Ottimizzazione dello smaltimento di filtri esauriti e fanghi generati in impianti trattamento di acque potabili ricche di arsenico

Responsabili di progetto

Barbara Casentini, Biswajit Ruj

Accordo

INDIA - CSIR-expired - Council of Scientific and Industrial Research

Bando

CNR-CSIR 2016-2018

Dipartimento

Scienze del sistema terra e tecnologie per l'ambiente

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Stato del progetto

Nuovo

Proposta di ricerca

Arsenic (As) concentration in distributed drinking water exceeding the proposed safe limit of 10 µg/L (WHO) are often registered in South East Asia, especially West Bengal region, and some countries in Europe, Italy included. In India groundwater arsenic contamination was first reported from the state of West Bengal in 1983. The problem of arsenic contamination in ground water is known to have affected a population of about 50 million in different districts of India. Consumption of ground water with As >50 ¼g/L (Indian limit) in certain wells over a prolonged period of time has resulted in serious health hazards, especially among the rural and semi-urban population in these regions. Until 2010, in Italy more than one million of people were still drinking water with As >10 µg/L (EU limit)). In Italy it is not allowed anymore to distribute drinking water containing above 10 µg As/L since 2013. Therefore, many water treatment plants have been recently installed.
Given the increased application of arsenic removal technologies in response to more stringent regulations it can be expected that greater quantities of As-bearing waste will be generated. Up-to-date most successfully implemented removal technologies are coagulation and co-precipitation with addition of Al and Fe salts; sorption on filters (Activated Alumina, Granular Iron Hydroxides, Iron Coated Sand and Ion Exchange Resin); membrane filtration (Reverse Osmosis). Currently the disposal of arsenic rich sludge generated from the treatment processes includes landfilling, stabilization, cow dung mining, passive aeration, pond disposal and soil application. Management of As-rich sludge is one of the issues that has received little attention from vendors of the technologies and also from the users, especially in low income countries. Solid arsenic concentration in Iron filters varies greatly and reported range is 1-80,000 mg/kg. Usually, concentration is higher than 200 mg/m3. New frontiers in As-treatment technologies tend to commercialize filters with increasing adsorption capacity (>50 mgAs/gFe). So, there is a strong demand for development of environmentally safe and effective disposal methods for arsenic contaminated sludge out of water treatment system.
Evaluation of As-sludge leaching potential is often performed using chemical leaching procedures [Toxic Characteristic Leaching Procedure (TCLP) and Waste Extraction Test (WET)]. The crucial parameters to properly assess leaching behavior in actual landfill conditions were proved to be solution properties, test duration, experimental headspace and biotic processes.
In Italy waste produced by water treatment are disposed according to EU Directive 99/31/EC transposed into the National DM 27/9/2010 very recently modified by DM 24/6/2015. Waste produced by any water treatment plants are coded as CER 19 09 and classified as not hazardous. They can be directly disposed in landfill if compliant to the leaching test (As

Obiettivi della ricerca

The main objective of this research proposal is the development of processes to improve safe management of arsenic-rich waste generated from arsenic removal plant. Main activities will be focused on assessing environmental risks posed by As contaminated sludge disposal in landfill under simulated real conditions and possible safe recycle of exhausted filter materials.

Different sub-objectives are proposed by each unit that contributes to the overall development of a suitable management options both in Europe and in India.
In details:
- to review current regulations in As-sludge management both in India and Italy and highlight possible improvements needed for a safe long term disposal;
- to determine a long-term, permanent and safe process to solidify and stabilize arsenic-sludge (probably in the form of stable As-Ca precipitates) by using stabilizing agents and converting it into a beneficial products like bricks, concrete blocks, pavement tiles having commercial values used for different construction and development works;
- to assess leaching processes and long term stability of iron-hydroxide As-rich sludge mimicking different landfill conditions (influence of biotic and abiotic processes);
- to compare different leaching procedures on As-rich collected sludge to outline main differences and to assess As leaching potentials of exhausted filters.

Ultimo aggiornamento: 21/05/2024