Inhibition Of Biofouling Aimed At Mitigating Heat Transfer Deterioration

Treated sewage is in huge quantity and its temperature?20-25°C in summer and10-15°C in winter?is ideal for maintaining a high efficiency for heat pump operations.Treated sewage source heat pump systems?TSSHPS?can reuse the low-rank energy in the treated sewage.However,the biofouling in the heat-exchangers in the TSSHPS would decrease the efficiency and security of the systems and prevent the systems from being widely used.This study focuses on the inhibition of the biofouling caused by the treaed sewage.The mechanisms of the biofouling formation,the effects and mechanisms of several physical and chemical biofouling inhibition strategies have been investigated,and the biofouling inhibition effects of several strategies have been evaluated based on their performance of mitigating the heat transfer deterioration in the heat exchangers.In this study,a mechanism experiment system and a heat transfer experiment system were designed,and model sewage was prepared,based on the microbiological practices,to simulate the treated sewage for biofouling formation.Analyses in both macro-and micro-levels were used in this study to investigate the mechanisms of biofouling formation and inhibition.Several water quality parameters and environmental parameters were investigated in the biofouling formation mechanism experiments to understand their influences on biofouling growth,and it was found that the biofouling growth was enhanced as the bacteria concentration,the nutrient concentration and the concentration of Ca²⁺increased,and the biofouling growth was inhibited as the concentration of Mg²⁺increased.The mechanisms of these parameters in the biofouling growth were investigated.Furthermore,based on the results in the biofouling formation experiments,it was proposed that inhibiting the bacteria settlement and decreasing the number of bacteria cells were critical in biofouling inhibition.Physical biofouling inhibition strategies,including micro-patterned surfaces and thermal shocks were investigated.It was found that micro-patterned surfaces with small pattern sizes could inhibit the bacteria settlement and the subsequent biofouling formation.Thermal shock could inactivate the bacteria cells in the biofouling and inhibit biofouling formation,and the bactericidal effect and biofouling inhibition effect of thermal shock were enhanced as the temperature and exposure time increased.Chemical biofouling inhibition strategies,including benzalkonium chloride immersion and sodium hypochlorite immersion were investigated.It was found that the immersion schemes influenced the biofouling inhibition effect signifantly and the bactericidal effect and biofouling inhibition effect of benzalkonium chloride were enhanced significantly as the immersion temperature and the concentration of benzalkonium chloride increased.Additionally,the two different mechanisms of benzalkonium chloride immersion and sodium hypochlorite immersion were investigated.Aimed at practical applications,the biofouling inhibition effects of thermal shock and benzalkonium chloride immersion were investigated,and their influences on the thermal resistance caused by biofouling were analyzed.It was found that parameters such as benzalkonium chloride concentration and thermal shock temperature had significant influences on the biofouling inhibition effects.It was proposed that thermal shocks with high temperatures and short exposure times and benzalkonium chloride immersions with high concentrations and short cleaning times were biofouling inhibition strategies that possess practical application potentials.This study contributes to understanding the mechanisms of the biofouling formation and inhibition,and provides guidances for selecting biofouling inhibition strategies in practical applications.