L.M. Ruiz

Removal performance of heavy metals in MBR systems and their influence in water reuse

The removal performance of heavy metals by two experimental full-scale membrane bioreactors (microfiltration and ultrafiltration) and the influence of activated sludge total suspended solid (TSS) concentration were studied under real operational conditions. Influent and effluent Be, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, As, Mo, Cd, Ba, Sn, Sb, Pb and U concentrations were analysed by inductively coupled plasma-mass spectrometry. An average contamination rate for most of the analysed heavy metals was observed in raw wastewater, resulting in effluents without limitation for reuse in agricultural destinations according to Spanish law. Removal efficiencies up to 80% were obtained regardless of whether microfiltration or ultrafiltration membranes were used, except for As, Mo and Sb. The removal yields of different heavy metals can be strengthened by increasing the activated sludge TSS concentration, mainly at concentrations above 10 g/L.

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 ...

Comparison of five wastewater COD fractionation methods for dynamic simulation of MBR systems

Five different wastewater COD fractionation methods were employed for simulating an experimental MBR wastewater treatment plant using WEST. The predictions of dynamic simulations using as input the data obtained according to each influent characterization methodology were compared with the results of the experimental system and differences between experimental and predicted values were analyzed in order to select the fractionation method which provides the best fitting and minimizes errors. Three of these methods were based on the determination of the biodegradable fractions using respirometric assays of real wastewater filtered through 0.45- and 0.22-μm pore size filters or adding a previous flocculation step before filtration. Moreover, a method based on physicochemical analyses and another one based on theoretical coefficients were also compared. Simulated system performance and effluent quality greatly depended upon the influent characterization and the proper model calibration. Thus the importance of selecting a suitable fractionation methodology is high, especially in MBR systems working at specific operational conditions that may alter COD fractions. In this study, MLSS in the bioreactors and sludge supernatant COD concentrations were better predicted when the influent characterization was based on respirometric methods. Both the method based on theoretical coefficients and the physicochemical method underestimated the particulate inert fraction and therefore, also the MLSS concentrations. Moreover, these results showed that for a correct effluent COD prediction in MBR systems, it is necessary to take into account that the membrane retained part of the soluble inert fraction.

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.