Aquatic Invasive Species

Water heating has been determined to be an effective ballast water treatment method; however the method has major limitations one in particular being the heating time required for efficiency.  Laboratory results have showed that conventional water heating requires a temperature of at least 35 ⁰C for 20-80 hours to be effective. However a novel technique, short-time technique, only requires temperatures between (40- 65 ⁰ C ) for 15 hours has been effective.

Quilez-Badia from the University of Newcastle upon Tyne, et al.(2008)  conducted  a  field study short-time high temperature under operational conditions, with the aim of monitoring the method’s effectiveness at removing bacteria, phytoplankton and zooplankton.

According to Badia et al.(2008) the results indicate that running the water through the pump system installed in the short-time method increased the  mortality rate of the microorganisms, but increasing the temperature above 55⁰C did not improve the efficiency of the short-time heat treatment.

Source: Marine Poll Bull 2008, 56(09) 1093-1097 DOI:   10.1016/j.marpolbul.1037.2007.09.036

Ballast water is a major vector for transporting aquatic alien species and The International Marine Organization (IMO) has implemented new international regulations to treat ship’s ballast water (BW) before discharge. One potential treatment is electrolysis; however electrolysis can corrode the interior of ballast tanks. Dr. Guangzhou Lui et al from Zhejiang University, Chemistry Department, China are analyzing the effects of electrolysis on Q235 steel.

Using four different concentrations of total residual chlorine (TRC) (0,5,10,20 mg/L) on Q235 steel, the group analyzed TRC’s effect on Q235 to determine which concentration will remain effective at treating ballast water without corroding the metal. The TRC was analyzed using electrochemical impedance spectroscopy. Concentration levels of 5 and 10 mg/L enhanced the corrosion of steel while 20mg/L TRC inhibited the corrosion

Dr Lui et al concluded that electrolysis which result in TRC levels greater than 10 mg/L is more efficient on alien species and these TRC levels are not detrimental to the ship’s structural integrity.

 Source: Acta Metall Sin 2010, 46(09) 1093-1097 DOI:   10.3724/SP.J.1037.2010.00239