Order Removal Rate Research Articles

Effects of pollutant speciation in treatment wetlands design

This paper reports on observed and potential effects of distributions of detention times and first order removal rate constants. Rate constants are distributed across the species that make up a grouped class of contaminants, such as total suspended solids (TSS) and biochemical oxygen demand (BOD). The existence of these distributions is shown to invalidate the plug flow (PF) model assumption in almost all cases. The tanks-in-series (TIS) model is shown to offer a better platform to accommodate distributed parameters. Detention time distributions (DTDs) and k-value distributions (kVDs) are shown to both lead to TIS models. Discrete, uniform and gamma distributions for detention and k-values are explored. The greater the variance, the more important the impacts on performance modeling. Data for the reduction of TSS are analyzed from the perspective of particle size distributions, and shown to result in the appearance of TIS behavior for the lumped TSS measure. The retarded rate constant concept is shown to be subsumed by the idea of a weathering mixture with a distribution of rate constants.

Stability of a lab-scale biofilm for simultaneous removal of phosphorus and nitrate

A lab-scale biofilm reactor for simultaneous removal of phosphorus and nitrate was operated for one and a half years. Despite using only well defined synthetic wastewater and well defined operation, the activity varied significantly over the months. It was speculated that microbial population shifts were causing this phenomenon. This could also explain a sudden break down of the process following a slight change in the operation. Over shorter periods of time (time-scale: days), the biofilm could be considered stable enough to perform series of comparable batch experiments. Batch experiments with different start concentrations of acetate, nitrate or phosphate were conducted. These verified 0.5 and 0 order removal rates in the bulk water depending on the concentration. This was taken as an indication of a zonation of the biofilm. Due to the measured variability in the activity and due to the importance of the history of the bacteria when considering biological P removal, on-line measurements are strongly recommended for research on this subject. Microbial characterisation methods are recommended as an assisting tool in further research.

Evaluation of trickle-bed air biofilter performance for styrene removal

A pilot-scale trickle-bed air biofilter (TBAB) was evaluated for the removal of styrene from a waste gas stream. Six-millimeter (6-mm) Celite pellets (R-635) were used as the biological attachment medium. The operating parameters considered in the study included the styrene volumetric loading, the empty-bed residence time (EBRT), the frequency and duration of backwashing, and nutrient–phosphorous (nutrient–P) management as a biomass control strategy. The aim of the study was to demonstrate that high removal efficiencies could be sustained over a long period. Periodic backwashing of the biofilter with full-medium fluidization was necessary for removing excess biomass and attaining stable, long-term high removal efficiencies. Styrene removal efficiencies in the 99%+ level were achieved for volumetric loading rates up to 2.93 kg COD/m 3·day and a 1-min EBRT. With a COD volumetric loading rate of 4.26 kg COD/m 3·day and a 0.67-min EBRT, removal efficiencies in the 97–99% level were achieved. Evaluations of pseudo steady-state performance data, 1 day following backwashing, yielded first order removal rate constants that were dependent on EBRT. Nutrient–phosphorus (nutrient–P) limitations failed to provide a strategy for biomass control while at the same time maintaining acceptable performance.

An autobiotic wetland phosphorus model

Constructed and natural wetlands are capable of absorbing new phosphorus loadings, and in appropriate circumstances can provide a low cost alternative to chemical and biological treatment. Phosphorus (P) interacts strongly with wetland soils and biota, which provide both short term and sustainable long term storage of this nutrient. Soil sorption may provide initial removal, but this partly reversible storage eventually becomes saturated. Uptake by biota, including bacteria, algae, and duckweed, as well as macrophytes, forms an initial removal mechanism. Cycling through growth, death and decomposition returns most of the biotic uptake, but an important residual contributes to long term accretion in newly formed sediments and soils. Despite the apparent complexity of these several removal mechanisms, data analysis shows that relatively simple equations can describe the sustainable processes. Previous global first order removal rates characterize the sustainable removal, but do not incorporate any biotic features. This paper presents an autobiotic model, based upon cycling through the biomass compartments, and calibrates it to data from 17 years of operation of the Houghton Lake, MI treatment wetland. This model replaces a first order concentration-based rate with a first order biomass-based rate. When coupled with mass balances, it describes the spatial distribution of both biomass and P concentrations, as well as the evolution of the new standing crop.

Supply rates of natural U‐Th series radionuclides from aquifer solids into groundwater

Supply rates of 224Ra and 212Pb from zircon and monazite grains to the aqueous phase are experimentally determined by dispersing these minerals in 1N nitric acid and PRL (Physical Research Laboratory) groundwater. In nitric acid medium, recoiled 224Ra and 212Pb behave conservatively and are not removed by solid surfaces. However, in groundwater, 212Pb is removed from the aqueous phase. A model relating the actual supply ratio of 212Pb/224Ra, the measured activities of 224Ra and 212Pb in the leachates at different times of contact and the first order removal rate constant of 212Pb is developed. At steady state, the supply ratio of 212Pb/224Ra in nitric acid from zircon and in groundwater from monazite is evaluated to be a unique value 2.3±0.3 which agrees with the model predicted value of 2.67 based on alpha recoil supply of the nuclides and their precursors. The residence time of 212Pb in groundwater, with respect to its first order removal, is estimated to be of the order of 39 minutes.

Removal of toluene in waste gases using a biological trickling filter

The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h−1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m−3 h−1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m−3 h−1, corresponding to a zero order removal rate of 0.11±0.03 g m−2 h−1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m−3, corresponding to inlet gas concentrations above 0.7–0.8 g m−3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k1A , was estimated to be 0.08–0.27 m h−1 (k1A a=24–86 h−1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, KLa, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface.

Biodegradation of Pentachlorophenol in Soil Amended with the White Rot FungusPhanerochaete chrysosporium

The effects of bioaugmentation of pentachlorophenol (PCP)-contaminated soil with the fungus Phanerochaete chrysosporium was evaluated using a chemical mass balance approach. While there was no observed PCP removal for the unamended soil, 93% of the initial mass of PCP was removed within 56 days in soil amended with P. chrysosporium-inoculated corncobs. Within the same incubation period, approximately 58% of the initial mass of PCP was removed from soil amended with uninoculated corncobs. PCP removal followed first order kinetics with rate constants of 0.04 ± 0.017 day−1, 0.06 ± 0.015 day−1, and 0.018 ± 0.006 day−1 for PCP contaminated soils amended with fungus-inoculated sterile corncobs, fungus-inoculated nonsterile corncobs, and uninoculated nonsterile corncobs, respectively. Comparison of the nonsterile systems indicated that the presence of the fungus increased the first order removal rate constant by more than 200% compared to the uninoculated system. The extent of PCP mineralization after 56 days of incubation was 7%, 17%, and 8% for PCP contaminated soil amended with fungus-inoculated sterile corncobs, fungus-inoculated nonsterile corncobs, and uninoculated nonsterile corncobs, respectively. The extent of bound residue formation was 13%, 19%, and 27% for PCP contaminated soil amended with fungus-inoculated sterile corncobs, fungus-inoculated nonsterile corncobs, and uninoculated nonsterile corncobs, respectively. Mass balance analyses indicated that soil aeration may enhance removal of PCP and/or its chemical intermediates through a process of facilitated transport and/or volatilization.

Efficiency of Faecal Bacterial Removal in Waste Stabilisation Ponds in Kenya

Results for faecal coliform die-off rates are presented for seven different waste stabilisation pond systems in Kenya, which were sampled as part of a national pond monitoring and evaluation study carried out during 1988-1989. The results showed that average die-off rates through each pond series were considerably lower than those predicted from traditional design equations which are based on temperature (Marais 1974). Die-off rates were surprisingly higher in the primary ponds, which are designed for BOD removal, than in the maturation ponds which are designed for pathogen removal. Good correlations were found between faecal coliform first order removal rate constants and (a) temperature for the pond series as a whole, and (b) influent faecal coliform concentration for individual ponds.

The importance of a benthic ecosystem to the removal of radioactive trace elements from coastal waters

Abstract From radiotracer experiments in model ecosystems (MERL tanks), it was established that the first order removal rate constants (λw’s) of various radiotracers in shallow coastal water columns are closely related to their distribution ratios between suspended particles and seawater (Kd), the particle flux through the system and to season. The seasonal change in the removal rate constants for the different radionuclides was mainly controlled by the benthic faunal activities, which was responsible for extent and changes of bioturbation and resuspension rates of bottom sediments.

Rate of elimination of the intralipid fat emulsion from the circulation in ICU patients.

The rate of removal of Intralipid was studied in 2 groups of intensive care patients by analysis of the fractional removal rate after a single iv dose and by analysis of the removal rate during a constant infusion of Intralipid which immediately followed. The patients in group I were moderately ill after uncomplicated surgery whereas group 2 patients were critically ill and had a mortality of 44%. The fractional removal rate was 2-fold greater in group 1 than group 2 and controls; the 2 latter groups had similar rates of removal. During the constant infusion of Intralipid, 0.42 g/min for 3 h, group 1 patients were found to have a first order removal rate with a constant plasma concentration of Intralipid. The rate constants were not different during the entire infusion from those obtained by the single injection. In all of the group 2 patients, a zero order removal rate was present as the concentration of Intralipid particles increased linearly with time. Group 2 patients had cleared all Intralipid within 6 h after the end of the infusion. Some patients were treated with heparin and/or insulin for clinical reasons. The removal rates were not influenced in either group by these drugs. Thus, moderately traumatized patients were found to clear plasma from Intralipid at recommended infusion rates. However, in critically ill patients, the infusion rate of Intralipid may have to be adjusted below the maximal elimination capacity to avoid Intralipid accumulation in plasma.