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Food Processing Technology > 2. Wastewater treatment > Flashcards

2. Wastewater treatment Flashcards

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1
Q

Examples of surface water

A

dams, lakes, rivers, sea, reservoirs

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2
Q

Examples of underground water

A

wells, springs

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3
Q

what is spring water

A

water that comes from an underground source and naturally flow to the surface

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4
Q

What is hard water

A
  • water that has high mineral content (Ca2+ and Mg2+)
  • generally not harmful
  • leaves hard, white, crusty deposits (CaCO3, Mg(OH)2)
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5
Q

Equation to express concentration (mg/L) of CaCO3?

A

mg/L species x (EW of CaCO3/EW of species)

EW = equivalent weight = MW/n

EW of CaCO3 = 50

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6
Q

equation for normality

A

N = (m/MW)/nV = n x Molarity

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7
Q

Classification of water hardness

A

note: defined as sum of polyvalent cations with units mg/L or mEq/L

soft: <17.1
slightly hard: 17.1 - 60
moderately hard: 60 - 120
hard: 120 - 180
very hard: >180

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8
Q

why is water treatment neccessary

A
  1. presence of biological/physical/chemical/radiological contaminants
  2. presence of organic matter, colour, taste and odour is unacceptable
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9
Q

four types of water in food industries

A
  1. process water
  2. general purpose water
  3. boiler feed water
  4. cooling water
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10
Q

what is general purpose water

A

all water used in washing and sanitizing raw materials, processing equipment, plant facility and ancillary equipment

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11
Q

characteristics of general purpose water

A
  • used in largest amount
  • portable, clear, colorless, free of contaminants that affect taste/odour

(refer to regulation of Menteri Kesehatan RI No 416/MENKES/PER/IX/1990)

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12
Q

Treatments used for general purpose water

A

IN PLANT CHLORINATION only
- microbe reduction on raw materials, prepared products and equipment surfaces

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13
Q

What is process water?

A

water used for cooking or added directly to the product

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14
Q

characteristics of process water

A
  • must be portable
  • of sufficient quality
  • meet safe drinking water standards

(refer to regulation of Menteri Kesehatan RI No 492/Menkes/Per/IV/2010 9 April 2010)

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15
Q

treatment processes of process water

A
  • softening
  • coarse filtering
  • filtering by membrane
  • deionization
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16
Q

why is hard water undesirable for food processing

A

contains minerals that can affect texture or raw materials to be processed

iron, manganese and sulfate can have undesirable effects on taste of product

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17
Q

regulations on consumble water based on SNI 01-3553-2006

A
  • no odour
  • max 500ml/L dissolved subqstance
  • organic substance 1.0 mg/L
  • chloride max 250 mg/L
  • ammonium max 0.15 mg/L
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18
Q

What is cooling water

A

cooling watre not in contact with food products or sealed containers

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19
Q

Characteristics of cooling water

A
  • does not have to be portable
  • removal of staining minerals and odours not important
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20
Q

Treatment of cooling water

A

treatment to prevent accumulation of scale in pipes and equipments, especially when cooling water recycled

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21
Q

Treatment of boiler feedwater

A
  • removal of hardness
  • demineralization/removal of all dissolved solids
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22
Q

flow of underground water processing

A

site selection > drilling > pumping > iron removal with sodium silicate > UV treatment for sterilization > addition of chlorine to disinfect > storage

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23
Q

flow of surface water processing

A

intake > sedimentation > coagulation with alum > flocculation > sedimentation > filtration > disinfecting with chlorine > product > reservoir

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24
Q

flow of spring/mineral water treatment

A

sand filtration > reservoir > carbon filter > softening > prefilter > final filter > UV > ozone > packaging > product

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25
Q

parameters for defining a treatment system

A

in: influent concentration
out: discharge requirements
out: air emissions
out: sludge disposal

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26
Q

physical/chemical methods for treatment of organic contaminants

A
  1. coagulation
  2. flocculation
  3. sedimentation
  4. adsorption
  5. manganese dioxide
  6. ion exchange
  7. chemical oxidation
  8. filtration
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27
Q

what is coagulation

A
  • addition of coagulants to reduce surface charge on colloids and encourage coagulation
  • colloidal particles are negatively charges and repel each other, while neutralized ones are more likely to stick with each other during collision and become larger
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28
Q

example of coagulants

A
  • ferric sulfate (Fe2(SO4)3)
  • alum/aluminium sulfate (Al2(SO4)3*18H2O)
  • synthetic polymers
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29
Q

what is flocculation

A
  • making small flocs and particle agglomerations into large flocs
  • mixing required to enhance agglomeration, but too much mixing leads to floc break up
30
Q

what can be used during mixing in flocculation

A
  • shaft/rotational blades
  • paddle blades
31
Q

what is sedimentation

A

removal of suspended matter from liquid phase by gravitational settling

32
Q

equipments used for sedimentation

A

sedimentation basins (clarifiers, settling tanks)

33
Q

two operating modes of adsorption

A
  1. physical (one way operation)
  2. chemical (regeneration operation)
34
Q

principles of one way operation in adsorption

A

when max capacity reached, adsorbent is changed. this happens when adsorbate (the material adsorbed) is trapped deep inside the porous structure

35
Q

principles of regeneration operation

A

when max capacity reached, adsorbent is regenerated
a. desorption (using chemical agent such as soda/acid)
b. neutralization (recovering full capacity)

36
Q

adsorption mechanism of activated carbon

A
  1. diffusion of molecules through liquid phase to the C particle
  2. diffusion of molecules through transport pores (macropores) to adsorption site
  3. adsorption of molecule to surface, usually in the micropores at the interior of the carbon particle

note: lab experiment required to see adsorption isotherm (calculate how much adsorbent required and max capacity of contaminants adsorbed)

37
Q

what is usage rate in activated carbon adsorption

A

pounds of carbon required for a given volume of liquid to maintain contaminant at desired level in the effluent

38
Q

what materials can be removed by activated carbon

A
  1. organic molecules that couse taste and odor, mutagenicity and toxicity
  2. natural organic matter (NOM) that causes odor
  3. disinfection by-products (DBPs)
  4. volatile organic compounds (VOCs) and synthetic organic chemicals (SOCs)
39
Q

forms of activated carbon

A
  1. granular (irregular granules, 0.2 - 0.5 mm; used in wide ranging liquid and gas phase)
  2. powdered (pulverized carbon, <0.18 mm; used in liquid phase and flue gas treatment)
  3. extruded (cylindrical pellets, 0.8 - 5 mm; gas phase application)
40
Q

what is manganese dioxide treatment used for

A

removing manganese and arsenic

41
Q

what is ion exchange treatment

A

removal of hardness and demineralization through a physicochemical process in which ions are transferred from solid to liquid and vice versa

ion exchangers have FIXED ionic groups that are balanced by MOBILE counter ions (anions/cations that exchange will ions in solution) of opposite charge to maintain electroneutrality

42
Q

examples of chemical oxidants in water treatment

A
  • chlorine
  • chlorine ioxide
  • permanganate
  • ozone
43
Q

mechanism of chemical oxidation

A

oxidise reduced inorganic species to:
1. destroy taste and odor causing compounds
2. eliminate odor

44
Q

principles of chemical oxidation with NaOCl

A

used for:
- oxidation of Fe and Mn
- taste and odor control
- color removal
- ammonium removal

45
Q

principles of chemical oxidation with KMnO4

A
  • injected in the water to be treated, contact time 5 min at 20C
  • more efficient in pH > 7.5
  • chemical regeneration of manganese dioxide in manganese removal filters
46
Q

principles of chemical oxidation with ozone

A
  • formation of ozone gas by passing dry air/oxygen through high voltage electric field, forming ozone enriched air added directly to water with porous diffusers/venturi systems
  • injection point at the base of tank (diffuser) or infeed supply (venturi system)
  • mixing and diffusion in contact tank 10-15 min, allows dissolution of gaseous ozone
47
Q

two types of filter

A
  1. cartridge filter
  2. membrane filter
48
Q

what is prefiltration

A
  • function: protect final membrane filtration, especially when theres no/limited clarification steps
  • anything that passes through this stage due to unloading, bleed-through or other mechanism will directly impact how expensive final filtration will be
  • pore size of membrane 0.3-1.0 micrometer
  • should be changed out multiple times
49
Q

what is final filtration

A
  • critical control point to filter particulate matter and microbes in water treatment
  • pore size 0.22 micrometer, 0.1 micrometer for pleated surfaces
  • small water bottlers use non mebrane (cartridge) filter
50
Q

transport mechanisms in membrane filter

A
  1. filtration controlled (microfiltration MF, ultrafiltration UF, and nanofiltration NF)
  2. diffusion controlled (reverse osmosis RO)
51
Q

membrane configurations in membrane filtration

A
  1. flat shaped
  2. tubular
  3. hollow fibre
  4. spiral wound
52
Q

operations of membrane filter

A
  1. constant TMP (rapid fouling due to initial high flux, then flux will decrease)
  2. constant flux (can limit fouling, pressure increase eventually to compensate fouling)
53
Q

key indicators of efficiency of membrane filtration

A
  1. pressure drop from upstream to downstream
  2. recovery = ratio of permeate : feed volume
  3. outlet water quality
  4. rejection rate
54
Q

biological treatments of organic contaminants

A

suspended growth reactors

55
Q

what is suspended growth reactor

A
  • used to biologicaly degrade organic constituents in wastewater under aerobic conditions
  • use diverse microbial populations freely suspended in aqueous conidtion
56
Q

what is MLSS

A

mixed liquor suspended solids
- solid portion of mixed liquor with organic (volatile) and inorganic/inert (non volatile) components
- concentration in adtivated sludge processes 1500 - 3000 mg/L
- concentration in groundwater applications 1500 - 10000 mg/L

57
Q

what is MLVSS

A

mixed liquor volatile suspended solids
- volatile portion of MLSS
- consists of mainly biomass (living and dead)

58
Q

Types of suspended growth reactors

A
  1. activated sludge
  2. sequencing batch reactor
  3. membrane bio reactor (MBR)
59
Q

characteristics of activated sludge in suspended growth reactors

A
  • produces low effluent concentrations
  • system can treat many organics simultanoeusly
  • cost of manpower adjusted to influent conditions
60
Q

characteristics of sequencing batch reactor in suspended growth reactors

A
  • BOD removal efficiency comparable to conventional sludge systems, 85-95%
  • operated under low concentrations of influent organics
61
Q

characteristics of membrane bio reactor in suspended growth reactors

A
  • combines suspended growth biological treatment with membrane filtration
  • membrane separator for solids removal, replacing secondary clarification and effluent filtration steps
  • can be configured with internal/external membrane modules
62
Q

functions of bioreactor and membrane module in membrane bioreactor

A

bioreactor: biological degradation of organic pollution by adapted microbes

membrane module: separation of microbes from treated wastewater; can be tubular MF or UF membrane

63
Q

boiler feed water treatments

A
  1. internal
  2. external
    - ion exchange
    - demineralization
    - de-aeration
    - reverse osmosis
64
Q

water treatment in boiler feed used to control what

A
  1. steam purity
  2. deposits
  3. corrosion

ensures efficient heat transfer if free from deposit-forming solids

65
Q

why is deposit control important

A

avoid efficiency loss and reduced heat transfer

notes:
- alkaline hardness can be removed by boiling
- non alkaline hardness is difficult to remove
- silica forms silica scales

66
Q

conditions of internal water treatment in boiler feed

A
  • feed water is low in hardness salts
  • low pressure
  • small quantities
67
Q

mechanism of internal water treatment in boiler feed

A

chemicals added to boiler to prevent scale
internal treatment alone not recommended

68
Q

what is external water treatment in boiler feed

A

removal of suspended/ dissolved solids and gases through:
1. pre treatment: sedimentation and settling
2. first treatment stage: removal of salts

69
Q

what is deaeration

A

expulsion of dissolved corrosive gases (o2 and co2) by preheating feed water

70
Q

two types of de-aeration

A
  1. mechanical: prior to addition of chemical o2 scavengers
  2. chemical: removes trace oxygen

Food Processing Technology (6 decks)

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