Electrochemical investigation of electrocoagulation reactors for water purification

Imperial Users onl

Tunable-porosity membranes from discrete nanoparticles

Thin film composite membranes were prepared through a facile single-step wire-wound rod coating procedure in which internally crosslinked poly(styrene-co-butadiene) polymer nanoparticles self-assembled to form a thin film on a hydrophilic ultrafiltration support. This nanoparticle film provided a defect-free separation layer 130–150 nm thick, which was highly permeable and able to withstand aggressive pH conditions beyond the range of available commercial membranes. The nanoparticles were found to coalesce to form a rubbery film when heated above their glass transition temperature (T(g)). The retention properties of the novel membrane were strongly affected by charge repulsion, due to the negative charge of the hydroxyl functionalized nanoparticles. Porosity was tuned by annealing the membranes at different temperatures, below and above the nanoparticle T(g). This enabled fabrication of membranes with varying performance. Nanofiltration properties were achieved with a molecular weight cut-off below 500 g mol(−1) and a low fouling tendency. Interestingly, after annealing above T(g), memory of the interstitial spaces between the nanoparticles persisted. This memory led to significant water permeance, in marked contrast to the almost impermeable films cast from a solution of the same polymer

Electrochemical investigation of electrocoagulation reactors for water purification

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Rapid screening test for primary hyperaldosteronism: ratio of plasma aldosterone to renin concentration determined by fully automated chemiluminescence immunoassays.

Contains fulltext : 57887.pdf (publisher's version ) (Closed access)BACKGROUND: The ratio of plasma aldosterone concentration to plasma renin activity (PAC/PRA) is the most common screening test for primary hyperaldosteronism (PHA), but it is not standardized among laboratories. We evaluated new automated assays for the simultaneous measurement of PAC and plasma renin concentration (PRC). METHODS: We studied 76 healthy normotensive volunteers and 28 patients with confirmed PHA. PAC and PRC were measured immunochemically in EDTA plasma on the Nichols Advantage chemiluminescence analyzer, and PRA was determined by an activity assay. RESULTS: In volunteers, PAC varied from 33.3 to 1930 pmol/L, PRA from 1.13 to 19.7 ng.mL(-1).h(-1) (0.215 ng.mL(-1).h(-1) = 1 pmol.L(-1).s(-1)), and PRC from 5.70 to 116 mU/L. PAC/PRA ratios ranged from 4.35 to 494 (pmol/L)/(ng.mL(-1).h(-1)) and PAC/PRC ratios from 0.69 to 71.0 pmol/mU. In PHA patients, PAC ranged from 158 to 5012 pmol/L, PRA from 0.40 to 1.70 ng.mL(-1).h(-1), and PRC from 0.80 to 11.7 mU/L. PAC/PRA ratios were between 298 and 6756 (pmol/L)/(ng.mL(-1).h(-1)) and PAC/PRC ratios between 105 and 2328 pmol/mU. Whereas PAC or PRC showed broad overlap between PHA patients and volunteers, the PAC/PRC ratio indicated distinct discrimination of these two groups at a cutoff of 71 pmol/mU. CONCLUSION: The PAC/PRC ratio offers several practical advantages compared with the PAC/PRA screening method. The present study offers preliminary evidence that it may be a useful screening test for PHA. Further studies are required to validate these results, especially in hypertensive cohorts

Influence of operating parameters during electrocoagulation of sodium chloride and sodium bicarbonate solutions using aluminium electrodes

Sodium salts are common in solutions used in electrocoagulation (EC) studies especially in relation to treatment of produced water. However, the influence of sodium salts upon electrocoagulation operating parameters is not well understood. Therefore, a multi-electrode electrocoagulation cell with aluminium electrodes was used to investigate the impact of polarity reversal period, electrode history, sodium chloride/sodium bicarbonate concentration, floc characteristics and starting solution pH. Effluent pH exhibited oscillating behaviour which related to electrode passivation, with cleaner electrodes raising pH and electrodes with oxide coatings decreasing pH due to variations in anode dissolution and oxidation of water. Polarity reversal could lower cell resistance by de-passivating the electrode surface with a 3 min reversal time recommended. However, electricity (2.56 kWh/kL) and electrode consumption (0.448 g/min) were enhanced. Imaging revealed that the presence of sodium chloride induced extensive pitting corrosion of the aluminium electrodes, whereas pitting was only observed with high concentrations of sodium bicarbonate. Sodium bicarbonate suppressed pH oscillation due to electrode passivation. The amount of electrode consumed was greater than predicted from Faraday’s Law and as such non-electrochemical processes occurred. The wear of electrodes was uneven with those with highest load at the EC cell extremities wearing the fastest. Floc settling rates were relatively slow and not significantly impacted by salt concentration. The settled volume after 1 h was still greater than 60 % of the initial volume, which may cause issues with floc separation. Residual aluminium ions in the effluent were present which may impact downstream membrane performance

Impact of turbidity, hydraulic retention time, and polarity reversal upon iron electrode based electrocoagulation pre-treatment of coal seam gas associated water

The applicability of iron (steel) electrodes in a continuous electrocoagulation (EC) process to treat coal seam gas (CSG) associated water comprising of a high level of turbidity (421 NTU) was studied. Key objectives were to understand the influence of turbidity upon water quality when hydraulic retention time (HRT) and polarity reversal time (PRT) were tested using a bench top EC unit. Extension of HRT promoted removal of dissolved alkaline earth ions (Ca 23 to 45 %; Mg 60 to 97 %; Ba 25 to 54 %; Sr 10 to 19 %), silicates (90 to 93 %) and boron (8 to 12.7 %); whereas turbidity was optimally reduced at a HRT value of 30 s (98.5 %). Turbidity particularly promoted magnesium removal which may be due to destabilization of the clay suspension. However, clay particles also inhibited the rate of floc settling. The greater performance of EC with increasing HRT was achieved at a cost of increased consumption of electrodes and electricity. PRT reduced power consumption with an optimal value being at least 5 min (4.12 to 3.88 kWh/kL for PRT values of 1 and 5 min, respectively). Removal rates of dissolved species were not greatly influenced by PRT. Surface passivation at low PRT values produced higher amounts of hydrogen gas which caused the flocs to float. In summary, HRT, PRT, turbidity level and solution composition were critical parameters in relation to the potential use of EC in the CSG industry.</p

The influence of coal seam water composition upon electrocoagulation performance prior to desalination

Abstract EC was investigated to ascertain its applicability to remove dissolved species from a variety of associated water samples typical of coal seam gas (CSG) operations. The hypothesis was that the CSG water composition may impact EC performance for the removal of problematic species such as alkaline earth ions and dissolved silicates. Bench top studies of a range of CSG associated water samples revealed that the greater total salinity (conductivity from 5290 to 15680 μS/cm) the less alkaline earth ions were removed. However, dissolved silicate remediation maintained high efficiency (89.5 to 98.0%) regardless of water salt content. Residual aluminium was present in treated water when aluminium electrodes were employed (4.6 to 39.0 mg/L) and correlated with increasing solution pH. In contrast, steel electrodes did not result in notable residual iron. Whether steel or aluminium electrodes were optimal depended upon the CSG water salinity. Aluminium based flocs were discovered to settle significantly slower than iron based flocs, with salinity influencing aluminium flocs properties more than iron flocs. Differences in the presence of amorphous species and crystalline gibbsite may in part explain the floc settling behaviour. In either case, dewatering of flocs represents a technical challenge. The major cost in terms of economics was electrode consumption whether iron or aluminium electrodes were used. The system with lowest operating cost was always iron (A$2.50 to 2.68 per kL compared to A$2.70 to 4.32, per kL for aluminium) regardless of water salinity