In an anaerobic/aerobic/anoxic (A/O/A) sequencing batch reactor (SBR), non-filamentous bulking sludge granulated after the adjustment of cycle duration and influent composition directed by pH, oxidation-reduction potential (ORP) and dissolved oxygen (DO). The turning points and plateaux of pH, ORP and DO profiles indicated the end of biochemical reactions, such as chemical oxygen demand (COD) consumption, P release, ammonium oxidation, P uptake and denitrification. The difference of nutrient concentration between the beginning and turning points represented the actual treatment capability of the sludge. Non-filamentous bulking with SVI30 of 255 mL g−1 resulted in a huge biomass loss. After regulation, the cycle duration was shortened from 310 to 195 min without unnecessary energy input. In addition, the settling ability was obviously improved as SVI30 reduced to 28 mL g−1. Moreover, matured granules with an average diameter of 600 μm were obtained after 45 days, and simultaneous COD, ammonium and phosphate (P) removal was also realized after granulation.

•Small (<800 μm) and stable aerobic granules were obtained with low energy input.•Simultaneous nitrification, denitrification and phosphate removal was realized.•LB PS and TB PS fascinate the formation and stability maintenance of granules.•Combined selective pressures was critical to control the size of aerobic granules.Diameter is the key factor that influencing the stability of granules. In this study, combined selective pressure generated by low strength wastewater (chemical oxygen demand, COD, 200 ± 40 mg/L), low hydrodynamic shear force (superficial gas velocity of 0.55 cm/s and agitation of 180 rpm), different sludge discharge mode and a sequencing batch bioreactor (SBR) with an alternating anaerobic/aerobic/anoxic (A/O/A) operational process were employed to limit the diameter of aerobic granules. Energy consumption was reduced as low superficial gas velocity and agitation were employed. Granulation process was completed after 40 days. The matured granules with small diameter (d (0.9) < 800 μm) were stable without disaggregation during the experiment period (220 days). The extracellular polysaccharide/extracellular protein (PS/PN) ratio increased along with granulation process, and maintained at a stable level in the following time. After granulation, the removal efficiencies of COD, NH4+–N, total nitrogen (TN) and phosphate (P) reached 99%, 98%, 90% and 99%, respectively. The majority of TN was consumed during aerobic stage after complete granulation. The effective TN removal was mainly due to the activities of denitrifying phosphate-accumulating organisms (DNPAOs) and denitrifying glycogen-accumulating organisms (DNGAOs).

•The mineral tourmaline was used to modify graphite electrode.•Tourmaline can enhance microbial growth and activity for better catalysis.•Tourmaline-modified cathode arose electricity generation compared to the controls.Bio-cathode which uses microorganisms as catalyst can reduce MFC cost and sustain similar power output compared to noble metal catalyst. Thereby, looking for a cathode material which is high conductivity, good biocompatibility and even can stimulate and enhance activity of bio-catalyst is of great interest. In this paper, modified electrode by tourmaline and polyaniline (reactor 3) was used as cathode. The output power density was improved by 492.6% and 192.8% compared to reactor 1 (unmodified cathode) and reactor 2 (cathode modified only by polyaniline) (54 mW m−2 for reactor 1, 138 mW m−2 for reactor 2 and 266 mW m−2 for reactor 3, respectively). When the external resistance was 800Ω, output voltages of reactor 1, 2 and 3 were kept at 0.20 ± 0.005 V, 0.26 ± 0.005 V and 0.37 ± 0.005 V, respectively. Cyclic voltammetry curves showed that reductive current of reactor 3 was higher than those of reactor 1 and 2, indicating that the cathode of reactor 3 had the strongest catalytic activity which was due to that tourmaline could help the interfacial electron transfer, and thereby facilitate the reduction of oxygen at the cathode. Results demonstrated that the tourmaline modified electrode could effectively improve the reduction reaction and enhance the performance of the whole MFC system.

In this study, polyvinyl alcohol nanospheres (PVA-NS) were successfully prepared by cross-linking in microemulsion system and the average size could be reduced to 225 nm. The characters of PVA-NS indicated that the hydrophilicity of PVA-NS was very strong, completely wettable by water owing to a mass of –OH on the PVA-NS surface and they were highly negatively charged (ζ = −51.4 mV). Then two types of modified non-woven fabric (NWF) membranes were prepared (deposited and self-assembly membranes) and their hydrophilicity and anti-fouling properties were investigated. PVA-NS were used to fabricate deposited membranes and Hexadecyl trimethyl ammonium bromide (HTAB)/PVA-NS were used for self-assembly membranes. Membrane performances were changed by self-assembling or depositing PVA-NS on the surface of NWF membranes. HTAB/PVA-NS self-assembly membrane showed stronger hydrophilicity, greater permeability and anti-fouling performance compared to that of PVA-NS deposited membrane. The stability experiment results showed that self-assembly NWF membranes had excellent stability and it can be concluded that HTAB/PVA-NS self-assembly membranes will be simple and powerful alternative for fouling mitigation in MBR application.Graphical abstractIn this study, small size cross-linking PVA nanopheres (PVA-NS) have been prepared in microemulsion system. Low-fouling modified membranes were synthesized by PVA-NS/HTAB self-assembly. The anti-fouling experiment showed that the self-assembly membrane had the greatest anti-fouling performance.Research highlights▶ Prepare polyvinyl alcohol nanospheres (PVA-NS) successfully in microemulsion system. ▶ Combine membrane hydrophilic modification with PVA nanospheres and prepare self-assembly and deposited membranes. ▶ The antifouling performance and the stability of PVA-NS on membrane surface of HTAB/PVA-NS self-assembly membrane and were both better than PVA-NS deposited membrane.

A rotating flat-sheet membrane bioreactor (RFMBR) was employed to start up anammox process, in comparison with a conventional membrane bioreactor (CMBR). The anammox process was successfully started up within around 16 days in both bioreactors. The particle image velocimetry (PIV) analysis showed a larger velocity gradient and a stronger shear stress on membrane surface in RFMBR than in CMBR. At the end of the experiment, the mean particle size of anammox granules achieved 899 μm in RFMBR, while the value reached 809 μm in CMBR, and the trans-membrane pressure (TMP) reached 4 and 16 kPa in RFMBR and CMBR, respectively. Furthermore, the scanning electron microscope (SEM) observation of the biofilm formed on membranes illustrated that a much thinner biofilm with the thickness of 35 μm was formed in RFMBR, compared to the value of 120 μm in CMBR.Highlights► A rotating flat-sheet membrane bioreactor was employed to start up anammox process. ► The anammox process was successfully started up within around 16 days. ► The hydrodynamic conditions were investigated by particle image velocimetry. ► After 60 days of operation, the membrane fouling in the novel MBR was very slight.

•Investigation of the effect of spacer location on concentration polarization (CP)•Use of spacers to mitigate dilutive internal CP without energy input•Only spacers with a certain pore size could mitigate CP.A major barrier for forward osmosis (FO) process is concentration polarization (CP) which dramatically reduces the performance of FO. This study focused on providing a simple method of mitigating CP, especially dilutive internal CP (DICP), in the absence of additional energy consumption and investigate the impact of spacer location on CP quantitatively in both FO (AL-FS) and PRO (AL-DS) mode; finally we tried to provide a spacer location that could best decrease the adverse effect of CP on FO performance.The findings of the research led to the conclusion that in FO mode, placing the spacer (1 mm × 1 mm) in the draw channel with one end connecting the membrane could well mitigate DICP. Besides, placing the same spacer in both feed and draw channels could be an acceptable method of decreasing concentrative external CP (CECP) and DICP simultaneously. If locating the spacer thus, the average water flux could increase by 7.57%, 14.1% and 18.7% when the concentration of the draw solution was 1 M, 2 M, and 4 M separately. Similarly, in PRO mode we found that spacer can also mitigate concentrative ICP and dilutive ECP. Besides, the pore size in the spacer should also be considered when it was used to mitigate CP.

The formation of aerobic granules with low organic loading synthetic wastewater (150–200 mg L−1 of influent COD, acetate/propionate = 1/3) at low aeration rate (0.6 cm s−1 of superficial gas velocity) had been investigated in the anaerobic/oxic/anoxic SBR. Aerobic granules with smooth surface and compact structure were successfully obtained after 50 days. However, these aerobic granules were unstable when the d(0.9) of granules increased to more than 1 mm. The results suggested that the aerobic granules with small diameter (smaller than 1000 μm) were more favorable for treating the low substrate loading wastewater at the low aeration rate. The cycle test revealed that most of the influent COD was removed at the anaerobic stage. The effluent concentrations of N–NH4+ and P–PO43− were lower than 1 mg L−1, and the effluent concentration of nitrate gradually decreased with the granulation. Phosphate accumulating organisms were found to utilize O2 or NOx− as electron acceptor for phosphorus removal in the study. Simultaneous nitrogen and phosphorus removal occurred inside the granules.