Viktor Schmalz

Electrochemical disinfection of biologically treated wastewater from small treatment systems by using boron-doped diamond (BDD) electrodes - contribution for direct reuse of domestic wastewater.

The aim of the study was to demonstrate the application potential of boron-doped diamond electrodes (BDD) in electrochemical disinfection of biologically treated sewage for direct recycling of domestic wastewater. Discontinuous bulk disinfection experiments with secondary effluents and model solutions were performed to investigate the influence of operating conditions and wastewater parameters on disinfection efficiency and formation of disinfection by-products (adsorbable organically bound halogens, AOX). The inactivation rate accelerates with increasing current density caused by a faster generation of electrochemical oxidants (ECO). It could be shown that the effect of OH radicals in case of the direct electrochemical disinfection of chloride-containing secondary effluents with BDD is negligible because of their fast reaction with typical radical scavengers. The dominating role of electrochemically generated free chlorine in the disinfection process could be explicitly verified. It could be also shown that the disinfection efficiency is strongly affected by the specific wastewater parameters temperature and pH. These effects can be explained by the behaviour of the reactive species. The migration-controlled generation of ECO can be accelerated under turbulent hydrodynamic conditions. The formation of disinfection by-products (AOX) correlates with the introduced electric charge Q applied per volume and is independent of the applied current density.

Influence of operating conditions and wastewater-specific parameters on the electrochemical bulk disinfection of biologically treated sewage at boron-doped diamond (BDD) electrodes

Abstract The aim of this study was to investigate an electrochemical process for bulk disinfection of biologically treated sewage. The influence of operating conditions (current density and flow rate) on the electrochemical formation of free chlorine in the sewage was determined. Furthermore, the effect of wastewater-specific parameters on the inactivation of Escherichia coli was studied. The disinfection capacity is primarily influenced by the concentration of electrochemically produced free chlorine. The production rate of free chlorine is independent of the flow rate within the range of 25–125 L h−1. The investigations have also shown that the electrochemical disinfection of E. coli in secondary effluents with BDD electrodes proceeds effectively at an electric charge input of 0.1–0.15 Ah L−1 corresponding to an energy expenditure of 2.0–2.6 kWh m−3. The electrochemically generated concentration of free chlorine (c = 0.4–0.6 mg L−1) is sufficient for an E. coli reduction of four log levels under the fol...

Comparison of different extractants for the determination of inorganic sulphate in gypsum-free agricultural soils

Four frequently used extractants (H2O, 0.1 M NaCl, 0.016 M KH2PO4, and 0.5 M NaHCO3) as well as different extraction conditions have been tested for sulphate extraction from gypsum-free agricultural soils. Water is the preferable extractant for soils with pH > 6. Two extraction steps have to be carried out for complete extraction (> 95%). A 0.016 M KH2PO4 solution was found to be the most efficient extractant for soils with a pH < 6 within a single extraction step. A shaking frequency of 170 min-1 and a duration of extraction of 4 hours are the optimized conditions for the sulphate extraction with H2O and KH2PO4 solution. Vergleich von verschiedenen Extraktionsmitteln zur Bestimmung von anorganischem Sulfat in gipsfreien landwirtschaftlich genutzten Boden Fur die Bestimmung von Sulfat in gipsfreien landwirtschaftlich genutzten Boden mit unterschiedlichen pH-Werten wurden vier haufig eingesetzte Extraktionslosungen (H2O, 0,1 M NaCl, 0,016 M KH2PO4 und 0,5 M NaHCO3) sowie unterschiedliche Extraktionsbedingungen getestet. In Boden mit pH > 6 wird Wasser als zu bevorzugendes Extraktionsmittel angesehen. Zwei Extraktionsschritte reichen fur eine vollstandige Extraktion (> 95%) aus. Eine 0,016 M KH2PO4-Losung stellt das gunstigste Extraktionsmittel bei einem einzigen Extraktionsschritt fur anorganisches Sulfat aus Boden mit pH < 6 dar. Eine Schuttelgeschwindigkeit von 170 min-1 und eine Extraktionsdauer von 4 Stunden sind die optimalen Bedingungen fur die Bestimmung von anorganischem Sulfat mit H2O und KH2PO4-Extraktionslosung.

Portable Analyzer for On-Site Determination of Dissolved Organic Carbon—Development and Field Testing

Dissolved organic carbon (DOC) is a sum parameter that is frequently used in water analytics. Highly resolved and accurate DOC data are necessary, for instance, for water quality monitoring and for the evaluation of the efficiency of treatment processes. The conventional DOC determination methods consist of on-site sampling and subsequent analysis in a stationary device in a laboratory. However, especially in regions where no or only poorly equipped laboratories are available, this method bears the risk of getting erroneous results. For this reason, the objective of the present study was to set up a reliable and portable DOC analyzer for on-site analysis. The presented DOC system is equipped with an electrolysis-based decomposition cell with boron-doped diamond electrodes (BDD) that oxidizes the organic compounds to carbon dioxide. Within this study, the influence of different electrode materials and the composition of the applied electrolytes on the DOC decomposition in an undivided electrolytic cell were systematically investigated. Furthermore, some technical aspects of the portable prototype are discussed. After a detailed validation, the prototype was used in an ongoing monitoring program in Northern India. The limit of detection is 0.1 mg L−1 C with a relative standard deviation of 2.3% in a linear range up to 1000 mg L C−1. The key features of the portable DOC analyzer are: No need for ultra-pure gases, catalysts or burning technology, an analyzing time per sample below 5 min, and a reliable on-site DOC determination.

REMOVAL OF DISSOLVED ORGANIC COMPOUNDS BY GRANULAR ACTIVATED CARBON

Granular activated carbon (GAC) adsorption is a widespread water treatment technology especially applied in waterworks for removing dissolved organic compounds (natural organic matter, micropollutants). Adsorption of organic compounds by GAC filters is influenced by a number of water characteristics as e.g. ionic strength, pH, water temperature and the initial concentration of organic compounds. The objective of our investigations is to find out if water temperature has to be considered for applying water purification technologies under various climatic conditions.