Modification of UK municipal activated sludge plant to incorporate onsite sludge digestion

Bassey O. Bassey1, Omoruyi P. Odigie1, Tochukwu O. Ajare1 and Funsho M. Oloruntoba2

1Coventry University, Coventry, United Kingdom

2University of Port Harcourt, Port Harcourt, Nigeria



A pocket ASP in Warwickshire County, United Kingdom, treats combined wastewater for 10,500 PE; with current discharge consent of 25/45/5 (BOD/SS/NH3). Sludge produced is presently trucked fortnightly to another treatment facility. There are 15 nearby sewage works with no sludge processing facilities, with combined capacity of 200,000 PE. A proposed petrochemical plant and university sewer are to channel their effluents to the ASP. Techno- economic evaluation of two options, plant upgrade for onsite sludge processing and biogas generation as against maintaining the status quo, forms the basis of this paper. The most appropriate design solution to retrofit the current plant, justification for design options selected, efficiency considerations, as well as the project delivery plan are presented. It was found that constructing anaerobic digesters within the retrofitted facility would be more economical than transporting the massive load of anticipated surplus activated sludge to the third party owned facility, as sludge mass balance and cost estimations indicate. Successful negotiations with the surrounding sewage works would also enable the operator achieve a shorter payback period for the project, while the produced biogas would power the entire facility and the excess sold to the national grid.  Lessons learnt would be useful for operators, contractors and consultants involved with similar projects in various parts of the world.


Anaerobic digestion, ASP, biogas generation, onsite power generation, population upsurge, plant retrofit, process optimisation, sludge dewatering, sludge thickening.


Larger volumes of wastewater sludge are generated by the day as a result of the increase in wastewater treatment plants, occasioned by global growth in urban population. Sewage sludge, which industry players now euphemistically term ‘biosolids’, is mainly a by-product of primary, secondary and tertiary wastewater treatment. It constitutes the largest volume of solid waste produced by municipal sewage works. Its processing, utilisation and disposal are easily the most difficult and expensive operations of city councils today (Yan et al. 2014). Being 95% water, sludge must undergo several treatment processes before its final reuse or disposal. Most of the sludge generated was traditionally disposed of in incinerators, landfills or ocean dumping, leaving very little for agricultural reuse. However, with stricter environmental legislation and monitoring, more elaborate sewage treatment became inevitable and the volume of sludge to be treated or disposed increased. Subsequent regulatory concerns about air and water quality as well as technological advances in recent years have seen the evolution of thermal sludge processing technologies that turn the waste into wealth (FRM 2013, Veenstra 1997).

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