Waste recycling

Recycling waste means that the material is reprocessed before being used to make new products. The reprocessing activities can have an impact on people’s health and the environment, but these impacts are usually lower than those from making the product from new, raw materials. Recycling means treating the materials as valuable resources rather than as waste. It has many benefits but it is important to have a market for the end product, otherwise the process will not be economically sustainable.

The options for recycling depend on the type of waste. For example, waste paper can be broken down to its fibres in a process called pulping. The pulp is cleaned and then formed into new paper to be used for printing or packaging. Waste metals and glass can also be recycled by melting them down into new raw materials. Sheet metals can be beaten and reformed into new products (Figure 8.3). Plastic bottles can be ground down and used to make plastic rope or plastic coating for electric wires. For some wastes, recycling involves complex technical processes and requires specialised machinery, but others can be recycled more simply and on a small scale. All types of organic waste can be recycled by composting, which can be carried out at home or on a larger scale. Composting is described in Section 8.5.2.

Figure 8.3 Large metal containers can be cut and reformed into new products like these sieves and stoves.

Waste separation

It is difficult to recycle materials once different wastes have been mixed together, so the first stage of the recycling process is to separate the materials into different categories. This is called waste segregation or separation at source and should be done by the householder when the waste items are finished with and discarded. Waste is separated by placing the different categories of waste into different bags or containers.

The degree of separation required will depend on the recycling opportunities that are available, but it is important to separate ‘dry’ and ‘wet’ materials. The simplest method of separation is to keep food waste separate from the remaining materials so that the food waste can be composted or used to make biogas (see Sections 8.5.2 and 8.6). If korales are active in the area, they may ask householders to keep all their recyclable materials (paper, metals, plastics and glass) together, or ask for just one or two materials to be separated.

If waste is not separated at the source, it ends up at a disposal site where all the waste is mixed up so separating the different types becomes much more difficult and hazardous. In many developing countries, collecting waste for recycling is often conducted by the informal sector. Such work can be done in a very labour-intensive, unsafe and polluting way, and for very low income. Often young children are employed as collectors. Part of a WASH team’s job is to help put the recycling industry on a more formal basis. This is another aspect of waste management that requires collaboration among stakeholders, including the informal sector and other concerned partners, to help improve the working conditions and provide protective equipment and training to the korales and other waste collectors.

It is possible to set up a more formal scheme to collect recyclable materials where the collectors provide separate receptacles for recyclable and non-recyclable wastes. Although separation has the advantage of promoting recycling, it also has the disadvantages of higher collection costs and needing special equipment and additional workers to collect each type of material. Therefore, in most urban and peri-urban areas, recycling collections are carried out by the informal sector.

Once separated materials have been collected from householders, they are passed on to merchants and eventually to the industrial operations that transform the wastes back into useful raw materials or products. Much of this part of the recycling chain falls outside the work of a local WASH team, but team members can still help people to become more aware of the importance of waste recycling and encourage them to separate materials for collection.

Composting

Composting is the process where biodegradable organic wastes (food and garden waste) are converted into compost in a natural biological process. Composting can be done by individual householders and community groups or on a commercial scale. On the larger scale, the waste from an entire town or city could be composted if sufficient land, labour and equipment is available. The benefits of composting are not only the reduction of waste, but also the production of compost which is a valuable soil improver. Soils treated with compost are better able to withstand droughts and are more fertile because plant nutrients are returned to the soil, which reduces the need for manufactured fertilisers. It is possible to add a certain amount of animal manure to residential waste for composting, which may help with other waste problems in the community and adds to the amount of useful soil improver that is made.

Refer back to Table 7.1 in Study Session 7 and estimate what proportion of the municipal waste from urban areas can be composted.

Show answer

According to the data in Study Session 7, municipal waste contains 44% food waste and 12% garden waste making a total of 56%, so more than half of the waste can potentially be composted.

As an urban WASH worker you may be required to help individuals or communities set up and operate composting processes (Figure 8.4). The stages in the composting process are outlined below.

Figure 8.4 The composting process.

  1. Separation of compostable materials: It is important to begin with an uncontaminated input to the process. Nearly all organic wastes can be composted, but if a composting pile attracts rodents and other scavenging animals it may be better to exclude meat products and cooked food from the process and just collect garden waste and raw vegetable waste.
  2. Grinding or shredding: To speed up the composting process it may be necessary to shred the raw waste before placing it in the compost pile. Shredding is normally required if a significant proportion of the waste has particles greater than about 50 mm. On a domestic scale this can be achieved simply by cutting up the waste into smaller pieces.
  3. Blending or proportioning of materials: Composting works best with the right mixture of wastes so that the moisture content and the proportions of the chemical elements carbon and nitrogen are suitable. Generally, the ideal mix for composting is three parts (buckets, for example) of ‘brown’ waste (such as leaves, hay, straw, eggshells, shredded paper, card and woody material), with one part ‘green’ material (such as grass, food waste and animal manure). ‘Brown’ waste contains a higher proportion of carbon and ‘green’ waste, contains more nitrogen and has a higher moisture content. Thus the ratio of brown waste to green waste is 3:1.
  4. Composting: Composting is normally carried out in a pile. For larger scale composting processes, piles are in the shape of long rows of waste, normally with a triangular cross-section (Figure 8.5). The ideal pile is 1.5–2 m wide and about 1.5 m high. The length of the pile is determined by the space and the amount of waste available. On the domestic scale the pile will be much smaller, forming a rounded heap. The pile can be built up as waste becomes available, but it is important to have enough material present to allow the biological processes to take place reasonably quickly, so as a guide a domestic compost heap should be at least 1 cubic metre to start the process.

Figure 8.5 Composting process: mixed waste is piled in long rows.

Composting is an aerobic process, so the pile needs to be turned regularly to introduce air. This means dismantling it, mixing the waste to introduce air and then rebuilding the pile. The first turning-over of the heap should be done after two to three weeks and then every three weeks or so. The composting process will be complete within three to six months. The composting process generates heat, so it is normal to see steam coming out of the pile.

The process is complete once the pile no longer heats up after mixing and rebuilding. The final product should be brown and crumbly and look like a good soil. If it still contains identifiable items, the process is not complete.

Summarise the advantages of composting.

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Composting provides an effective and safe way of disposing of a large proportion of a community’s waste that doesn’t involve specialised or costly equipment. It provides a valuable product that can be used by the community to improve the quality of its vegetables while reducing the need to buy fertilisers. Other wastes, such as animal manure, can also be added to the composting process.

Last modified: Tuesday, 23 August 2016, 9:25 PM