|M.Sc Student||Shulamit Atari Gorelik|
|Subject||Study of Biofouling in Dripping Irrigation Systems|
|Department||Department of Civil and Environmental Engineering||Supervisors||Full Professor Dosoretz Carlos|
|Dr. Avrahami Sharon|
|Full Thesis text - in Hebrew|
Irrigation with marginal water requires the application of dripping systems. A major agro-technical constraint concerning the application of marginal water in irrigation systems is fouling of pipes and distribution devices and especially clogging of emitters. The main objective of the study was to characterize the fouling layer chemical, physical and biological characteristics and use the accumulated knowledge in dealing with the problem. To achieve this, two drip irrigation systems were built and monitored over a year.
One irrigation system received secondary treated effluents from the Nir-Etzion wastewater treatment plant in six different treatments, with sodium hypochlorite and hydrochloric acid in different dossing programs and compared to the control. The second irrigation system received artesian water from Shamir’s drill alone or in combination with fertilization and/or mixing with water from the Dan waterworks. A 100 µm filtration was performed before irrigation in both cases.
Irrigation performance was determined by monitoring dripping-flow rate (manually and online) and temperature. Chemical and structural characteristics of the accumulated fouling layer were tracked as follows: weighting of the dry matter, analyzing the organic content in the dry matter, SEM-EDS, SEM-EDAX, ICP and CHON. Microbiological data was gathered by DGGE based fingerprinting and pyrosequencing followed by sequence analysis using the MOTHUR open code platform. In addition visual inspections were performed routinely. At the end of the experimental period a significant difference was observed between the two irrigation systems, in terms of chemical and biological composition of the accumulated fouling layer.
With secondary effluents the most significant flow rate decline was observed in the control (untreated) and the line treated only with acid whereas chlorination resulted the most effective to ameliorate biofouling. For the system fed with artesian water, a high potential for inorganic deposition was detected, augmented when fertigation was practiced, even when dilution with surface was performed. Biofouling was the main mechanism of fouling in the system fed with secondary effluents while chemical deposition of inorganic supersaturated species (scaling) was the main mechanism in the system fed with artesian water. Regardless of the type of treatment, biofouling developed in both irrigation systems and displayed a parallel population dynamics, which depended mainly on the environmental conditions and feedwater characteristics. The microbial community observed with secondary effluents was diverse, exhibiting high richness, mainly of heterotrophic populations (Proteobacteria, followed by Bacteroidetes where the most dominant phyla), versus a low richness community with artesian water, essentially composed by autotrophic species.