Microbial contamination of the air at the wastewater treatment plant

VITĚZOVA, M. , VITĚZ, T, MLEJNKOVA, H. , LOSAK, T. : Microbial contamination of the air at the wastewater treatment plant. Acta univ. agric. et silvic. Mendel. Brun. , 2012, LX, No. 3, pp. 233–240 Wastewater treatment plants (WWTPs) primarily serve to protect the environment. Their task is to clean waste water from the agglomerations. On the other hand wastewater treatment plants can also negatively aff ect the environment in their neighbourhood. These include emissions of odour and microorganisms. This article discusses the microbial contamination of the air, called bioaerosols in selected wastewater treatment plant for 18 000 p.e. From results of the work is evident that the largest group of microorganisms in the monitored air were psychrophilic and mesophilic bacteria and microscopic fungi. The number of psychrophilic bacteria ranged from 14 to 12 000 CFU/m3 (colony forming units in 1 m3), the number of mesophilic bacteria varied in the range from 20 to 18 500 CFU/ m3 and the fungi from 25 to 32 000 CFU/m3 in the air. The amount of actinomycetes ranged from 1 to 1 030 CFU/m3 and faecal coliform bacteria from 0 to 2 500 CFU/m3. Furthermore, it was confi rmed that the highest air contamination was around the activation tank, area for dewatered sludge and around the building of mechanical cleaning, depending on the season. The density of studied microorganisms correlated with air temperature. wastewater treatment plant, microbial air contamination, bioaerosol, bacteria Wastewater treatment plant may aff ect the environment in many diff erent ways, according to its basic parameters. These are mainly the size of wastewater treatment plant, technology used, machinery used and treating method used. One of the most important contaminants in the wastewater treatment are bioaerosols, which may contain diff erent types of microorganisms (Brenner et al., 1988; Fracchia et al., 2006). Bioaerosols are generated from the bursting bubbles produced by the aeration systems, which provide oxygen for the biodegradation processes. These bioaerosols may contain bacterial, viral and fungal species (Gerardi and Zimmerman, 2004; Fannin et al., 1985), and may cause potential health hazard for workers of wastewater treatment plants. A signifi cant risk is also posed by microbial allergens and endotoxins (Rylander, 1999; Thorn et al., 2002). The highest emission of bioaerosols are at the sites of pretreatment and the primary clarifi ers, as well as those sites containing moving mechanical equipments for water aeration (Pascual et al., 2003). Dose response relationships have not been established for most biological agents and knowledge about threshold values is sparse. In the Czech Republic there is only CSN P CEN/TS 16115-1 Ambient air quality – Measurement of bioaerosols – Part 1: Determination of moulds using fi lter sampling systems and culturebased analyses. The goals of the present study were to determine the degree of bacterial contamination of bioaerosols generated by wastewater treatment plant, determine the presence of fungi and bacteria. MATERIAL AND METHODS Sampling and weather condition characterisation To determine the microbial contamination of bioaerosols mechanical-biological wastewater treatment plant for 18 000 p.e. in the effl uent fl owing from a single sewer system was selected. Description of wastewater treatment plant and location of measurement points is shown in Fig. 1. 234 M. Vitězova, T. Vitěz, H. Mlejnkova, T. Losak At the selected wastewater treatment plant three sampling points (I–III) marked in Fig. 1 were defi ned. Point I was placed at the sand catcher and screens object (c, d) and (d), point II was placed near to the activation tank (f), point III was placed at the area for dewatered sludge (i). Control point IV for the estimation of the contamination the neighbouring air (background) was placed 150 meters from wastewater treatment plant and its placement depended on the prevailing wind direction in the collection time. The air sampler MAS-100 (Merck, Germany) was situated at individual locations at a height of 1.5 m above the earth’s surface. Strictly determined air volume was sucked directly onto Petri dish with agar medium placed in the sampler. Sampling rate was 1.6 dm3/s. The volume of the air passed through the air sampler was elected to the expected contamination of the air and ranged from 100 dm3–1 000 dm3. Air sampling was conducted from January to December 2010, by measurement conditions listed in Tab. I. Data on weather conditions (particularly wind speed) are of great importance due to the spread of microorganisms both the WWTP site, but also in its surroundings. Sampling was performed in three replications. N b c