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06 | 2008

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Basics Home Composting

Basics Home Composting ≠ iStockphoto Compost Heap Quick Composter iStockphoto By Michael Thielen In numerous publications, presentations, company brochures etc. one can read, or hear statements, about ‘home composting’. However, when taking a closer look into different areas of the world, it becomes obvious that different people have different definitions of the term ‘home composting’. Thus when describing a bioplastic material or packaging item as ‘home compostable’ this aspect should be taken into consideration. The ‘normal’ compost heap In many parts of the world, for example in my backyard, a simple, open compost heap is being used. Many people (like me - until now), who do not read books about the correct procedure for home composting, simply throw their yard- and kitchen waste onto this heap and once in a while they dig into it to get some humus to be spread on the garden. A little more sophisticated is a system of three heaps next to each other. Here the first compost heap is used to collect this year’s organic waste. The second section is last year’s collection that was turned upside down at the end of the season (this section is ‘resting or maturing’). And the third section (last year’s maturation section, which was again turned upside down at the end of the year) is used to spread on the garden. These home composting systems have one thing in common, i.e. there is no real control of humidity (except the rain) or temperature. In most cases the temperature is the ambient temperature. It may rise in the first few days after adding a large amount of grass clippings for example. If such compost heaps are well prepared, e.g. with loose soil underneath and a layer of straw, most probably a significant population of microorganisms as well as earth worms etc. will eventually appear and do their natural job. Quick Composter Do-it-yourself and gardening stores offer so called ‘quick composters’. In most cases these are plastic bins in which the sunshine is supposed to help achieve higher temperatures inside. However there are many experts who doubt the proper function of such quick composters, even if you can buy ‘accelerating additives’ such as organic nitrogen or ‘special worms’. Temperature and humidity control are even more complex in these systems. However, once again, if used properly, they might do a good job. But, as I learned, this is not so easy. Electric home composters Now, the main reason for this article was some kind of confusion that arose during the 1st PLA World Congress, hosted by bioplastics MAGAZINE in Munich this September. In a presentation (as well as in an article in our last issue pp. 24-25 ) an electrical home composting system was mentioned as it is being used, for example, in many Japanese households. As far as we have been able to discover so far, there are three main companies in Japan manufacturing these so-called ‘Home 40 bioplastics MAGAZINE [06/08] Vol. 3

Basics Home Composting Composting Devices’ - also referred to as ‘Home Garbage Processors (HGP)’. These companies are Hitachi, Sharp and Panasonic. In these garbage treatment systems two fundamentally different methods are applied. One is simply a drying system using warm or hot dry air to reduce the garbage volume, and the other one is a biodegrading system with microbial activity, which means some kind of composting system. The system mentioned in the presentation and the article in bM 05/2008 refers to the second group, i.e. the composting system with microbial reaction. And again, taking a closer look at these devices, there are two different types here. One treats the garbage at ambient temperature and the other uses higher temperatures. We were informed that the higher temperature treatment is better than the ambient temperature treatment because harmful bacteria cannot generally occur in high temperature conditions. In addition, hydrolysis of a biopolymer like PLA is promoted at high temperature and in conditions of high humidity. The sales price of such systems is between 40,000 – 80,000 Yen (about 300-600 Euros). In some Japanese municipalities such electric ‘Home Composting Devices’ are subsidized by the local authority. Bokashi Another interesting alternative, especially for smaller households or dwellings, is Bokashi. For this anaerobic fermentation process a specifically designed Bokashi bucket is used in combination with a special EM-additive (EM= effective microorganisms) ‘Bokashi’ is a Japanese word meaning ‘fermented organic matter’. When applied properly, it is a system of odorless composting. Socalled ‘effective microbes’ or ‘EM’ are used to decompose organic kitchen waste. Similar to the wine-making process, this system relies on fermentation rather than putrefaction. There are two steps to the Bokashi compost. First the organic waste is collected in a special bucket, the EM additive (Bokashimix, made using a combination of sawdust and bran that has been inoculated with the microorganisms) is sprinkled on daily. Due to the presence of the micro-organisms in the Bokashi mix and because the bucket is air tight the waste ferments. In this bucket the waste actually does not break down, it is just reduced in volume as the liquid content drains from the waste. However the bucket will eventually fill up. Then, in a second step the waste is buried in the garden under the soil. Here the organic waste will break down because the microbes have oxygen. For example in Sydney’s summer the breakdown of the waste takes about 3 to 4 weeks. The liquid extracted earlier is an additional bonus which when diluted is an excellent fertiliser. As biodegradable plastic material does not contain moisture as most organic kitchen or garden waste, the Bokashi system seems not suitable to treat bioplastics waste. References: Seitz P., Das Kompostbuch für Jedermann, Kosmos Hobbytip der WDR Hobbythek Nr. 202 Electric Home Composter (Source: Sharp) bioplastics MAGAZINE [06/08] Vol. 3 41

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