Subcritical water extraction of organic acids from chicken manure

Chicken manure waste has a wide range of organic substances and mineral elements. This enriched source has stimulated great scientific interest in finding cleaner and more environmentally benign nutrient recovery options. This study aimed to determine an effective and eco-friendly method (i.e. subcritical water extraction) for processing fresh poultry manure.

The high content of total organic carbon, including humic acids carbon and fulvic acids carbon, in extract was found to release under subcritical conditions. The organic compounds obtained by extraction with subcritical water correspond to humic acid in composition because of the presence in the sample of all the functional groups: polymer bonded by molecular hydrogen bond (3400 cm^-1 ), the presence of CH₂ and CH₃ groups (2870 cm^-1 ), the presence of carboxyl groups (1720 cm^-1 ) and quinones (1640-1680 cm^-1 ). The solid phase left over was characterized by a high content of organic carbon, phosphorus, potassium, and microelements. The maximum extraction of humic acid and fulvic acid carbon was found between 210 and 250 °C at a pressure of 50-60 atm, and the content was a maximum of 3647.2 × 10^-6 g kg^-1 at an extraction temperature of 250 °C.

Given the high content of humic acid found in the extracted medium, the proposed subcritical extraction opens up new opportunities for nutrients recovery in the poultry industry. © 2020 Society of Chemical Industry.