An application of hydrothermal process to treat palm oil mill effluent (POME)

This study evaluates the effects of subcritical hydrothermal treatment on palm oil mill
effluent (POME) and its concomitant formations of solid hydrochar, liquid product and
gaseous product. The reactions were carried out at temperatures ranged 493 K-533 K
for 2 h. The highest reduction of chemical oxygen demand (COD) and biochemical
oxygen demand (BOD) were 58.8% and 62.5%, respectively, at 533 K. In addition, the
removal of total suspended solids (TSS) achieved up to 99%, with the pH of POME
reaching 6 from the initial pH 4. The gas chromatography coupled with mass
spectroscopy (GC-MS) analysis showed that the fresh POME contained n-Hexadecanoic
acid as the dominant component, which gradually reduced in the liquid product in the
reaction with increased temperature, in addition to the attenuation of carboxyl
compounds and elevation of phenolic components. The gaseous products contained
C02, CO, H2, and C3 - C6 hydrocarbons. Traces of CH4 were only found at 533 K. C02
is the dominant species, where the highest of 3.99 val% per 500 ml working volume of
POME recorded at 533 K. The solid hydrochars showed negligible morphological
changes across the reaction temperature. The 0/C atomic ratio of the hydrochar range
from 0.157 to 0.379, while the H/C atomic ratio was in the range from 0.930 to 1.506.
With the increase of treatment temperature, the higher heating value (HHV) of the
hydrochar improved from 24.624 to 27.513 MJ kg-1. The characteristics of hydrochar
make it a fuel source with immense potential. POME decomposed into water-soluble
compounds, followed by deoxygenation (dehydration and decarboxylation) in producing
hydrochar with lower oxygen content and higher aromatic compounds in the liquid
product. Little gaseous hydrocarbons were produced due to subcritical hydrothermal
gasification at low temperature.