Over the past 15 years the biowaste collection and treatment industries in Italy and the UK have seen significant development and, combined, now process in excess of eight million tonnes of source-separated biowaste a year. Determined by local circumstances and policies, a range of different collection systems and tools have been adopted.

Italy chose a combination of intensive separate collection for food waste and household waste and recycling centres (HWRCs) for garden waste. The UK – whilst originally concentrating on kerbside garden waste, then on the co-collection of food with garden waste and occasionally cardboard – is seemingly now favouring the Italian model for food waste. Depending on what data you believe, the number of UK households receiving weekly separate food waste collection is at least equalling if not exceeding those on the commingled system (about 4.5 million each), compared to approximately eight million in Italy. The systems may vary, but one thing the two industries have in common is the issue of contamination.

A typical UK/Italian local authority contract will allow for five per cent non-compostable materials (NCM), like plastics or glass, which for an average 40-kilotonne (KT) plant could equate to 2,000 tonnes. This may not sound like much, but in fact can have a large effect. A new study by Consorzio Italiano Compostatori (CIC – Italy’s AfOR) has shown that NCM has a drag factor: the organic matter sticking to, or being trapped, in the screened residues, or plastics getting wrapped around branches so that, rather than generating revenue, additional costs of up to 200 per cent are incurred. For every tonne of non-compostable residues, at least 1.5-2 tonnes of organic material are lost. For a 40KT facility, the pre- and post-treatment cleaning process this necessitates and the associated disposal costs, add up to an enormous liability of over £300,000.

A common Horatio theme in these pages is the issue of decreasing quality of input materials for material recycling, and organic recycling is no different. The difference with organics recycling, particularly composting, is that by the end of the biological process the actual mass has, in effect, halved. So the contractual five per cent of allowable contamination has become 10 per cent. Not only that, the mechanical processes involved will reduce the NCM particle size significantly, which – given the maximum limit for plastics in PAS 100:2011 is 0.12 per cent – makes you wonder how any composter actually makes the grade. Some don’t, but with the forthcoming EU end-of-waste criteria looming, they will have to. Yet with the aid of a whole host of human/ mechanical separation techniques, many here do make the grade, but we are not the first to face this issue and on-site separation is only part of the solution.

In 1994, the small municipality of Bellusco in Lombardy became the first in Italy to introduce a frequent (at least weekly) separate collection of food waste using small caddies and compostable liners. Today, this method of collection has been adopted by over 2,000 municipalities in Italy and hundreds more across the world including the UK. In 2008, Italy’s 3.4 million tonnes of source-segregated biowaste resulted in almost one million tonnes of compost, along with 240KT of screening residues. Of these, 100KT were lignocellulosic materials (oversize) and 140KT were NCM, the majority of them being plastics.

In order to help them understand their particular issues, CIC routinely performs standardised waste input analyses for its members, both composters and more recently AD operators. From December 2008 to July 2010, 1,036 residential food waste samples from 42 Italian provinces (UK counties) were analysed. Almost 57 per cent of the samples showed less than five per cent contamination, whereas 28 per cent of the samples were between five per cent and 10 per cent.

The cost of higher contamination

Keeping contamination as low as possible is crucial because every percentage point of NCM causes a more than proportional production of residues during pre-sorting and final refining – the drag effect. In Italy, due to the robust nature of the NCM data and their associated costs, a gate fee model based on these factors has been developed and accepted by local authorities.

The approach involves using an acceptance formula for inputs that provides four options on the level of contaminants accepted and the relevant gate fees calculated based of the quality of the waste delivered. Feedstock deliveries are assessed according to their quality and the appropriate gate fee levied. Where testing shows high or increasing levels of NCM, the composter will go back to the local authorities to discuss the problem and often a small investment in public communication will yield the desired results. The approach has been widely implemented by CIC members and as a result the levels of contamination entering facilities has fallen.

In the UK, there is currently no regular analysis of waste inputs, monitoring of NCM or variable gate fees although this is an area where AfOR is becoming much more active.

The role of En13432 certified compostable food waste collection bags

In order to further investigate the relationship between different kinds of liners (compostable and non compostable) and their contents, between May and November 2010, CIC analysed 422 batches of feedstock from 126 municipalities. The question was whether the contamination of the food waste inside each single bag would change significantly according to the type of bag used (compostable versus non compostable). Of the 422 samples, 183 were collected in compostable liners and 239 in polyethylene bags. The contents were then compared for their relative amount of contaminants. The results of this study are shown in Table 1, opposite.

The difference in quality between the content of compostable liners and the content of polyethylene bags is stark – the analysis shows an average delta of 5.71 per cent in contamination of the contents of the bags analysed. This difference rises to 8.15 per cent if the polyethylene bag is also considered as a contaminant (which is the case). Polyethylene bags account for 2.44 per cent contamination whereas the remaining 7.48 is caused by other noncompostable materials found inside the bag, mainly plastic packaging and other items. Thus, it is clear that by tolerating the use of polythene bags, significant amounts of additional non compostables are collected. Both in the UK and Italy, contamination at biowaste treatment facilities is a challenge and the best way to overcome these challenges is for joint activity and responsibility between the local authority and the processor since both will benefit. The case study of Italy shows that whilst the integrated collection and treatment systems perform very well, perceived cost savings at the collection side will lead to massive increases in costs for the processor dealing with contamination.

In recent years, the UK has learned much from the Italian model of separate food waste collection, but this shouldn’t stop with a kitchen caddy, the odd liner and frequent collections. Like all household recycling, final product quality is closely associated to the way the inputs are collected, giving people the right tools. Communication from the start is not only priceless but, as our minister for communities would say, delivers best value.

CIC and Novamont are currently working on waste input analysis at AD facilities. If you would like to know more about this study and how your UK plant could contribute, please contact Tony Breton – tony.breton@novamont.com