Water extraction from mixed liquor of an aerobic bioreactor by forward osmosis: membrane fouling and biomass characteristics assessment

This study investigated membrane fouling and biomass characteristics during water extraction from mixed liquor of an aerobic bioreactor by a submerged forward osmosis (FO) system. As the sludge concentration in the reactor increased from 0 to 20 g/L, fouling of the FO membrane increased but was much less severe than that of a reference microfiltration membrane. The results also indicate that aeration can be used to effectively control membrane fouling. By increasing the draw solute concentration, as expected, the initial water flux was increased. However, there appears to be a critical water flux above which severe membrane fouling was encountered. A short-term osmotic membrane bioreactor experiment showed build-up of salinity in the bioreactor due to the reverse draw solute transport and inorganic salts rejection by the FO membrane. Salinity build-up in the bioreactor reduced the permeate flux and sludge production, and at the same time, altered the biomass characteristics, leading to more soluble microbial products and less extracellular polymeric substances in the microbial mass. Additionally, the inhibitory effects of the increased salinity on biomass and the high rejection capacity of FO led to the build-up of ammonia and ortho-phosphate in the bioreactor

Resource recovery from digested manure centrate:Comparison between conventional and aquaporin thin-film composite forward osmosis membranes

We compared the performance of conventional and aquaporin thin-film composite forward osmosis (FO) membranes (denoted as HTI and AQP membrane, respectively) for concentration of digested manure centrate. Results show that the two FO membranes were capable to concentrate digested centrate for resource recovery. During concentration of digested manure centrate, a cohesive fouling layer formed on the HTI membrane surface, resulting in more dramatic flux decline and less fouling reversibility in comparison to the AQP membrane. The two FO membranes exhibited effective and comparable rejection of bulk organic matter, total phosphorus, and heavy metals, leading to their notable enrichment in digested manure centrate. By contrast, ammonium nitrogen (NH4 +-N) was only retained by approximately 40% using the two FO membranes with a slightly higher retention by the HTI membrane, since it was less negatively charged. As a result, total nitrogen was ineffectively rejected by the two FO membranes. It is noteworthy that the HTI membrane also contributed to higher rejection of most antibiotics than the AQP membrane, possibly due to enhanced retention by the fouling layer and retarded forward diffusion. Results from this study evidence the outperformance of the AQP membrane as a new generation FO membrane over its conventional counterpart with respect to antifouling property, while further improvement in membrane selectivity, particularly of monovalent cations (e.g. NH4 +-N), is needed to advance FO applications in resource recovery from challenging waste streams.</p

Effects of surfactant addition to draw solution on the performance of osmotic membrane bioreactor

This study investigated the effects of surfactant addition to the draw solution on the performance of osmotic membrane bioreactor (OMBR). Forward osmosis (FO) tests were conducted with the addition of sodium dodecyl benzene sulfonate (SDBS), a representative surfactant, to both inorganic and ionic organic draw solutions, including sodium chloride (NaCl), sodium acetate (NaOAc), and sodium propionate (NaPro), to determine the desirable draw solution for OMBR operation. Results show that SDBS impacts were more notable for inorganic draw solution in comparison to its ionic organic counterparts at the same osmotic pressure (60 bar) in FO operation. In specific, SDBS addition up to 5 mM considerably reduced the reverse diffusion of NaCl draw solute (approximately 69.7%) with insignificant impact on water flux. Thus, salinity build-up in the bioreactor could be effectively mitigated when SDBS was added to the NaCl draw solution in OMBR operation. This mitigation led to stable sludge characteristics and biological treatment to sustain OMBR performance regarding water production (approximately 10 L/m2h) and contaminant removal (e.g. over 90% for pharmaceutically active compounds).</p

Emerging investigator series:Onsite recycling of saline-alkaline soil washing water by forward osmosis: Techno-economic evaluation and implication

This study investigated the techno-economic feasibility of forward osmosis (FO) for onsite recycling of saline-alkaline soil washing water with an all-purpose liquid fertiliser as a draw solution. Commercially available polyamide thin-film composite and aquaporin FO membranes (denoted HTI and AQP membranes, respectively) were compared under different operating conditions. Results showed that the incorporation of aquaporin vesicles offered the AQP membrane better transport properties (i.e. higher water permeability and lower salt permeability) than the HTI membrane. Thus, the AQP membrane exhibited a much higher water flux and lower reverse solute flux than the HTI membrane in response to either an increase in operating temperature or draw solution concentration. In particular, the water flux of the AQP membrane enhanced from 20.2 to 42.4 L m-2 h-1 with a temperature increase from 25 to 40 °C. Although over 85% water recovery with effective retention of dissolved inorganic salts could be achieved by both FO membranes in concentration of saline-alkaline soil washing water, the AQP membrane was more techno-economically feasible in practice, mainly due to its higher water flux and lower capital and operational expenses. Nevertheless, the economic favourability of the AQP membrane (i.e. the total water cost) over the HTI membrane was largely determined by its membrane element cost. </p