Inactivation of planktonic and biofilm cells by copper-based hybrid disinfection systems: Application to biofouling control on RO membranes

Abstract

Development of biofilm is easily found in any moist environment, and it causes a number of problems, especially financial losses in the industrial field, when it occurs in undesired places, such as membranes, heat exchanger systems, ship hulls, and drinking water distribution systems. In particular, the formation of biofilm on the membrane surface (biofouling) is one of the biggest challenges to the performance of the reverse osmosis (RO) process. In this dissertation, three different types of copper-based disinfection systems including oxidative disinfectants, biocides, and signal molecule were investigated to control biofilm formed on RO membrane. The first part of the dissertation investigates combinations of Cu(II) with hydroxylamine (HA) and hydrogen peroxide (H2O2) (i.e., Cu(II)/HA, Cu(II)/H2O2, and Cu(II)/HA/H2O2 systems) for the control of Pseudomonas aeruginosa biofilms on RO membranes. These Cu(II)-based disinfection systems effectively inactivated P. aeruginosa cells, exhibiting different behaviors depending on the state of bacterial cells (planktonic or biofilm) and the condition of biofilm growth and treatment (normal or pressurized condition). The Cu(II)/HA and Cu(II)/HA/H2O2 systems were the most effective reagents for the inactivation of planktonic cells. However, these systems were not effective in inactivating cells in biofilms on the RO membranes possibly due to the interactions of Cu(I) with extracellular polymeric substances (EPS), where biofilms were grown and treated in center for disease control (CDC) reactors. Differ from the results using CDC reactors, in a pressurized cross-flow RO filtration unit, the Cu(II)/HA/H2O2 treatment significantly inactivated biofilm cells formed on the RO membranes, successfully recovering the permeate flux reduced by the biofouling. The pretreatment of feed solutions by Cu(II)/HA and Cu(II)/HA/H2O2 systems (applied before the biofilm formation) effectively mitigated the permeate flux decline by preventing the biofilm growth on the RO membranes. The second part of the dissertation utilizes the copper-based system (Cu(II), Cu(II)/HA), which is known as an effective biocide, with norspermidine (Nspd) as a disassembly reagent to control biofilm formed on membrane, and evaluates its potential as a cleaning reagent for biofouling control. Combination with Nspd results in improved inactivation efficacy of the copper-based system in biofilm. In particular, the Cu(II)/HA/Nspd (2.0 log in 10 min) system showed significant enhancement compared to the Cu(II)/HA system (4.2 log in 5 min). The results indicated that disruption of EPS by Nspd contributed to higher penetration of copper rather than detachment of cells under the applied conditions. Furthermore, our finding showed that the combined system is applicable in practical conditions (under pressurized condition) with capable biofilm inactivation efficacy, and a valid degree of permeate flux recovery was also observed, approving the feasibility as a cleaning reagent for biofouling control. The third part of the dissertation assesses the biocidal effects of the Cu(II)-activated persulfate in the presence of chloride ion (i.e., PMS, Cu(II), Cu(II)/PMS, PMS/Cl-, and Cu(II)/PMS/Cl- systems) on planktonic and biofilm cells, and evaluates the feasibility of these disinfection systems in the RO desalination process. The SO4˙− was found to be the main produced oxidant via the Cu(II)-activated persulfate system. In addition, the production of sulfate radial likely occurred close to bacteria cells where the Cu(I) was interred, and the produced bacteria-bound sulfate radical would directly damage P. aeruginosa cells. The enhanced inactivation efficacy in the Cu(II)/PMS/Cl- system was attributed to the production of reactive species by a dual mechanism through the Cu(II)/PMS system and the Cu(II)/in situ production of HOCl system.