Performance of a novel vertical-flow settler: a comparative study.
By increasing particle concentration and G value (root-mean-square velocity gradient) to enhance flocculation, a novel vertical-flow settler was designed to increase sedimentation effectiveness, and to simultaneously improve operational stabilization. Due to the gradual decrease in upward flow-rate of raw water, a flocs blanket would form and suspend in the middle section of the settler, not at the bottom as in a conventional clarifier. Enough large flocs, resulted from flocculation or filtration, would continuously settle out of the flocs blanket, and simultaneously, the flocs in raw water or those forming above the blanket would ceaselessly enter the flocs blanket. As a result, the flocs concentration in the blanket could keep a dynamic balance. The hydrodynamic shear in the blanket was improved by flow separation, which was induced by the abrupt change in flow channel. Due to the floes blanket and improved hydrodynamic shear, flocculation would be enhanced, which was helpful for removing fine particles in raw water. A comparative study showed that the novel vertical-flow settler had a much better performance in the removal of the particles in raw water than a conventional one, when they treated kaolin suspensions of different concentrations (500, 100 and 50 mg/L, respectively) coagulated by polyaluminum chloride(PAC1) at the up-flow rates of I and 2 mm/s, respectively.
Integrating gravity settler with an algal membrane photobioreactor for in situ biomass concentration and harvesting.
Gravity settler was integrated into an algal membrane photobioreactor (MPBR) for in situ biomass concentration and harvesting of Graesiella emersonii. By continuous circulation of suspended biomass between MPBR and settler, biomass was sedimented in the settler and harvested. MPBR-Settler operations at different recirculation rates (0.15-2.4 L/d) and settler volumes (250-1000 mL) affected both suspended (0.4-3.4 g/L) and settled (16.1-31.1 g/L) biomass concentrations. Maximum biomass productivity of 0.26 ± 0.06 g/L/d was achieved in the 1000 mL settler operating at 0.6 L/d recirculation rate, which also yielded 9-131 times concentrated biomass (31.1 g/L) compared to the baseline MPBR (0.2-3.4 g/L). This novel design also facilitated MPBR operation at low solids retention times (6-8 d) without incurring large outflow of unfiltered effluent, while alleviating light limitation via biomass dilution. These results demonstrated that the MPBR-Settler system can provide an excellent way to mitigate light limitation, enhance biomass productivity, and simplify biomass harvesting.
PASSIVE AND LOW-ENERGY RESEARCH AND PRACTICES-DEHUMIDIFICATION
Methods of achieving acceptable indoor conditions in overheated, temperate, and underheated humid climates are discussed and compared. Desiccants and desiccant systems utilizing solid and liquid sorbents and various low-energy mechanical systems are described and evaluated.