Filamentous Organisms & Bulking
Identifying the specific filament behind a bulking event, and matching the fix to the actual cause.
Type 1701 / Sphaerotilus natans (Low DO)
The classic low-DO filament; raising and holding DO above 2.0 mg/L typically resolves it within one to two sludge ages.
Nocardia & Microthrix parvicella (Low F/M)
Starvation filaments linked to thick, greasy foam; the fix is reducing SRT, not adjusting DO.
Thiothrix & Beggiatoa (Septicity / Sulfide)
Sulfur-oxidizing filaments pointing to septic influent or a collection-system problem upstream of the plant.
Wet Mount Microscope Exam
A basic 100x-400x filament check that narrows the diagnosis in minutes.
Type 021N
A filament associated with high sulfide, high F/M, and nutrient-deficient conditions.
Zoogloea (Slime Bulking)
Not a true filament — excessive gelatinous exopolymer production that causes a similar settling problem.
H. hydrossis
A low-DO filament similar in cause to Type 1701 but often present with a different filament morphology.
Filament Index Scoring
A standardized 0-5 scale for rating filament abundance during a microscope exam, enabling trend tracking over time.
Chlorination for Filament Control
Low-dose RAS chlorination selectively targets filaments extending outside the floc, without killing the whole biomass.
Selector Basin Strategy
A small, high-F/M zone ahead of the main aeration basin that suppresses filament growth by favoring fast-growing floc formers.
The industry's most useful newsletter, straight from the plant floor.
One email. No fluff. New lessons, equipment breakdowns, and process control notes, delivered when there's something worth reading.