Full nitrogen recovery and potable water production from human urine by membrane distillation

Human urine offers some interesting possibilities for ammonia and potable water recovery. Membrane distillation holds possible advantages over existing urine treatment technologies, specifically regarding ammonia recovery. It was shown that up to 95 m% of all ammonia present in hydrolyzed urine could be recovered by increasing the urine pH to 10.5 or higher within a period of 2 hours, with a maximal separation factor of up to 16. The possibility of potable water production was investigated in human urine by assessing the permeate water quality, maximum recovery and mid-term process stability. It was shown that at least 75% of the available water could be recovered from non-hydrolyzed human urine without process failure. As such, membrane distillation is a viable alternative for existing urine treatment

Influence of osmotic energy recovery/osmotic dilution on seawater desalination energy demand

Supplying fresh, potable water to an ever increasing world population is becoming a major challenge. One possibility is to produce fresh water from seawater by Reverse Osmosis (RO), a process that is very energy intensive. To reduce the energy demand of this process, osmotic dilution (OD)/osmotic energy recovery (OER) systems can be used as pre-treatment. Both Reverse Electrodialysis (RED) and Pressure Retarded Osmosis (PRO) and their non energy-producing counterparts short-circuited RED/ Forward Osmosis (scRED/FO) and assisted RED/FO (ARED/AFO) were modelled as OD/OER devices for RO, in a thermodynamic way. Different mixing ratios of impaired versus salt water (0.5, 1 and 2) were compared at a realistic RO recovery of 50%. A realistic approach for the RED/PRO-RO hybrid process was also modelled incorporating some major losses, to gain a more realistic insight into its possibilities. The thermodynamic modelling revealed that a significant reduction of the SEC is possible with all hybrid processes. The reduction in SEC is less for the non energy-producing systems, but these have the added advantage of requiring a lower membrane area to achieve a similar extent of seawater dilution. From preliminary results of the more realistic modelling, it seems that RED-RO scores better when losses are incorporated. Further thermodynamic and realistic modelling will focus on different RO recoveries, capital cost calculations based on membrane requirements and sensitivity analysis of the different parameters implemented

Spectroscopic determination of water salinity in brackish surface water in Nandoni Dam, at Vhembe District, Limpopo Province, South Africa

The problem of limited water supply in the Vhembe District (Limpopo Province, South Africa) is exacerbated by a preponderance of dissolved salts, which cause disagreeable taste and odour in the water as reported by the communities using this water for drinking. The water treatment plant that supplies the treated water to the communities in the District sources this raw water from the Nandoni Dam at the Luvuvhu river catchment. There are no scientific studies that have been reported in the literature that focused on determining the levels of water salinity from various water sources in the municipalities of the District. Water samples from various sites across the Nandoni Dam, a primary source of domestic water supply in the region, were collected through each season over a period of twelve months in order to ascertain the concentrations of dissolved salts in the dam. Onsite analyses of the water samples were conducted using the YSI ProDSS multimeter, while the laboratory water analyses were conducted using the spectroquant and atomic absorption spectrometers. Although salinity tests seem to indicate that the water sampled across most of the Nandoni Dam is brackish during all seasons of the year with the highest being 750 mg/L, water samples from the dam mid-outlet and the treatment plant are slightly below the World Health Organization (WHO) brackish water bracket of 500 mg/L with unfavourable taste for drinking. Results from this study indicate that the water sourced from the Nandoni Dam is not suitable for human consumption and therefore requires integrated water resource management, as well as robust and cost-effective water desalination treatment

Assisted reverse electrodialysis : a novel technique to decrease reverse osmosis energy demand

Assisted reverse electrodialysis (ARED) was introduced as a pre-desalination technique for seawater reverse osmosis (RO) for drinking water production. ARED is comparable to an additional applied pressure along the osmotic pressure in pressure assisted osmosis; a small voltage is applied in the same direction as the open cell voltage to increase the desalination speed compared to reverse electrodialysis (RED). This decreases the required membrane area. The concentration of the dilute compartment increases significantly during ARED operation due to the increased speed of desalination. This results in an overall decrease in total cell resistance. Although the energy demand for ARED is higher than for RED, the ARED-RO process still achieves a decrease in overall energy requirements at higher RO recoveries when compared to stand-alone RO. However, ion-exchange membrane prices will have to come down to 1-10 €/m² for the ARED-RO hybrid to become economically viable at current energy prices