5. Mr. Osama Khoury

The growth in world population is a driving force for nutrient recovery from wastewater. In the developed countries, most of the humans’ waste is treated in wastewater treatment plants (WWTP) and most of the nutrients are settled down in the waste activated sludge (WAS). That provides a renewable source of macronutrients (N, P, K) and micronutrients (Fe ,Mn ,Zn ,Mg), an essential input in intensive agriculture. Here, we examined the efficiency of the HTC technology, a thermochemical process that takes place in subcritical water at moderate temperatures (180–375°C) and high pressures (2–22 Mpa), to convert organic feedstock into a carbonaceous product called hydrochar . WAS from a municipal WWTP was treated under several hydrothermal conditions of time (30–120 min) and temperatures (200–300 °C). Mass balances for phosphorus, magnesium, calcium, copper and zinc showed high recovery values of above 80%, while those for iron and manganese were higher or equal to 94%. The recovery values of nitrogen, potassium and sodium were less than 50%, which can be related to their high solubility in the liquid phase of the HTC reaction. To conclude, this study demonstrates the potential of HTC to treat WAS and recover vital plant nutrients. Implementation of this technology in WWTPs may provide a solution to the increasing volumes of WAS and a new renewable source of vital nutrients that is required to address future challenges of food insecurity.