Draft PPS18: Renewable Energy
Annex 1 Technology: Emissions to Watercourses
B33. A generating station may require a supply of water for steam production and condensing. Where water supplies present a problem, air cooling can be employed for steam condensing and other duties – thus reducing net abstraction to low levels. Advanced conversion processes such as gasification and pyrolysis may need lower levels of water use, depending on the technology.
B34. A generating plant will also have releases to the public sewer system comprising treated boiler drainings and condensate, effluent from the water treatment process and surface water run-off. Effluent from gasification plant may need treatment to remove organic contamination before release to the sewer.
B35. Large wood chip piles may produce liquids that could leach to watercourses, so a collection ditch may be required around the storage area. With regard to run-off water quality from wood stores, recent research indicates that nitrate concentrations are likely to be well below the 11.3 mg/l NO3 N maximum for drinking water specified in the Nitrate Directive. NH4 N concentrations are also likely to be well below the mandatory limits of 1.5 and 4.0 mg/l specified in the Directive.
B36. The Biological Oxygen Demand (BOD) values of run-off water are likely to be low (10 milligrams per litre) in comparison with agricultural effluent like manure slurry (10,000-30,000 mg/l), raw domestic sewage (300-400mg/l) or treated domestic sewage (20-60 mg/l).