Hexavalent chromium removal using aerobic activated sludge batch systems added with powdered activated carbon

The addition of powdered activated carbon (PAC) has been proposed as a suitable technique to protect activated sludge against toxic wastewaters. However, the literature data describing the combined effect of PAC addition on Cr(VI) removal using activated sludge are scarce. The objectives of this study were to investigate the effect of the initial Cr(VI) concentration, PAC and an electron donor addition on Cr(VI) removal using aerobic activated sludge batch reactors.The following Cr(VI) removal systems were tested: activated sludge alone; activated sludge with an external electron donor (5 g/. of lactose); activated sludge with PAC addition (4 g/.); activated sludge with both PAC and lactose; and PAC alone. The results reported here showed that activated sludges are capable of removing Cr(VI) via its reduction to Cr(III) only if a suitable electron donor (such as lactose) is available. For initial Cr(VI) concentration lower than 10 mg/., biomass alone can remove 100% of the Cr(VI). However, for higher initial Cr(VI) concentrations, removal efficiencies (RE) of the systemwith PAC were higher than RE corresponding to the system without PAC. In addition, as the initial Cr(VI) concentration increased, the rate of Cr(VI) removal and RE values decreased reflecting loss of metabolic activity of the activated sludge due to the toxicity of Cr(VI); however, this inhibition was less in systems with PAC. Whereas the removal of Cr(VI) using powdered activated carbon (PAC) alone is negligible, the addition of PAC can improve the biological reduction of Cr(VI) due to the stimulating or protective effect against the Cr(VI) toxicity. This protective effect was also observed in respiratory activityof the biomass

Cooling and Freezing of Fruits and Fruit Products

The use of low temperatures is an important factor for maintaining postharvest quality of fruits and greatly influences the rate of deterioration. The objective of cooling is to prolong the commercial life of perishable products, by decreasing metabolic activity without causing chilling or freezing injuries, reduction of microbial growth and water loss of the product, between others. On the other side, freezing results in improved effects with respect to shelf life of fruits and availability throughout the year, however various undesirable changes occur due to ice formation.In the present chapter pre-cooling treatments and refrigerated storage of fruits are analyzed. The use of controlled and modified atmosphere storage, novel technologies (thermal treatments, UV-C irradiation, etc.), minimally processed fruits and the use of edible coatings are analyzed.With reference to fruit freezing the formation of ice in tissues (nucleation and crystal growth, intra and extracellular ice), initial freezing point, state diagrams, glass transition temperature, freezing rates and the different equipment used for freezing are described.The effect of freezing rate on fruit quality, physical and chemical modifications, nutritional properties and microbial stability of frozen fruit are discussed. Preparatory operations for freezing such as pre-treatments of fruits using sugar syrups, and dehydrofreezing are explained. Recommended packaging and industrial freezing methods, shelf-life of frozen fruits and new trends in freezing technology are also analyzedFil: Chaves, Alicia Raquel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; ArgentinaFil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentin