WATER TREATMENT FINAL EXAM 2025

What is G? - -The velocity gradient used in coagulation and flocculation. What is tapered flocculation? - -Multiple stages have a decreasing velocity gradient in each successive stage. This is to help form floc and prevent it from breaking Type II Settling - -- Particles adhere to each other as they bump into each other - Faster settling particles overtake those that settle more slowly - Large number of particles form a blanket that overtake other particles What is the detention time for a sedimentation basin? - -1.5-4 hrs How is granular filtration layered? Why? - -Anthracite is the top layer and sand is the bottom layer. It is layered this way to increase the filter effectiveness: Larger particles get trapped first. It is also due to the backwash process: the sand settles first because it is denser What is ripening? - -Occurs immediately after backwashing. The effluent turbidity rises to a peak and then falls How are particles captured in rapid granular filtration? - -- Particles are removed by straining (particles are larger than the void spaces in the filter) - Van der Waal forces (attractive close range molecular forces) What is depth filtration? - -Using the whole bed to filter out the particles (large particles are filtered out first and smaller particles as you go down in layers). Utilizes Van der Waal forces. Where is a cross-flow configuration used? - -In industrial wastewater treatment Where is a dead-end configuration used? - -In municipal wastewater treatment What is the filtration mechanism of rapid granular filtration? - -Depth filtration What is the filtration mechanism of membrane filtration? - -Straining What are some important design parameters of membrane filtration? - -- A membrane filtration plant needs 100 times the filter area of a rapid granular filtration plant - Membrane filtration does not require pretreatment - Membrane filtration performance is not affected by the concentration of the feed water Water Water What is membrane filtration? - -A pressure- or vacuum-driven membrane separation process in which particles are removed from a suspension by straining as the fluid passes through the porous material What is reverse osmosis? - -A pressure-driven membrane separation process in which dissolved constituents are separated from a solution by preferential diffusion as the solvent and solute molecules pass through a permeable membrane What is the target contaminants of membrane filtration? - -Particles and bacteria What is the target contaminants of granular filtration? - -Particles What is the target contaminants of reverse osmosis? - -Dissolved solutes What is the configuration of membrane filtration? - -Hollow fibers What is the configuration of reverse osmosis? - -Spiral wound Cp = ? - -= Js/Jw Js = ? - -= ks * (Cf - Cp) Jw = ? - -= kw * (P - pi) As the feed concentration increases at a constant pressure, how is the permeate concentration effected? - -As the feed concentration increases, Js and pi increases. As pi increases, Jw decreases. Because Jw is in the denominator and Js is in the numerator, Cp increases As the pressure increases at a constant feed concentration, how is the permeate concentration effected? - -As the pressure increases, Jw increases, and since Jw is in the denominator, Cp will decrease What is the filtration rate of rapid granular filtration? - -5-15 m/hr What is the filtration rate if membrane filtration? - -0.3-0.17 m/hr What is the operating pressure of granular filtration? - -0.18-0.3 bar (1) What is the operating pressure of membrane filtration? - -0.2-1 bar (1) What is the operating pressure of reverse osmosis? - -5-85 bar What is the filtration cycle duration of rapid granular filtration? - -1-4 days What is the filtration cycle duration of membrane filtration? - -30-90 min Water What is the backwash cycle duration of granular filtration? - -10-15 min What is the backwash cycle duration of membrane filtration? - -1-3 min What is the backwash cycle duration of reverse osmosis? - -None What is the ripening duration for granular filtration? - -15-120 min What is the ripening duration for membrane filtration? - -None What is the ripening duration for reverse osmosis? - -None What is the recovery of granular filtration? - -95% What is the recovery of membrane filtration? - -95% What is the recovery of reverse osmosis? - -50% for seawater 90% for groundwater What is the physical design of granular filtration - -Bed of layered sand and anthracite Critical design parameters of reverse osmosis? - -- Electrostatic repulsion of the membrane surface - Neutral compounds tend to permeate - Small particles are likely to permeate Pretreatment of granular filtration? - -Coagulation, flocculation, and sedimentation Pretreatment of membrane filtration? - -None Pretreatment of reverse osmosis? - -Antiscalant, pre-filtration, and sometimes disinfection Mechanism of reverse osmosis? - -Differences in solubility and diffusivity rej = ? - -1 - (Cp/Cf) What is the typical overall dose of disinfectant? - -1-5 mg/L What is the type of UV that is typical for disinfection? - -UV-C What is t10? - -The time it take for the first 10% of a tracer t