We have produced and supplied ...

We have produced and supplied biochar made from different wood species for these types of tests in the past.   We also supply our biochar to commercial entities for biochar and sand filters for roadway culverts.   If I could be so bold, I would suggest you consider focusing on different species of soft woods and maybe throw in bamboo and some fast growing trees like Paulownia.   The faster growing softwoods and bamboo have larger cell structure which make larger macropores at the molecular level (once they are pyrolyzed) that are large enough to bind the largest organic pollutant  molecules.   The hardwood biochars do not have macropores as they grow slower and some of the larger molecules cannot be effectively bound as they simply cannot fit in the pores.     I have not personally seen any similar study using fast growing super trees or even fast growing Paulownia as the biochar feedstock as many in the industry studying the topic tend to be "nature purists" and do not want to work with biochar from GMO trees when it would seem they would be best to bind the larger molecules that need to be removed for a rural setting.