Evaluation of effectiveness of combined sewer overflow control measures by operational data.

The effect of combined sewer overflow (CSO) control measures should be validated during operation based on monitoring of CSO activity and subsequent comparison with (legal) requirements. However, most CSO monitoring programs have been started only recently and therefore no long-term data is available for reliable efficiency control. A method is proposed that focuses on rainfall data for evaluating the effectiveness of CSO control measures. It is applicable if a sufficient time-series of rainfall data and a limited set of data on CSO discharges are available. The method is demonstrated for four catchments of the Berlin combined sewer system. The analysis of the 2000-2007 data shows the effect of CSO control measures, such as activation of in-pipe storage capacities within the Berlin system. The catchment, where measures are fully implemented shows less than 40% of the CSO activity of those catchments, where measures have not yet or not yet completely been realised.

Evaluation of oxygen transfer efficiency under process conditions using the dynamic off-gas method.

The off-gas method can be used to investigate standard oxygen transfer efficiencies under process conditions (alphaSOTE) over the operating life of an aeration system. A method to evaluate alphaSOTE is described in detail by US and German standards. The standards, however, do not describe how to evaluate dynamic changes in aSOTE over a day, which can be useful to uncover problems and unfavourable process conditions. Based on over three years experience gained in off-gas testing in Berlin wastewater treatment plants (WWTPs) under operating conditions, a method to evaluate and interpret the dynamic changes in oxygen transfer is presented. The application of the dynamic off-gas method brings important additional information, which can be used to increase operational efficiency of the aeration basin and to increase process reliability, with a relatively small increase in effort. This paper shows how to perform dynamic measurements under process conditions. Some results of such measurements under dynamic process conditions, performed in a Berlin WWTP, are discussed.

Impact of colloidal and soluble organic material on membrane performance in membrane bioreactors for municipal wastewater treatment.

Two parallel membrane bioreactors (2 m3 each) were operated over a period of 2 years. Both pilots were optimised for nitrification, denitrification, and enhanced biological phosphorous elimination, treating identical municipal wastewater under comparable operating conditions. The only constructional difference between the pilots was the position of the denitrification zone (pre-denitrification in pilot 1 and post-denitrification in pilot 2). Despite identical modules and conditions, the two MBRs showed different permeabilities and fouling rates. The differences were not related to the denitrification scheme. In order to find an explanation for the different membrane performances, a one-year investigation was initiated and the membrane performance as well as the operating regime and characteristics of the activated sludge were closely studied. MLSS concentrations, solid retention time, loading rates, and filtration flux were found not to be responsible for the different performance of the submerged modules. These parameters were kept identical in the two pilot plants. Instead, the non-settable fraction of the sludges (soluble and colloidal material, i.e. polysaccharides, proteins and organic colloids) was found to impact fouling and to cause the difference in membrane performance between the two MBR. This fraction was analysed by spectrophotometric and size exclusion chromatography (SEC) methods. In a second step, the origin of these substances was investigated. The results point to microbiologically produced substances such as extracellular polymeric substances (EPS) or soluble microbial products (SMP).

Long-term comparison of trace organics removal performances between conventional and membrane activated sludge processes.

The removal of trace organic compounds through membrane bioreactors (MBR) compared with a conventional wastewater treatment plant (WWTP) in a long-term study was investigated. Two MBR pilot plants were operated in parallel to a full-scale WWTP fed with the same municipal raw wastewater. Polar compounds (phenazone-type pharmaceuticals, their metabolites, and carbamazepine) and less polar estrogenic steroids (estradiol, estrone, and ethinylestradiol) were quantified. The removal rate of phenazone, propyphenazone, and formylaminoantipyrine by the conventional WWTP was less than 15%. Significantly higher removal rates (60 to 70%) started to be clearly monitored in the pilot plants after approximately 5 months. Higher removal rates coincided with higher temperatures in the summer. The conventional WWTP removed, on average, more than 90% of the natural steroids estrone and estradiol and approximately 80% of the synthetic ethinylestradiol. Approximately 99% of estradiol and estrone and approximately 95% of ethinylestradiol was eliminated by the MBR processes.

Evaluation of ceramic and membrane diffusers under operating conditions with the dynamic offgas method.

The aeration systems of two full-scale, activated-sludge basins were compared during a period of three years, under the same operating conditions, using dynamic offgas testing. Only the material of the diffuser was different (membrane versus ceramic-tube diffusers). The investigation has shown that, although the membrane diffusers have higher initial standard-oxygen-transfer efficiency (alphaSOTE) and standard-aeration efficiency (alphaSAE), these decreased over time, while the alphaSAE of the ceramic diffusers started lower, but increased slightly over the whole period. A cost comparison makes clear how important it is to evaluate the aeration system under process conditions. The operating costs were the dominant factor (approximately 10x higher than capital costs), and operating costs were approximately 20% higher for membrane versus ceramic diffusers. The poor performance of the membrane-tube diffusers under process conditions could be explained on the basis of the actual alphaAE values in the basin, not the standardized values.

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.

Correlation between membrane fouling and soluble/colloidal organic substances in membrane bioreactors for municipal wastewater treatment.

Two similar membrane bioreactors of 2 m3 each were operated in parallel over two years under the same operational conditions, fed with the same municipal wastewater. The only process and operational difference between both pilot plants was the position of the denitrification zone (pre-denitrification in pilot 1 and post-denitrification in pilot 2). Despite parallel operation, the two MBRs exhibited different fouling rates and decreases in permeability. These differences could not be accounted for by MLSS concentrations, loading rates, or filtration flux. In a one-year investigation, soluble and colloidal organic material in the activated sludge of both MBR was regularly analysed by spectrophotometric and Size Exclusion Chromatography (SEC) methods. The larger organic molecules present in the sludge water phase (i.e. polysaccharides, proteins and organic colloids) originating from microbial activity (extracellular polymeric substances) were found to impact on the fouling and to explain the difference in membrane performance between the two MBR units. In both pilot plants, a linear relationship could be clearly demonstrated between the fouling rate of the membrane and the concentration of polysaccharides in the sludge water phase during a 5 month operational period at an SRT of 8 days.

Potential of OUR and OTR measurements for identification of activated sludge removal processes in aerated basins.

In order to develop a process control scheme to reduce energy costs for aeration in activated sludge systems with biological P removal, pre-denitrification and nitrification stages, the spatial distribution of carbon oxidation and nitrification was evaluated over a long full-scale plug flow aeration basin using an externally measured specific oxygen uptake rate (sOUR) and in basin measurement of the actual specific oxygen transfer rate (sOTR) with off-gas testing as well as with the calculated oxygen demand from NH4-N concentrations (sOTR(N)). Using a simple static model, a gas phase balance on oxygen and carbon dioxide, sOTR(N) values were also calculated from off-gas testing. Comparison of sOTR(N) to sOTR and sOUR for carbon oxidation (sOUR(C)) to nitrification (sOUR(N)) at different loading conditions allowed the oxidation processes to be followed over the three zones of the aeration basin. As expected, the distribution depended on the dissolved oxygen concentration (DO) in the basin. However, the major change was in the C-oxidation rate and not the nitrification rate. At a low DO, and when NH4-N was present in the zone, the amount of oxygen transferred for nitrification was nearly the same, but the overall sOTR was lower. The externally measured sOUR was only useful when it was differentiated into sOUR(N) and sOUR(C). sOUR(N) could be used to predict the nitrification rate in the basin. With further refinement, the gas phase balance model has potential to be used to monitor the degree of nitrification over the basin length. This can be integrated into a control scheme to reduce aeration costs by adjusting the DO setpoint according to loading conditions in the

Outcomes of a 2-year investigation on enhanced biological nutrients removal and trace organics elimination in membrane bioreactor (MBR).

Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2m3 each. Both configurations included an anaerobic zone ahead of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or post-denitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50 microgP/L in the effluent could be consistently achieved with two types of municipal wastewater, the second site requiring a low dose of ferric salt ferric salt < 3 mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1 mg of phosphorus was biologically eliminated for 10 mg BOD5 in the influent. The post-denitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration as low as 1 mgN/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone. Pharmaceuticals residues and steroids were regularly monitored on the two parallel MBR pilot plants during the length of the trials, and compared with the performance of the Berlin-Ruhleben WWTP. Although some compounds such as carbamazepine were persistent through all the systems, most of the compounds could be better removed by the MBR plants. The influence of temperature, sludge age and compound concentration could be shown, as well as the significance of biological mechanisms in the removal of trace organic compounds.

A control strategy for reducing aeration costs during low loading periods.

The efficiency of the aeration system in a full-scale activated sludge basin with 3 separately controlled aeration zones was improved for the low loading period in summer. The air flow rate to each aeration zone is currently regulated to hold a preset dissolved oxygen concentration (DO). Four different DO setpoint combinations were tested, each one for a one week period, using dynamic off-gas testing to measure the standardised oxygen transfer efficiency (alphaSOTE). As the DO setpoints were lowered, the total air flow rate to the basin decreased initially. A low DO in the first zones slowed biomass activity and pushed the load towards the end of the aeration basin. The relationship between alphaSOTE and the specific diffuser flow rate qD is different for each zone. In Zone 1 there was a strong decrease in alphaSOTE as qD increased, while Zones 2 and 3 were fairly independent of qD, Zone 2 at a higher level than Zone 3. Aeration costs were reduced by 15% for the most efficient combination. To achieve even more savings, a control strategy adjusting oxygen transfer rates over the aeration basin to the necessary oxygen transfer rates is suggested. It is based on changing the DO setpoints to reach the lowest total air flow rate while meeting the effluent requirements.

Occurrence of benzothiazoles in municipal wastewater and their fate in biological treatment.

A number of 2-substituted benzothiazoles that are known to be used as fungicides, corrosion inhibitors and vulcanization accelerators in industry have been analyzed in municipal wastewater and the effluents of activated sludge and membrane bioreactor (MBR) treatment over a three month period. All six analytes were regularly detected in the municipal wastewater by liquid chromatography-mass spectrometry and amount to a total concentration of 3.4 microg/L. Of these compounds benzothiazole-2-sulfonic acid (1,700 ng/L), benzothiazole (850 ng/L) and 2-hydroxybenzothiazole (500 ng/L) were most prominent. The source of the benzothiazole emission is yet unknown. Activated sludge treatment did not reduce total benzothiazole concentration significantly. Removals of the individual compounds ranged from 90% for 2-mercaptobenzothiazole and 70% for hydroxybenzothiazole to 40% for benzothiazole. The concentration of benzothiazole-2-sulfonic acid increased by 20%, whereas 2-methylthiobenzothiazole increased by 160% during activated sludge treatment, likely due to the methylation of mercaptobenzothiazole. Total benzothiazole removal in two parallely operated MBRs was significantly better (43%) than in the conventional activated sludge treatment. Namely benzothiazole and benzothiazole-2-sulfonic acid were more effectively removed. This first systematic study on the occurrence of benzothiazoles in municipal wastewater has shown that this is a relevant class of trace contaminants in municipal wastewater which is only incompletely removed in biological wastewater treatment. Emission from sewage treatment is dominated by the most polar benzothiazole-2-sulfonic acid. MBR treatment may reduce but cannot avoid this emission.

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.

Cost effective and advanced phosphorus removal in membrane bioreactors for a decentralised wastewater technology.

Future stringent phosphorus regulations (down to 50 microg/L in some cases) together with the availability of more cost effective and/or innovative membrane processes, are the bases for this project. In contrast to conventional activated sludge plants, process parameters are not optimised and especially enhanced biological phosphorus (Bio-P) removal in membrane bioreactors (MBRs) are not proven yet. Current practice of P-removal in MBRs is the addition of coagulants in a co-precipitation mode. Enhanced biological phosphorus removal, when adapted to MBR technology, might be a cost-effective process. For very stringent effluent criteria additional P-adsorption on activated clay after membrane filtration can be also an interesting solution. The objective of this research project is to identify and test various phosphorus removal processes or process combinations, including MBR technologies. This should enable us to establish efficient and cost effective P-removal strategies for upgrading small sewage treatment units (up to 10,000 PE), as needed in some decentralised areas of Berlin. In particular, enhanced Bio-P removal technology was developed and optimised in MBR. Combinations of co-precipitation and post-adsorption will be tested when low P-values down to 50 microg/L are required in the effluent. One MBR bench-scale plant of 200 to 250 L and two MBR pilot plants of 1 to 3 m3 each were operated in parallel to a conventional wastewater treatment plant (Ruhleben WWTP, Berlin, Germany). The MBR bench-scale and pilot plants were operated under sludge ages of respectively 15 and 25 days. In both cases, Bio-P was possible, and phosphorus effluent concentration of about 0.1 mg/L could be achieved. A similar effluent quality was observed with the conventional WWTP. Investigations with lab columns indicated that P-adsorption could lead to concentrations down to 50 microg/L and no particle accumulation occurred in the filter media. The three tested materials exhibited great differences in break-through curves. Granulated ferric hydroxyde (GEH) showed higher capacity than activated alumina and FerroSorpPlus.

Phosphorus removal with membrane filtration for surface water treatment.

Surface waters are often burdened with inflows of low quality water, so that drinking-water production, swimming or ground water charging must be restricted. To ensure the long-term use of such surface water it is necessary to treat the influents or the water used for ground water charging. The current treatment process for phosphorus and turbidity removal is a process combination called floc filtration. By using this conventional method it is possible to reduce the dissolved ortho-phosphate and the turbidity (particulate phosphorus) as well as the amounts of algae and pathogenic organisms to very low concentrations. The high degree of reduction is only achieved by a relatively high dosage of chemicals. A comparison will be made between this process, which represents the state-of-the-art, and the combination of precipitation/coagulation with micro-/ultrafiltration in dead-end filtration mode.

Hanced biological phosphorus removal in membrane bioreactors.

Enhanced biological phosphorus removal (Bio-P) in a membrane bioreactor (MBR) promises several advantages but was never attempted as not compatible with high sludge ages. This article includes description and results of bench-scale investigations on Bio-P removal in an MBR. An MBR bench-scale plant (210 L) was operated in parallel to a conventional WWTP under comparable process conditions. The results show that Bio-P removal is possible in MBR. The effluent qualities of the plants were comparable. The effluent P-concentration was always lower than 0.2 mg P(T)/L. In the MBR bench-scale plant P-uptake occurred mainly in the anoxic zone. Investigations with P-spiking showed higher Bio-P potential as P-removal increased up to 20-25 mg/L while P/TS rose up to >6%.

Comparison of the efficiency of large-scale ceramic and membrane aeration systems with the dynamic off-gas method.

The aeration systems of two full-scale activated sludge basins were compared over 2.5 years under the same operating conditions using dynamic off-gas testing. Only the material of the diffuser was different, membrane vs. ceramic tube diffusers. The experimental design took the complexity and dynamics of the system into consideration. The investigation has shown that, although the membrane diffusers have higher initial standard oxygen transfer efficiency (SOTE) and standard aeration efficiency (SAE), these decreased over time, while the SAE of the ceramic diffusers started lower, but increased slightly over the whole period. Measurement of air distribution in the basins along with dissolved oxygen concentration profiles have provided important information on improving process control and reducing energy costs. The results show that dynamic off-gas testing can effectively be used for monitoring the aeration system and to check design assumptions under operating conditions. The information can be used to improve the design of new aeration systems or in retro-fitting existing basins.

[Assessment and sex counseling in libido disorders]. / Abklärung und Sexualberatung bei Libidostörungen.

Individual problems, difficulties in the partnership, handicaps of the body and the influence of society contribute to sexual problems. In this article a definition of hypoactive sexual desire disorders (HSDD) is given. Then the author tries to show the many different reasons of disturbed sexual desire to help to see the problem from different points of view. Often it is very important for the patients to understand why they are unable to feel sexual wishes. In clarifying the personal reasons change begins and the couple can find out which next steps may be useful to solve the problem of not wanting to want.