Effect of passive and active heating on the performance of denitrifying bioreactors

Bioreactor;Denitrification;Hypoxia;Nitrate

Rendall, Timothy J ; Cooke ; Richard

关键词: Bioreactor;    Denitrification;    Hypoxia;    Nitrate;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/89097/RENDALL-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

In the Midwestern United States, the intensification of agriculture has led to increased yields, higher profits, and greater food availability.However, this productivity increase has not been without consequence. The Midwest’s agricultural industry has been linked to the region’s degrading water quality and the hypoxic zone in the Gulf of Mexico.Nutrient runoff via subsurface drainage flow enter surrounding water bodies and drain to the Gulf of Mexico causing lasting ecological damage.This influx of nutrients into these water bodies is challenging the scientific community to create innovative solutions to mitigate these problems. The use of denitrifying bioreactors is a management practice developed to reduce nitrate pollution from agricultural fields with subsurface drainage.Denitrifying bioreactors are woodchip filled trenches that provide the necessary energy source to allow for microbial communities to convert harmful nitrate (NO3-) into atmospheric nitrogen (N2). Bioreactors are a proven nitrate reduction technology and continued research is being conducted to develop more efficient systems. This study aimed to develop a paired bioreactor system for a study evaluating the effects of a bioreactor heating system. The treatment bioreactor was equipped with both solar powered underground electric heaters and a solar greenhouse in an attempt to raise internal temperature.The treatment and control bioreactors were compared based on temperature, nitrate, pH, and dissolved oxygen content.Temperature was analyzed for both submerged and unsubmerged portions of the bioreactors.The submerged section of the bioreactor had an average increase of 0.80 °C and the unsubmerged section had an average increase of 7.53 °C.The submerged temperature is of most interest because denitrification occurs in the submerged portion of the bioreactor.The submerged temperature increased longitudinally within the bioreactor as flow moved horizontally from inlet to outlet.Overall, there was an increase in temperature in the treatment bioreactor. The effect of bioreactor temperature on water quality was analyzed in this study. Nitrate data were inconclusive due to sampling errors resulting from nitrate stratification in the inlet structure. The pH levels in this investigation ranged from 6.51-6.98. The pH of the treatment bioreactor was statistically significantly lower than the pH of the control bioreactor, suggesting that an increase in bioreactor temperature lowers effluent pH. The dissolved oxygen content results confirmed that both the treatment and control bioreactors performed as expected. Dissolved oxygen content was statistically significantly lower in the treatment bioreactor compared to the control bioreactor, indicating more biological activity in the treatment bioreactor. The study proved it is possible to increase internal bioreactor temperature. This study did not determine an effect on nitrate reduction due to change in temperature in the paired system, however it is still hypothesized the increase in temperature will affect nitrate reduction.Future paired heated bioreactor research is needed to quantify the effect of temperature on nitrate reduction.