[Gasification] ash use, soil considerations, PAH pathways

[LINVENT at aol.com]

In a message dated 5/8/07 1:55:22 AM, pels at ecn.nl writes:


> No gasifier operator has ever given the guarantee that the PAH
> levels in their ash are safe
> 

The question is are polycyclic aromatic hydrocarbons in the solid state in 
minute quantities in a non-aerosol biological environment a danger? PAH's are 
long chain hydrocarbons which are very unstable and will spontaneously decompose 
under the right conditions. They are a major component of diesel engine 
exhaust and decompose in sunlight forming smog and ozone with other pollutants. The 
above PAH question is wrong. It depends upon the conditions which PAH's are 
within, Solid PAH's per se do not pose a problem to human exposure becuase they 
cannot be transferred without potential decomposition and in a soil, they 
break down quite quickly. It is when they are in an airborne condition that they 
are the problem. 

I wonder what the source of cadmium is for biomass? In New Hampshire, lead is 
high in the soil from native geology and wood burned generates lead emissions 
but gasified, the lead stays in the ash. One biomass burning plant had to 
show several tons/year lead in their emissions. 

If the ash contains cadmium, then the original source would also contain it 
and be a problem with land application as when the organic fraction is 
consumed, it would leave the cadmium also. Perhaps higher rates of application to 
achieve the same concentrations, but over time, the same level would occur. This 
logic progression leaves no possible land application for any organic material, 
period. Forests could not die and leave their plant matter on the ground. 
Other metals have similar considerations. One which is not generally considered 
is aluminum. If one takes a look at it in typical soils and plants, it is a 
problem. I am curious as to the other heavy metals of concern. 

The US EPA has a policy statement which says that gasifier ash passes EPA 
TCLP test which is toxic leach test and can be landfilled. All of the ash testing 
we have done on our fuels has passed this standard, including tires. More 
stringent standards would not necessarily meet this standard. 

In early days, wood ashes would be leached with water and hydroxides removed, 
forming soaps. This leaching supplies potassium and sodium hydroxide, the 
former being a very good nutrient for soils, the latter being tolerable in small 
applications. This is one of the fast benefits of ash application to the soil. 


Most soils and plants are tolerant of some heavy metal content, particularly 
to the plant as it acts as a filter. Microbes are somewhat tolerant in low 
concentrations likewise being a filter. At high concentrations, the process 
breaks down. However, liming quickly fixes many heavy metal concentrations and 
rasises the pH to the point where the metals are no longer soluble or 
exchangeable. Liming is a good agricultural practice under virtually any condition. The 
question is at what point does the concentration affect plant growth. This can 
take a very long time to define due to the number of variables presented. 
Making flat rules in this field is rife with dangers because of the number of 
variables and how they affect the biological system. 

Making bricks or blocks with a well broken down ash fixes them for a very 
long time and is an economic application. 



Sincerely,
Leland T. Taylor
Leland T."Tom" Taylor
President
Thermogenics Inc.
7100-F 2nd St. NW Albuquerque, NM 87107
Phone:505-463-8422 Fax:505-268-9206 (call first)
Web:thermogenics.com



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