April 18, 2005 | General


BioCycle April 2005, Vol. 46, No. 4, p. 75
Successful municipal program at more than 200 households shows backyard composting can play an “essential role in sustainable waste management strategies for recycling the organic fraction of MSW.”
Joaquim Mayoral and Antoni Sánchez

IN RECENT YEARS, the European policy on management of household waste has been increasingly directed towards recycling. Organic fraction of MSW – composed of kitchen, yard and pruning residuals – can account for about one-half of all household waste generated. Among the available technologies, composting is presented as one of the most promising options to recycle the organic fraction into a valuable organic fertilizer.
The region of Catalonia in Spain, with a population of over six million, is a well-developed and industrial area where the most important city, Barcelona, and its metropolitan area, include a population of over three million. Municipal solid waste produced in Catalonia reached over 3.5 million metric tons in 2002, and its destination has traditionally been sanitary landfill or incineration. However, new composting plants treating the source separated organic fraction of MSW have come into operation, most of them promoted by the local government.
In Catalonia, the composting process is traditionally conducted in industrial facilities where large amounts of organic wastes are processed. Recently, backyard composting has gained popularity in some regions of Catalonia. In backyard composting, local municipalities provide composter units to citizens and communities in an attempt to divert large quantities of organic wastes from local collection systems, adopting the programs developed in other countries, especially in the U.S.
Noncentralized backyard composting has several advantages over large composting plants. The main positive factor is the fact that municipal collection, preliminary treatment of organic wastes and marketing of produced compost is not necessary, resulting in a financial and infrastructure saving. Additionally, environmental impacts associated with collection and transport of large amounts of organic wastes are avoided. Moreover, new regulation drafts from the European Commission provide support to home and community composting, including composter supply and fiscal measures such as tax-breaks to householders who reduce the amount of biodegradable waste.
In this work, we present the results obtained in an extensive pilot program of backyard composting carried out in Catalonia. A local authority, named Mancomunitat Intermunicipal Voluntària “La Plana” (Sector El Quadro, s/n. 08519-Malla, Barcelona, Spain) distributed more than 200 individual composters among private households. Conditions for a successful experience with backyard composting were determined on the basis of the results obtained.
A survey was conducted of participants in the backyard composting program. People involved in the program had been using the composter for more than two years, and were distributed among the municipalities studied according to Table 1. In general, results from the backyard composting program were very positive, with a low percentage of withdrawals (around 16 percent in two years). Withdrawals were mainly associated to a lack of time to perform the maintenance operations of the composters. On the other hand, there is no correlation between withdrawals and a recent implementation of source separated collection systems for organics wastes, although in most cases they were “door to door” collection systems. This clearly implies a high level of satisfaction with backyard composting. In fact, most of the participants defined their experience with backyard composting as very good (68 percent) or good (24 percent). In general, backyard composting operations were perceived as a leisure activity more than a matter of ecological concern.
Different specific questions were posed to the participants in the backyard composting program, with the following results:
Organic wastes origin: Kitchen wastes (vegetable residuals) and garden wastes (grass clippings and pruning wastes) were the main organic materials composted. These two wastes were usually composted together. There seemed to be a negative predisposition to include meat and fish wastes in the composter (only six percent of participants did), although there were no reports on problems with these wastes (e.g., possible presence of rodents or cats).
Frequency of organic wastes additions: Most of the participants added wastes in a twice-a-week frequency (60 percent). The rest only used the composter in a fortnightly or monthly periodicity, which normally corresponded to second residences.
Presence of shredder: Only 11 percent of the participants owned a shredder. The necessity of shredding the wastes prior to composting (especially pruning wastes and kitchen wastes of big size) was confirmed as one of the crucial aspects in a successful composting process and reaching thermophilic temperatures. A conclusion from the study was the creation of a “mobile shredding service”, which provides a shredder for the participants in the backyard composting program.
Bulking agent: Proper utilization of a bulking agent was studied in detail due to the fact that it was a key factor in giving the material an adequate porosity. About 76 percent of the participants were bulking agent self-sufficient (from pruning wastes) whereas some of them obtained the bulking agent from neighbors. As the lack of bulking agent (and the necessity of shredding) was the reason for the majority of the detected composter failures, the “mobile shredding service” was complemented with a possible supply of bulking agent (shredded pruning wastes).
Turning: Participants conducted manual turning in different frequencies: more than once a week (eight percent), weekly (26 percent), fortnightly (20 percent) or monthly (46 percent). In general, it was observed that turning favored the composting process, especially in situations of porosity deficiency or moisture excess, so the recommendation of carrying out at least a turn per week was included.
Moisture content: Compost was classified into: excess moisture (30 percent), correct moisture (44 percent) or low moisture (26 percent). In this case, moisture was roughly estimated using the “squeeze test”. Since moisture is referred to as one of the most important parameters in the composting process, the excess moisture was corrected by adding dry bulking agent, whereas in “dry” compost water was added.
Presence of bad odors, leachates or rodents: Problems with bad odors, leachates or rodents were only detected on rare occasions. Concretely, four percent of participants reported presence of leachates (associated with excess moisture and irrigation), seven percent observed bad odors (normally in composters with very compacted materials, ammonia being the most perceived gas) and the presence of rodents or cats was detected in five percent of the composters.
Compost utilization: In all the cases, the compost produced was used by the participants in the backyard composting program. It was mainly applied to gardens and, in some cases, horticultural uses. In general, it was observed that a high degree of satisfaction in the compost’s final appearance and positive effects of the compost utilization were reported in several experiences.
Final Results
From the results obtained, it can be concluded that backyard composting is an effective method to divert organic wastes from municipal collection systems, thus providing an important saving of money. Concretely, for the community studied (26,243 inhabitants), it was estimated that the cost of traditional collection system for organic materials was around 235,000 euros/year, which could be reduced by more than 50 percent by using a massive backyard composting program.
Moreover, environmental impacts associated with collection, transport and processing of large amounts of organic wastes are removed or significantly reduced, especially those related to odor complaints or truck and machinery operation.
In the pilot program studied, the main recommendations to succeed in the composting process were: i) Shred the organic wastes, especially the bulking agent; ii) Use a sufficient ratio bulking agent:organic waste to have a highly porous material; iii) Turn the material at least once a week; iv) Avoid compaction and v) Check and adjust the moisture content periodically.
To summarize, backyard composting can play an essential role in the implementation of sustainable waste management strategies in future years, especially in the recycling of the organic fraction of municipal solid wastes.
Joaquim Mayoral and Antoni Sánchez are with the Universitat Autònoma de Barcelona in Barcelona, Spain. This study was done in cooperation with the Mancomunitat Intermunicipal Voluntària “La Plana” (Sector El Quadro, s/n. 08519-Malla, Barcelona, Spain). The authors wish to thank the special interest and dedication of David Segalés and Laura Soriano in the development of this work. This project has received financial support from the Spanish Ministerio de Ciencia y Tecnologìa (Project REN2003-00823).

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