A hybrid process integrating vapor stripping with vapor compression and vapor permeation membrane separation, termed Membrane Assisted Vapor Stripping (MAVS), was evaluated for recovery and dehydration of ethanol from aqueous solution as an alternative to conventional distillation–molecular sieve processes. Ethanol removal/drying performance of the MAVS system with binary ethanol–water mixtures and a yeast fermentation broth were evaluated and the fate of secondary fermentation products in the system was assessed. Simple alcohols, esters, and organic acids displayed varying degrees of recovery in the vapor stripping based on the relative vapor–liquid partitioning of the compounds. All volatilized organic compounds were concentrated to the same degree in the membrane step. Membrane permeance, permselectivity, and overall energy usage of the hybrid process were the same with the fermentation broth as with binary ethanol–water solutions. The MAVS system required less than half the energy of a distillation–molecular sieve system.
A novel muffle furnace (MF)-based potassium hydroxide (KOH) fusion digestion technique was developed and evaluated for different titanium dioxide materials in various solid matrices. Digestion of different environmental samples containing sediments, clay minerals and humic acid with and without TiO2 particles was first performed utilizing the MF-based KOH fusion technique and its dissolution efficacy was compared to a Bunsen burner (BB)-based KOH fusion method. The three types of TiO2 particles (anatase, brookite and rutile) were then digested with the KOH fusion techniques and microwave (MW)-based nitric (HNO3)–hydrofluoric (HF) mixed acid digestion methods. Statistical analysis of the results revealed that Ti recoveries were comparable for the KOH fusion methods (BB and MF). For pure TiO2 particles, the measured Ti recoveries compared to calculated values were 96%, 85% and 87% for anatase, brookite and rutile TiO2 materials, respectively, by the MF-based fusion technique. These recoveries were consistent and less variable than the BB-based fusion technique recoveries of 104%, 97% and 72% and MW-based HNO3–HF mixed acids digestion recoveries of 80%, 81% and 14%, respectively, for anatase, brookite and rutile. Ti percent recoveries and measurement precision decreased for both the BB and MF methods when TiO2 was spiked into sediment, clay minerals, and humic acid. This drop in efficacy was counteracted by more thorough homogenization of the spiked mixtures and by increasing the mass of KOH in the MF fusion process from 1.6 g to 10.0 g. The MF-based fusion technique is consistently superior in digestion efficiency for all three TiO2 polymorphs. The MF-based fusion technique required 20 minutes for digestion of 25 samples (based on in-house Lindberg MF capacity) compared to 8 hours for the same number of samples using the BB-based fusion technique. Thus, the MF-based fusion technique can be used to dissolve a large number of samples in a shorter time (e.g., 500 samples per 8 hours) while conserving energy and eliminating health and safety risks from methods involving HF.
Relatively little is known about the behavior and toxicity of nanoparticles in the environment. Objectives of work presented here include establishing the toxicity of a variety of silver nanoparticles (AgNPs) to Daphnia magna neonates, assessing the applicability of a commonly used bioassay for testing AgNPs, and determining the advantages and disadvantages of multiple characterization techniques for AgNPs in simple aquatic systems. Daphnia magna were exposed to a silver nitrate solution and AgNPs suspensions including commercially available AgNPs (uncoated and coated), and laboratory-synthesized AgNPs (coated with coffee or citrate). The nanoparticle suspensions were analyzed for silver concentration (microwave acid digestions), size (dynamic light scattering and electron microscopy), shape (electron microscopy), surface charge (zeta potentiometer), and chemical speciation (X-ray absorption spectroscopy, X-ray diffraction). Toxicities of filtered (100 nm) versus unfiltered suspensions were compared. Additionally, effects from addition of food were examined. Stock suspensions were prepared by adding AgNPs to moderately hard reconstituted water, which were then diluted and used straight or after filtration with 100-nm filters. All nanoparticle exposure suspensions, at every time interval, were digested via microwave digester and analyzed by inductively coupled argon plasma-optical emission spectroscopy or graphite furnace-atomic absorption spectroscopy. Dose-response curves were generated and median lethal concentration (LC50) values calculated. The LC50 values for the unfiltered particles were (in µg/L): 1.1 ± 0.1-AgNO(3) ; 1.0 ± 0.1-coffee coated; 1.1 ± 0.2-citrate coated; 16.7 ± 2.4 Sigma Aldrich Ag-nanoparticles (SA) uncoated; 31.5 ± 8.1 SA coated. LC50 values for the filtered particles were (in µg/L): 0.7 ± 0.1-AgNO(3) ; 1.4 ± 0.1-SA uncoated; 4.4 ± 1.4-SA coated. The LC50 resulting from the addition of food was 176.4 ± 25.5-SA coated. Recommendations presented in this study include AgNP handling methods, effects from sample preparation, and advantages/disadvantages of different nanoparticle characterization techniques.
Abstract BACKGROUND In Part1 of this work, a process integrating vapor stripping, vapor compression, and a vapor permeation membrane separation step, ‘membrane assisted vapor stripping’ ( MAVS ), was predicted to produce energy savings compared with traditional distillation systems for separating 1‐butanol/water and acetone‐butanol‐ethanol/water ( ABE /water) mixtures. Here, the separation performance and energy usage of a MAVS pilot system with such mixtures and an ABE fermentation broth were assessed . Results The simple stripping process required 10.4 MJ ‐fuel kg –1 ‐butanol to achieve 85% butanol recovery from a 1.3 wt% solution. Addition of the vapor compressor and membrane unit and return of the membrane permeate to the column raised 1‐butanol content from 25 wt% in the stripping vapor to 95 wt% while cutting energy usage by 25%. Recovery of secondary fermentation products from the ABE broth were based on their relative vapor–liquid partitioning. All volatilized organic compounds were concentrated to roughly the same degree in the membrane step. Membrane permeance, selectivity, and overall MAVS energy usage were the same with the broth as with the ABE /water solution . Conclusion Energy usage of the MAVS experimental unit corroborated process simulation predictions. Simulations of more advanced MAVS designs predict 74% energy savings compared with a distillation–decanter system. Published 2013. This article is a U.S. Government work and is in the public domain in the USA
Arsenic is considered a primary pollutant in drinking water because of its high toxicity. The unique property of water hyacinth roots (Eichhornia crassipes) to remove heavy metals is of great signiicance for the development of a cost-effective phytoremediation technology. An experimental test program was conducted at the United States Environmental Protection (USEPA) Test and Evaluation (T&E) Facility in Cincinnati, Ohio, to investigate the potential of water hyacinth roots to remove arsenic from spiked drinking water samples. Water hyacinth roots were washed, dried, and powdered to provide dried hyacinth roots (DHR) for batch and continuous column experiments, Various quantities of DHR were added to water spiked with 300 micrograms per liter (microg/L) arsenic. A concentration of 20 g/L DHR was found adequate for greater than 90% arsenic removal in the batch tests. Based on the batch test results, continuous column experiments were performed using a 2-L column. In a continuous system, 15 L of water containing 300 microg/L arsenic were treated to below 20 microg/L using 50 g DHR, and 44 L of water containing 600 microg/L arsenic were treated to below 20 microg/L using 100 g DHR, giving a specific accumulation rate of approximately 260 microg As/g DHR.
