Starting up a New Advanced Digestion Technology
Buchanan, A.1, Chan, T. F.1, Riches, S.2, Brookes, A.2, Brown, C.3,
1=Black & Veatch, 2=Anglian Water, 3=Imtech
(free)
Abstract
Four water recycling sludge treatment centres (STC) were upgraded by Anglian Water during AMP5 to produce an Enhanced Treated sludge product for recycling to agricultural land, utilising their new HpH pre-treatment technology. The HpH pre-treatment is followed by traditional mesophilic digestion and sludge dewatering. The biogas generated by the digestion processes is harvested and used in CHP (combined heat and power) engines to generate electricity and heat. The electricity is firstly used onsite and excess exported to the grid. The heat recovered from the CHP engines is used in two forms; hot water from the engine cooling circuit is used to pre-heat sludge received by the process via a hot water / sludge heat exchanger, and steam raised from exhaust gas is injected into the sludge to pasteurise it. At three of the sites, the centrate liquors from the sludge dewatering are being treated to reduce the ammonia concentration prior to returning it to the head of the water recycling centre. All four of the STCs were existing operational sites and construction and commissioning activities were sequenced to have minimal impact on operation.
Changing over from traditional digestion to advanced digestion involved changing or establishing new biological cultures within the existing (2 sites) or new digesters (2 sites). This paper aims to discuss the different options considered, lessons learnt from previous AD projects, as well as providing data to support the chosen methodology and its results.
Keywords
Commissioning, Enhanced Treated Sludge, HPH, Digestion, New Technology, Seeding.
Introduction:
Background:
In 2005, at the beginning of AMP4, Anglian Water (AWS) set out on a strategy to replace its lime stabilisation plants and other aging sludge treatment assets with new advanced digestion technology. During AMP4 five advanced digestion facilities were constructed at Cambridge, Kings Lynn, Milton Keynes, Northampton and Norwich. Following the successful delivery of the AMP4 strategy AWS has chosen to continue with this strategy with the ultimate aim of treating all of its raw sludge make via advanced digestion to an enhanced treated standard by the end of AMP6, in 2020.
This paper is a case study looking at the delivery of the four new advanced digestion facilities commissioned in the current AMP5 investment period; namely the plants constructed at Basildon, Ipswich (Cliff Quay), Colchester and Grimsby (Pyewipe). Although AWS are happy with the performance of the AMP4 sites, HpH was chosen as the advanced digestion pre-treatment stage for the AMP5 sites. Colchester HpH plant, with part of one of the digesters in the background to the right, is shown in Figure 1.
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