I'm investigating the relation between sedimentation and mixing levels in anaerobic digesters. I would like to use real sludge in my experiments, but this is a big issue for me to collect everyday or even weekly and store at 5°C. Another problem is that sludge varies in its content from day to day, sometimes even hourly. Considering that it's complicate to have a standardized experiment.
What are the implications for freezing sludge at -20°C for daily feeding? Shall I use synthetic sludge instead?
Dear Jose,
Please read the following text:
Disadvantages of the use of freeze-dried, heat-treated (FDH) activated sludge (AS):
A United States Environmental Protection Agency (USEPA) standard method (OPPTS 835.1110) for estimating soluble pollutant removal during wastewater treatment using freeze-dried, heat-treated (FDH) activated sludge (AS) has been recently proposed for predicting ENM fate in WWTPs. While soluble pollutants sorbed equally to fresh and FDH AS, fullerene, silver, gold, and polystyrene nanoparticles’ removals with FDH AS were approximately 60–100% less than their removals with fresh AS. Unlike fresh AS, FDH AS had a high concentration of proteins and other soluble organics in the liquid phase, an indication of bacterial membrane disintegration due to freeze-drying and heat exposure. This cellular matter stabilized ENMs such that they were poorly removed by FDH AS. Therefore, FDH AS is not a suitable sorbent for estimating nanoparticle removal in WWTPs, whereas fresh AS has been shown to reasonably predict full-scale performance for titanium removal.
http://pubs.acs.org/doi/abs/10.1021/es300339x
Disadvantages of the use of fresh sludge
For carrying: out sludge lab-scale tests, and interlaboratory trials for standards validation, the availability of samples with "certified and constant" characteristics is required. When "dried sludge" samples cannot be used, problems arise because (i) most fresh sludge characteristics change with storage time, also because some preservation practices are not applicable or their effects unknown, (ii) some fresh sludge characteristics are strongly affected by handling, and (iii) fresh sludge requires particular precautions and authorization for transportation. This means that using "fresh sludge" samples cannot guarantee reliability and reproducibility of results, so a valid alternative consists in testing "synthetic suspensions" samples to be on-site prepared. This should also give the possibility to compare results obtained in different places and times.
http://www.ncbi.nlm.nih.gov/pubmed/18025733
Synthetic Sludge:
The creation of a synthetic sludge was necessary because of the constant
changing of the characteristics of the activated sludge. As it is known, an activated
sludge is a complex mixture of various constituents and shows a wide variation in its physical, chemical and biological proprieties. The biggest problem in the study of this sludge is, undoubtly, the biological content. The living microorganisms are always changing proprieties, making it inapplicable to carry out the controlled experiments. To overcome this problem a synthetic sludge was created to surrogate the real one. This synthetic sludge was constituted by polystyrene particles with the size of bacteria to simulate the individual bacteria, alginate to simulate extracellular
material and calcium ions to bridging cations.
https://repositorio-aberto.up.pt/bitstream/10216/59017/1/000136253.pdf
Based on the the text mentioned above it is preferable to use synthetic sludge to avoid the drawbacks associated with the use of freeze-dried, heat-treated (FDH) and fresh activated sludge.
Hoping this will be helpful,
Rafik
There is a nice paper that you can read. The title is:
A Comparison of Physical Properties of Synthetic Sludge with Activated Sludge.
Which appeared in Water Environment Research 71(2):191-196 · March 1999.
This paper says that performing experiments with real sludge is difficult as it constantly changes properties. However, this challenge can be address by using a synthetic sludge that physically and chemically resembles the real sludge.
In this paper, the authors examined the physical properties of synthetic sludge and compared then to those of real sludge.
Interesting paper for your read.
Hope this helps answer your question.
Professor Yehia Khalil
Yale University
USA
Dear Jose Carlos
even though the actual sludge varied at different time and days it is better used the actual data and takes reading your average reading data. due to synthetic sludge would not reflected the actual sludge composition of sludge.
there is a basic problem of using freeze-dried sludge for studying sedimentation behaviour, because sludge properties are drastically changed by freezing and by drying.
Best approach seems to me to have a larger deposit of sludge in fridge without freezing. Measure characteristic properties before and during experiments after thorough homogenization of sludge. Try to finish experiments as soon as possible.
Thank you all for your advises, I am considering them all! One last question, does anyone know any method for measuring settling characteristics of sludge? I could only find methods for primary tank characterization and activated sludges, not concentrated sludge, i.e. the output from primary tanks. which I understand depends majority on the TSS concentration, but yet no method found..
Thank you in advance!
Best wishes, Jose
For concentrated sludge one could use diluted sludge volume index or centrifuge test.
To determine kinetics and extent of dewaterability you may use LUMiFuge testing.
- Badges
- Science topic
- Similar topics
- Engineering
- Modeling