Application of wetlands for the treatment of chromium-containing wastewater.

摘要

The objective of this thesis was to identify the capacity of different constructed wetlands to treat chromium containing wastewater, obtain the kinetic and hydraulic parameters that describe the chromium hexavalent reduction occurring, and develop a suitable model to describe such behavior. The approach involved building several lab scale constructed wetlands of different types, including a subsurface flow wetland (SSF), a surface flow wetland (SF), a pond, and complete stirred tank reactors (CSTR), planted mainly with Juncus effusus and fed with synthetic wastewater containing chromium dichromate.; The dissertation begins with a literature review, covering aspects of traditional wastewater treatment and how the design of the facilities has been conducted under certain conditions and assumptions. The use of constructed wetlands to treat wastewater is also covered. The review then focuses on work dealing with the treatment of heavy metals using constructed wetlands, and describes some of the work dealing specifically with chromium. The chemistry of chromium is also described.; The reactors were built and operated continuously over two phases, taking water samples to monitor the Cr(VI) reduction performance and other water quality parameters. Additional substances participating in chromium reduction were added and analyzed, such as sodium acetate, iron, and humic acids. Plant stress was measured using chlorophyll fluorescence to identify the damage imposed by chromium, and a chromium extraction was performed on the plant tissue to determine the amount reduced and absorbed, and its distribution in the plants. Hydraulic parameters were obtained for each wetland through tracer tests, and the kinetic parameters were determined by batch operation.; The results show that the constructed wetlands were able to reduce Cr(VI), with the SSF wetland showing the best performance in terms of chromium depletion. The kinetic and hydraulic parameters were used to develop a model describing the Cr(VI) reduction. A coupled kinetic-hydraulic model, to account for dispersion, was a better model in terms of describing the behavior compared to other models that included the traditional plug flow, the Kadlec wetland, a series of CSTRs, or the fitting of a Gamma function. It was also observed that other factors play an important role in Cr reduction including the iron content of the soil, the microbial community, and the root/rhizosphere system.