Proceedings

The Eco-solids Process (ESP) is an advanced lime stabilization process, with numerous
benefits over standard systems. Recent work investigating the process has identified further
efficiency savings to optimise the process and significantly reduce the operating costs.
Having considered the reaction kinetics of the lime reacting with the sludge we have shown
the benefits of recirculating treated sludge into the mixing hopper at the reactor inlet.
Increasing the amount of recycle provides two main benefits; increasing the conversion of the
lime and making the temperature profile of the sludge in the reactor more uniform. This latest
work has identified that a recycle rate in the order of 2-3 will provide the optimum recycle rate.
This increased recycle significantly reduces the amount of lime required in the process,
typically by half, and will still produce a stable Enhanced Treated or Class A/EQ biosolid.

KEY WORDS
Alkaline disinfection, biosolids, enhanced treatment, lime, pathogens, recirculation