A New Approach for Mitigating Biofouling by Promoting Online Cleaning Using a Sacrificial Paraffin Coating

Abstract

The presence of biofouling layers on heat transfer surfaces can reduce heat transfer efficiency markedly. A new method for inhibiting biofouling growth and promoting rapid online cleaning for heat exchangers recovering thermal energy from treated sewage streams based on a temporary coating is reported. A paraffin wax coating is cast in place without needing to disassemble the device, while the low roughness and the hydrophobicity of the coating inhibit bacterial growth. The coating and any attached biofouling can be removed by raising the surface temperature above the wax melting point. The effectiveness of this online cleaning and inhibition strategy was investigated using a simple laboratory test channel, representing a plate heat exchanger, and a process stream simulating treated sewage. The thermal resistance was monitored and showed that the reduction in biofouling thermal resistance eventually outweighed the additional thermal resistance resulting from the coating. A techno-economic analysis is presented to quantify the advantages of the paraffin coating method in terms of energy saving and cost reduction.

Using Thermal Shock to Inhibit Biofilm Formation in the Treated Sewage Source Heat Pump Systems

“…Previous studies [11,41] have shown that the thermal resistance of the biofilms were linearly correlated with the biofilm thickness and the wet weight. In this study, the thermal resistance is of the main interest and the wet weight of the biofilms, instead of the cell count or the dry biomass, was measured.…”

“…However, the high bacterial concentration and the rich nutrient environment in the treated sewage cause biofilm formation on the stainless steel plates in the plate heat exchangers [9][10][11], which are important components in the TSSHPS to transfer heat from the treated sewage to the clean working medium due to their compactness and high thermal efficiency [12]. Biofilms reduce the heat transfer coefficient of the heat exchangers and the coefficient of performance of the whole heat pump system.…”

“…Due to the enclosed environment of the plate heat exchangers, external biofilm-inhibition forces, such as gas discharge plasmas, would be difficult to be used. Additonally, as the treated sewage is in large flow rate and drained to nearby rivers after the heat transfer process, the application of chemical and biological antimicrobial agents is limited due to the large consumption and environmental protection concerns [11].…”