The present investigation elicits a comparative study for recovering urea from human urea via adsorption onto three biosorbents: Microwave Activated Carbonized Bamboo Shoots (MACBS), Walnut Shells (MACWS) and Coconut Shells (MACCS). The rate of sorption was investigated under different process parameters including initial sorbate concentration, amount of sorbent, temperature and agitation speed, and further, sorption capacity of MACBS, MACWS and MACCS was compared. Batch results indicated that urea uptake capacity increased with an increase in sorbate concentration and a decrease in sorbent loading and temperature. The experimental data were tested against the Langmuir, Freundlich, Tempkin, Flory-Huggins and Dubinin-Radushkevich (D-R) isotherms with the D-R model being a good fit for MACBS and MACCS and the Freundlich model for MACWS. Kinetic studies were performed to understand the order and rate of the sorption process. While pseudo-second-order kinetic model fits best for MACBS and MACWS, pseudofirst order was followed by MACCS. Based on the urea sorption capacity, the following order of suitability of precursors for activated carbon preparation was established: MACBS > MACCS > MACWS. This study illustrates the suitability of biomass-based precursors for activated carbon preparation and nutrient recovery from wastewater streams like human urine for subsequent use as fertilizers on agricultural land.
A comprehensive hydrodynamic study of a Liquid -Solid Circulating Fluidized Bed (LSCFB) is conducted with changes in viscosity of the fluidizing medium and the inventory height of solids initially fed into the system. An LSCFB of height 2.95m and riser outer diameter 0.1m was chosen for experimentation. The three liquid media systems with varying viscosities that were chosen were water, glycerol 10% (v/v) and glycerol 20% (v/v). Effect of inventory on the hydrodynamics was also studied, by taking initial heights of inventory to be 15cm, 25cm and 35cm. The hydrodynamic studies concentrated on pressure gradients along the axial pressure tapings, axial solid holdup, average solid holdup, solid circulation rate and slip velocity. Uniformity in axial solid holdup and average solid holdup was validated for changes in viscosity and inventory. Solid flux was seen to follow an inverse relationship to holdup. The changes in slip velocity with varying viscosity and inventory were studied, and found to decrease with both variables. The distribution parameter, Co of the drift flux model was found to be in the range of 0.983-0.994, suggesting non-uniformity in radial solid distribution, with higher solid concentration by the walls compared to the core of the column.
Circulating fluidized beds (CFB) play a major role in the chemical industry especially as heterogeneous catalytic reactors. Research on hydrodynamic properties of Liquid – Solid CFBs (LSCFB) is significantly under-reported as compared to Gas – Solid CFBs (GSCFB). Steadily, prominent research is being established in fields like food industry (whey protein recovery), waste management (removal of heavy metals from radioactive wastes) and others, which use LSCFBs. In this context, it is important to have significant knowledge about the changes occurring in hydrodynamic properties like solid hold-up, rate of solid circulation etc., on changing certain critical physical properties such as inventory height. An LSCFB of height 2.95 m and riser outer diameter 0.1 m was chosen and the effect of inventory height on the properties was studied by taking the initial inventory heights as 15 cm, 25 cm and 35 cm. The hydrodynamic studies concentrated on axial solid holdup, average solid holdup, solid circulation rate and slip velocity. On increasing the inventory, uniformity of axial solid holdup was confirmed along with studying holdup patterns. Solid flux was seen to follow an inverse relationship to holdup, as expected. The change in slip velocity with varying inventory was also checked, and was found to decrease with inventory. The distribution parameter, Coof the drift flux model was used to determine the extent of non-uniformity in solid distribution. Cowas calculated to be less than unity in the range of 0.983–0.994, suggesting non-uniformity in solid distribution, with higher solid concentration by the walls compared to the core.
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