Study of the activity of quaternary ammonium compounds in the mitigation of biofouling in heat exchangers–condensers cooled by seawater

Abstract

The effectiveness of two quaternary ammonium compounds (QACs) (non-oxidising biocides) to reduce the growth of biofilm adhering to the tubes of a heat exchanger-condenser cooled by seawater was evaluated. Their effectiveness was compared to that of a conventional oxidising biocide (sodium hypochlorite [NaOCl]) under the same testing conditions. Each biocide was applied intermittently (6 h on, 6 h off) in a first shock stage (1.5 ppm over 8 days) and a second stabilising stage (0.5 ppm over 20 days). The results showed that the antifouling effectiveness of the first of the QACs (fifth generation) was comparable to that shown by the oxidising power of NaOCl. Although the reaction time was longer than that of NaOCl, both the compounds removed the biofilm, and the tube was practically restored to its clean condition. Treatment with the second of the QACs (fourth generation) allowed for the stabilisation of biofilm growth, but not for its removal. Ecotoxicology studies classified the QACs as environmentally harmless under the testing conditions.

The effect of electromagnetic fields on biofouling in a heat exchange system using seawater

“…The concentration of dissolved solids was 4.7 mg cm −2 , of which 74% was inorganic matter and 26% was organic matter (Figure 4). As in previous experiments (Eguía et al 2008;López-Galindo et al 2010;Trueba et al 2013), these results demonstrated that the hydraulic-thermal conditions in the untreated heat exchanger favour the formation of biofouling on the internal surfaces of the tubes. Therefore, the effectiveness of AF treatment using EMFs could be assessed under stringent conditions.…”

“…Measurements were taken at the end of the experiment (shutdown of the plant was necessary) using a test tube of known dimensions and weight placed at the outlet of each tube in a test tube holder system described by . The biofilm thickness was calculated in accordance with Equation 1 (Trueba et al 2013).…”

“…The fluid frictional resistance (f [dimensionless]) was calculated using Equation 2 (Trueba et al 2013).…”

“…When selecting an AF method, it is important to consider the nature of the microorganisms, the thermo-hydraulic conditions of the process, treatment costs, security guidelines and environmental impacts (Eguía et al 2008). Chemical AF methods include oxidising ) and non-oxidising biocides (Trueba et al 2013); physical AF methods can involve electronic technology (Cho & Choi 1999), electric fields (Abou-Ghazala & Schoenbach 2000), ultrasound (Bott 2001), magnetic fields (Fathi et al 2006), reverse flow (Eguía et al 2008), ultraviolet light (López-Galindo et al 2010, and heat treatment (Rajagopal et al 2012); there are also biological AF methods (Dobretsova et al 2013).…”

The ability of an antimicrobial agent to penetrate a biofilm is not correlated with its killing or removal efficiency

“…The mechanism of action of cationic surfactants (BAC, BDMDAC and CTAB) is the same as the general mechanism of QACs. The hydrophilic headgroup of QACs is adsorbed to the cell wall and reacts with the cytoplasmic mem-brane, allowing the release of intracellular constituents (Salton 1968;Ferreira et al 2011;Trueba et al 2013). The strong affinity of CTAB for the protein and lipid components of the membrane suggests that this QAC is spent before it reaches the under-layers of the biofilm (Simões et al 2006).…”