EC law could poison green agenda
The European Commission is developing new standards for sludge spread on land. If these are made law, an increasing number of water companies could opt for incineration.
The levels proposed in the EC's Working Document on Sludge, 2nd Draft (12/1/2000 ENV.E.3/LM) are very strict in comparison with the levels set in 1986 (directive 86/278). If one or more of the levels set are exceeded, it will be illegal to use the sludge on land.
Once the EC has produced final proposals for the European Council of Ministers, a formal debate will take place in 2001. It will then take two or three years for the proposed levels to be made law.
At present it is legal under directive 86/278 to use sludge containing up to 1,200mg/kg of lead. This would be cut to 750mg/kg in 2003 or 2004, 500mg/kg in the 'medium-term' and 200mg/kg in the 'long-term'. The exact schedule is still to be decided.
Permissible levels for zinc, copper, cadmium, mercury, and nickel would also be reduced, making great demands of the treatment processes employed at many STWs. In the UK treated sludge typically exceeds the long-term levels for lead, copper, cadmium and mercury. Mercury levels are already close to the first level for implementation of 25mg/kg.
Limits for several organic compounds could also be introduced. Compounds listed in the Draft include nonyl-phenols, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), halogenated organics and dioxins. Technologies capable of removing these substances are available, the critical factor being relative cost.
The UK's Department of the Environment, Transport and the Regions (DETR) has taken exception to a few of the EC's proposals, for instance the level proposed for a detergent called linear alkylbenzene sulphonate (LAS).
Jill Thatcher, sewage sludge advisor at the DETR's water quality division, told WWT: "We do not think the EC's standard is scientifically justified because although present in sludge, LAS has a very short half-life in soil, and therefore any impact would be transient." She added: "The DETR also does not believe the limits should be revised as frequently as suggested, unless there is evidence of a signif-icant risk to human or animal health. Frequent revision is likely to make farmers, food retailers and the public anxious about the safety of recycling to land ...and encourage alternative disposal options."
The UK is also likely to fall foul of measurement rules, because under the existing law it is legal to use a measurement of 'loading rate' to the soil in question, rather than actual concentrations.
If the new levels are introduced and water companies persist with land disposal, many waste streams will have to be separated to prevent toxic effluents contaminating the final sludge product. Although processes such as steam hydrolysis are capable of destroying organic compounds, heavy-metal removal is much more difficult.