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Thesis for Master of Science
Lília
João Talhinhas Alexandre Abstract: A denitrification process for industrial effluents, with nitrate concentrations of the order of 800 ppm, was developed based on constructed macrophyte beds. The size and operational parameters of the system were determined by trials on a pilot scale, these indicated above all the selection of a supplementary carbon source and the optimisation of the C/N ratio. Average hydraulic loads of 4 cm day-1 and average nitrogen mass loads of 7 g N m-2 day-1 were applied to two beds, with a surface area of 0.64 m2, planted with Phragmites australis and using a support matrix of light expanded clay aggregates. In a series of different trials, the effluent was supplemented with methanol, ethanol, sucrose or acetic acid. In each case the nitrogen and nitrate removal efficiencies were determined for different C/N ratios. Control of the nitrite and ammonia content of the effluent was also carried out, as well as that of the residual, CQO pH and temperature. Nitrogen removal efficiencies greater than 99% were obtained for all of the carbon sources used, the optimal C/N ratio being 1.45 (g/g), 1.2 (g/g) and 1.47 (g/g) for ethanol, sucrose and acetic acid respectively. Characterisation of the microbial population in the matrix and the rhizosphere showed an increase in the average number of total bacteria and Pseudomonas, as a response to the application of the effluent, these being principally responsible for the denitrification. The average number of fungi and actinomicetes decreased in the presence of the effluent and carbon sources, these being essential aerobic microorganisms that prefer acidic environments. The results obtained were confirmed in demonstration beds with a total area of 1500 m2, using ethanol as the external carbon source, in the ambit of the programme Life 98 ENV/P/00562. Keywords: Denitrification; Reed Beds / Constructed Wetlands; Industrial Effluents Treatment; Light Expanded Clay Aggregates; External Carbon Source; C/N Ratio
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