanisms of this novel adsorbent including hydrophobic interaction and electrostatic interaction were also clarified in this study. The adsorption kinetic parameters of the two optimum synthesized sorbents were determined using the Thomas model, the Yoon-Nelson model, and batch isotherm studies, and compared with those found with activated carbon and the starting WAX resin. Good agreement of the batch isotherm and column studies with respect to adsorption capacities trends between all three polymers (Sepra-WAX, Sepra-WAX-KelF, and Sepra-WAX-KelF-PEI) were noted.

Reduction of hexavalent chromium by the thermophilic methanogen Methanothermobacter thermautotrophicus.

Despite the significant progress on iron reduction by thermophilic microorganisms, studies on their ability to reduce toxic metals are still limited, despite their common co-existence in high temperature environments (up to 70°C). In this study, Methanothermobacter thermautotrophicus, an obligate thermophilic methanogen, was used to reduce hexavalent chromium. Experiments were conducted in a growth medium with H2/CO2 as substrate with various Cr6+ concentrations (0.2, 0.4, 1, 3, and 5 mM) in the form of potassium dichromate (K2Cr2O7). Time-course measurements of aqueous Cr6+ concentrations with the 1, 5-diphenylcarbazide colorimetric method showed complete reduction of the 0.2 and 0.4 mM Cr6+ solutions by this methanogen. However, much lower reduction extents of 43.6%, 13.0%, and 3.7% were observed at higher Cr6+ concentrations of 1, 3 and 5 mM, respectively. These lower extents of bioreduction suggest a toxic effect of aqueous Cr6+ to cells at this concentration range. At these higher Cr6+ concentrations, methanogenesis was inhibited and cell growth was impaired as evidenced by decreased total cellular protein production and live/dead cell ratio. Likewise, Cr6+ bioreduction rates decreased with increased initial concentrations of Cr6+ from 13.3 to1.9 µM h-1. X-ray absorption near-edge structure (XANES) spectroscopy revealed a progressive reduction of soluble Cr6+ to insoluble Cr3+ precipitates, which was confirmed as amorphous chromium hydroxide by X-ray diffraction and selected area electron diffraction pattern. However, a small fraction of reduced Cr occurred as aqueous Cr3+. Scanning and transmission electron microscope observations of M. thermautotrophicus cells after Cr6+ exposure suggest both extra- and intracellular chromium reduction mechanisms. Results of this study demonstrate the ability of M. thermautotrophicus cells to reduce toxic Cr6+ to less toxic Cr3+ and its potential application in metal bioremediation, especially at high temperature subsurface radioactive waste disposal sites, where the temperature may reach ∼70°C.

Methanol oxidation using ozone on titania-supported vanadia catalyst.

Ozone-enhanced catalytic oxidation of methanol has been conducted at mild temperatures of 100-250 degrees C using a V2O5/ TiO2 catalyst prepared by the sol-gel method. The catalyst was characterized using XRD, surface area measurements, and temperature-programmed desorption of methanol. The oxidation of methanol with ozone in the absence of a catalyst gave about 30% conversion at 100 degrees C. Methanol oxidation over a V2O5/TiO2 catalyst at 100 degrees C gave very little conversion with oxygen, whereas the conversion increased to 80% with ozone. Methanol, having an inlet stream concentration of 15 000 ppmv, can be completely oxidized to CO(x) with an ozone-to-methanol ratio of 1.2, a temperature of 150 degrees C, and a gas hourly space velocity (GHSV) of 60 000 h(-1). The apparent activation energy with ozone was calculated to be ca. 40 kJ/mol, which is much lower than that calculated with oxygen (60 kJ/mol). At low methanol conversion methyl formate was the main product, whereas higher conversions favored oxidation to CO(x). The results imply a consecutive reaction of adsorbed methanol species, favoring selectivity toward methyl formate at lower temperatures and ozone-to-methanol ratios and CO(x) at higher temperatures and ozone-to-methanol ratios. Langmuir-Hinshelwood kinetics was used to model the reaction with and without ozone in the feed. The model parameters were obtained using least-squares fit to a selected set of experimental data, and the model was subsequently compared to all experimental data obtained in this study.