Biological Water Quality Testing
Membrane Filter Test
(Practical)
The DELAGUA Test Kit
Filtration Apparatus
Pre-field



Sterilize equipment
Prepare media
Check field kit (checklist in back of manual)
Consumables
Equipment
Filtration apparatus Culture medium
filters
•sample cup & Membrane
cable
•vaccuum cup Absorbant pads and dispenser
•petri dishes DPD No 1 tablets
DPD No 3 tablets
Turbidity Tubes
Phenol Red
Chlorine/pH comparator
Methanol
Tweezers
Daily reports and marker, pens
Spares box
Paper towels/clean cloth
Lighter
Clean water
Sample Collection
From tap
- let water run ~1 min
- use sterile sample cup
or rinse 3x
From flowing water
- collect sample
against current
From surface water source
- collect sample from
~30 cm below surface
Where necessary . . .
- lower sample cup into
water using 2m cable
Field tests



Turbidity
Chlorine
pH
Prepare Workspace

“sterile” conditions





Clean surfaces
Wash hands
Work near flame
Alternate sterilization methods
Etc
Prepare petri dish
Dispense broth pad
onto petri dish
Pour media (~2ml)
onto pad
Cover petri dish
Filter Sample (1)
Flame tips of tweezers
Place where they
will not come in contact
with non-sterile items
Assemble
filtration apparatus
Filter Sample (2)
Mark sample #
and remove membrane
from packet
Place membrane
on filter support
(grid-side up)
Fit the filter funnel
and plastic collar
Note 3 positions:
- free
- loose
- fully tightened
Filter Sample (3)
Pour sample
into filtration funnel
(note 100 ml mark)
Attach vaccuum pump
and draw sample through
the filter
Remove
Filter membrane
Filter Sample (4)
Open petri dish and
carefully place membrane
onto broth pad
Replace cover
and label
Stack petri dishes
and place in
incubator to
resuscitate
(min 1 hour)
(Re-)sterilize Apparatus /
prepare for next sample
Dry sample cup
Add 20 drops
(~1ml) methanol
Ignite
close
Incubate



Resuscitate – allow minimum 60
minutes before turning incubator on
44 °C, 16-18 hours → thermotolerant
(e.coli) bacteria
37 °C → total coliforms (must adjust
incubator)
Count Colonies

Count yellow (thermotolerant)
colonies 1-3mm diameter





If two colonies merge, count as 2
If many colonies, use grid to divide plate
and multiply
> 100 colonies, test is only an estimate
“Lawn” implies too numerous to count
↑colonies ↓size due to competition for food
Cleanup/Disposal



Sterilize absorbent pad and filter (burn)
Wash petri dishes with soap and water
before storing; sterilize before next use
Wipe inside of incubator with alcohol
Questions / Comments
Your turn!
Practical – MF Test
1. Feed
2. Filter
3. Incubate
4. Sterilize
Practical – Count Colonies