Biodegradable waste includes anyorganic matter inwaste which can be broken down intocarbon dioxide,water,methane,compost,humus, and simple organicmolecules bymicro-organisms and other living things bycomposting,aerobic digestion,anaerobic digestion or similar processes. It mainly includeskitchen waste (spoiled food, trimmings, inedible parts), ash, soil, dung and other plant matter. In waste management, it also includes some inorganic materials which can be decomposed by bacteria. Such materials includegypsum and its products such asplasterboard and other simplesulfates which can be decomposed bysulfate reducing bacteria to yieldhydrogen sulfide in anaerobic land-fill conditions.[1][2]
Indomestic waste collection, the scope of biodegradable waste may be narrowed to include only those degradable wastes capable of being handled in the local waste handling facilities.[3] To address this, many local waste management districts are integrating programs related tosort the biodegradable waste forcomposting or otherwaste valorization strategies, where biodegradable waste gets reused for other products, such as usingagricultural waste for fiber production orbiochar.
Biodegradable waste when not handled properly can have an outsized impact onclimate change, especially throughmethane emissions from anaerobic fermentation that produceslandfill gas. Other approaches to reducing the impact include reducing the amount of waste produced, such as through reducingfood waste.
Biodegradable waste can be found inmunicipal solid waste (sometimes called biodegradable municipal waste, or asgreen waste,food waste,paper waste andbiodegradable plastics). Otherbiodegradable wastes includehuman waste,manure,sewage,sewage sludge andslaughterhouse waste. In the absence ofoxygen, much of this waste will decay tomethane byanaerobic digestion.[4]
In the UK, 7.4 million tonnes of biodegradable waste was sent tolandfill in 2018 having reduced from 7.8 million tonnes in 2017.[5]
In many parts of the developed world, biodegradable waste is separated from the rest of the waste stream, either by separate curb-side collection or by waste sorting after collection. At the point of collection such waste is often referred to asgreen waste.[6] Removing such waste from the rest of the waste stream substantially reduces waste volumes for disposal and also allows biodegradable waste to becomposted.
Biodegradable waste can be used for composting or a resource for heat, electricity and fuel by means ofincineration oranaerobic digestion.[7] SwissKompogas and the DanishAIKAN process are examples of anaerobic digestion of biodegradable waste.[8][9] While incineration can recover the most energy, anaerobic digestion plants retain nutrients and make compost for soil amendment and still recover some of the contained energy in the form ofbiogas. Kompogas produced 27 millionKwh of electricity and biogas in 2009. The oldest of the company's lorries has achieved 1,000,000 kilometers driven with biogas from household waste in the last 15 years.[10]
One of the more fruitful fields of work is food waste—when deposited in landfills, food waste producesthe greenhouse gas methane and other toxic compounds that can be dangerous to humans and local ecosystems.[11]Landfill gas utilization andmunicipal composting can capture and use the organic nutrients.[11] Food waste collected from non-industrial sources is harder to use, because it often has much greater diversity than other sources of waste—different locations and different windows of time produce very different compositions of material, making it hard to use for industrial processes.[11][12]
Transforming food waste to either food products, feed products, or converting it to or extracting food or feed ingredients is termed as food waste valorisation. Valorisation of food waste offers an economical and environmental opportunity, which can reduce the problems of its conventional disposal. Food wastes have been demonstrated to be valuable bioresources that can be utilised to obtain a number of useful products, includingbiofertilizers,bioplastics,biofuels, chemicals, and nutraceuticals. There is much potential to recycle food wastes by conversion toinsect protein.[13]
Reuse of human excreta is the safe, beneficial use of treatedhuman excreta after applying suitable treatment steps and risk management approaches that are customized for the intended reuse application. Beneficial uses of the treated excreta may focus on using theplant-available nutrients (mainly nitrogen, phosphorus and potassium) that are contained in the treated excreta. They may also make use of the organic matter and energy contained in the excreta. To a lesser extent, reuse of the excreta's water content might also take place, although this is better known aswater reclamation from municipalwastewater. The intended reuse applications for the nutrient content may include:soil conditioner orfertilizer inagriculture orhorticultural activities. Other reuse applications, which focus more on the organic matter content of the excreta, include useas a fuel source or as an energy source in the form ofbiogas.
There is a large and growing number of treatment options to make excreta safe and manageable for the intended reuse option.[14] Options include urine diversion and dehydration of feces (urine-diverting dry toilets), composting (composting toilets or externalcomposting processes),sewage sludge treatment technologies and a range offecal sludge treatment processes. They all achieve various degrees of pathogen removal and reduction in water content for easier handling. Pathogens of concern are enteric bacteria, virus, protozoa, andhelminth eggs in feces.[15] As the helminth eggs are the pathogens that are the most difficult to destroy with treatment processes, they are commonly used as anindicator organism in reuse schemes. Other health risks and environmental pollution aspects that need to be considered include spreadingmicropollutants,pharmaceutical residues andnitrate in the environment which could causegroundwater pollution and thus potentially affectdrinking water quality.
Landfill gas is a mix of different gases created by the action ofmicroorganisms within alandfill as they decompose organic waste, including for example,food waste andpaper waste. Landfill gas is approximately forty to sixty percentmethane, with the remainder being mostlycarbon dioxide. Trace amounts of othervolatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simplehydrocarbons.[16]
Landfill gases have an influence onclimate change. The major components areCO2 andmethane, both of which aregreenhouse gases. Methane in the atmosphere is a far more potent greenhouse gas, with each molecule having twenty-five times the effect of a molecule of carbon dioxide. Methane itself however accounts for less composition of the atmosphere than does carbon dioxide. Landfills are the third-largest source of methane in the US.[17]
Because of the significant negative effects of these gases, regulatory regimes have been set up tomonitor landfill gas, reduce the amount of biodegradable content inmunicipal waste, and to createlandfill gas utilization strategies, which includegas flaring or capture for electricity generation.
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The causes of food going uneaten are numerous and occur throughout thefood system, duringproduction,processing,distribution,retail and food service sales, andconsumption. Overall, about one-third of the world's food is thrown away.[19][20] A similar amount is lost on top of that by feeding human-edible food to farm animals (the net effect wastes an estimated 1144 kcal/person/day). A 2021meta-analysis, that did not include food lost during production, by theUnited Nations Environment Programme found that food waste was a challenge in all countries at all levels ofeconomic development.[21] The analysis estimated that global food waste was 931 million tonnes of food waste (about 121 kg per capita) across three sectors: 61 percent fromhouseholds, 26 percent fromfood service and 13 percent fromretail.[21]
Food loss and waste is a major part of theimpact of agriculture on climate change (it amounts to 3.3 billion tons ofCO2e emissions annually[22][23]) and otherenvironmental issues, such asland use,water use andloss of biodiversity. Prevention of food waste is the highest priority, and when prevention is not possible, the food waste hierarchy ranks the food waste treatment options from preferred to least preferred based on their negative environmental impacts.[24] Reuse pathways of surplus food intended for human consumption, such as food donation, is the next best strategy after prevention, followed byanimal feed, recycling of nutrients and energy followed by the least preferred option,landfill, which is a major source of thegreenhouse gasmethane.[25] Other considerations include unreclaimed phosphorus in food waste leading to furtherphosphate mining. Moreover, reducing food waste in all parts of thefood system is an important part of reducing theenvironmental impact of agriculture, by reducing the total amount of water,land, and other resources used.
The UN'sSustainable Development Goal Target 12.3 seeks to "halve global per capita food waste at the retail and consumer levels and reduce food losses along production and supply chains, including post-harvest losses" by 2030.[26]Climate change mitigation strategies prominently feature reducing food waste.[27] In the2022 United Nations Biodiversity Conference nations agree to reduce food waste by 50% by the year 2030.[28]
