Re: Biomethane Report - California #bioenergy #ad

Charles Hegberg


You are walking down the right path.  Have discussed this with a number of USA WWTP operators.  I think the stated price point is off considerably for many reasons such as the plant buying the biochar rather than producing their own biochar, other operational offsets etc.  Primarily they are not accounting for the many economic and regulation externalities.  For example, in the not so distant future, the USEPA is likely to ban all biosolids land applications including digestate.  This is due to the fact the processes does not get to sufficient temperatures to destroy PFOS, antibiotics, estrogen, microplastics and other pollutants.  Everything is based on harmful bacteria.  However, gasification is one technology that does.     


Many places that have already installed AD systems, might as well make them operate better. So add biochar.  However the systems are very sensitive and the regulatory fines and penalties are very large for a system that goes out of balance.  Most operators do not want to take that risk without some assurance that things will not go off the rails.    


For those that have AD, the only reason they make money at this time is subsidies and reduced disposal costs.  If they are removed then it all falls a part or becomes a burden on the rate payers.  AD systems really do nothing but extract the gas from the waste and at the most reduces volumes by 50% or less and not at high enough temperatures to destroy the bad stuff other than the bad bugs.  Thus in that case it is worth a gasifier attached to the AD to provide supplemental heat especially in the winter.  For plants in some highly urbanized areas such as the Chesapeake Bay region, they also have a Biological Nitrogen Removal (BNR) system which must also be kept at the right temperature and even more critical than the AD system. 


The key is converting it into something that can be spread on the field, forests (Class B) or compost (Class A).  However, few get a payback on it.  Just another disposal method.  An example is Blue Plains in Washington DC. They spent I believe  $400M for the AD system and will never pay them back.  It was done really to remove odors that would cover the Washington DC especially in the summer.  While they get other benefits, the number one reason was high level public pressure.


For those in AD scenario, it would be best to produce biochar from the communities green waste which could be used in the AD system.  Better yet use the green waste to blend with the digestate and run it all through the gasifier together. This process would reduce the volume and destroy all the bad stuff in the biosolids.      


If a WWTP hasn’t installed an AD system then it is a waste of money to even consider it.  Go straight to a gasifier and process the biosolids through it. If a plant doesn’t have a BNR, then just look to make some electricity as that is the biggest operational cost to a WWTP.  If it has BNR flip over in the winter for the heat needed.  The processing of biosolids and green waste can be scheduled to fit the plant operations.


My only disagreement is on cleaning up syngas from a gasifier.  IMO, it is a waste of time and unnecessary expense.  Best to go straight to electricity or other uses.  In general, WWTPs have a lot of moving parts that must be carefully considered before entering another component.  Agriculture systems don’t have any real constraints as WWTP systems do so might be best to work out the operations on those first.

Chuck H. 






From: <> on behalf of "George "Kim" Chaffee" <kim.chaffee2@...>
Reply-To: "" <>
Date: Sunday, March 1, 2020 at 2:47 PM
To: "" <>
Cc: Nando <d.nando@...>
Subject: Re: [Biochar] Biomethane Report - California #bioenergy #AD




I read the Executive Summary twice and have a couple thoughts.  The last paragraph identifies the economic barrier as the requirement that the biochar cost $66.00 to $80.00 per ton to make the process cost neutral.


If the wastewater treatment plant had a biochar gasifier located next to the AD unit, it could use the heat energy to warm the digestate, which should accelerate the digestion process.  Also, it may be possible for the gasifier to co-produce syngas without significantly degrading the suitability of the biochar to improve the digestion process.  The syngas could be cleaned up along with the AD unit’s digestate gas.


This would, of course, add the capital cost of the gasifier to the equation.  However, if the financing were creatively structured, it might just work out.  After all, the biochar supplier has his own plant’s capital costs factored into his selling price.


Also, I saw in the ES that the digester gas would qualify for tax credits, due to its replacing natural gas.  


I’d be interested in any thoughts on this idea.  Thanks.




On Mar 1, 2020, at 9:17 AM, Ron Larson <rongretlarson@...> wrote:

Nando and list:


I also have not read this report thoroughly, but from my scan believe there is no discussion of pore size optimization - nor optimization of much else.  They strove for small particle size - which gave many problems.  My guess is that using pore and particle sizes optimum for a final use in agriculture might give them the best economics - an approach not even hinted at here,


I haven’t heard much of your own recent biochar work.  What’s happening for you?



On Mar 1, 2020, at 6:34 AM, nando@... wrote:



Interesting report. I've only had time to scan it, but so far I don't see mention of the amount of micropores in the biochar produced. From what I've read in other papers, maximizing the number of micropore sites in a biochar will increase the amount of CO2 sequestered when adding biochar to a digester. This would require an accurate pyrolysis technique and preferably a feedstock that can optimally produce micropores. As far as I understand, micropore formation requires a certain minimum highest pyrolysis temperature, but if the particles get too hot the micropores that have formed tend to fissure open too wide to capture CO2 molecules. 

The increase in value of the biochar would most likely boil down to its ability to adsorb ammonia in a way that is plant available.

My have the impression so far that some combinations of digester feedstock / technique and a certain type of biochar at the correct dosage may be financially viable. Correct me if I'm wrong, but this study doesn't seem to have been designed to nail that down with any precision.

Nando Breiter
CarbonZero Sagl
Astano, Switzerland


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