Martin Jekel

Kinetic and thermodynamic aspects of adsorption of arsenic onto granular ferric hydroxide (GFH)

Relatively limited information is available regarding the impacts of temperature on the adsorption kinetics and equilibrium capacities of granular ferric hydroxide (GFH) for arsenic (V) and arsenic (III) in an aqueous solution. In general, very little information is available on the kinetics and thermodynamic aspects of adsorption of arsenic compounds onto other iron oxide-based adsorbents as well. In order to gain an understanding of the adsorption process kinetics, a detailed study was conducted in a controlled batch system. The effects of temperature and pH on the adsorption rates of arsenic (V) and arsenic (III) were investigated. Reaction rate constants were calculated at pH levels of 6.5 and 7.5. Rate data are best described by a pseudo first-order kinetic model at each temperature and pH condition studied. At lower pH values, arsenic (V) exhibits greater removal rates than arsenic (III). An increase in temperature increases the overall adsorption reaction rate constant values for both arsenic (V) and arsenic (III). An examination of thermodynamic parameters shows that the adsorption of arsenic (V) as well as arsenic (III) by GFH is an endothermic process and is spontaneous at the specific temperatures investigated.

Identification and quantification of major organic foulants in treated domestic wastewater affecting filterability in dead-end ultrafiltration

Ultrafiltration (UF) membranes can be used after conventional wastewater treatment to produce particle free and hygienically safe water for reuse. However, membrane fouling affects the performance of UF to a large extent. Stirred cell tests with UF membrane show high flux decline filtering treated domestic wastewater. Investigation on the impact of size fractioned substances indicates that dissolved substances are major foulants affecting water filterability. Dissolved organic substances in feed and permeate samples of the stirred cell tests are analyzed by liquid chromatography with online organic carbon detection (LC-OCD). The resulting chromatograms displayed a significant difference of feed and permeate samples in the range of large molecules identified as biopolymer peak. The substances detected in this peak (mostly macro polysaccharide-like and protein-like molecules) are almost completely retained by UF membranes. Quantified investigation shows that biopolymer concentration influences filterability of corresponding water sample proportionally. The apparent magnitude of delivered biopolymer to membrane has a striking correlation with fouling resistance. The relationship was verified to be reproducible using different water samples. Mechanism analysis demonstrates that based on the delivered biopolymer load to membrane pore blocking or cake/gel fouling is the main fouling mechanism in the present experiment conditions.

Complexity of ultrafiltration membrane fouling caused by macromolecular dissolved organic compounds in secondary effluents

Recent investigations indicate the relevance of extracellular polymeric substances (EPS) in terms of fouling of low-pressure membranes in advanced wastewater treatment. In this study, the high impact of the macromolecular fraction of effluent organic matter on fouling was confirmed in cross-flow ultrafiltration experiments using secondary effluent with and without autochthonous biopolymers. A method for the extraction of a natural mixture of EPS derived from the bacterium Sinorhizobium sp. is presented. Ultrafiltration of solutions of this bacterial EPS extract revealed a correlation between the concentration of EPS and the loss of permeate flux. However, in ultrafiltration tests using extracted bacterial EPS in a model solution as well as in secondary effluent without autochthonous biopolymers, the extent of membrane fouling was not identical with the fouling provoked by secondary effluent organic matter, although the biopolymer concentrations were comparable. The differences in the fouling behaviour of the extracted bacterial EPS and effluent organic matter are considered to be due to different compositions of the biopolymer fraction in terms of proteins, polysaccharides, and other organic colloids, indicating a particular impact of proteins on ultrafiltration membrane fouling.

Predicting anion breakthrough in granular ferric hydroxide (GFH) adsorption filters

Adsorption of arsenate, phosphate, salicylic acid, and groundwater DOC onto granular ferric hydroxide (GFH) was studied in batch and column experiments. Breakthrough curves were experimentally determined and modelled using the homogeneous surface diffusion model (HSDM) and two of its derivatives, the constant pattern homogeneous surface diffusion model (CPHSDM) and the linear driving force model (LDF). Input parameters, the Freundlich isotherm constants, and mass transfer coefficients for liquid- and solid-phase diffusion were determined and analysed for their influence on the shape of the breakthrough curve. HSDM simulation results predict the breakthrough of all investigated substances satisfactorily, but LDF and CPHSDM could not describe arsenate breakthrough correctly. This is due to a very slow intraparticle diffusion and hence higher Biot numbers. Based on this observation, limits of applicability were defined for LDF and CPHSDM. When designing fixed-bed adsorbers, model selection based on known or estimated Biot and Stanton numbers is possible.

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.

Protein fouling of ultrafiltration membranes — investigation of several factors relevant for tertiary wastewater treatment

The fouling of two different ultrafiltration membranes by solutions of three globular proteins with different molecular weights and isoelectric points was investigated at low concentrations relevan...

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.

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.