Integrated waste disposal strategy for the Orkney Islands - A case study

The Orkney Islands are situated several miles off the north east coast of Scotland and comprise about 40 separate islands, of which about 16 have a significant number of inhabitants. The total population is about 20,000 with 7,500 living in Kirkwall, the main town. The EU Urban Waste Water Treatment Directive (UWWTD) has presented the Orkney Islands Council with an opportunity to develop an integrated waste disposal strategy for the entire group of islands, The problems which must be overcome are common to many island communities with limited land availability and seasonal industries based on agriculture and fishing. The waste disposal strategy developed by Orkney Islands Council provides an integrated solution to a complex problem and takes into account the shortage of available land for sludge disposal and the effect of effluent treatment costs on the economics of interdependent island industries. The strategy involves the construction of a new sewerage system to intercept the Kirkwall outfalls and deliver the sewage to a new treatment site prior to long sea outfall discharge. The most significant industrial discharges each contain a very high proportion of soluble BOD. As a result, primary treatment alone cannot achieve the reductions is SS and BOD required by the UWWTD. Some industrial. effluents will therefore be pre-treated before discharge to sewers. The sludge disposal strategy has been developed to provide sustainability and outlet security. Accordingly two disposal routes have been proposed. These are land disposal or drying and co-incineration with domestic waste in a new incineration complex. Sludge from the outlying communities will be dewatered using a mobile centrifuge before being transported to Kirkwall for ultimate disposal.