Influence of pH on hydrothermal treatment of swine manure: Impact on extraction of nitrogen and phosphorus in process water

This study investigates the influence of pH on extraction of nitrogen and phosphorus from swine manure following hydrothermal treatment. Conditions include thermal hydrolysis (TH) at 120 degrees C and 170 degrees C, and hydrothermal carbonisation (HTC) at 200 degrees C and 250 degrees C in either water alone or in the presence of 0.1 M NaOH, H2SO4, CH3COOH or HCOOH. Phosphorus extraction is pH and temperature dependent and is enhanced under acidic conditions. The highest level of phosphorus is extracted using H2SO4 reaching 94% at 170 degrees C. The phosphorus is largely retained in the residue for all other conditions. The extraction of nitrogen is not as significantly influenced by pH, although the maximum N extraction is achieved using H2SO4. A significant level of organic-N is extracted into the process waters following hydrothermal treatment. The results indicate that operating hydrothermal treatment in the presence of acidic additives has benefits in terms of improving the extraction of phosphorus and nitrogen. (C) 2016 Published by Elsevier Ltd.