Nutrient recycling from the effluent of a decentralized anaerobic membrane bioreactor (AnMBR) treating fresh domestic wastewater by cultivation of the microalgae Acutodesmus obliquus.

This study investigates the feasibility of microalgae cultivation with the effluent (permeate) of a decentralized anaerobic membrane bioreactor (AnMBR) treating high strength domestic wastewater. Two experiments, consisting of three and two successive batch experiments with incubation times varying between 5 and 9 days, were conducted. Nutrient removal and growth of the microalgae species Acutodesmus obliquus were studied for the following culture media: (A) permeate, (B) permeate enriched with iron (Fe), magnesium (Mg), manganese (Mn), sulfur (S) and the chelating agent EDTA, (C) commercial fertilizer as control culture. Initial nutrient concentrations in the culture media ranged from 9.3 to 16.6 mg·L-1 total phosphorus (TP) and from 85.1 to 126.2 mg·L-1 total nitrogen (TN). TP reached an average removal of 97%, 98% and 99% in (A), (B) and (C) respectively. An average TN removal of 94% and 96% was achieved in (B) and (C). Starting from the third batch of the first experiment and the second batch of the second experiment, the culture with permeate (A) showed a decrease in TN removal. Further batch experiments showed the need to add iron to ensure an optimal TN removal from the permeate.

Application of an early warning indicator and CaO to maximize the time-space-yield of an completely mixed waste digester using rape seed oil as co-substrate.

In order to increase the organic loading rate (OLR) and hereby the performance of biogas plants an early warning indicator (EWI-VFA/Ca) was applied in a laboratory-scale biogas digester to control process stability and to steer additive dosing. As soon as the EWI-VFA/Ca indicated the change from stable to instable process conditions, calcium oxide was charged as a countermeasure to raise the pH and to bind long-chain fatty acids (LCFAs) by formation of aggregates. An interval of eight days between two increases of the OLR, which corresponded to 38% of the hydraulic residence time (HRT), was sufficient for process adaptation. An OLR increase by a factor of three within six weeks was successfully used for biogas production. The OLR was increased to 9.5 kg volatile solids (VS) m(-3) d(-1) with up to 87% of fat. The high loading rates affected neither the microbial community negatively nor the biogas production process. Despite the increase of the organic load to high rates, methane production yielded almost its optimum, amounting to 0.9 m(3)(kg VS)(-1). Beneath several uncharacterized members of the phylum Firmicutes mostly belonging to the family Clostridiaceae, a Syntrophomonas-like organism was identified that is known to live in a syntrophic relationship to methanogenic archaea. Within the methanogenic group, microorganisms affiliated to Methanosarcina, Methanoculleus and Methanobacterium dominated the community.

Early warning indicators for process failure due to organic overloading by rapeseed oil in one-stage continuously stirred tank reactor, sewage sludge and waste digesters.

Early warning indicators for process failures were investigated to develop a reliable method to increase the production efficiency of biogas plants. Organic overloads by the excessive addition of rapeseed oil were used to provoke the decrease in the gas production rate. Besides typical monitoring parameters, as pH, methane and hydrogen contents, biogas production rate and concentrations of fatty acids; carbon dioxide content, concentrations of calcium and phosphate were monitored. The concentration ratio of volatile fatty acids to calcium acted as an early warning indicator (EWI-VFA/Ca). The EWI-VFA/Ca always clearly and reliably indicated a process imbalance by exhibiting a 2- to 3-fold increase 3-7days before the process failure occurred. At this time, it was still possible to take countermeasures successfully. Furthermore, increases in phosphate concentration and in the concentration ratio of phosphate to calcium also indicated a process failure, in some cases, even earlier than the EWI-VFA/Ca.

Comparison of different procedures to stabilize biogas formation after process failure in a thermophilic waste digestion system: influence of aggregate formation on process stability.

Following a process failure in a full-scale biogas reactor, different counter measures were undertaken to stabilize the process of biogas formation, including the reduction of the organic loading rate, the addition of sodium hydroxide (NaOH), and the introduction of calcium oxide (CaO). Corresponding to the results of the process recovery in the full-scale digester, laboratory experiments showed that CaO was more capable of stabilizing the process than NaOH. While both additives were able to raise the pH to a neutral milieu (pH>7.0), the formation of aggregates was observed particularly when CaO was used as the additive. Scanning electron microscopy investigations revealed calcium phosphate compounds in the core of the aggregates. Phosphate seemed to be released by phosphorus-accumulating organisms, when volatile fatty acids accumulated. The calcium, which was charged by the CaO addition, formed insoluble salts with long chain fatty acids, and caused the precipitation of calcium phosphate compounds. These aggregates were surrounded by a white layer of carbon rich organic matter, probably consisting of volatile fatty acids. Thus, during the process recovery with CaO, the decrease in the amount of accumulated acids in the liquid phase was likely enabled by (1) the formation of insoluble calcium salts with long chain fatty acids, (2) the adsorption of volatile fatty acids by the precipitates, (3) the acid uptake by phosphorus-accumulating organisms and (4) the degradation of volatile fatty acids in the aggregates. Furthermore, this mechanism enabled a stable process performance after re-activation of biogas production. In contrast, during the counter measure with NaOH aggregate formation was only minor resulting in a rapid process failure subsequent the increase of the organic loading rate.

Fungal diversity in activated sludge from membrane bioreactors in Berlin.

The objective of this study was to evaluate the occurrence of fungi in aerobic and anoxic activated sludge from membrane bioreactors. Thirty-six samples from each aerobic and anoxic activated sludge were taken from two membrane bioreactors treating domestic wastewater. Over a period of 9 months, four samples from each plant were taken per month. The samples were prepared for count and identification of fungi. Sixty species belonging to 30 genera were collected from activated sludge samples under aerobic and anoxic conditions. In terms of fungal identification, under aerobic conditions Geotrichum candidum was found at 94.4% followed by Penicillium species at 80.6%, yeasts at 75.0%, and Trichoderma species at 50.0%; under anoxic conditions G. candidum at 86.1%, yeasts at 66.6%, and Penicillium species at 61.1% were the most prevalent. The results indicate that activated sludge is a habitat for growth and sporulation of different groups of fungi, both saprophytic and pathogenic.

Mycological survey of activated sludge in MBRs.

The objective of this research was to conduct a survey of fungi in activated sludge plants with membrane bioreactors (MBRs). Thirty-six samples of both aerobic and anoxic activated sludge were taken from two plants with MBRs treating domestic wastewater. Over a period of 8 months, two samples from each plant were taken per month. The samples were prepared for count and identification of fungi. The obtained data show that 61 species belonging to 30 genera were identified from activated sludge samples, under aerobic conditions (27 genera and 54 species) and anoxic conditions (21 genera and 39 species), by culturing at 30 °C for 15 days. In aerobic activated sludge samples, the prevalence of Geotrichum candidum was 100% followed by Fusarium (72.2%), yeast (61.1%), Aspergillus (50.0%), Penicillium (50.0%) and Trichoderma (41.6%), while in anoxic activated sludge, G. candidum (94.4%), Fusarium (91.6%), Aspergillus (77.7%), yeast (63.8%), Penicillium (50.0%) and Trichoderma (50.0%) species were the most prevalent. In addition, the other genera found included Chaetomum, Chrysosporium, Cladosporium, Doratomyces, Gibberella, Gliocladium, Gymnoascus, Mucor, Paecilomyces, Phialophora, Rhizopus, Scopulariopsis, Stachybotrys, Stemphylium and others. The results indicate that aerobic and anoxic activated sludge provides a suitable habitat for the growth and sporulation of different groups of fungi, both saprophytic and pathogenic.

Online- and offline- monitoring of stem cell expansion on microcarrier.

In the biopharmaceutical industry, adherent growing stem cell cultures gain worldwide importance as cell products. The cultivation process of these cells, such as in stirred tank reactors or in fixed bed reactors, is highly sophisticated. Cultivations need to be monitored and controlled to guarantee product quality and to satisfy GMP requirements. With the process analytical technology (PAT) initiative, requirements regarding process monitoring and control have changed and real-time on-line monitoring tools are recommended. A tool meeting the new requirements may be the dielectric spectroscopy for online viable cell mass determination by measurement of the permittivity. To establish these tools, proper offline methods for data correlation are required. The cell number determination of adherent cells on microcarrier is difficult, as it requires cell detachment from the carrier, which highly increases the statistical error. As an offline method, a fluorescence assay based on SYBR(®)GreenI was developed allowing fast and easy total cell concentration determination without the need to detach the cells from the carrier. The assay is suitable for glass carriers used in stirred tank reactor systems or in fixed bed systems, may be suitable for different cell lines and can be applied to high sample numbers easily. The linear dependency of permittivity to cell concentration of suspended stem cells with the dielectric spectroscopy is shown for even very small cell concentrations. With this offline-method, a correlation of the cell concentration grown on carrier to the permittivity data measured by the dielectric spectroscopy was done successfully.

Process control in cell culture technology using dielectric spectroscopy.

In the biopharmaceutical industry, mammalian and insect cells as well as plant cell cultures are gaining worldwide importance to produce biopharmaceuticals and as products themselves, for example in stem cell therapy. These highly sophisticated cell-based production processes need to be monitored and controlled to guarantee product quality and to satisfy GMP requirements. With the process analytical technology (PAT) initiative, requirements regarding process monitoring and control have changed and real-time in-line monitoring tools are now recommended. Dielectric spectroscopy (DS) can serve as a tool to satisfy some PAT requirements. DS has been used in the medical field for quite some time and it may allow real-time process monitoring of biological cell culture parameters. DS has the potential to enable process optimization, automation, cost reduction, and a more consistent product quality. Dielectric spectroscopy is reviewed here as a tool to monitor biochemical processes. Commercially available dielectric sensing systems are discussed. The potential of this technology is demonstrated through examples of current and potential future applications in research and industry for mammalian and insect cell culture.

Monitoring of transparent exopolymer particles (TEP) in a membrane bioreactor (MBR) and correlation with other fouling indicators.

The occurrence of Transparent Exopolymer Particles (TEP), an acidic fraction of polysaccharides, was monitored for more than six months in the activated sludge of three MBR units, and the relationship between TEP and other fouling indicators was studied. These compounds consist mainly of exopolysaccharides of a sticky nature, a characteristic which makes them a group of interesting substances in processes like sedimentation, flocculation and membrane fouling. The relationship between capillary suction time (CST) and polysaccharides (PS) was linear for the three tested sludges, although the correlation with TEP concentrations was stronger. A slight linear correlation of both TEP and PS was found with the critical flux (CF) measured with a small filtration test cell, which was submerged in the membrane tank to assess the filterability performance of the sludge in situ. However, the correlation CF-PS was clearer. The relationship between TEP, polysaccharides and sludge filterability highlights the potential of this parameter for the monitoring of membrane systems.

Phosphorus recovery in aerated systems by MAP precipitation: optimizing operational conditions.

An attractive way of recovering essential phosphorus from digested sludge of a WWTP is the precipitation in the sludge directly, as part of the continuous treatment process. For optimizing the precipitation, 1 litre-batch tests were performed in a model system to examine the MAP-crystallization kinetics. Different parameters such as e.g. the aeration flow rate were investigated. The aim was to find an optimized setting for a pilot reactor for the continuous production of MAP. This reactor performed as an airlift reactor for an improved mixing and stripping the dissolved CO2 and separating the MAP-crystals. The optimal condition for the airlift pilot reactor is given when the air flow rate for mixing the system and for stripping CO2 for a maximum MAP precipitation is aligned with the particle size distribution.

Membrane bioreactor aeration: investigation of the velocity flow pattern.

Results of investigations concerning membrane bioreactor aeration are presented which were carried out at the Institute of Environmental Engineering of RWTH Aachen University (ISA) in cooperation with the Department of Chemical Engineering of the Technische Universität Berlin. In the field of industrial and municipal wastewater treatment the use of membrane bioreactors (MBR) is of increasing interest especially due to the high requirements on effluent quality nowadays. The design of aeration systems is a very important aspect of MBR development because it influences both cost of operation and filtration flux. The ISA has carried out tests concerning the velocity flow pattern in flat sheet membrane modules (developed by the A3 Water Solutions GmbH) to identify the effects of different aeration systems, aeration intensities and module constructions. The Department of Chemical Engineering is currently using the results obtained from the ADV to calibrate a numerical model which simulates two phase water and gas flow within an aerated membrane module. Optical investigations concerning the bubble distribution give a better understanding of the flow conditions in MBR. Developing a numerical tool for membrane module optimization concerning the hydrodynamics is the aim of the investigation of membrane bioreactor aeration.

Side effects of flux enhancing chemicals in membrane bioreactors (MBRs): study on their biological toxicity and their residual fouling propensity.

Soluble and colloidal materials like soluble microbial products (SMP) or extracellular polymeric substances (EPS) are considered to be major foulants in membrane bioreactors (MBRs). Removing these fouling causing substances is thus thought to reduce the fouling of the membrane in general. In addition to traditional strategies for fouling prevention which mostly try to remedy the effects of fouling by air scour, etc., the new and promising method of adding chemicals is being investigated here. Previous tests with 30 different substances have shown that several of these reduce SMP concentration in the supernatant and enhance filtration. Nevertheless, additive dosing might have unknown side effects in filtration systems. Results presented in this study indicate that these additives may themselves cause severe fouling on different membranes if they remain unbound in the liquid phase. Therefore, the thorough control of the dosing rate of these chemicals will be of paramount importance in full scale applications. Biological toxicity of additives was measured in terms of respiration. OUR tests did not show inhibiting effects for most additives. Chitosan even showed an enhanced OUR due to biodegradability. Oxygen transfer could be enhanced for 25% with the addition of a polymer.

Continuous measurement and control of fouling active compounds in membrane bioreactor systems.

For a more effective fouling reduction in membrane bioreactors (MBR) the approach of continuous measurement and control of protein and polysaccharide concentrations is followed. So called extra-cellular polymer substances (EPS) can be partially measured by a newly developed protein sensor based on sequential injection analysis. The sensor is validated by real MBR pilot data, stating the feasibility of the technique for continuous monitoring. Parallel to EPS, other fouling active compounds such as organic bio-polymer were determined in two parallel MBR pilot lines by size exclusion chromatography, proving desired comparable conditions in both lines for later parallel testing. The daily variation of EPS in MBR operation are moderate, where protein changes tend to react more pronounced to operational changes than polysaccharides. This was also the case for the organic bio-polymer fraction, especially in manipulated bench experiments at abruptly changing redox conditions.

Impact of different recirculation schemes on nitrogen removal and overall performance of a laboratory scale MBR.

For membrane bioreactors (MBR) with enhanced nutrients removal, rather complex recirculation schemes based on the biological requirements are commonly recommended. The aim of this work was to evaluate other recirculation options. For a laboratory scale MBR, four different recirculation schemes were tested. The MBR was operated with COD degradation, nitrification, post-denitrification without carbon dosing and biological phosphorus removal. For all configurations, efficient COD, nitrogen and phosphorus removal could be achieved. There were no big differences in elimination efficiency between the configurations (COD elimination: 96.6-97.9%, nitrogen removal: 89.7-92.1% and phosphorus removal: 97.4-99.4%). Changes in the degradation, release and uptake rates were levelled out by the changes in contact time and biomass distribution. With relatively constant outflow concentrations, different configurations are still interesting with regard to oxygen consumption, simplicity of plant operation or support of certain degradation pathways such as biological phosphorus removal or denitrification.

Biomass effects on oxygen transfer in membrane bioreactors.

Ten biomass samples from both municipal and industrial pilot and full scale submerged membrane bioreactors (MBRs) with mixed liquor suspended solids concentrations (MLSS) ranging from 7.2 to 30.2g L(-1) were studied at six air-flow rates (0.7, 1.3, 2.3, 3, 4.4 and 6m(3)m(-3)h(-1)). Statistical analyses were applied to identify the relative impacts of the various bulk biomass characteristics on oxygen transfer. Of the biomass characteristics studied, only solids concentration (correlated with viscosity), the carbohydrate fraction of the EPS (EPS(c)) and the chemical oxygen demand (COD) concentration of the SMP (SMP(COD)) were found to affect the oxygen transfer parameters k(L)a(20) (the oxygen transfer coefficient) and alpha-factor. The relative influence on k(L)a(20) was MLSS>aeration>EPS(c)>SMP(COD) and on alpha-factor was MLSS>SMP(COD)>EPS(c)>aeration. Both k(L)a(20) and alpha-factor increased with increasing aeration and EPS(c) and decreased with increasing MLSS and SMP(COD). MLSS was found to be the main parameter controlling the oxygen transfer.

Enhanced post-denitrification without addition of an external carbon source in membrane bioreactors.

This study investigates a post-denitrification process without the addition of an external carbon source combined with an enhanced biological phosphorus removal (EBPR) in a membrane bioreactor (MBR). Three trial plants, with two different process configurations, were operated on two different sites, and a variety of accompanying batch tests were conducted. It was shown that even without dosing of an external carbon source, denitrification rates (DNR) much above endogenous rates could be obtained in post-denitrification systems. Furthermore, the anaerobic reactor located ahead of the process had a positive impact on the DNR. Given these surprising results, the project team decided to identify the carbon source used by the microorganisms in the post-denitrification process. Batch tests could demonstrate that lysis products do not play a major role as a C-source for post-denitrification. The following hypothesis was proposed to explain the observations: the glycogen, internally stored by the substrate accumulating bacteria, if anaerobic conditions are followed by aerobic conditions could act as carbon source for denitrification in post-denitrification system. First exploratory batch tests, where the glycogen evolution was monitored, corroborate this assumption.

Nutrients removal in MBRs for municipal wastewater treatment.

Owing to increasingly stringent effluent quality requirements, intensifications of the conventional activated sludge process (ASP) are required. Due to high biomass concentrations employed, higher metabolic rates and better nutrient removal are possible in membrane bioreactors (MBRs). Decoupling of hydraulic and solids residence times offers additional possibilities for process design and optimisation. Recently, unconventional concepts like post-denitrification and enhanced biological phosphorus removal in MBRs have emerged. The objective of this paper is to present current knowledge on nutrients removal in MBRs and trends in process optimisation in comparison with conventional ASP.

Enhanced biological phosphorus removal process implemented in membrane bioreactors to improve phosphorous recovery and recycling.

The enhanced biological phosphorus removal (EBPR) process was adapted to membrane bioreactor (MBR) technology. One bench-scale plant (BSP, 200-250 L) and two pilot plants (PPs, 1,000-3,000 L each) were operated under several configurations, including pre-denitrification and post-denitrification without addition of carbon source, and two solid retention times (SRT) of 15 and 26 d. The trials showed that efficient Bio-P removal can be achieved with MBR systems, in both pre- and post-denitrification configurations. EBPR dynamics could be clearly demonstrated through batch-tests, on-line measurements, profile analyses, P-spiking trials, and mass balances. High P-removal performances were achieved even with high SRT of 26 d, as around 9 mgP/L could be reliably removed. After stabilisation, the sludge exhibited phosphorus contents of around 2.4%TS. When spiked with phosphorus (no P-limitation), P-content could increase up to 6%TS. The sludge is therefore well suited to agricultural reuse with important fertilising values. Theoretical calculations showed that increased sludge age should result in a greater P-content. This could not be clearly demonstrated by the trials. This effect should be all the more significant as the influent is low in suspended solids.

Investigation of nitrogen removal in a cascaded membrane bioreactor.

Two different plants in different scales were compared. The main characteristic of the plants is the division of the nitrification volume into separate chambers. To gain more information about the internal conversion processes, concentration profiles of COD, NO3-N and NH4-N along the pathway of the waste water were measured. Moreover, the effect of different plant configurations and different operation conditions involving the internal circulation streams on the biological conversion processes were studied. Except for some temporary operation problems, the treatment performance of the plants was very stable and on a high level. There was a high correspondence between the plants. Operation without internal recirculation leads to lower effluent concentrations of ammonium. Beside this, operation of several nitrification chambers instead of only one chamber results in lower ammonium effluent concentrations.

Performance of a bioreactor with submerged membranes for aerobic treatment of municipal waste water.

Aerobic treatment of municipal waste water in a membrane bioreactor was studied for 535 d. Apart from sampling, sludge was retained completely by a submerged hollow fibre membrane with a pore-size of 0.2 microm. The pilot plant comprised an anoxic zone to enable denitrification. The maximum liquid hold-up of the plant was 3.9 m3. In this study the reactor performance and the stability of the process and the membrane capacity were investigated. A stable flux of 181 m(-2)h(-1) could be realised with a mean transmembrane pressure difference of 0.3bar with air-bubbling and backflushing the membrane and cleaning it in place every two months for one or two hours. For about 140d, a flux of 271 m(-2)h(-1) was achieved, but cleaning became necessary more often. The hydraulic retention time (HRT) varied between 10.4 and 15.6h. Accordingly the volumetric loading rate was between 1.1 and 1.7kg CODm(-3)d(-1). No inoculum was used. The mixed liquor suspended solids (MLSS) concentration gradually increased to 18-20g MLSSl(-1). The feed to microorganism (F/M) ratio varied according to the operation conditions but decreased against a value of 0.07 kg COD kg(-1) MLSSd(-1). Treatment performance was very stable and on a high level. The COD was reduced by 95%. Nitrification was complete and up to 82% of the total nitrogen could be denitrified.