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An assessment of constructed wetlands for the treatment of greenhouse wastewaters

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Title: An assessment of constructed wetlands for the treatment of greenhouse wastewaters
Author: Prystay, Ward A.
Degree Master of Science - MSc
Program Bio-Resource Engineering
Copyright Date: 1997
Abstract: The greenhouse vegetable industry in British Columbia is an expanding agricultural sector producing peppers, English cucumbers, tomatoes, and butter lettuce. Current production methods generate up to 4.5 litres of high nutrient runoff per square metre production area per day. The disposal of this wastewater untreated poses a significant environmental concern due to the potential for the high concentrations of nitrate and phosphate to induce eutrophication and alter the structure and dynamics of aquatic ecosystems. Technical problems surrounding the sterilization and recycling of greenhouse overdrain has lead the greenhouse industry to investigate the use of constructed wetlands as a wastewater treatment option. In the spring of 1995 a pilot scale research project was initiated to assess the use of constructed wetlands for treatment of this low organic carbon, high nutrient wastewater. Five wetland designs, based on conventional surface flow (SF) and subsurface flow (SSF) design approaches, were assessed. These designs were: 15 cm water depth planted SF wetlands; 30 cm water depth planted SF wetlands; 30 cm water depth unplanted SF wetlands; 60 cm depth gravel bed planted SSF wetlands; and, 60 cm depth gravel bed unplanted SSF wetlands. Samples were collected every second week between April and December 1996 from three sites within each wetland and analyzed for: ammonia, nitrate, total Kjeldahl nitrogen, total phosphorus, ortho-phosphate, total solids, total organic carbon and biochemical oxygen demand. Results of this study indicate that none of the individual designs assessed is capable of providing the highest treatment effect for all parameters concerned; however, the surface flow design emerged as the most appropriate design for the remediation of greenhouse wastewaters. No treatment effect was observed for either total Kjeldahl nitrogen or total solids in any of the designs assessed. The highest mean reductions of phosphorus was 65 % observed in one of the two unplanted SF wetlands. Peak nitrate reductions of 54% were observed in the 15 cm deep SF wetlands and ammonia removal of 74% were achieved in the unplanted SF wetlands. An increase in biochemical oxygen demand and total organic carbon was seen in all wetland designs. Based on available literature and the results of this research project, a multi-stage design, consisting of an unplanted pre-treatment basin followed by a 25 to 35 cm deep surface flow marsh with open water components, is recommended.
URI: http://hdl.handle.net/2429/7685
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]

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