Validation and optimization of a multi-processor UV-C reactor for inactivation of potato brown rot and soft rot pathogens in surface irrigation water in the Nile Delta.

Bacterial wilt and soft rot, caused by Ralstonia solanacearum and Pectobacterium carotovorum, are major threats to potato production and export. Surface irrigation water (SIW) can transmit these pathogens. This study validated and optimized a multi-processor UV-C (MP UV-C) reactor to ensure effective pathogen inactivation while minimizing energy use and operational cost. Physicochemical analysis revealed moderate turbidity and total suspended solids (TSS) in SIW, with UV transmittance (UVT) levels below the optimal range. This necessitates pre-filtration. Passing water through a 5-micron sediment filter improved UVT from 75% to 85%, reduced turbidity from 7.82 to 2.7 nephelometric turbidity units, and lowered TSS, chemical oxygen demand, and total dissolved solids, thereby placing the water within recommended ranges for UV-C disinfection. Collimated beam tests established UV dose-response curves, showing strong polynomial correlations (R2 > 0.99) between the applied UV dose and log inactivation. R. solanacearum exhibited higher UV sensitivity (6.23 mJ/cm2/log) than P. carotovorum (10.30 mJ/cm2/log). Reactor optimization identified an operational optimal setting of 270 W lamp power at a 35 m3/h flow rate, delivering 52.54 mJ/cm2 and achieving a 4-log reduction in both pathogens. Scanning electron microscope (SEM) analysis of R. solanacearum revealed severe cell wall damage at higher UV doses. Bioassays confirmed that UV-C-treated SIW significantly suppressed bacterial wilt in tomato seedlings and soft rot in potato tubers. Future work should assess the large-scale economic feasibility of UV-C treatment and its long-term effects on soil microbial biodiversity to ensure both sustainability and microbial balance in agricultural systems.