Effect of CaCO3 particles and suspended bacteria on biofilm components and activity in the model recirculating cooling water system

Biofilms are a serious problem in industrial recirculating cooling water systems. Biofilm formation and properties are affected by many factors, such as inorganic particles and suspended bacteria. In this research a laboratory model recirculating cooling water system was applied to investigate the effects of CaCO3 concentration and suspended bacterial count on extracellular polymeric substances (EPS) content and dehydrogenase activity (DHA) in the attached biofilms. In addition, nutrient level was also the key factor when investigating the effect of suspended bacterial count. The results showed that EPS content and DHA first increased and then decreased with the increase of CaCO3 concentration from 0 to 200 mg/l. At the low nutrient level, with the increase of suspended bacterial count from 4.04 to 5.78 log(10) c.f.u./ml, biofilm EPS content decreased firstly and then increased. However, biofilm DHA always gradually increased. At the medium nutrient level, biofilm EPS content increased firstly and then decreased and DHA always gradually decreased when suspended bacterial count ranged from 4.04 to 5.78 log(10) c.f.u./ml. At the high nutrient level, biofilm EPS content and DHA both showed the increasing trend with the increase of suspended bacterial count. This work provides the basis and reference for management strategies in actual recirculating cooling water systems.