Characterization and Assessment of a Novel Plate and Frame MD Module for Single Pass Wastewater Concentration-FEED Gap Air Gap Membrane Distillation.

Membrane distillation (MD) is an up and coming technology for concentration and separation on the verge of reaching commercialization. One of the remaining boundaries is the lack of available full-scale MD modules and systems suitable to meet the requirements of potential industrial applications. In this work a new type of feed gap air gap MD (FGAGMD) plate and frame module is introduced, designed and characterized with tap water and NaCl-H2O solution. The main feature of the new channel configuration is the separation of the heating and cooling channel from the feed channel, enabling a very high recovery ratio in a single pass. Key performance indicators (KPIs) such as flux, gained output ratio (GOR), recovery ratio and thermal efficiency are used to analyze the performance of the novel module concept within this work. A recovery rate of 93% was reached with tap water and between 53%-32% with salt solutions ranging between 117 and 214 g NaCl/kg solution with this particular prototype module. Other than recovery ratio, the KPIs of the FGAGMD are similar to those of an air gap membrane distillation (AGMD) channel configuration. From the experimental results, furthermore, a new MD KPI was defined as the ratio of heating and cooling flow to feed flow. This RF ratio can be used for optimization of the module design and efficiency.

Simulation and source identification of X-ray contrast media in the water cycle of Berlin.

This article describes the development of a model to simulate the fate of iodinated X-ray contrast media (XRC) in the water cycle of the German capital, Berlin. It also handles data uncertainties concerning the different amounts and sources of input for XRC via source densities in single districts for the XRC usage by inhabitants, hospitals, and radiologists. As well, different degradation rates for the behavior of the adsorbable organic iodine (AOI) were investigated in single water compartments. The introduced model consists of mass balances and includes, in addition to naturally branched bodies of water, the water distribution network between waterways and wastewater treatment plants, which are coupled to natural surface waters at numerous points. Scenarios were calculated according to the data uncertainties that were statistically evaluated to identify the scenario with the highest agreement among the provided measurement data. The simulation of X-ray contrast media in the water cycle of Berlin showed that medical institutions have to be considered as point sources for congested urban areas due to their high levels of X-ray contrast media emission. The calculations identified hospitals, represented by their capacity (number of hospital beds), as the most relevant point sources, while the inhabitants served as important diffusive sources. Deployed for almost inert substances like contrast media, the model can be used for qualitative statements and, therefore, as a decision-support tool.

Sustainable removal of iodinated X-ray contrast media (XRC) by ozonation in a complex wastewater matrix--urine as example.

Pharmaceutical and diagnostic substances like antibiotics, cytostatics and iodised X-ray contrast media (XRC) are well-known for not being metabolised and are excreted soon after application. As a result, these preparations are difficult to biodegrade and their adsorption behaviour is rather poor. Finally, the refractory properties of these substances are leading to an accumulation in the natural waterbody depending on the hydrological situation. The elimination of contrast media from urine and diluted urine solutions by ozonation was investigated using a bubble column reactor to remove and recover the formed elemental iodine from the solution by gas stripping and down stream absorption. The experiments showed that the destruction of XRCs from concentrated solutions like urine is feasible and a recycling of elemental iodine from the exhaust gas is technically and economically possible.

Influence of mass transfer on the ozonation of wastewater from the glass fiber industry.

The mass transfer rate (kLa) is one of the most important parameters in the ozonation of wastewater, because it frequently constitutes the rate-determining step. This study investigated the influence of kLa on the ozonation of glass fiber wastewater using a high-performance jet loop reactor (HJLR), which is well known for its high mass transfer property, and compared the results of this investigation with those obtained using the bubble column reactor. It was found that the higher kLa achieved by increasing the energy input did not lead to higher ozonation efficiency, since the reaction involving the OH radical was greatly hindered at the low pH produced as a result of ozonation. By maintaining the pH at a value greater than 8.0, the higher kLa in the HJLR reactor contributed to increasing not only the TOC removal of wastewater, but also the ozone consumption efficiency, as expressed by the specific ozone consumption. The specific ozone consumption in the HJLR reactor (7.1 g ozone/ g TOC) was 20% better than that in the bubble column reactor.

Photocatalytical polishing of paper-mill effluents.

Photocatalytic oxidation (PCO) is a promising technology for purification of biological pretreated wastewater or destruction of non-biodegradable compounds. For this reason PCO has been investigated as a last step of purification of biologically pre-treated paper-mill effluents. The influence of the parameters pH, TiO2-modification, TiO2-concentration, catalyst re-use, concentration of substances to be oxidised (wastewater quality) has been determined. The TOC of the biologically pretreated wasterwater was up to 55 mg L(-1). This wastewater was treated with a previously presented aerated cascade photoreactor which was modified for batch experiments. A high specific oxidation rate of up to 0.76 g TOC m(-2) h(-1) as well as a complete TOC mineralization has been achieved after the optimisation of the process parameters. The complete destruction of recalcitrant compounds will offer the opportunity to reuse the wastewater in the production process. The increase of the BOD5/TOC ratio after a short irradiation period indicates the transformation of recalcitrant organic compounds to better biodegradable intermediates. The use of PCO as a pre-treatment step for the enhancement of the biodegradability of wastewater, containing recalcitrant or inhibitory compounds is an alternative to a long and energy-intensive total pollutant mineralization.

Textile wastewater treatment and reuse by solar catalysis: results from a pilot plant in Tunisia.

Based on results from bench-scale flow-film-reactors (FFR) and aerated cascade photoreactors, a solar catalytic pilot plant has been built at the site of a textile factory. This plant has an illuminated surface area of 50 m2 and is designed for the treatment of 1 m3 h(-1) of wastewater. The preliminary results are presented and compared with a bench-scale FFR using textile wastewater and dichloroacetic acid. Equivalent degradation kinetics were obtained and it was demonstrated that the solar catalytic technology is able to remove recalcitrant compounds and color. However, on-site optimization is still necessary for wastewater reuse and for an economic application.

Solar detoxification of wastewater in a novel aerated cascade photoreactor (ACP).

A newly developed aerated cascade photoreactor (ACP), based on a non-concentrating suspension photoreactor, combines the advantages of a cascade with the increased mass-transfer and the use of oxygen from air as an oxidizing agent in a bubble column. Systematic studies of the limiting hydrodynamic conditions in the ACP and the solid/liquid-separation of the photocatalyst from the treated wastewater have shown that the ACP is technically and commercially attractive. The ACP outperforms the thin-film fixed-bed reactor (TFFBR) with respect to a 3-13 times higher degradation efficiency for the model compound dichloroacetic acid (DCA). The treatment of two biologically pretreated real wastewaters, one from a textile factory and one from car-washing, have been successfully carried out under artificial light and sunlight.

Comparison of suspended and fixed photocatalytic reactor systems.

Photocatalysis is a promising technology for the purification of pretreated wastewaters in sun-rich countries if an economically applicable reactor system is available. Within this project the catalyst separation as an essential process step of suspended reactor systems was investigated. For the separation of suspended catalyst a sedimentation basin with and without lamella and a membrane filtration were investigated. The sedimentation was found to be very sensitive to the kind of the ion background of wastewater, the pH, the TiO2 influent concentration as well as the hydrodynamics in the clarifier. Under optimized conditions effluent concentrations of less than 5 mg SS/L and a clear water without turbidity could be reached with a specific flow rate of up to 0.7 m3/m2/h. The best performance for P25 was achieved with a TiO2 influent concentration of 5 g/L. Membrane filtration was the only method to guarantee a complete retention of the TiO2 as well as a rejection of microorganisms and high molecular compounds. With cross-flow velocities of 3 m/s and a transmembrane pressure of 100 kPa flux rates up to 1,200 L/m2/h were achieved. A flow-film-reactor (FFR) was operated with the model compound DCA under identical conditions with fixed and suspended TiO2. Whereas the fixed system has the advantage that no separation step is necessary and a simple construction can be used, suspended systems offer a three times higher reaction velocity for a catalyst concentration of 10 g/L, but are also characterized by higher investment costs.

Photochemical oxidation of iodized X-ray contrast media (XRC) in hospital wastewater.

Iodized X-ray contrast media (XRC) for medical applications are responsible for the high concentration of AOX (halogenated organic compounds adsorbable on activated carbon) in hospital wastewater exceeding the legal German discharge limit. The refractory properties of these substances lead to an accumulation in the natural waterbody. The elimination of contrast media from hospital wastewater by photochemical oxidation with hydrogen peroxide was investigated. The mechanism and the kinetics of the degradation of XRC were examined. These experiments demonstrate that a complete removal of the organically bonded iodine and a partial mineralization is feasible. The degradation in the UV reactor could be enhanced by adding hydrogen peroxide and by using a bubble column to remove the formed elemental iodine from the solution by stripping. Furthermore, the influence of various operating parameters such as gas flowrate, H2O2 input, XRC concentration and kind of XRC were investigated. Experiments showed that a recycling of elemental iodine from the exhaust gas is technically and economically possible.

Separation of titanium dioxide from photocatalytically treated water by cross-flow microfiltration.

This study focuses on the separation of titanium dioxide from water by cross-flow microfiltration (CMF) within wastewater treatment by photocatalysis using slurry reactor systems. The systematic studies have shown that the separation performance of TiO2 particles is strongly affected by cross-flow velocity, transmembrane pressure, feed concentration, pH of the suspension and ionic strength. An extreme sensitivity to pH and electrolyte concentration indicates the importance of interfacial effects in solid-liquid separation of TiO2 particles. Under optimal conditions, permeate fluxes of up to 1250 l m-2 h-1, approaching those of pure water, could be obtained with a polypropylene membrane which is not sensitive to abrasion. The obtained results makes TiO2 separation by cross-flow microfiltration attractive in solar-catalytic detoxification.