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Forward osmosis is a low-energy water treatment emerging technology, which has demonstrated improved solute rejection and low fouling propensity. In this study, the applicability of aquaporinbased forward osmosis membranes during separation of biogas digestate liquid fractions was investigated. The results showed that Total Ammonia-Nitrogen rejection was higher than 95.5% in all experiments, independently of the type of draw solution (NaCl and hide preservation effluents), experimental period and the use of feed acidification. The results also confirmed that high draw osmotic pressures (i.e. 3.5M sodium chloride and hide preservation wastewater) combined with feed acidification had a negative effect on the membrane water permeability. Membrane rinsing after fouling was also successful in recovering the membrane initial water flux as well as removing 2 the remaining foulants on the membrane surface. The membrane inspection results from Scanning-Electron Microscope, Energy-Dispersive X-Ray analysis and Fourier Transform Infrared-Attenuated Total Reflectance showed that fouling in this application was mild and reversible after membrane rinsing. The applicability of aquaporin-based forward osmosis membranes during separation of biogas digestate liquid fractions has been demonstrated. The results showed the potential of this technology to achieve enhanced ammonia-nitrogen rejections and low-fouling propensity.

Osmotic membrane bioreactor (OMBR) is an emerging membrane process which has gained interest in the recent years because of the low energy consumption and the high effluent quality. The osmotic membrane bioreactor combines a forward osmosis (FO) membrane and a biological treatment. However, salt reverse flux is the main problem because of the negative effect of the salt concentration increase in the reactor on the microbial activity. This is the reason why the study of a suitable draw solution (DS) is very important in the overall performance of the reactor. This study compares the process performance using two draw solutions: a 53 g•L-1 NaCl solution and a real waste water solution (waste water from an absorption column consisting mainly of SO4-2 and NH4-N with concentrations of 153 g•L-1 and 19 g•L-1 , respectively). The comparison is focused on the salt reverse flux during the reactor operation, the mixed liquor characteristics, the membrane fouling and the overall performance. The results indicated that the industrial wastewater showed a higher salt reverse flux, but also a less severe fouling and a higher the osmotic pressure difference in comparison with the NaCl solution. In terms of chemical oxygen demand (COD) removal efficiencies, both draw solutions attained values higher than 80%, though the efficiency was slightly lower when the industrial effluent was used as DS. This was related to the higher conductivity reached in the bioreactor when the industrial effluent was used as draw solution. In spite of it, the use of this industrial effluent as draw solution is strongly recommended because of the high permeate fluxes yielded, the low membrane fouling and the lack of necessity of regenerating the draw solution.

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The performance of an osmotic membrane bioreactor (OMBR) for treating tannery wastewater at laboratory scale has been evaluated in this study. The forward osmosis (FO) membrane tested was CTA-NW from HTI. As draw solution, actual waste water from an absorption column for ammonia separation, which consists mainly of ammonium sulphate was used. The study was focused on the salt reverse flux during the OMBR operation, membrane water flux, biomass characteristics and membrane fouling.Regarding membrane water flux change with the time, the measured values diminished from 3.44 to 0.72 LMH due to the membrane fouling and the salt accumulation in the biological reactor. The stable mixed liquor conductivity value at the end of the experiment was 29.8 mS•cm -1 . The chemical oxygen demand (COD) removal efficiencies were maintained near 80% until the first 50 days of operation, considering the soluble COD in the reactor instead of the COD in the membrane permeate for the performance calculation. Thence, COD removal efficiencies decreased progressively due to the accumulation of non degradable COD coming from the tannery wastewater.Concerning to the membrane fouling, FESEM/EDX analysis corroborated that organic fouling was predominant on the membrane active layer.