Dewatering waste-activated sludge using dissolved gas-flotation followed by filtration
After the successes of flotation of waste-activated sludge (WAS), using the new technique utilizing CO 2 gas as well as using model gas (80% N 2 +20% CO 2 ) in previous research because of the high water solubility of CO 2 gas, the aim of this study is to develop a simple method for dewatering WAS for easier reuse and safe disposal. The paper introduces a laboratory model for dewatering WAS in two stages: flotation followed by filtration. The first stage enables recycling a mixture of greenhouse gases containing 20% of CO 2 and 80% of N 2 gases by volume. The second stage uses a simple compression cell for dewatering WAS. Experiments were carried out to reduce the moisture content and volume of WAS. This was executed using compression force introduced by a low value of air pressure. Using the experimental dewatering model, promising results were obtained. Furthermore, other data were obtained, such as the effect of temperature on the efficiency of dewaterability. It is hoped that the results of this study will lead to further study of collecting industrial CO 2 gas emissions from burning fossil fuels for use in wastewater treatment to decrease the resulting harmful effects of global warming.
Principles and applications of dissolved air flotation
Principles of dissolved air flotation (DAF) discussed include: bubble formation and size, bubble-particle interactions, measures of supplied air, and modeling of the reaction and clarification zones of the flotation tank. Favorable flotation conditions for bubble attachment or adhesion to particles requires a reduction in the charge of particles and production of hydrophobic particles or hydrophobic spots on particle surfaces. A conceptual model for the bubble-particle reaction zone based on the single collector collision efficiency is summarized and discussed. An alternative modeling approach is considered. Clarification or separation zone modeling is based on particle-bubble agglomerate rise velocities. The application of DAF in drinking water treatment is addressed beginning with summaries of design and operating parameters for several countries. DAF should not be considered as a separate process, but integrated into the design and operation of the overall treatment plant. This concept shows that flocculation ahead of DAF has different requirements regarding floc size and strength compared to sedimentation. The efficiency of DAF in removing particles and reducing particle loads to filters needs to be integrated into DAF plant design. The impact on filtration performance is illustrated. Finally, fundamental and applied research needs are addressed.
Growth from Solutions
Growth from solutions is the crystallization of a compound whose chemical composition differs markedly from that of the initial liquid phase. Commonly used solvents are water, multicomponent aqueous or nonaqueous solutions, and melts of some chemical compounds. Differentiations are made based on growth temperatures and on the chemical nature of the solvent. In growth from low-temperature aqueous solutions, the temperatures generally do not exceed 80–90°C; in growth from superheated aqueous solutions (hydrothermal method), they reach 800°C, and in growth from salt melts (molten-salt, flux, or fluxed melt growth), they usually do not exceed 1200–1300°C, but sometimes reach 1500°C.