Mechanical processes Questions Flashcards
What is the equalization tank?
Fully mixed tank with a stirrer. It’s used to equalize the flow rate and concentration as within production cycles and seasonal variations, you get fluctuating wastewater flows and varying concentrations.
What can arise from equalization problems?
Large fluctuations can be a problem for the biological systems while chemical dosages might not be able to follow certain fluctuations. Can lead to degradation of the effluent quality and so have an impact on the environment.
Whats is the screening process for?
To remove coarse material from wastewater and is classified using pore size and screen fabrication
What are different screening processes?
For medium screens a bar screen or rake is used. For micro screens a drum screen is used.
What is the sedimentation process for?
To remove mineral fractions in order to avoid wearing and deposition and separation of biological/chemical sludge.
What are some problems with conventional settling tanks?
There can be fluctuating flow rates where the horizontal velocity can’t be kept constant. Can be replaced with parallel arranged chambers or an aerated grit chamber.
Different devices used in the sedimentation process?
A lamella plate seperator, which reduces the height of separation and results in a good separation efficiency. Also a Hydrocyclone, which creates centrifugal acceleration and increases gravitation.
What’s the skimming process?
Skimming is applied for the seperation of light liquids, as there’s a density difference between water and the light liquids i.e. fat.
What does the skimming efficiency depend on?
Efficiency depends on density of material and the temperature of the wastewater.
What are the 4 steps of flotation?
1- generation and insertion of gas bubbles into the reactor.
2- building of an ongoing contact between gas bubbles and solid particles.
3- upward movement of gas/solid agglomerate.
4- skimming of froth.
What is DAF
DAF is dissolved air flotation, where air is dissolved in water under pressure and then is depressurized as it turns from dissolved into a gaseous state. It follows Henry’s law.
Why is filtration needed?
Filtration is needed for the retention of particles, where the driving force is the pressure between two sides of the filter.
What’s the difference between depth filter and a surface filter?
Depth filter is made up of sand and traps the particles, where they are separated throughout the entire filter. A surface filter stops the particles on the surface using a thin filtration media.
