Two more unions — the Hawaii Laborers’ Union Local 368 and the Operating Engineers Union Local 3 — today endorsed Kirk Caldwell for mayor.

The setting for their announcement — the Sand Island Wastewater Treatment Plant — was used to raise concerns about the city’s sewer system. Caldwell, according to a press release, said Mayor Peter Carlisle should be doing a better job working with the Honolulu City Council to construct a second digester to turn sewage sludge into fertilizer pellets.

Carlisle’s had trouble on that front. Just last week the administration said it would not cancel its contract with Synagro, and the council threatened to cut the $24 million project from the mayor’s capital budget. It promises to be one of the fiercest budget battles this year.

Read Civil Beat‘s previous coverage of union endorsements in the 2012 mayoral election: Kirk Caldwell, Friend of the Working Man

Here’s a video the campaign put out after the event:

(Photo courtesy Kirk Caldwell for Mayor)