L9- Membranes & Other Technology

Question 1

Filtration

Answer 1

Separation of particulate and colloidal matter from liquid

Question 2

Membrance process - define streams

Answer 2

Feed water - influent water to membrance
Permeate - compounds passing through membrane
Retentate - compounds not passing through membrane

Question 3

Pressure driven membrane- Size of separation

Answer 3

Low P: Microfiltration (MF) & Ultrafiltration (UF)
High P: Nanofiltration (NF) & Reverse Osmosis (RO)

Smallest size filtered: RO < NF < UF < MF

Question 4

Membrane configuration types and materials

Answer 4

Tubular, hollow fine fibre, spiral wound, plate and frame

Materials: symmetric, asymmetric, thin-film composites

Question 5

Driving force of membrane separation

Answer 5

Hydraulic pressure or vacuum

Question 6

Desalination

Answer 6

Mineral components from saline water (salty)
Desalinated for human consumption or irrigation

Dis: High operation costs, produces salty brine, no materials in water

Question 7

Cross-flow operational mode

Answer 7

Feed water tangental to membrane

Ptm = [(Pf + Pr)/2] - Pp

Ptm = transmembrane pressure gradient (bar)
Pf, Pr, Pp = pressure of feed, retentate, permeate (bar)

Question 8

Dead-end operational mode

Answer 8

All feed water passes through membrane

Ptm = Pf - Pp

Ptm = transmembrane pressure gradient (bar)
Pf, Pp = pressure of feed, permeate (bar)

Question 9

Recovery, r(%) - define variables

Answer 9

r(%) = (Vp/Vf)100 (Also (Qp/Qf)100)

Vp, Vf = volumetric flow of permeate and feed (m3/d)

Question 10

Permeate flowrate, Qp - define variables

Answer 10

Qp = Fw*A

Fw = transmembrane water flux rate (m/h)
A = membrane are (m2)

Question 11

Rejection of contaminant, R(%) - define variables

Answer 11

R(%) = [1-(Cp/Cf)]100 (Also [(Cf-Cp)/Cf]100)

Cp, Cf = concentrations of permeate and feed (kg/m3)

Question 12

Log rejection, LR - define variables

Answer 12

LR = -log(1-R) = log(Cf/Cp)

Cp, Cf = concentrations of permeate and feed (kg/m3)

Question 13

Membrane mass balance

Answer 13

Water: Qf = Qr + Qp
Contaminant: QfCf = QpCp + Qr*Cr

Recovery = Qp/Qf

Cp, Cf, Cr = concentrations of permeate, feed and retentate (kg/m3)
Qp, Qf, Qr = volumetric flow of permeate, feed and retentate (m3/d)

Question 14

Membrane fouling types

Answer 14

Particulate fouling: Build-up of substances
Scaling: precipitation of salts
Organic fouling: presence of organics
Biological fouling: presence of m/o

Chemicals that react with membranes = permanent damage

Question 15

Osmotic pressure of solution - define variables

Answer 15

PI = sum(iMRT)

PI = osmotic pressure (atm)
i = van’t Hoff factor of solute
M = molar concentration of solute (mol/L)
R = universal gas constant (0.08206 Latm/molK)
T = temperature (K)

Question 16

Feed water flux, Fw - define variables

Answer 16

Fw = kw*(Delta P - Delta PI) = Qp/A

Fw = feed water flux (L/m2h)
kw = mass transfer coefficient for water flux (L/m2h*bar)
Qp = permate flowrate (L/h)
A = membrane area (m2)
Delta P = average applied pressure gradient, [(Pf+Pr)/2] - Pp (bar)
Delta PI = osmotic pressure gradient, [(PIf+PIr)/2] - PIp (bar)

Question 17

Silt Density Index (SDI) - define variaibles

Answer 17

SDI = [100*(1-(ti/tf))]/t

SDI = treatability of given water/wastewater with NF/RO membranes
ti, tf,t = time to collect initial, final samples of 500mL and total time for running the test

Question 18

Management of retentate

Answer 18

Concentrated brine solution: heavy metals, sals, organics, m/o
Treatment: solar evaporator, spray dryers
Disposal: deep well injection, to WWTP, to ocean

Question 19

Control of membrane fouling

Answer 19

Pre-treatment of feed water: reduce TSS, colloids and bacteria (water conditioning)

Membrane backflushing: with water/air

Chemical cleaning: removes substances not removed by backflushing

Question 20

Summary of other treatment technologies

Answer 20

Advanced oxidation processes (AOPs), phytoremediation, distillation

Question 21

Advanced oxidation processes (AOPs) purpose, types and applications

Answer 21

Chemical oxidation aiming at mineralisation of contaminants to CO2, water and inorganics or at least transformation into harmless products

Types: Fenton, Photo-Fenton, electrodialysis

Applications: Polishing step in WWTP, remove persistent organic pollutants (POPs), disinfection

Question 22

Describe types of AOPs

Answer 22

Wet oxidation: oxygen/air to achieve pollutant oxidation at high T&P - high operating costs

Fenton’s reagent: Destroy toxic compounds in WW using hydrogen peroxide with iron - low pH

Photo-Fenton: UV-Vis at 300nm> (control pH, dose, irradiation time)

Electrolysis: Uses DC to drive non-spontaneous chemical reaction; for WW with high alkalinity/salinity; no pH restriction

Question 23

Design considerations of AOPs

Answer 23

HO(radical) + R -> byproducts
rR = -kCHOCR

Question 24

Phytoremediation purpose, targets and factors affecting

Answer 24

Use living plants to clean up soil, air and water contaminated with hazardous contaminants (hyperaccumulators)

Targets: toxic heavy metals and organic pollutants

Factors: type of plants, type & conc. of pollutants, climate

Question 25

Distillation (importance of evaporation and condensation) & disadvantages

Answer 25

Separate and extract clean water by vaporisation and condensation, i.e. Solar distillation

Evaporation to remove impurities; Condensation to collect water

Dis: scaling and corrosion problems, disposal of concentrated waste, high energy requirements

Question 26

Phytoremediation advantages and disadvantages

Answer 26

Adv: low cost, low environmental impact, preserve soil health, ease process monitoring

Dis: long treatment time, leaching of contaminants into ground water