Molar concentration | EPFL Graph Search

Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solution. In chemistry, the most commonly used unit for molarity is the number of moles per liter, having the unit symbol mol/L or mol/dm3 in SI unit. A solution with a concentration of 1 mol/L is said to be 1 molar, commonly designated as 1 M. Molarity is often depicted with square brackets around the substance of interest, molarity of hydrogen ion is depicted as [H+]. Definition Molar concentration or molarity is most commonly expressed in units of moles of solute per litre of solution. For use in broader applications, it is defined as amount of substance of solute per unit volume of solution, or per unit volume available to the species, represented by lowercase c: :c = \frac{n}{V} = \frac{N}{N_\text{A}

Wastewater and green waste biorefinery Degradation of simple sugars using mixed cultures of purple non-sulfur bacteria: an insight into microbial interactions

Guillaume Crosset-Perrotin

Purple non-sulfur bacteria (PNSB) are phototrophic organisms that have raised interest for both industrial and domestic wastewater treatment and valorization because of their very high assimilation (~1 g CODX g-1 COD substrate) and valuable compounds production (i.e hydrogen, polyhydroxyalkanoates, pigments). PNSB have been studied mostly in pure- or co-cultures with fermentative bacteria. Mixed cultures have been little described. This work aims to enrich a stable association of fermenters and PNSB on a carbohydrate-rich wastewater in a single-step process with a mixed culture. Batches with glucose and acetate at different concentrations were inoculated with an in-house mixed-culture. A chemostat was continuously supplied with glucose (5 g COD L-1) and run at a dilution rate of 0.05 h-1 after start-up under batch mode and baseline stabilization of the PNSB enrichment with acetate. The reactor was constantly illuminated with a light filtered at wavelengths superior to 700 nm. Biomass, pigments expression and substrate depletion were tracked along the experiment. A model was developed to anticipate the biomass growth and the substrates consumption. In the batches fed with acetate, PNSB were dominant in purple biomass (>80% vs. total sequencing read count). The main PNSB population were Rhodopseudomonas and Rhodobacter. With glucose, the biomass turned white. The fermenter Enterobacter dominated the microbiomes (>95% abundance). In the stirred-tank reactor, batch operation with acetate led to the production of a substantial biomass enriched in PNSB (4.0 g VSS L-1) that assimilated the nutrients in a molar C-N-P ratio of 100:9.5:0.1 (- n/n/n). Under chemostat regime with glucose, PNSB were efficiently associated with fermenters in a biomass of 1.0-1.5 g VSS L-1. Phase-contrast microscopy displayed the typical morphotypes of Rhodopseudomonas and the fermenter Clostridium. The glucose was completely depleted. The main fermentation products were acetate (between 3 and 10 mmol L-1), ethanol (between 6 and 9 mmol L-1) and butyrate (between 2 and 4 mmol L-1). The hydrogen yield was low (0.033±0.012 mol H2 mol-1 glucose). A fermenters-PNSB mixed culture was successfully built by microbial community engineering by harnessing the chemostat regime to establish the ecological niches and interactions of these organisms. It provides an excellent opportunity to clean carbohydrate-rich wastewater in a compact single-stage process. In the case of direct application of PNSB, a concentrated biomass can be produced. The biomass can even find interesting applications for resource recovery in the form of, e.g., a protein-rich fertilizing biomass (on food and agricultural aqueous wastes), biogas, bulk chemicals and biopolymers.

2019

Effect of alkali, aluminium and equilibration time on calcium-silicate-hydrates

Yu Yan

Calcium silicate hydrate (C-S-H) is the main hydration product in Portland and blended cements, and greatly affects durability and mechanical properties of the hydrated cement. In the presence of Al-rich supplementary cementitious materials (SCMs), C-(A-)S-H can contain more Al than C-S-H in plain Portland cements. The use of SCMs in cementitious system not only lowers CO2 emission, but may also enhance the mechanical properties in the long term, its durability and can help to suppress alkali silica reaction. However, important questions regarding the effect of Al, alkali and equilibration time on C-A-S-H structure and solubility are still not fully understood. This thesis focuses on the interplay between aluminium, alkali hydroxides in solution, the structure of C-A-S-H and aluminium, alkali uptake by C-A-S-H and kinetics of C-A-S-H formation. For aluminium free C-S-H, KOH and NaOH have a similar effect, they increase pH values and silicon concentrations, and decrease calcium concentrations. At higher alkali hydroxide concentrations, more portlandite precipitates, while amorphous silica dissolves. This increases the Ca/SiC-S-H at low Ca/Sitarget but lowers the maximum Ca/SiC-S-H from 1.5 to 1.2 in 1 M KOH/NaOH. The amount of alkalis bound in C-S-H increases with increasing alkali hydroxide concentrations and is higher at low Ca/SiC-S-H. KOH/NaOH lead to a structural rearrangement in C-S-H, increasing the interlayer distance, number of layers stacked in c direction and shortening the silica chains. Comparison with the independently developed CASH+ thermodynamic model showed a good agreement between the observed and modelled changes, including the shortening of the MCL.For C-A-S-H with Ca/Si=1, the presence of Al led to higher amounts of secondary phases, larger interlayer distance, longer silicate chain, higher dissolved Al and Si, and lower Ca concentrations. The amount of secondary phases is reduced at higher pH; strätlingite and Al(OH)3 dominate at lower pH, and katoite at higher pH values. High pH is also associated with shortened silicate chain length, increased Al and Si concentrations, maximum Al/SiC-S-H and lower Ca concentrations. The Al uptake in C-A-S-H increased with aluminum concentration in solution, indicating the predominance of a common Al sorption mechanism independent of dissolved Al concentration or pH values. XANES data showed the presence of both Al(IV) and Al(VI) with different chemical environments in C-S-H.The effect of equilibration time on C-A-S-H was investigated from 6 hours to 3 years. Rapid changes within the first day were observed in both the solid phase and the aqueous phase. Portlandite was formed in all samples with different Ca/Si and its amount decreased rapidly within the first day and remained stable after more than 7 days. Gismondine-P1 precipitated between 1 and 3 years and destabilized the C-A-S-H phases at target Ca/Si 0.6. In the solid phase, the Al migration from secondary phases to C-A-S-H and an increasing fraction of Al(V) and Al(VI) in C-S-H were observed with longer equilibration time. The Ca/Si ratio of C-S-H played an important role on the extent of changes in aqueous concentration: an increasing of Al concentrations with time was observed in C-A-S-H with Ca/Sitarget=0.6, while a decrease was observed for C-A-S-H with Ca/Sitarget=1.0. The uptake of Al and Na in C-A-S-H was observed to decrease after 4 days and 1 day separately, which indicates a rearrangement of C-A-S-H with time.

EPFL2022

The effect of alkali hydroxides and equilibration time on Al uptake by calcium silicate hydrates (C-S-H)

Sonya Barzgar

Cement production accounts for approximately 8% of man-made CO2 emissions. Lowering these CO2 emissions is currently one of the most important and urgent research topics within the cement community. To reduce these emissions, the Portland cement (PC) is partially replaced by supplementary cementitious materials (SCM) such as blast furnace slag, fly ash or silica fumes. Reaction of these SCM with PC during hydration leads to the formation of additional calcium silicate hydrates (C-S-H), which is the single most important phase in cements based on silica-rich SCM. The high Al2O3 and SiO2 content of the SCM results in C-S-H compositions with more Si and Al than in PC, which affects the stability and durability of such cements. Therefore, it is crucial to determine the role of Al on C-S-H properties to predict the formed hydrate phase assemblages and their effect on durability. Al sorption isotherms including very low Al concentrations have been determined for C-S-H with Ca/Si ratios from 0.6 to 1.4. The solubility, structure and composition of calcium silicate hydrates incorporating aluminum âC-A-S-Hâ as a function of different parameters such as Ca/Si ratio, equilibration time, Al and alkali contents were investigated. Elemental measurements were performed with ICP MS and ICP-OES. The presence of secondary phases was investigated by using TGA and XRD and the structure of C A S H was investigated by FTIR. High alkali hydroxide concentrations led to an increased Al(OH)4- formation in solution, which reduced the Al uptake in C-S-H. Increasing the pH values and decreasing the Ca/Si in C-S-H increased not only the Al concentrations but also in parallel the Si concentrations in solution. This comparable behavior of Al and Si towards changes in pH, pointed towards the uptake of Al within the silica chain both at low and high Ca/Si ratios. A higher Al uptake in C-S-H was observed at higher Ca/Si ratios, which indicated a stabilizing effect of Ca in the interlayer on Al uptake. The effect of equilibration time on Al uptake in C-S-H was investigated using equilibration times from 7 days up to 3 years. Lower Al concentrations were measured in the solution after longer equilibration times. In addition, a decrease in the content of secondary phases was observed by TGA indicating a higher uptake of Al in C-S-H. Little further decrease in Al concentrations was observed after 2 years and longer at low Ca/Si ratios. At high Ca/Si ratios no significant change in solution concentrations was observed after more than 3 months, while the destabilization of secondary phases continued up to 1 year, indicating that a (meta)stable equilibrium was reached faster at higher Ca/Si ratios. In addition to the C-A-S-H phase, the formation of secondary phases such as strÃ€tlingite, katoite and Al(OH)3 was observed at Al/Si â¥ 0.03, which limited the Al uptake in C-S-H. More secondary phases were observed at higher Al concentrations and/or lower pH values. At low Al/Si ratios, a more significant decrease of Al concentrations with time was observed indicating a slower equilibration than at higher Al concentrations. The Al sorption isotherms showed a linear trend between the Al in solution and Al in C-A-S-H from Al/Si of 0.001 up to 0.2. The linear trend pointed towards an Al uptake on one or several types of sorption sites, with a high sorption capacity, which would be consistent with an Al uptake in the bridging position of the silica chains suggested based on NMR studies

EPFL2021