Papers by Peter Janknecht
Reviews in Environmental Science and Bio/Technology, 2000
A review of online biofilm monitoring techniques is presented focusing on methods based on differ... more A review of online biofilm monitoring techniques is presented focusing on methods based on differential turbidimetry, light scattering, heat transfer, pressure drop, real-time measurement of metabolic products, image analysis, radiation signals (spectroscopy, fluorometry, photoacoustic spectroscopy, etc.), electric and mechanical (vibration) signals. The different methods are compared in terms of their applicability to practical situations and the know detection limits are reported.
Bioresource Technology, Apr 1, 2010
Stream biofilms are exposed to dynamic conditions of flow velocity and organic carbon availabilit... more Stream biofilms are exposed to dynamic conditions of flow velocity and organic carbon availability. Thus, the aim of this study was to investigate the response of biofilms formed with and without humic substances (HSs) to an increase in flow velocity (0.04-0.10 m s À1 ) and HSs concentration (9.7 ± 1.0 to 19.8 ± 0.4 mg L À1 C). The highest amount of biofilm, measured as volatile suspended solids and total countable cells, was observed at 0.10 m s À1 without HSs. The bacterial community composition of the biofilm with HSs was characterized by sequences with high similarities (P97%) to the genus Dokdonella and to the genera Comamonas, Cupriavidus and, Ralstonia. Sequences retrieved from the biofilm without HSs presented high similarities (P97%) to the genus Sphingomonas and the genus Nitrosospira. Experimental results suggested that the presence of HSs under different concentrations and flow velocities did not significantly enhance the cell density of biofilms but influenced its microbial composition.
Acta hydrochimica et hydrobiologica, 2004
ABSTRACT
Separation and Purification Technology, 2001
A common process in water treatment is the wet oxidation for the removal of certain organic and i... more A common process in water treatment is the wet oxidation for the removal of certain organic and inorganic pollutants. The strongest oxidant technically applied in this process is ozone, which is an unstable gas under normal conditions, and therefore is produced from oxygen on site, usually by electrical discharge. After that the ozone has to be transferred from that gas into the water to be treated. Conventionally ozone transfer is achieved by bringing the gas and water in direct contact by means of bubble columns, injectors or other similar devices. Under unfavorable conditions, however, these methods suffer from excessive formation of foam requiring an extra treatment and a high-energy demand for pumping gas or water. This project's approach was to improve the transfer by better control of gaseous and aqueous phase's conditions at the contact surface. This was achieved by means of a membrane both separating the two phases and allowing for an ozone transfer between them. Due to ozone's high oxidation potential, chemically inert ceramic membranes were chosen for that purpose. In experiments, it was found that the transfer of the unstable ozone molecules is not obstructed by ceramic membrane material. Transfer rates between gaseous ozone and model water were measured for conventional ceramic membranes, as well as specially designed ones. They are comparable to conventional methods or better on the base of mass transfer per reactor volume. In conventional oxide membranes, water enters the pores because of capillary effects in the hydrophilic material [Burggraaf, A.J. and Cot, L., 1996, Fundamentals of inorganic Membrane Science and Technology Elsevier Science, The Netherlands]. The water in the pores raises the diffusion resistance for the ozone thus decreasing the transfer itself. Consequently, the modification of the hydrophilic material features into a hydrophobic behavior was one promising approach for the optimization of the process. It was achieved through the application of a hydrophobic coating to the membrane surface, which greatly improved the transfer efficiency.
Ozone: Science & Engineering, 2000
Ozone transfer was investigated using various oxide ceramic membranes and different process param... more Ozone transfer was investigated using various oxide ceramic membranes and different process parameters. The ozone mass transfer per contactor volume through hydrophilic membranes was in the same order of magnitude as conventional bubble contacting. The pressure differential between the gaseous and aqueous phase as well as the membrane material's microstructure was found to widely determine the transfer rate. A hydrophobic
Journal of Industrial Microbiology & Biotechnology, 2008
BioWlms are major sites of carbon cycling in streams. Therefore, it is crucial to improve knowled... more BioWlms are major sites of carbon cycling in streams. Therefore, it is crucial to improve knowledge about bioWlms' structure and microbial composition to understand their contribution in the self-puriWcation of surface water. The present work intends to study bioWlm formation in the presence of humic substances (HSs) as a carbon source. Two bioWlm Xowcells were operated in parallel; one with synthetic stream water, displaying a background carbon concentration of 1.26 § 0.84 mg L ¡1 , the other with added HSs and an overall carbon concentration of 9.68 § 1.00 mg L ¡1 . From the bioWlms' results of culturable and total countable cells, it can be concluded that the presence of HSs did not signiWcantly enhance the bio-Wlm cell density. However, the bioWlm formed in the presence of HSs presented slightly higher values of volatile suspended solids (VSS) and protein. One possible explanation for this result is that HSs adsorbed to the polymeric matrix of the bioWlm and were included in the quantiWcation of VSS and protein. The microbial composition of the bioWlm with addition of HSs was characterized by the presence of bacteria belonging to beta-Proteobacteria, Cupriavidus metallidurans and several species of the genus Ralstonia were identiWed, and gamma-Proteobacteria, represented by Escherichia coli. In the bioWlm formed without HSs addition beta-Proteobacteria, represented by the species Variovorax paradoxus, and bacteria belonging to the group Bacteroidetes were detected. In conclusion, the presence of HSs did not signiWcantly enhance bioWlm cell density but inXuenced the bacterial diversity in the bioWlm.
Journal of Environmental Monitoring, 2009
Humic acids (HAs) content of raw water is an important analytical parameter in water treatment fa... more Humic acids (HAs) content of raw water is an important analytical parameter in water treatment facilities because HAs in the presence of chlorine may lead to the formation of dangerous by-products (e.g., trihalomethanes). The concentration of HAs in water is not directly accessible by common analytical methods due to their heterogeneous chemical structure. The aim of this study was to compare two methods to assess humic acids (HAs) in surface water namely absorbance of ultraviolet light at 254 nm (UV(254)) and total organic carbon (TOC), as well as to evaluate the effects of calcium and magnesium concentrations, pH and sample filtration on the methods' results. An aqueous solution of a commercial HA with 10 mg L(-1) was used in the present work. Quantification of the HA was carried out by both UV(254) and TOC (combustion-infrared method) measurements. UV(254) results were converted to TOC using a calibration curve. The effects of calcium (0-136.3 mg L(-1)) and magnesium (0-34.5 mg L(-1)) concentrations, pH (4.0, 7.0 and 9.0) and sample filtration on UV(254) and TOC measurements of the HA suspension were evaluated. More accurate TOC values of HA suspensions were obtained by the combustion-infrared method than by the UV(254) absorbance method. The higher differences of TOC values between unfiltered and filtered samples were detected in the presence of calcium at pH 9.0 using the spectrophotometric method.
Environmental Science & Technology, 2004
The utilization of micro- and ultrafiltration with polymeric membranes for treatment of industria... more The utilization of micro- and ultrafiltration with polymeric membranes for treatment of industrial cutting oil emulsion was investigated. The performance of 14 different membranes with pore sizes in the range of 1-800 nm, representing 8 different materials and varying hydrophobicity, was determined experimentally. Membrane permeances between 1.6 and 939 L m 2 h(-1) bar(-1) have been observed for the different samples as well as oil rejections between 3.42% and 99.99%. Membrane pore size and contact angle showed little influence on both values, while an interesting correlation is displayed to the individual membranes' capillary pressures. A possible explanation for this phenomenon is suggested based on the formation of oil films on the membrane surface. From the investigated membranes, the best-suited one for cutting oil treatment was selected and subjected to further experiments. The effect of process temperatures between 22 and 43 degrees C and of feed oil concentrations between 0 and 20 vol % on the removal performance was determined. The results correspond to the explanation suggested previously.
Environmental Management, 2010
Page 1. Life Cycle Assessment of a Wastewater Treatment Plant Focused on Material and Energy Flow... more Page 1. Life Cycle Assessment of a Wastewater Treatment Plant Focused on Material and Energy Flows Jian-Guang Wu Xiang-Yu Meng Xiao-Meng Liu Xian-Wei Liu Zhi-Xia Zheng De-Qian Xu Guo-Ping Sheng Han-Qing Yu ...
Annales de Chimie Science des Matériaux, 2001
Ozone, due to its high oxidative capacity, is often used in water treatment for the degradation o... more Ozone, due to its high oxidative capacity, is often used in water treatment for the degradation of organic pollutants. Unfortunately, the application of ozone in the form of gas bubbles causes foam problems. To avoid the development and accumulation of foam, the transfer of ozone into the water through gas permeable membranes was investigated. Ceramic membranes were used because of the chemical inertness of the material. The hydrophilic behaviour of ceramic membranes made of metal oxides causes the water to penetrate into the pores. This creates a diffusion resistance for the ozone which decreases the transfer rates. To keep the water out of the porous structure and maintain the gas/water interface at the membrane surface, the surface properties of the membrane were changed. The membrane was soaked in a solution of a fluorinated compound. Water drop measurements and transfer rates were investigated and confirmed the stability of the hydrophobic nature of the membrane surface. The ozone transfer rates thus achieved were in the range of 12 grams of ozone per square meter per hour.
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Papers by Peter Janknecht