Anglian Water’s New Scheme Will Treat 80 000 tDS/year to Produce Enhanced Treated Sludge for Agricultural Use and Generate 5 MW of Renewable Electricity
Hoyland, G.1, Newton, J.1, Riches, S.2, and Bland, R.2
1Mott MacDonald, 2Anglian Water
(free)
Anglian Water’ new sludge treatment scheme has been designed to treat annually 80 000 t of sludge solids to the enhancedtreated standard. The production of such sludge in the form of cake will increase the agricultural outlet capacity and ease
sludge disposal for the foreseeable future. Currently, the sludge is treated to the conventional treated standard using either
mesophilic anaerobic digestion (MAD) or lime dosing.
The new treatment will be provided at four large existing sludge treatment centres. Sludge throughput will be increased at all
four centres by importing sludge, mostly in the form of cake, from other works where any treatment, other than dewatering,
will be shut down. Sludge throughput at the largest centre in the new scheme will be some three times higher than current
throughput.
In the design of the new scheme, emphasis has been placed on energy conservation. Over 5 MW of electricity will be
generated by consuming in CHP engines the biogas produced by the new treatment. This electricity will satisfy most of the
operational demand at the centres, for wastewater as well as sludge treatment. Further, the new sludge treatment centres
will be largely self sufficient in terms of the thermal requirements.
Treatment at the four centres will be provided in a phased programme and, at the time of this paper, construction has started
at one of the sites. The preferred enhanced-treatment technologies chosen for application at the centres were identified from
a wide range of such technologies, using a generalised risk analysis.
The assessment identified two preferred technologies, namely CAMBI and Monsal EEH. Both these technologies are
implemented as pre treatment plants, installed immediately upstream of mesophilic anaerobic digestion (MAD). Apart from
ensuring the digested sludge is enhanced treated by destroying pathogens, both pre-treatment technologies increase
substantially VM destruction and biogas production in the subsequent MAD and improve the dewatering characteristics of the
digested sludge, although this latter effect is much more evident in the case of CAMBI. The two pre-treatments work very
differently. CAMBI is a thermal process, in which the raw sludge at DS concentrations up to 15 w/w% is heated to 165oC,
and Monsal EEH is a biological process in which the raw sludge at DS concentrations up to 7 w/w% is treated at temperatures
up to 55oC.
This paper describes and compares the two preferred pre-treatment technologies, drawing comparisons particularly in relation
to operational requirements and risks, biogas production rates and energy balances. Developments and enhancements to
the technology, needed to reduce particular operational risks at the treatment centres, are also described.
The paper outlines Anglian Water’s Scheme, giving the reasons for choosing one or other of the pre-treatment technologies
at each particular treatment centre. A rigorous assessment of the technologies involving a range of criteria including the
capital and whole-life costs of the whole disposal route, operational risks including odour, implications for liquor treatment and
footprint requirements was undertaken for each site. A detailed sensitivity analysis is presented for one of the treatment
centres.
