Title : Experimental investigation on the effects of oxidizing and non-oxidizing biocides on microbial disinfection of cooling tower of Kangan Petro refining company
Abstract:
Cooling water systems play a crucial role in a wide variety of industrial processes, from large-scale power plants to smaller setup like air compressor systems in individual buildings. The excessive growth of microorganisms in cooling water system is a significant issue that can negatively impact system performance. To manage microbial growth in the cooling towers of industrial plants, both oxidative and non-oxidative biocides are utilized. The selection of a suitable biocide is determined by factors such as the type of cooling tower, water quality, and compliance with regulatory standards. In this scientific investigation, the impact of alerting the biocide injection regime- both oxidizing (Calcium hypochlorite) and non-oxidizing (Isothiazolinone and Glutaraldehyde) in continuous and intermittent modes was evaluated, with a focus on its effects on efficacy of microbial disinfection, chemical, and physicochemical properties in the open recirculating cooling tower of Kangan Petro Refining Company. In the batch mode, 1m3 of 8%wt. calcium hypochlorite solution was injected into 16000 m3 every 2 days and in the continuous mode, this solution (50 lit/h) was continuously injected to remain the amount of residual Cl2 in range of 0.2-0.5 ppmmol. The TBC of the water sample before oxidizing biocide was 104 cfu/ml. Following the injection, the parameter decreased to negative under both continuous and batch modes, However, in the continuous injection mode, the TBC exhibited greater stability and improved microbial control compared to the batch mode. In contrast, non- oxidizing biocides of Isothiazolinone and Glutaraldehyd were able to reduce the TBC parameter to 100 and 1000 cfu/ml, respectively. The physicochemical parameters, such as TDS, pH and electrical conductivity of cooling water, remain largely unchanged, indicating stable chemical conditions in both regimes. This confirms that altering the bleach injection method does not necessitate adjustments in chemical control. It is important to highlight that during the course of the study, the condition of the circulating cooling water was significantly influenced by hydrocarbon gas leakage of a heat exchanger, creating an environment highly conductive to microbial growth. Therefore, the experimental data and microbial control results obtained from this industrial-scale work, can be regarded as a highly valuable dataset for use in future scientific research.
