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Films People| Flexibles | Bags Bags in industrial composting Do biowaste bags decompose fast enough in industrial composting or AD plants? By C. Letalik, B. Schmidt, A. Ziermann C.A.R.M.E.N. e.V Straubing, Germany Industrial composting has widely implemented across in Germany for over 20 years. During the last decade and driven by legislation, the separate collection of organic waste has grown more and more popular. As a result, a broad variety of technologies of industrial composting and anaerobic digestion are in place. According to the Bundesgütegemeinschaft Kompost’s (BGK; the German Quality Assurance Association for Compost) classification scheme, there are eight major types of process, so-called Hygiene-Baumusterkategorien, which differ a lot with regard to their technical components and composting/digestion times. Compostable biowaste bags have been on the market for more than 15 years. As soon as biodegradability and compostability according to DIN EN 13432 or DIN EN 14995 have been demonstrated under laboratory conditions and have then been certified, the product can be labelled with the compostability logo. Nevertheless, compostable biowaste bags have not systematically been field-tested in all of the different types of industrial composting or anaerobic digestion plants until now. As a result, there is still uncertainty among operators and local authorities as to whether or not compostable bags are technically compatible with on-site technology, especially as to whether the bags decompose fast enough within the usual decomposition times. At the same time, the interest in the subject is increasing, as compostable bags may increase the amount and quality of organic waste collected by households. This article is based on a more comprehensive paper [1] which outlines a project performed in Germany from April 2010 to November 2011. Part of this project was to evaluate the relevant industrial composting and anaerobic digestion technologies for the treatment of organic waste. On the one hand, there are partly enormous procedural differences between these processes. On the other hand, the composting time is typically much shorter in practice than the twelve or five weeks required in DIN EN 13432/14995. Plant operators and representatives of local authorities who are critical of compostable biowaste bags conclude from this that the bags do not meet the requirements of composting practices because they do not degrade fast enough. For this purpose, all plants that are members of the BGK were evaluated. The results showed that six types of process cover approximately 50 % of the total number of plants and the annual capacity of all composting and anaerobic digestion plants listed by BGK. In a second part, the specifications of these types of process were first determined by means of telephone interviews. Subsequently, five different kinds of biowaste bags were practically tested, each on one plant of a certain plant design. The biowaste bags for testing were added to the plants’ normal bio-waste streams. Samples were taken at different times. Material degradation was documented by photographs and by weight determination. 22 bioplastics MAGAZINE [06/13] Vol. 8

Films | Flexibles | Bags Product type Bioplastics type Bioplastics manufacturer Supply source Filling volume [l] Wenterra T-shirt bag Mater-Bi ® NF Novamont (I) Profissiomo biowaste bag Mater-Bi ® CF Novamont (I) biomasse (D), retailer of biobased products dm-drogerie markt (D), chemist’s shop Biowaste bag Bioplast ® Biotec (D) Rewe (D), grocery store 10 + Bio4Pack waste bag Ecopond Flex ® KingFa (Hong Kong), internet portal for the purchase of detergents Biowaste bag Bio-Flex ® FKuR (D) Real (D), grocery store 10 + < 10 10 + < 10 Table 1: Overview of the sample materials tested Number and type of process Active Composting time Turning process Additional Aeration Humidification 1.1 Herhof boxes 7 days not applicable forced aeration process water, industrial water 3.6 Horstmann WTT tunnel 7 days not applicable forced aeration process water, industrial water 5.2 Bühler-Wendelin 9 weeks ≥ 9x forced aeration industrial water, process water up to 4.5 weeks 6.2 triangular wind-row, not covered 6.3 trapezoidal windrow, open- air (I) 6.8 triangular wind-row, covered 6 weeks ≥ not later than once every four weeks not applicable During the turning process when required. Industrial and process water up to 3 weeks. 5 weeks ≥ 4x not applicable During the turning process when required. Industrial and process water up to 2.5 weeks. 4 weeks wheel loader or compost turner ≥ 1x not applicable During the turning process when required. Industrial and process water up to 2 weeks. Table 2: Practice-relevant types of process with process description (BGK 2010) Type of process 6.3 6.8 1.1 5.2 3.6 6.2 Number of plants 22 26 19 8 7 127 Capacity of the smallest plant [t/a] 2,900 4,500 8,000 15,000 10,000 6,500 Capacity of the largest plant [t/a] 50,000 85,000 36,000 80,000 85,000 87,500 Average capacity [t/a] 15,782 13,842 17,924 36,937 34,286 10,392 Total capacity [t/a] 347,199 359,885 340,550 295,500 240,000 1,319,792 Table 3: Number and annual capacity of practicerelevant types of process (plants listed at BGK) In summary, it can be said that standard types of bio waste bags quickly achieved high degradation rates in the field test. The test showed that the degradation requirements according to DIN EN 13432 or 14995 were met in nearly all kinds of plants. It can thus be concluded that these bio waste bags do not cause any visible compost contamination or technical problems in all the practice-relevant plant types that were tested. German legislation and current situation In 2015 the biowaste bin will be introduced nationwide throughout Germany (BMU 2011). Many people, however, refuse to collect their kitchen waste separately because they consider it unhygienic. Thus, large amounts of valuable biowaste are not utilised for the production of compost and bioenergy. Another problem is that households use conventional plastic bags for collecting their kitchen waste. These are not biodegradable or compostable and can cause technical problems in composting and anaerobic digestion plants and may also contaminate the compost. Different types of bags tested Within this project four types of standard certified compostable biowaste bags and one T-shirt bag were field-tested. All products are available in German retail stores or online shops. All bags were filled with fresh biowaste and then put into the different composting systems. bioplastics MAGAZINE [06/13] Vol. 8 23

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