Metastable hydrated carbonates for algae biofuel production

In this work, we present a study to develop a mineralization process to capture and reuse carbon dioxide (CO2) for the growth of algae, from which then carbon is extracted and converted into a biofuel. The classical CO2 mineralization process consists in fixing CO2 into stable carbonates. During the formation of the carbonates hydrated phases can form, which transform into stable carbonates, eventually. However, if carbonates are designed to be reused, e.g., to provide carbon to a bioprocess through dissolution within a brine, the formation of metastable carbonate phases is preferred as these phases have a solubility which is much higher than the solubility of the anhydrous phases. To design a process that can capture CO2 into hydrated minerals and provide carbon for algal growth, meeting the requirements of the synthesis of the carbon into fatty acids, requires a well-constrained mineralization. In particular, optimal thermodynamic conditions for precipitation and dissolution must be selected. Here, we present an experimental and modeling study of the precipitation and the dissolution of nesquehonite (MgCO3·3H2O). We investigated the process between 25ºC and 50ºC and 1 and 5 bar of CO2. Batch experiments were performed using MgCl2-CO2-Na2CO3 aqueous system and monitored with online Raman spectroscopy. Precipitation and dissolution were modeled using a population balance equation (PBE) coupled with a geochemical model. Nucleation, growth, and dissolution rates were described by constitutive equations based on classical nucleation theory, the birth-and spread growth mechanism, and transition state theory, respectively. The kinetic parameters were estimated by fitting Raman spectroscopy measurements using multivariate kinetics modeling

Increasing acceptance of chlorination for household water treatment: observations from Bangladesh

Point-of-use water treatment, especially chlorination, is an effective intervention to reduce diarrhoea, a leading cause of death for children under five. Yet success in chlorination uptake has been limited. One obstacle is objection to treated water's taste/odour. Protective chlorine residuals that are not offensive to users require accurate dosing - a challenge in practice. Further, taste sensitivity may be different for populations never exposed to chlorinated water. Here, household chlorination trials in Bangladesh similarly revealed dissatisfaction with treated water due to taste and odour, although attempts to quantify chlorine sensitivity disputed the dissatisfaction at lower residuals. A granular activated carbon (GAC) filter fitted to the spigot of a covered tank removed the remaining chlorine residual prior to drinking and increased user satisfaction. Such a filter removes taste as a barrier and allows over-dosing contaminated water to ensure disinfection, with implications for areas with high source water variability and for emergency situations

Fabrication and evolution of multilayer silver nanofilms for surface-enhanced Raman scattering sensing of arsenate

Surface-enhanced Raman scattering (SERS) has recently been investigated extensively for chemical and biomolecular sensing. Multilayer silver (Ag) nanofilms deposited on glass slides by a simple electroless deposition process have been fabricated as active substrates (Ag/GL substrates) for arsenate SERS sensing. The nanostructures and layer characteristics of the multilayer Ag films could be tuned by varying the concentrations of reactants (AgNO3/BuNH2) and reaction time. A Ag nanoparticles (AgNPs) double-layer was formed by directly reducing Ag+ ions on the glass surfaces, while a top layer (3rd-layer) of Ag dendrites was deposited on the double-layer by self-assembling AgNPs or AgNPs aggregates which had already formed in the suspension. The SERS spectra of arsenate showed that characteristic SERS bands of arsenate appear at approximately 780 and 420 cm-1, and the former possesses higher SERS intensity. By comparing the peak heights of the approximately 780 cm-1 band of the SERS spectra, the optimal Ag/GL substrate has been obtained for the most sensitive SERS sensing of arsenate. Using this optimal substrate, the limit of detection (LOD) of arsenate was determined to be approximately 5 μg·l-1

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) Reduction by Granular Zero-Valent Iron in Continuous Flow Reactor

Wastewater streams containing hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) are subject to regulatory discharge regulations that require processing through industrial waste treatment. Thus, the development of easy-to-apply technologies for the treatment of RDX-laden wastewater streams is imperative. In the present study, the reduction of RDX by granular zero valent iron (GZVI) in batch and column experiments was investigated. Preliminary batch tests conducted under both oxic and anoxic conditions showed that after 3.0 hours of reaction with GZVI, RDX was mainly converted to formaldehyde (CH2O), nitrate (NO3 - ), and ammonium (NH4 + ). Column filtration tests showed that pre-treatment of the GZVI media with 10 acid wash and low influent pH (4.0±0.1) achieved 99% removal of RDX up to 5000 bed volume. BOD tests carried out on the post-treatment streams showed increased biodegradability of the treated wastewater, leading to a lower environmental impact for the final waste

Degradation of 3-Nitro-1, 2, 4-Trizole-5-One (NTO) in Wastewater with UV/H2O2 Oxidation

Insensitive Munition (IM) formulations contain 3-nitro-1,2,4-trizole-5-one (NTO), an energetic compound with the highest aqueous solubility (16 g L−1) among all IM explosives, including 2,4-dinitroanisole (DNAN) and 1-nitroguanidine (NQ); as a result wastewater streams from IM processing facilities can be highly contaminated and potentially toxic. The removal of energetic compounds from wastewater streams prior to their discharge in the environment is imperative, and new technology must be developed to efficiently treat high levels of NTO and other IM compounds in these streams. In this study, the treatment of NTO wastewater by a UV/H2O2 oxidation process under acidic conditions (pH = 3.0 ± 0.1) and a hydrogen peroxide concentration of at least 1500 mg L−1 resulted in successful removal of the energetic compound. The organic carbon from the NTO ring was completely converted to inorganic carbon (CO2), as confirmed through TOC measurements and GC–MS analysis on the reactor headspace. Nitrate and ammonium ions were the major nitrogen by-products, as indicated by mass spectrometry. The results obtained in this work demonstrate that the UV/H2O2 oxidation process can effectively mineralize high concentrations of NTO in wastewater streams leading to recovery of valuable nutrients that can be used for supporting algal biomass growth for biofuel/biogas generation