Biotrickling Filtration for the Reduction of N2O Emitted during Wastewater Treatment: Results from a Long-Term In Situ Pilot-Scale Testing.

Wastewater treatment plants (WWTPs) are a major source of N2O, a potent greenhouse gas with 300 times higher global warming potential than CO2. Several approaches have been proposed for mitigation of N2O emissions from WWTPs and have shown promising yet only site-specific results. Here, self-sustaining biotrickling filtration, an end-of-the-pipe treatment technology, was tested in situ at a full-scale WWTP under realistic operational conditions. Temporally varying untreated wastewater was used as trickling medium, and no temperature control was applied. The off-gas from the covered WWTP aerated section was conveyed through the pilot-scale reactor, and an average removal efficiency of 57.9 ± 29.1% was achieved during 165 days of operation despite the generally low and largely fluctuating influent N2O concentrations (ranging between 4.8 and 96.4 ppmv). For the following 60-day period, the continuously operated reactor system removed 43.0 ± 21.2% of the periodically augmented N2O, exhibiting elimination capacities as high as 5.25 g N2O m-3·h-1. Additionally, the bench-scale experiments performed abreast corroborated the resilience of the system to short-term N2O starvations. Our results corroborate the feasibility of biotrickling filtration for mitigating N2O emitted from WWTPs and demonstrate its robustness toward suboptimal field operating conditions and N2O starvation, as also supported by analyses of the microbial compositions and nosZ gene profiles.

Onsite paper-type colorimetric detector with enhanced sensitivity for alkali ion via polydiacetylene-nanoporous rice husk silica composites.

A paper-type colorimetric detector for identifying the degree of alkali ion concentration with the naked eye was fabricated using polydiacetylene/nanoporous rice husk silica (PDA/NP-SiO2) nanocomposites as a potentially effective, rapid, and facile approach to detect alkali ion in aqueous solution. This study is worth investigating because it has the advantage of visually confirming the alkaline ion in aqueous solution without the aid of other analytical instruments directly at on-site as if pH indicator analysis. The concept of this study is the facile synthetic route of PDA and NP-SiO2. Nanoporous rice husk silica (NP-SiO2) with a high specific surface area 450 m2/g was extracted from leached rice husk ash via a sol-gel process and utilized for efficient absorption of alkali ion. PDA was used as a material to differentiate the degree of alkali ion drawing using only the change of color. By compositing these two materials on the surface of filter paper using the spray drying method, the resulting PDA/NP-SiO2 composites with NP-SiO2 of the different specific surface areas showed a different change of color indicated by the degree of alkali ions even at a low concentration of less than 122 µm. The composite was further analyzed by UV spectroscopy for a change of color and images for screening depending on the alkali ion concentrations. The color response percentage of the PDA/NP-SiO2 composites (PDA/449S; SBET 449.9213 m2/g) was 23.39% at 0.122 mM of NH4OH. Consequently, the result from this study showed the possibility of sensitively distinguishing the alkali ions ranging from pH 9.86 to pH 11.38 using only the naked eye, brought potential features that can be used as a convenient and facile primary water testing kit in practical applications.

Effect of Acidity Levels and Feed Rate on the Porosity of Aerogel Extracted from Rice Husk under Ambient Pressure.

Silica aerogels have attracted tremendous interest due to their high specific surface area and the physical, chemical, and mechanical properties as promising materials for thermal insulation, chemical sensors, and energy storage devices. However, large-scale production of silica aerogels remains a challenge due to costly alkoxide precursors and energy-intensive supercritical drying processes. This paper analyzes the effect of acidity levels and feed rate on the porosity of rice husk aerogels with high specific surface area under ambient pressure. This synthetic approach is cost-effective, eco-friendly, and facilitates recycling. Rice husk ash, which consists of 92% amorphous pure silica, was produced by combustion. A process of solvent exchange and surface modification under ambient pressure at different pH levels was conducted for synthesis of the aerogel. The specific surface area of rice husk aerogel was confirmed as ranging from 385 to 861 m²/g under pH 1 to pH 9 and acid feed rate of 0.5 to 5.0 mL/min. The optimized aerogel had a specific surface area of 861 m²/g, a pore volume of 3.33 cm³/g, and an average pore diameter of 12 nm when synthesized at pH 1 and an acid feed rate of 2.5 mL/min. The aerogel was found to be highly hydrophobic, with a water contact angle of 156° up to about 340 °C.