Cake layer reformation rates on self forming dynamic membranes and performance comparison with microfiltration membranes.

Dynamic membranes (DMs) keep on attracting attention progressively as an alternative to conventional membranes because they can be operated with relatively higher fluxes and lower fouling rates. However, there are many factors affecting the performance of DMs, such as DM pore size, structure, and operating conditions. In this study, mainly focused on the investigation of cake formation rates both in initial formation and reformation rates after physical/chemical cleaning. In this context, it has been evaluated the performances of DMs with different pore sizes (171 µm, 90 µm, and 30 µm) and different structures under the same conditions and compared their performances with microfiltration (MF) membranes (0.45 µm and 0.22 µm) in a single reactor. In the study, the effects of different fluxes (15-, 20-, 25 L/m2·h (LMH), SADm (1-, 0.8-, 0.5 m3-air /m2·h) and F/M (0.095, 0.125, 0.19 g-COD/g-MLSS·day) conditions on the treatment and filtration performance of DMs were investigated. High COD (>95%) and turbidity (<10 NTU) removals were obtained in this study. In particular, the 30 µm DM (0.65 ± 0.47 NTU) produced quite close effluent turbidity compared to MFs (0.12 ± 0.05 NTU). Low SADm and high F/M values resulted in increased effluent COD concentrations and turbidity values. By decreasing the SADm, the cake formation rate and the fouling rate increased, which showed that there is a definite relationship between the cake formation rates and the fouling rates. Additionally, considering all the results, the most stable operation was obtained in the 30 µm DM, although it has been occurred the least fouling in the 90 µm membrane in the study. This study, focused on cake reformation rates, attempts to show that DMs can be used as an alternative to MBRs. Especially, when taking into account the results of the reformation rate of 30 µm DM (6.09 NTU/h) and other high filterability features.

Treatment of landfill leachate using single-stage anoxic moving bed biofilm reactor and aerobic membrane reactor.

Landfill leachate (LFL) is one of the most serious environmental problems due to the high concentrations of toxic and hazardous matters. Although several physical, chemical, methods have been tested, biological processes and single or multiple-stage combinations of them have been receiving more attention due to their cost-effective and environmentally-friendly manner. The present work recommended coupling of conventional single-stage A/O with moving bed biofilm reactor and membrane bioreactor (AnoxMBBR/AeMBR) for LFL treatment. The system performance was evaluated for 233 d under varying nitrate concentrations (100-1000 mgNO3--N/L), sludge retention time (SRT) (30-90 d), and HRT (24-48 h) in AnoxMBBR, and constant SRT (infinite) and HRT (48 h) in the AeMBR. The best system performances were observed at 1000 mgNO3--N/L concentration, SRT of 90 d and HRT of 48 h, and the average removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and nitrate­nitrogen (NO3-N) were 74.2%, 99.7%, and 89.1%, respectively. Besides, the AeMBR was achieved above 99% NH4+-N removal and not adversely affected by varying operation conditions of AnoxMBBR. A slight increase in selected phthalic acid ester (PAE) concentrations (diethyl phthalate (DEP), di (2-Ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP)) was detected in the AnoxMBR, and complete PAEs removal was attained in the AeMBR. Mg, Al, Si, Na, Fe was detected by SEM-EDX analyses in both biofilm of AnoxMBBR and the cake layers of AeMBR. Nitrobacter and Nitratireductor which showed a relatively high abundance played an important role in the removal of NH4+-N and COD in LFL. The results confirmed that the proposed sequence is efficient for COD removal, nitrogen removal, and PAEs being an acceptable treatment for landfill leachates.

Performance of anaerobic membrane bioreactor treating landfill leachate.

BACKGROUND: Landfill leachate has been known as non-biodegradable/hardly-biodegradable wastewater, which contains significant amount of soluble organic and inorganic compounds. However, membrane bioreactor (MBR) technology have become a more viable treatment option for complex and recalcitrant compounds compared to activated sludge systems. METHODS: This study aims at evaluating the performance of anaerobic membrane bioreactor (AnMBR) for the treatment of middle/old-aged landfill leachate (LFL).AnMBR was operated at different hydraulic retention times (HRTs) (48-12 h) and relaxation and backwashing (30 min-5 min, 5 min-0.5 min) periods. Additionally, Air stripping (pH 8, 24 g lime/L, 1.4 L/s air flow rate) as a pretreatment was evaluated prior to AnMBR. RESULTS: Air stripping removed about 90%, 25%, and 64% NH4 +, COD (Chemical Oxygen Demand) and color (RES620), respectively. The best results were obtained in combined air stripping-AnMBR operation corresponding to 95%, and 83% overall removals of color, and COD removals, respectively. Maximum methane yield and COD removal rate in AnMBR were 0.35 L methane/g COD removed and 5 gCOD removed /L.d, respectively. CONCLUSION: Pretreatment provided higher AnMBR flux that reached to 5.5LMH but increased fouling frequency due to the calcium precipitates in AnMBR which was verified with SEM-EDX analysis. Additionally, DEHP and DINP were not detected in permeate indicating AnMBR was successful for removing these micropollutants. This study showed that pretreatment clearly increased methane yield and COD removal rate.

Optimization of bioelectricity generation in fed-batch microbial fuel cell: effect of electrode material, initial substrate concentration, and cycle time.

Effective wastewater treatment and electricity generation using dual-chamber microbial fuel cell (MFC) will require a better understanding of how operational parameters affect system performance. Therefore, the main aim of this study is to investigate the bioelectricity production in a dual-chambered MFC-operated batch mode under different operational conditions. Initially, platinum (Pt) and mixed metal oxide titanium (Ti-TiO2) electrodes were used to investigate the influence of the electrode materials on the power generation at initial dissolved organic carbon (DOC) concentration of 400 mg/L and cycle time of 15 days. MFC equipped with Ti-TiO2 electrode performed better and was used to examine the effect of influent DOC concentration and cycle time on MFC performance. Increasing influent DOC concentration resulted in improving electricity generation, corresponding to a 1.65-fold increase in power density. However, decrease in cycle time from 15 to 5 days adversely affected reactor performance. Maximum DOC removal was 90 ± 3 %, which was produced at 15-day cycle time with an initial DOC of 3,600 mg/L, corresponding to maximum power generation of about 7,205 mW/m(2).

Effect of cycle time on polyhydroxybutyrate (PHB) production in aerobic mixed cultures.

The aim of this study was to investigate the effect of cycle time on polyhydroxybutyrate (PHB) production under aerobic dynamic feeding system. The acetate-fed feast and famine sequencing batch reactor was used to enrich PHB accumulating microorganism. Sequencing batch reactor (SBR) was operated in four different cycle times (12, 8, 4, and 2 h) fed with a synthetic wastewater. The system performance was determined by monitoring total dissolved organic carbon, dissolved oxygen, oxidation-reduction potential, and PHB concentration. In this study, under steady-state conditions, the feast period of the SBR was found to allow the PHB storage while a certain part of stored PHB was used for continued growth in famine period. The percentage PHB storages by aerobic microorganism were at 16, 18, 42, and 55% for the 12, 8, 4, and 2-h cycle times, respectively. The PHB storage was increased as the length of the cycle time was decreased, and the ratio of the feast compared to the total cycle length was increased from around 13 to 33% for the 12 and 2-h cycle times, respectively.

Bioelectricity generation in continuously-fed microbial fuel cell: effects of anode electrode material and hydraulic retention time.

The main aim of this study is to investigate the bioelectricity production in continuously-fed dual chambered microbial fuel cell (MFC). Initially, MFC was operated with different anode electrode material at constant hydraulic retention time (HRT) of 2d to evaluate the effect of electrode material on electricity production. Pt electrode yielded about 642 mW/m(2) power density, which was 4 times higher than that of the MFC with the mixed metal oxide titanium (Ti-TiO2). Further, MFC equipped with Pt electrode was operated at varying HRT (2-0.5d). The power density generation increased with decreasing HRT, corresponding to 1313 mW/m(2) which was maximum value obtained during this study. Additionally, decreasing HRT from 2 to 0.5d resulted in increasing effluent dissolved organic carbon (DOC) concentration from 1.92 g/L to 2.23 g/L, corresponding to DOC removal efficiencies of 46% and 38%, respectively.

Treatment of azo dye-containing synthetic textile dye effluent using sulfidogenic anaerobic baffled reactor.

This study aims at investigating azo dye reduction performance of a sulfidogenic anaerobic baffled reactor (ABR) for around 400 days. ABR was operated at 30 °C in a temperature-controlled room and hydraulic retention time (HRT) was kept constant at 2 days. The robustness of ABR was assessed under varying azo dye loadings and COD/sulfate ratios. Additionally, oxygen was supplied (1-2 L air/m(3)reactor min) to the last compartment to investigate the removal of azo dye breakdown products. ABR performed well in terms of COD, sulfate and azo dye removals throughout the reactor operation. Maximum azo dye, COD and sulfate removals were 98%, 98% and 93%, respectively, at COD/sulfate ratio of 0.8. Aeration created different redox conditions in last compartment, which enhanced the removal of COD and breakdown products. The adverse effects of aeration on azo dye reduction were eliminated thanks to the compartmentalized structure of the ABR.

Effect of electron donor source on the treatment of Cr(VI)-containing textile wastewater using sulfate-reducing fluidized bed reactors (FBRs).

The treatment of Cr(VI) containing textile wastewater was studied in ethanol and glucose-fed sulfate-reducing fluidized bed reactors at 35°C for around 250 days. The synthetic wastewater contained Cr(VI) (5-45 mg L(-1)), azo dye (Remazol Brilliant Violet 5R) (100-200 mg L(-1)), sulfate (2000 mg L(-1)) and ethanol or glucose (2000 mg L(-1) chemical oxygen demand (COD)). The robustness of two FBRs was assessed under varying Cr(VI) and azo dye loadings. Both reactors performed well in terms of COD, sulfate, color and Cr(VI) removals. However, ethanol-fed FBR performed better than glucose-fed one. The COD, sulfate, chromium and color removals at the highest Cr(VI) concentration (45 mg L(-1)) in ethanol-fed FBR were around 75%, 95%, 93%, and 99%, respectively. Further increase in influent Cr(VI) concentration adversely effected reactor performance. The COD, sulfate, chromium and color removals at 45 mg L(-1) Cr(VI) in glucose-fed FBR were around 60%, 50%, 93%, and 76%, respectively.

The effect of biological sulfate reduction on anaerobic color removal in anaerobic-aerobic sequencing batch reactors.

Combination of anaerobic-aerobic sequencing processes result in both anaerobic color removal and aerobic aromatic amine removal during the treatment of dye-containing wastewaters. The aim of the present study was to gain more insight into the competitive biochemical reactions between sulfate and azo dye in the presence of glucose as electron donor source. For this aim, anaerobic-aerobic sequencing batch reactor fed with a simulated textile effluent including Remazol Brilliant Violet 5R (RBV 5R) azo dye was operated with a total cycle time of 12 h including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (sulfate). Performance of the anaerobic phase was determined by monitoring color removal efficiency, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), color, specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2-dioxygenase), and formation of aromatic amines. The presence of sulfate was not found to significantly affect dye decolorization. Sulfate and azo dye reductions took place simultaneously in all operational conditions and increase in the sulfate concentration generally stimulated the reduction of RBV 5R. However, sulfate accumulation under anaerobic conditions was observed proportional to increasing sulfate concentration.

Effect of nitrate on anaerobic azo dye reduction.

The aim of the study was to investigate the effect of nitrate on anaerobic color removal efficiencies. For this aim, anaerobic-aerobic sequencing batch reactor (SBR) fed with a simulated textile effluent including Remazol Brilliant Violet 5R azo dye was operated with a total cycle time of 12 h, including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (nitrate) and performance of the system was determined by monitoring color removal efficiency, nitrate removal, nitrite formation and removal, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2 dioxygenase), and formation and removal of aromatic amines. Variations of population dynamics of microorganisms exposed to various amount of nitrate were identified by denaturing gradient gel electrophoresis (DGGE). It was found that nitrate has adverse effect on anaerobic color removal efficiency and color removal was achieved after denitrification process was completed. It was found that nitrate stimulates the COD removal efficiency and accelerates the COD removal in the first hour of anaerobic phase. About 90 % total COD removal efficiencies were achieved in which microorganism exposed to increasing amount of nitrate. Population dynamics of microorganisms exposed to various amount of nitrate were changed and diversity was increased.

The effect of cyclic anaerobic-aerobic conditions on biodegradation of azo dyes.

The effect of cyclic anaerobic-aerobic conditions on the biodegradative capability of the mixed microbial culture for the azo dye Remazol Brilliant Violet 5R (RBV-5R) was investigated in the sequencing batch reactor (SBR) fed with a synthetic textile wastewater. The SBR had a 12-h cycle time with anaerobic-aerobic periods of 3/9, 6/6 and 9/3 h. General SBR performance was assessed by measurement of catabolic enzymes (catechol 2,3-dioxygenase, azo reductase), chemical oxygen demand (COD), color and amount of aromatic amines. In this study, under steady-state conditions, the anaerobic period of the cyclic SBR was found to allow the reductive decolorization of azo dye. Longer anaerobic periods resulted in higher color removal efficiencies, approximately 71% for the 3-h, 87% for 6-h and 92% for the 9-h duration. Total COD removal efficiencies were over 84% under each of the cyclic conditions and increased as the length of the anaerobic period was increased; however, the highest color removal rate was attained for the cycle with the shortest anaerobic period of 3 h. During the decolorization of RBV-5R, two sulfonated aromatic amines (benzene based and naphthalene based) were formed. Additionally, anaerobic azo reductase enzyme was found to be positively affected with the increasing duration of the anaerobic period; however; it was vice versa for the aerobic catechol 2,3-dioxygenase (C23DO) enzyme.