Dear researcher

You can refer to the most useful book in this field and have a look at chapters of  7 and 8.

Regards

What is the relation between river water treatment plant ( your project) and the MLVSS? As there is no biological treatment in river water treatment plant.Good luck  

we have river water treatment plant for upgrading the polluted river. the RWTP is act same like WWTP. the problem we face is the MLVSS is very low compare to low strength WW.

Dear Hairun,

The low strength river water is indeed a major challenge for biomass growth and retention. If the pollutants are readily biodegradable and soluble organics then some biofilm systems could work but not the classic MBBR. as well as floating water plant beds. If the targeted pollutants would be slowly biodegradable and/or  non-soluble organics and nitrogen compounds then an advanced activated sludge (AAS) would probably be the best option. On very diluted sewage we achieve up to 6 g/l MLVSS in AAS. Most existing activated sludge (AS) systems can be retrofit upgraded to AAS without extending the AS tanks/basins.

Dear Hairun,

Further to the reply from Bruno  Peeters, I would like to add my comments. Your need to know the analysis of the river water especially the BOD5, ammonia nitrogen and COD.In order to remove BOD5 from the river water, activated sludge process is normally used and if the flow rate of  river water to be treated is very high ,membrane bioreactor is not used as the capital cost will be higher than the conventional activated sludge process.

To treat this river water, you need to maintain the correct F/M (food to micro-organism ) ratio  between 0.15 and 0.2 and sludge age between 8 and 12 days to treat the river water for removal of BOD5 and ammonia nitrogen. If the BOD5 of the river water is low, MLVSS concentration between 4 gm litre and 6 gm/ litre is normally used. You need to remove sludge from the activated sludge process plant in order to maintain the MLVSS concentration to maintain between 4 and 6gm/ litre.In addition, you need to maintain the dissolved oxygen concentration between 1 and 2 mg/litre.

I think you mean the aeration tank!. 

One should not conceive MBR any different that the Activated Sludge (AS) process!..

The kinetics of the AS process defines  the active heterotrophic biomass, XH as:

XH = CS YNH SRT/HRT

You should add to XH the particulate microbial products, XP and the influent inert particulate COD.

How to add: look up Germirli et al. (2009) IWA Press

XVSS = 0.75 XT (XH + XP + X)  according to ASM3.

The about relationship shows that there is no typical value for XVSS; it varies as a function of SRT/HRT ratio selected.

For very low rate MBRs it may go up  to  50.000 mg/L ; or for very high rate MBRs it may go down to 1000 mg/L.

You should keep in minds that MBR has the potential to hold  more biomass as compared to conventional AS process.

Yes, I agree for low rate MBR ,the MLVSS concentration can go up to 50gr/ litre and it will remove BOD5 and ammonia nitrogen from the river water.

In this case very high rate MBR and MLVSS concentration of 1000mg/ litres are not applicable as it is necessary to remove virtually  up to 99.5% of BOD5 from the river water.

MBR is normally considered for the following conditions exit on site:

1.Not enough space / footprint is available on site to install the conventional activated sludge process plant and very compact plant is needed at the expense of higher capital cost and running cost.

2.The flow rate of river water to be treated is not very high. MBR is an ideal option if the flow rate of feedwater is very low and the the concentration of BOD5 in the feed water is very high.

3.Virtually complete removal BOD5 is required from the river water..

MBR would be a waste of CAPEX and OPEX especially for treating a complete river as in Hairun's case!

There are far more sustainable and cost-effective solutions as already indicated.

Yes , I agree to Bruno Peeters' comments.

Going to the original question, a traditional activated sludge plant would typically have between 2000 and 4000 mg/l MLVSS.  If it is tried to go higher than 4000 mg/l MLVSS, the sludge settling in the plant's clarifiers can begin to fail.  For an MBR, which has no settling tank limitations, MLVSS can run as high as 18,000 mg/l.  Hence the advantage of the MBR in terms of aeration tank volume required.  MBR effluent can also be much more suitable for reuse applications due to higher quality and reliability.

On the second issue that arose in the conversation above, treatment of river water and other wastewaters with low organic load, I would recommend that trickling filters should be included in the options to consider.  Low O&M and can be very effective.  Another option that can work with low levels of organics and with the appropriate soils is river bank infiltration.  The infiltration gallery can be constructed using imported granular materials if the existing materials are not suitable.

I answered earlier, comparing conventional activated sludge with an Membrane Bio-Reactor (MBR).  Reviewing the original question, the alternative was an MBBR - Moving Bed Bio-Reactor.  The answer to this question is quite different.  The MBBR is very different from a traditional A/S plant in that the micro-organisms responsible for the breakdown and consumption of the organic matter in the wastewater are attached to the surfaces of the moving bed, so there are essentially no MLVSS involved.  The MBBR organisms consume the organic matter and grow more organisms, and eventually die and become part of the Total Organic Carbon in the tank effluent.  So, the question really has no answer.

Yes, I agree with Floyd Mitchel. MBBR has no MLVSS .

Membrane Bioreactor (MBR) is a modified activated sludge process can be operated with wider range of MLVSS, ranging from 2500mg/l to 30,000mg/l. For treating river water with very high concentration of BOD5,( higher BOD loading), higher MLVSS concentration is required in order maintain  a lower F/ M ratio between 0.15 and 0.20.

Conventional activated sludge process normally operate with MLVSS concentration ranging from 1800 mg/l and 4500 mg/l. If you operate activated sludge process with MLVSS  higher than 4500 mg/l and with higher sludge age, sludge bulking is more likely and the quality of treated water will be poor.    

The value of average MLVSS in 7 different river water treatment plant are shown in the figure attached. the range is between 2-30 mg/L MLVSS.

This is a unique question and would tend to concur with Mr. Mitchell, however, very few people understand how to monitor the MLVSS of an MBBR system. You need to remove the biomass from the attached growth media to measure. The biomass controls its own concentration through sloughing. To measure, the media needs to be dried, cleaned and re-dried. Results are in gMLSS/m^2 of media.

A product we also use is called LuminUltra which measures active biomass by extracting ATP.

If you are measuring the liquid around the media it is the same as what is in the aeration effluent which could be going to a clarifier for settling and removal.