Effect of Chlorination and Acidification on Clogging and Biofilm Formation in Drip Emitters Applying Secondary Sewage Effluent

Abstract. The risk and inducing mechanism of emitter clogging vary with the types of ions in the irrigation water. The effectiveness of chlorination and acidification treatments in reducing emitter clogging has seldom been comparatively studied. The objective of this study was to quantify the influence of chlorination and acidification in reducing clogging in emitters applying secondary sewage effluent with different types of ions. Two types of emitters with plain channels and one type of emitter with a labyrinth structure were selected to investigate the clogging control strategy by measuring the dry weight of biofilm substance (DW) and the organic matter fraction in the biofilm and analyzing the mineral constituents of the clogging solids and the extracellular polymeric substance (EPS) of the attached biofilm. In general, chemical injection decreased the DW and EPS, resulting in less clogging than in emitters without chlorine and acid injection. For the emitter structures tested, chemical injection was more effective in controlling clogging in plain channel emitters than in labyrinth emitters. Different chemical injections produced similar mineral constituents of the clogging solids: quartz, calcium + magnesium carbonate, silicate, and iron oxide. Chlorine injection interval and targeted acidification pH are both important parameters in determining chemical injection schemes. Under the experimental conditions, weekly chlorination of sewage effluent acidified to pH 6.5 was more effective in reducing the growth and reproduction of microorganisms and the precipitation of solid particles in the drip emitters when applying sewage effluent containing high iron + calcium. However, when sewage effluent containing high calcium was used, acidification was more effective in removing the chemical precipitates. We conclude that the selection of chemical treatment strategies should consider the constituent ions in the sewage effluent. Keywords: Acid injection, Chlorine injection, Extracellular polymeric substance (EPS), Mineral constituents, Microirrigation.