Sulfate Concentration Ratio Research Articles

Optimization of sulfate removal by sulfate reducing bacteria using response surface methodology and heavy metal removal in a sulfidogenic UASB reactor

Biological treatment using sulfate reducing bacteria (SRB) has been found out to have the potential for treatment of wastewaters containing sulfate and heavy metals. In the present study, in addition to the investigation of carbon source effect on the growth and sulfate removal, a statistical model using the design of experiments methodology has been developed to optimize the removal of sulfate by the obtained consortium from the anaerobic digested. All parameters were selected in three levels. Investigating the data collected from experiments using response surface methodology proved that the interactions between parameters were insignificant and could be neglected. The optimum removal conditions were achieved at pH of 7.19, initial sulfate concentration of 2153.15mg/L, COD (Chemical Oxygen Demand) to initial sulfate concentration ratio (COD/SO42−) of 2.72 and the COD related to ethanol to total COD ratio (CODethanol/CODtotal) of 1 which led to sulfate removal of 98%. In five different batch experiments done in UASB reactor, the optimum conditions were applied to evaluate SRB performance in real and synthetic wastewater treatment mostly in all experiments. The differences of experiments were in real or synthetic wastewater, having an extra stage of treatment by H2S, using organic wastewater as carbon source and presence of heavy metal in bacteria medium. The maximum obtained removal percentage for Zn and Ni were 99.996 and 96.87, respectively.

Removal of sulfate by fluidized bed crystallization process

This study investigated the behavior of sulfate removal and gypsum crystallization in an FBR with varying seed dosage, initial sulfate concentration and calcium to sulfate concentration ratio. The effect of recycling and use of silica carriers were also evaluated. A bench-scale glass fluidized-bed reactor (FBR) with gypsum seed crystals was used. Results showed that sulfate removal and gypsum crystallization increased with the tested parameters. Sulfate conversion increased from 70.29% to 77.69% and sulfate removal from 52.34% to 65.87% when seed dosage was increased from 4.0g/L to 11.0g/L. Similar trend was observed when the initial sulfate concentration was increased from 80mM to 160mM, sulfate conversion also increased from 75.05% to 85.40% and removal from 55.29% to 77.88%. When calcium to sulfate concentration ratio was increased from 1.0 to 2.0, sulfate conversion increased from 70.40% to 79.19% and removal increased from 49.45% to 65.08%. Product crystals and silica sand carriers were found to be as effective as fresh gypsum seed crystals, hence, the potential for economic recovery of sulfate.

Annual variations in wet-deposition chemistry related to changes in climate

National Atmospheric Deposition Program (NADP)/National Trends Network precipitation type, snow-season duration, and annual timing of selected chemical wet-deposition maxima vary with latitude and longitude within a 35-year (1979–2013) data record for the contiguous United States and Alaska. From the NADP data collected within the region bounded by 35.6645°–48.782° north latitude and 124°–68° west longitude, similarities in latitudinal and longitudinal patterns of changing snow-season duration, fraction of annual precipitation recorded as snow, and the timing of chemical wet-deposition maxima, suggest that the chemical climate of the atmosphere is linked to physical changes in climate. Total annual precipitation depth has increased 4–6 % while snow season duration has decreased from approximately 7 to 21 days across most of the USA, except in higher elevation regions where it has increased by as much as 21 days. Snow-season precipitation is increasingly comprised of snow, but annually total precipitation is increasingly comprised of liquid precipitation. Meanwhile, maximum ammonium deposition occurs as much as 27 days earlier, and the maximum nitrate: sulfate concentration ratio in wet-deposition occurs approximately 10–21 days earlier in the year. The maximum crustal (calcium + magnesium + potassium) cation deposition occurs 2–35 days earlier in the year. The data suggest that these shifts in the timing of atmospheric wet deposition are linked to a warming climate, but the ecological consequences are uncertain.

The altitude of snow growth by riming and vapor deposition in mixed-phase orographic clouds

Oxygen isotopic ratios ( δ 18 O) and sulfate concentrations were measured in cloud water and snow collected at Storm Peak Laboratory (SPL) during winter, 2007. The rimed mass fraction (RMF) was estimated as the ratio of sulfate concentration in snow to that in cloud water. A sharp increase in the RMF at mean droplet diameters above 10 μm confirmed the expected relationship between riming efficiency and cloud droplet size. The mass-weighted altitude of snow formation was inferred from δ 18 O in cloud water and snow and did not exceed 300 m above SPL. The mass-weighted altitude of snow growth by vapor deposition alone was no higher than 900 m above SPL. The results suggest that snow crystals nucleated under water-sub-saturated conditions at higher elevations attained a significant fraction of their water content as they grew by riming and vapor deposition in transit through the low-level orographic cloud near the mountain crest. This approach provides a direct means of validating model simulations of snow growth processes in cold mountain clouds.

Behaviour of Nafion " 350 membrane in sodium sulfate electrochemical splitting: continuous process modelling and pilot scale tests

A two-compartment membrane electrolysis cell is used to split sodium sulfate into sulfuric acid and sodium hydroxide. The cell is equipped with a Nafion® 350 cation-exchange membrane. Due to the dissociation of the strong acid, free hydrogen ions migrate through the membrane together with sodium ions. This transfer decreases current efficiency. The transport properties of Nafion® 350 membrane are studied in a laboratory cell. Current efficiency varies either with sulfuric acid to total sulfate concentration ratio in the anolyte or with sodium hydroxide concentration depending on the membrane state. Water transport through the membrane is due to electroosmosis. Hydrogen and sodium ions carry three to four molecules of water per ion. Modelling of a continuous feed and bleed process in the steady-state is performed using material balance and transport data obtained in a laboratory scale. Tests in a pilot plant (scaling factor 13) were undertaken. The model predictions agree well with experimental results. As a consequence, the model may be used for industrial purposes. Due to current efficiency decrease when salt conversion increases, the use of a cascade of cells in series is advantageous compared to a single stage.