this topic is quite interesting to me cause it is my measure for my graduate project... But I have one question I hope to find to it an answer, " What is the affect of sludge age on these transformation, and what are the characteristics of the sludge that are suitable for these transformation??"
Even the breakup of sludge into less toxic material is a worthwhile cause. For that case, it happens as the sun shines, albeit slower in some locations than others. Perhaps that should be a major goal as opposed to justifying on the basis of electric energy produced.
Very interesting. Any new methods for generating electricity (that actually work) are very welcome. And in this case, there is also the claimed additional benefit of cleaning up toxic waste as well, rather than generating some kind of toxic or otherwise hazardous material as a by-product.
If the sludge only contains organic poisons or chemicals that are only poisonous as a compound then this process can reduce toxicity by breaking it down into inert or harmless components (eg benzene can be burnt to produce carbon dioxide and water). But if it contains heavy metals then these are likely to remain toxic in all forms and there is a danger that they will be converted into soluble oxides from insoluble forms, thus presenting a greater hazard, or could be released in toxic airborne forms. I don't see any mention of scrubbers to reduce S02/NOx emissions. Energy from waste plants also run the risk of liberating carbon which would otherwise have been locked away - if the carbon came from fossil fuels rather than biomass then this presents a net increase in carbon emissions. Although this sounds a promising approach, the devil really is in the detail!
I presume that any spare electricity is a bonus - the point of this use of solar power is to avoid buying any energy to do the work on the sludge. If the relevant government gives financial incentives to use low-carbon power then this may also help the financial side, but this should pay attention to the content of any emissions!
It looks like the "char" is the solid residue from this process which will have further concentrated any toxic materials or elements which are not broken down by the pyrolysis. The good news is that the pyrolysis will have broken down most compounds (such as drugs) that are toxic to the environment. Perhaps some useful elements can be extracted from the char before it is finally disposed of.