The group has sold the interest in UBB Waste (Gloucester) Holdings, the owner of the energy from waste facility at Javelin Park near Gloucester, to Urbaser Investment.
The project reached financial close in February 2013, but faced major delays after Gloucestershire County Council refused planning permission for the £180m plant.
In November 2015, the council finally gave the go-ahead to the deal, after an intervention from then-Communities Secretary Eric Pickles, who backed the plans and returned them to the local authority for further consideration.
Balfour also announced the sale of a 50% interest in the Moretti multifamily housing community in Birmingham, Alabama to Henssler Capital.
The firm said the two disposals provided a combined gain of £25.8m, which it said was “in line” with its expectations for 2023 gains on disposal of £15 - 30m.