Your idea sounds very interesting. Just try a preliminary experiment using the fungus which is available and then focus on the downstream processing of the citric acid and its estimation as a function of the substrate utilized.

Independently of the waste, the principles of a SSF process are always the same. The main point is the optimization of the process parameters. Downstreaming, as Jai says, is another important part of CiOH production.

Here is an article on optimization of organic acid production with a simultaneous solubilization of rock phosphate

Optimization of Aspergillus niger rock phosphate solubilization in solid‐state fermentation and use of the resulting product as a P fertilizer

GO Mendes, NMRM da Silva, TC Anastácio, NB Vassilev, JI Ribeiro Jr, ...

Microbial biotechnology 8 (6), 930-939

Hi,

You can use the dates waste.