Control and Stabilisation of Odorous Sludge from Fleetwood Sewage-Treatment Works

Following completion of the construction of Fleetwood sewage-treatment works in 1996, the sludge (from the plant) was causing health and safety problems for the workforce and there were complaints of odour from the local community. Problems arose due to overloading of the biological-treatment units, resulting in little or no dissolved oxygen in parts of the process. There was a need to stabilise the sludge in the short term, culminating in the need for chemical conditioning, and an investigation into operational procedures to stabilise the sludge in the long term. The sludge was successfully stabilised using ferric chloride and sodium hydroxide. The long-term stability of the sludge was further improved using operational changes (such as the inclusion of step feeding and by demonstrating the effect of load removal upstream from the existing biological process) via pilot-plant studies.