Data+to+measure

This is the beginning of a document to guide sharing of information about Anaerobic Digesters.
 * Terms for Anaerobic Digesters**

The discussion can be found in the REPP Archives at [] starting in late December 2009 in the thread "Biogas from urban waste", later changing to "Biogas terms and tests" in January 2010

On December 31, 2009, Alexander Eaton posted a message in response to some eariler discussion in which he said:- "is anyone aware at an attempt at defining terms surrounding biodigester use? I see this at invaluable, especially in forums such as this when those of us who are working in the field (often with small systems and crude measurement) are communicating with people in industrial or laboratory settings. Both ends of the spectrum can learn from each other, but better with a common language. Even just a general list of terms and agree upon definitions would be useful, and might open up some interesting debate in the process.

This is something that we are willing to take on (and translate), but I want to make sure we are not duplicating efforts.

Please advise.

Best in 2010,

Alex"

On 1/1/2010 10:53 AM, David House (in reply to another message from Alexander Eaton) wrote (expanding on his own earlier message):

But, more productively and specifically:

> //For my part, I would suggest that any of us who are interested in// > //reporting our results should characterize substrates with at least// > //the following minimum parameters:// > > //* %TS// > Per European standard SFS-EN 12880 (SFS-EN, 2000b), the sample must be dried overnight in an oven at 105°C to a constant mass.

> //* %VS// > Per SFS-EN 13137 (SFS-EN, 2001), the sample must be burned in an oven at 500-550°C to a constant mass.

> //* %grit// > S and and similar materials are allowed to settle out of a sample, then they are dried and weighed. Substrate must be collected as it would be under conditions of use. This parameter can be of considerable importance in the design or planning for a digester.

> //* Particle size profile// > Sieve the normal (undried) substrate using appropriately sized screens, then (drying if desired and) weighing each sieved portion. If desired, volume may be estimated or measured as well. Knowing this profile may have an impact on digester design.

> //* C/N// > Can be done by an amateur chemist with suitable equipment, but more usually requires analysis done in a lab.

> //* %H_2 O as digested// > One wt/wt basis, with previously measured TS weight as the dry basis.

> //* Consistency at dilution// > For low-tech situations, I recommend using a correlation based on common substances such as water, half and half (50% cream/milk), butter milk, pancake batter, cocktail dip or pickle relish (as shown in The Biogas Handbook, p. 47). In any case, this parameter is most useful where pumping the slurry is being considered. (See Hart, Moore and Hale, 1966, "Pumping Manure Slurries".)

> //And likewise that digester parameters and biogas production be// > //characterized with at least the following minimum parameters:// > > //* Loading rate reported as VS/time/vol digester// > Calculated based on known/calculated volume of digester and %VS as previously determined.

> //* HRT/SRT// > Hydraulic Retention Time is easier to calculate, based simply on daily volume of substrate/slurry in, divided into the volume available in digester. Solids Retention Time, for most simple digesters, will be approximately the same, because solids and liquids will not be separated either by design or at the outlet. (If solids simply settle and do not move through the digester, the process will of course eventually fail.) However, the best source of innoculum for the digester will be the digestate, and methanogens prefer to adhere to solids. Thus separation of solids at the outlet ("dewatering"), with some return thereof (which, if memory serves, is done with some versions of the Nisargruna technology), has certain advantages.

> //* periodic temperature of digestion// > //* periodic pH// > //* periodic VFAs/buffering// > Finding pH and temperature are so simple as to not (in my opinion) need any description.

Determining VFAs and buffering capacity in the digester, as I mentioned previously, are the most complex of the suggested tests, but for any really useful characterization of the digestion process, such a determination is essential. (pH is important, but it is a lagging not a leading indicator of process health.) The method of choice for VFA/buffer determination is titration with solutes of known strength, and there are a number of methods of titration which can be used. Forgive me, however, for not taking the time to offer further details at this time.

> //* Gas production, reported as vol. gas/vol. digester, and// > //as wt gas/wt VS// > //* %CO_2 (and by assumption, %CH_4 )// > Gas production can be measured in a large number of ways, but as Mr. Bapat has indirectly pointed out, the relevant temperature and barometric pressure must be recorded at the time of measurement. As regards the latter parameter, Paul has provided a very useful method of determining CO2 ([]), and has been previously mentioned, for most situations knowing the amount of CO2 and the temperature allows for a reliable determination of the %CH4 and those parameters that follow therefrom.

With further regard to terms and tests, I recommend considering "Defining the biomethane potential (BMP) of solid organic wastes and energy crops: a proposed protocol for batch assays <[]>" which was released in March of this year. In some cases it offers recommendations which would not work in low tech situations, but overall it not only gives a fairly comprehensive approach to substrate characterization, although it does not offer information about tracking VFA production or buffering, crucial parameters for good process control. (Of course, the paper is not aimed at characterizing the digestion process, but only substrates per se.)

David House.

David,

Good guidance. It would be useful to see a table of these qualities for different substrates and reactors. Paul's biogas Wiki would be a convenient place to build a table or database of these values. (Biogas Wiki http://biogas.wikispaces.com/ ) You probably have tables of comparative value in your book.

In the recent discussion I see four very different substrates and reactors: 1) the food wastes specified by ARTI (Dr. Karve) for their domestic digester; 2) urban and domestic solid wastes described by Mr. Bapat for the Greenleaf/ARI digesters which appear to be directed to industrial or commercial users; 3) manures; and 4) sewerage described by Mr. Weisman. Perhaps Dr. Karve, Mr. Bapat and Les Gornal could collectively characterize the first two while others could characterize the last two in a variety of reactors.

It would be useful to have a common taxonomy of substrates so similar terms would be used to described wastes of hopefully similar composition.

A good project for the New Year.

Tom Miles

All,

There is a large amount of literature on biomethane potential for many feedstocks and mixtures (starting with Buswell and Neave in the 1920's), biochemistry of reactions, as well as AD system designs. More difficult to find is reliable third-party (or peer reviewed) reporting on system performance of large scale AD systems for mixed or separated ofMSW. Europe has many operating AD plants for industrial wastes and ofMSW. The IEA Biogas Task (Task 37) has some information; http://www.iea-biogas.net/abouttask37.htm

For several reasons, there is much interest among California regulators and solid waste management jurisdictions in anaerobic digestion of the organic fraction of municipal (or urban) solid waste (AD of ofMSW). We produced a report for CalRecycle (formerly Integrated Waste Management Board) in 2008 on "Current AD Technologies Used for Treatment of Municipal Organic Solid Waste" which can be accessed here;

http://www.calrecycle.ca.gov/Publications/default.asp?pubid=1275

It has some information on system performance, not necessarily all from third-party or peer reviewed sources.

Regards, Rob Williams

Postscripts
There is some information on Biogas Production Data here In February the ISO started seeking input about Biogas Standards

Compiled/Edited by Paul Harris – paul.harris@adelaide.edu.au