in terms of nutrient recovery ...

in terms of nutrient recovery from sludge and supernatant/centrate streams arising from digestion and dewatering, there are several technologies being introduced in to the market - the challenge I see is to get the sanitation systems formalised in the countries lacking this, once this is established, maintained and operated accordingly, the nutrient recovery will be relatively simple. BOOT/BOOM type concessions are probably the best option as it relieves the developing country's utilities to find the necessary skills. Co-digestion with other organic waste streams can improve this recovery, as well as increase biogas generation, coupled with the implementation of some really smart established thermal hydrolysis type of pre-digestion will probably give the best result. It is a well documented fact that natural phosphate resources are being depleted.