Ceramic vs polymeric membrane implementation for potable water treatment.

The continued technological developments and decreased purchase costs of ceramic membranes have seen increased recent interest in the technology as an alternative to the more widely used polymeric membranes. This paper assesses the relative technical, practical and economic merits of the two membrane materials in the context of potable water production from surface water sources. The work focuses on phenomena of direct technoeconomic significance, namely cleaning efficacy (manifested as permeability recovery), membrane integrity and incurred labour effort. Topics reviewed thus comprise: (a) practical comparison of the two technologies challenged with the same feedwater, (b) comparative technoeconomic analyses, (c) membrane integrity studies of polymeric membranes - incorporating aged samples extracted from operating installations, (d) sludging incidents, and (e) pilot and full-scale data. Available relevant data reveal: (a) bench-scale comparative tests do not indicate a consistent significant difference in the net permeability between the two membranes; (b) polymeric membranes are subject to a decline in both mechanical strength and permeability from the loss of the hydrophilic agent over a period of years from the action of hypochlorite used for cleaning; (c) the decreased mechanical strength with age of polymeric membranes increases the manual repair requirement and shortens membrane life, respectively impacting on labour and membrane replacement costs where the latter is also determined by the permeability; (d) the chemical and mechanical robustness of ceramic membranes permits more aggressive chemical cleaning, which then affects the chemicals consumption cost; and (e) anecdotal evidence suggests that polymeric membranes challenged with pre-coagulated surface waters may be subject to sludging, the agglomeration of solids in the membrane channels, which may also be age-related. Notwithstanding the above, data from published comparative technoeconomic studies indicate a linear relationship between the overall cost benefit and the membrane module cost ratio mitigated by the relative membrane life and operating flux.

Low-pressure membrane technology for potable water filtration: true costs.

The overall cost, expressed as the present value (PV), of the construction and operation of low-pressure membrane filtration of inland water for potable water supply has been determined for membrane installations across the UK. The analysis was based on 15 full-scale installations installed with hollow fibre and capillary tube polymeric membranes, for which cost and related data were available. The analysis encompassed labour, in addition to energy, chemicals and critical component replacement. PV data were presented as functions of flow capacity (i.e. as cost curves), delineated as capital (CAPEX), operating (OPEX) and total PV normalised against flow rate (PV') the CAPEX excluding the site-specific civil engineering costs. Captured CAPEX data revealed these to be lower than those previously reported, and with a reduced economy of scale. The OPEX PV exceeded the CAPEX by a factor of 3-6 based on a 20-year life cycle, the difference increasing with decreasing flow capacities. Costs associated with unplanned (or "reactive") maintenance, partly associated with the repair of breached membranes and/or permeability recovery following membrane clogging, were found to make up around half the labour costs. Labour costs as a proportion of the flow increased with decreasing flow, exceeding the CAPEX at flows below 30,000 m3/d. Outcomes indicate labour costs associated with process upsets to contribute significantly to the overall cost of the installation over its life cycle, particularly at flows below ~30,000 m3/d. A clear trade-off exists between supplementary capital investment to allay process upsets and the operational costs associated with such events.

Fate of thiabendazole through the treatment of a simulated agro-food industrial effluent by combined MBR/Fenton processes at µg/L scale.

This study has been carried out to assess the performance of a combined system consisting of a membrane bioreactor (MBR) followed by an advanced oxidation process (Fenton/Photo-Fenton) for removing the fungicide thiabendazole (TBZ) in a simulated agro-food industrial wastewater. Previous studies have shown the presence of TBZ in the effluent of an agro-food industry treated by activated sludge in a sequencing batch reactor (SBR), thus reinforcing the need for alternative treatments for removal. In this study, a simulated agro-food industry effluent was enriched with 100 µg L(-1) TBZ and treated by combined MBR/Fenton and MBR/solar photo-Fenton systems. Samples were directly injected into a highly sensitive liquid chromatography-triple quadrupole-linear ion trap-mass spectrometer (LC-QqLiT-MS/MS) analytical system to monitor the degradation of TBZ even at low concentration levels (ng L(-1)). Results showed that the biological treatment applied was not effective in TBZ degradation, which remained almost unaltered; although most dissolved organic matter was biodegraded effectively. Fenton and solar photo-Fenton, were assayed as tertiary treatments. The experiments were run without any pH adjustment by using an iron dosage strategy in the presence of excess hydrogen peroxide. Both treatments resulted in a total degradation of TBZ, obtaining more than 99% removal in both cases. To assure the total elimination of contaminants in the treated waters, transformation products (TPs) of TBZ generated during Fenton degradation experiments were identified and monitored by liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS/MS). Up to four TPs could be identified. Two of them corresponded to mono-hydroxylated derivatives, typically generated under hydroxyl radicals driven processes. The other two corresponded with the hydrolysis of the TBZ molecule to yield benzoimidazole and thiazole-4-carboxamidine. All of them were also degraded during the treatment.

Localized secretion of ATP and opioids revealed through single Ca2+ channel modulation in bovine chromaffin cells.

In bovine chromaffin cells, the Ca2+ channels involved in exocytosis are effectively inhibited by ATP and opioids that are coreleased with catecholamines during cell activity. This autocrine loop causes a delay in Ca2+ channel activation that is quickly removed by preceding depolarizations. Changes in Ca2+ channel gating by secreted products thus make it possible to correlate Ca2+ channel activity to secretory events. Here, using cell-attached patch recordings, we found a remarkable correlation between delayed Ca2+ channel openings and neurotransmitter secretion induced by either local or whole-cell Ba2+ stimulation. The action is specific for N- and P/Q-type channels and largely prevented by PTX and mixtures of purinergic and opioid receptor antagonists. Overall, our data provide evidence that exocytosis, viewed through the autocrine inhibition of non-L-type channels, is detectable in membrane patches of approximately 1 microm2 distributed over 30%-40% of the total cell surface, while Ca2+ channels and autoreceptors are uniformly distributed over most of the cell membrane.