Should we be using sludge as a fertilizer?
Great for land spread if treated correctly. A lime stabilization process is used to assist in neutralization. You want to kill any pathogens left over in sludge. Normally good for farm spreading on hay and pasture land. Its best to only apply Class A biosolid to land application. Not for vegetables. Good on wastewater treatment plant flower beds. Personally tested.
Yes you certainly can and should use all waste including sludge for compost/fertilizers. There are 2 major benefits in this mixture. First is you have built up a wide variety of beneficial bacteria and fungi. The other even more important is it will have sufficient levels of micronutrients that would ordinarily have to be added to reach a nutritional balance. The only difficulty is getting the sludge before they kill the microbes with chlorine. The 100% safe way to eliminate all pathogens and toxins is to add the Archaea microbes. This is part of building your microbial balance to match your nutritional balance. Some refer to micronutrients as "Heavy metals". They are called "Heavy" because man made them into metal compounds. They are one or more ions heavy. (toxic). But as soon as you add the Archaea they will consume all the loose electrons, leaving micronutrients only, and will reduce all other organic compounds into their elemental state. This ensures ZERO pathogens. Most people forget their high school science in regards to metals. (Micronutrients initiate and maintain all immune systems in plants and animals. All part of zero waste technology. Good luck and enjoy!