M.A. Gómez

Influence of velocity gradient in a hydraulic flocculator on NOM removal by aerated spiral-wound ultrafiltration membranes (ASWUF).

A hydraulic coagulation-flocculation processes combined with aerated spiral-wound ultrafiltration membranes (ASWUF) was designed with the objective of improving natural organic matter (NOM) removal by ASWUF in the treatment of water for human consumption. The pilot-scale experimental system had capacity for treating 0.9 m(3)/h. Dosage of Cl(3)Fe as coagulant and hydraulic retention time (HRT) were calculated to generate microflocculation and different velocity gradients (G=27, 47, 87 and 104 s(-1)) were applied in the hydraulic flocculator. Operating alone, the ASWUF system achieved an NOM removal performance of 39% without problems of membrane clogging, although there was a significant correlation between effluent and influent quality. Application of microflocculation achieved considerable improvement in NOM removal, but values of G< or =87 s(-1) resulted in rapid clogging of the membrane due to flocs disintegration in the aerated membrane tank. Particle analysis revealed that the reduction of the velocity gradient had the effect of inclining the particle size distribution towards larger sizes, affecting both NOM removal capacity and membrane clogging. For G=104 s(-1) an NOM removal yield of 90% was reached, while transmembrane pressure (TMP) was stabilised as a result of the control of membrane clogging.

Wastewater polycyclic aromatic hydrocarbons removal by membrane bioreactor

Abstract The capacity of removal polycyclic aromatic hydrocarbons (PAHs) by membrane bioreactor (MBR) has been studied. The study has been developed at pilot scale using a pre-denitrifying MBR and several stages have been checked at bench-scale. Concentration of PAHs was determined by gas chromatography (GC) and mass spectrometry (MS) with twister and a balance on the MBR system was achieved. The system was feeded with raw wastewater which contains usually pyrene, phenanthrene and fluoranthene at low concentration (<0.3 ppb). Treated wastewater concentration was under detection limits for all detected PAHs and sludge accumulation was not observed. Under operational MBR conditions, several removal mechanisms and different removal rates for each compound are presented along the treatment process. Bench-scale experiments reveal that PAHs removal is mainly due to sorption and air stripping, however the volatilization and biodegradation present a questionable insignifi cant contribution. Toxicity by PAHs durin...

Evolution of filamentous bacteria during urban wastewater treatment by MBR

Evolution of filamentous bacteria in two full-scale experimental MBR systems (microfiltration and ultrafiltration) was studied during two years. Sludge Retention Time (SRT) and Hydraulic Retention Time (HRT) were modified and acted as variables, together with temperature and variation in loading. With SRT values between 20 and 35 d and HRT between 31 and 40 h, both MBR systems presented a high density of filamentous bacteria, according to the Filamentous Index (FI) and Simplified Technique of Filamentous Count (STFC). Highest density was achieved when contaminant loads were high and temperature was low. However, the elevated presence of filamentous bacteria did not affect the quality of effluent or the permeability of the membranes. Nocardioform bacteria showed a high degree of adaptation to the characteristics of the system. Predominance of Nocardioforms gave rise to isolated episodes of massive growth at temperatures between 15 and 20°C, which in turn caused episodes of intense foaming whose most significant consequence was a loss in biomass, leading to a slight increase in transmembrane pressure. In the light of these results, FI and STFC should not be considered as suitable tools for predicting operational problems deriving from filamentous bacteria in MBR systems, which could be prevented through identification.

The IFAS-MBR process: a compact combination of biofilm and MBR tecnnology as RO pretreatment

Abstract An advanced treatment for wastewater reclamation has been studied for nine months in a pilot plant in the south of Spain. This consisted in a combination of integrated fixed-film activated sludge (IFAS) and membrane bioreactor (MBR) technology (called here IFAS-MBR) with posterior reverse osmosis (RO) for the achievement of a high-quality effluent. The pilot plant was obtained from a former MBR plant, where plastic carriers for the support of the biology were introduced in the second aerobic chamber. The system consisted of two parallel lines, one working with a hollow fibre module and the other with a flat sheet module. After the hollow fibre line, an RO system treated the effluent. The permeability of the process decreased gradually along the experimentation period and after six months, the membrane modules of both lines were chemically cleaned. The RO membranes showed a stable permeability working with the IFAS-MBR permeate and chemically cleaned after four months of operation. The studied sys...

A comparative study of ultrafiltration and physicochemical process as pretreatment of seawater reverse osmosis

Abstract The effectiveness of two pretreatments for open intake seawater reverse osmosis (RO), aerated spiral wound ultrafiltration (ASWUF) and physicochemical (PC) pretreatment, were evaluated. Their efficiency in removing particulate materials was assessed by SDI, turbidity and Particle Size Distribution. Aerobic bacteria levels indicated the effectiveness of bacterial removal. Organic matter was characterized by TOC and UV254. The apparent molecular weight (MW) distribution of organic matter was determined by centrifugal ultrafiltration fractionation and the effect of pretreated effl uent on seawater RO flux decline was evaluated by a bench-scale test. Both pretreatments lowered feed water SDI to 2 and turbidity to 0.4 NTU and were highly efficient in removing particles larger than 1 μm. In general, ASWUF was more effective than PC, although PC removed TOC more effi ciently. For both pretreatments, TOC fractions with a MW of under 3 kDa remained in treated water. Both pretreatments made effl uents of e...

Influence of operational variables on nitrogen removal in two full-scale MBR systems

Abstract The influence of the operational variables (sludge retention time, temperature, recirculation rate, and organic loading) on nitrogen transformations in two full-scale pre-denitrification submerged membrane bioreactor (MBR) was investigated. The study was carried out in two predenitrification MBR full-scale plants, (ultrafiltration and microfiltration) with different recirculation rates. Both installations were fully automated and recorded continuously all flows, temperature, transmembrane pressure (TMP), and dissolved oxygen concentration (DO). Sludge retention time (SRT), activated sludge temperature and organic loading varied between 20–43 days, 13–30°C, and 0.40–1.1 kg COD/m3 h, respectively. Biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) removal yield were over 99.5 and 95%, respectively. Both MBR systems demonstrated excellent removal with yields concerning 99%, and effluent concentrations lower than 1 mg/L independently of operational conditions. In contrast, the total ni...

Influence of operational parameters over biomass growth and decay kinetic constants on membrane bioreactors

ABSTRACT In this study, activated sludge from two experimental full-scale membrane bioreactor (MBR) systems (microfiltration and ultrafiltration) working in parallel has been used to determine YH and bH in a batch respirometer. Both systems were equipped with a pre-denitrification stage and followed the same configuration: anoxic bioreactor, aerobic bioreactor and MBR. Nowadays, describing a conventional or MBR biological process cannot be understood without determining the values of several bio-kinetic parameters describing biomass growth and decay. The aim of this study is to evaluate the influence of several operational parameters related to MBR systems such as sludge retention time (SRT), hydraulic retention time, organic load, sludge temperature and aerobic bioreactor height over the heterotrophic decay coefficient (bH ) and the heterotrophic yield (YH ), whose values ranged from 0.0088 to 0.31 d−1 and from 0.40 to 0.88 mgCOD/mgCOD, respectively. Average sludge temperature and SRT have statistically ...

Behaviour of the main nonsteroidal anti-inflammatory drugs in a membrane bioreactor treating urban wastewater at high hydraulic- and sludge-retention time

The behaviour and removal efficiency of ibuprofen (IBU), diclofenac (DCF), ketoprofen (KPF), and naproxen (NPX) during the real urban wastewater treatment by an experimental full-scale MBR working at high sludge and hydraulic retention time (SRT, HRT) were determined. The MBR worked in denitrification/nitrification conformation at 35.4h of HRT (Q=0.45m3/h), 37 d of SRT and a recirculation flow rate of 4Q. The experiments were made under steady-state conditions, reaching a biodegradable organic matter removal higher than 99.5%. The MBR system showed similar removal capacity for IBU, NPX, and KTP (>95%), whose main transformation occurred in the aerobic reactor with a low contribution from the anoxic reactor. The system worked with complete nitrification, also achieving an effective retention of the unbiodegradable organic matter due to recirculation. DCF removal was low with negative removal yields for several samplings. Both removal and increase transformation of DCF also occurred in the aerobic reactor, this not being observed in the anoxic one. DCF tends to accumulate in the system and to be recirculated. Thus, during the sampling in which DCF influent concentration decreases, removal yields turn negative. The increase of DCF concentration in the aerobic bioreactor also contributes to the negative removal yields.

Ultrasonic irradiation for ultrafiltration membrane cleaning in MBR systems: operational conditions and consequences

Ultrasonic irradiation is one of the most promising membrane cleaning techniques for membrane bioreactors (MBRs) because of several advantages such as high flux-recovery capacity and in situ application without interrupting the filtration process. However, significant contradictions may be found and, consequently, this method has not yet been widely developed. In this paper, four MBRs equipped with hollow-fibre polyvinylidene fluoride ultrafiltration membranes were operated continuously. The cleaning method applied consisted of sonication at low power (15 W) with different frequencies (20, 25, 30, and 40 kHz) for each module and aerated backwashing. The different MBRs were analysed comparatively between them and with a conventional MBR in order to check the effects of the irradiated waves on membrane integrity, effluent quality and process performance. Effluent turbidity and chemical oxygen demand, total and volatile suspended solid concentration and activated sludge viscosity were affected by biomass fragmentation or membrane cake removal, mainly at lower frequencies. The best transmembrane pressure control was achieved at the frequency of 20 kHz without a significant effect on membrane integrity. The results showed that under these operational conditions, no negative effects on effluent quality or membrane integrity were found, suggesting that this method was suitable for this type of membrane.

Sensitivity analyses and simulations of a full-scale experimental membrane bioreactor system using the activated sludge model No. 3 (ASM3)

An ASM3-based model was implemented in the numerical software MATHEMATICA where sensitivity analyses and simulations of a membrane bioreactor (MBR) system were carried out. These results were compared with those obtained using the commercial simulator WEST. Predicted values did not show significant variations between both software and simulations showed that the most influential operational conditions were influent flow rate and concentrations and bioreactor volumes. On the other hand, sensitivity analyses were carried out with both software programs for the same five outputs: COD, ammonium and nitrate concentrations in the effluent, total suspended solids concentration and oxygen uptake rate in the aerobic bioreactor. Similar results were in general obtained in both cases and according to these analyses, the most significant inputs over the model predictions were growth and storage heterotrophic biomass yields and decay coefficient. Other parameters related to the hydrolysis process or to the autotrophic biomass also significantly influenced model outputs.