Effect of mixing ratios of natural inorganic additives in removing ammonia and sulfide in the liquid phase during anaerobic digestion of slaughterhouse waste

In this study, the efficacy of inorganic additives in the removal of total ammonia nitrogen (TAN) and sulfide in the aqueous phase of slaughterhouse waste undergoing anaerobic digestion in the batch reactor was investigated. A mixture of natural inorganic additives processed from the anthill and red rock soil samples collected from Arusha, Tanzania were used as adsorbents in different ratios. These materials were chosen in regard to their abundance in the local environment, surface properties, and elemental composition. Before analysis, the materials were pulverized and calcined at 700 and 900 °C for 2 h in a furnace and then sieved to 250 μm fine particle size. XRD analysis revealed that the anthill soil sample is endowed with major mineral phases of quartz and hematite while red rock soil contains albite, pyroxene, and quartz as predominant phases. The anthill and red rock soil samples calcined at 900 °C displayed higher BET surface areas of 815.35 and 852.35 m²/g, respectively. The mixture of anthill soil and red rock soil in a ratio of 3:1 had a higher TAN removal efficiency of 92% at a contact time of 30 min compared to other ratios. On the other hand, a ratio of 1:2 showed a higher sulfide removal efficiency of 79% at a contact time of 60 min. Adsorption isotherm studies revealed that the Jovanovich model fitted better to the experimental data than the Langmuir and Freundlich models. The results demonstrated further that inorganic additives have a synergistic effect on stimulating methanogenesis as well as eliminating ammonia and sulfide during anaerobic digestion of slaughterhouse waste. Our findings demonstrate that anthill and red rock soils can be exploited as affordable, ecofriendly, and efficient adsorbents for mitigation of TAN and sulfide from the liquid phase and sustenance of methanogenesis.     

Effect of drying technique on the physicochemical properties of sodium silicate-based mesoporous precipitated silica

The conventional drying (oven drying) method used for the preparation of precipitated mesoporous silica with low surface area (>300 m²/g) and small pore volume is often associated with a high production cost and a time consuming process. Therefore, the main goal of this study was to develop a cost-effective and fast drying process for the production of precipitated mesoporous silica using inexpensive industrial grade sodium silicate and spray drying of the precipitated wet-gel silica slurry. The precipitated wet-gel silica slurry was prepared from an aqueous sodium silicate solution through the drop-wise addition of sulfuric acid. Mesoporous precipitated silica powder was prepared by drying the wet-gel slurry with different drying techniques. The effects of the oven drying (OD), microwave drying (MD), and spray drying (SD) techniques on the physical (oil, water absorption, and tapping density), and textural properties (specific BET surface area, pore volume, pore size, and % porosity) of the precipitated mesoporous silica powder were studied. The dried precipitated mesoporous silica powders were characterized with field-emission scanning electron microscopy; Brunauer, Emmett and Teller and BJH nitrogen gas adsorption/desorption methods; Fourier-transform infrared spectroscopy; thermogravimetric and differential analysis; N₂ physisorption isotherm; pore size distribution and particle size analysis. There was a significant effect of drying technique on the textural properties, such as specific surface area, pore size distribution and cumulative pore volume of the mesoporous silica powder. Additionally, the effect of the microwave-drying period on the physicochemical properties of the precipitated mesoporous silica powder was investigated and discussed.     

Production of low-density sodium silicate-based hydrophobic silica aerogel beads by a novel fast gelation process and ambient pressure drying process

We report a method to synthesize low-density transparent mesoporous silica aerogel beads by ambient pressure drying (APD). The beads were prepared by acid–base sol–gel polymerization of sodium silicate in aqueous ammonia solution via the ball dropping method (BDM). To minimize shrinkage during drying, wet silica beads were initially prepared; their surfaces were then modified using trimethylchlorosilane (TMCS) via simultaneous solvent exchange and surface modification. The effects of the volume percentage (%V) of TMCS on the physical and textural properties of the beads were investigated. The specific surface area and cumulative pore volume of the silica aerogel beads increased with an increase in the %V of TMCS. Silica aerogel beads with low packing bed density (0.081 g/cm³), high surface area (917 m²/g), and large cumulative pore volume (2.8 cm³/g) was obtained when 10%V TMCS was used. Properties of the final product were examined by FE-SEM, TEM, BET, and TG–DT analyses. Surface chemical modifications were confirmed by FTIR spectroscopy. The hydrophobic silica aerogel beads were thermally stable up to 411 °C. We discuss our results and compare our findings for modified versus unmodified silica beads.     

Reinforced silver-embedded silica matrix from the cheap silica source for the controlled release of silver ions

In this study, a reinforced silver-embedded silica matrix was designed by utilizing the interaction between the [AlO₄]⁻ tetrahedral and the Ag⁺ in sol-gel process using sodium silicate as a silica precursor. The Ag⁺ mole ratio in each sample was significantly varied to examine the influence of silver concentration on the properties of the final product. Aluminium ions were added to reinforce and improve the chemical durability of silver-embedded silica. A templated sample at Al/Ag = 1 atomic ratio was also synthesized to attempt a possibility of controlling porosity of the final product. Also, a sample neither embedded with silver nor templated was synthesized and characterized to serve as reference. The material at Al/Ag = 1 was found to have a desirable properties, compared to its counterparts, before and even after calcination up to 1000 °C. The results demonstrate that materials with desirable properties can be obtained by this unprecedented method while utilizing sodium silicate, which is relatively cheap, as a silica precursor. This may significantly boost the industrial production of the silver-embedded silicas for various applications.     

Facile route for preparation of silver nanoparticle-coated precipitated silica

In this research, a facile route was used to prepare silver nanoparticle-coated precipitated silica using sodium silicate, a cheap precursor. Precipitated silica (PS) was synthesized by dropping 8% H₂SO₄ into a mixed solution of sodium silicate 24% (Na₂O·3.4SiO₂) and NaCl 4%; under constant stirring. The precipitated silica was then modified by simultaneous addition of 3-aminopropyltriethoxysilane (3-APTES) and 8% H₂SO₄. The resulting material was aged at 80 °C for 1 h to produce amino-functionalized precipitated silica (AFPS). Silver nanoparticle-coated precipitated silica (Ag-NPS) was synthesized by adding silver nitrate (AgNO₃). The synthesis procedure also involved mixing for 2 h and dropping 0.05 M sodium borohydride (NaBH₄). The final products, namely, PS, AFPS, and Ag-NPS were characterized using BET analyzer, FE-SEM, TEM and XRD. Silver nanoparticles with an average size ranging from 18 to 25 nm were found mostly coated on the exterior layer of the precipitated silica. The synthesis method reported in this work is facile and might be used for large-scale industrial production of inexpensive Ag-NPS.     

Influence of annealing conditions on the properties of reinforced silver-embedded silica matrix from the cheap silica source

The influence of annealing conditions on the properties of reinforced silver-embedded silica matrix was systematically investigated in the present study. The samples were prepared via a recently reported method using sodium silicate as a silica precursor. Aluminium ions were used to reinforce and improve the chemical durability of silver-embedded silica; and the mole ratio of the precursors was fixed at Al/Ag = 1. The properties of the final product were examined in relation to its counterparts; namely pure silica, aluminium-embedded silica (without silver), and silver doped silica (without aluminium). The materials were heat treated at the range of 600-1000 °C under the constant supply of argon (inert atmosphere). The properties of the final product were compared with those of the previously reported materials prepared via the same method but calcined in air. The current material was found to have pure silver nanoparticles (without AgCl nanoparticles) while the previous material had both silver and AgCl nanoparticles. The results demonstrate that materials with more desirable properties can be obtained by this newly developed technique while utilizing sodium silicate, which is relatively cheap, as a silica precursor. This may significantly boost the industrial production of the silver-embedded silicas for various applications.     

Synthesis of sodium silicate-based hydrophilic silica aerogel beads with superior properties: Effect of heat-treatment

This work demonstrates the synthesis of hydrophilic and hydrophobic high surface area silica aerogel beads with a large pore volume. Wet gel silica beads were modified and heat-treated under atmospheric pressure after modification of the surface by trimethychlorosilane (TMCS). The effects of heat treatment on the physical (hydrophobicity) and textural properties (specific surface area, pore volume, and pore size) of silica aerogel beads were investigated. The results indicated that hydrophobicity of the silica aerogel beads can be maintained up to 400 °C. The hydrophobicity of the silica aerogel beads decreased with increasing temperature in the range of 200-500 °C, and the beads became completely hydrophilic after heat treatment at 500 °C. The specific surface area, cumulative pore volume, and pore size of the silica aerogel beads increased with increasing temperature. Heating the TMCS modified bead gel at 400 °C for 1 h resulted in silica aerogel beads with high surface area (769 m²/g), and large cumulative pore volume (3.10 cm³/g). The effects of heat treatment on the physical and textural properties of silica aerogel beads were investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric and differential analysis (TG-DTA), Fourier-transform infrared spectroscopy (FT-IR), and Brunauer, Emmett and Teller (BET) and BJH nitrogen gas adsorption and desorption methods.