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