Thi Phuong Thuy Pham

Food waste-to-energy conversion technologies: current status and future directions.

Food waste represents a significantly fraction of municipal solid waste. Proper management and recycling of huge volumes of food waste are required to reduce its environmental burdens and to minimize risks to human health. Food waste is indeed an untapped resource with great potential for energy production. Utilization of food waste for energy conversion currently represents a challenge due to various reasons. These include its inherent heterogeneously variable compositions, high moisture contents and low calorific value, which constitute an impediment for the development of robust, large scale, and efficient industrial processes. Although a considerable amount of research has been carried out on the conversion of food waste to renewable energy, there is a lack of comprehensive and systematic reviews of the published literature. The present review synthesizes the current knowledge available in the use of technologies for food-waste-to-energy conversion involving biological (e.g. anaerobic digestion and fermentation), thermal and thermochemical technologies (e.g. incineration, pyrolysis, gasification and hydrothermal oxidation). The competitive advantages of these technologies as well as the challenges associated with them are discussed. In addition, the future directions for more effective utilization of food waste for renewable energy generation are suggested from an interdisciplinary perspective.

Structural effects of ionic liquids on microalgal growth inhibition and microbial degradation

In the present study, we investigated structural effects of various ionic liquids (ILs) on microalgal growth inhibition and microbial biodegradability. For this, we tested pyridinium- and pyrrolidinium-based ILs with various alkyl chain lengths and bromide anion, and compared the toxicological effects with log EC50 values of imidazolium-based IL with the same alkyl chains and anion from literature. Comparing determined EC50 values of cationic moieties with the same alkyl chain length, pyridinium-based ILs were found to be slightly more toxic towards the freshwater green alga, Pseudokirchneriella subcapitata, than a series of pyrrolidinium and imidazolium except to 1-octyl-3-methylimidazolium bromide. Concerning the biodegradation study of 12 ILs using the activated sludge microorganisms, the results showed that the pyridinium derivatives except to 1-propyl-3-methylpyridinium cation were degraded. Whereas in case of imidazolium- and pyrrolidinium-based compounds, only n-hexyl and n-octyl substituted cations were fully degraded but no significant biodegradation was observed for the short chains (three and four alkyl chains).

Using Pseudomonas aeruginosa PAO1 to evaluate hydrogen peroxide as a biofouling control agent in membrane treatment systems

Hydrogen peroxide (H2O2) is widely used in water treatment for biofouling control and, in conjunction with catalysts, as a powerful oxidant for contaminant destruction. H2O2 could potentially serve as an antifouling agent in reverse osmosis systems in lieu of chlorine‐based disinfectants. The dependence of the biocidal efficiency of H2O2 on cell density, temperature and H2O2 concentration by determining the growth, attachment and viability of the model bacterium Pseudomonas aeruginosa PAO1 was studied. For controlling growth of planktonic PAO1 cells, the minimally required H2O2 concentration depends on the cell density and temperature. The effect of H2O2 to remove the existing biofilm was found to be effective in the presence of a high concentration bicarbonate (8·4 g l−1), which forms peroxymonocarbonate, a strong oxidant and disinfectant. Treatment with H2O2–bicarbonate reduced the density of live PAO1 cells, removed extracellular polymeric substances and lowered the average biofilm thickness while maintaining the integrity of the membrane, suggesting that this type of treatment may be a suitable ‘in‐place‐cleaning’ procedure for biofouled membranes.

Three degradation pathways of 1-octyl-3-methylimidazolium cation by activated sludge from wastewater treatment process.

The biodegradability and degradation pathways of 1-octyl-3-methylimidazolium cation [OMIM](+) by microbial community of wastewater treatment plant in Jeonju city, Korea were investigated. It was found that [OMIM](+) could be easily degraded by the microbial community. New degradation products and pathways of [OMIM](+) were identified, which are partially different from previous results (Green Chem. 2008, 10, 214-224). For the analysis of the degradation pathways and intermediates, the mass peaks observed in the range m/z of 50-300 were screened by using a tandem mass spectrometer (MS), and their fragmentation patterns were investigated by MS/MS. Surprisingly, we found three different degradation pathways of [OMIM](+), which were separated according to the initially oxidized position i.e. middle of the long alkyl chain, end of the long alkyl chain, and end of the short alkyl chain. The degradation pathways showed that the long and short alkyl chains of [OMIM](+) gradually degraded by repeating oxidation and carbon release. The results presented here shows that [OMIM](+) can be easily biodegraded through three different degradation pathways in wastewater treatment plants.

Algal Biosensor-Based Measurement System for Rapid Toxicity Detection

Microalgae are now widely used as relevant biological indicators in the field of environmental impact studies. Owing to their ubiquity, short life cycles, easiness of culture and high sensitivity to a number of pollutants, these organisms are frequently utilized in ecotoxicological screening of contaminated freshwater (Lewis, 1995). As primary producers, either directly or indirectly, of organic matter required by small consumers in aquatic food webs, microalgae serve an important role in nutrient recycling and equilibrium of aquatic ecosystems (Raja et al., 2008). The most important common biochemical attribute that unites algae is their ability to split water, producing molecular oxygen during photosynthesis and concomitantly assimilating carbon dioxide. Furthermore, the rest of biotic communities are strictly dependent upon the photosynthetic activity of these organisms. Perturbations of microalgal photosynthesis might lead to alterations of their primary production, which in turn causes severe repercussions on the aquatic biota (Morris, 1981). Nowadays, the development of convenient methods or parameters for assessment of the presence of pollutants and their toxicity has become a major goal in environmental monitoring research. Growth rate, fluorescence induction and photosynthetic activity (through oxygen evolution or incorporation of 14C) are the most popular endpoints studied (Jensen, 1984; Puiseux-Dao, 1989). Particularly, photosynthesis inhibition is a reliable indicator that rapidly demonstrates the toxic effect of hazardous contaminants (Overnell, 1976). Table 1 displays a brief review on the literature concerning research on application of microalgal photosynthesis to detect the effects of pollutants. The advantage of photosynthesis inhibition assay is the short duration of the test, usually 2–4 h compared to 48–96 h of chronic exposure (Hall et al., 1996). Bioassays involving photosynthesis process; however, are contingent upon light intensity and initial algal cell concentration. In this regard, light is the most critical element influencing phytoplanktonic photosynthetic activity (Aiba, 1982). In most cases, microalgae-based biosystems are restricted by light, which is easily absorbed and scattered by the microalgal cells (Yun & Park, 2001). It is therefore crucial to figure out and monitor the light dependence of microalgal activity for the sake of designing an efficient algal biosensor-based measurement system for toxicity assessment. Other than irradiance, algal cell concentration and initial dissolved oxygen level applied in the test are also important and should be evaluated to give a better performance of the proposed algal biosensor. 11