The efficiency of home composting programmes and compost quality

Highlights

• High moisture but good compost quality, reaching 12.8 C/N ratio and 2.1% N (n = 90).

• As for the heavy metals, 94% of the samples were suitable for agricultural use.

• Home composting programmes showed an efficacy of 77% in the capture of organic waste.

• Home composters treated 380 kg/unit or 126 kg/person per year of biowaste.

• Results support composting of all organic wastes including meat and fish remains.

Abstract

The efficiency of home composting programmes and the quality of the produced compost was evaluated in eight rural areas carrying out home composting programmes (up to 880 composting bins) for all household biowaste including meat and fish leftovers. Efficiency was analysed in terms of reduction of organic waste collected by the municipal services. An efficiency of 77% on average was obtained, corresponding to a composting rate of 126 kg/person·year of biowaste (or 380 kg/composter·year). Compost quality was determined for a total of 90 composting bins. The operation of composting bins by users was successful, as indicated by a low C/N ratio (10–15), low inappropriate materials (or physical contaminant materials, mean of 0.27 ± 0.44% dry matter), low heavy metal content (94% of samples met required standards for agricultural use) and high nutrient content (2.1% N, 0.6% P, 2.5% K, 0.7% Mg and 3.7% Ca on average, dry matter). The high moisture (above 70% in 48% of the samples) did not compromise the compost quality. Results of this study show that home composting of household organic waste including meat and fish leftovers is a feasible practice. Home composting helps individuals and families to reduce the amount of household waste at the same time gaining a fertiliser material (compost) of excellent quality for gardens or vegetable plots.

Introduction

Home composting has great potential for the sustainable management of organic waste generated in the home, gardens and vegetable plots. The implementation of home composting in recent years has been very intense in several areas of Spain, such as Galiza, Basque Country, Navarre, Catalonia and others (Soto, 2014). A similar trend is observed in many other parts of the world (Smith and Jasim, 2009, Adhikari et al., 2010, Faverial and Sierra, 2014). Adhikari et al. (2010) estimated a potential for decentralised composting systems to accommodate up to 50% of generated municipal organic waste in Europe and Canada, thus reducing costs and greenhouse gas emissions by 34–50 and 40%, respectively, as compared to standard landfill disposal.

Properly managed, important economic and environmental benefits are obtained by home composting (Andersen et al., 2012, Faverial and Sierra, 2014, Vázquez et al., 2015). The combined option of segregating domestic biodegradable waste at the source and directing it to home composting is considered a valuable preventative action which contributes to reducing the generation of household waste (Tatàno et al., 2015). Individuals or family users may benefit from a reduction in the rate of service of waste management, while gaining a fertiliser material (compost) with excellent quality for gardens or vegetable plots. Councils and other entities involved will benefit from a reduction in the costs of collection and waste treatment. This is important from the economic point of view, because waste collection is becoming more common in rural areas of low population density where it is usually accompanied by a revenue deficit. This deficit is caused because the costs of waste collection in rural areas are higher than the service tax applied. From the environmental point of view, the non-necessity of collection, transportation and treatment of this waste implies a clear benefit by reducing all kinds of impacts, in addition to saving fertilisers from other sources.

Some scientific studies assessed the environmental sustainability of home composting, comparing various operating options among them and with other waste treatment systems, such as industrial composting, incineration, landfilling or co-evacuation with wastewater (Martínez-Blanco et al., 2010, Chan et al., 2011, Andersen et al., 2012, Lleó et al., 2013, Adhikari et al., 2013). These studies were based on gas emissions monitoring and life cycle assessment and conclude that home composting is as, or even more, sustainable than other options of biowaste treatment and that the main impact factor is related to the greenhouse gas emissions. On the other hand, the intensity in the use of the domestic composters also affects the environmental balance of this alternative in organic waste management, since an analysis of the life cycle identified the composting bin manufacturing as one of the main factors causing emissions of greenhouse gases (Martínez-Blanco et al., 2010). However, the information about compost quality continues to be scarce and a lack of data exists about the efficiency of composting programmes, i.e. the fraction of biowaste diverted to home composting as a function of the number of composting bins used.

It is important to quantify the amount of waste processed by home composting, in order to determine the consequent reduction of organic waste at source (Torras, 2010). Because of the environmental impacts of composters manufacturing (Martínez-Blanco et al., 2010), a low use of composters could not justify the promotion of their installation by waste management responsible bodies. There are different procedures to calculate the amount of organic waste treated in compost, that is, to determine the efficiency of home composting (Puig et al., 2008, ADT, 2009, Resse and Bioteau, 2012). In this study, we chose to determine the real impact of home composting programmes in reducing amounts of organic waste managed by the municipal services of collection and disposal, in specific areas.

In rural areas where a high percentage of households have been equipped with home composting, the quantitative determination of the incidence of home composting programmes (i.e. the composting programme efficiency) in the amount of organic waste collected by local waste services is possible. In these areas the content of organic waste going into municipal bins should decline sharply, allowing the efficient use of a single waste container for collecting the resulting dry fraction. This would lead to a sharp reduction in costs of collection, transportation and waste treatment in rural areas.

The destination of domestic compost is always the vegetable or family garden (Adhikari et al., 2010, Scheromm, 2015). The quality of domestic compost has environmental and public health significance to their users, and society in general (Domingo and Nadal, 2009). One of the crucial aspects of the quality is the chemical composition and the level of contamination with heavy metals, something that is regulated for commercial plant composts, for organic amendments and for compost use in agricultural activities. Other aspects of compost quality are its stability and fertiliser power (Vázquez et al., 2015), and the presence of physical contaminants resulting from inappropriate waste sorting at home.

Current limited scientific literature suggests the properties of home compost are within the compost quality limits and similar to industrial compost from separated organic waste sources (Martínez-Blanco et al., 2010, Andersen et al., 2012, Karnchanawong and Suriyanon, 2011), except for moisture content, which was usually higher. However, available data is scarce and restricted to only a few parameters, mainly moisture content, volatile solids, carbon and nitrogen, while other characteristics are rarely reported. Moreover, the majority of studies were carried out under well-controlled experimental conditions in small scale pilot composting bins but more rarely in field applications of home and other small scale composting systems (Smith and Jasim, 2009, Faverial and Sierra, 2014, Tatàno et al., 2015).

Therefore, the objectives of this research are: (1) to determine the efficiency of home composting programmes, and (2) to determine the quality of the compost produced in the local programmes of home composting. Composting efficiency has been determined in eight rural areas corresponding to three Galician councils while 90 compost samples from eight Galician councils were analysed in order to determine the compost quality.