According to the well-established waste hierarchy model of sustainability the re-use and, below re-use in the hierarchy, the recycling of manufacturing waste is a more environmentally sustainable approach to the handling of waste than its disposal or conversion to energy (e.g. biogas). For waste biomass this delineation in the waste hierarchy is not so clear. This is because with emerging technologies, biological materials, unlike plastic and metal wastes, can be more radically transformed, either physically, chemically or biologically into a broad plethora of end use products with significantly different properties and end-use market values including of course, liquid fuels such as ethanol and butanol.
Generally speaking there is rough correlation between the technological cost and complexity input into the transformation of the biomass waste and its end-use market value. These end-use products and applications are therefore better considered as a value chain than a hierarchy, where biomass waste is the input feedstock.
Typical low tech / low value markets for biomass wastes uses the adsorbent or absorbency properties of biomass to remove pollutants – sometimes highly selectively – from the environment. Good examples of this include the use of wood waste as an absorbent of toxic heavy metals in mining waste streams or the use of chicken feathers to remove hazardous dyes from textile waste streams. A long-established and arguably higher value end-use application of waste biomass is as a nutrient source. This includes waste protein in animal feed and land spreading. A more technical, higher value end use for non-food waste is through fabrication of marketable materials, for example construction materials or disposable utensils made from wood waste and straw.
Biotechnological transformation of non-food waste to liquid biofuels and commodity chemicals is now becoming established with demonstration plants announced on a regular basis. Use of related technology to either extract or produce high value specialty chemicals from food and non-food waste has the potential to become the market-transforming commercial technology of the 21st century. Examples include ‘natural’ vanillin from lignin in wood waste, glucosamine and carotenoids from prawn shells and succinic acid and polyhydroxybutyrates (PHBs) from bakery wastes.
Whilst it is important for academic and industrial research to expand the technological possibilities, it is unrealistic to expect traditional manufacturers, who have traditionally sought to dispose of their waste, to become the early-adopters of new technologies with their inherent development risks. Public resource interventions should be aimed at lowering the technical and financial barriers to entering the low-tech, lower value end of the value chain. When simple technologies and routes to market that support the marketing of waste-derived products become established practices amongst traditional manufacturers, a collective competency is created for the adoption of the more complex technologies required to produce higher value end-use products.