The sewage sludge is just that, fecal matter. In today's environment of depressed immune diseases I can think of hundreds of reasons that these materials would be a health risk, not benefit. All minerals used in nutrient manufacture are basically dirt. The iron, calcium, zinc etc. are just mined ore, pulverised and powdered to a fine dust. This doesn't make it any easier to assimilate.
Some calcium is made from ground up oyster shells.
This reminds me of when I was a kid watching the Three Stooges fix dinner, they would throw the oysters away and try and chew the shells. We all laughed at them and now we are doing the same thing. The manufacturers response to this is to add pig digestive enzymes, which supposedly pre-digests it or chelates it, in their attempts to force our body to accept this toxic material. We are currently entering a new era of nutrition. It is no longer a matter of how many milligrams you take of a particular nutrient but how much of what you are taking is actually getting into your bloodstream, and the organs that need it.