When i try to grow bacterial biofilm I make sure that

1. I start with an exhausted starter culture

2 I limit the amount of nutrients

3 I choose the correct temperature

4 I choose a compatible surface for the biofilm to attach

5 I allow the biofilm more time to form than I would do for a planktonic suspension.

6 Usually organisms require some kind of stress to form a biofilm

It is very difficult to answer this question without knowing the strains you are working with. Typically, microalgae don't form strong biofilms (compared to heterotrophs). Their EPS generally has low protein and high polysaccharide, which is not good for adhesion. First thing to do is to investigate EPS production by consortium, both soluble and bound. Under different conditions, EPS production can be enhanced. Find the conditions. If your consortium is bacteria contaminated, it often helps. Next, the substratum - charge, texture, light availability - all are crucial.

As pointed above by Gerry, give time. Algae double in 20 h (optimistic scenario), and has low EPS productivity. It would take several weeks to produce mature biofilms.

Thank you Mr Gerry and Mr Prashant for your valuable suggestions. I will try to work on your suggestions.