Technical Note: The Potential of Municipal Yard Waste to be Denitrification Bioreactor Fill

The use of denitrification bioreactors to mitigate nitrate in agricultural drainage has recently gained much interest in the Midwestern United States and in similarly drained agricultural regions. However, as the number of bioreactor installations has increased, questions have been raised about the supply and consistency of denitrification carbon source material. In selecting such material, there is an important balance between optimal media properties (e.g., hydraulic properties, chemical composition), practicality, and material cost. The use of free material such as municipal yard waste may help minimize the cost of this voluntary water quality improvement strategy in the Midwestern United States, but may not provide other sufficient media properties. To investigate this, pilot-scale bioreactors were used to compare hardwood chips with free, chipped municipal yard waste in terms of nitrate removal potential and changes in the media. Sampling of bioreactor influent and effluent over a range of retention times showed the yard waste had higher removal efficiencies at a given retention time and higher removal rates than the woodchips. However, buried carbon media bags revealed the yard waste lost weight to a greater extent and more consistently than the woodchips meaning the woodchips had a half-life over two times greater than the yard waste. This, combined with the low carbon-to-nitrogen ratio of the yard waste, indicated yard waste material is not ideal for bioreactor installations that are intended to be low maintenance for at least ten years

An Initial Effort to Count Environmental Engineers in the USA

This paper critiques available environmental engineering demographics and presents estimated populations for students, faculty, and practitioners in the USA. Limited environmental engineering demographics exist because most data are collected for named environmental engineering degrees and named environmental engineering departments. American Association of Engineering Societies Engineering Workforce Commission (http://www.asee.org, 2004) has the best student data with comprehensive participation, and annual reports. Estimates for 2004 graduates suggest approximately 496 bachelors, 590 masters, and 119 doctorate degrees. However, many academic programs do not offer undergraduate environmental engineering degrees. Based on civil engineering student populations, the authors suggest that 1,245 undergraduates who will practice environmental engineering received engineering degrees (regardless of title) in 2004. American Society for Engineering Education is the main source for demographics for faculty; however, only members in standalone departments are counted, and the data were first reported in 2003. 2003 estimates are just over 100; however, the authors suggest that there are approximately 1,100 environmental engineering faculty based on Association of Environmental Engineering and Science Professors membership. For environmental engineering practitioners, the Bureau of Labor Statistics (BLS) provides a reasonable, 2003 lower end estimate (based on statistical samples) of 45,500. Based on population, the authors conclude that environmental engineering is midsized relative to other engineering disciplines. Recognized sources of demographics for engineers should be encouraged to report environmental engineering as a distinct category. Also, relevant organizations should work with EWC and ASEE to determine better estimation methods for those environmental engineering students, faculty, and resources currently aggregated with other disciplines

Internal hydraulics of an agricultural drainage denitrification bioreactor

Denitrification bioreactors to reduce the amount of nitrate-nitrogen in agricultural drainage are now being deployed across the U.S. Midwest. However, there are still many unknowns regarding internal hydraulic-driven processes in these engineered treatment systems. To improve this understanding, the internal flow dynamics and several environmental parameters of a denitrification bioreactor treating agricultural drainage in Northeastern Iowa, USA were investigated with two tracer tests and a network of bioreactor wells. The bioreactor had a trapezoidal cross section and received drainage from approximately 14.2 ha at the North East Research Farm near Nashua, Iowa. It was clear from the water surface elevations and the continuous pressure transducer data that flow was attenuated within the bioreactor (i.e., reduction in peak flow as the hydrograph moved down gradient). Over the sampling period from 17 May to 24 August 2011, flow conditions and internal parameters (temperature, dissolved oxygen, oxidation reduction potential) varied widely resulting in early samplings that showed little nitrate removal ranging to complete nitrate removal (7–100% mass reduction; 0.38–1.06 g N removed per m3 bioreactor per day) and sulfate reduction at the final sampling event. The bioreactor\u27s non-ideal flow regime due to ineffective volume utilization was a major detriment to nitrate removal at higher flow rates. Regression analysis between mass nitrogen reduction and theoretical retention time (7.5–79 h) suggested minimum design retention times should be increased, though caution was also issued about this as increased design retention times and corresponding larger bioreactors may exacerbate detrimental by-products under low flow conditions. Operationally, outlet structure level management could also be utilized to improve performance and minimize detrimental by-products

Technical Note: Hydraulic Property Determination of Denitrifying Bioreactor Fill Media

Denitrification bioreactors are one of the newest options for nitrate removal in agricultural drainage waters. Optimization of denitrification bioreactor design requires the ability to identify concrete values for the hydraulic properties of bioreactor fill media. Hydraulic properties, chiefly saturated hydraulic conductivity but also porosity and particle size, are not known for many types of possible bioreactor media though they have a significant impact upon bioreactor design and performance. This work was undertaken to more fully quantify the hydraulic properties of the major type of fill media used in Iowa denitrification bioreactors through a series of porosity, hydraulic conductivity, and particle size analysis tests. In addition, a particle size analysis was performed for two types of woodchips and one type of wood shreds in order to quantify and highlight the differences between what is commonly referred to as wood fill. Saturated hydraulic conductivity was determined for blends of woodchips, corn cobs, and pea gravel. For one of the most common types of woodchips used in bioreactors, the porosity varied from 66% to 78% depending on packing density and the average saturated hydraulic conductivity was 9.5 cm/s. It was found that additions of pea gravel significantly increased the hydraulic conductivity of woodchips though additions of corn cobs did not. Regardless of the fill mixture used, it is vital to design the bioreactor using the hydraulic properties for that specific media

Performance Evaluation of Four Field-Scale Agricultural Drainage Denitrification Bioreactors in Iowa

Recently, interest in denitrification bioreactors to reduce the amount of nitrate in agricultural drainage has led to increased installations across the U.S. Midwest. Despite this recent attention, there are few peer-reviewed, field-scale comparative performance studies investigating the effectiveness of these denitrification bioreactors. The object of this work was to analyze nitrate removal performance from four existing bioreactors in Iowa, paying particular attention to potential performance-affecting factors including retention time, influent nitrate concentration, temperature, flow rate, age, length-to-width ratio, and cross-sectional shape. Based on a minimum of two years of water quality data from each of the four bioreactors, annual removal rates ranged from 0.38 to 7.76 g N m-3 bioreactor volume d-1. Bioreactor and total (including bypass flow) nitrate-nitrogen load reductions ranged from 12% to 76% (mean 45%) and from 12% to 57% (mean 32%), respectively, removing from 0.5 to 15.5 kg N ha-1 drainage area. Multiple regression analyses showed that temperature and influent nitrate concentration were the most important factors affecting percent bioreactor nitrate load reduction and nitrate removal rate, respectively. This analysis also indicated that load reductions within the bioreactor were significantly impacted by retention time at three of the four reactors. More field-scale performance data from bioreactors of different designs and from multiple locations around the Midwest are necessary to further enhance understanding of nitrate removal in these systems and their potential to positively impact water quality

Efficacy of a monovalent human-bovine (116E) rotavirus vaccine in Indian children in the second year of life

Rotavirus gastroenteritis is one of the leading causes of diarrhea in Indian children less than 2 years of age. The 116E rotavirus strain was developed as part of the Indo-US Vaccine Action Program and has undergone efficacy trials. This paper reports the efficacy and additional safety data in children up to 2 years of age. In a double-blind placebo controlled multicenter trial, 6799 infants aged 6-7 weeks were randomized to receive three doses of an oral human-bovine natural reassortant vaccine (116E) or placebo at ages 6, 10, and 14 weeks. The primary outcome was severe (≥11 on the Vesikari scale) rotavirus gastroenteritis. Efficacy outcomes and adverse events were ascertained through active surveillance. We randomly assigned 4532 and 2267 subjects to receive vaccine and placebo, respectively, with over 96% subjects receiving all three doses of the vaccine or placebo. The per protocol analyses included 4354 subjects in the vaccine and 2187 subjects in the placebo group. The overall incidence of severe RVGE per 100 person years was 1.3 in the vaccine group and 2.9 in the placebo recipients. Vaccine efficacy against severe rotavirus gastroenteritis in children up to 2 years of age was 55.1% (95% CI 39.9 to 66.4; p<0.0001); vaccine efficacy in the second year of life of 48.9% (95% CI 17.4 to 68.4; p=0.0056) was only marginally less than in the first year of life [56.3% (95% CI 36.7 to 69.9; p<0.0001)]. The number of infants needed to be immunized to prevent one episode of severe RVGE in the first 2 years of life was 40 (95% CI 28.0 to 63.0) and for RVGE of any severity, it was 21 (95% CI 16.0 to 32.0). Serious adverse events were observed at the same rates in the two groups. None of the eight intussusception events occurred within 30 days of a vaccine dose and all were reported only after the third dose. The sustained efficacy of the 116E in the second year of life is reassuring