Analysis of metals and EOX in sludge from municipal wastewater treatment plants: a case study.

The monitoring of extractable organic halogen (EOX) and heavy metal contents in sludge coming from 10 different municipal wastewater treatment plants (MWWTP) located in Friuli Venezia Giulia (Italy) is reported. In this work, sludge samples drawn from sludge treatment units have been digested and analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for metal evaluation. Samples were also extracted and analyzed by microcoulometric titrations, following modified DIN 38414 T17 standard, for EOX analysis. Analytical results showed a slight enrichment of the contents of certain metals (Cd< 2mg/kg, Cr< 51.5mg/kg, Cu<105.8 mg/kg, Hg<1.4 mg/kg, Ni<35.9 mg/kg, Pb<58.7 mg/kg, Zn<410.1 mg/kg, Ba<317.1 mg/kg, Co<1 mg/kg, Mo< 5 mg/kg, Mn<106.7 mg/kg), so almost all of the sludge would be suitable for agricultural use following Italian and European regulations. The evaluation of EOX was carried out by using hexane and ethyl acetate as extraction solvents, and a measurable organic halogen content (ranging from 0.31 to 39.5 mg Cl/kg DM) was clearly detected in the sludge. The lowest concentrations of EOX were found in sludge coming from the smallest MWWTPs, which is to be considered more suitable for agricultural use. Additionally, analytical assays on composts, peat and soils were performed to compare EOX concentrations between these matrices and sludge.

Evaluation of chlorinated by-products in drinking waters of Central Friuli (Italy).

Drinkable water supplied by aqueducts undergoes preliminar potabilization which, in Italy, is mainly accomplished by chlorine addition. The bactericidal action involved in this process is always accompanied by chlorination and oxidation of organic species (mainly humic and fulvic acids) naturally present in treated waters, so that many disinfection by-products (DBPs) are formed, such as trihalomethanes (THMs) and halo-acetic acids (HAA), which can represent a chemical risk for public health. The aim of this study was the monitoring of DBPs in drinking water disinfected by chlorination, supplied by four different aqueducts of Central Friuli (Italy). DBP evaluations were performed in water samples consisting of both input and output of disinfection plants. The results of analytical determinations were worked out to provide the THM and HAA parameters for disinfected waters, while in feeding waters the following different conventional parameters were adopted: (i) trihalomethanes formation potential (THMFP), (ii) halo-acetic acids formation potential (HAAFP) and (iii) UV absorbance at 254 nm (UV254). The quite moderate content of chlorinated products found in all samples considered highlighted the excellent quality of potabilized waters available in Central Friuli. Moreover, our results confirmed that the majority of DBPs formed when chlorine is used for water disinfection consists of THMs, while chlorites and chlorates prevailed when potabilization is accomplished by using chlorine dioxide. Finally, simple UV254 monitoring turned out to be a profitable approach for the determination of chlorinated by-products only when THMs prevail among DBPs.

Salt-assisted thermal desorption of mercury from contaminated dredging sludge.

In this study, we tested a new procedure for the decontamination of mercury-polluted dredging sludge (Marano-Grado Lagoon, northeastern Italy) based on cationic exchange associated with thermal desorption at a low temperature. Four mercury-polluted sludge slurries were treated using thermal desorption at 393 K for 2h. Three different salts, NaCl (sodium chloride), (CH(3))(4)NCl (tetramethylammonium chloride) and (C(4)H(9))(4)NCl (tetrabutylammonium chloride) were used as exchangers. The selected salts have a monovalent cationic part that progressively increases in molecular weight. The results show that the association of cationic exchange with thermal treatment leads to a significant improvement in the removal of mercury from the contaminated material at a low temperature compared to samples that were not treated with salt. The highest levels of decontamination were attained were obtained when the slurries, which had mercury pollution ranging from 20 to 200 ppm, were treated with a 15% solution of (C(4)H(9))(4)NCl. The efficiency of the removal at 393 K (from 24% up to 60%) depended on the nature of the sample. When the samples were treated at a similar temperature without the salt, no remediation of mercury was detected. Our results show that the thermal decontamination temperature can be significantly lowered by this remediation approach, which is the first example based on cationic exchange of the pollutant with an appropriate salt.