Garden waste arising from private households represents a major component of the biodegradable municipal waste stream. To design effective waste valorisation schemes, detailed information about garden waste is a prerequisite. While the biochemical composition of this material is well documented, there is a lack of knowledge regarding both the quantities arising, and quantities entering the services operated by waste management authorities. This work studied the quantities of garden waste arisings at urban and rural households along with the disposal methods used. A door-to-door interview survey, an analysis of kerbside collections of garden waste, and an assessment of materials brought by citizens to a waste recycling site were carried out in Hampshire, UK. If extrapolated nationally, the results indicate that households in England produce an average of 0.79 kg of garden waste per day, or 288 kg per year. On a per capita basis, this corresponds to an annual arising of 120 kg per person, out of which around 70% enters the collection schemes of the waste management authorities. The quantity generated by rural and urban households differed substantially, with rural households producing 1.96 ± 1.35 kg per day and urban households 0.64 ± 0.46 kg per day. Rural households adopted self-sufficient methods of garden waste management such as home composting or backyard burning to a much greater extent compared with urban households. Less than half of the generated rural garden waste entered services operated by the waste collection authorities, while urban households strongly relied on these services. A detailed breakdown of the disposal routes chosen by urban and rural householders can support authorities in tailoring more effective waste management schemes.

The Bioganix in-vessel composting system at Leominster, UK, received 33 515 t of waste from January 2006 to December 2007, of which 9200 t was source-segregated biodegradable municipal waste (BMW). The process operated with a nominal in-vessel retention time of 4 days. Mass balances indicated 17·1% reduction (excluding reject materials). The process was estimated to consume 186 kWh/t of waste processed as electrical energy for static plant and a further 9·6 kWh as diesel for mobile plant. Taking into account transportation and application of the compost, the estimated consumption was ~560 kWh/t of waste processed, calculated as primary energy (including electrical conversion). 96·7% of this was for processing; transportation consumed 1·3% and application 2·0%. The mixed waste compost had a high nitrogen content but, for a typical source-segregated biodegradable municipal waste, the energy potentially offset from nitrogen fixation is likely to be considerably less than that used in processing.

No abstract