[Stoves] What about carbonization? Re: Composting at 70 deg C ?

[Paul S. Anderson]

Dear all,

Frank's original message was about creation of fixed carbon at low  
temperatures in a composting situation.  I think it cannot happen.     
Any comments?

-- 
Paul S. Anderson, PhD
Known to some as:  Dr. TLUD    Doc    Professor
Phone (USA): 309-452-7072   SKYPE: paultlud   Email: psanders at ilstu.edu
www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf   (Best ref.)


Quoting ajheggie at gmail.com:

> On Monday 30 May 2011 03:00:04 rajan_jiby at dataone.in wrote:
>
>>
>> Dear Frank,
>>
>> Pasteurization of Milk is carried out around 70 deg C ( hope I remember
>> correctly ), when most of the bacteria are destroyed ( some bacteria
>> must be surviving ).
>
> Yes but all the pathogenic ones should be gone and the souring ones
> reduced to low levels which they take a long time to recover from in a
> sealed container.
>>
>> My question is : Can composting happen naturally at 70 deg C ( ie.
>> without any external heating to assist ) ?
>
> Definitely; in UK legislation requires us to deal with food waste
> containing animal products by heating it to 70C ( following breakdown in
> swill sterilisation feeding this waste to animals is now banned to break
> the pathogen cycle, principally following Foot and Mouth Disease).
>
> There are a number of ways of doing this and the output from these systems
> is generally spread on the land.
>
> Because of the problem from vermin and pathogens all need to take place
> inside buildings whereas green waste composting without animal by
> products can take place in the open in windrows which are regularly
> turned to allow air to oxygenate the pile.
>
> In vessel composting of waste combined with animal by product waste seems
> to be becoming the norm but I have serious reservations that it is
> properly meeting the legal requirements, UK has a derogation from the EU
> standard which allows lower temperatures for longer duration. The general
> rule is that every part of the heap must reach 70C for at least one hour.
> The thermophylic microbes that compost the sugary and fatty parts of the
> biomass raise the temperature of the compost to 70C by oxidising these
> high energy volatile fractions of the waste. This plus the following
> maturation period where mesophylic bugs continue to break down the less
> available parts of the biomass reduce the biological oxygen demand such
> that it becomes benign for application as compost. All the energy in the
> waste is lost and the biomass is essentially returned to water and CO2
> within a few years.
>
> A division of the vegetation management company I work for has a more
> refined version of this for food waste only ( i.e. discarded food with no
> woody fraction) This is macerated into a soup and fed into a succession
> of sealed, well insulated, cylindrical silos which are agitated and fed
> with compressed air. Their temperature rises rapidly to 70 C and they
> stay in the first vessel at this temperature for a few hours. Because
> this is a technically refined and homogeneous method it is better
> monitored than ordinary in vessel methods and guarantees all the liquid
> reaches 70C using a smaller proportion of the energy in the food. Because
> of this the BOD of the liquid is too high to apply straight to land ( you
> would get spectacular growths of mould on the soil and oxygen would be
> robbed from the soil as well as runoff being a problem)  maturing in
> another large vessel reduces the BOD.Again there is no energy benefit and
> the process consumes significant amounts of electricity..
>
> The method preferred by government is to recover energy from the volatile
> solids in the food waste by digestion in anaerobic conditions to produce
> biogas, a mixture of methane and CO2, which can be refined and fed into
> the natural gas grid, burned for process heat or in an engine. A D Karve
> has posted much on this subject. These methanogenic bacteria are
> mesophylic and work best at around blood temperature ( they have evolved
> to live in bovine rumen) and, as much of the energy remains in the gas,
> the vessel often needs external heating, to keep them working optimally.
> Even though the temperatures are lower the system neutralises most
> pathogens and there are restrictions on which land can be dosed with the
> digestate to guarantee any pathogens don't survive into the food chain.
> At the industrial level anaerobic digestion for methane to power is
> fairly capital intensive and UK government offers a large incentive (Feed
> in Tarriff) to encourage the investment in capital. Unfortunately as
> there is a large gate fee (about £50/tonne) for this waste it has paid
> operators to invest in the much cheaper in vessel systems and probably
> fudge the temperature monitoring in unfavourable conditions. The
> dewatered sludge from anaerobic digestion has proved to be an interesting
> feedstock for biochar but I have lost the cite. An anaerobic digester
> with biochar production should give both energy and environmental
> benefit.
>>
>> If external heat is applied, what could be the maximum arrived
>> temperature range for the compost pile ?
>
> I don't think any bugs living on these biomass substrates will survive
> much higher than 70C although there are some that feed on iron salts and
> sulphur that exist at higher temperatures in volcanic regions i.e.
> undersea or in geysers.
> AJH
>
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