Biobeds: A New Approach To Pesticide Rinsate Disposal
Modern agriculture relies heavily on the use of chemicals for pest control to increase crop yields. However, improper handling and disposal of pesticides and pesticide waste may compromise surface water and groundwater quality. In farmyards, point-source contamination includes spills occurring during filling operations, sprayer rinsate, leaks, internal and external sprayer cleaning, and spray leftovers, and accounts for 40 to 90% of surface water and groundwater contamination by pesticides. Over the years, various biopurification systems have been developed to minimize the risk of point-source contamination by pesticides. One such system is the biobed. It consists of an active matrix (straw, peat or compost, and topsoil) in a ratio of 2:1:1 (v/v/v) in a pit. The effectiveness of the biobed mix is based on its ability to adsorb pesticides into its active matrix or stimulate their rapid biodegradation by offering suitable biological and physicochemical conditions for optimum microbial activity. The objective of this project was to study the efficiency of biobeds under Saskatchewan climatic conditions. Two laboratory studies and one field study were conducted in Saskatoon, SK. In the first laboratory study, the degradation of 2,4-D dimethylamine salt (2,4-D DMA) in single and multiple additions to the biobed mix and topsoil was investigated at 20 and 15 oC, respectively. In both studies, net CO2 evolution was correlated with 2,4-D degradation. Degradation of 2,4-D was more rapid in the biobed mix, with more than 99.9% degradation in 10 d, compared to topsoil with only 35% degradation in 28 d of incubation at 20 oC. In the multiple additions experiment, more than 99.9 and 70% of the applied amount of 2,4-D DMA was degraded in the biobed mix and topsoil, respectively, within 60 d of incubation at 15 oC. A mass balance showed that 93 and 51% of the C added as 2,4-D dimethylamine salt was mineralized within 60 d of incubation at 15 oC in the biobed mix and topsoil, respectively. These results suggest that net CO2 could be used as an indicator of 2,4-D DMA degradation in the biobed mix and topsoil used. A second laboratory experiment examined the degradation of seven pesticides at three temperatures (5, 13, and 20 oC). Pesticide degradation was more rapid at 20 oC compared to 13 and 5 oC. A significant interaction (sampling time x temperature) was observed in the degradation of thifensulfuron-methyl, 2,4-D DMA, pyrasulfotole, and bromoxynil. For metsulfuron-methyl, tribenuron-methyl, and thiencarbazone-methyl, degradation was a function of sampling time and temperature with no interaction. After 35 d of incubation at 20 oC, 38, 94, 99, 77, 77, and 99% of applied amounts of metsulfuron-methyl, tribenuron-methyl, thifensulfuron-methyl, thiencarbazone-methyl, pyrasulfotole, and bromoxynil, respectively, were degraded while more than 99% of the applied amount of 2,4-D DMA was degraded within 7 d. The results suggest that high pesticide degradation could be anticipated during warm conditions (summer) compared to fall or spring. A field study examined the degradation of six pesticides in two designs of biobed (the traditional below-ground biobed and a newly designed above-ground biobed) during two growing seasons. The above-ground biobed reached peak temperatures faster than the traditional below-ground biobed and was more efficient in water management. The above-ground biobed was more vulnerable to pesticide leaching out of the bottom compared to the below-ground biobed. The most leached pesticide was metsulfuron-methyl, with 4 and less than 0.01% of the applied amount leaching out of the bottom of the above-ground biobed and below-ground biobed, respectively. More than 99% of the applied amounts of tribenuron-methyl, thifensulfuron-methyl, thiencarbazone-methyl, pyrasulfotole, and 2,4-D DMA were either retained by the biobed matrix or degraded within 2 growing seasons in both biobeds. This research shows that biobeds are capable of degrading herbicides from different chemical classes and could be used to reduce surface water and groundwater contamination arising from point sources in Saskatchewan in particular and the prairies in general. However, consideration in their design should include leaching potential, water management, early-season biobed temperature and they must be closed.
DegreeMaster of Science (M.Sc.)
SupervisorKnight, Diane J.; Wolf, Thomas M.
CommitteeSi, Bing; Farrell, Richard E.; Cessna, Allan J.; Maulé, Charles
Copyright DateJanuary 2013