Analysis of Possibility of Using the Process of Photocatalysis for Disinfection of Municipal Wastewater

The supply of clean, safe drinking water is of paramount importance for the country. It would seem that the massive use of the equipment for the chlorination of water and wastewater in the twentieth century would finally end the era of epidemic and pandemic diseases having their base in water contaminated by bacteria found in the feces of humans and animals [5], [10]. The reality, however, is different. The last epidemic in Germany in 2011, caused by a strain of Escherichia coli 0104 (EHEC) killed 48 people out of more than 4,000 who fell ill. Protozoa of the Cryptosporidium genus were responsible for approximately 400 000 cases during the epidemic in Milwaukee (Wisconsin, USA) in 1993 [7], [11]. The subject of pure, drinking water is most frequently mentioned in the category of disinfection. Very few people in Poland, as well, around the world, see the need for the proper purification, but also disinfection of wastewater. There are no strict guidelines defining the bacteriological quality of the wastewater coming from sewage treatment plant to the receiver. However, the rules determining the bacteriological requirements concerning e.g. bathing areas [12] are already being created. Regulation of the Minister of Health on the supervision over the quality of bathing water and the sites used for bathing contributed to the closure of a number of bathing sites throughout the country.In the region of Malopolska, out of 44 bathing areas being in the records of the State Sanitary Inspectorate in 2010, after the introduction of the new rules only one remains [3], [4]. The specific bacteriological requirements determining the allowable number of Escherichia coli bacteria had a great influence on the reduction of the number of bathing areas. This single provision cased the loss of many jobs, reduced the income of the municipalities and cities and stopped the development of tourism in the region. The problem of the bad sanitary state of water bodies should be resolved in the locations of the emergence of contamination, i.e. before the introduction of wastewater into the receiver. The treated wastewater must comply with the physico-chemical requirements to reduce its impact on the eutrophication of water [2] and to prevent it from presenting a toxic threat to the environment. Water Law [18] does not take into account the microbiological hazards, posed by the not disinfected municipal wastewater leaving the treatment plant [19]. And the risk is high. Wastewater carries a diverse mix of bacteria, viruses and protozoa coming from human or animal gastrointestinal tracts. These organisms are characterized by a high resistance to environmental influences and, in some cases, indicate a high degree of pathogenicity. In order to counteract the bacteriological contamination of the water bodies, particularly in the USA the chlorination of waste water is used. It must, however, be combined with the process of dechlorination. Otherwise, the effects of chlorination would be worse than the introduction of undisinfected wastewater. Studies indicate high toxicity of even dechlorinated wastewater [14]. In addition, during the disinfection various by-products of chlorination are formed [9]. However, the process of chlorination coupled with the subsequent dechlorination is the most frequently used process in wastewater treatment plants in the United States [16]. Various types of chlorine compounds are most often used for the disinfection of treated wastewater. Among them can be mentioned: sodium hypochlorite, calcium hypochlorite, chlorine dioxide and, of course, chlorine gas [11].