Recycling Food Scrap? | What’s with the Stink?by Terry Green on 11/17/12
In the US over 34 million tons of food scrap are produced annually (about 3 lbs per day for every man, woman and child). There are compelling economical and environmental reasons for stopping the disposal of food scrap (http://www.wellhome.com/blog/2011/04/the-energy-cost-of-food-waste/). Aside from reducing the amount of waste generated through better distribution and management of food in the first place, more effort needs to also be spent in finding better ways of recycling food scrap which otherwise would normally be destined for landfills. Municipalities are no longer allowed by the EPA to dispose of food scrap in landfills.
A pressing issue is how to recycle the food scrap efficiently outside of landfills. Conventional large scale commercial composting facilities are ill-suited in processing food scrap. Those that do create considerable stench attributable to processing of the food scrap all too familiar to anyone having the misfortune of living downwind from such composting facilities. Let’s take a moment to talk about stench and consider the prospect of alternative and more economical options in processing food scrap.
In a nutshell, stench production is fundamentally intertwined with the science behind the processes of degradation of organic matter. Food scrap, unlike other inedible waste, is rapidly degraded by microorganisms. Since microorganisms by and large use the same mechanisms in breaking down food scrap as are used in our bodies, and since the food that we eat (and scrap waste we discard) is easily digestible, and rich in nutrients used to sustain life, this is not surprising. This fundamental principle however creates a problem in composting wastes that are rich in readily accessible nutrients.
Consider, for example, that aerobic microorganisms, those requiring oxygen in order to metabolize and breakdown organic matter, having first access to food scrap, rapidly consume all of the available oxygen in the vicinity of the food scrap they are growing off of in the process of breaking it down. Oxygen, typically within seconds, becomes depleted in the area where the aerobic organisms started breaking down the food scrap. Anaerobic microorganisms, organisms capable of growing off of and metabolizing nutrients in the absence of oxygen, quickly take over. These organisms produce significant quantities of volatile and putrid smelling byproducts which include well-known volatile fatty acids, mercaptans and amines, compounds which to a large extent, wafting from the composting site, account for the stench picked up downwind from composting facilities.
Even though commercial composters take great strides to mechanically aerate wastes they process, it is neither feasible or possible to adequately aerate these wastes to a level where stench is not a problem. Anaerobic bacteria present in the waste simply grow at a rate far exceeding the rate that oxygen can be delivered in pockets of the decaying waste depleted of oxygen. In practice all composting operations involve a combination of aerobic and anaerobic metabolic transformations associated with the turnover of organic matter as it gets broken down and mineralized. The attendant stench associated with composting can to a large extent be attributed to the byproducts formed by anaerobes in this process.
There are alternative technologies worthy of consideration which may be better suited in processing food scrap. Food scrap can be recycled, for example, using newer more advanced anaerobic fermentation technologies as a means of generating methane gas as a fuel in the generation of electricity, two-step fermentation and burial technologies aimed at recycling food scrap back into the soil as a means of reducing greenhouse gas emissions and improving the nutrient and microbial ecology of soils, and as a nutrient source processed by Black Soldier fly larvae as a means of reducing greenhouse emissions while also producing valuable byproducts derived from the larvae growing off of the waste.
Several of these newer technologies can be decentralized and carried out in the home setting further reducing the cost of processing food scrap while making better use of the byproducts realized in processing the waste. The use of Black Soldier fly larvae, in combination with microbial degradation of food scrap, now receiving significant attention, is especially attractive because it has recently been shown that the larvae voraciously consume volatile fatty acids while concomitantly mineralizing organic nitrogen waste products formed as food scrap decays (http://www.bioone.org/doi/abs/10.1603/EC11192).
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