|
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. |
