Upgrading a sludge treatment facility to handle the impact of the Freshwater Fisheries Directive
Minall,R.1, Hemfrey, J.2, Green, S.3 and Ellis, T.3, 1ARUP, UK, 2Earthtech Morrison, UK, 3Yorkshire Water, UK
(free)
The Freshwater Fisheries Directive (FFD) has imposed stricter regulations upon contaminants discharged to receiving watercourses, creating significant improvements within the waterborne environment. However the impact of the legislation has necessitated the introduction of new activated sludge treatment processes, which are both costly to operate and yield more sludge than traditional attached growth processes.
This paper describes the significant efforts made by one water utility to upgrade one major wastewater treatment works to achieve the requirements of the FFD. A sludge treatment facility has been present on site since the 1970’s and had been relatively underutilised, however the increased sludge yields have presented an opportunity to refurbish and renovate the existing anaerobic digesters bringing them back into full service. In order to handle the sludge, the site has become a sizeable sludge handling centre with dedicated process streams.
Where possible existing assets have been reused and upgraded, however new assets include the provision of pre-digestion thickening and the installation of decanting centrifuges to dewater digested sludges. The opportunity created by the significant increase in sludge to generate energy has resulted in the installation of up to 1MW electrical generation and 1.2MW of heat generation using Combined Heat and Power (CHP) units, which heat the digesters and partially offset the operational cost of the new processes
In order to produce an advanced treated product, the dewatered, digested sludge is subject to high rate composting with municipal green waste and phyto-conditioning to destroy any remaining harmful materials that may remain within the product.
