Pilot-scale study of powdered activated carbon recirculation for micropollutant removal.

Adsorption onto powdered activated carbon (PAC) is a promising technique for the removal of organic micropollutants (OMPs) from treated wastewater. To enhance the adsorption efficiency, PAC is recycled back into the adsorption stage. This technique was examined in pilot scale in comparison to a reference without recirculation. Coagulation with Fe(3+) was carried out simultaneously to adsorption. Extensive OMP measurements showed that recirculation significantly increased OMP eliminations. Thus, significant PAC savings were feasible. The PAC concentration in the contact reactor proved to be an important operating parameter that can be surrogated by the easily measurable total suspended solids (TSS) concentration. OMP eliminations increased with increasing TSS concentrations. At 20 mg PAC L(-1) and 2.8 g TSS L(-1) in the contact reactor, well-adsorbable carbamazepine was eliminated by 97%, moderately adsorbable diclofenac was eliminated by 92% and poorly-adsorbable acesulfame was eliminated by 54% in comparison to 49%, 35% and 18%, respectively, without recirculation. The recirculation system represents an efficient technique, as the PAC's adsorption capacity is practically completely used. Small PAC dosages yield high OMP eliminations. Poorly-adsorbable gabapentin was eliminated to an unexpectedly high degree. A laboratory-scale biomass inhibition study showed that aerobic biodegradation removed gabapentin in addition to adsorption.

Rapid small-scale column testing of granular activated carbon for organic micro-pollutant removal in treated domestic wastewater.

This study investigates the applicability of the rapid small-scale column test (RSSCT) concept for testing of granular activated carbon (GAC) for organic micro-pollutants (OMPs) removal from wastewater treatment plant (WWTP) effluent. The chosen experimental setup was checked using pure water, WWTP effluent, different GAC products, and variable hydrodynamic conditions with different flow velocities and differently sized GAC, as well as different empty bed contact times (EBCTs). The setup results in satisfying reproducibility and robustness. RSSCTs in combination with WWTP effluent are effective when comparing the OMP removal potentials of different GAC products and are a useful tool for the estimation of larger filters. Due to the potentially high competition between OMPs and bulk organics, breakthrough curves are likely to have unfavorable shapes when treating WWTP effluent. This effect can be counteracted by extending the EBCT. With respect to the strong competition observed in GAC treatment of WWTP effluent, the small organic acid and neutral substances are retained longer in the RSSCT filters and are likely to cause the majority of the observed adsorption competition with OMPs.

Tertiary treatment of Berlin WWTP effluents with ferrate (Fe(VI)).

New and higher standards in the EU water framework directive necessitate advanced treatment of secondary effluents for reduction of trace organic compounds (TrOCs) and nutrients before the discharge into receiving surface waters. Due to its dual function as oxidant and coagulant, ferrate is considered as a promising alternative for tertiary treatment. The oxidation of selected TrOCs and simultaneous flocculation of phosphates by ferrate was tested in batch experiments with secondary effluent from Berlin Ruhleben. The concentrations of carbamazepine (CBZ) and diclofenac were reduced by >90% with ferrate dosages of 6 mg/L as Fe. CBZ was transformed to 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one, which is known as the major product from the reaction of CBZ with ozone. In contrast to ozonation, no further transformation of this product was observed. The concentration of ibuprofen was not reduced by ferrate treatment. For efficient removal of 60-100 µg/L phosphate-P to values <20 µg/L, ferrate dosages of 3-4 mg/L as Fe were sufficient.

Energy analysis of conventional and source-separation systems for urban wastewater management using Life Cycle Assessment.

This study investigates the cumulative energy demand (CED) of different systems for the management of urban wastewater, following the methodology of Life Cycle Assessment. In a hypothetical case study for an urban area (5,000 inhabitants), all relevant processes for wastewater collection and treatment and the construction of infrastructure are described in a substance flow model. The conventional system requires 1,250 MJ/(pe*a), with the operation contributing 45%, the infrastructure 7%, and the system expansion (production of mineral fertilizer and electricity) 48% to the total CED. The separation systems have a CED of 930-1,182 MJ/(pe*a) depending on their configuration. Results of the impact assessment show that recovering energy from the organic matter of toilet wastewater and household biowaste in a digestion process can decrease the cumulative energy demand by 13-26%. Energetic benefits of mineral fertilizer substitution are relatively small compared to the energy recovered from organic matter. Decisive parameters for the energy analysis are the amount of biowaste which is co-digested with toilet wastewater and the energy demand of the vacuum plant.

Comparison of two treatments for the removal of selected organic micropollutants and bulk organic matter: conventional activated sludge followed by ultrafiltration versus membrane bioreactor.

The potential of membrane bioreactor (MBR) systems to remove organic micropollutants was investigated at different scales, operational conditions, and locations. The effluent quality of the MBR system was compared with that of a plant combining conventional activated sludge (CAS) followed by ultrafiltration (UF). The MBR and CAS-UF systems were operated and tested in parallel. An MBR pilot plant in Israel was operated for over a year at a mixed liquor suspended solids (MLSS) range of 2.8-10.6 g/L. The MBR achieved removal rates comparable to those of a CAS-UF plant at the Tel-Aviv wastewater treatment plant (WWTP) for macrolide antibiotics such as roxythromycin, clarithromycin, and erythromycin and slightly higher removal rates than the CAS-UF for sulfonamides. A laboratory scale MBR unit in Berlin - at an MLSS of 6-9 g/L - showed better removal rates for macrolide antibiotics, trimethoprim, and 5-tolyltriazole compared to the CAS process of the Ruhleben sewage treatment plant (STP) in Berlin when both were fed with identical quality raw wastewater. The Berlin CAS exhibited significantly better benzotriazole removal and slightly better sulfamethoxazole and 4-tolyltriazole removal than its MBR counterpart. Pilot MBR tests (MLSS of 12 g/L) in Aachen, Germany, showed that operating flux significantly affected the resulting membrane fouling rate, but the removal rates of dissolved organic matter and of bisphenol A were not affected.

Treatment of membrane concentrates: phosphate removal and reduction of scaling potential.

The widespread application of nanofiltration (NF) and reverse osmosis (RO) membranes in wastewater reuse inevitably generates a concentrate stream. Due to high concentrations of phosphate and salts, disposal of membrane concentrates is a problem which seriously constrains the application of this technology, especially in inland applications. There is a need for technologies which facilitate an affordable and environmentally-safe disposal of membrane concentrates. The objectives of this study are to investigate appropriate treatment techniques to (1) increase the recovery of the membrane filtration thus minimising the volume of the concentrate stream, and (2) increase the concentrate quality to enable discharge into surface water bodies. The results show that both adsorption onto granular ferric hydroxide (GFH) and chemical precipitation are generally effective for phosphate removal from NF concentrates. Chemical precipitation by dosing of sodium hydroxide solution is rapid and removes more than 90% of phosphate and calcium ions. By the removal of calcium ions, chemical precipitation can significantly reduce the scaling potential of NF and RO concentrates. This may allow higher recoveries in the NF/RO process.

Sustainable wastewater management: life cycle assessment of conventional and source-separating urban sanitation systems.

Conventional and source-separating urban sanitation systems are compared with regard to their ecological sustainability using the methodology of Life Cycle Assessment. A substance flow model of all relevant processes in a settlement with 5,000 inhabitants is set up and evaluated with environmental indicators for resource demand and emissions to air, water, and soil. The comparison shows that source separation does not necessarily result in a system with less environmental impacts. If the conventional system is energetically optimized and equipped with extended nutrient removal, its impact is comparable to the source-separating systems. However, source separation has the potential to offer ecological benefits depending on the system configuration. Especially the input of toxic heavy metals to agriculture with sewage sludge can be substantially lowered if separately collected urine and faeces are used as organic fertilizer.

Reductive dehalogenation of iopromide by zero-valent iron.

Iodinated X-ray contrast media (ICM), as derivatives of 2, 4, 6-triiodo benzoic acid, are applied in high doses to humans and are excreted unchanged via urine within 24 h. Common as well as advanced wastewater treatment is not able to remove the iodinated compounds leading to an environmental pollution. A specific treatment of contaminated urine or hospital wastewater could minimise the emission. For that reason the deiodination of iopromide, the most commonly used ICM, was investigated using zero-valent iron. Initial experiments carried out in stirred batch reactors with an initial pH of 2 using iron powder and iopromide dissolved in ultra pure water showed that iopromide can be deiodinated by zero-valent iron. Even in contaminated urine collected in a hospital a deiodination of ICM was possible. Further experiments at different constant pH values, temperatures and stirring speeds were performed. The kinetic studies at constant pH showed that the deiodination can be described by pseudo-first order for equal iopromide and iron concentrations. In general, the reaction depends strongly on the pH, the temperature and the stirring speed. The observed rate constant K(obs) has an optimum at pH 3 and rises with increasing temperature and stirring speed.

Impact of temperature on biodegradation of bulk and trace organics during soil passage in an indirect reuse system.

Investigations on the behavior of bulk organics and trace organic compounds in a temperature controlled soil column system are reported. Objective of the research was to assess the importance of temperature for the degradation of bulk and trace organics. The analysis of the bulk organic behavior showed a fast mineralization of easily degradable organic carbon in the first few centimetres of the columns, which does not seem to be temperature-dependent. Along the further infiltration path an influence of the different temperatures on the bioactivity was clearly visible. However, a significant increase of mineralization potential of bulk organic compounds with increasing temperature was shown. The monitoring of the single organic pollutants Iopromide, Sulfamethoxazole and naphthalenedisulfonic acids showed that temperature has an influence on the degradation behavior of the monitored compounds. In most cases higher temperatures increased the mineralization potential.

An integrated wastewater reuse concept combining natural reclamation techniques, membrane filtration and metal oxide adsorption.

In a Sino-German research project, a sustainable water reclamation concept was developed for different applications of municipal water reuse at the Olympic Green 2008 in Beijing, China. Results from pilot-scale experiments in Beijing and Berlin show that selective nutrient removal by adsorption onto granular ferric hydroxide (GFH) after a membrane bioreactor (MBR) can maintain a total phosphorus concentration of <0.03 microg L(-1) P, thus preventing eutrophication of artificial lakes. Operation time of GFH adsorption columns can be extended by regeneration using sodium hydroxide solution. A subsequent ultrafiltration (UF) membrane after bank filtration creates an additional barrier for pathogens and allows for further urban reuse applications such as toilet flushing. Short term bank / bio-filtration prior to UF is shown to effectively remove biopolymers and reduce membrane fouling.

Development of a continuous protein and polysaccharide measurement method by sequential injection analysis for application in membrane bioreactor systems.

Polysaccharides and proteins are the main components of extracellular polymeric substances, which are considered to give a major contribution to the overall fouling potential of the MBR system. This work focuses on the automation of spectrophotometrical assays for protein and polysaccharide determination for on-line measurement in MBR. Sequential Injection Analysis (SIA) was identified as more suitable for continuous measurements. In screening tests the selection of an appropriate assay for the successful automation by means of SIA was carried out. Lowry Assay and Dubois Assay were chosen for protein and polysaccharide determination. Lowry Assay could be successfully automated by means of SIA. The automated method shows a lower sensitivity than the manual Lowry method, what can be contributed to specific characteristic of SIA. The confidence limit was calculated to 2.8 mg/L. The automated method shows in validation tests good correspondence with protein concentrations measured with the manual assay (R(2)=0.971). The successful establishment of the Dubois Assay for polysaccharides failed so far due to sensitivity problems.

Potentials of real time control, stormwater infiltration and urine separation to minimize river impacts: dynamic long term simulation of sewer network, pumping stations, pressure pipes and waste water treatment plant.

River Panke (Berlin, Germany) suffers from hydraulic peak loads and pollutant loads from separate sewers and combined sewer overflows (CSOs). Pumping the wastewater through long pressure pipes causes extreme peak loads to the wastewater treatment plant (WWTP) during stormwater events. In order to find a good solution, it is essential not to decide on one approach at the beginning, but to evaluate a number of different approaches. For this reason, an integrated simulation study is carried out, assessing the potentials of real time control (RTC), stormwater infiltration, storage and urine separation. Criteria for the assessment are derived and multi-criteria analysis is applied. Despite spatial limitations, infiltration has the highest potential and is very effective with respect to both overflows and the WWTP. Due to a high percentage of separate systems, urine separation has a similar potential and causes the strongest benefits at the WWTP. Unconventional control strategies can lead to significant improvement (comparable to infiltrating the water from approximately 10% of the sealed area).

Ozonation and reductive deiodination of iopromide to reduce the environmental burden of iodinated X-ray contrast media.

The potential of ozonation for the removal of iodinated X-ray contrast media (ICM) with focus on the oxidation products was examined. Iopromide used as model compound was dissolved in tap water, respectively in the effluent of a membrane bioreactor and was ozonated. Ozone (10 mg/L) was continuously introduced into a semi-batch reactor (35 L/h). After 30 minutes the ozone concentration was increased to 30 mg/L. In all experiments the iopromide concentration decreased very fast, whereas the decrease of the amount of organic bound iodine (AOI) was much lower. The concentration of iodate, the inorganic oxidation product increases with time, depending on the AOI decrease. The data clearly show that the ozonation of iopromide using a common applied ozone dosage leads to the formation of numerous iodinated transformation products, which are detectable by LC-ESI-MS. As an alternative treatment, especially for the treatment of urine or hospital waste water, the source for the contamination, it was tested if iopromide can be deiodinated by zero-valent iron. First experiments done in stirred batch reactors using iopromide dissolved in ultra pure water and urine with an initial pH of 2 showed that iopromide can be deiodinated completely by zero-valent iron. Even in contaminated urine collected in a hospital a deiodination of ICM was possible. Kinetic studies at constant pH showed that the deiodination can be described by pseudo-first order for equal iopromide and iron concentrations. The observed rate constant kobs increased with decreasing pH with a maximum at pH 3 with 4.76x10(-4) s(-1). The concentration of iopromide can be decreased by ozonation and by the reductive dehalogenation. In case of ozonation iodinated organic compounds are the main reaction products, whereas the reductive dehalogenation leads to transformation products which are not iodinated and are thus most probable biodegradable.

SUVA as control parameter for the effective ozonation of organic pollutants in secondary effluent.

Recent research projects have shown a good suitability of the ozonation process to transform trace concentrations of most pharmaceuticals in wastewater treatment plant (WWTP) effluents. The concentrations of carbamazepine and 17 alpha-ethinylestradiol, for instance, were reduced below their detection limits by use of ozone dosages resulting in a specific ozone consumption of 0.5 mg O3/mg DOC0. At the same time a good disinfection performance was achieved. The given hygienic requirements of the EU bathing water directive (e.g. 2,000 N/100 mL faecal coliforms) are fulfilled without the formation of bromate (<10 microg/L). As technical control parameter of the ozonation process usually the residual ozone in the liquid phase or in the off-gas are used. However, at very low specific ozone consumptions, ozone reacts instantaneously with dissolved compounds and cannot be detected. Hence, alternative parameters should be used for effective operation control. The present paper evaluates the relation between UVA decrease and the removal of different compounds (endocrine disrupting compounds, pharmaceuticals, iodinated X-ray contrast media), microbial parameters and bromate formation. The results can be used as a guideline for the control of the oxidation performance at large scale ozonation units.

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 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).

The benefits of powdered activated carbon recirculation for micropollutant removal in advanced wastewater treatment.

PAC adsorption is a widespread option for the removal of organic micropollutants (OMP) from secondary effluent. For an optimal exploitation of the adsorption capacity, PAC recirculation is nowadays a common practice, although the mechanistic interrelations of the complex recirculation process are not fully resolved. In this work, extensive multi-stage batch adsorption testing with repeated PAC and coagulant dosage was performed to evaluate the continuous-flow recirculation system. Partly loaded PAC showed a distinct amount of remaining capacity, as OMP and DOC removals considerably increased with each additional adsorption stage. At a low PAC dose of 10 mg PAC L(-1), removals of benzotriazole and carbamazepine were shown to rise from <40% in the first stage up to >80% in the 11th stage at 30 min adsorption time per stage. At a high PAC dose of 30 mg PAC L(-1), OMP and DOC removals were significantly higher and reached 98% (for benzotriazole and carbamazepine) after 11 stages. Coagulant dosage showed no influence on OMP removal, whereas a major part of DOC removal can be attributed to coagulation. Multi-stage adsorption is particularly beneficial for small PAC doses and significant PAC savings are feasible. A new model approach for predicting multi-stage OMP adsorption on the basis of a single-stage adsorption experiment was developed. It proved to predict OMP removals and PAC loadings accurately and thus contributes towards understanding the PAC recirculation process.

Removal of dissolved metals by zero-valent iron (ZVI): kinetics, equilibria, processes and implications for stormwater runoff treatment.

Infiltration of stormwater runoff contaminated with metals is often questionable in several cases due to its long-term potential to cause deterioration of groundwater quality. To ensure the quality of filtrate, a pre-treatment of contaminated runoff is required. This study investigates the processes of copper and zinc ion removal from stormwater runoff using zero-valent iron (ZVI, Fe0). Kinetic and equilibrium tests were performed with laboratory-prepared and in situ stormwater runoff samples collected from roof, street and highway catchments. Based on the results, a substantial portion of Cu2+ is reduced and transformed to insoluble forms of Cu0 and Cu2O. Unlike copper, the adsorption and co-precipitation associated with freshly precipitated iron oxides play important roles for the removal of Zn2+. Investigations under various water quality conditions demonstrated a relatively minor impact on Cu2+ uptake rates. However, the different conditions apparently altered the removal stoichiometry and phases of the copper deposits. The removal rates of Zn2+ increase with higher dissolved oxygen (DO), ionic strength (IS), temperature (T) and pH. Dissolved organic carbon (DOC) in runoff samples forms complexes with metals and Fe2+, thereby kinetically decreasing the metal uptake rates. Furthermore, depending on its composition, a larger molecular weight organic fraction was found to preferentially compete for the adsorption sites. The study demonstrates that ZVI is a promising medium for achieving comparable capacity to a commercial adsorbent like granular ferric hydroxide (GFH). Long-term performance of ZVI, however, may be limited and governed by the formation of non-conductive layers of iron and cuprous oxides.

Planning, modelling and assessing source control concepts on catchment scale.

Today's water management practice was identified often not to be consistently structured. Usually the decision space is not clearly depicted and then systematically explored. Often stakeholders are involved too late and many objectives are neglected. An adaptive DSS is being developed to help overcoming these problems. Core of the DSS is a "decision matrix", which has been implemented as a web based application (www.wsm300.de). The management objectives are represented by the indicators labelling the rows. They will be the result of a discussion of the objectives and problems in the specific sub-basin, which is supported by the catalogue of indicators. The columns of the matrix are specified by the scenarios whose development is supported by the database of measures and a Geographical Information System (GIS). The matrix, once the labels are defined, serves as a plot for the planning process, defining clearly which objectives have to be considered and which indicator-values have to be calculated. The DSS further includes a concept and tools for the combination of existing software components and supports the processing of model-outputs to indicator-values. Filled with the indicator-values the matrix allows a comparison of the scenarios and provides a good base for a decision. Multi-criteria decision aid methods can (if desired) further help to find the optimal scenario and to mediate between stakeholders. Finding the optimal scenario will likely be an iterative process.

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.