Organic-waste treatment

A yellow wheel loader implements composting in a composting plant.Click to enlarge
Wheel loader being used to turn compost
Source: Tim Hermann / UBA

High quality compost and digestate for agricultural and horticultural use can be obtained from organic waste, provided that the waste is collected and composted separately and in a manner that is as environmentally sound as possible.

Table of Contents


Composting and fermentation

Compost and digestate from organic waste make for an ideal organic fertilizer for agricultural purposes, and also promote soil humus content stabilization or improvement. However, to achieve this it is necessary for organic waste to be collected separately, as this is the only way that allows for the production of quality compost and digestate that are suitable for agricultural and horticultural use. They also make an excellent substitute for horticultural peat and in this way reduce greenhouse gas emissions, and protect plant and animal habitats. However, the treated organic waste must meet the relevant quality standards and the treatment process should be as ecofriendly as possible.

In Germany, the practice of collecting organic waste separately and then composting it began around 25 years ago, and the use of recycled organic waste has risen steadily since then. According to Federal Statistical Office (Statistisches Bundesamt) figures, in 2011 around 14 million tons of organic waste were composted or converted into digestate (in biogas facilities) for use as fertilizer.

The organic waste processed at composting or anaerobic digestion plants stems from the following sources: households; yards and parks waste; restaurant and canteen kitchens; food processing plants; and agricultural residues. In 2011 alone, four million tons of organic waste were collected in bio bins from households in Germany, with yard and park residues contributing an additional five million tons. Most organic waste is still composted nowadays, and only a small portion of it is used to make biogas and digestate.

According to a study commissioned by the UBA titled Aufwand und Nutzen einer optimierten Bioabfallverwertung, in 2008 there were around 1,000 composting plants and 85 anaerobic digestion plants in Germany that used organic waste from households, businesses, yards and parks. For a complete listing of Germany’s composting and biogas facilities, see Handbuch Bioabfallbehandlung (UBA, 2012).

Compost and digestate derived from organic waste make for excellent fertilizer and promote humus formation. A study commissioned by the UBA titled Optimierung der Verwertung organischer Abfälle found that separate collection and recycling of organic waste are more ecofriendly than any other approach to organic waste management. The organic waste management alternatives investigated by the study included leaving organic waste mixed in with residual waste and then processing it at an incineration or mechanical-biological treatment facility. However, organic waste recycling is only ecologically advantageous if the waste is treated using state of the art techniques and if recycling is carried out in accordance with the highest possible quality standards. Organic waste should be processed in an anaerobic digestion whenever possible, as this allows for the energy in the waste to be used as biogas. Residues can be marketed either as liquid digestate or, after being composted, as solid digestate. This translates into a cascade that allows the energy content of organic waste to be used, followed by its substance properties.

According to the study titled Aufwand und Nutzen einer optimierten Bioabfallverwertung, only around 46 percent of consumers have an organic-waste container (bio bin) at their disposal, while the remaining 54 percent cannot or do not wish to collect organic waste separately. Expanding Germany’s organic waste container fleet could potentially increase organic waste output by two million tons. Altogether, separate collection of organic waste reduces the amount of residual household waste by up to one third. Added to this is the fact that separating residual waste from wet elements simplifies downstream processes such as mechanical sorting.

Germany’s 2012 Kreislaufwirtschaftsgesetz law is the first federal statute to require for the national level that organic waste be collected separately. This practice will become mandatory as of 1 January 2015.

The pamphlet jointly issued by the Federal Ministry for the Environment (BMU) and the UBA titled Ecologically sustainable recovery of bio-waste provides municipal decision makers with advice concerning the implementation and optimization of separate organic waste collection.


Statutory requirements for compost and digestate

The requirements concerning the properties and quality of compost and digestate derived from organic waste are set forth in the Bioabfallverordnung (Ordinance on Biowastes) of 21 September 1998, which governs the following: contaminant and hygiene parameters; allowable biowaste input; monitoring; limits on the allowable amounts of compost/digestate used on soil. In the interest of facilitating quality assessments of compost produced at composting facilities, in 2004 the UBA commissioned a study titled Neubewertung von Kompostqualitäten (A new look at compost quality), which discusses the heavy metal content of compost in Germany and the limit values mandated by the Bioabfallverordnung. The study was conducted in collaboration with the Bundesgütegemeinschaft Kompost. This organization supplied the data for the study comprising anonymized measurement data from voluntary quality assurance certifications. The study came to the conclusion that as a rule, the compost produced at composting facilities adheres to the Bioabfallverordnung limit values, and even undercuts them for the particularly toxic heavy metals that were investigated.


Statutory requirements concerning the operation of composting and fermentation facilities

The requirements governing the operation of compost and digestion facilities are governed by the regulation known as TA Luft, whose section stipulates minimum distances and to operate in enclosed structures for composting installations that are produce more than 3,000 tons of compost annually. TA Luft also defines odour and dust emission limits for composting facilities. The regulation’s section also sets forth requirements in this regard for organic-waste anaerobic digestion installations. The requirements set forth in TA Luft were to be implemented by operators of pre-existing installations by 31 October 2007.

Furthermore, TA Luft requires to survey state of the art of bacterial-emission reduction methods; this requirement was discussed at a conference titled Mikroorganismen in der Umgebung von Bioabfallbehandlungsanlagen (Microorganisms in the environs of organic-waste treatment facilities) that was held on 30 September 2004, with delegates from the BMU, BMBF and UBA in attendance. Information concerning the findings presented and discussed at the conference are available for download.