Biodegradable waste

In domestic 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. To address this, many local waste management districts are integrating programs related to sort the biodegradable waste for composting or other waste valorization strategies, where biodegradable waste gets reused for other products, such as using agricultural waste for fiber production or biochar.

Biodegradable waste when not handled properly can have an outsized impact on climate change, especially through methane emissions from anaerobic fermentation that produces landfill gas. Other approaches to reducing the impact include reducing the amount of waste produced, such as through reducing food waste.

Collection and processing

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 as green waste. Removing such waste from the rest of the waste stream substantially reduces waste volumes for disposal and also allows biodegradable waste to be composted.

Biodegradable waste can be used for composting or a resource for heat, electricity and fuel by means of incineration or anaerobic digestion. Swiss Kompogas and the Danish AIKAN process are examples of anaerobic digestion of biodegradable waste. 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 of biogas. Kompogas produced 27 million Kwh 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.

Valorization

Crop residue

Crop residue, such as corncob, and other residues from the food processing industry, such as residues from biorefineries, have high potential for use in further processes, such as producing biofuel, bioplastics, and other biomaterials for industrial processes.

Food waste

One of the more fruitful fields of work is food waste—when deposited in landfills, food waste produces the greenhouse gas methane and other toxic compounds that can be dangerous to humans and local ecosystems. Landfill gas utilization and municipal composting can capture and use the organic nutrients. 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.

Transforming food waste into either food products, feed products, or converting it to or extracting food or feed ingredients is termed 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, including biofertilizers, bioplastics, biofuels, chemicals, and nutraceuticals. There is much potential to recycle food wastes by conversion to insect protein.

Human excreta

Reuse of human excreta can be safe or unsafe. Beneficial uses of the treated excreta may focus on using the plant-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 as water reclamation from municipal wastewater. The intended reuse applications for the nutrient content may include: soil conditioner or fertilizer in agriculture or horticultural activities. Other reuse applications, which focus more on the organic matter content of the excreta, include use as a fuel source or as an energy source in the form of biogas.

There is a large and growing number of treatment options to make excreta safe and manageable for the intended reuse option. Options include urine diversion and dehydration of feces (urine-diverting dry toilets), composting (composting toilets or external composting processes), sewage sludge treatment technologies and a range of fecal 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, and helminth eggs in feces. As the helminth eggs are the pathogens that are the most difficult to destroy with treatment processes, they are commonly used as an indicator organism in reuse schemes. Other health risks and environmental pollution aspects that need to be considered include spreading micropollutants, pharmaceutical residues and nitrate in the environment which could cause groundwater pollution and thus potentially affect drinking water quality.