List of abbreviations: PHA, polyhydroxyalkanoate; PHB, polyhydroxybutyrate; DO, dissolved oxygen; DCW, dry cell weight; COD, chemical oxygen demand; VFA, volatile fatty acid; D-COD, dissolved chemical oxygen demand; GC, gas chromatography; PHB-PHV, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) 2 ABSTRACT We investigated the effects of different feeding regimens (1-pulse, stepwise, and continuous) of fermented food-waste liquid on polyhydroxybutyrate (PHB) production.The fermentation liquid was filtered with a membrane filter (pore size, 0.45 μm) to remove anaerobic microorganisms and solids and used as a carbon source for Cupriavidus necator. One-pulse feeding yielded the highest cell concentration of C.necator. However, the PHB concentration was higher in the stepwise-and continuous-feeding regimens. Therefore, the continuous-feeding regimen was used for continuous PHB production. PHB could be produced over 259 h (8 draw-fill cycles) with a maximal PHB content of 87%, but the PHB concentration and content decreased with an increase in the operation time.
A zirconium sulfate-surfactant micelle mesostructure (ZS) was synthesized to investigate its capacity for phosphate removal from water. Its phosphate adsorption kinetics, the effect of pH and interfering anions, adsorption isotherm, desorption capacity, and reusability were investigated. The adsorption isotherms could be described by the Langmuir model. The ZS was an effective adsorbent for phosphate with a very high adsorption capacity (114 mg P/g ZS). The phosphate adsorption capacity increased with decrease in pH.Although the adsorption of nitrate, chloride and acetate ions was negligible, bicarbonate ions were found to be possible interfering anions. The adsorbed phosphate was desorbed effectively using NaOH solution. Since breakage of ZS particles resulted when using NaOH, ZS was immobilized on a polymer matrix and a 50-cycle adsorption-desorption test was carried out to determine the ZS-immobilized polymer (P-ZS) reusability. The P-ZS retained its functionality and adsorption and desorption capacity over 50 cycles without loss of original capacity. A phosphate solution containing about 10 mg P/L was treated in a column packed with P-ZS. The phosphate could be adsorbed completely onto P-ZS up to 1020 bed volumes. These results indicate clearly that ZS is a highly effective adsorbent for phosphate and enables the removal of phosphate from water.
In coagulation-membrane filtration water treatment processes, it is still difficult to determine the optimal coagulation condition to minimize irreversible membrane fouling. In microfiltration (MF), meso-particles (i.e., 20 nm-0.5 μm) are thought to play an important role in irreversible membrane fouling, especially their characteristics of particle number (PN) and zeta potential (ZP). In this study, a new nanoparticle tracker combined a high-output violet laser with a microscope was developed to identify the physicochemical characteristics of these microscopic and widely dispersed meso-particles. The effects of pH and coagulant dose on ZP and PN of micro-particles (i.e., >0.5 μm) and meso-particles were investigated, and then coagulation-MF tests were conducted. As the result, irreversible membrane fouling was best controlled for both types of membranes, while meso-particle ZP approached zero at around pH 5.5 for both types of natural water. Since PN was greatest under these conditions, ZP is more important in determining the extent of irreversible membrane fouling than PN. However, the acidic condition to neutralize meso-particles is not suitable for actual operation, as considering residual aluminum concentration, pipe corrosion, and chlorination efficiency. It is therefore necessary to investigate coagulants or other methods for the appropriate modification of meso-particle characteristics.
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