Dear Mehran,

Attached please find some publications that cover the answer to your question:

1-THE SPECIFIC OXYGEN UPTAKE RATE (SOUR) (See attached file named Protocol 2)

Professor Ed Stentiford

School of Civil Engineering, University of Leeds, UK

Abstract - The SOUR method for determining compost stability is described.

Results for its use with a wide range of waste are discussed and specific

comparisons are made with solid matrix respiration tests (DSOUR), self-heating,

germination index and Solvita. SOUR is shown to be a robust indicator of progress

in the rapid biooxidative stage of composting. In addition it is both low costs and

has demonstrated its effectiveness as a tool for process control and monitoring.

Key words: composting, respiration, stability, organic waste

2-Sour Test Vector Attraction Reduction Option 4 (See attached file; Protocol 3)

Conducting a SOUR Test

 Equipment required

 500 mL Container

300 mL BOD bottle

Dissolved Oxygen Meter (calibrated)

Magnetic stirrer and stir bar

Stopwatch

Thermometer

Equipment to measure total solids (if conducted on-site)

 Calibration

Calibrate the oxygen probe and meter according to Standard Methods (SM 4500-O.G.).

 Total Solids

Determine the total solids of the sludge. The sludge must be less than or equal to two percent (2%) total solids.  If the solids are greater than 2% but less than 4%, dilute the sample to 2% solids in the BOD bottle using decant from the digester or deionized water.

 Preparation of Sample

 Collect several grab samples of digested sludge in the digester using a liquid core sampler.  Composite grab samples in a large container or bucket.  Aerate the sample using a pump and weighted air diffuser for at least 3 hours.  Aerating the sample will remove any volatile acids that have been trapped and accumulated in the solids.  Pour the aerated sample into a 500 mL sample bottle.  Fill the bottle only to the 75% level, leaving an air gap between the sludge and the top of the bottle.

 Increase the dissolved oxygen concentration of the sample by shaking the bottle vigorously for approximately 30 seconds.  It is recommended to have an initial dissolved oxygen reading (after shaking) greater than 4 mg/L.

 Measure Oxygen Consumption Rate

 Take a magnetic stir bar and place it in a clean 300 mL BOD bottle. Take the 500 mL bottle into which you placed your composite sample, and pour the sample into the 300 mL BOD bottle. Make sure to fill the BOD bottle completely to the top. Immediately insert the D.O. probe into the BOD bottle, making sure that the probe tightly seals the sludge from the atmosphere.  Activate the magnetic stirrer.

Note: adequate mixing is essential.

 Record Dissolved Oxygen Readings

 Once the probe is placed into the bottle, wait 30 seconds and begin recording the dissolved oxygen (D.O.) readings.  Record levels at 30-second time intervals.  Record data over a 15-minute period or until the D.O. becomes limiting, whichever occurs first.  Record the final temperature.

3-Environment Protection Engineering  (See attached file; Protocol 4)

Vol. 38 2012 No. 2

DOI: 10.5277/epe120204

MAGDALENA ZIELIŃSKA*, KATARZYNA BERNAT*,

AGNIESZKA CYDZIK-KWIATKOWSKA*, IRENA WOJNOWSKA-BARYŁA*

RESPIROMETRIC ACTIVITY OF ACTIVATED SLUDGE

IN SEQUENCING BATCH REACTOR DEPENDING ON

SUBSTRATE AND DISSOLVED OXYGEN CONCENTRATION

The effect of the food/microorganisms (F/M) ratio and dissolved oxygen (DO) concentration in sequencing batch reactors (SBRs) on the microbial activity has been examined. One of the SBRs was fed with synthetic wastewater containing inorganic carbon compounds (COD/N ratio 0.7 g COD/g N). To the other SBR, both inorganic and organic carbon was supplied leading to 6.9 g COD/g N. The F/M ratios in the reactors were 0.02 and 0.065 g COD/g cell COD, respectively.

Under the above feeding conditions, two experimental series were carried out at DO concentration of 0.5 and 1.5 mg O2/dm3 . The activity of the biomass was determined through respirometric tests based on the determination of oxygen uptake rate (OUR). Independently on operational parameters, nitrification

was the process consuming the highest amount of oxygen. Both at the F/M ratio of 0.02 and 0.065 g COD/g cell COD, higher DO concentration resulted in increased carbonaceous and endogenous respiration.

Hoping this will be helpful,

Rafik

Using of respirometer may be a good option. It can measure oxygen uptake with respect time. You can plot that using the software attached used with the instrument. From the graph you can determine rate and if you divide by substrate concentration you can get specific rate.

Dear Prasenjit, you are right, but your proposition is for assessing of microbial activity of suspended solids. What should we do when we are going to assess microbial activity of biofilm using respirometer? 

Maybe an "in situ" experiment can help.

I suggest you take a look to this paper:

A.Ordaz,et al.,Determination of apparent kinetic and stoichiometric parameters in a nitrifying fixed-bed reactor by in situ pulse respirometry,Biochem.Eng.J (2011),doi:10.1016/j.bej.2011.03.015

If you are not interested in kinetic parameters, you can just make an interpretation of the oxygen dynamics obtained by respirometry to get the oxygen uptake rate, then you will have to know an idea of the biomass concentration in the reactor to make it specific OUR.

Regards

If you are doing this on lab scale I would test in situ following a procedure along the lines described below.  Even better, apply the in situ methodologies suggested by others responding to your question.  I'm assuming you are working pilot scale or larger and that in situ measurements are not practical at present.

Assuming you are not using sheet media for the attached growth, my approach would be simple (hopefully not over-simplified).  Rather than the typical "small bottle" approach I would use a larger container, say 2 liters, in order to get a reasonably representative sample of both suspended and attached growth.  Then apply the normal OUR procedure (aerate and record oxygen depletion with time, with as little delay between sample collection and testing as possible).  Determine the effective solids concentration by a tedious procedure: count all the carriers in your sample, remove the solids from a sample of those carriers (by washing using a known volume of water and scraping), measure and calculate the mass of solids per carrier, calculate the mass of solids on all carriers, measure the remaining volume of the original sample with all carriers removed, measure and calculate the mass of suspended solids in the remaining volume and calculate the total mass of solids per original volume of sample.  Then, finally, you can calculation SOUR.

You could use a similar procedure with sheet media.  However, you would need to construct a smaller fixed film carrier unit that would have a specific surface area comparable to your full-scale system but that would fit in your OUR test chamber.

Dear Mehran,

We have some experiences in respirometry using activated sludge but also biofilm carriers (MBBR processes). I think this paper of a colleague of mine could help to answer your question. 

http://www.sciencedirect.com/science/article/pii/S1369703X06003408

If you relate your OUR profile to any measurement (e.g. TS or COD) that gives you a clue about the content of your biomass it will result in SOUR.

I just recently used among others SOUR to assess MBBR properties in the frame of my PhD thesis. The protocol followed in general respirometer techniques based on activated sludge published among others by professor Peter Vanrollgehem (Laval University, CA). I used the heterotrophic maximum OUR (resulting from 1 spike of ATU to inhibit nitrifiers and 1 spike of acetate as heterotrophic substrate) and related the max OUR to the total COD content (biomass concentration in 1L reactor volume). The tricky part was the determination of the biofilm content. We used ultrasonication of a sample of 20 AnoxKaldnes K1 carriers in a 0.14 M NaCl solution. There are also other approaches but we tried to apply a sound method since we further used the extracted biofilm for enzyme fingerprinting.  Since biofilm carriers are not so easy to mix in a lab-scale reactors your repirometer should have an appropriate size. Our vessels had a volume of 4L.

I hope I could help you a bit. Don't hesitate to contact me in case you need further details.

Regards,

Christian