The projects are designed to reduce the impact of discharges to the River Clyde from the waste water works.
The first project involves designing and delivering a tertiary chemical dosing plant. The second project also expected to cost around £55m will involved design and building a granular activated sludge plant.
Scottish Water said it had split the work into two project races to improve flexibility in delivery but would prefer to award both jobs to a single preferred bidder.
The water company is presently determining the treatment process to be adopted and the process provider will be named as nominated or novated as subcontractor to the lead construction partner.
PQQ documentation will be released on the Public Contracts Scotland — tenders website, with bids due to be invited from around five firms by the end of September.