| What is recycling? It is the process by which | | | | groups of people are reluctant to participate in |
| materials are collected and used as "raw" materials | | | | recycling, no matter what incentives are given, and |
| for new products. | | | | some property types make recycling harder. Older |
| There are three steps in recycling: 1. Materials are | | | | flats for example have only single rubbish chute. |
| collected. 2. Materials are processed and | | | | This means that in most areas if recycling is to be |
| manufactured into new products. 3. Consumers | | | | taken much above 15% to 2o%, additional separation |
| purchase the goods made with reprocessed materials. | | | | of the waste will be needed. This is called mechanical |
| Materials are either source-separated and collected, | | | | sorting, and carried out in MRFs (Materials Recycling |
| or collected without segregation. The latter is often | | | | Facilities) and these may also be called MBT |
| called black-bag waste, due to the colour of the bags | | | | (Mechanical Biological Treatment) Plants when they |
| used in most countries. | | | | include a method for biologically treating the |
| Before we go any further though, we should | | | | putrescible (organic) content after mechanical sorting. |
| consider what the average typical analyses of | | | | Mechanical Sorting of Household Refuse |
| household refuse in the UK might contain. Detailed | | | | This is usually done to increase the proportion of |
| lists are available on the web for the contents of | | | | material which is separated, and very many of these |
| these bins and wheelies, but in short the components | | | | sorting plants will be needed in the next few years |
| can be classified as putrescibles, paper, glass, plastics, | | | | to achieve EU targets for improved and much higher |
| metals, textiles, unsorted fines, and unclassified | | | | recycling rates. |
| material | | | | Mechanical Sorting can also be undertaken to recover |
| The largest quantities are of paper (and card), and | | | | additional recyclable materials not already separated |
| putrescible fractions, and together these contribute | | | | at source, or simply to provide a better feedstock |
| most of the organic matter and moisture content of | | | | for incineration or production of refuse-derived fuel. |
| the waste. Plastics make up a large and increasing | | | | Dry pulverising and screening is the most common to |
| proportion of the volume. | | | | provide a crude separation into an oversize |
| Another contributor to waste is Household Recycling | | | | combustible "paper and plastics" fraction and an |
| Centre or Civic Amenity Site waste. Civic amenity | | | | undersize "putrescible and glass" fraction for |
| waste contains large and variable proportions of | | | | anaerobic digestion or conventional composting. Wet |
| wood and garden wastes, building rubble, furniture | | | | pulverising will direct more of the paper into the |
| and miscellaneous large objects. | | | | "putrescible and glass" fraction. |
| | | | Density separations and air-classification techniques |
| Source Separation | | | | can further separate and concentrate the heavy |
| Source separation recycling schemes are the lowest | | | | glass and light plastics to provide improved materials |
| cost, and most sustainable and are preferred. They | | | | recovery and a wider range of recovered products, |
| are likely to concentrate on the easily recognisable | | | | and there is a "trade-off" between product quality |
| metal, glass and plastics fractions to provide clean | | | | and the yield of any selected fraction. |
| feedstocks for recycling. Together for household | | | | Conclusion |
| waste these can be assumed to comprise about a | | | | There is a rapidly increasing demand for expansion of |
| quarter of the wet weight and a similar proportion of | | | | the waste industry, and even if the public do their |
| the dry weight of the refuse. | | | | best to recycle, we will have to carry out more and |
| The paper fraction comprises mostly newsprint, | | | | more sophisticated waste separation as the target |
| which is easily separated but difficult to recycle | | | | rates rise. This will be achieved by source separation |
| economically as there tends to be more paper | | | | and by mechanical separation techniques in facilities |
| available from recycling than is used by industry. The | | | | called MRFs and MBT Plants. In fact these plants will |
| glut which results depresses the value of the | | | | include a wide variety of processes of which we |
| recycled material. | | | | have only touched the tip of the iceberg in this |
| So, source separation will only be effective for a | | | | article, and which are described in detail at Waste |
| proportion of the wastes, and it will not be suitable | | | | Technology and Mechanical Biological Treatment |
| everywhere. Some inner city areas find that certain | | | | (MBT). |