Glyphosate degradation by immobilized bacteria: laboratory studies showing feasibility for glyphosate removal from waste water

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Abstract
To evaluate immobilized bacteria technology for the removal of low levels of glyphosate (N-phosphonomethylglycine) from aqueous industrial effluents, microorganisms with glyphosate-degrading activity obtained from a fill and draw enrichment reactor inoculated with activated sludge were first exposed to glyphosate production wastes containing 500–2000 mg glyphosate/L. The microorganisms were then immobilized by adsorption onto a diatomaceous earth biocarrier contained in upflow Plexiglas® columns. The columns were aerated, maintained at pH 7.0–8.0, incubated at 25 °C, supplemented with NH4NO3 (50 mg/L), and exposed to glyphosate process wastes pumped upflow through the biocarrier. Glyphosate degradation to aminomethylphosphonic acid was initially >96% for 21 days of operation at flows yielding hydraulic residence times (HRTs) as short as 42 min. Higher flow rate studies showed >98% removal of 50 mg glyphosate/L from the waste stream could be achieved at a HRT of 23 min. Glyphosate removal of >99% at a 37-min HRT was achieved under similar conditions with a column inoculated with a pure culture of Pseudomonas sp. strain LBr, a bacterium known to have high glyphosate-degrading activity. After acid shocking (pH 2.8 for 18 h) of a column of immobilized bacteria, glyphosate-degrading activity was regained within 4 days without reinoculation. Although microbial growth and glyphosate degradation were not maintained under low organic nutrient conditions in the laboratory, the low levels of degradable carbon (45–94 mg/L) in the industrial effluent were sufficient to support prolonged glyphosate-degrading activity. The results demonstrated that immobilized bacteria technology is effective in removing low levels of glyphosate in high-volume liquid waste streams. Key words: glyphosate, degradation, immobilized bacteria technology.

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