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A decade ago, membrane bioreactors (MBR) were considered as a potential technology for replacing conventional activated sludge (CAS) processes. Indeed, MBR experienced a period of rapid development around 2009, especially in China. In recent years, however, there has been a sharp drop in the number of MBR installations all around the world – with the exception of in China. It is important to understand the reasons for this difference between the reactions of China and other countries. High-quality effluent and a smaller MBR footprint are also associated with high energy consumption and operational costs. Therefore, it is necessary to carefully evaluate the advantages and disadvantages of MBR. In this study, a model (including capital and operational costs, operational efficiency and stability, resources saving and recovery and an evaluation of the sustainability index (S I ) of MBR over CAS) was established to comprehensively evaluate the effects of MBR on economy, technology and management. The model calculations of S I demonstrate S I  > 1.0. This means, briefly put, that MBR is not a sustainable process when compared to CAS, which is extensively applied but generally thought to be an unsustainable process. The sensitivity analysis of both related factors and weighted coefficients in the model reveals that there is almost no possibility of attaining S I  < 1.0 (more sustainable than CAS). For this reason, it is not recommended that MBRs extensively replace CAS when upgrading and constructing wastewater treatment plants (WWTPs). Alternative technologies may be considered, such as aerobic granular sludge (GAS). [ABSTRACT FROM AUTHOR]

It was recently discovered that vivianite (Fe 3 (PO 4) 2.8H 2 O) could be magnetically extracted from digested activated sludge which opened a new route for phosphorus recovery (Wijdeveld et al. 2022). While its formation in digested sludge is regularly reported, it is not yet studied for fresh, undigested activated sludge. In particular, the extent to which vivianite could form during sludge storage is missing. The current research showed that iron reduction was completed after 2–4 days of anaerobic storage, and the vivianite appeared to form quickly from the pool of reduced iron made available. After sludge thickening at the wastewater treatment plant (30 h retention time), around 11% of the iron was vivianite. With subsequent 1–3 days of anaerobic storage, this fraction increased to 50–55%. After this storage, almost all the vivianite that could potentially form did form. This research concluded that efficient vivianite formation can be achieved without a sludge digester, showing phosphorus recovery potential from undigested sludge via vivianite recovery. Besides, the recovery of vivianite from undigested sludge presents advantages like the reduction of the sludge to dispose of and mitigation of the vivianite scaling formation. [Display omitted] • More than 80% of the Fe in WAS was reduced after 3 days of anaerobic storage. • Vivianite formation in excess activated sludge quickly followed iron reduction. • Vivianite bore up to 55% of the Fe and 60% of the P after 2–4 days of storage. • Vivianite formation was almost completed after 2–4 days of anaerobic storage. • A sludge digester is not necessary for the formation of vivianite in sewage sludge. [ABSTRACT FROM AUTHOR]

Abstract: Phosphorus limitation has been demonstrated for heterotrophic growth in groundwater, in drinking water production and distribution systems, and for nitrification of surface water treatment at low temperatures. In this study, phosphorus limitation was tested, in the Netherlands, for nitrification of anaerobic groundwater rich in iron, ammonium and orthophosphate. The bioassay method developed by was adapted to determine the microbially available phosphorus (MAP) for nitrification. In standardized batch experiments with an enriched mixed culture inoculum, the formation of nitrite and nitrate and ATP and the growth of ammonia-oxidizing bacteria (AOB; as indicated by qPCR targeting the amoA-coding gene) were determined for MAP concentrations between 0 and 100 μg PO4–P L−1. The nitrification and microbial growth rates were limited at under 100 μg PO4–P L−1 and virtually stopped at under 10 μg PO4–P L−1. In the range between 10 and 50 μg PO4–P L−1, a linear relationship was found between MAP and the maximum nitrification rate. AOB cell growth and ATP formation were proportional to the total ammonia oxidized. Contrary to , biological growth was very slow for MAP concentrations less than 25 μg PO4–P L−1. No full conversion nor maximum cell numbers were reached within 19 days. In full-scale groundwater filters, most of the orthophosphate was removed alongside with iron. The remaining orthophosphate appeared to have only limited availability for microbial growth and activity. In some groundwater filters, nitrification was almost totally prevented by limitation of MAP. In batch experiments with filtrate water from these filters, the nitrification process could be effectively stimulated by adding phosphoric acid. [Copyright &y& Elsevier]

Abstract: Current strategies to control biofouling in nanofiltration and reverse osmosis membrane systems such as chemical cleaning and use of low fouling membranes are not always successful. Based on recent studies, an alternative approach is derived, combining a lower linear flow velocity in lead modules and adapted designs for feed spacer with an advanced cleaning strategy. This approach can be realized by small adaptations in current plant design. A lower linear flow velocity in lead spiral wound membrane modules results in (i) lower energy use, (ii) lower impact of biomass on the feed channel pressure drop, and (iii) more fluffy biofilm that may be easier to remove from the lead membrane modules, especially when adapted feed spacers combined with a reversed enhanced flush are applied. This rational scenario can result in effective biofouling control at low energy requirements, minimal chemical use and minimal cost. [Copyright &y& Elsevier]

Abstract: Traditionally, the performance of full-scale wastewater treatment plants (WWTPs) is measured based on influent and/or effluent and waste sludge flows and concentrations. Full-scale WWTP data typically have a high variance which often contains (large) measurement errors. A good process engineering evaluation of the WWTP performance is therefore difficult. This also makes it usually difficult to evaluate effect of process changes in a plant or compare plants to each other. In this paper we used a case study of a full-scale nutrient removing WWTP. The plant normally uses presettled wastewater, as a means to increase the nutrient removal the plant was operated for a period by-passing raw wastewater (27% of the influent flow). The effect of raw wastewater addition has been evaluated by different approaches: (i) influent characteristics, (ii) design retrofit, (iii) effluent quality, (iv) removal efficiencies, (v) activated sludge characteristics, (vi) microbial activity tests and FISH analysis and, (vii) performance assessment based on mass balance evaluation. This paper demonstrates that mass balance evaluation approach helps the WWTP engineers to distinguish and quantify between different strategies, where others could not. In the studied case, by-passing raw wastewater (27% of the influent flow) directly to the biological reactor did not improve the effluent quality and the nutrient removal efficiency of the WWTP. The increase of the influent C/N and C/P ratios was associated to particulate compounds with low COD/VSS ratio and a high non-biodegradable COD fraction. [Copyright &y& Elsevier]

Abstract: Measured data of wastewater treatment plants (WWTPs) often contains errors. These errors can prohibit the use of WWTP data for process evaluation, process design, benchmarking or modelling purposes. In this paper a practical stepwise methodology is presented to check WWTP data using mass balances. The presented results show that poor WWTP data quality leads to large errors when calculating key operational conditions such as the solids retention time (SRT), oxygen consumption (OC) and the different internal conversions rates. By improving WWTP data quality using mass balance calculations useful new information becomes available for process evaluation, WWTPs design and benchmarking. [Copyright &y& Elsevier]

Abstract: The BCFS® process was developed to optimize the activity of denitrifying and P-removing bacteria. In this technology in combination with optimal operating conditions for biological nitrogen removal, chemical precipitation of phosphorus is used to ensure compliance with effluent standards regarding phosphorus. This work addresses the potential of the BCFS® technology for phosphorus recovery and the interactions with the biological process. The TUD model calibrated for the Hardenberg WWTP was used. Nitrification was the biological process most influenced by the P stripper operation; however, further research is needed into the effect of limiting phosphate concentrations. Phosphate removal in the anaerobic reactor causes a decrease in the sludge poly-P content. The evaluation of the process operation under dynamic conditions showed that the P stripper use for phosphate recovery does not imply complicated control strategies. The use of the BCFS® for phosphate recovery implies a change in the design philosophy not only to achieve the effluent requirements but also to maximize the anaerobic phosphate release and thereby recovery. [Copyright &y& Elsevier]

Polyhydroxyalkanoates (PHAs) are the polymers of hydroxyalkanoates that accumulate as carbon/energy or reducing-power storage material in various microorganisms. PHAs have been attracting considerable attention as biodegradable substitutes for conventional polymers. To reduce their production cost, a great deal of effort has been devoted to developing better bacterial strains and more efficient fermentation/recovery processes. The use of mixed cultures and cheap substrates can reduce the production cost of PHA. Accumulation of PHA by mixed cultures occurs under transient conditions mainly caused by intermittent feeding and variation in the electron donor/acceptor presence. The maximum capacity for PHA storage and the PHA production rate are dependent on the substrate and the operating conditions used. This work reviews the development of PHA research. Aspects discussed include metabolism and various mechanisms for PHA production by mixed cultures; kinetics of PHA accumulation and conversion; effects of carbon source and temperature on PHA production using mixed cultures; PHA production process design; and characteristics of PHA produced by mixed cultures. [Copyright &y& Elsevier]

Presents a simulation of a biological phosphorus and nitrogen removing wastewater treatment plant. Kinetics of the metabolic biological phosphorus model; Accumulation of total-phosphorus in the sludge; Formation rate of glycogen.

Abstract Biofouling severely impacts operational performance of membrane systems increasing the cost of water production. Understanding the effect of critical parameters of feed water such as biodegradable substrate concentration on the developed biofilm characteristics enables development of more effective biofouling control strategies. In this study, the effect of substrate concentration on the biofilm characteristics was examined using membrane fouling simulators (MFSs). A feed channel pressure drop (PD) increase of 200 mbar was used as a benchmark to study the developed biofilm. The amount and characteristics of the formed biofilm were analysed in relation to membrane performance indicators: feed channel pressure drop and permeate flux. The effect of the characteristics of the biofilm developed at three substrate concentrations on the removal efficiency of the different biofilms was evaluated applying acid/base cleaning. Results showed that a higher feed water substrate concentration caused a higher biomass amount, a faster PD increase, but a lower permeate flux decline. The permeate flux decline was affected by the spatial location and the physical characteristics of the biofilm rather than the total amount of biofilm. The slower growing biofilm developed at the lowest substrate concentration was harder to remove by NaOH/HCl cleanings than the biofilm developed at the higher substrate concentrations. Effective biofilm removal is essential to prevent a fast biofilm regrowth after cleaning. While substrate limitation is a generally accepted biofouling control strategy delaying biofouling, development of advanced cleaning methods to remove biofilms formed under substrate limited conditions is of paramount importance. Highlights • Faster flow channel pressure drop increase at higher substrate concentration. • Lower permeate flux decline at higher substrate concentration. • More biomass accumulated at higher substrate concentration. • Permeate flux decline not predictive for amount of accumulated biomass. • Slower growing, harder to remove biofilms at lower substrate concentration. [ABSTRACT FROM AUTHOR]

A new acid soluble extracellular polymeric substance (acid soluble EPS) was extracted from an acetate fed aerobic granular sludge reactor operated at 35 °C. Acid soluble EPS dominated granules exhibited a remarkable and distinctive tangled tubular morphology. These granules are dominated by Defluviicoccus Cluster II organisms. Acetic acid instead of the usually required alkaline extraction medium was needed to dissolve the granules and solubilise the polymeric matrix. The extracted acid soluble EPS was analysed and identified using various instrumental analysis including 1 H and 13 C Nuclear Magnetic Resonance, Fourier Transform Infrared Spectroscopy and Raman spectroscopy. In addition, the glycoconjugates were characterized by fluorescence lectin-binding analysis. The acid soluble EPS is α-(1 → 4) linked polysaccharide, containing both glucose and galactose as monomers. There are OCH 3 groups connected to the glucose monomer. Transmission and scanning electron microscopy (TEM, SEM) as well as confocal laser scanning microscopy (CLSM) showed that the acid soluble EPS was present as a tightly bound capsular EPS around bacterial cells ordered into a sarcinae-like growth pattern. The special granule morphology is decided by the acid soluble EPS produced by Defluviicoccus Cluster II organisms. This work shows that no single one method can be used to extract all possible extracellular polymeric substances. Results obtained here can support the elucidation of biofilm formation and structure in future research. [ABSTRACT FROM AUTHOR]

• Anaerobic feeding mode drives substrate distribution over granules based on size. • Bottom-feeding favours substrate accumulation by granules with a larger volume. • Completely mixed pulse-feeding favours granules with a larger area-to-volume ratio. • PHA storage polymer levels and EBPR are impacted by the anaerobic feeding mode. • Design of the anaerobic zone is crucial for formation of AGS in continuous reactors. There is a growing interest to implement aerobic granular sludge (AGS) in existing conventional activated sludge (CAS) systems with a continuous flow-through configuration. The mode of anaerobic contact of raw sewage with the sludge is an important aspect in the adaptation of CAS systems to accommodate AGS. It remains unclear how the distribution of substrate over the sludge by a conventional anaerobic selector compares to the distribution via bottom-feeding applied in sequencing batch reactors (SBRs). This study investigated the effect of the anaerobic contact mode on the substrate (and storage) distribution by operating two lab-scale SBRs; one with the traditional bottom-feeding through a settled sludge bed similar to full-scale AGS systems, and one where the synthetic wastewater was fed as a pulse at the start of the anaerobic phase while the reactor was mixed through sparging of nitrogen gas (mimicking a plug-flow anaerobic selector in continuous flow-through systems). The distribution of the substrate over the sludge particle population was quantified via PHA analysis, combined with the obtained granule size distribution. Bottom-feeding was found to primarily direct substrate towards the large granular size classes (i.e. large volume and close to the bottom), while completely mixed pulse-feeding gives a more equal distribution of substrate over all granule sizes (i.e. surface area dependant). The anaerobic contact mode directly controls the substrate distribution over the different granule sizes, irrespective of the solids retention time of a granule as an entity. Preferential feeding of the larger granules will enhance and stabilise the granulation compared to pulse-feeding, certainly under less advantageous conditions imposed by real sewage. [Display omitted] [ABSTRACT FROM AUTHOR]

Poly(3-hydroxybutyrate) (PHB) was accumulated in full-scale municipal waste activated sludge at pilot scale. After accumulation, the fate of the PHB-rich biomass was evaluated over two weeks as a function of initial pH (5.5, 7.0 and 10), and incubation temperature (25, 37 and 55 °C), with or without aeration. PHB became consumed under aerobic conditions as expected with first order rate constants in the range of 0.19 to 0.55 d−1. Under anaerobic conditions, up to 63 percent of the PHB became consumed within the first day (initial pH 7, 55 °C). Subsequently, with continued anaerobic conditions, the polymer content remained stable in the biomass. Degradation rates were lower for acidic anaerobic incubation conditions at a lower temperature (25 °C). Polymer thermal properties were measured in the dried PHB-rich biomass and for the polymer recovered by solvent extraction using dimethyl carbonate. PHB quality changes in dried biomass, indicated by differences in polymer melt enthalpy, correlated to differences in the extent of PHB extractability. Differences in the expressed PHB-in-biomass melt enthalpy that correlated to the polymer extractability suggested that yields of polymer recovery by extraction can be influenced by the state or quality of the polymer generated during downstream processing. Different post-accumulation process biomass management environments were found to influence the polymer quality and can also influence the extraction of non-polymer biomass. An acidic post-accumulation environment resulted in higher melt enthalpies in the biomass and, consequently, higher extraction efficiencies. Overall, acidic environmental conditions were found to be favourable for preserving both quantity and quality after PHB accumulation in activated sludge. [Display omitted] • Intracellular PHB depolymerase activity can be constrained anaerobically. • Changes in environmental conditions cause polymer loss even for short term storage. • Extracellular depolymerase activity is limited if PHB remains intracellular. • Acidic conditions are preferred to preserve quantity and quality for PHB recovery. • The melting properties of PHB in the biomass may influence the polymer extractability. [ABSTRACT FROM AUTHOR]

Understanding the factors that determine the spatial and temporal biofilm development is a key to formulate effective control strategies in reverse osmosis membrane systems for desalination and wastewater reuse. In this study, biofilm development was investigated at different water temperatures (10, 20, and 30 °C) inside a membrane fouling simulator (MFS) flow cell. The MFS studies were done at the same crossflow velocity with the same type of membrane and spacer materials, and the same feed water type and nutrient concentration, differing only in water temperature. Spatially resolved biofilm parameters such as oxygen decrease rate, biovolume, biofilm spatial distribution, thickness and composition were measured using in-situ imaging techniques. Pressure drop (PD) increase in time was used as a benchmark as to when to stop the experiments. Biofilm measurements were performed daily, and experiments were stopped once the average PD increased to 40 mbar/cm. The results of the biofouling study showed that with increasing feed water temperature (i) the biofilm activity developed faster, (ii) the pressure drop increased faster, while (iii) the biofilm thickness decreased. At an average pressure drop increase of 40 mbar/cm over the MFS for the different feed water temperatures, different biofilm activities, structures, and quantities were found, indicating that diagnosis of biofouling of membranes operated at different or varying (seasonal) feed water temperatures may be challenging. Membrane installations with a high temperature feed water are more susceptible to biofouling than installations fed with low temperature feed water. [ABSTRACT FROM AUTHOR]

• Phosphorus was recovered as vivianite from digested sludge by a pilot-scale magnetic separator. • Vivianite content in the feed determines the recovery. • Sludge dry matter and viscosity do not influence vivianite recovery. • Vivianite particles of all sizes can be recovered from the magnet. • Particles of less than 10 µm have a lower recovery rate. Phosphorus recovery via vivianite extraction from digested sludge has recently gained considerable interest. The separation of vivianite was demonstrated earlier at the pilot scale, and operational parameters were optimized. In this study, we tested the robustness of this technology by changing the sludge characteristics, such as dry matter, and via that, sludge viscosity, and vivianite particle size. It was proven that the main factor influencing recovery was the concentration of vivianite in the feed. The technology can extract vivianite even when the sludge has higher dry matter (1.8% - 3.3%) and, therefore, higher viscosity. Smaller vivianite sizes (< 10 µm) can still be recovered but at a lower rate. This made magnetic separation applicable to a wide range of wastewater treatment plants. [Display omitted] [ABSTRACT FROM AUTHOR]

The influence of organic nutrient load on biomass accumulation (biofouling) and pressure drop development in membrane filtration systems was investigated. Nutrient load is the product of nutrient concentration and linear flow velocity. Biofouling – excessive growth of microbial biomass in membrane systems – hampers membrane performance. The influence of biodegradable organic nutrient load on biofouling was investigated at varying (i) crossflow velocity, (ii) nutrient concentration, (iii) shear, and (iv) feed spacer thickness. Experimental studies were performed with membrane fouling simulators (MFSs) containing a reverse osmosis (RO) membrane and a 31 mil thick feed spacer, commonly applied in practice in RO and nanofiltration (NF) spiral-wound membrane modules. Numerical modeling studies were done with identical feed spacer geometry differing in thickness (28, 31 and 34 mil). Additionally, experiments were done applying a forward osmosis (FO) membrane with varying spacer thickness (28, 31 and 34 mil), addressing the permeate flux decline and biofilm development. Assessed were the development of feed channel pressure drop (MFS studies), permeate flux (FO studies) and accumulated biomass amount measured by adenosine triphosphate (ATP) and total organic carbon (TOC). Our studies showed that the organic nutrient load determined the accumulated amount of biomass. The same amount of accumulated biomass was found at constant nutrient load irrespective of linear flow velocity, shear, and/or feed spacer thickness. The impact of the same amount of accumulated biomass on feed channel pressure drop and permeate flux was influenced by membrane process design and operational conditions. Reducing the nutrient load by pretreatment slowed-down the biofilm formation. The impact of accumulated biomass on membrane performance was reduced by applying a lower crossflow velocity and/or a thicker and/or a modified geometry feed spacer. The results indicate that cleanings can be delayed but are unavoidable. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed to investigate differences in the gel matrix of aerobic granular sludge and normal aerobic flocculent sludge. From both types of sludge that fed with the same municipal sewage, the functional gel-forming exopolysaccharides, alginate-like exopolysaccharides, were isolated. These two exopolysaccharides were chemically fractionated, and investigated by FT-IR spectroscopy. The isolated polymers were made into a gel by calcium addition and the mechanical properties of these reconstituted gels were measured by a low load compression tester. The viscoelastic behavior of the gels was described by a generalized Maxwell model. The alginate-like exopolysaccharides derived from aerobic granules had significantly higher amount of poly(guluronic acid) blocks but lower amount of poly(guluronic acid-manuronic acid) blocks in the chemical structure, while the alginate-like exopolysaccharides derived from aerobic flocculent sludge had equal amount of poly(guluronic acid) blocks and poly(guluronic acid-manuronic acid) blocks. These differences result in a perfect gel-forming capability of alginate-like exopolysaccharides derived from aerobic granules and bestowed this exopolysaccharides gel a stronger mechanical property as compared to alginate-like exopolysaccharides derived from aerobic flocculent sludge. The different chemical and mechanical properties of these two exopolysaccharides contributed to the distinguished characteristics between aerobic granular sludge and aerobic flocculent sludge. [Copyright &y& Elsevier]

Abstract: The impact of feed spacers on initial feed channel pressure (FCP) drop, FCP increase and biomass accumulation has been studied in membrane fouling simulators using feed spacers applied in commercially available nanofiltration and reverse osmosis spiral wound membrane modules. All spacers had a similar geometry. Our studies showed that biofouling was not prevented by (i) variation of spacer thickness, (ii) feed spacer orientation, (iii) feed spacer coating with silver, copper or gold and (iv) using a biostatic feed spacer. At constant feed flow, a lower FCP and FCP increase were observed for a thicker feed spacer. At constant linear flow velocity, roughly the same FCP development and biomass accumulation were found irrespective of the feed spacer thickness: hydrodynamics and substrate load were more important for development and impact of biofouling than the thickness of currently applied spacers. Use of biostatic and metal coated spacers were not effective for biofouling control. The same small reduction of biofouling rate was observed with copper and silver coated spacers as well as uncoated 45° rotated spacers. The studied modified spacers were not effective for biofouling prevention and control. The impact of biofouling on FCP increase was reduced significantly by a lower linear flow velocity, while spacer orientation and spacer thickness in membrane modules had a smaller but still significant effect. [Copyright &y& Elsevier]

Abstract: Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH4 +–N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides. [Copyright &y& Elsevier]

Abstract: Anaerobic ammonium oxidation, nitrification and removal of COD was studied at ambient temperature (18 °C ± 3) in an anoxic/aerobic granular sludge reactor during 390 days. The reactor was operated in a sequencing fed batch mode and was fed with acetate and ammonium containing medium with a COD/N ratio of 0.5 [g COD/gN]. During influent addition, the medium was mixed with recycled effluent which contained nitrate in order to allow acetate oxidation and nitrate reduction by anammox bacteria. In the remainder of the operational cycle the reactor was aerated and controlled at a dissolved oxygen concentration of 1.5 mg O2/l in order to establish simultaneous nitritation and Anammox. Fluorescent in-situ hybridization (FISH) revealed that the dominant Anammox bacterial population shifted toward Candidatus “Brocadia fulgida” which is known to be capable of organotrophic nitrate reduction. The reactor achieved stable volumetric removal rates of 900 [g N2–N/m3/day] and 600 [g COD/m3/day]. During the total experimental period Anammox bacteria remained dominant and the sludge production was 5 fold lower than what was expected by heterotrophic growth suggesting that consumed acetate was not used by heterotrophs. These observations show that Anammox bacteria can effectively compete for COD at ambient temperatures and can remove effectively nitrate with a limited amount of acetate. This study indicates a potential successful route toward application of Anammox in granular sludge reactors on municipal wastewater with a limited amount of COD. [Copyright &y& Elsevier]

Abstract: A two-dimensional (2-d) mathematical model describing the effect of biofilm development on the performance of a spiral-wound reverse osmosis (RO) membrane device was developed. The micro-scale model combines hydrodynamics and mass transport of solutes (salt and substrate) with biomass attachment, biofilm growth and detachment due to mechanical stress induced by liquid flow in the feed channel. The model explains several experimental observations when operating at constant pressure: loss of permeate flux with increased salt passage in time and achievement of a quasi-steady state flux and biomass amount. The model also shows how the local balance between biofilm growth and detachment leads to irregular biofilm distribution in the feed channel and suggests places where most biomass accumulation is expected. Numerical simulations were performed in configurations without spacer or with different spacer geometries (submerged, cavity and zigzag). Three mechanisms were identified by which biofilms on RO membranes contribute to performance loss: (i) biofilm-enhanced concentration polarization; (ii) increased hydraulic resistance to trans-membrane flow; and (iii) increased feed channel pressure drop. For seawater and brackish water desalination, biofilm-enhanced concentration polarization appears to affect most the local flux. This modeling approach, combining computational fluid dynamics (CFD) with biofilm models allows a systematic study of biofouling in membrane systems. Moreover the approach is useful for improving feed spacer design and to evaluate operational conditions for minimum biofouling of reverse osmosis and nanofiltration (NF) membrane devices. [ABSTRACT FROM AUTHOR]

Abstract: Reverse osmosis (RO) is an important membrane separation process, widely used for desalination applications. RO is part of a rapidly growing market as the demand for clean fresh water around the world continues to expand. A major industrial challenge for RO operations is control of fouling of the membrane modules. Fouling decreases production capacity and water quality and increases operating costs. Biofilm growth in the membrane modules, commonly referred to as biofouling, is in practice arguably the major fouling type. Different cleaning strategies are employed to remove such foulants and evaluation of cleaning effectiveness is often difficult, with operators relying on indirect measurements of fouling such as the pressure drop across the membrane module. The present study aims to evaluate chemical cleaning of biofouled RO membranes using magnetic resonance imaging (MRI). Membrane fouling simulators (MFS) were fouled in the laboratory, then subsequently cleaned using combinations of sodium dodecyl sulphate (SDS) and sodium hydroxide (NaOH) and observed using MRI. Both MRI structural and velocity images showed marked changes in biofilm distribution. A small volume of accumulated biomass had a large impact on the effective surface area for water production, the value of which was more accurately calculated using the velocity images. The extracted effective membrane surface area correlated well with the feed channel pressure drop. Additionally with this in situ MRI technique, the effect of fouling extent and time on cleaning effectiveness (biomass removal and effective surface area) were investigated. Cleanings at an early stage of biofouling was more efficient in removing biomass than cleaning performed at a later stage. [ABSTRACT FROM AUTHOR]

Abstract: To understand functional gel-forming exopolysaccharides in aerobic granular sludge, alginate-like exopolysaccharides were specifically extracted from aerobic granular sludge cultivated in a pilot plant treating municipal sewage. The exopolysaccharides were identified by the FAO/WHO alginate identification tests, characterized by biochemical assays, gelation with Ca2+, blocks fractionation, spectroscopic analysis as UV-visible, FT-IR and MALDI-TOF MS, and electrophoresis. The yield of extractable alginate-like exopolysaccharides was reached 160±4mg/g (VSS ratio). They resembled seaweed alginate in UV-visible and MALDI-TOF MS spectra, and distinguished from it in the reactions with acid ferric sulfate, phenol-sulfuric acid and Coomassie brilliant blue G250. Characterized by their high percentage of poly guluronic acid blocks (69.07±8.95%), the isolated exopolysaccharides were capable to form rigid, non-deformable gels in CaCl2. They were one of the dominant exopolysaccharides in aerobic granular sludge. We suggest that polymers play a significant role in providing aerobic granular sludge a highly hydrophobic, compact, strong and elastic structure. [Copyright &y& Elsevier]

Abstract: This study presents a new three-dimensional (3-d) computational model that couples fluid dynamics, solutes transport and biofouling by biofilm formation in NF and RO membrane modules. A computational domain of 3×5 feed spacer frames with geometry as applied in practice was used in the model. Comparing the hydrodynamics computed with the realistic spacer geometry and with a spacer made from straight cylindrical filaments, like in previous modeling studies, showed that cylindrical filament feed spacers are too simplified for representative modeling studies. The 3-d numerical simulations showed that biomass accumulation, by attachment and biofilm growth in time, strongly affected the feed channel pressure drop, liquid velocity distribution and residence time distribution. The main pressure drop is encountered by the flow passing over the spacer filaments. Simulations showed the development of a heterogeneous flow pattern and formation of preferential flow channels. This study indicates that the real impact of biofouling is on the flow regime leading to quasi-stagnant zones and an increase in the dispersion of the residence time distribution. The presented 3-d mathematical modeling approach in (bio)fouling of membrane modules may have significant implications for membrane system design and operation to have stable membrane installation performance at minimal costs. [Copyright &y& Elsevier]

Abstract: A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800mg NH4 +-NL−1) was considered here. The influent for the Anammox process must be composed of NH4 +-N and NO2 −-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH4 +-N and NO2 −-N at the right stoichiometric ratio. The equal ratio of HCO3 −/NH4 + in reject water results in a natural pH decrease when approximately 50% of NH4 + is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40mg NH4 +-Ng−1 volatile suspended solids (VSS)h−1, but in terms of absolute nitrogen removal the SBR conversion was 1.1kgNday−1 m−3, whereas in the SHARON chemostat was 0.35kgNday−1 m−3 due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed. [Copyright &y& Elsevier]

Phosphate can be recovered as struvite or apatite in fluidised bed reactors. Urine has a much higher phosphate concentration than sludge reject water, allowing simpler (and less expensive) process for precipitation of phosphates. A stirred tank reactor with a special compartment for liquid solid separation was used to precipitate struvite from urine. Magnesium ammonium phosphate as well as potassium magnesium phosphate are two forms of struvite that were successfully precipitated. Liquid/solid separation was very effective, but the compaction of struvite was rather poor in the case of potassium struvite. Crystals did not form clusters and maintained the typical orthorhombic structure. Ammonium struvite had slightly lower effluent phosphate concentrations, but an average of 95% of influent phosphate was removed regardless of ammonium or potassium struvite precipitation. Fluid mechanics is believed to be important and should inform further work. [Copyright &y& Elsevier]

Abstract: Anaerobic digestion is a multistep process, mediated by a functionally and phylogenetically diverse microbial population. One of the crucial steps is oxidation of organic acids, with electron transfer via hydrogen or formate from acetogenic bacteria to methanogens. This syntrophic microbiological process is strongly restricted by a thermodynamic limitation on the allowable hydrogen or formate concentration. In order to study this process in more detail, we developed an individual-based biofilm model which enables to describe the processes at a microbial resolution. The biochemical model is the ADM1, implemented in a multidimensional domain. With this model, we evaluated three important issues for the syntrophic relationship: (i) Is there a fundamental difference in using hydrogen or formate as electron carrier? (ii) Does a thermodynamic-based inhibition function produced substantially different results from an empirical function? and; (iii) Does the physical co-location of acetogens and methanogens follow directly from a general model. Hydrogen or formate as electron carrier had no substantial impact on model results. Standard inhibition functions or thermodynamic inhibition function gave similar results at larger substrate field grid sizes (>10μm), but at smaller grid sizes, the thermodynamic-based function reduced the number of cells with long interspecies distances (>2.5μm). Therefore, a very fine grid resolution is needed to reflect differences between the thermodynamic function, and a more generic inhibition form. The co-location of syntrophic bacteria was well predicted without a need to assume a microbiological based mechanism (e.g., through chemotaxis) of biofilm formation. [Copyright &y& Elsevier]

Abstract: Temperature changes can influence biological processes considerably. To investigate the effect of temperature changes on the conversion processes and the stability of aerobic granular sludge, an aerobic granular sludge sequencing batch reactor (GSBR) was exposed to short-term and long-term temperature changes. Start-up at 8°C resulted in irregular granules that aggregated as soon as aeration was stopped, which caused severe biomass washout and instable operation. The presence of COD during the aerobic phase is considered to be the major reason for this granule instability. Start-up at 20°C and lowering the temperature to 15°C and 8°C did not have any effect on granule stability and biomass could be easily retained in the system. The temperature dependency of nitrification was lower for aerobic granules than usually found for activated sludge. Due to decreased activity in the outer layers of granules at lower temperatures, the oxygen penetration depth could increase, which resulted in a larger aerobic biomass volume, compensating the decreased activity of individual organisms. Consequently the denitrifying capacity of the granules decreased at reduced temperatures, resulting in an overall poorer nitrogen removal capacity. The overall conclusion that can be drawn from the experiments at low temperatures is that start-up in practice should take place preferentially during warm summer periods, while decreased temperatures during winter periods should not be a problem for granule stability and COD and phosphate removal in a granular sludge system. Nitrogen removal efficiencies should be optimized by changes in reactor operation or cycle time during this season. [Copyright &y& Elsevier]