|M.Sc Student||Meir Arnon|
|Subject||Comparative Study of the Effect of Disinfection by UV|
Irradiation and Chlorination on Clogging of Drip
Irrigation System Fed with Tertiary
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Eran Friedler|
|Full Thesis text - in Hebrew|
The widespread use of drippers in treated effluent irrigation systems results from its water efficiency while lowering operational costs and minimizing the exposure of farmers and consumers to microbial contamination. Due to their internal structure, emitters easily become clogged by particles transported with the flow. As a result, non-uniform flow through the emitters is often observed when drip irrigation with wastewater effluent is practiced. Three main factors leading to clogging are chemical precipitation, sedimentation of suspended solids, and formation of biofilms.
The goal of this research was thus to perform a comparative study of the effects of two disinfection technologies of tertiary effluent (UV irradiation and chlorine disinfection) on clogging of irrigation emitters.
A pilot plant was constructed in a municipal WWTP consisting of activated sludge, media filtration and chlorination. On the first stage, three treatments were investigated after the media filtration: control - filtration without disinfection ; chlorine - filtration and a daily batch chlorine disinfection; and UV - filtration and UV radiation (dose of 10 mJ/cm2). On the second stage only two treatments were studied: control group - chlorination followed by media filtration, and UV treatment - chlorinantion, media filtration followed by UV irradiation.
At the end of stage I, the average emitter's flow of the control group reduced by 9%, while no flow reduction was observed for the two treatment groups. Best flow uniformity was observed for in the emitters fed with the UV group effluent. In the second stage no flow reduction was observed in both control and UV groups, nevertheless the emitters of the UV group exhibited higher flow uniformity.
In the first stage the average biofilm weights (accumulated inside the emitter) of the chlorine and the UV treatment groups were similar (0.0091 g), while the average biofilm weight of the control group was 9%, higher. In the second stage the average biofilm weight of the treatment group (chlorine+UV) was only 55% of that of the control group (chlorine alone). Statistical analysis of the results (t-test) showed that this difference is statistically significant (p=0.032). It can be postulated that filtration alone is not efficient enough to eliminate clogging in emitters fed with tertiary effluents. UV irradiation was found to be more efficient than the chlorination, as an anti bio-clogging treatment. Further, addition of a UV irradiation stage may enhance the performance of drip irrigation systems fed with chlorinated effluent.