Rotifers as Bioindicators of Advanced Biological Purification in Activated Sludge SystemsBy Dr. Hossein Ataei FarIn wastewater treatment, micros...
Published on by Hossein Ataei Far, Ambassador for Sustainability | Water & Energy PPP Finance Facilitator
By Dr. Hossein Ataei Far
In wastewater treatment, microscopic observation often reveals the true health of activated sludge systems. Among metazoans, rotifers stand out as reliable signs of biological stability and advanced purification.
These tiny multicellular organisms thrive only under optimal conditions¹²:
High oxygenation (DO > 2 mg/L)
Low organic loading & readily biodegradable substrates
Long sludge retention times (SRT > 10–15 days)
Low food-to-microorganism (F/M) ratios
Their presence indicates:
High BOD/COD removal efficiency
Excellent effluent clarity and sludge settleability
A mature microbial community shifted toward maintenance metabolism
Small, mobile genera like Cephalodella spp. are especially telling — they require stable floc structure and minimal disturbance, appearing only in well-structured, equilibrium systems³.
Key reminders:
Rotifers are consequences of good process control (adequate aeration, balanced nutrients, no toxicity), not drivers of performance⁴. They don't independently confirm nitrification, denitrification, or regulatory compliance — always pair microscopy with operational data⁵.
When rotifers coexist with crawling/attached ciliates and compact flocs, it signals a harmonious biocenosis in these challenging engineered ecosystems.
Rotifers silently highlight well-managed plants operating near optimal balance.
What bioindicators do you observe most in your activated sludge? Share your microscope stories!
#WastewaterTreatment #ActivatedSludge #Bioindicators #Rotifers #WaterQuality #EnvironmentalEngineeringReferences
References:
[1] Curds & Cockburn (1970); Madoni (2011)
[2] Jenkins et al. (2004); Metcalf & Eddy (2014)
[3] Salvado et al. (1995)
[4] Curds (1982)
[5] Madoni (1994)
The contained video and content were taken by José Antonio Tomás Miranda, WWTP Technical Manager and Site Manager.
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