Pollutants and Drinking water Treatment Flashcards
list some conventional and some emerging pollutants
conventional- pathogens, organic matter, salts, toxic substances
emerging- nanomaterials, endocrine disrupting chemicals, plastics.
emerging pollutants are synthetic or uncommon natural chemicals, potentially damaging to the ecosystem and human health
Define dissolved oxygen (DO) and biochemical oxygen demand BOD
the amount of molecular oxygen dissolved in water in liquid phase. Oxygen demand is the amount required to degrade pollutants. BOD gives a measure of the oxygen used by microorganisms during oxidation of organic matter. it indirectly measures concentration of organic matter.
how would you conduct a standard BOD test?
conditions: conducted over 5 days, 20 degrees, dark, excess of nutrients, dilution.
1. 10ml of sample is taken into 300ml bottle then filled with dilution water
2. initial DO is calculated then again after 5 days (20 degrees)
3. difference in reading is multiplied by dilution factor gives BOD
How do you calculate BOD from a test?
BOD= ((DOi - DOf) - (1 - p)(Bi - Bf))/p P= dilution factor = Vs/Vt B= blank dissolved O2 concentration
How do you calculate BOD at a given time (t)?
BOD(t) = L0 (1 - e^-(kt))
L0= oxygen equivalent of organic matter at t=0
L0=BODu
What is Chemical oxygen demand (COD)?
the equivalent amount of oxygen required to oxidise any organic matter in water by means of a strong oxidising agent. This is much faster and has better repeatability than BOD.
How would you model a ‘sag’ curve?
- determine the initial conditions of the river
- determine the deoxygenation rate (BOD test)
- determine the reaeration rate
- calculate DO deficit as a function of time
- calculate critical distance and time
How do you calculate deoxygenation rate constant in a river?
Kd(20) = k + vη/H
Kd= Kd(20) * θ^(T-20)
This accounts for increase in microorganisms activity in warmer temperatures
How do you calculate the reaeration rate constant in a river?
Kr(20) = (3.9 * v^0.5)/(H^1.5)
varies with temp in the same way as Kd
list some important water quality parameters
turbidity(cloudy), pH, hardness, alkalinity, nutrients, microorganisms.
Define total suspended solids
solids in water that are large enough to settle out of the solution, or that can be filtered.
TSS = (final mass of filter- initial mass of filter)/water volume
How can pH of water cause issues?
pH<7 corrodes metal pipes, pH>8 decreases efficiency of chlorine disinfectant. acceptable range 6.5
What is hardness?
the amount of dissolved calcium and magnesium in the water. Carbonate hardness (CH) is temporary (removed by hot water) but non-carbonate hardness (NCH) is permanent.
list the stages of drinking water treatment
screening, coagulation, flocculation, flotation and sedimentation, softening, filtration, disinfection, storage, distribution.
What happens during screening?
relatively simple process by mechanically removing large solids such as logs, branches and fish as to protect pumps and pipes.
What happens during coagulation and flocculation?
grouping small suspended particles and colloids into larger flocs, which can then later be removed. with coagulation we neutralize the surface charge of the particles by adding coagulants allowing particles can group (fast mixing tank). flocculation aims to achieve the optimal conditions for floc growth (slow mixing tank).
What’s the difference between discrete particles and flocculating particles?
discrete particles do not change shape, size or velocity gradient over time. flocculating particles do.
list the important processes in the global water cycle
precipitation, evaporation, transpiration, surface run-off (overland flow, water network run off), infiltration, interflow (soil moisture, vadose zone), base flow, groundwater flow (aquifers)
