Production of Amorphous Silica from Rice Straw
Using Dry Anaerobic Digestion Pretreatment
Safoora Mirmohamadsadeghia, Keikhosro Karimia, Akram Zamania,b, Ilona
Sárvári
a Department
b
b
Horváth
of Chemical Engineering, Isfahan University of Technology, Isfahan, Iran
Swedish Centre for Resource Recovery, University of Borås, Sweden
Abstract
The feasibility of amorphous silica production
from rice straw residues of anaerobic digestion
was investigated in this research. The residue
of the 60-day solid-state anaerobic digestion
(SSAD) , after removing the sludge, was
combusted at to obtain the silica. X-ray
diffraction (XRD) and X-ray fluorescence (XRF)
analysis were performed on the silica. XRD
analysis confirmed the existence of amorphous
silica in the ash. The silica content in the ash
was increased by 55% after SSAD process.
XRD and XRF analysis were performed on the
silica and the results were compared with the
ash obtained from untreated rice straw.
Results and discussion
The methane yield obtained from SSAD during
batch experiments was 120 litter CH4 per kg of
volatile solid. XRF analysis (Table 1) showed
that silica content was increased from 37.7 to
58.4% using anaerobic pretreatment before
combustion.
Table 1. XRF chemical analysis of ash samples
Introduction
Experimental
Rice straw was provided from Lenjan field
(Isfahan, Iran) and cut to about 1 cm length. It
was fermented in the presence of a microbial
consortium obtained from Isfahan municipal
sewage treatment digester at TS content of
20% and feed to inoculum ratio (F/I) of 3 based
on VS contents. After 60 days mesophilic
digestion, the solid residues were thoroughly
washed with tap water on a 20 mesh and
calcined in a muffle furnace at 550°C for 8 h.
Ash samples
SiO2
K2O
CaO
Cl
Untreated
37.70
30.40
10.40
10.20
Digested
58.36
0.916
23.66
0.30
The broad peak centered at 2θ=23° in XRD
pattern confirmed the existence of amorphous
silica in the ash obtained from SSAD residues.
1200
Ash of digested rice straw
1000
Intensity
The residues of rice straw from anaerobic
digestion are mainly inorganic constituents
which contribute approximately 11–12% by
weight of rice straw and are rich in silica.
Common procedures for silica production
combust the organic parts of rice straw. These
methods waste organic materials and also need
large furnaces to combust bulky straw. Using
rice straw as a substrate for anaerobic digestion
before silica production process can improve
the economy of the process by converting
organic part to biogas and decreasing the
volume of the furnace to 11-12% of that for
untreated straw. This innovation has not been
mentioned in previous studies. Therefore, the
feasibility of silica production from rice straw
residues
of
anaerobic
digestion
was
investigated.
Chemical content (%w/w)
Ash of raw rice straw
800
600
400
200
0
5
25
Conclusions
45
2θ (degree)
65
Anaerobic digestion of rice straw before
common methods for silica production is a
novel method to improve quality of the silica
and improve the economy of the process by
biogas production.
References
Wattanasiriwech, S., Wattanasiriwech, D., Svasti,
J. (2010). Journal of Non-Crystalline Solids,
356(25), 1228-1232.