Marine environmental engineering

In this study, 26,315 mg/kg of diesel oil was mixed with food waste; the mixture was subjected to composting and monitored for temperature, pH, and moisture content to assure a normal composting process. Variation of total petroleum hydrocarbon (TPH) in the compost was monitored to better understand the progress of diesel decomposition. Samples were also collected for identifying Oleiphilus species. Results showed that food waste composting is effective in decomposing diesel oil, as the TPH was reduced to 2000 mg/kg with about 90%-92% removal efficiencies at the 24th day. Eleven Oleiphilus species were isolated during various composting stages: five from the initial stage, two from the temperature-rising stage, one from the thermophilic stage, one from the temperature-recovering stage, and two from the maturing stage. These observations reveal that the food waste composting pile contained a wide variety of microorganisms, and microorganisms with different oil-decomposing capabilities developed during the various stages of the composting process. After isolation and enrichment, these microbial consortiums may be developed to improve the novel biological method for treating oils in contaminated environment using food waste composting process. It was observed that major decomposition occurred in the thermophilic stage, a divergence from conventional biological treatment approaches conducted in mesophilic environments. Therefore, the proposed composting process involving various diesel-degrading thermophiles facilitated the biodegradation of diesel oil without bioaugmentation, reducing the bioremediation time and cost.

The superior oil absorption capacity of recycled polypropylene (PP) fiber and waste tire powder were used to recover spilled engine oil. We used ASTM F726-99 method to evaluate oil adsorbing capability of PP fiber and found it to have a large, rapid oil sorption capacity. However, its lack of elasticity dramatically limited that capacity after repeated use. Tire powder, which absorbs less oil more slowly, is more elastic than PP fiber and can be used repeatedly up to a hundred times without losing its oil adsorption capability. We combined PP fiber and tire powder to develop a composite material capable of recovering greater amounts of oil than any of its components. This composite can be use repeatedly for at least 100 times. Thus, the material cost for recovering 1 ton of spilled oil is about USD $0.03, making it very competitive on the market.

The photocatalytic bleaching of dyes using TiO 2 has appeared promising in laboratory studies, but little attention has been focused on whether other species such as might be found in wastewater have a deleterious effect on the photobleaching. This study describes the effects that result from the presence of ionic species, organic solvents and humic substances on the photobleaching of several dyes. The manner in which the photobleaching was affected by the presence of adventitious materials was carefully examined with an eye toward elucidating the mechanistic origin of the loss of the photochemical efficiency in the reaction. The overall retardation effects can be attributed to the combination of light attenuation, inhibition and competition effects. Ó

A reaction mixture containing DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), methylene green (as the photosensitizer), and triethylamine (as the electron donor) in acetonitrile:water (1:1) was irradiated by an ordinary 150-W GE-Miser spotlight to facilitate visiblelight photosensitized DDT dehalogenation. The intermediates and reaction products were identified by GC/MS (gas chromatography/ mass spectrometer) and NMR (nuclear magnetic resonance). The photosensitized dehalogenation method partially degraded DDT via an electron transfer relay mechanism. Results indicate that DDT lost about three chlorines after a total of 19 days of irradiation. Aliphatic chlorines were found to be removed easier than aromatic chlorines. Various types of reductants were compared for electron donation efficiency, and photosensitizer concentration was optimized for our reaction system. In most cases, clean and simple dechlorinated products were observed. The proposed photosensitized reduction was coexisted with a thermal elimination effect for the first chlorine removal of DDT, and the photosensitized electron transfer reduction was shown to be the dominating mechanism responsible for further dechlorination after the initial stage. A sequential dechlorination pathway was proposed, with each successive dehalogenation, the reaction proceeds more slowly. The results have shown the feasibility of utilizing visible light, nontoxic dyes and electron donors to render a toxic compound less toxic and to enhance the natural carbon regeneration rates.

Titanium dioxide was shown to be generally effective as a catalyst for photobleaching many structural classes of organic dyes in aqueous solution, using visible light. However, results from study of 15 dyes indicate that photobleaching rates differ significantly from families of dyes with different functionalities, and are dependent on the light source and crystalline form of TiO2 used. Sorption characteristic on the TiO2 surface and the aqueous solubility of the dyes also play an important role in the photobleaching rate. Kinetic analysis indicates that the dye photobleaching rates can usually be approximated as pseudo-first-order kinetics. In addition to the generally proposed photocatalytic oxidation mechanism for TiO2 reactions, we observed evidence for two kinds of electron transfer mechanisms that are “photosensitized reduction” and “photosensitized oxidation”. Natural sunlight was effectively used to photobleach some of the dyes.

The photocatalytic bleaching of dyes using TiO2 has appeared promising in laboratory studies, but little attention has been focused on whether other species such as might be found in wastewater have a deleterious effect on the photobleaching. This study describes the effects that result from the presence of ionic species, organic solvents and humic substances on the photobleaching of several dyes. The manner in which the photobleaching was affected by the presence of adventitious materials was carefully examined with an eye toward elucidating the mechanistic origin of the loss of the photochemical efficiency in the reaction. The overall retardation effects can be attributed to the combination of light attenuation, inhibition and competition effects.

TiO2/UV photocatalytic oxidation of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), 1,2,3-trichlorobenzene and 4-chlorophenol were examined in aqueous solution in the presence of humic substances and organic mixtures to study if the degradation rates were affected. Both commercial and natural humic substances were observed to retard the photodegradation rates, with a greater effect from the natural humic substances. Acetonitrile and isopropanol also caused significant retardation of 4-chlorophenol photodegradation. The overall retardation can be attributed to the combination of light attenuation, inhibition and competition effects. Moreover, the TiO2/UV system favors the decomposition of compounds that have stronger adsorption onto the TiO2 surface. To engineer effective treatment facilities that use the TiO2/UV system for the treatment of toxic substances in wastewater, the methodology must allow for concerns about adventitious species which are present.

A reaction mixture containing DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), methylene green (as the photosensitizer), and triethylamine (as the electron donor) in acetonitrile:water (1:1) was irradiated by an ordinary 150-W GE-Miser spotlight to facilitate visible-light photosensitized DDT dehalogenation. The intermediates and reaction products were identified by GC/MS (gas chromatography/mass spectrometer) and NMR (nuclear magnetic resonance). The photosensitized dehalogenation method partially degraded DDT via an electron transfer relay mechanism. Results indicate that DDT lost about three chlorines after a total of 19 days of irradiation. Aliphatic chlorines were found to be removed easier than aromatic chlorines. Various types of reductants were compared for electron donation efficiency, and photosensitizer concentration was optimized for our reaction system. In most cases, clean and simple dechlorinated products were observed. The proposed photosensitized reduction was coexisted with a thermal elimination effect for the first chlorine removal of DDT, and the photosensitized electron transfer reduction was shown to be the dominating mechanism responsible for further dechlorination after the initial stage. A sequential dechlorination pathway was proposed, with each successive dehalogenation, the reaction proceeds more slowly. The results have shown the feasibility of utilizing visible light, nontoxic dyes and electron donors to render a toxic compound less toxic and to enhance the natural carbon regeneration rates.

A pilot-scale active aeration reactor was studied for composting food wastes in an open-top container aerated with negative pressure by vacuum. A biological filter bed was used to remove NH3 from the emission. In addition to monitoring system parameters, the compost stability and fertilizer content were also examined to ensure product quality. The compost temperature rose to above 65 °C the first day and maintained at the high temperature fermentation level for 30 days. The pH decreased from the initial 5.2 to 4.3 on the first day and then rose slowly to 7.4 on the 60th day. After 60 days, the C/N ratio dropped from 32 to below 20. The final compost contains 1.6% nitrogen, 0.6% phosphate, and 1.4% potassium with total coliforms below 3 MPN/100 mL. Using the biological filter to remove NH3, the emission contains less than 1 ppm of NH3. This system proves to be effective and environmental friendly.