Lars-Flemming Pedersen - Academia.edu (original) (raw)

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Papers by Lars-Flemming Pedersen

Research paper thumbnail of Effects of hunger level and nutrient balance on survival and acetylcholinesterase activity of dimethoate exposed wolf spiders

Entomologia Experimentalis Et Applicata, 2002

Research paper thumbnail of Long term/low dose formalin exposure to small-scale recirculation aquaculture systems

Aquacultural Engineering, 2010

Research paper thumbnail of Degradation and effect of hydrogen peroxide in small-scale recirculation aquaculture system biofilters

Aquaculture Research, 2009

From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared wi... more From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared with other disinfectants in terms of its ready degradation and neutral by-products. The rapid degradation of HP can, however, cause difficulties with regard to safe and efficient water treatment when applied in different systems. In this study, we investigated the degradation kinetics of HP in biofilters from water recirculating aquaculture systems (RAS). The potential effect of HP on the nitrification process in the biofilters was also examined. Biofilter elements from two different pilot-scale RAS were exposed to various HP treatments in batch experiments, and the HP concentration was found to follow an exponential decay. The biofilter ammonia and nitrite oxidation processes showed quick recuperation after exposure to a single dose of HP up to 30 mg L−1. An average HP concentration of 10–13 mg L−1 maintained over 3 h had a moderate inhibitory effect on the biofilter elements from one of the RAS with relatively high organic loading, while the nitrification was severely inhibited in the pilot-scale biofilters from the other RAS with a relatively low organic loading. A pilot-scale RAS, equipped with two biofilter units, both a moving-bed (Biomedia) and a fixed-bed (BIO-BLOK®) biofilter, was subjected to an average HP concentration of ∼12 mg L−1 for 3 h. The ammonium- and nitrite-degrading efficiencies of both the Biomedia and the BIO-BLOK® filters were drastically reduced. The filters had not reverted to pre-HP exposure efficiency after 24 h, suggesting a possible long-term impact on the biofilters.

Research paper thumbnail of Dose-dependent decomposition rate constants of hydrogen peroxide in small-scale bio filters

Aquacultural Engineering, 2006

Research paper thumbnail of Temperature-dependent and surface specific formaldehyde degradation in submerged biofilters

Aquacultural Engineering, 2007

Research paper thumbnail of Low-Dose Hydrogen Peroxide Application in Closed Recirculating Aquaculture Systems

North American Journal of Aquaculture, 2012

The aim of the present work was to simulate water treatment practices with hydrogen peroxide (HP)... more The aim of the present work was to simulate water treatment practices with hydrogen peroxide (HP) in recirculating aquaculture systems (RAS). Six identical 1,700-L pilot-scale RAS were divided into two experimental groups based on daily feed allocation and operated under constant conditions for a period of 3 months. The organic and nitrogenous loadings of the systems differed fourfold between the two groups and were achieved by predefined constant daily feed loads and constant additions of water. The fixed cumulative feed burden was 1.6 × 103 mg feed/L in the low-intensity RAS and 6.3 × 103 mg/L in the high-intensity RAS. The decay of HP in rearing tanks and disconnected biofilter units was investigated by means of HP spiking experiments. The decay in high-intensity RAS rearing units and biofilters was orders of magnitude faster than that in low-intensity units. The application of HP impaired biofilter nitrite oxidation in low-intensity RAS but not in high-intensity RAS. The impact of HP exposure time on biofilter nitrification capacity was then assessed in biofilter bench-scale experiments with nitrite spiking. Exposure time was found to significantly affect nitrite oxidation. Compared with unexposed biofilter elements, nitrite oxidation was reduced more than 90% following 3 h of exposure to 15 mg HP/L, whereas 30 min of exposure had only minor negative effects on nitrite oxidation. The findings of this study demonstrate the potential for developing HP water treatment practices for RAS and contradict prevailing notions that HP cannot be used safely in RAS that employ biofiltration. The development of effective new HP treatment protocols for recirculating aquaculture could reduce the current dependence on formalin to improve water quality and control parasitic loads.Received January 12, 2011; accepted June 22, 2011

Research paper thumbnail of Peracetic acid degradation and effects on nitrification in recirculating aquaculture systems

Research paper thumbnail of Temperature-Dependent Formaldehyde Degradation in Trickling Filters

North American Journal of Aquaculture, 2006

We investigated formaldehyde (HCHO) degradation in a trickling filter at three different temperat... more We investigated formaldehyde (HCHO) degradation in a trickling filter at three different temperatures. Formalin, equivalent to an initial concentration of 40 mg of formaldehyde per liter of water, was applied to a closed experimental setup that included an active trickling filter. Water samples were taken regularly over a 96-h period and analyzed for formaldehyde. Decomposition of HCHO was significantly related to water temperature; estimated half-lives were 5.0, 9.5, and 16.5 h at 14.5, 10.0, and 5.5°C, respectively. Evidence of microbial decomposition indicated that formaldehyde reduction was correlated to the available trickling-filter surface area at a removal rate of 8.3–21.3 mg formaldehyde·m−2·h−1. These findings permit the calculation of formaldehyde decomposition rates during treatments in recirculating systems and make it possible to design trickling filters with a specific decomposition capacity.

Research paper thumbnail of Effects of hunger level and nutrient balance on survival and acetylcholinesterase activity of dimethoate exposed wolf spiders

Entomologia Experimentalis Et Applicata, 2002

Research paper thumbnail of Long term/low dose formalin exposure to small-scale recirculation aquaculture systems

Aquacultural Engineering, 2010

Research paper thumbnail of Degradation and effect of hydrogen peroxide in small-scale recirculation aquaculture system biofilters

Aquaculture Research, 2009

From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared wi... more From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared with other disinfectants in terms of its ready degradation and neutral by-products. The rapid degradation of HP can, however, cause difficulties with regard to safe and efficient water treatment when applied in different systems. In this study, we investigated the degradation kinetics of HP in biofilters from water recirculating aquaculture systems (RAS). The potential effect of HP on the nitrification process in the biofilters was also examined. Biofilter elements from two different pilot-scale RAS were exposed to various HP treatments in batch experiments, and the HP concentration was found to follow an exponential decay. The biofilter ammonia and nitrite oxidation processes showed quick recuperation after exposure to a single dose of HP up to 30 mg L−1. An average HP concentration of 10–13 mg L−1 maintained over 3 h had a moderate inhibitory effect on the biofilter elements from one of the RAS with relatively high organic loading, while the nitrification was severely inhibited in the pilot-scale biofilters from the other RAS with a relatively low organic loading. A pilot-scale RAS, equipped with two biofilter units, both a moving-bed (Biomedia) and a fixed-bed (BIO-BLOK®) biofilter, was subjected to an average HP concentration of ∼12 mg L−1 for 3 h. The ammonium- and nitrite-degrading efficiencies of both the Biomedia and the BIO-BLOK® filters were drastically reduced. The filters had not reverted to pre-HP exposure efficiency after 24 h, suggesting a possible long-term impact on the biofilters.

Research paper thumbnail of Dose-dependent decomposition rate constants of hydrogen peroxide in small-scale bio filters

Aquacultural Engineering, 2006

Research paper thumbnail of Temperature-dependent and surface specific formaldehyde degradation in submerged biofilters

Aquacultural Engineering, 2007

Research paper thumbnail of Low-Dose Hydrogen Peroxide Application in Closed Recirculating Aquaculture Systems

North American Journal of Aquaculture, 2012

The aim of the present work was to simulate water treatment practices with hydrogen peroxide (HP)... more The aim of the present work was to simulate water treatment practices with hydrogen peroxide (HP) in recirculating aquaculture systems (RAS). Six identical 1,700-L pilot-scale RAS were divided into two experimental groups based on daily feed allocation and operated under constant conditions for a period of 3 months. The organic and nitrogenous loadings of the systems differed fourfold between the two groups and were achieved by predefined constant daily feed loads and constant additions of water. The fixed cumulative feed burden was 1.6 × 103 mg feed/L in the low-intensity RAS and 6.3 × 103 mg/L in the high-intensity RAS. The decay of HP in rearing tanks and disconnected biofilter units was investigated by means of HP spiking experiments. The decay in high-intensity RAS rearing units and biofilters was orders of magnitude faster than that in low-intensity units. The application of HP impaired biofilter nitrite oxidation in low-intensity RAS but not in high-intensity RAS. The impact of HP exposure time on biofilter nitrification capacity was then assessed in biofilter bench-scale experiments with nitrite spiking. Exposure time was found to significantly affect nitrite oxidation. Compared with unexposed biofilter elements, nitrite oxidation was reduced more than 90% following 3 h of exposure to 15 mg HP/L, whereas 30 min of exposure had only minor negative effects on nitrite oxidation. The findings of this study demonstrate the potential for developing HP water treatment practices for RAS and contradict prevailing notions that HP cannot be used safely in RAS that employ biofiltration. The development of effective new HP treatment protocols for recirculating aquaculture could reduce the current dependence on formalin to improve water quality and control parasitic loads.Received January 12, 2011; accepted June 22, 2011

Research paper thumbnail of Peracetic acid degradation and effects on nitrification in recirculating aquaculture systems

Research paper thumbnail of Temperature-Dependent Formaldehyde Degradation in Trickling Filters

North American Journal of Aquaculture, 2006

We investigated formaldehyde (HCHO) degradation in a trickling filter at three different temperat... more We investigated formaldehyde (HCHO) degradation in a trickling filter at three different temperatures. Formalin, equivalent to an initial concentration of 40 mg of formaldehyde per liter of water, was applied to a closed experimental setup that included an active trickling filter. Water samples were taken regularly over a 96-h period and analyzed for formaldehyde. Decomposition of HCHO was significantly related to water temperature; estimated half-lives were 5.0, 9.5, and 16.5 h at 14.5, 10.0, and 5.5°C, respectively. Evidence of microbial decomposition indicated that formaldehyde reduction was correlated to the available trickling-filter surface area at a removal rate of 8.3–21.3 mg formaldehyde·m−2·h−1. These findings permit the calculation of formaldehyde decomposition rates during treatments in recirculating systems and make it possible to design trickling filters with a specific decomposition capacity.