- 3:40 PM

Development and Optimization of a Highly Effective and Low Energy Intensive Electro-Disinfection System for Ballast Water Treatment

K.G.Nadeeshani Nanayakkara1, Yu-Ming Zheng2, and J. Paul Chen2. (1) Division of Environmental Science & Engineering, National University of Singapore, 10 Kent Ridge Cresent, Singapore, 119260, Singapore, (2) Environmental Science and Engineering, Natioanl University of Singapore, Singapore, 117576, Singapore

Ballast water (BW) is carried inside ships in order to maintain the stability during the voyage. Few billion tones of BW, which may contain various living organisms, are transferred throughout the world per year and upon discharge, may severely disrupt the native ecology, impact economic activities and cause diseases in humans.

Purpose of this study is to develop an efficient and economical technology to treat BW in order to meet the International Maritime Organization (IMO) guidelines for discharging BW. A reactor consisting selected electrodes to produce disinfection agents such as active chlorine and free radicals was developed and used in this study. E. coli, an IMO regulated microorganism, is chosen as a model organism. Operational parameters such as hydraulic retention time (HRT) and applied current were optimized to achieve the desired level of E. coli disinfection, 250 CFU/100 ml, based on the IMO regulations. For this purpose, a series of experiments was designed statistically using a response surface methodology. It was found that, to achieve the IMO regulation for E. coli, HRT and current in the designed reactor are 30 seconds and 0.3 ampere respectively. The specific energy to be applied to gain the above reactor conditions is as low as 0.004 kWh/m3 of BW. Moreover, the disinfection efficiency is higher than 4 log and the total residual chlorine concentration is only around 1 mg/L under the optimized reactor parameters. The experimental results also imply that approximately 80% of killing of E. coli is due to the effect of active chlorine while 20 % is via other mechanisms such as free radicals. These results suggest that the developed electro-disinfection technology can be served to effectively disinfect E. coli in BW and the technology can be developed to an energy-efficient and effective option to treat BW.