Heavy metal buildup
I am extremely interested in using this technique for a new permaculture farmstead, but would like to ask for your opinion / experience with regards to the long term buildup of heavy metals and how to deal with this potential problem. The work you have done is fantastic and I look forward to hearing from everyone.
The range of scientific studies on vermicomposting of sewerage show that heavy metals are sequestered by the worms and stored in their bodies. For example - http://www.sciencedirect.com/science/article/pii/S0960852416310239 (behind a paywall) and http://www.sciencedirect.com/science/article/pii/S0960852416310239. None of the studies I've checked appear to address what happens at the end of the worms' lives.
My feeling here would be that this is more a problem of municipal-scale sewerage treatment than at an individual household level. If you're setting up a permaculture farmstead, then the presumption would be that you're not using agricultural chemicals, or installing infrastructure that could lead to heavy metal contamination, so the likelihood of this developing into a problem over any sort of human timescale is vanishingly small. We've only really just begun to understand the biology of the soil, but I'd be willing to place good money on nature already having all the detoxification solutions necessary.