The possibility of continuous hygienic water production from wastewater in a combined system comprising an innovative air lift bioreactor and a membrane module was investigated. To improve the performance of a commercial poly acrylonitrile ultra-filtration membrane, layer by layer method was used. The effect of bilayer number (1, 3 and 5) and the type of polyanions on the membrane surface characteristics was investigated. Poly (4-styrenesulfonic acid-co-maleic acid) and poly (methacrylic acid) with different molecular weights were considered as polyanions and poly diallyl dimethyl ammonium as a polycation was used for surface modification. The polyelectrolyte multilayer fabrication was verified via attenuated total reflection, scanning electron microscope, atomic force microscopy, and contact angle characterization. According to the results, poly (4-styrenesulfonic acid-co-maleic acid) with higher molecular weight and charge density showed a better performance in terms of antifouling performance and flux recovery ratio compared to poly (methacrylic acid). An increase in bilayer numbers caused an increase in hydrophilicity and antifouling property. A membrane with 5 bilayers of Poly (4-styrenesulfonic acid-co-maleic acid) and poly diallyl dimethyl ammonium presented the highest hydrophilicity (the lowest contact angle) and flux recovery ratio (100%), and showed a gel-like layer on the surface. The production of hygienic water was confirmed by microbial test results.

This study surveys the effect of different operational models, batch, continuous, and continuous feeding with intermittent discharge (CFID), on the performance of an air lift reactor (ALR) and a stirred tank reactor (STR) in terms of simultaneous removal of CNP from milk processing wastewater. The experimental data were recorded under similar operating conditions with HRT of 10 h, air flow rate of 2 l/min, and biomass concentration of 5–6 g/l. The obtained results indicated that the CFID mode was a promising regime which ensured the occurrence of anaerobic, anoxic, and aerobic conditions in the air lift bioreactor. This gave favorable conditions for simultaneous COD and nutrient removal processes in one compartment. At the optimum condition obtained, 170 mg/l (79%) of total nitrogen (TN) and 25 mg/l (63%) phosphorus (TP) were removed in the CFID-ALR, while, batch and continuous operational conditions did not create anaerobic and efficient anoxic zones in the air lift bioreactor. The ALR was more effective to remove nutrients when compared to the STR at all different operational modes studied. The microbial community at different experimental conditions was also investigated to detect Candidatus Accumulibactor as a common species of phosphate accumulating organism (PAOs) through PCR method. From the PCR results, Candidate Accumulibactor was detected in the CFID-ALR, underpinning the observed TP removal.

In this research, continuous feed and intermittent discharge air lift bioreactor (CFIDAB) was evaluated under two independent variables to treat milk processing wastewater (MPW). The effect of HRT (6-14 h) and air flow rate (1-3 l/min) on the performance of CFIDAB was studied in a laboratory scale of the bioreactor. The optimum values of HRT and air flow rate were 10 h and 3 l/min, reaching SCOD, TN, and TP removal efficiency around 98%, 85%, and 78%, respectively. The results showed that TP and TN removal were enhanced simultaneously with an increase in HRT and air flow rate. Oxidation-reduction potential (ORP) measurement at the optimal condition showed the successful occurrence of anaerobic, anoxic, and aerobic zones in the CFIDAB. Moreover, the effect of feed characteristics on the process performance for milk processing and soft drink wastewaters was investigated. Based on the obtained data, CFDIAB operated with soft drink wastewater (SDW) showed a better performance in removal of carbon and phosphorus compounds, while nitrogen content was removed more efficient for MPW. As a result, the performance of CFIDAB is sensitive to BOD₅/COD ratio of wastewater. Overall, this single compartment air-lift bioreactor could act as an efficient biological nutrient removal system, providing the conditions for good carbon and nutrient removal. It showed an excellent reactor geometry as well as operating strategy to be used as a membrane bioreactor.