Comparing a microbial biocide and chlorine as zebra mussel control strategies in an Irish drinking water treatment plant

A need exists for an environmentally friendly mussel control method to replace chlorine and other traditional control methods currently utilised in drinking water plants and other infested facilities. Zequanox® is a newly commercialised microbial biocide for zebra and quagga mussels comprised of killed Pseudomonas fluorescens CL145A cells. The objective of this study was to compare the efficacy of a developmental formulation of Zequanox (referred to as MBI 401 FDP) and chlorine treatments on adult and juvenile zebra mussels by running a biobox trial in conjunction with chlorine treatments at an infested Irish drinking water treatment plant. Since 2009, the plant management has used a residual chlorine concentration of 2 mg/L in autumn to control both adult zebra mussels and juvenile settlement in their three concrete raw water chambers. Juvenile mussel settlement was monitored in three bioboxes as well as in three treatment chambers in the plant for three months prior to treatment. Adult mussels were seeded into the chambers and bioboxes four days before treatment. In October 2011, the bioboxes were treated with MBI 401 FDP at 200 mg active substance/L, while chlorine treatment took place in the water chambers. The MBI 401 FDP treatment lasted only 8 hours while chlorine treatment lasted seven days. Juvenile numbers were reduced to zero in both the bioboxes and treated chambers within seven days. Adult mussel mortality reached 80% for both the chlorine and MBI 401 FDP treatment; however, mortality was achieved faster in the chlorine treatment. These results provided important insights into zebra mussel control alternatives to chlorine and supported further development of the now commercial product, Zequanox.