Elimination of micropollutants by activated carbon produced from fibers taken from wastewater screenings using hydrothermal carbonization

Activated Carbon (AC) can be used to reduce organic micropollutants (OMPs) in wastewater treatment plants (WWTPs). While producing ACs conventionally still damages the environment, this can be reduced by using renewable raw material from waste streams und producing AC locally. In this study, fibers (toilet paper) were separated out of wastewater by screening WWTP influents in full scale and then used as a no-cost, carbon-rich and heavy metal-poor raw material to produce ACs. Pretreatment was hydrothermal carbonization (HTC). Thereafter, they were activated using KOH to generate activated carbons (HTC-ACs). Their functional groups were characterized using FT-IR, and the alteration of their chemical composition was traced by elementary analysis. Adsorption tests were performed with nitrogen (BET surface) and methylene blue as standard tests. The adsorption capacity was tested with WWTP effluent and the removal of UVA₂₅₄ as a surrogate for OMP removal was measured. After HTC and activation 13-16% of the fibers dry mass was obtained as HTC-ACs. Higher dehydration and formation of aromatic structures on the HTC-ACs were detected with FT-IR as HTC and activation temperature increased. BET surface and methylene blue adsorption of some HTC-ACs was higher than the Reference AC. Nevertheless, their ability to reduce OMPs is still lower than the Reference AC due to the different nature of their functional groups and their microporous structure that is not fully accessible for OMPs in real wastewater. Further research has to be carried out to adjust the production process so as to obtain mesoporous HTC-ACs tailored to reduce OMP concentrations and to close the carbon loop within WWTPs.

Status quo report on wastewater treatment plant, receiving water's biocoenosis and quality as basis for evaluation of large-scale ozonation process

The project DemO₃AC (demonstration of large-scale wastewater ozonation at the Aachen-Soers wastewater treatment plant, Germany) of the Eifel-Rur Waterboard contains the construction of a large-scale ozonation plant for advanced treatment of the entire 25 million m³/yr of wastewater passing through its largest wastewater treatment plant (WWTP). In dry periods, up to 70% of the receiving water consists of treated wastewater. Thus, it is expected that effects of ozonation on downstream water biocoenosis will become observable. Extensive monitoring of receiving water and the WWTP shows a severe pollution with micropollutants (already prior to WWTP inlet). (Eco-)Toxicological investigations showed increased toxicity at the inlet of the WWTP for all assays. However, endocrine-disrupting potential was also present at other sampling points at the WWTP and in the river and could not be eliminated sufficiently by the WWTP. Total cell counts at the WWTP are slightly below average. Investigations of antibiotic resistances show no increase after the WWTP outlet in the river. However, cells carrying antibiotic-resistant genes seem to be more stress resistant in general. Comparing investigations after implementation of ozonation should lead to an approximation of the correlation between micropollutants and water quality/biocoenosis and the effects that ozonation has on this matter.

Carbon recovery from screenings for energy-efficient wastewater treatment

The energy content of screenings from six municipal wastewater treatment plants (WWTPs) was examined. Hourly samples of separated screenings were taken over 24 hours at three of the plants to illustrate diurnal variations. To recover the chemical energy, which usually leaves the WWTP with the screenings, a screenings wash press was used to transfer organic matter from the solid into the liquid phase. The chemical energy of raw and compacted washed screenings as well as the chemical energy of washing water were determined by measuring the chemical oxygen demand (COD) for the six WWTPs. A mass weighted average of 1.35 g_COD/g_dm (dm: dry matter) was found in the raw screenings of three WWTPs. The overall recovered energy from screenings was found to range from 0.27 to 0.62 g_COD/g_dm. This washed-out COD found in the washing water could be sent for anaerobic digestion or to the wastewater treatment process as a carbon source for denitrification.

Characteristic numbers of granular activated carbon for the elimination of micropollutants from effluents of municipal wastewater treatment plants

Adsorption on granular activated carbon (GAC) is a promising step to extend existing treatment trains in municipal wastewater treatment plants (WWTPs) and, thus, to reduce the concentration of micropollutants (MPs) (e.g. pharmaceuticals) in wastewater. It is common practice to use characteristic numbers when choosing GAC for a specific application. In this study, characteristic numbers were correlated for five different GACs, with measured adsorption capacities of these carbons for three pharmaceutical MPs (carbamazepine, diclofenac and sulfamethoxazole) and dissolved organic carbon of a WWTP effluent. The adsorption capacities were measured using rapid small scale column tests. Density of GAC showed the highest correlation to adsorption of MP. All other characteristic numbers (iodine number, Brunauer-Emmett-Teller (BET) surface and methylene blue titre) are not suitable markers for choosing an appropriate activated carbon product for the elimination of MPs from municipal wastewater.

Improving vacuum-UV (VUV) photolysis of organic compounds in water with a phosphor converted xenon excimer lamp emitting at 193 nm

A novel vacuum ultraviolet excimer lamp emitting light at 193 nm was used to investigate the degradation of organic micropollutants in ultrapure water and wastewater treatment plant (WWTP) effluent. Overall, light at 193 nm proved to be efficient to degrade the investigated micropollutants (diclofenac, diatrizoic acid, sulfamethoxazole). Experiments with WWTP effluent proved the ability of radiation at 193 nm to degrade micropollutants which are hardly removed with commonly used oxidation technologies like ozonation (diatrizoic acid, ethylenediaminetetraacetic acid, perfluorooctanoic acid, and perfluorooctanesulfonic acid).

Response surface method for the optimisation of micropollutant removal in municipal wastewater treatment plant effluent with the UV/H2O2 advanced oxidation process

Experiments with the ultraviolet (UV)/H2O2 advanced oxidation process (AOP) were conducted to investigate the abatement of micropollutants in wastewater treatment plant effluent. The fluence and the starting concentration of H2O2 in a bench-scale batch reactor were varied according to response surface method (RSM) to examine their influence on the treatment efficiency. It was shown that the investigated AOP is very effective for the abatement of micropollutants with conversion rates typically higher than 90%. Empirical relationships between fluence, H2O2 dosage and the resulting concentration of micropollutants were established by RSM. By this means it was shown that X-ray-contrast media had been degraded only by UV light. Nevertheless, most substances were degraded by the combination of UV irradiation and H2O2. Based on RSM an optimisation of multiple responses was conducted to find the minimal fluence and H2O2 dosage that are needed to reach an efficient abatement of micropollutants.

The removal and degradation of pharmaceutical compounds during membrane bioreactor treatment

Pharmaceutical compounds such as non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics have been detected in sewage treatment plant (STP) effluents, surface and ground water and even in drinking water all over the world, and therefore have developed as compounds of concern. Membrane bioreactor (MBR) treatment has gained significant popularity as an advanced wastewater treatment technology and might be effective for an advanced removal of these pollutants. This paper evaluates the treatment of wastewater containing three NSAIDs (acetaminophen, ketoprofen and naproxen) and three antibiotics (roxithromycin, sulfamethoxazole and trimethoprim) performed in two MBRs with sludge retention times (SRTs) of 15 (MBR-15) and 30 (MBR-30) days over a period of four weeks. It was observed that NSAIDs were removed with higher efficiencies than the antibiotics for both MBRs, and the MBR-30 presented higher removal efficiencies for all the compounds than obtained by MBR-15. Removal rates ranged from 55% (sulfamethoxazole) up to 100% (acetaminophen, ketoprofen). Besides mineralisation biological transformation products of ketoprofen and naproxen produced by wastewater biocoenosis were identified in both MBR permeates using liquid chromatography coupled with mass spectrometry (LC-MS). The results indicated the importance of investigating the environmental fate of pharmaceuticals and their transformation products reaching the environment.

An advanced simulation model for membrane bioreactors: development, calibration and validation

Membrane wastewater treatment plants (WWTPs) have several advantages compared with conventionally designed WWTPs with classical purification techniques. The filtration process is the key to their commercial success in Germany with respect to energy consumption and effectiveness, enabled by the optimization of filtration using a dynamic simulation model. This work is focused on the development of a robust, flexible and practically applicable membrane simulation model for submerged hollow-fibre and flat-sheet membrane modules. The model is based on standard parameters usually measured on membrane WWTPs. The performance of the model is demonstrated by successful calibration and validation for three different full-scale membrane WWTPs achieving good results. Furthermore, the model is combinable with Activated Sludge Models.

MBR technology: a promising approach for the (pre-)treatment of hospital wastewater

Membrane bioreactor (MBR) technology is a very reliable and extensively tested solution for biological wastewater treatment. Nowadays, separate treatment of highly polluted wastewater streams especially from hospitals and other health care facilities is currently under investigation worldwide. In this context, the MBR technology will play a decisive role because an effluent widely cleaned up from solids and nutrients is absolutely mandatory for a subsequent further elimination of organic trace pollutants. Taking hospital wastewater as an example, the aim of this study was to investigate to what extent MBR technology is an adequate 'pre-treatment' solution for further elimination of trace pollutants. Therefore, we investigated - within a 2-year period - the performance of a full-scale hospital wastewater treatment plant (WWTP) equipped with a MBR by referring to conventional chemical and microbiological standard parameters. Furthermore, we measured the energy consumption and tested different operating conditions. According to our findings the MBR treatment of the hospital wastewater was highly efficient in terms of the removal of solids and nutrients. Finally, we did not observe any major adverse effects on the operation and performance of the MBR system which potentially could derive from the composition of the hospital wastewater. In total, the present study proved that MBR technology is a very efficient and reliable treatment approach for the treatment of highly polluted wastewater from hospitals and can be recommended as a suitable pre-treatment solution for further trace pollutant removal.

Fate of pharmaceuticals and bacteria in stored urine during precipitation and drying of struvite

Experiments were conducted to measure the behaviour of eight pharmaceuticals during urine treatment as part of the project 'SANIRESCH - Sustainable sanitary recycling Eschborn'. Urine was collected from 200 people in a public building via waterless urinals and NoMix toilets. It was then stored at room temperature at different pH values to analyse the extent to which bacteria and pharmaceuticals are eliminated over time. Although a partial elimination of pharmaceuticals could be detected, the storage at defined pH values cannot be advised. As the persons tested used pharmaceuticals with different structures, in different amounts and at varying intervals, this method of treatment is insufficient for removing them from urine. Precipitating the urine with MgO, washing it with saturated struvite solution and drying it at 30 °C will result in a free-flowing granular powder of struvite (NH(4)MgPO(4)·6H(2)O) that is free of pharmaceuticals and pathogens and can be used as fertiliser and a source of nitrogen, magnesium and phosphorus.

Modular operation of membrane bioreactors for higher hydraulic capacity utilisation

Using data from 6 full-scale municipal membrane bioreactors (MBR) in Germany the hydraulic capacity utilisation and specific energy consumption were studied and their connexion shown. The average hydraulic capacity utilisation lies between 14% and 45%. These low values are justified by the necessity to deal with intense rain events and cater for future flow increases. However, this low hydraulic capacity utilisation leads to high specific energy consumption. The optimisation of MBR operation requires a better utilisation of MBR hydraulic capacity, particularly under consideration of the energy-intensive membrane aeration. A first approach to respond to large influent flow fluctuations consists in adjusting the number of operating modules. This is practised by most MBR operators but so far mostly with variable flux and constant membrane aeration. A second approach is the real-time adjustment of membrane aeration in line with flux variations. This adjustment is not permitted under current manufacturers' warranty conditions. A further opportunity is a discontinuous operation, in which filtration takes place over short periods at high flux and energy for membrane aeration is saved during filtration pauses. The integration of a buffer volume is thereby indispensable. Overall a modular design with small units, which can be activated/ inactivated according to the influent flow and always operate under optimum conditions, enables a better utilisation of MBR hydraulic capacity and forms a solid base to reduce MBR energy demand.

Full scale membrane bioreactor treatment of hospital wastewater as forerunner for hot-spot wastewater treatment solutions in high density urban areas

Membrane Bioreactors (MBR) are a very attractive option for the treatment of hospital wastewater and elimination of pharmaceuticals in high density urban areas. The present investigation showed that, depending on the substance, between 19% and 94% of the level of antibiotics found in the environment originate from hospitals. Because of their ecotoxic potential, hospital wastewaters can have a significant impact on the environment. The segregation of these wastewaters and their separate treatment at the source can reduce the entry of drugs in waterways and enable water reuse after adequate polishing treatment processes.

Biological wastewater treatment followed by physicochemical treatment for the removal of fluorinated surfactants

Perfluorinated surfactants (PFS) have become compounds of high concern during the last decade. While "conventional surfactants" are degraded to a great extent in the biological wastewater treatment process, partly or perfluorinated surfactants are not only stable against biodegradation but also against oxidizing agents, they even resist OH-radical attacks. Our objectives were to eliminate the fluorinated surfactants perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) by adsorption, separation or degradation with a balance of precursor compounds and follow-up of degradation products. Therefore, municipal wastewater was spiked with these fluorinated surfactants before membrane bioreactor (MBR) treatment-applying microfiltration membranes--was performed and before permeates were treated using ozone (O3) or different advanced oxidation treatment (AOP) techniques. O3 or hydrogen peroxide (H2O2), both in combination with UV radiation or in combination with catalysts, was applied. Removal by adsorption or membrane separation as well as degradation were monitored by substance specific determination and identification. High resolution mass spectrometry after high performance liquid chromatography (HPLC/HRMS and -MS(n)) was used for analysis. Contact to Teflon and/or glass during all analytical procedures was avoided.

Treatment of hospital wastewater effluent by nanofiltration and reverse osmosis

Considerable concern exists regarding the appearance and effects of trace and ultra trace pollutants in the aquatic environment. In this context, it is necessary to identify relevant hot spot wastewater - such as hospital wastewater - and to implement specific wastewater treatment solutions. Membrane bioreactor (MBR) technology seems to be a suitable pre-treatment approach for the subsequent advanced treatment by high pressure membrane systems such as nanofiltration (NF) and reverse osmosis (RO). This paper is based upon investigations on the first full scale MBR for separate treatment of hospital wastewater in Germany. In this study an NF as well as an RO module for further treatment of the MBR filtrate were tested. The removal efficiencies were assessed using the following target compounds: bezafibrate, bisoprolol, carbamazepine, clarithromycin, ciprofloxacin, diclofenac, ibuprofen, metronidazole, moxifloxacin, telmisartan and tramadol. In summary, the results of this study confirmed that MBR technology followed by an advanced treatment for trace pollutant removal is an adequate approach for specific treatment of hot spot wastewater such as hospital wastewater. In particular, it was shown that - comparing the tested NF and RO - only (a two stage) RO is appropriate to remove pharmaceutical residues from hospital wastewater entirely. The recommended yield of the 2-stage RO is 70% which results in a retentate sidestream of 9%. Our investigations proved that RO is a very efficient treatment approach for elimination of trace pollutants.

Design and operating experiences of municipal MBRs in Europe

The number of membrane bioreactor (MBR) installations is increasing worldwide, not only for small-scale industrial WWTPs but also for larger-scale municipal WWTPs. In Europe, MBR has been installed in municipal WWTPs since late 1990s, and more than 100 full-scale plants are operated at the moment. In this paper, present state of European municipal MBRs is described in terms of design and operating conditions, as well as operating problems and their solutions, based on the information collected from 17 full-scale WWTPs by interview and questionnaire survey. Decisive factors of MBR installation at these plants were footprint and effluent quality. Full-aerobic and pre-denitrification were the most common reactor configurations, nearly half of them being equipped with independent filtration tanks. Operating conditions of bioreactor and filtration, including membrane flux and cleaning strategy, were different from plant to plant, as a result of plant-specific optimization experiences, even among the similar type of membrane. Operating problems specific for MBR were reported, including blocking/failure of pre-screen, sludging/hair-clogging of membrane, damage on membrane unit, air in permeate pipes, as well as conventional troubles including occurrence of scum and initial trouble in instrumentation and control systems. Aspects for further optimization of MBR design were also pointed out by the operators.

In situ measurements of shear stresses of a flushing wave in a circular sewer using ultrasound

Deposits build up in sewer networks during both spells of dry weather and in connection with storm water events. In order to reduce the negative effects of deposit on the environment, different cleaning technologies and strategies are applied to remove the deposits. Jet cleaning represents the most widely used method to clean sewers. Another alternative cleaning procedure is flushing. On account of new developments in measurement and control panels, the flushing method is becoming more important. Therefore, in the last few years a number of new flushing devices have been constructed for application in basins, main sewers and initial reaches. Today, automatic flushing gates are able to accomplish cleaning procedures under economical and ecological conditions. The properties of flushing waves for cleaning sewers have been determined by several mathematical-numerical studies. These various investigations use altering numerical schemes, are based on different sets of physical equations and take one- or more dimensional aspects into account. Considering that bottom shear stress is the key value to evaluate the beginning of motion of any deposit, one may use this value that has to be determined by measurements. This paper deals with shear stresses caused by flushing waves which have been measured by an ultrasonic device that can determine the velocity in different depths of flow. Thus, it is possible, within certain limits, to calculate bottom shear stresses based on the log-wall law. Further discussion will deal with the requirements of measurements, its uncertainty and aspects in respect to the application of simulation of flushing waves.

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.

Evaluation of advanced treatment technologies for the elimination of pharmaceutical compounds

Pharmaceuticals and their metabolites have developed as ecotoxicologically relevant micropollutants in the aquatic environment. During conventional biological wastewater treatment they are eliminated insufficiently and therefore reach surface waters via discharges. They are either partially or completely non-biodegradable and/or hardly eliminable by activated sludge adsorption because they often have polar structures. Membrane bioreactor treatment (MBR) was applied to pre-treat wastewater containing pharmaceutical compounds, e.g., antibiotics like floxacins and their synthetic precursor compounds. Our objectives were to eliminate these persistent target compounds from wastewater prior to discharge into receiving waters. Therefore an advanced treatment applying MBR combined with different chemical and physicochemical processes was performed. The addition of powdered activated carbon (PAC), nano filtration (NF), reverse osmosis (UO) or ozone (O3) and O3/UV were applied to MBR permeate spiked with the selected target compounds. Treatment efficiency was assessed using conventional inorganic and organic chemical analyses besides advanced physicochemical methods like liquid chromatography coupled with mass and tandem mass spectrometry (LC-MS and -MS-MS).

Performance of membrane bioreactors used for the treatment of wastewater from the chemical and textile industries

Within the scope of the study, nine waste waters from the chemical and textile industries were treated in bench-scale (laboratory scale) and small-scale (pilot scale) membrane bioreactors. Depending on wastewater characteristics, the resulting performance varied significantly. It was observed that MBR effectiveness was determined primarily by the degree of biodegradability of the wastewater. In the course of several months of operation, no significant changes associated with the complete retention of the biomass by the membranes were observed. In some cases, it was possible to improve effluent quality by using smaller molecular separation sizes. The flux performance of the membrane modules was dependent on wastewater composition. Occasionally, non-degradable macromolecular substances concentrated in the bioreactor, resulting in strongly reduced filterability and flow performance of the membrane modules, consequently also reducing the economic viability of the process. The results demonstrate that wastewater-specific pilot tests are absolutely necessary, in particular if the technology is to be used for new applications.