Rather simple questions about a hugely complex issue. Few risks as most pathogens would be reduced massively in numbers or eradicated. Smell too is massively reduced with aerated sludge, so more pleasant to work with. It seems irrelevant to ask if one product or the other would be safer - ask the 'scientist' what is required in the experiment. If activated sewage sludge is acceptable consider using that, since it will give you a more pleasant (?) and reproducible alternative. But the 'scientist' should be capable of managing the experiment and any inherent risks before embarking upon the work, so the question seems rather irrelevant. However, the biological activity, standardisation and reproducibility of this sewage reagent seems a not inappropriate issue here and for a successful experiment that alone may dictate the product to be selected.

I'd deliberately avoided the obvious but perhaps it's now worth putting this into some sort of context. Every one of us defecates daily. So managing raw sewage under laboratory conditions need not be that big a job..............!