Insight into fouling potential analysis of a pilot-scale pressure-assisted forward osmosis plant for diluted seawater reverse osmosis desalination

An integrated MDC-FO membrane configuration for simultaneous desalination, wastewater treatment and energy recovery

A novel microbial desalination cell (MDC) configuration was developed by introducing a forward osmosis (FO) membrane, separating the cathode chamber from a fourth extra chamber. Wastewater is treated using a sequential anode-cathode feed. The new chamber then serves as a FO draw chamber, where a saline solution is used to recover freshwater from the adjacent cathode chamber. The diluted saline solution then goes to the MDC middle chamber for further desalination. Three identical cells were constructed and operated in cyclic-batch-flow mode at different initial wastewater and saline solution concentrations. Up to 84.8 ± 1.7% of the wastewater was recovered as freshwater. Freshwater recovery decreases at lower salt concentrations and higher wastewater COD concentrations due to the lower osmotic pressure difference. Salinity of saline water was decreased by up to 69.57 ± 3.85% at the highest initial salinity. COD removal up to 94.42 ± 4.15% was reached. COD removal rates were higher at higher COD concentrations. Polarization curves show the effect of COD on the internal resistance, where cells operated at lower COD experienced higher internal resistance. Scanning electron microscopy (SEM) images revealed the extent of fouling on the ion exchange membrane and biofilm formation on the FO membranes and the electrodes.

Lateral force removal of fungal spores to demonstrate how surface properties affect fungal spore retention

Microbial biofouling on polymer surfaces can lead to their biodeterioration. This may result in deterioration of the surface, leading to cracking and fracturing. Fungal spores from Aspergillus niger 1957, Aspergillus niger 1988 and Aureobasidium pullulans were tested to determine their strength of attachment on three surfaces, p(γ-MPS-co-MMA), p(γ-MPS-co-LMA) and spin-coated poly(methyl methacrylate) (PMMAsc), using lateral force measurements. The results demonstrate that A. niger 1957 and A. niger 1988 spores were most easily removed from the p(γ-MPS-co-MMA) surface, which was the surface with the highest R_a value. The A. niger 1957 and A. pullulans spores were most difficult to remove from the PMMAsc surface, which was the hardest surface. A. niger 1988 spores were the most difficult to remove from p(γ-MPS-co-LMA), the most hydrophobic surface. The results with A. pullulans were difficult to elucidate since the spores bound to all three surfaces and were removed with similar rates of force. The lateral force results demonstrate that spore attachment to a surface is a multi-factorial process, and independent surface and microbial factors influence spore binding. Thus, each environmental scenario needs to be considered on an individual basis, since a solution to one biofouling issue will probably not translate across to other systems. This article is part of the theme issue 'Nanocracks in nature and industry'.

Reverse Osmosis Treatment of Wastewater for Reuse as Process Water-A Case Study

The aim of this work was to purify mixed wastewater from three different production processes in such a manner that they could be reused as process water. The maximum allowed concentrations (MAC) from the Environmental Standards for emissions of substances released into surface water were set as target concentrations. Wastewaters contained solid particles, sodium, aluminium, chloride, and nitrogen in high amounts. Quantitatively, most wastewaters were generated in the production line of alumina washing. The second type of wastewater was generated from the production line of boehmite. The third type of wastewater was from regeneration of ion exchangers, which are applied for feed boiler water treatment. The initial treatment step of wastewater mixture was neutralisation, using 35% HCl. The precoat filtration followed, and the level of suspended solids was reduced from 320 mg/L to only 9 mg/L. The concentrations of ions, such as aluminium, sodium and chlorides remained above the MAC. Therefore, laboratory reverse osmosis was applied to remove the listed pollutants from the water. We succeeded in removal of all the pollutants. The concentration of aluminium decreased below 3 mg/L, the sodium to 145 mg/L and chlorides to 193 mg/L. The concentration of nitrate nitrogen decreased below 20 mg/L.