Document Type : Original Article


1 Soils, Water and Environ. Res. Inst. Agric. Res. Cent. (ARC), Egypt

2 Soil Sci. Dept., Fac. Agric., Zagazig Univ., Egypt


Different organic materials such as town refuse, compost, sewage sludge and biogas
have been used as sources of humic acids (HA). However, a systematic characterization of these
organic materials and their comparison of humic acids which extracted from them have not been
reported. This is essential to decide the relative merits and demerits of these substances as sources of
humic acids. The objective of this work was to extract and characterize the chemical compositions of
the different four organic materials and humic acids which extracted from them. Results showed that
the four organic materials which used in this study were, generally, different in all studied properties.
Sewage sludge sample recorded high values of moisture content, saturation percent, cation exchange
capacity, organic carbon and organic matter content and lower values in each of bulk density, pH and
EC as compared to other organic samples. Also, the highest value for each of total and available
nitrogen (NH4
+ and NO3
-) was shown with sewage sludge and town refuse, respectively, while total
and available phosphorus and potassium along with C/N ratio were recorded with compost sample.
Furthermore, the four organic materials were different in total micronutrients and heavy metals. The
highest value for each of Fe, Co and Ni was recorded with compost sample as well as similar results of
Pb, Zn and Cu were observed with sewage sludge sample. Moreover, elementary composition of
humic acids extracted from different samples was rich in carbon, nitrogen and oxygen and poor in
sulfur except for sewage sludge sample. The C/N ratio was relatively high in HA extracted from
biogas as well as HA from compost was superior in C/H, O/H, N+O/C and E4/E6 values. The lowest
value of N/H was observed in HA extracted from biogas. On the other hand, obtained results reported
that HA percentage was relatively high in biogas sample and the four organic materials can be
arranged as following biogas > town refuse > compost > sewage sludge. Also, total acidity of humic
acid samples reveals that, HA of sewage sludge was superior as compared to the other organic
materials. The highest value for each of total carboxyl groups and carboxyl/phenol ratio was found
with HA extracted from town refuse sample, whereas the greatest value of total phenolic groups was
recorded with HA derived from sewage sludge. Furthermore, Infrared spectral (IR) analysis provides
further useful information concerning the molecular structures and characteristic bonds and scanning
electron microscopy (SEM) showed some crystal forms found in all HA samples. These results
elucidated that the chemical composition and the molecular structure of HA samples varies as per the
origin and environment where decomposition has occurred. Present study also documented that the
spectroscopic and imaging techniques can be successfully used to bring out the finer differences
among HA extracted from different organic sources.