Nitrate removal from irrigation run-off using packed-bed bioreactors

Abstract

Denitrification of irrigation runoff was achieved using a fixed colony of facultative, heterotrophic bacteria in an anaerobic environment (1.0 to 2.0 ppm DO). The seed colony was derived from stirred pond water acquired from golf course runoff holding ponds. Methanol was supplied at a ratio of 3.5:1 C:N as the electron donor, and NH4NO3, Supplied the electron acceptor (NO3-). The fate of N03-, N02-, and NW, as they passed up the columns was analyzed along four equal regions of the columns at an influent of I 00 ppm N03-and a flow rate of 1.0 gpm (0.58 hour HRT). The majority of the N03-(76.5%) were removed in the first region of the columns with subsequent regions removing 4.8-7.6%. Nitrite was produced (1.0 ppm) within the first region of the columns with the majority (21.12%) being removed in the final region. Intermediate regions reduced 5.2-16.5%. Ammonium concentrations remained steady with slight removal (6.3-1 1. I%) occurring in the first two regions. Efficiency of N03- and N02-removal was observed along 16 treatment combinations of N03'(50, 100, 150, and 200 ppm) and flow rate (I. 0, 1. 5, 2.0, and 2.5 gpm). Efficiency of N03-and N02-removal was observed to be greatest at a treatment combination of 1.0 gpm and 200 ppm for N03-(96% removal) and 1.0 gpm and 50 ppm for N02-(O.3 ppm effluent). Transient response time, or colony equilibration, was also observed at 1.0 gpm with negative concentration step changes from 150 to 100 ppm and 100 to 50 ppm. Approximately two days were needed for equilibration to steady state. Microbial species dominating in the bioreactor were identified as those in the genera Pseudomonas, Hydrogenophaga, Chromobacterium, Rhodobacter, Acidovorox, and Methylobacterium. A sub-irrigation growth study utilizing the discharged bioreactor water from a treatment combination of 1.0 gpm and 150 ppm was performed on Catharanthus roseus. Those treated with bioreactor water showed severe chlorosis and necrosis of leaf material.