The larger deal, worth 9.9 million levs, concerns the reconstruction of the Sliven waste water treatment plant (WWTP), ViK Sliven said in a notice to the public procurement agency.
The second contract envisages reconstruction of the Nova Zagora WWTP.
The tender for the larger deal attracted three offers, while two bidders tabled offers for the other deal.
Both contracts will benefit from EU financing under operational programme Environment 2014-2020.
According to registry agency data, Nivel Stroy and Aqua Construction hold equal stakes in the tie-up.
(1 euro = 1.95583 levs)