Relationship between SV30, SVI, & MLVSS

8/12/2015

SV30 Test

We often do common wastewater tests daily and rarely think about how they are all related. In the next few posts, I am going to cover how biological unit tests are all data points that help operators get a picture of the unit's "biological health". While under good operating conditions, you do not need to run all the tests or do them on a daily basis; under changing conditions frequent tests help operators head-off problems before effluent quality is compromised.

Today, I am going to relate how settling rates and solids mass tests are related.

SV30
The SV30 is a settling rate test. When mixed liquor is poured into a graduated settling vessel (large graduated cylinder or single purposed SV30 container); it is allowed to settle, undisturbed, for 30 minutes. Some operators record the solids volumes at 5 minute intervals to give a settling rate plot. What we are trying to determine is how well the system is flocculating and what to expect from secondary clarification. In addition to the biomass volume, operators should also note supernatant turbidity and if fines or small floc are floating.

MLVSS or MLSS
Biological solids are measured in a lab procedure to determine the weight of solids. The difference is the MLSS is total solids weight and MLVSS is the volatile fraction of the total solids (usually just biological solids - but can also include fibers and other organic influent solids).

SVI
After getting both the SV30 and the MLVSS numbers, we can calculate the SVI. The purpose of the SVI is to get a standardized number for settling rates. For example a system with an MLVSS of 2,000 should have a lower SV30 than the same system run with a MLVSS of 4,000. To relate settling performance when running different MLVSS numbers, we divide the SV30 number by the MLVSS number (in grams rather than milligrams).

In most system we look for an SVI between <120 ml/g and consider the system bulking with SVI >150 ml/g. If settling happens too quickly as seen with longer sludge ages, you may have pin floc or high turbidity in the supernatant. This is why I like operators to note turbidity and pin floc in the SV30 test.

What do I need to run on a daily basis?
In systems with very uniform operations (little influent variation in flow or makeup), a daily SV30 test with weekly MLVSS checks may be enough for operations. Certain industrial system may require daily MLVSS and 2x daily SV30 tests as influent can change quickly and settling is often the first thing impacted during a spill or upset event. Base your frequency based on the variation that you have seen in the past and since the SV30 is a low cost, simple test - run it on a frequent basis.

Dennis Buccella

6/28/2016 08:18:49 am

We use the MLSS number and the SV30 number to get our SVI number. Are we using the wrong number to get theSVI.

Erik Rumbaugh

6/28/2016 12:17:36 pm

While the "textbook" SVI number is based on using the MLVSS number, many facilities manage their biomass using SVI calculated from the MLSS number. Not everyone has a furnace for MLVSS testing. Key is run the test often and be consistent.

Your SVI number will just be a little lower than if you divided by MLVSS. MLSS is always greater than MLVSS by rule.

6/28/2016 01:06:23 pm

Thank you for your time.

Dennis Buccvella

8/29/2016 08:34:08 am

Last 2 weeks my mlss test floc look like a dirt like instead of the normal. Trying to determan the cause.
dennis

8/29/2016 09:19:40 am

Few questions:

1. Did the color of the MLSS change - for example from brown to gray.
2. Has the sludge age or influent loading (BOD) changed?

8/29/2016 11:44:05 am

The MLSS went from a brown to black but this is may not be bad because we have differnt colars of dies that come into our plant.Sludge age is in the middle with mostly stalked ciliates and rotifer. No waterbears or bristle worms. I have no info on BOD loading.

8/30/2016 09:00:11 am

You have the ideal indicator protozoa for activated sludge. Does the floc settle more rapidly than before? If so, I think we are moving more toward an older sludge or lower F/M ratio. It could also have been a response to influent makeup changes.... however with good indicator protozoa activity it is not a toxic shock.

8/31/2016 01:02:58 pm

Floc settles down to 150 in 5 min. then to 130 after 30 min. This seems to be the norm for the last mount or so. So if it is the low F/M would we waste more? We doe nothave a way to test for BOD5 to see what the influent is but we had a outside test run on the influent and had a BOD5 of 240. We have average flow of about 800,000 gpd.

9/2/2016 06:58:05 am

Based on such rapid settling, should think that you have low F/M. Often we see "fines" or turbidity above the fast settling sludge in the SV30 test. If so, I would increase wasting by 10% and see if it slows the settling rate and makes the floc increase in size (more beneficial EPS = bigger floc).

Izreen

9/5/2016 10:37:16 pm

Is the TSS (total suspended solid) and MLSS (mixed liquor suspended solid) is the same parameter?

9/6/2016 04:34:57 am

TSS typically refers to influent or effluent total suspended solids. While, MLSS is the suspended solids in the biological treatment unit. They are both measured in the same way and are the same thing - filtered solids dried at 103 Deg C for one hour.

9/6/2016 05:35:17 pm

Thanks for the reply, (in my best understanding) from theory the aeration time (air blower timing) is linear to the COD consumption, is this applicable in the real situation?

Don

10/22/2018 02:06:24 pm

Referring to the TSS/MLSS comment above. What formula do I use to measure SVI using Sludge Volume(ml/l) x 1000 / ????? if want to use TSS data.

9/7/2016 07:03:25 am

Biological respiration rates are inversely related to soluble organics - in most wastewater without toxicity. Aeration time or aerobic basin residence time - depends upon COD loading and the rates at which COD components are biologically degraded.

The ideal is to keep biomass in "decline" phase growth where cellular reproduction is minimized and F/M is at target levels. At this point you have the best operational characteristics and use of oxygen.

Yasir

6/3/2017 09:05:49 pm

Dear sir,
In Aeration sv30 is high but MLSS are under control how we can reduce SV30 & also sludge is not settled good.

Erik Rumbuagh

6/4/2017 09:48:09 am

The first step is to look at the MLSS under a microscope. Do you have filamentous microbes creating settling problems? If filaments are not abundant (this is subjective), then look into using India Ink to see if you have non-filamentous bulking. You can also see non-filamentous bulking as round shaped floc under a microscope with smooth, fingers. In seetling tests, it does not compact like "good" floc. Once we know the cause of the settling problems, we can start to control actions.

Farhad

6/4/2017 06:42:08 pm

If SSV increse then SVI also increase (what was the relation in both?)
MLSS is still under Controll value but SVI higher than the limit why it's like and what was the immediate solutions to control SVI value? How?

Erik R Rumbaugh

6/5/2017 05:22:33 am

SSV is the volume occupied by MLSS after settling for 30 minutes it can be ml/L or a % depending on how you calculate. The SVI is SSV (ml/L form) divided by the MLSS or MLVSS in g/L. Any SVI above 150 is considered bulking. Normally we want it to be between 100 - 120 which is the settling of a near ideal sludge age or F/M ratio in most wastewater systems.

Immediate control of bulking can be effected by adding coagulants such as aluminum chloride, ferric chloride or organic coagulants - often a secondary high molecular weight organic polymer is added to increase coagulant effectiveness.

10/8/2017 04:53:40 am

Our system is SBR, so the adding external chemicals to control SVI or bulking issues not possible,
We required a solution by process to reduce bulking and decrease SVI

10/8/2017 10:21:55 am

I have worked with controlling bulking in SBR systems. First, what is causing the high SVI? Microscopic exam can see if you have filamentous or non-filamentous (often called zoogleal) bulking. Are loadings or flows beyond design? Sometimes we can alter cycles to encourage better settling and there are other corrections that can help. Just give me a response @ [email protected] and I can help you work through this problem.

Rajayogan

10/15/2017 05:26:51 am

Hi Sir,
We are building up the MLSS in aeration tank(2000 m3 capacity) for a new plant, We were seeding from an existing plant and filled the tank gradually for 15 days and then gradually filled clarifier and now continuous sludge recirculation is done. We were continuously running the blower for 15 days(at low speed) but still the DO is above 6 and we are getting only 300 m3 of sewage to and while testing MLSS in aeration tank it is around 3000 mg/l and SVI is around 100. The supernent is very turbid while doing SV30 but supernent from clarifier is somewhat clear (40 NTU), how to solve this issue, we requested for more sewage (600 m3+ per day) and hopefully which will reduce the DO, but is there anyhting else we can do? your help is highly appreciated.

10/15/2017 05:29:54 am

Corrected
Hi Sir,
We are building up the MLSS in aeration tank(2000 m3 capacity) for a new plant, We were seeding from an existing plant and filled the tank gradually for 15 days. Then gradually filled clarifier and now continuous sludge recirculation is done. We were continuously running the blower for 15 days at low speed while startup and now e DO in aeration tank is above 6 . we are getting only 300 m3 of sewage per day as feed.
while testing MLSS in aeration tank it was around 3000 mg/l and SV30 is 100. The supernent is very turbid while doing SV30 but supernent from clarifier is somewhat clear (40 NTU), how to solve this issue, we requested for more sewage (600 m3+ per day) and hopefully which will reduce the DO, but is there anything else we can do? your help is highly appreciated.

10/15/2017 07:20:04 am

As you already know, the 300 m3 flow is not giving you enough "food" to keep the F/M in target range. So you have two options:

1. Waste to lower the MLSS - this will not reduce the D.O. but will increase the % active bacteria for when flows increase. MLSS will have to build read time - and you may have to use polymer to the secondary clarifiers.

2. In the past we often supplemented BOD with methanol. Now, I use almost any available highly degradable substance such as molasses. Another option is take in a highly degradable BOD/COD waste that is being held by a local industrial facility.

It all depends on the location of the facility to nearby sources of sludge or wastes. And, don't discount the ability to to a "hot start" if the MLSS is 1,000 mg/L.

PR Sudhakar

10/27/2017 08:43:04 pm

Where to take sample for measuring MLSS in the waste water treatment . I have a sample containing 800 g suspended solid settled in 30 min in a 1 lt jar . How to extrapolite the same into MLSS.

10/28/2017 07:51:03 am

If you have a normal activated sludge system, the normal place to grab MLSS samples is the effluent of the aeration basin or before the wastewater goes to the secondary clarifiers.

Trying to extrapolate SV30 to MLSS is not a normal practice. SV30 measures settling rates and sludge volume. Whereas MLSS/MLVSS actually measure the mass by removing water and via the furnace removing inorganics from the MLVSS. While SV30 & MLSS have a strong correlation, for running a system you the relationship varies with filaments, viscous bulking, or floc density changes.

siti

2/20/2018 07:58:03 pm

Dear Sir,

WWTP-BP, we are growth activated slugde in biology treatment tank. now our MLVSS (3000-5000) is 90% MLSS, SV30 around 20%-50%. after calculated my SVI around 5-6 mg/L.

question:
1) Why MLVSS over than 80% and what fenomena will be occur?
2) Why SVI lover than 50mg/L and impact of my bio treatment tank.

Thank you.

2/21/2018 06:06:09 am

Don't worry about the numbers above if the secondary clarifier is producing good low TSS, low turbidity effluent. Recycle (RAS) concentration is at target. And, if basing MLSS/MLVSS is within range. Remember the MLSS to MLVSS ratio changes with different influents, sludge ages, and many other variables.

Again, look under the microscope for indicator protozoa and metazoa. If sludge is "old" waste - move in 10% increase/decrease in wasting steps.

My number one suggestion is to not just rely on calculations and make too many changes to quickly in operating a system. Look at oxygen uptake rates, microscopic, ATP, settling rates, and all other factors to make wasting rate decisions.

R Kumar

6/4/2018 06:41:43 pm

What is a good ATP level in an aeration basin. Can that be used as an standard tool to identify the MB activity in the aeration basin?

6/4/2018 06:49:48 pm

ATP is one of the tests for microbial activity in wastewater treatment. To be most useful, you need to run Cellular (bound in cells) vs Free (in solution) ATP. As with tests like DOUR, microscopic exam - ATP requires you to find levels and ratios specific to your system.

You should run ATP along with other tests. Some systems that I work with find ATP a great predictor, other industrial systems have found ATP to be of little value. Try it and see if you can draw correlations with effluent quality.

Manobalan

3/15/2018 06:02:53 am

How to maintain SV30 with in 250 to 450 mg/lit? this is very challenging for me to maintain in my 2800 m3/day STP plant.please give me a solution to maintain it with in 250 to 450 mg/lit.It was rapidly increasing to 700 to 800 mg/lit with in 2 days even though we are waste the sludge in three shift for 10 mins basis.

vikul kumar link

9/1/2018 09:15:07 pm

mlss& sv30 is depndeed by mbr plant

Nels Weaver

10/26/2018 08:53:04 am

MLSS includes volatile organic & inert suspended solids, not of the crucible weight, measured in gram weight(s). When we subtract volatile grams from MLSS grams x 1,000,000, divided by the sample gram weight we report that as the volatile portion but is actually the inorganic measurement?

Sonpal Sharma

11/20/2018 06:25:34 am

If our MLSS is 3500 in aeration , its means our CETP's health is good. It will reduce COD/BOD in a proper way. Please give suggestion regarding the relationship of MLSS, COD,BOD.

11/20/2018 06:49:02 am

You relate MLSS or MLVSS to BOD/COD removal using the F/M or Food/Mass calculation. Food is the loading in kg. Mass is your system biological solids in kg. This number is used to adjust wasting rates and keep the system in proper decline phase growth where BOD/COD & TSS removal is maximized.

Phil Tetley link

1/10/2019 08:33:16 am

I have a SVI that has increased from an average of 80 up to 120 and then over last two years increased up to 150 and causing issues with carry over of floc with TSS regularly exceeding 30 thus taking plant out of consent. My DO in aeration tank is around 5 and I use a DAF to lift the floc. I'm struggling to bring down the SVI. MLSS is currently 6000 and planning to waste sludge. welcome any thoughts

1/11/2019 12:11:56 pm

I would look to what MLSS the DAF was designed to handle. 6,000 seems high for most suspended growth systems unless you are operating a membrane (MBR) system. Here is what I recommend --> (1) look for filaments, (2) use India ink to see if you have non-filamentous bulking, and (3) get MLSS to target range for the system's design by wasting.

di2c

2/15/2019 04:26:08 am

what causes low sv30 (150) but MLSS in the normal range 4000 to 5000. Thank.

2/17/2019 07:27:13 am

With a low SV30 (150) and MLSS in target range of 4,000 - 5,000 mg/L, I would think that you are operating at a very low F/M or high MCRT. Even then, the SVI would be 30 - 37. Is the supernatant turbid or have "fines" floating? Does it settle extremely fast? If so, then you may want to waste. Also unusual SV30 can be a part of influent, polymer use, or other factors.

Keith Watson link

10/14/2019 04:38:25 am

Appreciate your advice. For the WWTP of a 'Further Meat processing plant' ( not slaughterhouse), would the use of a quat based sanitiser (with a solution of 200ppm of available quat ) for disinfection of food contact surfaces, affect the MLSS and SV30 ? We have been using for 3 weeks with no adverse affect . Also, we have consistent 'OK' Chloride.

10/14/2019 04:42:03 am

Usually there are steps taken to neutralize the quat. So, it would not impact your MLSS/SV30. However, if too much quat is used or not neutralized sufficiently - you can see a loss of slower growing organisms such as nitrifiers (AOB/NOB) before you would see a change in MLSS/SV30

Sandeep Pandharkar

1/18/2020 08:37:25 pm

In an activated sludge TP,
FM. = 0.04
mLSS = 7500
SV 30 = 990

How to reduce SV ?

1/21/2020 06:43:23 am

SV is appropriate for teh MLSS that you are running. To standardize the data you calculate SVI = 990/7.5 = 141. This is on the edge of bulking but not out of line with what I see in practice.

However, unless you are designed to operate as such high solids (clarifier limitations), you should waste to reduce the MLSS. If you do this, the SV30 should decrease.

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Relationship between SV30, SVI, & MLVSS

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