Effect of an electro phosphorous removal process on phosphorous removal and membrane permeability in a pilot-scale MBR

The pilot membrane bioreactor (MBR) was equipped with an electro-coagulation process for phosphorous removal (EPR process). The effect of the EPR process on nutrient removal and membrane permeability was investigated in this study.Experiments were carried out for about 5 months with the pilot MBR that treated wastewater at a capacity of 50 m³/day. And the MBR used two different materials of the plate type membrane: polyvinylidene fluoride (PVDF) and polyethersulfone (PES). Phosphorous ion released from the anaerobic settling tank was coagulated by electrochemical reaction with aluminum ion discharged from aluminum plate electrodes in the EPR tank. The phosphate (PO₄³⁻-P) removal efficiency and the total phosphorous (TP) removal efficiency by electro-coagulation were 89.2% and 79.9%, respectively. Results of particle size distribution (PSD) analysis showed that the particle sizes of flocs were mostly in the range of 50-150 μm, and the membrane resistance decreased significantly in the MBR as the EPR proceeded. Consequently, this study showed that the EPR process was useful for reducing trans-membrane pressure (TMP) and for removal of phosphorous in the MBR, which was operated in long sludge retention time (SRT) conditions.     

Sludge filterability and dewaterability in a membrane bioreactor for municipal wastewater treatment

The physical properties of excess sludge wasted from a large pilot scale membrane bioreactor (MBR) have been routinely monitored over almost two years. A statistical analysis highlighted the significant impact of temperature on the capillary suction time and sludge filterability, due to the increase of organic matter in the liquid phase. Suspended solids have resulted to be the most important component affecting sludge filterability, although the impact of colloids and solutes increased when temperature decrease, thus confirming the generally worse characteristics of sludge in such conditions. Conditioning and dewatering test have been performed on a pilot scale fixed volume recessed plate filter press. Six different chemicals were used for sludge pre-conditioning and, for each additive, three dosages were tested in the range 5-25 g_polymer kgMLSS^− 1. After about sixty filtration trials at three different pressure values (7, 11 and 15 bar), the kind of polymer seem to be the most important factor influencing the final cake-dryness, with less evident impact for dosage and operational pressure. Finally, when performed on the aerobically digested excess sludge wasted from a conventional activated sludge plant, the filtration tests show no differences with the MBR sludge.     

Filtration characteristics of activated sludge in hybrid membrane bioreactor with porous suspended carriers (HMBR)

The suspended carriers were efficient in controlling membrane fouling in hybrid membrane bioreactor with porous suspended carriers (HMBR). The purpose of this study consisted in investigating the effect of suspended carriers on the sludge suspension, especially the filterability of sludge suspension. The filterability of sludge suspension in HMBR and general membrane bioreactor (MBR) were investigated and compared in parallel conditions by dead-end filtration for better evaluating the influence of suspended carriers on the sludge suspension. Several aspects of sludge suspension such as filtration resistance, specific cake resistance and particle size were discussed. During long-term operation the filtration resistances rose gradually in the early stage (about 100 days) and then increased rapidly, but there was a slight difference between MBR and HMBR with the prolongation of operation time. The granulometric analysis revealed that the mean particle size of sludge suspension of HMBR decreased more sharply than that of MBR, because the fluidized carriers in HMBR would impose shear stresses on sludge flocs and induce the destruction of the network of sludge zoogloea. Dead-end filtration experiments indicated that the resistance-increasing rates of three portions of sludge suspension were in the order of supernatant > dissolved organics > microbial flocs. In order to further understand the filterability of sludge suspension, the specific cake resistance (α or α.C) of sludge suspension and supernatant in HMBR and MBR were determined. During long-term operation the α and α.C increased with operation time. These results revealed that the suspended carriers in HMBR had appreciably negative effect on the biological characteristics and filterability of the sludge suspension, but they were efficient in controlling membrane fouling during continuous operation of HMBR.     

Effects of the sludge reduction system in MBR on the membrane permeability

For the sludge volume reduction, gravity thickening and mechanical thickening processes have been mainly applied. However, these processes usually cause several problems such as large footprint, low thickening efficiency, etc. To solve these problems, a sludge reduction system using submerged membrane in a reactor with excess sludge from a biological nutrient removal (BNR) system was investigated. Both lab and pilot scale experiments for sludge reduction were carried out. The hydraulic retention time (HRT) was in a range of 4.5-6.7 days during the experimental period. A flat-sheet membrane with a mean pore size of 0.08 µm was used and operated at a flux range of 7-20 L/m²·h.During the experimental period, concentrations of BOD and SS were maintained less than 8 mg/L, 3 mg/L, respectively, which indicated the high quality of treated wastewater. While extracellular polymeric substances (EPS) were lowest at a coagulant concentration of 15 ppm, soluble microbial product (SMP) concentrations did not have any correlation with coagulant concentrations. The critical flux was observed in a range of 18-24 L/m²·h.These results suggested that the sludge reduction system using membrane bioreactor (MBR) could be applied as one of suitable processes to overcome problems of conventional processes such as gravity and mechanical thickening.     

Greywater recycling in Vietnam — Application of the HUBER MBR process

Greywater is the part of domestic wastewater that is free of faeces. The volume and concentration of this separately collected wastewater flow depend on the consumer behaviour and vary according to its source. The average amount of greywater produced per day in a German household is 70 l per person, which is more than 50% of the total wastewater production [5]. This figure corresponds with the average figures provided for Chinese households (80 l per person/day, GB/T 50331-2002), but significantly exceeds the South African average of 20 l per person and day [1].Compared to domestic wastewater, greywater generally contains less organic pollutants, less nutrients but a high amount of tensides. The effluent from bath tubs, showers or wash hand basins contains for example a by approx. two decimal orders lower number of total and faecal coliform bacteria (Escherichiacoli) [2] and [6].Due to its relatively low content of pollutants, greywater is easy to treat with MBRs. The pollutants contained are decomposed by the bacteria of the activated sludge tank. The following membrane filtration unit separates the treated greywater from the activated sludge. The treated greywater is of high quality and hygienically safe so that it can be reused, alone or combined with rain water, for toilet flushing water, laundry washing or for irrigation purposes.Within the scope of the SANSED II research project HUBER has been successful in adapting the MBR system for greywater treatment to the specific conditions in Vietnam and testing the system in operation in a small city in the Mekong delta, South Vietnam. The wastewater from kitchen sinks and the bathrooms of a dormitory on the campus of Can Tho University was clarified in the HUBER GreyUse^® plant over a period of three months. The project aim was the production of high quality service water from greywater for safe reuse as toilet flush water.     

Effect of Sludge Retention Time on Membrane Bio‐Fouling Intensity in a Submerged Membrane Bioreactor

Abstract

The submerged membrane bioreactor (sMBR) is being increasingly applied for municipal and industrial wastewater treatment. This paper examines the role of sludge retention time (SRT), an important operating parameter of the MBR as it affects the biological characteristics of the sludge and therefore influences membrane fouling. Well controlled runs were carried out at short SRT (10days) and moderate SRT (30days) in a 30 L submerged MBR equipped with KUBOTA flat‐sheet membranes. At steady operation, the mixed liquor suspended solids (MLSS) stabilized at approximately 5–6 g/L and 8.5–10 g/L for SRT 10 and 30days respectively. The DGGE profiles suggested a shift in the dominant bacterial community with the prolonged SRT. The soluble microbial products (SMP) were 9.3 mg/L and 5.4 mg/L at the SRTs of 10days and 30days respectively. The total amount of extracellular polymeric substance (EPS) extracted from the floc and the supernatant was approximately constant at the two SRTs under the same organic loading rate. However, the polysaccharide concentration in the supernatant was about 100% higher for the SRT of 10days than that for 30days. The viscosity of the biomass increased with the prolonged SRT, while the estimated average air induced water velocity was similar for the two SRTs. The results of flux stepping tests showed that the membrane fouling rate (dTMP/dt) at SRT 10days was always higher than that at 30days at each flux step. Similarly, long term experimental runs at a constant flux of 20 L/m²·h clearly showed more severe membrane fouling for the SRT of 10days than that at 30days. This implies that fouling is more influenced by the concentration of SMP and Polysaccharides than the MLSS.     

Characteristics of simultaneous nitrogen and phosphorus removal in a pilot-scale sequencing anoxic/anaerobic membrane bioreactor at various conditions

This study was conducted to evaluate the performance of pilot-scale sequencing anoxic/anaerobic membrane bioreactor (SAM) process under various real situations. During the pilot experiment, the effect of three important operational parameters, such as hydraulic retention time (HRT), solids retention time (SRT) and internal recycling time mode were estimated and the long-term membrane fouling behaviour was also investigated. During the operation period, the COD removal efficiency was higher than 95% regardless of change of operational conditions because the membrane significantly contributed to remove COD by the complete retention of all particulate COD and macromolecular COD components. The change of Ax/An ratio representing internal recycling time mode significantly affected on nitrogen and phosphorus removal. As increasing Ax/An ratio, nitrogen removal efficiency increased but phosphorus removal efficiency decreased. As HRT decreased, phosphorus removal efficiency increased and nitrogen removal efficiency also increased until a certain limit of HRT (6.5 h in this study). However, when HRT decreased over the limit, nitrogen removal efficiency decreased because of insufficient nitrification. Relation between phosphorus removal efficiency and SRT was a little bit complex because SRT determined both the phosphorus content in the sludge and the sludge wasting rate. However, in this study, the shorter SRT resulted in the higher phosphorus removal efficiency. The effect of changes in all operational conditions was sensitive on phosphorus rather than on nitrogen removal efficiency. The increasing in influent flowrate resulted in the increase of flux and caused a rapid membrane fouling. Thus, the flux of 7.7 L/m²/h was more desirable compared to the 10.7 or 15.4 L/m²/h in this study.     

Distribution profile of water and suppression of methanol crossover in sulfonated polyimide electrolyte membrane for direct methanol fuel cells

We have developed novel cross-linked sulfonated polyimide (c-SPI) membrane as an electrolyte for direct methanol fuel cells (DMFCs). When the DMFC using the c-SPI membrane (thickness = 155 μm), Pt-Ru dispersed on carbon black (Pt-Ru/CB) anode and Pt/CB cathode with a Nafion^® ionomer was operated at 80 °C and 0.1 A cm⁻² with 1 M CH₃OH and oxygen (oxidant), the methanol crossover rate, j(CH₃OH), was suppressed to about 1/2 compared with that of the Nafion^® 117 membrane (thickness = 180 μm) with the same electrodes. It was found for both cells that the j(CH₃OH) was not so small as expected from the membrane thickness. In order to obtain a clue for the suppression of j(CH₃OH), the distribution profiles of water (containing CH₃OH) in thickness direction were investigated by measuring the specific resistances (ρ) between Pt probes inserted into the electrolyte membrane. Values of ρ at the anode side were low irrespective of the discharge current density, because such a part of the membrane was humidified thoroughly by liquid water (1 M CH₃OH) allowing free penetration of CH₃OH into the swollen polymer. In contrast, the values of ρ at the cathode side were high at the low current density due to drying of the membrane contacting with oxidant gas (O₂ or air) in low humidity. We have succeeded to suppress the j(CH₃OH) further (about 1/2 at 0.2 A cm⁻²) by using bilayer c-SPI, having a low ion exchanging (low swelling) barrier layer at the anode side without increasing the ohmic resistance, compared with that of the single c-SPI.     

CO tolerance effects of tungsten-based PEMFC anodes

The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PtWO_x/C and phosphotungstic acid (PTA) impregnated Pt/C electrocatalysts. A quite high performance was achieved for the PEMFC fed with H₂ + 100 ppm CO with anodes containing 0.4 mg PtWO_x cm⁻² and also for those with 0.4 mg Pt cm⁻² impregnated with ca. 1 mg PTA cm⁻². A decay of the single cell performance with time is observed, and this was attributed to an increase of the membrane resistance due to the polymer degradation promoted by the crossover of the tungsten species throughout the membrane.     

Application of MBR for hospital wastewater treatment in China

In China, the number of hospitals has increased to 19,712 in 2008, with the production of hospital wastewater reaching 1.29 × 10⁶ m³/d. Membrane bioreactor (MBR) technology presents a more efficient system at removing pathological microorganism compared with existing wastewater treatment systems. In the past 8 yr, over 50 MBR plants have been successfully built for hospital wastewater treatments, with the capacity ranging from 20 to 2000 m³/d. MBR can effectively save disinfectant consumption (chlorine addition can decrease to 1.0 mg/L), shorten the reaction time (approximately 1.5 min, 2.5-5% of conventional wastewater treatment process), and attain a good effect of inactivation of microorganism. Higher disinfection efficacy is achieved in MBR effluents at lower dose of disinfectant with less disinfection by-products (DBPs). Moreover, when capacity of MBR plants increases from 20 to 1000 m³/d, their operating cost decreases sharply.     

High-rate fermentative hydrogen production from palm oil mill effluent in an up-flow anaerobic sludge blanket-fixed film reactor

The major problem associated with UASB reactors for biotransformation of organic matter to hydrogen is the long start-up period (2–4 months) required for the growth of the microbial granules. In this study, an integration of granular sludge system and a fixed film reactor in a single reactor was applied to overcome this problem. An up-flow anaerobic sludge blanket-fixed film (UASB-FF) reactor was initially inoculated with heat pretreated seed sludge as inoculum and operated as closed-loop fed-batch for five days (HRT = 24 h; 38 °C; pH 5.5). The reactor was continuously fed with fresh pre-settled POME in order to shorten the start-up period. The organic loading was gradually increased from 4.7 to 51.8 g/L d. Granular sludge rapidly developed within 22 days. Specific hydrogen production rate was 0.514 L H₂/g VSS d at the end of the start-up period. Speedy development of bio-granules was attributed to biomass recirculation and the establishment of a fixed film at the upper section of the UASB-FF reactor that resulted in improved interactions among the bacterial consortium.     

Influence of sewage sludge on the slurryability of coal-water slurry

In this study, the maximum solids loading, stability and rheological properties of coal-sludge slurries were investigated and compared with those of coal-water slurries. The maximum solids content of coal-sludge slurry was much lower than that of coal-water slurry because of the ∼82% water in sewage sludge. NaOH addition as a pre-treatment of sewage sludge improved the maximum solids content to 61% and 60% for dispersants A₁ and A₂, respectively, for a sludge-coal mass ratio of 22.1:100. Compared to coal-water slurries, the stability of coal-sludge slurries was better, with no solid deposition after 96 h. Coal particles and sewage sludge formed a stable medium and settlement of large coal particles was prevented. All the coal-sludge slurries exhibited pseudo-plastic behavior; this type of fluid is shear-thinning and is easy to transport.     

Characteristics of soluble microbial products in membrane bioreactor and its effect on membrane fouling

In this study, the accumulation and characteristics of soluble microbial products (SMP) in the mixed liquor and the effluent of the membrane bioreactor (MBR) were measured and compared. It was found that the concentration of SMP decreased when the SRT was increased from 10 days to 30 days, and then stabilized as SRT was increased to 60 days. The molecular weight (MW) distributions of SMP indicated that the SMP of larger MW (> 30 kDa) was the most abundant fraction in the MBR. The similar MW distributions of SMP in the mixed liquor and effluent implied that membrane fouling due to SMP in the initial slow fouling stage was not due to size sieving. After the MBR was operated for a period of time, only the SMP of relatively large MW (> 30 kDa) was detected in the mixed liquor. The result indicated that size sieving of SMP occurred only after a cake layer was formed on the membrane surface although the effect was not significant and only worked on larger molecules. The accumulation of hydrophilic components of SMP in the mixed liquor of the bioreactor suggested that the hydrophilic fraction (in carbohydrates) could be the major cause for membrane fouling.     

Nitrogen biotransformation in anaerobic treatment of phenolic wastewater

Effect of nitrogen on methanogenesis of phenol has been evaluated. Methane generation rate constant (k) has been found to vary from 0.12 to 0.21 d^− 1. The process was not impaired due to reduction of COD:N from 300:10 to 300:1. However, a definite decreasing trend in k was noticed at COD:N < 300:1. The µ_b at 90 days (µ_b90) was reduced from 0.94 to 0.12. Gas generation completely ceased at COD:N equal to 300:0. The trend of sludge activity was also found to be similar to that of k and µ_b90. The variation of COD:N from 300:1 to 300:0 in a UASB reactor, did influence the conversion of phenol COD to methane COD i.e. the (i) CH₄-COD decreased from 90 to 40%, and (ii) cell yield reduced to 25-50%. The average cell yield was 3.5%. Percent N in cells varied from 10 to 14%. The activity of the sludge assessed as SMA was found in the range from 0.15 to 0.66 g CH₄-COD/g VSS/d. The optimum COD:N for phenolic wastewater from both bench-scale batch and continuous reactor study has been estimated to be 300:1.     

Optimization of biological nutrient removal in a pilot plant UCT-MBR treating municipal wastewater during start-up

This study shows that an MBR pilot plant with UCT configuration is able to obtain high nutrient removal efficiency already during start-up. The biological nutrient removal (BNR) efficiencies significantly increased towards the end of the experimental run, achieving a COD removal efficiency exceeding 94% and N removal efficiency in the range of 89 to 93%. P removal efficiencies in the range of 80 to 92% have been obtained. During the experimental period (4 months) the evolution of the activity of polyphosphate-accumulating organisms, obtained from P_release and P_uptake rates, showed a small increase in the activity of polyphosphate-accumulating organisms (PAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs). The specific phosphate accumulation at the end of the experimental run amounted to 8.0 mg P g^− 1VSS h^− 1 and 3.29 mg P g^− 1VSS h^− 1, for the PAOs and DPAOs respectively. Moreover, the DPAOs activity increased faster than PAOs activity, i.e. from 0.36 to 0.41 of phosphate uptake rate (PUR) ratio.     

Network structures and dynamics of dry and swollen poly(acrylate)s. Characterization of high- and low-frequency motions as revealed by suppressed or recovered intensities (SRI) analysis of C NMR

We recorded temperature-dependent high-resolution ¹³C NMR spectra of dry and swollen poly(acrylate)s [poly(2-methoxyethyl acrylate) (PMEA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(tetrahydrofurfuryl acrylate) (PTHFA)] by dipolar decoupled-magic angle spinning (DD-MAS) and cross-polarization-magic angle spinning (CP-MAS) methods, to gain insight into their network structures and dynamics. Suppressed or recovered intensities (SRI) analysis of ¹³C CP-MAS and DD-MAS NMR was successfully utilized, to reveal portions of dry and swollen polymers which undergo fast and slow motions with fluctuation frequencies in the order of 10⁸ Hz and 10⁴-10⁵ Hz, respectively. Fast isotropic motions with frequency higher than 10⁸ Hz at ambient temperature were located to the portions in which ¹³C CP-MAS NMR signals of swollen PMEA were selectively suppressed. In contrast, low-frequency motion was identified to the portions in which ¹³C DD-MAS (and CP-MAS) signals are most suppressed at the characteristic suppression temperature(s) T_s. Network of PMEA gels (containing 7 wt% of water) turns out to be formed by partial association of backbones only, as manifested from their T_s gradient at lowered temperature, whereas networks of PHEMA (containing 40 wt% of water) and PTHFA (9 wt% of water) gels are tightly formed through mutual inter-chain associations of both backbones and side-chains, as viewed from the raised T_s values for both near at ambient temperature. It is also interesting to note that flexibility of gel network (PMEA > PTHFA > PHEMA) characterized by the suppression temperature T_s (PMEA < PTHFA < PHEMA) is well related with a characteristic parameter for biocompatibility such as the production of TAT (thrombin-antithrombin III complex) as a marker of activation of the coagulation system.     

Impacts of wind velocity on sand and dust deposition during dust storm as inferred from a series of observations in the northeastern Qinghai-Tibetan Plateau, China

The monthly sand and dust deposition flux and modern dust storms were monitored in the northern Qaidam Basin of the Qinghai-Tibetan Plateau. The monthly sand and dust flux varied between 0.57 and 18.12 mg cm^− 2 month^− 1 from June 2003 to April 2005, and was well correlated with the monthly extreme wind velocity (V_extr) (r² = 0.60, n = 23). Sand and dust was mainly deposited in spring and early summer in the study area. The weight of settled sand and dust collected during dust storms exhibited a positive correlation with the mean 10-min wind velocity (r² = 0.60, n = 16) during the dust storms. For the typical dust storms, the weight and flux of settled sand and dust will linearly increase with the increasing wind strength and fluctuation amplitude of wind velocities. The coarse fraction (> 63 μm) also increases with them, in contrast, the fine-grained fraction (< 63 μm) decreases. It is plausible to assume that most of the fine-grained dust particles are lifted and transported far from the region under dust storm conditions, especially under the stronger and more variable wind conditions. The results demonstrate that the wind regime (strength and variability) is a key control on the sand and dust deposition during dust storm; dust can be emitted from the Qaidam Basin as one of dust source areas in China.     

Swelling behavior of amphiphilic gels based on hydrophobically modified dimethylaminoethyl methacrylate

The amphiphilic gels based on hydrophobically modified dimethylaminoethyl methacrylate with different 1-bromoalkanes (1-C_nH_2n+1Br, n = 2, 4, 6, 8, 12) were synthesized by radiation-induced polymerization and crosslinking. The length of alkyl side chains had significant influence on the swelling behavior of the resulting gels. The swelling degree of the gels decreased with the increase of side chain length, and the gel hardly swelled when n = 12. The effect of temperature and ionic strength on the swelling behavior of the resulting gels revealed that (1) the gels with longer side chains (n ≥ 8) had upper critical solution temperature, while other gels were not thermo-sensitive. (2) Antipolyelectrolyte effect was observed when immersing the gels (n ≥ 8) in NaCl solutions in certain concentration range. The dramatic difference in swelling behavior was attributed to the different gel structures. The gels with short side chains (n ≤ 6) had cellular structure of normal polyelectrolyte gels. The gels (n ≥ 8) had an aggregation gel structure caused by the hydrophobic interaction among alkyl groups and the formation of ion-cluster between tetra-alkyl ammonium cation and Br⁻, which had been analyzed with the aid of SEM, Br⁻-selective electrode and fluorescence molecular probe.     

Water density effects on methanol oxidation in supercritical water at high pressure up to 100 MPa

Reaction kinetics of methanol oxidation in supercritical water at high pressure condition (420 °C; 34-100 MPa; ρ = 300-660 kg/m³) was investigated. Pseudo-first order rate constant for methanol decomposition increased with increasing water density. Effects of supercritical water on the reaction kinetics were investigated using a detailed chemical kinetics model. Incorporating the effect of diffusion in a reduced model revealed that overall kinetics for SCWO of methanol is not diffusion-limited. Roles of water as a reactant were also investigated. The dependence of sensitivity coefficient for methanol concentration and rate of production of OH radical on water density indicated that a reaction, HO₂ + H₂O = OH + H₂O₂, enhanced the OH radical production and thereby facilitated the decomposition of methanol. It is presumed that concentration of key radicals could be controlled by varying pressure intensively.     

Removal of caffeine and diclofenac on activated carbon in fixed bed column

The occurrence of emerging contaminants in wastewaters, and their behaviour during wastewater treatment and production of drinking water are key issues in the re-use of water resources. The objective of this study was the adsorption of caffeine and diclofenac from aqueous solutions on fixed beds of granular activated carbon. Several operation conditions on the shape of breakthrough curves were investigated. Adsorption equilibrium is reached after 3 days for caffeine and after 14 days for diclofenac. In caffeine, breakthrough times, corresponding to C/C₀ = 0.02 were found to be 19.1, 47.6 and 48.5 h for the columns operating with bed weights of 0.6, 0.8 and 1.0 g, respectively. Saturation times (corresponding to C/C₀ = 0.95) were found to be 91.8, 114.3 and 121.0 h, respectively. The activated carbon is not an efficient adsorbent for diclofenac.