Jun 1, 2015
Thanks for your interesting submission Michael. I like your idea of utilizing existing infrastructure with alternative inputs to increase system-wide conservation. One question that popped into my mind is about the proportion of energy being saved by recycling paper and plastic and replacing that component of the waste stream with forestry products instead. I'm rather sure it would be net positive savings, but the results would be interesting. I do have some concerns about the utilization of forestry products as a replacement, however. The UK has been in something of a frenzy in recent years in its use of wood chips as a fuel source, not necessarily to the benefit of the climate. Need has already grossly exceeded domestic supply, so that most of their burned wood chips now come from the US and mainland Europe. The transportation adds to the carbon footprint. More importantly, however, is that it may not approach a carbon-neutral strategy. Forestry products are considered renewable because trees grow back, but it takes decades to absorb the carbon of an old tree. As such, there may be a significant decades-long delay for carbon neutrality. Your point about the versatility of potential inputs raises an interesting possibility, however. Rather than slow-growing forestry products, localized algae blooms may be dried and burned quite rapidly as something far closer to carbon neutrality. Just some food for thought. Best regards, Dustin Carey Catalyst
Jun 2, 2015
Hi Dustin, Thanks for the thoughtful comments. While I'm not a forestry management expert, I think I can answer most of your questions. You are correct that to use biomass properly, one has to use good management. Clear cutting old growth forests and letting the land sit, is probably not a good idea. There are typically 2 ways of sustainably managing forests with wood use. One is selective cutting and the other is cutting and replanting a certain percentage a year. For example, if the economics of wood growth shows that 20 year old trees are good, then 5% of the forest would be harvested per year using either technique. That balances the commercial uses with sustainability. I believe that is the kind of approach taken by the state of Massachusetts in planning for forestry use. You are also correct that recycling paper and plastic takes energy and we want to make sure the systemic energy balance works as one shifts from incineration to recycling. Generally, recycling uses less energy and resources that starting from raw material. To make paper from wood, there is the logging and pulping. Pulping removes hemicellulose and lignin from the wood and mostly burns them for energy to run the pulping plant. Cellulose is only ~40% of the wood. So ~60% of the incoming biomass is being burned to clean it up. Repulping recycled paper only requires washing and slurrying the paper since the other parts have been removed. It is similar with plastics processing. Perhaps the best way to think about it is from the economics: In my city when I throw paper and plastic in the trash, the local incinerator charges $69/ton (not including transport). If I put that same paper and plastic in a recyling bin, my city gets paid $10/ton. So the market economics are pushing us to higher recycling rates and one supposes incinerators will want to replace the lost materials.