Normand Thérien

Production of GHG from the Decomposition of in vitro Inundated Phytomass and Soil

A set of experiments was designed to measure the production of carbon dioxide and methane during decomposition of inundated samples of representative vegetation and soil samples originating from the James Bay territory over a period of approximately one year. Controlled laboratory conditions were set for water temperature (4–22°C), pH (4.5–7.0) and dissolved oxygen concentration ( 2 mg·L−1). These conditions covered the range of conditions under which vegetation and soil are submitted during permanent flooding in newly created hydroelectric reservoirs. Representative phytomass samples consisted of spruce needles (Picea mariana sp.), alder leaves (Alnus sp.), lichen (Cladonia sp.), green moss (Pleurosium sp.) and herbaceous plants (mixed species). Representative forest soil samples consisted of lichen (Cladonia sp.) humus and green mosses (Pleurosium sp.) humus with Sphagnum moss (Sphagnum sp.) used as a representative ground component (phytomass) for wetlands. Production of carbon dioxide over time was observed from all samples under the given experimental conditions. The quantities of carbon dioxide produced from the vegetation samples were largest under oxic conditions at the higher temperature. The average cumulative quantities produced over 345 days ranged from 201 mg CO2·g−1 (dry weight) to 447 mg CO2·g−1 (dry weight) with the largest quantities produced from green moss. For the soil samples, the largest quantities of carbon dioxide produced occurred also at the higher temperature but were 15–40% larger under anoxic conditions. Under such conditions, the average cumulative quantities produced over 320 days from lichen humus and green moss humus were 72 g CO2·m−2 and 140 g CO2·m−2 respectively. Small quantities of methane were produced from the soil samples but only under the most favourable temperature and pH conditions and were higher under anoxic conditions. pH conditions and were higher under anoxic conditions. Under such conditions, the average cumulative quantities of methane produced over 320 days from lichen humus and green moss humus were 0.21 g CH4·m−2 and 0.56 g CH4·m−2 respectively. Production of methane from vegetation samples was significant only for the higher temperature under anoxic conditions. Under such conditions, the average cumulative quantities produced over 345 days were largest for green moss with a value of 1.72 mg CH4·g−1 (dry weight). Results have shown that, under the most favourable conditions for decomposition, the production of carbon dioxide and methane from inundated phytomass and humus soil samples was still very active after 345 and 320 days respectively. Rates of production of CO2 and CH4 calculated from the cumulative quantities released from the flooded vegetation and soil samples under the given experimental conditions represent a reference data set from which production of CO2 and CH4 emitted from reservoirs under field conditions can be estimated (Therien and Morisson, Chap. 25).

A respirometric study of the influence of aliphatic alcohols on activated sludges

Abstract The influences of primary aliphatic alcohols on oxygen consumption of activated sludges in endogenous states were measured using a laboratory respirometer. The alcohols studied were n -propanol to n -octanol. Using beef extract as a reference substrate, results demonstrated a two-stage action for all the primary alcohols studied. It was found that these alcohols enhanced the dissolved oxygen uptake rate by the biomass when they were below critical concentrations, but had inhibiting effects above these concentrations. The critical concentration has been observed to decrease with increasing size of the alcohol molecule. The results obtained are explained in terms of modifications to lipid membranes observed by other workers.

Modelling the dynamics of the activated sludge wastewater treatment process in terms of the carbon variable

Abstract Carbon as a process variable was used to characterize adequately the dynamic nature of the activated sludge process. In this study an unsteady state mass balance model in terms of the soluble organic and suspended solid organic carbons has been posed. This model considers the concentration of organic substrate, the concentration of cellular material and the concentration of products stocked in the cells for the aeration unit of the process. Predictions of the models for the substrate and biomass concentrations in the aerator are compared to the observed results of the earlier work. The proposed model is also compared to simpler models based uniquely on the growth kinetic concept using Monod or two-phase expressions. The inadequacy of the simple models in predicting some important aspects of the unsteady state operation is discussed.

Pre-drying Textile Fabrics with Infrared Radiation

A number of different fabrics were pre-dried in a pilot-scale electric infrared oven, using tubular radiant heaters placed evenly above and below the web. For most of the fabrics, the degree of drying, for given conditions using both medium- and short-wave sources, was independent of the nature of the fibers and the material construction. The textile simply served as an inert support for a sheet of water. This was true provided the wet fabric was thick enough to avoid any significant transmission of the radiation incident on it, and its final water content was not much below the critical value cor responding to the end of the constant rate drying period. At the optimum fabric width, the energetic efficiency for pre-drying using this particular oven was 73% for medium- wave quartz tubes and 56% for short-wave T-3 tubes. The lower efficiency of the short- wave sources was a consequence of decreased absorption of radiation by the wet web at wavelengths below 1.5-2.0 μm. The effects of source-web distance and fabric width were determined with the aid of view factor calculations based on the specific geometry of the dryer. The drying rate was not greatly influenced by variations in the rate of air flow. There was a contribution from convective heat transfer between the warm air and the textile, but this was difficult to assess.

Numerical Control of a Continuous Infrared Dryer

This study compares the relative performance of distinct microcomputer control algorithms for drying a textile sheet in an infrared oven. The process responses to changes in the set point as well as perturbations in the traveling velocity of the sheet and the inlet humidity of the sheet are analyzed. Feedback, feedforward, and hybrid control algorithms are considered. The results indicate that the performance of the feedback control algorithm is negatively affected by the time delay associated with the traveling of the sheet in the dryer. The feedforward control algorithm exhibits more rapid dynamics, but falls short of reaching the set point because of model imperfection. The hybrid control algorithm, combining the feedback and feedforward controls, gives the best results overall.

Measuring the Water Content of a Textile Fabric Using a Radio Frequency Sensor

Application of radio frequency sensors for the automatic control of a pilot-scale infrared drying range for textiles is described. This was most successful for the classical proportional-integral-differential (PID) negative feedback control system, but with some important restrictions—the drying of a single fabric with a relatively low initial water content and at constant tension. The radio-frequency sensor detects changes in water content of the textile from capacitance variations arising from changes in the dielectric constant of the wet fabric. This parameter was influenced by many variables in addition to the amount of water in the fabric. In particular, the dielectric constant depended on the characteristics of the fabric and was very sensitive to the presence of ionic substances in the water. Thus, this sort of sensor is less appropriate for control of textile drying under industrial conditions.

In Vitro Release of Mercury and Methylmercury from Flooded Organic Matter

Dominant vegetation and soil types found within the La Grande complex of northern Quebec were subjected to flooding under controlled laboratory conditions of temperature, pH and levels of dissolved oxygen. For all substrates, the cumulative quantities of mercury (Hg) released showed an asymptotic behaviour as a function of time. Under the conditions set for the experiments, Hg releases to the water column occurred rapidly but were of relatively short duration (< 1 year). Of the different vegetation types, sphagnum moss (Sphagnum sp.) released the greatest amount per unit dry weight of total Hg, ~ 40 ng g-1 dry weight. Alder (Alnus sp.), lichen (Cladonia sp.) and spruce (Picea mariana) were all within the range of 4–10 ng g-1 regardless of the treatment applied. Alder released the greatest amount of methylmercury (MeHg), 5 ng g-1 representing ~ 60% of total Hg. For sphagnum moss, MeHg released 3 ng g-1, ~ 8% of total Hg. Alder and spruce were within the range of 1–2 ng g-1. Globally, there were no clear effects of temperature, pH and levels of dissolved oxygen on releases of total Hg or MeHg, although for individual substrates there were some differences. For the humus samples, feather moss (Pleurozium sp.) humus yielded greater levels of both total Hg and MeHg per unit area, ~ 45 ng m-2 and ~ 1.2 ng m-2 respectively, as compared to lichen (Cladonia sp.) humus, ~ 4.3 ng m-2 and ~ 0.35 ng m-2 respectively. For both types of humus, ambient temperature treatment always produced the highest quantities of total Hg relative to colder temperature. This was also observed in the case of feather moss humus for MeHg. The results permit estimation of the contributions of total and MeHg from the dominant vegetation and soil types of proposed reservoirs.

Calculated Fluxes of Mercury to Fish in the Robert-Bourassa Reservoir

A detailed analysis of existing fish and plankton data allowed estimation of biomass and mercury (Hg) fluxes in fish during the years 1978–1984 immediately following the flooding of the reservoir. Fish were divided into two arbitrary groups: piscivores and prey (non-piscivores) accounting globally for more than 90% of all fish biomass captured during the 7 years period. Extensive catch-per-unit-effort data available over time was used to estimate fish yield based on productivity and to calculate standing stocks allocated to both groups. A strictly pelagic food chain (from plankton to non-piscivorous fish to piscivores) was assumed for the computation of the biomass and Hg fluxes from one trophic level to another. Using a verified plankton model for the reservoir, “available” biomass and Hg fluxes to prey fish (non-piscivores) were calculated. From the field data and calculated standing stocks, the “available” biomass and Hg fluxes from the prey fish to the piscivorous fish were also calculated. Conversely, from field data and the calculated standing stocks for both groups of fish, fluxes “required” to explain the fish biomass and Hg concentration of fish, were also computed. The magnitude of the deficits between the “available” and “required” fluxes showed that an entirely pelagic food chain could not account for observed Hg in fish, but that the greatest vector of Hg transfer to fish must have been the benthos. This conclusion was supported independently by analyses of fish stomach contents and recent data on Hg concentrations in benthos. The fluxes of total Hg, as dissolved Hg but more likely Hg associated with particulates, from decomposing vegetation and soil to the water column were also calculated in order to estimate the global fluxes of Hg within several compartments of the reservoir in the first few years after flooding.

Modelling the GHG emission from hydroelectric reservoirs

A mechanistic model has been constructed to compute the fluxes of CO2 and CH4 emitted from the surface of hydroelectric reservoirs. The structure of the model has been designed to be adaptable to hydroelectric reservoirs of different sizes and configurations and the reservoir can be partitioned into one, two or three vertical volumetric zones. Each zone may accommodate a number of influents and effluents including turbined flow and discharged flow. Each zone consists of a surface water layer (0–10 m) and a bottom water layer (>10 m). The model considers advective and diffusive mass transfers of dissolved CO2 and CH4 between zones and water layers, the rates of CO2 and CH4 produced from the decomposition of flooded vegetation and soil in the reservoir, and, mass transfer of CO2 and CH4 at the water-air interface. Global mass balance equations are solved to compute the magnitude of the advective flows between zones and water layers. Component mass balance equations are solved to compute the concentrations of CO2 and CH4 as a function of time in the surface and bottom water layers of each of the zones of the reservoir. The rates of CO2 and CH4 emitted from the surface water layer are computed using the two-film theory. Data from the Robert-Bourassa reservoir, a large operational hydroelectric reservoir, has been used as input data to the model. Results from the model were first compared with experimental data available for the calculation of dissolved CO2 concentration in the surface water layer. Secondly, results from the model were compared with fluxes of CO2 and CH4 emitted from that reservoir as calculated from the experimental determination of dissolved CO2 in water. Also, they were compared with direct measurements of the fluxes at the water-air interface. It has been observed that concentrations of CO2 computed by the model are in the range of values reported for the surface water layer. No data was available for comparison with concentration of CH4. Emissions of CO2 computed by the model were in the range of fluxes calculated from the experimental determination of dissolved CO2 in water. The computed flux as a function of reservoir age was also coherent with the CO2 flux measurements data. The transitional emissions of CO2 resulting from the decomposition of flooded vegetation and soil were found to be significant during not more than 6 to 8 years depending of the volumetric zones of the reservoir considered. Simulations were done under two distinct scenarios for the CO2 content of the influents to the reservoir. The first scenario used data which reflected the contribution of carbon originating from the drainage basin. The second scenario assumed the CO2 concentration in the influent water to be at equilibrium with the atmospheric CO2. From the simulation results and the data available an important finding is that the main source of carbon contributing to the GHG emission from the hydroelectric reservoir after the transitional emissions of CO2 due to the decomposition of the flooded vegetation and soil have faded away appears to be essentially the carbon originating from the drainage basin.

Résumé et synthèse

Dans cet ouvrage, nous presentons une synthese des etudes portant sur la problematique du mercure (Hg) dans les milieux aquatiques naturels et les reservoirs hydroelectriques du Nord du Quebec. Cette synthese est basee sur plus de vingt ans de suivi environnemental au complexe La Grande realise par Hydro-Quebec, ainsi que sur les resultats d’etudes menees pendant plus de dix ans par des equipes de recherches de l’Universite du Quebec a Montreal, de l’Universite de Sherbrooke, de la Faculte de Medecine veterinaire de l’Universite de Montreal, du Service canadien de la faune et d’Hydro-Quebec.