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On-line optical monitoring ofactivated sludge floc morphology
17.9.2015Elisa Koivuranta
Fibre and particle engineeringUniversity of Oulu
FIBRE AND PARTICLE ENGINEERINGRESEARCH GROUP
Professor: Mirja IllikainenFiDiPro-professor: Kristiina OksmanStaff: 30
Background
• Activated sludge process is the most commonmethod in municipal and industrial wastewatertreatment
• The efficiency of the ASP is highly dependent onthe solid-liquid separation which is affected by thestructure and the strength of the flocs
• Evaluation and modeling of the wastewatertreatment process by image analysis methods willbring new horizons in the monitoring and controlapproaches
Background: Activated sludge process
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• Municipal and industrialwastewater contain usually highamounts of COD, nitrogen andphosphorous, which can beremoved by biologicalprocesses
• Biological flocs are formed inaeration tanks and removed bysettling in settling tank
Background: Floc formation
• The floc formation is complex phenomenon whichmechanisms are still poorly understood
• Flocs are made up of a variety of microorganismsas well as organic and inorganic particles
• Different disturbances in the process has effectson the floc structure
• Unsatisfactory floc formation is a common problemin activated sludge plant worldwide which haveboth environmental and economic consequences
Background: Floc morphology indifferent situations
Lots of filaments Small flocs Big flocs, enoughfilaments
Background
• Floc formation and settling properties of activated sludge are criticalfor the purification process
• There is still lack of a proper on-line measurement of flocculation
• Optical monitoring of flocs wouldenable better control of the wholeactivated sludge process
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Floc imaging device - MOFI
• From laboratory scale toin situ scale
• Basic principle is thesame in both:”Only needed pre-treatment is dilution”
• Image size is 5.01mm x3.74mm and imaged pixelsize is 3.6µm
Image analysis
(1) the original image; (2) background removal; (3) adjustment of image intensityvalues to increase contrast; (4) creating negative image; (5) median filtering; (6)thresholds to create binary images; (7) filling holes; (8) dilation; (9) filamentimage; (10) floc image; (11) processed floc image; and (12) processed filamentimage.
Image analysis
Blue: Accpeted flocs Red: Small particleGreen: Too light Purple: Air bubble
Image analysis
Blue: Flocs Red: Filaments
Image analysis
Analyzing:- Form factor- Roundness- Equivalent diameter- Aspect ratio- Total filament
length/total floc area- Mean area of
particles- Amount of small
particles (<25 µm)
Preliminary tests
• Two different situation were compared• Bigger flocs, less filaments better settling properties
Preliminary tests
Evaluation of the flocmorphology in the industrialwastewater treatment plant
On-line optical monitoringAt Viikinmäki
• Sludge is taken from theprocess line into deairingcontainer
• From the container thesample is diluted andpumped through cuvetteof imaging unit
• The sample dilution,pumping, image grabbingand cuvette flushing iscontrolled by PC softwareand control electronics
On-line optical monitoring
- 1000 images/film (4 films/day)- 100 individual flocs/image
400 000 individual flocs are analyzed daily
On-line optical monitoring
18On-line optical monitoring
• Imaging unit consists of flow throughcuvette, standard machine visioncamera and LED lighting
• The imaging unit captures flocimages 30 frames/second
• Image size is 5.01mm x 3.74mmand imaged pixel size is 3.6µm
• Floc images are analyzed andseveral morphological featurescalculated in floc analysis
Results
Possibilities and challenges
• Would enable better control of theactivated sludge process
• Early warning system
• Challenges:– Outdoor conditions– Representative sampling
