| Failure |
Effect |
Recommended
Monitoring Practice |
| Antiscalant. |
Scale formation on membranes, usually in the
back-end stages – high salt passage, Pressure difference
in final stage. |
Check dosing equipment and monitor changes in
water quality. |
| Ineffective sanitization procedures. |
Bio-fouled pipe-work, cartridge filters and membranes
- high Pressure difference. |
Sanitize sand filters and GAC filters. Microbiological
analysis, chlorine dosing, contamination in chemical dosing
tanks. |
| High iron content. |
Iron loading on cartridge filters. Iron fouling
of membranes – high Pressure difference, low permeate
flow. |
Pipe-work corrosion, ferric breakthrough from
media beds, failure of media filters. |
| High organic content. |
Humic substances and organic fouling on membrane
– low permeate flow, high feed Pressure |
Feed water composition, review flocculation procedures,
feed watercolor, TOC. |
| Colloidal breakthrough. |
Colloidal particles foul micron filters and membranes
– high Pressure difference, low permeate flow. |
Silt Density Index (SDI), condition of cartridge
filters, eliminate media fines. |
| Granular activated carbon filters. |
Carbon fines foul micro filters and membranes. |
Check washing procedure to remove fines from
GAC filters. |
| Overdosing of coagulant. |
Cationic coagulant fouls membrane – low
permeate flow, high feed Pressure. |
Check dosing levels and detect excess traces. |
| Overdosing of chlorine. |
Membrane damage – high salt passage and
increased flux. |
Dosing equipment, Redox meters, bisulfite dosing
levels and positioning of dosing point, chlorine test kit. |
| Permeate tube “O” ring failure. |
High salt passage. |
Check individual pressure vessel conductivity,
probe suspect PV’s to check individual membrane product
conductivity. |
| Ineffective biocide. |
High bacterial/fungal counts in water samples.
Biofouling of membranes – high Pressure difference. |
Biocide adsorption on GAC, check contact times
and dose rate, select broad-spectrum biocide, Select biocide
for organic content. |
| Sand/Multi-media filter breakthrough. |
Colloidal and bacterial fouling of micron filters
and membranes. |
Check wash procedures to remove fines. |
| Acid dosing. |
Scale formation – CaCO3 only. |
pH monitor/controller. |
| Seasonal algae blooms (sea water). |
High microbiological loading, biofilm, severe
cartridge filter fouling. |
Microbiological counts in water samples, evidence
of biofilms, check algae counts. |
| Poor performance on start up after shutdown. |
Fouling/scaling of membranes. |
Check membrane flush procedures on shut down
and preservation procedures on extended shutdown. |
