Removal of heavy metal ions from wastewaters: A review

Waste biomass adsorbents for copper removal from industrial wastewater--a review.

Dissolved air flotation and me.

Heavy metal pollution is a major problems in the environment. The impact of toxic metal ions can be minimized by different technologies, viz., chemical precipitation, membrane filtration, oxidation, reverse osmosis, flotation and adsorption. But among them, adsorption was found to be very efficient and common due to the low concentration of metal uptake and economically feasible properties. Cellulosic materials are of low cost and widely used, and very promising for the future. These are available in abundant quantity, are cheap and have low or little economic value. Different forms of cellulosic materials are used as adsorbents such as fibers, leaves, roots, shells, barks, husks, stems and seed as well as other parts also. Natural and modified types of cellulosic materials are used in different metal detoxifications in water and wastewater. In this review paper, the most common and recent materials are reviewed as cellulosic low-cost adsorbents. The elemental properties of cellulosic materials are also discussed along with their cellulose, hemicelluloses and lignin contents.

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Removal of heavy metals from emerging cellulosic low-cost adsorbents: a review

Algae are an attractive biofuel feedstock because of their fast growth rates and improved land use efficiency when compared with terrestrial crops. Process train components needed to produce algal biofuels include (1) cultivation, (2) harvesting, and (3) conversion into usable fuel. This paper compares various process train options and identifies knowledge gaps presently restricting the production of algal biodiesel and algae-derived biogas. This analysis identified energy-intensive processing and the inability to cultivate large quantities of lipid-rich algal biomass as major obstacles inhibiting algal biodiesel production. Anaerobic digestion of algal biomass requires fewer process train components and occurs regardless of lipid content. In either scenario, the use of wastewater effluent as a cultivation medium seems necessary to reduce greenhouse gas emissions and maximize water use efficiency. Furthermore, anaerobically digesting algal biomass generated from low-technology wastewater treatment processes represents an appropriate technology approach to algal biofuels that is poorly investigated. Coupling these processes can improve global health by improving sanitation, while providing a cleaner burning biogas alternative to indoor biomass cooking systems typical of less-developed areas.

Production of Biodiesel and Biogas from Algae: A Review of Process Train Options

Experimental studies of the fluid dynamics in the separation zone in dissolved air flotation

The influence of contact zone configuration on the flow structure in a dissolved air flotation pilot plant

The flow structure in the separation zone of a DAF pilot plant and the relation with bubble concentration.

A numerical and analytical investigation is performed on a dissolved air flotation (DAF) pilot tank by using the residence time distribution (RTD) of the conservative dye rhodamine measured with a fluorometer. The experiments are numerically analyzed with regard to the total volume of the DAF tank separation zone in order to detect differences between observed separation zone flow structures in previous studies. The mean hydraulic detention time, the variance, and the estimated number of completely mixed tanks (N-cstr) in a series model are calculated. The variance is found to relate to the flow structure and the N-cstr is used for characterizing the occurrence of a stratified flow structure, which is beneficial for particle separation by DAF. The result shows a significant difference in RTD depending on expected flow structure. Analytically, a conceptual model is defined by dividing the DAF tank into an upper and a lower layer. In the upper layer, the water flow is horizontal and in the lower the water flow is vertical. The hypothesis is that mixing of the tracer takes place in the upper layer and that there is no significant mixing in the lower layer. Two simple mixing models are evaluated for the upper layer; the completely mixed tanks in series model, characterized by the number of tanks, and the dispersed plug flow model, characterized by the Peclet number. The models show good agreement with the experiments when the stratified flow structure is expected, but less agreement when the flow deviates from the stratified flow structure. The dispersed plug flow model shows the best fit with the experiments. The completely mixed tanks in series model is less sensitive, generating greater changes to the modeled RTD curve, which makes it more difficult to fit the model to the experiments. (Less)

Residence Time Distribution Characterization of the Flow Structure in Dissolved Air Flotation

Dissolved Air Flotation (DAF) is a separation process in water and wastewater treatment. The removal function is based on reducing the density of the particle by producing aggregates of the particles and added micro-bubbles of air, thus lifting the aggregates to the water surface, where they can be removed as sludge. One parameter that is believed to be of crucial importance is fluid dynamics. The hypothesis is that complex hydraulic effects occur inside a DAF process for clarification, and that these effects have consequences for the separation of particles. Hydraulic loading, air content and internal geometry are believed to control the hydraulic behaviour inside a specific DAF tank. By mapping the flow structure and defining the relationship to these factors, it should be possible to partially predict the separation performance of the unit. The measurements were performed in a rectangular pilot tank. The hydraulic loading over the separation zone was varied in nine cases, from 11.3 m/h to 24.7 m/h, and the recycle rate varied from 5% to 15% of the head flow, generating air contents of 3-12 ml air/l water. Changes in internal geometry were achieved by modifications of the contact zone shaft wall. The flow structure was defined through measurements with an Acoustical Doppler Velocimeter and the separation efficiency was determined through measurements of suspended solids. Numerical and analytical analyses of the flow structure were performed with tracer measurements. A conceptual model was defined based on the cascade box model and the dispersion plug-flow model. The results show that a stratification of the water body exists inside the separation zone. The structure is generated by density gradients caused by spatial differences in air content. The stratification is achieved for the low to average hydraulic surface loading and for the average to high air-content. For the low air-content, a short-circuit flow structure was developed. There appears to be a relationship between the flow structure and the removal efficiency of particles. A high concentration of suspended solids seem to influence the short-circuit flow structure by a transformation towards a stratified flow structure. This, in turn, was observed to improve the separation of particles as well, further strengthening the hypothesis that the flow structure is important for the separation function and that a stratified structure should be maintained. Numerically, there seem to be a relationship between the estimated number of boxes in a cascade box model, calculated from the measured time-concentration curve (retention time distribution) from a tracer test. Visually, the time-concentration curve displays a high, narrow peak for the stratified flow structure and a low, more spread-out distribution for the short-circuit flow structure. Analytical analysis of the stratified flow structure seems feasible with the cascade box model or the dispersion plug-flow model in the upper layer of the stratification. However, the model can only be used for defining the stratified flow structure. (Less)

Måns Lundh

Papers

Experimental studies of the fluid dynamics in the separation zone in dissolved air flotation

The influence of contact zone configuration on the flow structure in a dissolved air flotation pilot plant

The flow structure in the separation zone of a DAF pilot plant and the relation with bubble concentration.

Residence Time Distribution Characterization of the Flow Structure in Dissolved Air Flotation

Effects of Flow Structure on Particle Separation in Dissolved Air Flotation