Treatment and treatability of hospital wastewaters.

In the last years, increasing attention has been paid to the presence of emerging pollutants in wastewaters, surface waters and groundwaters (Daughton and Ternes, 1999; Heberer 2002, Barcelò 2003, Daughton 2004). Emerging contaminants correspond in most cases to unregulated pollutants, which may be candidate for future regulation depending on research on their potential health effects and monitoring data regarding their occurrence. They include surfactants, pharmaceuticals and personal care products (PPCPs), endocrine disruptors, illicit drugs, gasoline additive.... Referring to pharmaceuticals, large amounts of different compounds are used worldwide and, in the last decade, their sales are continuously increasing (Kummerer, 2001; Ternes and Joss, 2006). After administration, the active substances of medicaments are metabolized, but only to some extent. The unmetabolized active substances are excreted in urine and faecis as unchanged substances, as a mixture of metabolites or conjugated with an inactivating compound attached to the molecule (Halling-Sorensen et al., 1998), thus entering in the water cycle. Hospitals are important sources for these compounds, but not unique. Residues of pharmaceuticals can be found in all wastewater treatment plant (WWTP) effluents, due to their inefficient removal in the conventional systems (Kummerer, 2001, Petrovic et al., 2003; Carballa et al., 2004, Onesios et al., 2009). A great variety of microcontaminants are present in hospital effluents resulting from diagnosis, laboratory and research activities from one side and medicine excretion by patients from the other side. They include active principles of drugs and their metabolites, chemicals, heavy metals, disinfectants and sterilizants, specific detergents for endoscopes and other instruments, radioactive markers, iodinated constrast media, ... Despite their specific nature, quite often, hospital effluents are considered of the same pollutant load of urban wastewaters (UWWs), so they are discharged into the sewer network, collected to a WWTP and cotreated with UWWs. Before immission into the municipal sewer, a chlorination is sometimes required for the whole hospital wastewater (HWWs) flow rate, sometimes only for the effluent from infectious disease wards (Emmanuel et al., 2003). The common practice of cotreatment of hospital and urban wastewaters at a municipal WWTP is not considerated an adequate solution by many Authors (among them Altin et al, 2003, Pauwels et al., 2006, Vieno et al., 2007) because it is based on dilution of different discharges and it does not provide a segregation/separation of pollutants, in particular of emerging contaminants and toxic substances from the liquid phase which than is discharged into the environment. The difficulties in removing micropollutants, in particular pharmaceuticals, from wastewaters are due to the fact that their concentrations are in the range 10-3-10-6 mg L-1, lesser than those of conventional macropollutants (BOD5, COD, nitrogen and phosphorus compounds...). Moreover, they include a broad spectrum of compounds with great differences in the main properties which affect their behaviour and fate in the WWTP: solubility, volatility, adsorbibility, absorbibility, biodegradability, polarity and stability. Municipal WWTPs were first built, then upgraded, with the principal aim of removing carbon, nitrogen and phosphorus compounds, as well as microbiological organisms: pollutants which regularly arrive at the WWTP in concentrations of the order of mg/L and at least 106 MPN/100 mL. Conventional treatments are not able to greatly remove also microcontaminants. Moreover, HWW flow rates generally amount to only a small percentage of the total influent flow rate for co-treatment at a municipal WWTP. Consequently, dilution of HWWs with UWws will result in a decrement of the PhCs content in the final effluent (from mg L-1 to ng L-1), but not in their load, that is, the quantity released daily into the receiving water body. In this paper, a comparison between quali-quantitative characteristics of hospital and urban wastewaters is carried out, based on an in-depth literature review. First water consumptions and wastewater production variation along the year are discussed for hospitals and urban settlements. Then chemical and physical characteristics of HWWs and UWWs are analized in terms of conventional macropollutants (BOD5, COD, SS, nitrogen and phosphorus compounds, E. coli,... ) as well as micropollutants (main pharmaceuticals, detergents, disinfectants). An overview of the sustainable treatment options for HWWs is presented and finally the main outlines of a study carried out on the characteristics and adequate treatments of HWWs are reported. In particular the management of the effluent in a specific case study at the large hospital complex (900 beds), near Ferrara, Northern Italy, is examined through an evaluation and comparison of the design alternatives for its treatment and the main outlines of the final approved project are presented.