Sources of recovery
Resource recovery can be enabled by changes in government policy and regulation, circular economy infrastructure such as improved 'binfrastructure' to promote source separation and waste collection, reuse and recycling,[5] innovative circular business models,[6] and valuing materials and products in terms of their economic but also their social and environmental costs and benefits.[7] For example, organic materials can be treated by composting and anaerobic digestion and turned into energy, compost or fertilizer.[8] Similarly, wastes currently stored in industrial landfills and around old mines can be treated with bioleaching[9] and engineered nanoparticles[10] to recover metals such as lithium, cobalt and vanadium for use in low-carbon technologies such as electric vehicles and wind turbines.[11]
A limiting factor of resource recovery is the irrevocable loss of raw materials due to their increase in entropy in our current linear business model.[12] Starting with the production of waste in manufacturing, the entropy increases further by mixing and diluting materials in their manufacturing assembly, followed by corrosion and wear and tear during the usage period. At the end of the life cycle, there is an exponential increase in disorder arising from the mixing of materials in landfills.[12] As a result of this directionality of the entropy law, the potentials of rescource recovery are diminishing. This further motivates a circular economy infrastructure and business model.
Solid waste
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Main article: Recycling |
Recycling is a resource recovery practice that refers to the collection and reuse of disposed materials such as empty beverage containers. The materials from which the items are made can be reprocessed into new products. Material for recycling may be collected separately from general waste using dedicated bins and collection vehicles, or sorted directly from mixed waste streams.
The most common consumer products recycled include aluminium such as beverage cans, copper such as wire, steel food and aerosol cans, old steel furnishings or equipment, polyethylene and PET bottles, glass bottles and jars, paperboard cartons, newspapers, magazines and light paper, and corrugated fiberboard boxes.
PVC, LDPE, PP, and PS (see resin identification code) are also recyclable. These items are usually composed of a single type of material, making them relatively easy to recycle into new products. The recycling of complex products (such as computers and electronic equipment) is more difficult, due to the additional dismantling and separation required.
The type of recycling material accepted varies by city and country. Each city and country have different recycling programs in place that can handle the various types of recyclable materials.
Wastewater and excreta
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Main articles: Reuse of excreta, Wastewater reuse, and Ecological sanitation |
Valuable resources can be recovered from wastewater, sewage sludge, fecal sludge and human excreta.[13] These include water, energy, and fertilizing nutrients nitrogen,[14] phosphorus,[15] potassium, as well as micro-nutrients such as sulphur and organic matter. There is also increasing interest for recovering other raw materials from wastewater, such as bioplastics and metals such as silver.[16] Originally, wastewater systems were designed only to remove excreta and wastewater from urban areas. Water was used to flush away the waste, often discharging into nearby waterbodies. Since the 1970s, there has been increasing interest in treating the wastewater to protect the environment, and efforts focused primarily on cleaning the water at the end of the pipe.[citation needed] Since around the year 2003, the concepts of ecological sanitation and sustainable sanitation have emerged with the focus on recovering resources from wastewater.[citation needed] As of 2016, the term "toilet resources" came into use, and encouraged more attention to the potential for resource recovery from toilets.[4]
The following resources can be recovered:
- Water: In many water-scarce areas there are increasing pressures to recover water from wastewater.[13] In 2006, the World Health Organization, in collaboration with the Food and Agriculture Organization of the United Nations (FAO) and the United Nations Environment Program (UNEP), developed guidelines for safe use of wastewater.[17] In addition, many national governments have their own regulations regarding the use of recovered water.[13] Singapore for example aims to recover enough water from its wastewater systems to meet the water needs of half the city.[18] They call this NEWater. Another related concept for wastewater reuse is sewer mining.
- Energy: The production of biogas from wastewater sludge is now common practice at wastewater treatment plants. In addition, a number of methods have been researched regarding use of wastewater sludge and excreta as fuel sources.[19]
- Fertilizing nutrients: Human excreta contains nitrogen, phosphorus, potassium and other micronutrients that are needed for agricultural production. These can be recovered through chemical precipitation or stripping processes, or simply by use of the wastewater or sewage sludge. However, reuse of sewage sludge poses risks due to high concentrations of undesirable compounds, such as heavy metals, environmental persistent pharmaceutical pollutants and other chemicals.[13] Since the majority of fertilizing nutrients are found in excreta, it can be useful to separate the excreta fractions of wastewater (e.g. toilet waste) from the rest of the wastewater flows.[20] This reduces the risk for undesirable compounds and reduces the volume that needs to be treated before applying recovered nutrients in agricultural production.
Other methods are also being developed for transforming wastewater into valuable products. Growing Black Soldier Flies in excreta or organic waste can produce fly larvae as a protein feed.[21] Other researchers are harvesting fatty acids from wastewater to make bioplastics.[22]
Organic matter
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Main articles: Composting, Home composting, Anaerobic digestion, and Microbial fuel cell |
Disposed materials that are organic in nature, such as plant material, food scraps, and paper products, can be recycled using biological composting and digestion processes to decompose the organic matter. The resulting organic material is then recycled as mulch or compost for agricultural or landscaping purposes. In addition, waste gas from the process (such as methane) can be captured and used for generating electricity and heat (CHP/cogeneration) maximising efficiencies. The intention of biological processing is to control and accelerate the natural process of decomposition of organic matter.
There is a large variety of composting and digestion methods and technologies varying in complexity from simple home compost heaps, to small town scale batch digesters, industrial-scale enclosed-vessel digestion of mixed domestic waste (see mechanical biological treatment). Methods of biological decomposition are differentiated as being aerobic or anaerobic methods, though hybrids of the two methods also exist.
Anaerobic digestion of the organic fraction of municipal solid waste (MSW) has been found to be more environmentally effective, than landfill, incineration or pyrolysis.[citation needed] Life cycle analysis (LCA) was used to compare different technologies. The resulting biogas (methane) though must be used for cogeneration (electricity and heat preferably on or close to the site of production) and can be used with a little upgrading in gas combustion engines or turbines. With further upgrading to synthetic natural gas it can be injected into the natural gas network or further refined to hydrogen for use in stationary cogeneration fuel cells. Its use in fuel cells eliminates the pollution from products of combustion. There is a large variety of composting and digestion methods and technologies varying in complexity from simple home compost heaps, to small town scale batch digesters, industrial-scale, enclosed-vessel digestion of mixed domestic waste (see mechanical biological treatment).
Industrial waste
Waste valorization, beneficial reuse, beneficial use, value recovery or waste reclamation[23] is the process of waste products or residues from an economic process being valorized (given economic value), by reuse or recycling in order to create economically useful materials.[24][23][25] The term comes from practices in sustainable manufacturing and economics, industrial ecology and waste management. The term is usually applied in industrial processes where residue from creating or processing one good is used as a raw material or energy feedstock for another industrial process.[23][25] Industrial wastes in particular are good candidates for valorization because they tend to be more consistent and predictable than other waste, such as household waste.[23][26]
Historically, most industrial processes treated waste products as something to be disposed of, causing industrial pollution unless handled properly.[27] However, increased regulation of residual materials and socioeconomic changes, such as the introduction of ideas about sustainable development and circular economy in the 1990s and 2000s increased focus on industrial practices to recover these resources as value add materials.[27][28] Academics focus on finding economic value to reduce environmental impact of other industries as well, for example the development of non-timber forest products to encourage conservation.
