A national plan to sharply reduce landfilling is driving the growth of green waste composting in France.
"In theory, it may seem temptingly simple to compost communities' vegetative waste," said the French Agency for the Environment and Energy Management (Ademe), but a marketable soil amendment will result only through coherent planning and "rigorous" management operations.
In 1995, the municipal green waste that can be "mobilized" for composting was generated at an estimated rate of 0.3 cubic meters per person per year, resulting in 17 million cubic meters, according to Ademe. This total includes grass clippings, leaves, tree trimmings and flower bed waste generated in yards, public parks and gardens, tree-lined streets and other public and private green spaces such as hospital grounds and sports fields.
Volumes tend to be underreported, however, due to the diversity of service providers. Meanwhile, urban environments are becoming greener; rapidly spreading housing developments have privacy screen plantings around yards; and more leisure time is boosting interest in amateur gardening.
Although approximately the size of Texas, France has climactic variations that cause regional differences in green waste amounts and types. Hot and dry summers in the Mediterranean region provide growing conditions for laurel and olive trees, while a mild and moist climate in other regions produces temperate-zone vegetation.
Outside of Paris, the population is widely dispersed among at least 20 large cities, plus numerous small cities and rural communities. Household yard waste is collected door-to-door or taken to drop-off sites, whereas green waste from other sources is collected by municipal services or lawn care companies.
As volumes continue to rise, green waste management techniques are changing, according to a study of 84 cities in 1987 and 190 cities in 1993 (see figure). Incineration rose for all green waste types despite inherent problems such as the charging of hoppers with branches, grass clippings' high moisture content and equipment damage from temperature fluctuations. Overall, about half of the green waste collected continues to be landfilled.
To counteract its landfill shortage, as of 2002, France will no longer allow land disposal of untreated wastes, including fermentable wastes, which produce nitrogen-rich leachate that can impact water quality.
Open burning is prohibited during certain times of the year and banned altogether if green waste is strictly classified as municipal solid waste. Residents sometimes illegally dump green waste outside city limits, where it accumulates in malodorous heaps.
The number of mixed green waste composting operations doubled between 1994 and 1995, Ademe reports. As of last year, about 12 percent of the nation's total volume was composted at 56 sites, counting 14 that co-compost other organic wastes (excluding the widespread city leaf-composting programs). The average size was 6,700 metric tons per year. In addition, 18 facilities were planned or under construction.
In 1995, 65 percent of the facilities were run by private companies, 25 percent by municipalities and 11 percent by farmers. At a growth rate of 10 percent per year, the trend is toward privatization.
France's basic green waste processing is known as "grinding-composting," according to Ademe. General features include a paved surface; size reduction of ligneous components (typically by hammermill); turned windrows; and screening of the finished compost (typically by trommels).
In a mass balance comparison of composting 20,000 cubic meters of green waste for six to eight months using two different windrow turners, Ademe determined the following: * A drum-type turner will reduce the original volume to 11 percent after composting and 9 percent after refining. Gross weight will be reduced to 33 percent after composting and 32 percent after refining.
* A manure spreader adapted for turning will reduce the original volume to 17 percent after composting and 13 percent after refining. Gross weight will be reduced to 33 percent after composting and 28 percent after refining.
In both cases, the moisture content will be reduced from 50 to 40 percent.
"Treating urban ... vegetative waste by grinding-composting appears to offer an alternative to the strangle hold on [other] waste management methods, while minimizing environmental harm and treatment facility damage at a cost that is noticeably lower than at sanitary landfills and can be partially recouped by selling the [soil] amendment," Ademe concluded.