Is it possible to use the SVI as a performance indicator of Activated Sludge Process in WWTP?
The evolution of SVI as indicator of pollution reduction, Nitrogen removal efficiency, Phosphorus removal efficiency, and TSS, COD and BOD5 removal efficiency (in AS process)?
There is a recent RG discussion, see link below and some other links:
https://www.researchgate.net/post/Whats_the_best_range_of_SVI_Sludge_Volume_Index_for_best_performances_of_Activated_sludge_in_Wastewater_treatment_plant
http://www.maine.gov/dep/water/wwtreatment/activated_sludge_process_control.pdf
http://dnr.wi.gov/regulations/opcert/documents/WWSGActSludgeINTRO.pdf
https://www.diva-portal.org/smash/get/diva2:694836/FULLTEXT01.pdf
http://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1058&context=cee_ewre
https://www.michigan.gov/documents/deq/wrd-ot-activated-sludge-manual_460007_7.pdf
http://nepis.epa.gov/Exe/ZyNET.exe/9100PNIQ.TXT?ZyActionD=ZyDocument&Client=EPA&Index=Prior+to+1976&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C70thru75%5CTxt%5C00000014%5C9100PNIQ.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL#
Dear Messaoud.
The SVI test indicates how well the activated sludge solids will settle and compact in the final clarifiers. It does not provide information on the removal of N & P, BOD or Suspended Solids.
However, as reported by the earlier excellent answer provided by Randa M Osman, some information can be indirectly inferred.
• Cloudiness with little or no settling could be due dispersed flocs caused by very low MLSS solids, under-aeration or toxicity. Both BOD and SS will be high.
• An SVI value < 80 g/ml may not capture all the small particulate floc solids resulting in a effluent with a degree of turbidity. It may also indicate a pin-point floc due to over-aeration.
• An SVI value of 100 to 150 g/L indicates good settleability with a clear effluent expected.
• A high SVI result is due to sludge bulking with a risk loss of sludge blanket control in the clarifiers and possibly solids washout.
• If the compacted solids rise to the top of the test cylinder one or two hours after initially settling, there is a de-nitrification issue.
SVI mainly serves as a very important empirical measurement used to maintain sufficient concentration of activated sludge in the aeration basin whereby too much or too little can be considered detrimental to the system’s overall health.
Typically a healthy sludge aeration pond basin should have the value registered within 80 to 150 mL/g and the MLSS concentration between 3000 – 5000ppm
Obviously SVI out of proper range shows that AS is not working well and you need some modifications for operation. However, its value can not be compared as an indicator for analyzing treatment efficiency. For example, SVI equals to 150 may have 30% BOD removal or SVI equals 350 may come with 95% removal. In a word it is only an indicator of settleability of sludge. As an example, You can imagine to add acids to reduce pH below 5. Here, SVI is good but it does not work biologically at all.
Sludge volume index is used as an indication of the settling characteristics of the sludge. It tells something about the flocculation and settling characteristics of activated sludge. The SVI is reciprocal of sludge concentration in the sludge phase after 0.5 hr settling in a cylinder glass. The lower the sludge volume index the better flocculation and settling characteristics. SVI values of 100ml/g are usually consider to be satisfactory to ensure good functioning of activated sludge plants.In this way it will be possible to maintain a satisfactory return sludge concentration and have a well functioning settling.
SVI and Wastewater Treatment Plant functioning operationally thus has direct relationship.
Thus broadly it can be stated that the Wastewater Treatment plant shall function properly if SVI values are found suitable
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