Masters Theses

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Daniel C. Yoder

Committee Members

Thomas C. Mueller, James B. Wills, C. Roland Mote, William E. Hart

Abstract

One of the consequences of modem agriculture's reliance on chemicals is the production of pesticide-contaminated wastes. Much of this waste is made up of equipment rinsewater and spray tank rinsates, inappropriate disposal of which threatens the quality of the nation's water resources. One promising disposal technique employs an evaporation/degradation system, which consists of a lined bed or pit filled with soil and into which the wastewater is placed. The water evaporates, and the pesticide residues are adsorbed onto the soil and are eventually degraded by soil micro-organisms. Researchers have investigated variations of this system and obtained promising results. However, none of the previous reports indicate that much background analysis went into the designs. The goal of this research was to seek the combination of factors resulting in the optimum combination of evaporation and degradation. The variables that influence both of these processes include; (1) temperature, (2) soil texture, (3) evaporation rate, (4) mode of application of the pesticide solution to the soil, and (5) time.

A test apparatus was constructed employing individual soil columns to simulate conditions in a soil bed. Individual column treatments consisted of all possible combinations of two temperature levels, two soil types, two airflow rates, four application methods, and four run times. A mixture made up of water and the herbicides atrazine and fluometuron at low concentrations (10 parts per million) was continually supplied to the columns. Records were kept of the amount of herbicide solution supplied to each soil column to meet its evaporation requirements. At prescribed time intervals, the soil in the columns was tested for herbicide concentration levels as an indication of the rate dissipation.

Results indicate that substantial volume reduction (water evaporation) and decontamination (herbicide dissipation) of pesticide rinsate material in a soil disposal system can be achieved through simple application techniques. Under conditions of continual loading, the columns ability to degrade the herbicides was not overwhelmed by the increase in concentration levels. Soil type plays an important role in both processes. Although evaporation in the sandy soil columns was slightly greater (about 10%) than in those containing silty soil, the overall average herbicide degradation was much higher in the silty soil columns. The silty soil columns experienced an average of 85% atrazine and 59% fluometuron degradation (of that applied to the columns). Additionally, the evaporation (per surface area) from the silty soil columns averaged 3095 L/m2 [76 gal/ft2] under low temperature, low airflow conditions and [176 gal/ft2] under high temperature, high airflow conditions. In the proper design of such a system, greater emphasis should be placed upon elevating temperatures rather than facilitating air movement.

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