Microbial Fuel Cell-driven caustic potash production from wastewater for carbon sequestration.

This work reports on the novel formation of caustic potash (KOH) directly on the MFC cathode locking carbon dioxide into potassium bicarbonate salt (kalicinite) while producing, instead of consuming electrical power. Using potassium-rich wastewater as a fuel for microorganisms to generate electricity in the anode chamber, has resulted in the formation of caustic catholyte directly on the surface of the cathode electrode. Analysis of this liquid has shown to be highly alkaline (pH>13) and act as a CO2 sorbent. It has been later mineralised to kalicinite thus locking carbon dioxide into potassium bicarbonate salt. This work demonstrates an electricity generation method as a simple, cost-effective and environmentally friendly route towards CO2 sequestration that perhaps leads to a carbon negative economy. Moreover, it shows a potential application for both electricity production and nutrient recovery in the form of minerals from nutrient-rich wastewater streams such as urine for use as fertiliser in the future.

Biogas upgrading by chemical absorption using ammonia rich absorbents derived from wastewater.

The use of ammonia (NH3) rich wastewaters as an ecological chemical absorption solvent for the selective extraction of carbon dioxide (CO2) during biogas upgrading to 'biomethane' has been studied. Aqueous ammonia absorbents of up to 10,000 gNH3 m(-3) demonstrated CO2 absorption rates higher than recorded in the literature for packed columns using 20,000-80,000 g NH3 m(-3) which can be ascribed to the process intensification provided by the hollow fibre membrane contactor used in this study to support absorption. Centrifuge return liquors (2325 g m(-3) ionised ammonium, NH4(+)) and a regenerant (477 gNH4(+) m(-3)) produced from a cationic ion exchanger used to harvest NH4(+) from crude wastewater were also tested. Carbon dioxide fluxes measured for both wastewaters compared reasonably with analogue ammonia absorption solvents of equivalent NH3 concentration. Importantly, this demonstrates that ammonia rich wastewaters can facilitate chemically enhanced CO2 separation which eliminates the need for costly exogenic chemicals or complex chemical handling which are critical barriers to implementation of chemical absorption. When testing NH3 analogues, the potential to recover the reaction product ammonium bicarbonate (NH4HCO3) in crystalline form was also illustrated. This is significant as it suggests a new pathway for ammonia separation which avoids biological nitrification and produces ammonia stabilised into a commercially viable fertiliser (NH4HCO3). However, in real ammonia rich wastewaters, sodium bicarbonate and calcium carbonate were preferentially formed over NH4HCO3 although it is proposed that NH4HCO3 can be preferentially formed by manipulating both ion exchange and absorbent chemistry.

A preliminary survey of bacterial contamination of the dialysate circuit in continuous veno-venous hemodialysis.

AIMS: The problem of dialysate bacterial contamination has not been defined in continuous renal replacement therapy. We assessed the bacterial integrity of source bicarbonate dialysate (study 1) and the continuous veno-venous HD (CVVHD) bicarbonate dialysate circuit (study 2). METHODS: Study 1: 50 ml dialysate were collected from 41 bags randomly selected from 150 consecutively made dialysate bags, immediately after manufacture or after 24, 48 or 72 h. Study 2: 10 ml dialysate were drawn from 4 sample points ranged along the dialysate circuit in 18 therapies (mean duration 119.5 +/- 72.0 h). All points were sampled at therapy start then daily, bar the proximal point which was sampled after each dialysate bag change. All dialysate samples underwent Gram stain and aerobic/anaerobic culture. Samples over 10 ml were cultured after centrifugation (15 min, 4,000 rpm). A disseminated contamination (DC) involved > or = 1 sample point at a time and/or was sustained over time. RESULTS: Study 1: One bag was culture-positive (staphylococcal/diphtheroid growths; 48-h sample). Study 2: Six DCs developed in 6 therapies (1 at therapy end, 5 sustained to therapy end (duration 57.25 +/- 45.95 h), 5 with Gram-negative bacilli, all involving reported growths of > or = 1,000 cfu). Dialyzer-inclusive dialysate circuit changes were more frequent in non-DC therapies (change rate: DC, 0.08 +/- 0.12/day, non-DC, 0.34 +/- 0.23, p = 0.02, permutation tests with general scores) but did not entirely prevent DC or alter it once underway. CONCLUSIONS: Sustained bacterial contamination of bicarbonate-based CVVHD is common and could relate to the completeness of dialysate circuit change. The importance of technique and regular quality control is highlighted.

Leucine metabolism in preterm infants receiving parenteral nutrition with medium-chain compared with long-chain triacylglycerol emulsions.

BACKGROUND: Although medium-chain triacylglycerols (MCTs) may be utilized more efficiently than long-chain triacylglycerols (LCTs), their effect on protein metabolism remains controversial. OBJECTIVE: The aim of the study was to compare the effects of mixed MCT-LCT and pure LCT emulsions on leucine metabolism in preterm infants. DESIGN: Fourteen preterm [gestational age: 30+/-1 wk; birth weight: 1409+/-78 g (x +/- SE)] neonates were randomly assigned to receive, from the first day of life, either a 50:50 MCT-LCT (mixed MCT group; n = 7) or an LCT (LCT group; n = 7) lipid emulsion as part of an isonitrogenous, isoenergetic total parenteral nutrition program. On the fourth day, infants received intravenous feeding providing 3 g lipid, 15 g glucose, and 3 g amino acids kg(-1) x d(-1) and underwent 1) indirect calorimetry and 2) a primed, 2-h infusion of H13CO3Na to assess the recovery of 13C in breath, immediately followed by 3) a 3-h infusion of L-[1-13C]leucine. RESULTS: The respiratory quotient tended to be slightly but not significantly higher in the mixed MCT than in the LCT group (0.96+/-0.06 compared with 0.93+/-0.03). We did not detect a significant difference between the mixed MCT and LCT groups with regard to release of leucine from protein breakdown (B; 309+/-40 compared with 257+/-46 micromol x kg(-1) x h(-1)) and nonoxidative leucine disposal (NOLD; 296+/-36 compared with 285+/-49 micromol x kg(-1) x h(-1)). In contrast, leucine oxidation was greater in the mixed MCT than in the LCT group (113+/-10 compared with 67+/-10 micromol x kg(-1) x h(-1); P = 0.007). Net leucine balance (NOLD - B) was less positive in the mixed MCT than in the LCT group (-14+/-9 compared with 28+/-10 micromol x kg(-1) x h(-1); P = 0.011). CONCLUSION: Mixed MCTs may not be as effective as LCT-containing emulsions in promoting protein accretion in parenterally fed preterm neonates.

A liquid-liquid blood-gas exchange for the treatment of acute respiratory failure. A new blood gas exchange using artificial blood as an oxygen carrier.

A new liquid-liquid blood gas exchange system was investigated using a venovenous low flow extracorporeal circuit. A 2 m2 hollow fiber dialyzer served as the interface of the blood and oxygen carrier (a 38 percent FC-43, perfluorocarbon emulsion in a buffered electrolyte solution), which was continuously recycled through a bubble oxygenator. Experiments were performed on five mongrel dogs under general anesthesia. Upon the arrest of spontaneous ventilation, the dogs' lungs were inflated with 50% oxygen gas under a positive pressure of 10 cmH2O. After 10 min of apnea the dogs' PaO2 decreased to 37 +/- 14 mmHg, and the extracorporeal circulation was started at 10 ml/min/kg b./w. At 15 min the PaO2 had risen to 80 +/- 41 mmHg and at 30 min to 121 +/- 17 mmHg. The oxygen transfer was 8.3 +/- 2.3 ml/min. The extracorporeal circulation was continued 5h, when PaO2 reached 156 +/- 90 mmHg, and PaCO2 148 +/- 43 mmHg, then stopped. Fifteen minutes later, the PaO2 had returned to 32 +/- 10 mmHg. These findings indicate that our blood gas exchange system can supply a sufficient amount of oxygen to the body under apnea with continuous positive airway pressure.