Basics should be
Basics should be biodegradable in order to be compatible. Whether bioplastics are produced from renewable resources or not, doesn‘t matter. The key element is that they must be biodegradable under anaerobic conditions or at least be compatible with an anaerobic digestion process. Anaerobic digestion plant in (two-phase) at Vitoria (Spain) (all photos: OWS nv) Concerning technical preconditions of treating bioplastics in anaerobic digestion plants, a distinction must be made between wet and dry technologies. In general, wet technologies, especially in the pretreatment phase, cannot treat bioplastics easily: in the first pulping and hydrolysis phase they are removed either by flotation or by sedimentation and therefore are not really entering the digestion (except when bioplastics are quickly soluble or dispersible, which is rarely the case). A solution could be to add the bioplastics directly to the second step, the aerobic composting step (considering the retention time in this second step is much shorter than the residence time in a typical composting process). Another solution might be new developments in the pretreatment phase. In most dry systems, bioplastics can be added when some random conditions are fulfilled: they should be shredded (to reduce the particle size) before entering the digestion (just like biowaste itself) and sieving is better located at the end of the process in order to enable as much biodegradation and disintegration as possible in both the anaerobic digestion and the aerobic composting step. The major underlying reason why several bioplastics show a different biodegradation behavior in aerobic composting from their behavior in anaerobic digestion is the influence of fungi. Fungi are abundantly available and very active in aerobic composting while in anaerobic fermentation no fungi are active. Some polymers are mainly (or even only) degraded by fungi and not by bacteria and will therefore biodegrade in aerobic composting and not in anaerobic digestion - or only much slower. As a matter of fact, this is also the case for the natural polymer lignin which can be found in wood, straw, shells, etc. On the other hand, when bioplastics do also biodegrade in anaerobic fermentation there is a double benefit. First of all, energy is produced from the bioplastics in the form of biogas that can be converted to electricity. Secondly, as most bioplastics are very rich in carbon and do not contain nitrogen (or very little), the addition of bioplastics to biowaste will improve the C/N ratio of the mixture. Biowaste tends to be low in C/N, which is sometimes a problem in anaerobic digestion, by adding a carbon-rich substrate the C/N ratio is increased. So far, the knowledge of anaerobic biodegradation and treatability of bioplastics is limited and further research would be welcome. Ideally, bioplastics would biodegrade and also disintegrate during the anaerobic phase in an anaerobic digestion plant, just as the major part of ‘natural‘ biowaste does. However, if the bioplastic disintegrates during the anaerobic phase and then afterwards biodegrades completely during the aerobic stabilization phase or during the use of digestate or compost in soil, it can also considered to be compatible with anaerobic digestion. www.ows.be 44 bioplastics MAGAZINE [06/09] Vol. 4
Events Event Calender December 2-3, 2009 Dritter Deutscher WPC-Kongress Maritim Hotel, Cologne, Germany www.wpc-kongress.de December 2-3, 2009 Sustainable Plastics Packaging Sheraton Hotel, Brussels, Belgium http://sustainableplasticspackaging.com March 8-10, 2010 GPEC 2010 Global Plastics Environmental Conference The Florida Hotel & Conference Center Orlando, Florida, USA www.4spe.org March 15-17, 2010 4th annual Sustainability in Packaging Conference & Exhibition Rosen Plaza Hotel, Orlando, Florida, USA www.sustainability-in-packaging.com March 16-17, 2010 EnviroPlas 2010 Brussels, Belgium www.ismithers.net April 13-15, 2010 Innovation Takes Root 2010 The Four Seasions - Dallas, Texas, USA www.InnovationTakesRoot.com June 22-23, 2010 8th Global WPC and Natural Fibre Composites Congress an Exhibition Fellbach (near Stuttgart), Germany www.wpc-nfk.de You can meet us! Please contact us in advance by e-mail. Editorial Planner 2010 # - Month Publ.-Date Edit/Ad/Deadl. Editorial Focus (1) Editorial Focus (2) Basics Fair Specials 01 - Jan/Feb 08.02.2010 15.01.2010 Automotive Foams Basics of Cellulosics 02 - Mar/Apr 05.04.2010 12.03.2010 Rigid Packaging Material Combinations Basics of Certification 03 - May/Jun 07.06.2010 14.05.2010 Injection Moulding Natural Fibre composites Basics of Bio-Polyamides 04 - Jul/Aug 02.08.2010 09.07.2010 Additives / Materbatches / Adhesives Bottles / Labels / Caps Compounding of Bioplastics 05 - Sep/Oct 04.10.2010 10.09.2010 Fiber Applications Polyurethanes / Elastomers Basics of Bio-Polyolefins K‘2010 preview 06- Nov/Dec 06.12.2010 12.11.2010 Films / Flexibles / Bags Consumer Electronics Recycling of Bioplastics K‘2010 review Further topics to be covered in 2010: Beauty and Healthcare Non-Food Bioplastics Printing inks Lignin Paper-Coating and much more … bioplastics MAGAZINE [06/09] Vol. 4 45
