•Structure of cake layers at different times & depths were measured by various methods.•Membrane resistance was highly correlated with cake layer thickness (r = 0.98, p = 0.005).•Specific pore volume displayed an initial decline with time, as 1–10 nm pores reduced.•Specific pore volume decreased from top to bottom layers, as 30–250 nm pores blocked.•Porosities from BET results were more comprehensive than from SEM pictures.The cake layers play a key role in the rejection of particles in dynamic membrane bioreactors and produces most of the resistance. This research aims to directly observe and measure the transient structure of the cake layers at different times and depths. The results showed the membrane flux remained relatively stable for the first 30 h, but decreased from 110 L/m2 h to 88 L/m2 h in the next 20 h. The membrane resistance was highly correlated with the cake layer thickness. The porosity and average pore diameter obtained from the scanning electron microcopy (SEM) pictures displayed no temporal variations, as only the new generated surface of the cake layer can be observed by SEM. However, the specific pore volume and surface area based on the Brunauer–Emmett–Teller (BET) nitrogen adsorption results displayed an initial decline, from 0.30 cc/g to 0.22 cc/g, due to the disappearance of the small diameter pores (1–10 nm) with time. The large diameter pores (30–250 nm) accounted for the majority of the cumulative pore volumes in all samples, as well as in the top layer, middle layer, and bottom layer. The specific pore volume and specific surface area exhibited a decline from the top layer to bottom layer, from 0.38 cc/g to 0.21 cc/g, due to the blockage of large diameter pores. In addition, BET nitrogen adsorption data provided comprehensive structural characteristics of the cake layers.

Ebullition of gas bubbles through sediment can enhance the migration of gases through the subsurface and potentially affect the emission of important greenhouse gases to the atmosphere. To better understand the parameters controlling ebullition, investigations of gas ebullition in the Grand Calumet river (Indiana, USA) were conducted. We found that gas ebullition might shift and change with different vertical hydraulic gradients and temperatures. CO2 and CH4 flux for each site increased with an increase in temperature. A comparatively simple linear relationship existed between the gas flux and the measured parameters (GF = 0.316T + 300.66i, R2 = 0.82). The gas flux in the sand cap was more variable than that in sediment. Moreover, the total field gas fluxes varied from 10 to 180 mmol m−2 d−1 for sediment and from 5 to 35 mmol m−2 d−1 for the sand cap, which proved an in situ sand cap could provide effective remediation. The analysis presented here has shown that gas fluxes and reactive transport modeling can provide effective means of investigating ebullition and quantifying gas transport.

•We design a ‘self-adaptive membrane tube’ for the dynamic membrane filtration process.•We compare performances of different modules in submerged/recirculated bioreactor.•The self-adaptive membrane had a sustainable stable flux and longest operation time.•The flow fields of submerged/recirculated bioreactor were compared by using CFD.•A pilot scale test of recirculated DMBR was carried out lasting for 12 months.A gradual decline of membrane flux or gradual rise of filtration resistance appeared during the dynamic membrane running processes in previous studies, limiting the acceptance of dynamic membrane bioreactor in a wastewater treatment. In this study, we designed a special tubular membrane module, which can be self-adaptive according to the dynamic membrane filtration process, to gain a sustainable stable flux and enhance the backwashing effect. The comparison among different membrane modules in submerged bioreactor and the performance of the self-adaptive module in recirculated bioreactor were investigated. A pilot scale test lasting for 12 months was conducted to evaluate the long-term applicability of the self-adaptive membrane module. The results demonstrate that the self-adaptive structure had a beneficial effect on the formation and backwashing of the dynamic membrane. The formation time of dynamic membrane was much shorter than the flat module and the average turbidity of effluent was excellent. The self-adaptive membrane module had the longest stable operation time, up to 72.3 h when operated in submerged bioreactor, much larger than other membrane modules. When operated in 60 L/m2 h in recirculated dynamic membrane bioreactor, the stable operation time reached up to 480.3 h, due to the uniform flow field and effective impulse backwashing. The effluent concentrations of COD, TP, NH3-N and SS as well the turbidity in the pilot scale test were similar to or even below the values achieved in the wastewater treatment plants.

Studies were conducted to evaluate the performance of sodium hydroxide solution (NaOH) immersed lemon grass (ILG) adsorbing copper (Cu), zinc (Zn) and cadmium (Cd) in single-metal and multi-metal solutions, respectively. Parameters included pH, sorbent dosage and contact time. Fourier transform infrared (FTIR) spectrophotometer was used to elucidate ILG sorption mechanisms. Results indicated that sorption isotherms of ILG for all three metals were well described by Langmuir equation, with a maximum uptake at 13.93 mg Cu, 15.87 mg Zn and 39.53 mg Cd per g ILG. The change of peaks in FTIR spectrum were observed after being immersed by 0.2 M sodium hydroxide solutions (NaOH), which was likely to increase the number of sorption sites for metal uptake. Obtained results implied that ILG had a great potential for the removal of heavy metals in aqueous solutions.