Abstract. High fertilizer inputs and uncontrolled subsurface drainage can result in the export of nutrients from farmland, leading to negative environmental impacts. Controlled drainage can be an effective best management practice to minimize the export of nutrients. However, information about controlled drainage in the Canadian Prairies is scarce. The objective of this study was to compare free drainage with overhead irrigation (FDIR) to controlled drainage with sub-irrigation (CDSI) in terms of nitrogen, phosphorus, and salt exports from corn fields in the Canadian Prairies. The irrigation water had low concentrations of nitrate (â¤0.2 mg L-1) and orthophosphate (<0.1 mg L-1) and low electrical conductivity (0.55 dS m-1), which were assumed to have low influence on the export of nutrients and salts. In 2010, the exports of NO3-N (138 kg ha-1), PO4-P (0.6 kg ha-1), and salts (2.34 Mg ha-1) from the FDIR treatment during the growing season were significantly larger (p < 0.05) than exports from the CDSI treatment, which were 0.07 kg ha-1, 0.08 kg ha-1, and 0.41 Mg ha-1, respectively. This comparison did not include the drainage outflow arising from spring snowmelt due to delays in the installation of monitoring equipment. In 2011, which included the drainage outflow due to spring snowmelt events, the exports of NO3-N (36 kg ha-1), PO4-P (0.27 kg ha-1), and salts (1.1 Mg ha-1) from FDIR were significantly larger (p < 0.05) than the exports from CDSI, which were 10 kg ha-1, 0.08 kg ha-1, and 0.39 Mg ha-1, respectively. Therefore, controlled drainage with subirrigation (CDSI) showed significant reductions in export of NO3-N (71%), PO4-P (69%), and salts (64%) compared to free drainage with overhead irrigation (FDIR). This study shows the advantage of controlled drainage over free drainage in reducing the export of nutrients and salts.
Abstract. Off-gas analysis is a common method for assessing the performance of many bioprocesses, but often little regard is given to the dissolved gas concentrations to which the microbes are actually exposed. In this work, a membrane-inlet mass spectrometer (MIMS) was used to quantitatively assess dissolved gas (H2 and CO2) concentrations during thermophilic fermentation of 2 g L-1 cellobiose with Clostridium thermocellum in a N2-sparged bioreactor. During baseline operating conditions (100 rpm mixing and 10 mL min-1 N2 sparging) H2(aq), and to a lesser extent CO2(aq), were detected in levels higher than would be predicted using gas-phase measurements and the assumption of equilibrium with the liquid phase. Under these conditions, H2 supersaturation ratios (RH2) as high as 22.8 were observed, and CO2 supersaturation ratios were measured to be as high as 1.6. In an effort to improve liquid-to-gas mass transfer and reduce supersaturation, a second condition was evaluated in which stirring was increased to 200 rpm, N2 sparging was increased to 100 mL min-1, and surface mixing was applied. Under this condition, H2 supersaturation was reduced (maximum RH2 = 9.6), while CO2(aq) measurements showed no significant supersaturation. Accounting for the elevated [H2](aq) in the measured with the MIMS led to an improved electron balance, and in a similar way the additional CO2(aq) (when supersaturated) led to improved carbon recovery. This work shows how liquid-to-gas mass transfer can influence carbon flux in microbial metabolism, which is an important process engineering parameter in scale-up.
The objective of the study was to develop a mechanistic model of methane (CH 4 ) producing processes in unstirred conditions with potential application for estimating CH 4 emissions from anaerobic manure storage facilities. Although models for describing anaerobic digestion processes are available, they largely relate to anaerobic digesters, and do not directly apply to the prediction of CH 4 emissions from liquid manure storage. Based on extant models, six biochemical steps were described: hydrolysis, acetogenesis, hydrogenogenesis, homoacetogenesis, hydrogenous methanogenesis and acetic methanogenesis, performed by five bacterial groups. The model contains six state variables, and mass flow is mostly generated and quantified using bacterial kinetics. The model was coded in acslX and a fourth-order Runge-Kutta method with an integration step size of 0.05 d was used for numerical integration. The time courses of CH 4 production and volatile fatty acid (VFA) concentration of two laboratory-scale liquid manure storage tanks, both filled with liquid sow manures and running in unstirred and constant 25°C conditions, were well predicted, with correlation coefficients over 0.90. Discrepancies between predicted and measured CH 4 production and VFA concentration were mainly due to random variation of observed data. The model was sensitive to parameters describing hydrolysis and the kinetics of acetogenic and acetate methanogenic bacteria. Simulations based on the Intergovernmental Panel on Climate Change model (Tier II) predicted 260 g CH 4 kg -1 volatile solids (VS, assuming maximum CH 4 producing capacity of 0.48 and methane conversion factor of 80%), whereas the measured value was 78.3 g CH 4 kg -1 VS after 146 d and the mechanistic model predicted 74.8 g CH 4 kg -1 VS. The model developed in this study appears to be better suited to batch manure storage than the IPCC model.
Northern Aboriginal communities in Canada suffer from poor wastewater treatment. Treatment systems on 75% of Manitoban Aboriginal communities produce substandard effluent despite the presence of sophisticated treatment systems. A 200-litre, pilot-scale membrane bioreactor (MBR) was established on the Opaskwayak Cree Nation to investigate the feasibility of MBRs in mitigating Aboriginal wastewater treatment issues. The pilot system was remote controlled and monitored via the Internet using the program pcAnywhere. The community utilized two existing sequencing batch reactors (SBR) and three sand filters for wastewater treatment. The community wastewater was relatively weak and highly fluctuating which led to poorly settling sludge that readily fouled the sand filters. A comparison study between the MBR and SBR was undertaken from September to December 2003. Operated at a 10-hour hydraulic retention time and 20-day solids residence time, the MBR outperformed the SBR and sand filtration on BOD and suspended solids removal. Furthermore, the MBR showed high levels of nitrification despite relatively cold water temperatures.
Abstract Increasing attention has been focused on endocrine disrupting compounds (EDCs) as pollutants in municipal wastewater. Recent studies have shown that these compounds can have a negative impact on the environment, and that in many cases they are not efficiently removed in wastewater treatment plants (WWTPs). Studies have also revealed that their destruction and transport out into the environment depend on the design and operational characteristics of these treatment systems and on the properties of the chemicals themselves. This paper reviews the current knowledge on EDCs, natural and synthetic hormones including estrone (E1), 17β~estradiol (E2), and 17α~ethinylestradiol (EE2) in WWTP. Several key data gaps are addressed when assessing the removal of EDCs in WWTPs. First, analytical methods used by most researchers do not account for the inactive or conjugated form of the compounds, yet they can become deconjugated to active forms during treatment, leading to an additional source of contaminant load. Next, insufficient measurements are made at various stages within the WWTP preventing adequate analyses on how each unit process contributes to degradation. Currently, there is no standardized procedure for assessing degradation of EDCs in WWTPs, and it is often difficult to compare published data generated by individual test protocols. This paper identifies streams that should be sampled in WWTPs and suggests a mass balance approach that takes into account all forms of the compound in both liquid and solid phases. Issues of potential concern in performing mass balances are discussed leading to a proposal of variables that should be analyzed and included in published articles. The adoption of similar methods by researchers in future work will produce a better picture of the presence and fate of these compounds in the environment. Keywords: ENDOCRINE DISRUPTING COMPOUNDSWASTEWATER TREATMENT PLANTMASS BALANCEADSORPTIONCONJUGATIONDECONJUGATION
Dose–response modelling was performed for several infectious disease viruses using the exponential, exact beta-Poisson, and approximate beta-Poisson models using existing datasets of animal infections. The exact beta-Poisson model was found to provide the best fit of the three models. The aerosol transmission route was found to require the lowest dose to cause infection compared to the intra-nasal and oral transmission routes for porcine reproductive and respiratory syndrome virus (PRRSV) and H9N2 avian influenza virus. Foot and mouth disease virus required lower doses with the aerosol transmission route than the intra-nasal transmission route. Liquid oral transmission required lower doses than feed transmission to cause infection for African swine fever virus and overall oral transmission required low doses to cause infection by porcine epidemic and diarrhoea virus. A computational fluid dynamics simulation was coupled with the dose–response modelling to simulate aerosol transmission of PRRSV in two experimental case studies. The coupled model predicted a probability of infection between 82% and 100% using the exact beta-Poisson model, which was in good agreement with the observed rate of infections in the two experimental case studies (84% and 90%).
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