Elimination of Clogging of a Biogas Slurry Drip Irrigation System Using the Optimal Acid and Chlorine Addition Mode

Abstract

As an emerging contaminant, the clogging substances of emitters in biogas slurry drip irrigation systems affect the efficient return and utilization of biogas slurry to the field to a great extent. This can be prevented using acid and chlorination as engineering measures. Through a hydraulic performance test and sampling detection and analysis, under the same acid addition conditions (pH = 5.5–6.0), three chlorine addition concentrations (0, 1–3, and 4–9 mg/L) and four chlorine addition cycles (6, 10, 14, and 20 days) were tested, aimed to clarify the influence of acid and chlorine addition parameters (chlorine adding cycle, chlorine adding concentration, etc.) on the anti-clogging performance of emitters in biogas slurry drip irrigation system. The results showed that compared with no acid and chlorination treatment (CK), only acid and a reasonable combination of acid and chlorination can significantly reduce the probability of serious and complete clogging of biogas slurry drip irrigation emitters, and they can stabilize the relative average flow of emitters by more than 75%. The measures of adding acid and chlorine change the distribution characteristics of clogging substances at the front and rear of the drip irrigation belt. Furthermore, they promote the migration of clogging substances to the rear of the drip irrigation belt, facilitating the clogging of emitters located thereat. The measures of acid addition and sequential addition of acid and chlorine significantly inhibit the growth of an extracellular polymer in the emitter, and the effect of inhibiting the increase in extracellular polymer concentrations is relatively poor when the acid addition period is excessively long or short. There exists a negative correlation between the extracellular polymer content in the emitter and the change in the emitter flow. Based on the obtained results, to ensure excellent anti-clogging performance of biogas slurry drip irrigation systems, for acid-only treatment measures, the acid dosing cycle is recommended to be 10 days. When acid and chlorination measures are implemented sequentially, the acid chlorination cycle is recommended to be 14 and 10 days when the chlorine concentration is 1–3 and 4–9 mg/L, respectively. This study has important scientific significance and practical value for the establishment of long-term operation management and protection technologies of large-scale biogas slurry drip irrigation systems.