Alok Bhandari

Atrazine sorption on surface soils: time-dependent phase distribution and apparent desorption hysteresis

Non-equilibrium sorption-desorption behavior of atrazine was studied on two surface soils. Impact of sorption contact time was evaluated by interpreting temporal variations in Freundlich sorption isotherm parameters n(t) and K(F)(t) obtained from the phase distribution relationships. The extent of sorption linearity was very similar (n approximately 0.90) for the two soils at all sorption contact times. K(F)(t) increased with contact time and stabilized upon reaching apparent equilibrium. K(F) for woodland soil was significantly higher than that for agricultural soil. The Apparent Hysteresis Index (AHI) parameter was used to quantify sorption-desorption hysteresis arising from non-equilibrium sorption. AHI was a function of the sorption contact time and correlated well with K(F)(t). The woodland soil sorbed more herbicide due to its higher organic matter content. However, a larger fraction of the herbicide sorbed to this soil was released rapidly (within 24 h) following sorptive uptake. The differences in sorption-desorption behavior of atrazine in the two soils appear to be related to variations in the type and location of organic matter in the two soils. The parameters K(F)(t) and AHI(t) consistently demonstrated the effects that arise when batch systems are not brought to equilibrium during sorption studies.

Occurrence of ciprofloxacin-, trimethoprim-sulfamethoxazole-, and vancomycin-resistant bacteria in a municipal wastewater treatment plant.

The occurrence of antibiotic-resistant bacteria was evaluated in aqueous samples obtained from a municipal wastewater treatment plant. Samples collected from the influent, clarifier effluent, and disinfected effluent were assayed for fecal coliforms, E. coli, and enterococci exhibiting resistance to ciprofloxacin, trimethoprim-sulfamethoxazole, and vancomycin. Membrane filtration of samples was followed by plating on growth media containing various concentrations of antibiotic. Bacterial colonies on plates with antibiotic exposures greater than the clinical minimum inhibitory concentrations were counted and considered resistant. The numbers of drug-resistant organisms in influent ranged from nondetectable to 7 x 10(5) colony-forming units (CFU)/100 mL for fecal coliforms, nondetectable to 5 x 10(4) CFU/100 mL for E. coli, and nondetectable to 6 x 10(5) CFU/100 mL for enterococci. Fecal coliforms, E. coli, and enterococci with reduced susceptibility to antibiotics were also detected in influent and clarifier effluent; however, the disinfected effluent did not contain resistant bacteria. Species-level identification of enterococci revealed that resistant enterococci were predominantly E. faecalis.

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.

Contaminants of emerging environmental concern.

This book is a must-have for both undergraduate and graduate students in environmental engineering and resources; teachers; researchers; and practicing environmental engineers.

A Practice-oriented Review of Woodchip Bioreactors for Subsurface Agricultural Drainage

Woodchip or denitrification bioreactors are an innovative, engineering-based technology to reduce the amount of nitrate in agricultural drainage. Increased interest in improving water quality in areas impacted by agricultural drainage has given bioreactors a boost of publicity over the past several years. While bioreactors continue to be an area of active research and are not a silver bullet to address drainage water quality concerns, the growing number of bioreactor installations by practitioners not involved in research demonstrates a need for a practice-oriented review of important aspects of these systems. This article provides context for enhanced-denitrification treatment of agricultural drainage, discusses the design and installation of bioreactors, and presents factors affecting their nitrate removal performance. Additionally, this review offers ideas for management and monitoring of agricultural drainage bioreactors. Bioreactors are a promising technology for improving drainage water quality, but much work remains to understand and optimize their performance. With additional evaluation and improved monitoring of bioreactors, a more complete picture of the potential contribution of these systems will be developed.

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.

Woodchip Denitrification Bioreactors: Impact of Temperature and Hydraulic Retention Time on Nitrate Removal

Woodchip denitrification bioreactors, a relatively new technology for edge-of-field treatment of subsurface agricultural drainage water, have shown potential for nitrate removal. However, few studies have evaluated the performance of these reactors under varied controlled conditions including initial woodchip age and a range of hydraulic retention times (HRTs) and temperatures similar to the field. This study investigated (i) the release of total organic C (TOC) during reactor start up for fresh and weathered woodchips, (ii) nitrate (NO-N) removal at HRTs ranging from 2 to 24 h, (iii) nitrate removal at influent NO-N concentrations of 10, 30, and 50 mg L, and (iv) NO-N removal at 10, 15, and 20°C. Greater TOC was released during bioreactor operation with fresh woodchips, whereas organic C release was low when the columns were packed with naturally weathered woodchips. Nitrate-N concentration reductions increased from 8 to 55% as HRT increased. Nitrate removal on a mass basis (g NO-N m d) did not follow the same trend, with relatively consistent mass removal measured as HRT increased from 1.7 to 21.2 h. Comparison of mean NO-N load reduction for various influent NO-N concentrations showed lower reduction at an influent concentration of 10 mg L and higher NO-N reductions at influent concentrations of 30 and 50 mg L. Nitrate-N removal showed a stepped increase with temperature. Temperature coefficient () factors calculated from NO-N removal rates ranged from 2.2 to 2.9.

Student Learning in a Multidisciplinary Sustainable Engineering Course

An existing multidisciplinary course on sustainable engineering in developing societies was expanded to include sustainability issues and challenges faced in the developed world. The new course consisted of independent modules on general background, sustainability concepts and tools, sustainable water and waste systems, sustainable energy systems, sustainable agricultural and food systems, and sustainable building systems. The course included a semester-long project experience conducted in interdisciplinary teams. Projects were sourced from local businesses and institutions or from organizations involved in international development. Course evaluation included an end-of-semester self-assessment by students and an analysis of project reports. Thirteen out of 18 students surveyed (72%) agreed that their ability to consider techno-economic, environmental, and social aspects of sustainability was improved as a result of the course. An improved student understanding of aspects of sustainability and its measure...

Isotherms for Atrazine Desorption from Two Surface Soils

The Freundlich isotherm model was used to describe desorption behavior of atrazine from two surface soils. Soils were contacted with five different initial aqueous atrazine concentrations—0.25, 1.0, 2.5, 10, and 25 μM—for a period of 7 days at a solid/liquid ratio of 0.175 (w/w). Desorption data was obtained by allowing the adsorbed atrazine to desorb for 14 days at solid/liquid ratios of 0.175, 0.110, 0.075, 0.047, and 0.027. Data were fitted to the Freundlich model and interpreted in terms of the linearity and capacity parameters for adsorption (n and KF) and desorption (nd and KFd). Atrazine adsorption to both soils was described as near-linear. Desorption isotherms, however, were more nonlinear than the adsorption isotherms. Desorption linearity (nd) and capacity (KFd) were related to the initial aqueous concentration (C0) of atrazine during adsorption. Both linearity and capacity were lower at smaller values of C0 and increased logarithmically with C0.

Natural Processes and Systems for Hazardous Waste Treatment

Sponsored by the Natural Processes and Systems for Hazardous Waste Treatment Task Committee of the Environmental Council of the Environmental and Water Resources Institute of ASCE.