There are many related articles in this field. Firstly the solution of pollutant (e.g. dye solution) is prepared, then the nanoparticles are added to the solution.

Please have a look at the following search link:

https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=allintitle%3A+water+treatment+graphene&btnG=

And

https://pubs.rsc.org/en/content/articlehtml/2014/ra/c3ra45013a

https://www.tandfonline.com/doi/abs/10.1080/21622515.2016.1264489

https://idp.springer.com/authorize/casa?redirect_uri=https://link.springer.com/article/10.1007/s11356-017-0481-5&casa_token=wi2UZQuWiwcAAAAA:oXs3uy92a4xYRRrdjjt4mFjI_99_8vTJYb-BJSQvlv58lw90XmV_bAJdqxePsB2puMrSWscD2uFBYMy2xw

https://www.sciencedirect.com/science/article/pii/S0045653519305600

https://www.sciencedirect.com/science/article/pii/S0167732216315513

https://www.sciencedirect.com/science/article/pii/S0011916415001915

https://www.sciencedirect.com/science/article/pii/S0045653517320313

https://idp.springer.com/authorize/casa?redirect_uri=https://link.springer.com/article/10.1007/s10450-014-9615-y&casa_token=XJMwVodKQW8AAAAA:HVWvSPIxLGcx_AQRJecKmsqMQUcY1S71cs-BEMaOCeVJLuqapAs_cUSGrd1fV69ebacWglS8PTRcoqjEhg

https://www.tandfonline.com/doi/abs/10.1080/19443994.2016.1172989

https://www.sciencedirect.com/science/article/pii/S0920586117302572

Depending on the kind of wastewater. If you want to use graphene with raw wastewater I think it will be unuseful with high concentration of contaminants. therefore, you need to treat your wastewater sample first, then you can use graphene in different ways as Mohamed Bayati and Mohsen Zolghadr mentioned.

Good Luck with your work!!