Biomedical subjects

Michael K Stenstrom

Publications and source records attributed to Michael K Stenstrom.

At least 19 recordsLinked to original sources

PubMed2006

Implications of a kinematic wave model for first flush treatment design.

A deterministic model was developed to predict pollutant mass first flush and to utilize it for better design of best management practices (BMPs) that focus on treating the first flush. The model used the kinematic wave equation to calculate flow and mass transport, and erosion equations to calculate pollutant concentrations, which were assumed to be from a short and a long term source. The model parameters were calibrated with a parameter estimation procedure using three years' monitoring data from a highway runoff site in west Los Angeles. The simulation results showed that there exists an optimum watershed size to maximize first flush. Contours of watershed length, developed from simulations for different conditions of rainfall and watershed geometry, can be used to design runoff collection systems for highways and parking lots to maximize first flush.

Models, Theoretical↗

PubMed2006

Using satellite imagery for stormwater pollution management with Bayesian networks.

Urban stormwater runoff is the primary source of many pollutants to Santa Monica Bay, but its monitoring and modeling is inherently difficult and often requires land use information as an intermediate process. Many approaches have been developed to estimate stormwater pollutant loading from land use. This research investigates an alternative approach, which estimates stormwater pollutant loadings directly from satellite imagery. We proposed a Bayesian network approach to classify a Landsat ETM(+) image of the Marina del Rey area in the Santa Monica Bay watershed. Eight water quality parameters were examined, including: total suspended solids, chemical oxygen demand, nutrients, heavy metals, and oil and grease. The pollutant loads for each parameter were classified into six levels: very low, low, medium low, medium high, high, and very high. The results provided spatial estimates of each pollutant load as thematic maps from which the greatest pollutant loading areas were identified. These results may be useful in developing best management strategies for stormwater pollution at regional and global scales and in establishing total maximum daily loads in the watershed. The approach can also be used for areas without ground-survey land use data.

Bayes Theorem↗

PubMed2006

Surfactant effects on alpha-factors in aeration systems.

Aeration in wastewater treatment processes accounts for the largest fraction of plant energy costs. Aeration systems function by shearing the surface (surface aerators) or releasing bubbles at the bottom of the tank (coarse- or fine-bubble aerators). Surfactant accumulation on gas-liquid interfaces reduces mass transfer rates, and this reduction in general is larger for fine-bubble aerators. This study evaluates mass transfer effects on the characterization and specification of aeration systems in clean and process water conditions. Tests at different interfacial turbulence regimes show higher gas transfer depression for lower turbulence regimes. Contamination effects can be offset at the expense of operating efficiency, which is characteristic of surface aerators and coarse-bubble diffusers. Results describe the variability of alpha-factors measured at small scale, due to uncontrolled energy density. Results are also reported in dimensionless empirical correlations describing mass transfer as a function of physiochemical and geometrical characteristics of the aeration process.

Air↗

PubMed2006

Economic implications of fine-pore diffuser aging.

Aerobic biological treatment, such as the activated sludge process, is commonly used for municipal wastewater treatment. Fine-pore diffusers have virtually replaced coarse-bubble diffusers in such operations, but most of the plant's energy expenditure is still consumed by aeration. Therefore, the performance of diffusers will critically affect plant economics. This paper analyzes and quantifies the consequences of aging processes on fine-pore diffusers. Datasets from 94 field measurements were analyzed and showed a clear pattern of performance decline with time in operation. Efficiency declines rapidly during the first 24 months of operation when the rate of decline decreases and efficiency stabilizes at a low value. For example, cost analysis scenarios were performed using the measured rate of decline in diffuser performance. The analyses include loss of transfer efficiency and elevated headloss, which both increase operating cost. Cleaning the diffusers within 12 months of operation is generally economically favorable, restores efficiency, and reduces power overhead. Periodic cleaning prolongs the economically viable lifespan for the aeration system.

Bioreactors↗

PubMed2006

Spatial estimates of stormwater-pollutant loading using Bayesian networks and geographic information systems.

Stormwater runoff has become the primary source of many pollutants to the Santa Monica Bay watershed (California), and managing stormwater inputs to the bay has become the primary objective of new regulatory efforts. Empirical methods to estimate stormwater pollution have been developed using land-use data; however, land-use data collected from traditional ground surveys are expensive and time consuming and may not be available. This study used an alternative approach and estimated land use from satellite-image classification using Bayesian networks. The results were converted to thematic maps using a geographic information system to visualize spatial estimates of runoff coefficients of the given area, event-mean concentrations (EMCs) of target pollutants, and their pollutant loads. The stormwater-pollutant-loading maps identified areas of high annual-mass loads, which were more affected by impervious areas, because of their high runoff coefficients, rather than their EMCs. In this watershed, the major sources of nonpoint-source pollution are the multiple-family-residential (14%), commercial (7%), public (6%), industrial (3%), and transportation (7%) land uses adjacent to Marina del Rey and the Ballona wetlands. The contributions of single-family-residential (30%) and open (33%) land uses are less important.

Bayes Theorem↗

PubMed2005

Metals and PAHs adsorbed to street particles.

Particles were collected from 18 different city streets adjacent to five different landuses in the City of Santa Monica, California. Landuses were classified as industrial, roads, multifamily residential, commercial and single family residential. Particles were collected using a vacuum cleaner with a 0.1-microm filter and a rotating brush head. Particles were first sized into six fractions from 43-2200 microm using two sets of sieves. Representative samples of the four size fractions smaller than 841 microm from each landuse were separately digested to extract metals and polynuclear aromatic hydrocarbons (PAHs). Smaller particles had higher solid-phase concentrations, but not as high as the ratios of their specific surface areas, assuming spherical shape. Relative PAHs concentrations were higher on small particles than were metal concentrations. Single-family residential areas were the lowest in metals and PAHs, with only a few exceptions. The greatest mass of pollutants was associated with the particles in the 100-250 microm range.

Adsorption↗

PubMed2005

Modeling of highway stormwater runoff.

Highways are stormwater intensive landuses since they are impervious and have high pollutant mass emissions from vehicular activity. Vehicle emissions include different pollutants such as heavy metals, oil and grease, particulates from sources such as fuels, brake pad wear and tire wear, and litter. To understand the magnitude and nature of the stormwater emissions, a 3-year study was conducted to quantify stormwater pollutant concentrations, mass emission rates, and the first flush of pollutants. Eight highway sites were monitored over 3 years for a large suite of pollutants. The monitoring protocol emphasized detecting the first flush and quantifying the event mean concentration. Grab and flow-weighted composite samples, rainfall, and runoff data were collected. A new runoff model with four parameters was developed that to describe the first flush of pollutants for a variety of rainfall and runoff conditions. The model was applied to more than 40 events for 8 pollutants, and the parameters were correlated to storm and site conditions, such as total runoff, antecedent dry days, and runoff coefficient. Improved definitions of first flush criteria are also presented.

California↗

PubMed2005

Degradation mechanism and the toxicity assessment in TiO2 photocatalysis and photolysis of parathion.

The photocatalytic degradation of methyl parathion was carried out using a circulating TiO2/UV reactor. The experimental results showed that parathion was more effectively degraded in the photocatalytic condition than the photolysis and TiO2-only condition. With photocatalysis, 10mg/l parathion was completely degraded within 60 min with a TOC decrease exceeding 90% after 150 min. The main ionic byproducts during photocatalysis were measured. The nitrogen from parathion was recovered mainly as NO3-, NO2- and NH4+, 80% of the sulfur as SO4(2-), and less than 5% of the phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and paraoxon were also identified, and these were further degraded. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by photocatalysis and photolysis. A Microtox test using V. fischeri showed that the toxicity, expressed as the relative toxicity (%), was reduced almost completely after 90 min under photocatalysis, whereas only an 83% reduction was achieved with photolysis alone. Another toxicity test using D. magna also showed that the relative toxicity disappeared after 90 min under photocatalysis, whereas there was a 65% reduction in relative toxicity with photolysis alone. The pattern of toxicity reduction parallels the decrease in parathion and TOC concentrations.

Aliivibrio fischeri↗

PubMed2005

Comparative economic analysis of the impacts of mean cell retention time and denitrification on aeration systems.

Biological nutrient removal is practiced in various modifications of the activated sludge process (ASP) throughout the world. This paper compares conventional, nitrifying-only and combined nitrifying/denitrifying (NDN) processes. The authors performed 113 oxygen transfer efficiency measurements with the off-gas method over 20 years. This dataset was analysed and used to perform an economic analysis for three example scenarios, one for each layout (conventional, nitrifying-only and NDN). Field oxygen transfer efficiency and relevant plant operative costs and credits were considered (i.e., aeration cost, sludge disposal cost, methane production credit). The conclusion is that NDN operations always have lower aeration costs, and generally have the lowest combined operating cost. Reduced aeration costs result because of improved aeration efficiency at higher mean cell retention times and the use of nitrate as an electron acceptor. The improved aeration efficiency overcomes the increased oxygen required at higher cell retention time due to cell decay.

Biodegradation, Environmental↗

PubMed2004

Event mean concentration and loading of litter from highways during storms.

Total captured gross pollutants in stormwater runoff were monitored at six Southern California highway sites over 2 years. Gross pollutants were defined as larger than 0.5 cm and were classified into three categories. The gross pollutants were 90% vegetation and 10% litter. Approximately 50% of the litter was composed of biodegradable materials. Event mean concentrations and mass emission rates are presented. No statistically significant correlations of litter production were noted, although the event mean concentrations show an increasing trend with antecedent dry days and a decreasing trend with total runoff volume or total rainfall. The mass emission rates will be useful to estimate total litter production for developing total maximum daily loads.

California↗

PubMed2004

Phosphorus release rates from sediments and pollutant characteristics in Han River, Seoul, Korea.

The Han River is 469.7-km long and drains a 26219-km(2) watershed. The sediments in the river are highly polluted due to inputs from upstream tributaries as well as partially treated municipal wastewaters that are discharged to the river. The water quality and strategy for control are important because the river is the primary drinking water supply for the City of Seoul, as well as being a major source for irrigation and industrial water. The Jamsil submerged dam partitions the river to isolate an upstream area for drinking water, but also captures sediments. Samples from four sites were studied to determine sediment pollutant concentrations and phosphorus release rates. Phosphorus tends to desorb from sediments when the concentration of overlying water is less than 1.4 mg/l. Water column P concentrations range from 0.04 to 0.1 mg/l, which suggests that sediments will act as a P source. In a series of batch experiments, P was released at approximately 15-20 mg/m(2)week in the winter (1-5 degrees C) and as much as 90 mg/m(2)week in the summer (20-24 degrees C), and is also a function of pH and dissolved oxygen concentration. The sediment total phosphorus concentration, which averages 833 mg/kg, is evenly distributed among non-apatite-P (33%), apatite-P (32%) and residual-P (34%). An equilibrium model is proposed to describe release rate.

Chromatography, Ion Exchange↗

PubMed2004

Seasonal first flush phenomenon of urban stormwater discharges.

California's climate, typified by winter and spring precipitation and summer drought, is often called a Mediterranean climate, and creates a long period for pollutant build-up. The initial storms of the winter season usually have higher pollutant concentrations, which is called a seasonal first flush. To investigate the existence of a seasonal first flush, we analyzed four major data sets, collected over the 1999-2000 to 2002-2003 wet seasons. Trends in seasonal loads were quantified by plotting pollutant concentrations or cumulative pollutant load versus cumulative rainfall or cumulative runoff volume. Pollutant concentrations in the first part of the wet season were ranged from 1.2 to 20 times higher than concentrations near the end of the season, and mass emission rates were similarly higher at the beginning of the season. A seasonal first flush existed for most cases and was strongest for organics, minerals and heavy metals except lead. This result suggests that applying treatment Best Management Practices (BMPs) early in the season could remove several times more pollutant mass than randomly timed or uniformly applied BMPs.

California↗

PubMed2003

Identification of land use with water quality data in stormwater using a neural network.

To control stormwater pollution effectively, development of innovative, land-use-related control strategies will be required. An approach that could differentiate land-use types from stormwater quality would be the first step to solving this problem. We propose a neural network approach to examine the relationship between stormwater water quality and various types of land use. The neural network model can be used to identify land-use types for future known and unknown cases. The neural model uses a Bayesian network and has 10 water quality input variables, four neurons in the hidden layer, and five land-use target variables (commercial, industrial, residential, transportation, and vacant). We obtained 92.3 percent of correct classification and 0.157 root-mean-squared error on test files. Based on the neural model, simulations were performed to predict the land-use type of a known data set, which was not used when developing the model. The simulation accurately described the behavior of the new data set. This study demonstrates that a neural network can be effectively used to produce land-use type classification with water quality data.

Agriculture↗

PubMed2003

Sediment characteristics, phosphorus types and phosphorus release rates between river and lake sediments.

The Han river is 469.7 km long with 26219-km2 area watershed, and is the primary drinking water source for the 20 million people that live in Seoul, Kangwon-Do and Kyunggi-Do, Korea. Phosphorus release from sediments impacts water quality, and is endangering the beneficial use of the river. This research measures phosphorus release and predicts future releases from bottom sediments of two tributary areas (Chungpyung Lake (CPL) and Jamsil submerged dam (JSD) area in the Han river). Sediment samples were taken over a 4-year period from four points in the Jamsil dam area and from 92 points in CPL. The sediments were analyzed for total phosphorus, the form of the phosphorus and release rates under different conditions to the water column. Sediment phosphorus distribution from CPL was 3-5% adsorbed-P (Ads-P), 15-20% non-apatite-P (NAI-P), 25-30% apatite-P (A-P) and 45-57% residual-P (R-P). In the JSD area, the phosphorus distribution ranges were 1-3% Ads-P, 22-39% NAI-P, 26-40% A-P and 30-39% R-P. Laboratory experiments showed that phosphorus release rates from 60 to 80 mg/m2 week in JSD area and ranged from 25 to 40 mg/m2 week in CPL sediments.

Aerobiosis↗

PubMed2003

A dynamic model for anaerobic filter.

Anaerobic filters are frequently used to treat medium to high strength wastewater (2000-20000 mg/L COD), but have fewer applications to low strength wastewater (< 1000 mg/L COD). In order to understand the applicability of anaerobic treatment for low strength wastewater, such as domestic sewage, a dynamic mathematical model was developed. This Monod-type kinetic model, which predicts treatment efficiency and gas production, was used to describe literature observations and is offered as a predictive tool.

Bacteria, Anaerobic↗

PubMed2002

Application of a membrane bioreactor for treating explosives process wastewater.

A bench-scale anoxic membrane bioreactor (MBR) system, consisting of a bioreactor coupled to a ceramic cross-flow ultrafiltration module, was evaluated to treat a synthetic wastewater containing alkaline hydrolysis byproducts (hydrolysates) of RDX. The wastewater was formulated the same as hydrolysis wastewater and consisted of acetate, formate and formaldehyde as carbon sources and nitrite and nitrate electron acceptors. The MBR system removed 80-90% of the carbon sources, and approximately 90% of the stoichiometric amount of nitrate, 60% of nitrite. The reactor was also operated over a range of transmembrane pressure, temperature, suspended solids concentration, and organic loading rate to maximize treatment efficiency and permeate flux. Increasing the transmembrane pressure and temperature did not improve flux significantly. Increasing mixed liquor volatile suspended solids (MLVSS) concentration in the bioreactor decreased the permeate flux significantly. The maximum volumetric organic loading rate was 0.72 kg COD/m3/day. The maximum food-to-mass ratio was 0.50 kg N/kg MLVSS/day and 1.82 kg COD/kg MLVSS/day. Membrane permeate was clear and essentially free of bacteria, as indicated by heterotrophic plate count. Permeate flux ranged between 0.15 and 2.0 m3/m2 day and was maintained by routine backwashing every three days. Backwashing with tap water containing chlorine bleach every fourth or fifth backwashing was able to restore membrane flux to its original value.

Bioreactors↗

PubMed2002

Fenton oxidation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX).

Oxidation of the high explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1.3,5,7-tetrazocine (HMX) using Fenton's reagent proceeds rapidly between 20 degrees C and 50 degrees C at pH 3. At an H2O2: Fe2+: RDX molar ratio of 5,178: 48: 1, RDX and HMX were completely removed in 1 to 2 h. All the experimental data could be fit to a pseudo first-order rate equation. The reaction rate was also strongly dependent on Fenton's reagent concentrations. NO3- and N2 were identified as nitrogen byproducts from RDX and HMX oxidation. The experiment with radiolabeled RDX showed that approximately 37% of organic carbon in RDX was mineralized to CO2. We observed formaldehyde and formic acid as a short-lived intermediate. No other volatile or nonvolatile byproducts were found from GC/MS analysis. The results show that RDX and HMX can be effectively mineralized with Fenton's reagents.

Azocines↗

PubMedDate not supplied

Utility of stormwater monitoring.

Stormwater runoff is now a major contributor to the pollution of coastal waters in the United States. Public agencies are responding by requiring stormwater monitoring to satisfy the National Pollutant Discharge Elimination System stormwater permit. However, studies to understand the utility of the current programs or to improve their usefulness have not yet been performed. In this paper, we evaluate the land-use-based program, the industrial stormwater permit program, and beach water-quality monitoring in the County of Los Angeles, California, to determine if the results will be helpful to planners and regulators in abating stormwater pollution. The utility of the program has been assessed based on the programs' ability to accurately estimate the emissions for different classes of land use. The land-use program appears successful, while the industrial monitoring program does not. Beach water-quality monitoring suffers from a lack of real-time monitoring techniques. We also provide suggested improvements, such as sampling method and time, and parameter selection.

Environmental Monitoring↗