Modelling of Harvesting Techniques for the Evaluation of the Density of Microalgae.

A better estimation of the density of cells has great relevance in the design of harvesting units. In the case of microalgae, the density is a function of the internal composition, which in turn is affected by external environmental conditions. The density of microalgae is often regarded as a constant or a generic value is retrieved from literature. This study proposes a procedure to evaluate the density of Chlorococcum sp. with simple sedimentation and centrifugation experiments coupled with the population balance equation (PBE), which is solved numerically. The density of cells is not constant; instead, it is a function of the size of particles, which in turn changes with the cells' phase of their life cycle. The calculated cellular density ranged between 1000 and 1100 kg m-3 in function of the cell size in both the sedimentation and centrifugation tests. The method can be extended to other microalgae species as well as to other types of cells.

A practical approach for modelling the growth of microalgae with population balance equation.

Microalgae are versatile microorganisms with applications in food, energy and fine chemicals, among others. Modelling the dynamics of microalgae inside a photobioreactor is a convenient and inexpensive way to determine the concentration of cells over time. Numerous models have been developed in the literature, but only a few are able to give relevant biological information. Such information can then be used to further improve the production process. The objective of this work was to develop a model for the determination of microalgal dynamics inside a photobioreactor as a function of the environmental conditions, to retrieve the size-specific growth and division rates as well as the number of daughter cells. The results demonstrate how to evaluate the time needed for microalgae to complete a full life-cycle. Inexpensive laboratory-based procedures and mathematical modelling are combined for the determination of relevant biological parameters.

Aqueous mercury adsorption by activated carbons.

Due to serious public health threats resulting from mercury pollution and its rapid distribution in our food chain through the contamination of water bodies, stringent regulations have been enacted on mercury-laden wastewater discharge. Activated carbons have been widely used in the removal of mercuric ions from aqueous effluents. The surface and textural characteristics of activated carbons are the two decisive factors in their efficiency in mercury removal from wastewater. Herein, the structural properties and binding affinity of mercuric ions from effluents have been presented. Also, specific attention has been directed to the effect of sulfur-containing functional moieties on enhancing the mercury adsorption. It has been demonstrated that surface area, pore size, pore size distribution and surface functional groups should collectively be taken into consideration in designing the optimal mercury removal process. Moreover, the mercury adsorption mechanism has been addressed using equilibrium adsorption isotherm, thermodynamic and kinetic studies. Further recommendations have been proposed with the aim of increasing the mercury removal efficiency using carbon activation processes with lower energy input, while achieving similar or even higher efficiencies.

Waste printed circuit board recycling techniques and product utilization.

E-waste, in particular waste PCBs, represents a rapidly growing disposal problem worldwide. The vast diversity of highly toxic materials for landfill disposal and the potential of heavy metal vapors and brominated dioxin emissions in the case of incineration render these two waste management technologies inappropriate. Also, the shipment of these toxic wastes to certain areas of the world for eco-unfriendly "recycling" has recently generated a major public outcry. Consequently, waste PCB recycling should be adopted by the environmental communities as an ultimate goal. This article reviews the recent trends and developments in PCB waste recycling techniques, including both physical and chemical recycling. It is concluded that the physical recycling techniques, which efficiently separate the metallic and nonmetallic fractions of waste PCBs, offer the most promising gateways for the environmentally-benign recycling of this waste. Moreover, although the reclaimed metallic fraction has gained more attention due to its high value, the application of the nonmetallic fraction has been neglected in most cases. Hence, several proposed applications of this fraction have been comprehensively examined.