Effects of Chlorination Schemes on Clogging in Drip Emitters during Application of Sewage Effluent

Chlorination is usually an economic method for treating clogging in drip emitters due to biological growth during sewage application. However, limited information is available for determining an optimal chlorination scheme. In this study, experiments were conducted to quantify the impact of chlorine injection concentrations and intervals on clogging and system performance of drip irrigation units that are used to apply a stored secondary effluent. Various chlorination schemes with concentrations of free chlorine residual at the end of laterals ranging from 0 to 10 mg L-1 and injection intervals ranging from one to four weeks were assessed using seven types of emitters with a nominal discharge of 1.0 to 2.6 L h-1 at 0.1-MPa pressure. It was found that emitter clogging was significantly affected by chlorination scheme and emitter type as well as their interaction. Clogging was greatly reduced by chlorination, especially for the emitters with a nominal discharge of less than 1.38 L h-1. Chlorination is therefore highly recommended for emitters with a relatively small discharge when sewage effluent is applied. Both the chlorine concentration during chlorination and the injection frequency had an impact on the effectiveness of reducing clogging. The weekly chlorination of 1.5 and 2.5 mg L-1 of free chlorine residual at the end of laterals and the biweekly chlorination at 5 mg L-1 generally produced less clogging and more uniform water application than the weekly chlorination at 0.5 mg L-1 and the chlorination every four weeks at 10 mg L-1. In general, a more frequent chlorination at a lower concentration is more effective in maintaining good system performance than a less frequent chlorination at a higher concentration, and is therefore recommended by this study.