France’s options for organic waste

France should consider building large incinerators and industrial plants to recover energy and minerals from human and animal waste, says a new report.

But the Science and Decision Unit of the French National Centre for Scientific Research (CNRS) warns that France needs to choose carefully amongst different methods of treating organic waste to gain the public’s approval and minimise the environmental impacts of treating waste.

France produces 600 millions tonnes of waste a year, two thirds of which is organic. Agriculture is responsible for 94% of organic waste, followed by municipal (5%) and domestic (1%) waste. Since 1992, the amount of sludge produced by French wastewater plants has increased by 50%, says the CNRS report.

France must weigh up the different methods of waste treatment and recovery with the aim of abating global warming by replacing fossil fuels with biomass, reducing the amount of artificial fertiliser spread on farmland and limiting the mining of minerals such as potassium, says CNRS. But the choice of method must be based on local needs, the costs of collecting and storing waste, the need to minimise unpleasant odours and the limits of nitrogen and phosphorus loading onto land, warns the report.

A further complication is the difficulty of cost-benefit-analysis of different methods because of variations in taxes and subsidies. There are also risks associated with methods such as the spreading of waste on food crops, although these can be minimised by spreading 18 months before harvest to prevent pathogens from entering the food chain. Heating and composting also reduce pathogens in sewage.

In 1999 only 2% of farmland was treated with sludge. Should France decide to spread more sewage onto agricultural land, says the report, a plant handling waste from 3,000 people would require 30 hectares to ensure a maximum loading of 150 kg of nitrogen and 100 kg of phosphorus per hectare of soil. Pig and poultry waste poses even more of a problem because it is particularly rich in phosphorus.

France currently incinerates 15% of its sewage. If more sludge were to be incinerated, says the report, the average incinerator should manage at least 30,000 tonnes of waste a year, with the cost per tonne of waste halving when capacity jumps from 20,000 to 150,000 tonnes. Incinerators designed to process several hundred thousand tonnes of waste a year would be ideal and could generate €30 per tonne of waste in revenue. Pyrolysis is another alternative, best suited to small quantities of waste, but this option is still being debated, says the report.

Better controls over the handling of waste, with sanctions in the case of breaches in the law, would improve public confidence in practices such as sewage spreading on land. Finally, France could establish an industrial process for turning sewage into fertiliser products competitive with commercial ones. But while this approach is at the heart of European policy, it receives little attention in France, concludes the report.

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