Chlorination Systems to Control Escherichia Coli in Irrigation Water
Wesley Kline, New Jersey Agricultural Experiment Station, Rutgers Cooperative Extension, 291 Morton Ave., Millville, New Jersey 08332

Escherichia coli (E. coli) above acceptable levels (126 CFU/100 ml) have been observed in some surface New Jersey irrigation water. The frequency and level of the E. coli depends on environmental conditions, which makes it difficult for growers to know when to stop using the water source. To control E. coli growers need a reliable and cost effective method. Evaluation of a control system for E. coli was the objective of this study.

A PPG Industries tablet chlorination system (calcium hypochlorite) was attached at the intake irrigation line to inject chlorine on a continual basis. Dry tablets 3 inches in diameter were placed in a PCV container and water flowed over the bottom of the tablets releasing chlorine into the system. Water samples were collected from 30 June to 2 September 2009 (10 sampling dates) from three locations (pond, injection filter and at the end of a drip line) at the site. Water was collected in sterile 100 ml containers then analyzed in a commercial laboratory using the EPA 1603 method for generic E. coli. The goal was to maintain free chlorine levels at the pump at 4-5.0 ppm and 2.0 ppm at the end of the drip line. Chlorine levels were monitored from 1 July to 2 September.

Over the ten sampling dates, E. coli levels were above 126 MPN/100 ml for five dates from 27 July to 2 September. Chlorine at the intake registered 4 ppm on 1 July, but was not detected until 14 July at the end of the drip line. Organic matter had built up in the drip line from earlier irrigation, which tied up the chlorine. The chlorine level ranged from 1-4.0 ppm at the intake and between 0.5 to 1.5 ppm in the line during the sampling period. E. coli in the pond ranged from 110 CFU/100 ml to 800 CFU/100 while at the end of the drip line it was less than 10 CFU/100 ml for all sampling dates. This system adequately controlled E. coli and would be easy for a grower to manage.