What to do if there is white moss on the walls after flooding?

We have a townhouse made of ceramic bricks with monolithic slabs (20 cm) on the ground and first floors. Plastered with gypsum plaster.

We had a burst pipe on the first floor (broke the flexible connection to the faucet). Water poured on the walls, the ceiling half a day. Half the house was in the water, but well, that it flowed into the basement through the hole for the drain. It must have been 4 weeks after that. The temperature in the house is 8 to 12 degrees Celsius. The walls are plastered with gypsum plaster, almost dry.

Today we came in and there were little ginger growths. What is it?

There's white moss on the plastered concrete slab. What is it and what to do about it?

We did not put a drying gun, we thought only heating would dry out by itself. Ventilation is closed, because for some reason there is a reverse draft, but there are a few cracks.

We can demolish these walls, as they are not load-bearing, although it would be expensive.