Masters Theses

Date of Award

12-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering Technology

Major Professor

Raj Raman

Committee Members

Robert T. Burns, Reid R. Gerhardt, Mary Sue Younger

Abstract

Both subsurface flow (SSF) and free water surface (FWS) constructed wetland (CW) systems have been used for partial treatment of wastewater from animal production facilities. SSF systems are considerably more expensive, especially with regard to capital costs. However, the less expensive FWS systems have tremendous mosquito production potential; a factor which cannot be ignored by design engineers, especially given increasing public concern about emerging and reemerging vector borne diseases.

One promising method of reducing mosquito production in FWS CW systems is periodic drying. By disrupting the development of larval mosquitoes, this strategy may prevent the emergence of adult mosquito species associated with FWS CW systems. To test the efficacy of this method, experiments were conducted on 12 CW mesocosms (0.7m2 surface area each), divided into three groups. Each group received dairy wastewater, pretreated by a high-rate anaerobic filter (AF), and all mesocosms were populated by cattail (Typha latifolia). Group 1 consisted of FWS cells filled with plants that had been established for three years. Group 2 consisted of newly established FWS cells, and Group 3 consisted of newly established SSF cells. The SSF cells were loaded continuously with wastewater, while the FWS cells received wastewater periodically: 7-d on, 7-d off. While receiving flow, each mesocosm was operated at a 7-d hydraulic retention time (HRT); two mesocosms in series thus had a net HRT of 14 d.

Emergence of adult mosquitoes from FWS cells was monitored during the drying phase. The removal rates of organic matter (measured as chemical oxygen demand) (COD), total nitrogen (TN), ammonia nitrogen (NH3-N) and total phosphorous (TP) were monitored in all cells, to compare pollutant removal between groups. Periodic drying of FWS CW systems successfully killed mosquito larvae and pupae, thereby preventing adult mosquito emergence, as long as there was no significant rainfall within the first two days of the drying phase. Water quality data indicated that FWS CW cells with established plants do not achieve significantly greater or less pollutant removal rates than newly established FWS cells for COD, TP, NH3-N, or TP at a 7-d HRT.

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