Abstract-The aim of the study was to determine the effectiveness of in-situ-formed monochloramine for the control of Legionella growth in a real cooling tower system. The cooling tower utilizes an industrial water (makeup) made of by blending industrial raw water and decarbonated raw water. A generator device injecting in-situ-formed monochloramine into the cooling system was installed. The detection of Legionella, heterotrophic plate count (HPC -22°C) and continuous monitoring of oxidation reduction potential (ORP) were carried out to check the efficacy of monochloramine. Water samples were monthly collected for 6 months from the makeup, two collecting basins and the blow-down. Monochloramine was injected at 4 mg/L for 60 days to achieve a mean residual concentration of 0.145 mg/L in the blow-down. Over time, at the same pumping rates, a greater monochloramine residual was achieved so the dosage was decreased at 2.5 mg/L. L. pneumophila (SG 7-14) decreased from an initial load >10.000 cfu/L to undetectable levels and remained stable till the end of the experimental period while HPC decreased slowly (mean count <10.000 cfu/ml) after the first 60 days. From an initial value of 300-400 mV during the first 60 days, the ORP dropped to around 150 mV, which rather explains why monochloramine residuals in the blow-down increased at the end of the experimental time. The results indicate that insitu-formed monochloramine can control Legionella and HPC growth in industrial cooling towers using industrial raw water and decarbonated raw water. Moreover, the ORP can be useful for monitoring the effectiveness of monochloramine. Keywords: legionella sp.; in-situ formed monochlorammine; industrial cooling tower. # I. Introduction ooling towers have been consistently attributed to community-acquired legionellosis outbreaks (Engelhart et al. 2007;Yu 2008) because Legionella emitted by contaminated cooling towers can be transported over several kilometers within respirable vesicles (Walser et al. 2013). Typical operating conditions maintained in a cooling system, such as temperature range, pH as well as continuous airflow, make it ideal for biological growth or biofouling. In cooling towers biofouling can interfere with normal system operation (for example, heat transfer resistance) and it can also enhance corrosion and scaling problems, which may be critical risk factors for Legionella growth together with stagnant water and nutrient availability in the makeup water (Ludensky 2005). Thus, in order to minimize the production of contaminated aerosols by Legionella it is necessary to minimize microbial multiplication. Due to its low cost and high effectiveness, chlorine is the most used biocide as antifouling agent in cooling towers (Nebot et al. 2007;Rubio et al. 2015). However, it is highly reactive with natural organic matter contained in water -especially when the cooling tower utilizes wastewater as makeup water (Hsieh et al. 2010;Li et al. 2011a) -leading to the formation of by-products such as trihalomethanes or haloaceto-nitriles which can have adverse impact on human health and ecosystems (Schwarzenbach et al. 2006;Nieuwenhuijsen et al. 2000). In cooling water bromine is less effective than chlorine against L. pneumophila. Nonetheless, with continuous or semi-continuous low level dosing it can reduce and control Legionella populations as long as the residual concentrations are maintained in the circulating water (Thomas et al. 1999). Bromine is also used for the oxidation of biofouling but unfortunately it is toxic for the environment, in which it is released via blow-down water (Meesters et al. 2003). Among the oxidizing agents, monochloramine seems to be the most materials respectful and to produce the lowest concentration of by-products in drinking water (Melada et al. 2015). It is also more effective for decreasing Legionella within the biofilms in drinking water systems (Coniglio et al. 2015) and even at concentrations as low as 1 ppm it is able to penetrate complex biofilm matrixes like that in cooling towers (Turetgen 2004;van Schalkwyk et al. 2010). It has been demonstrated that in the presence of organic nitrogen compounds, like in cooling systems employing secondary-treated municipal wastewater as makeup water, adding pre-formed monochloramine to reduce biological growth of Legionella species is better than forming monochloramine in-situ (Chien et al. 2012). Moreover, pre-formed monochloramine was found to be Year 2 015 less aggressive than free chlorine, while still being an effective biocide (Li et al. 2011b). Thus, as far as we know, at the moment there are few studies on the effectiveness against Legionella of in-situ-formed monochloramine in cooling systems. For this reason, in the present study the effectiveness of in-situ formed monochloramine was evaluated for its ability to control biological growth in a cooling system. # II. Materials and Methods A cooling tower system of an Italian industrial plant was considered. The cooling tower system studied has a flow rate of 270-300 m 3 /h of recirculating cooling water, an average of 6-10 m 3 /h of makeup water and a water evaporation of about 4 m 3 /h. The water lost by evaporation is reintegrated with an industrial water (makeup water) made of by blending industrial raw water and decarbonated raw water. A drawing of the cooling system is depicted in Figure 1. # Figure 1: A drawing of the cooling system Prior to the application of monochloramine, to minimize biofouling, the water of the cooling circuit was successfully decontaminated via continuous disinfection with bromine at low levels (assuring a residual concentration of free chlorine of ~ 0.1 ppm) added with a scale and corrosion inhibitor. To prevent legionellae growth additional periodic chlorine shock was made with 5 ppm free chlorine for 5h. In order to verify the effectiveness of in-situ formed monochloramine for the control of Legionella growth in the cooling tower considered for the study, on July 2014 the injection of bromine was stopped and water samples were collected every 15 days till the detection of Legionella (> 100 cfu/L). When, on September 2014, L. pneumophila SG7-14 was recovered in the cooling tower (makeup water, the two collecting basins and the blow-down) at high concentrations (>10.000 cfu/L), a patented generator device continuously injecting in-situ-formed and heterotrophic plate count (HPC) at 22°C was carried out to check the efficacy of the water treatment with insitu formed monochloramine. The makeup water and water samples taken from the cooling tower collecting basins and the blowdown were collected weekly from September 2014 to March 2015. At the time of each sampling, the cooling system was operating. As shown on Table 1, for the makeup water and the blow-down physical and chemical parameters (DPD Free and Monochlor-F methods, Nitriver and Nitraver, HACH Company, USA) were determined. For Legionella determinations, 1L water samples were collected, taking care to gently resuspend the fluffy sediment at the bottom of the collecting basins. Effectiveness of in-Situ Generated Monochloramine for the Control of Legionella in a Real Industrial Cooling Tower monochloramine into the cooling system was installed. A regular testing program for the detection of Legionella suggestive for Legionella were confirmed on the basis of cultural testing and serogrouped by slide agglutination using commercial antisera (Oxoid and Biogenetics). Results were expressed in cfu/L and the counts referred # *oxidation reduction potential The biocide effect of monochloramine towards Legionella and HPC is shown on Figure 2. At the beginning of the disinfection program, one week after the continuous injection of monochloramine, the load of L. pneumophila SG7-14 decreased at undetectable levels, with the exception of the makeup water, where Legionella was recovered at a concentration of 200 cfu/L. Effectiveness of in-Situ Generated Monochloramine for the Control of Legionella in a Real Industrial Cooling Tower to water samples concentrated 100 times (1L in 10 ml of the water sample). The detection limit of the culture procedure was 10 cfu/L. The HPC at 22°C was detected in accordance with ISO 6222 (International Standard Organization 1988) to provide information on the disinfection process with monochloramine. For HPC, 100 ml of water were sampled. Sampling bottles for Legionella and HPC were steam sterilized and contained sufficient sodium thiosulfate to neutralize chlorine. All samples were stored at 4°C and analyzed within 12 h. # Global Journal of Medical Research # III. Results and Discussion After the start of the cooling water in-situ monochloramination, a total of 32 water samples were monthly collected for 6 months from the same sites of the cooling tower: the makeup, the two collecting basins (named BASIN 1 and BASIN 2, respectively) and the blow-down. An interesting phenomenon was observed when the response of monochloramine residuals was tracked over time. As shown on Table 1, at the beginning of the experimental period monochloramine had to be injected into the cooling water system at an average concentration of 4 mg/L for about 60 days in order to achieve a mean residual concentration of 0.145 mg/L in the blow-down. Over time, at the same pumping rates, a greater monochloramine residual could be achieved. For this reason, subsequently the dosage was regulated to obtain a continuous concentration of 2.5 mg/L monochloramine. We attributed this increase in residual to at least two main reasons: i. the monochloramine biocide effect towards Legionella, and ii. the monochloramine reaction with biofilm constituents that probably bromine could not get to. Year 2 015 Further analyses showed that in the makeup water entering the cooling system Legionella was absent, while the bacterium was isolated by means of swabs in the tap from where the makeup water had been collected, showing that it was a local contamination instead of makeup water contamination. In fact, two weeks after the sanitization of the tap and the monochloramination of the entire cooling system, the load of Legionella decreased at undetectable levels also in the sampling site of the makeup water and remained stable in all the sampling sites till the end of the experimental period. On the contrary, during the entire experimental period the HPC load decreased slowly, with a mean count ranging lower than 10.000 cfu/ml after the first 60 days. The interaction between monochloramine and the biofilm is probably confirmed by the minimal algae growth on the partially wetted structure of the cooling tower at the end of the experimental time. In fact, to get an idea of how well algae growth was being controlled, the cooling tower was visually inspected three times during the experimental time. As shown on Photographs 2 and 3, two months after the start of the disinfection program (Photograph 2) with monochloramine and at the end of the experimental period (Photograph 3) small amount of green algae growth was observed on collecting basins, much less than when bromine was used (Photograph 1). 3 shows the response of ORP with time during the entire experimental period. The monochloramine field trial and the continuous monitoring of ORP started on September 18 th , 2014. On November 13 rd , the probe was found incorrectly calibrated but it was recalibrated on November 20 th . Anyway, from an initial value of 300-400 mV during the first 60 days, the ORP dropped to around 150 mV, which rather explains why monochloramine residuals in the blow-down increased at the end of the experimental time. One week after the continuous injection of monochloramine, the load of L. pneumophila SG7-14 decreased at undetectable levels from an initial value >10.000 cfu/L and remained stable in all the sampling sites till the end of the experimental period. This data probably show that in-situ formed monochloramine can adequately control Legionella growth in industrial cooling towers using blended industrial raw water as makeup water. Nonetheless, the high load of HPC observed during the first 60 days, when residual concentrations of monochloramine were low and in turn ORP was high, probably suggests that at the beginning of the disinfection program some bacteria may require higher concentrations of the disinfectant to be completely killed. Anyway, our data suggest that ORP values and HPC measurements can play an important role in verification of treatment cooling tower procedures with monochloramine. Finally, our data show that monochloramine was effective also at controlling algae growth. In fact, comparison of visual inspections of the collecting basins (Photographs 1-3) showed a decrease in green algae growth at the end of the experimental period. This could also explain why as time passed the residual monochloramine concentration that could be achieved in the blow-down increased. ![Journals Inc. (US)](image-2.png "C") ![Isolation of Legionella was performed in accordance with standards procedures ISO 11731 (International Standard Organization 1988). Colonies Journals Inc. (US)](image-3.png "") ![Journals Inc. (US)](image-4.png "") 2![Figure 2 : The biocide effect of monochloramine towards Legionella and HPC](image-5.png "Figure 2 :") 101523![Photograph 1 : Visual inspection of the collecting basin -September 2014](image-6.png "Photograph 1 : 015 Photograph 2 :Photograph 3 :") 3![Figure 3 : The response of ORP with time during the entire experimental periodIV. ConclusionsThe primary objective of this study was to investigate the effectiveness of in-situ-formed monochloramine as a biocide to control Legionella and HPC growth in a cooling tower system employing treated industrial water as makeup water. In particular, the HPC and continuous monitoring of ORP were](image-7.png "Figure 3 :") 1MakeupBlow-downwaterNov 2014Nov 14Dec 14Jan 15Feb 15Mar 15Free chlorine (mg/l)0.020.040.040.020.030.09Total residual chlorine0.030.330.11(mg/l)Monochloramine0.000.350.230.170.110.38(mg/l)Ammomium ion (mg/l)0.000.080.130.090.060.08Nitrite (mg/l)0.0110.1210.2340.0660.1380.217Nitrate (mg/l)15.426.6100.821.326.831Chloride (mg/l)390320pH7.47.57.87.77.8Conductivity (?S)890172718701790ORP * (mV)174180160152 ## Conflict of interest statement Dr Stefano Melada, responsible for the Research & Development department of Sanipur Srl, contributed with a scientific and technical support necessary for the development of the management plan. He did not participate to the samplings of the water, isolation and identification of legionellae. No financial support was given to the authors. * Control of biological growth in recirculating cooling systems using treated secondary effluent as makeup water with monochloramine SHChien IChowdhury MHHsieh VADzombak RDVidic Water Res 46 2012 * Monochloramine for controlling Legionella in biofilms: how much we know? MAConiglio SMelada HMohamed Yassin J Nature and Science 1 e44 2015 * Hospital-acquired legionellosis originating from a cooling tower during a period of thermal inversion SEngelhart SPleischl CLück GMarklein SMartin ASimon MExner Int J Hyg Environ Health 211 2008 * Corrosion control when using secondary treated municipal wastewater as alternative makeup for cooling tower systems MKHsieh HLi SHChien JDMonnell IChowdhury VADzombak RDVidic Wat Envir Res 82 2010 * ISO (International Standard Organization) 1988. Water Quality Detection and Enumeration of Legionella ISO 11731 * ISO (International Standard Organization) 1988. Water Quality. Enumeration of Viable * Colony Count by Inoculation in or on a Solid Medium Microorganisms 6222 Geneva * Chlorination by-products in chlorinated cooling water of some European coastal power stations HAJenner CjlTaylor MVan Donk MKhalanski Mar Environ Res 43 1997 * Escalating water demands for energy production and the potential for use of treated municipal wastewater HLi SHChien MKHsieh VADzombak RDVidic Environ Sci Techn 45 2011a * Control of mineral scale deposition in cooling systems using secondarytreated municipal wastewater HLi MKHsieh SHChien JDMonnell VADzombak RDVidic Water Res 45 2011b * Microbiological Control in Cooling Water Systems. Directory of Microbiocides for the Protection of Materials: A Handbook MLudensky 2005 * Biofouling reduction in recirculating cooling systems through biofiltration of process water KphMeesters JWVan Groenestijn JGerritse Water Res 37 2003 * Monochloramine for Remediation of Legionella Only in Domestic Hot Water Systems: an Iron Fist in a Velvet Glove SMelada MAConiglio OJPM 5 2015 * Model for fouling deposition on power plant steam condenses cooled with seawater: effect of water velocity and tube material ENebot JFCasanueva TCasanueva DSales Int J Heat Mass Tran 50 2007 * Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review MJNieuwenhuijsen MBToledano NEEaton JFawell PElliot Occup Environ Med 57 2000 * Assessment of the antifouling effect of five different treatment strategies on a seawater cooling system DRubio JFCasanueva ENebot Appl Therm Eng 5 2015 * The challenge of micropollutants in aquatic systems RPSchwarzenbach BIEscher KFenner TBHofstetter CAJohnson UVon Gunten BWehrli Science 313 2006 * Laboratory observations of biocide efficiency against Legionella in model cooling tower systems WMThomas JEccles CFricker ASHRAE Trans 105 1999