Rheological parameters are very important in sewage sludge management, not only as designing parameters in transporting, storing, landfilling and spreading operations, but also as controlling ones in many treatments, such as stabilisation and dewatering. To study how different treatments affect sludge rheological behaviour, research has been undertaken at CNR-Istituto di Ricerca Sulle Acque (CNR-IRSA), and the preliminary results are discussed in this paper. Sludge samples taken from three municipal wastewater treatment plants at different steps of treatment have been tested by a rotational viscometer and data interpreted through both Bingham plastic and Ostwald pseudoplastic models. Coefficients of those models have been then correlated to solids concentration. Results confirmed that solids concentration is the main parameter affecting sludge rheology and evidenced that a single parameter is not sufficient to represent the rheological behaviour, thus indicating that other parameters should be introduced and characteristics considered for a better understanding of the phenomenon.

No abstract

Sludge produced by municipal wastewater treatment plants (WWTPs) amounts to only a few percent by volume of the processed wastewater, but its handling accounts for up to 50% of total operating costs. Moreover, the need to achieve a sustainable sludge management strategy has become of great concern. It follows that as conventional and more traditional options, such as land spreading for agricultural purposes, are progressively restricted, and often legally banned, the development of innovative systems to maximize the recovery of useful materials and/or energy is required. A change toward more sustainable procedures can be promoted through an integrated approach, including the assessment of management routes capable of maximizing the recycle/recovery benefits, through low energy impact systems, and the development of operational systems appropriate to local circumstances. Based on the above considerations, an integrated system is proposed in this paper. It includes Anaerobic digestion, Dewatering/Drying, and Pyrolysis/Gasification processes which are efficiently coupled for the recovery of products for material reuse and/or energy purposes. Such an integrated system should also allow the recovery of one or more materials, depending on the combination of processes which best fit specific local situations

No abstract

No abstract

No abstract

The shape of sewage sludge regulation in Europe is outlined as it undergoes a period of rapid evolution. The overall governing policy is embodied in European Directive ED91/156, the Waste Basis Directive, which sets general parameters for waste management. Descriptions are given of the terms of the more specific directives that apply to the major routes for sludge management: land application, composting incineration, and landfill.

The paper gives an overview of the possibilities to achieve a more sustainable sludge management strategy by recovering and reusing valuable products as much as possible. Discussion separately deals with the recovery of products suitable for "material" uses and those for "energy" ones. Discussion on material recoveries includes organic matter, nutrients, carbon source, coagulant, bricks, pumice, slag, artificial lightweight aggregate (ALWA) and Portland cement. Regarding energy recovery, (i) conversion processes, including thermo-chemical conversion of dry sludge to oil, thermo-chemical liquefaction of wet sludge to oil and conversion/combustion processes, (ii) deep shaft wet air oxidation, and (iii) gasification processes, including starved air combustion, are outlined. Only general indications are given because the selection of an appropriate system for sludge management is strongly influenced by many other important factors, such as local economy and geography, climate, land use, regulatory constraints and public acceptance of the various practices. Also, the conventional and more traditional recycling options, like agricultural and other land uses, and incineration with energy recovery, are not dealt with because they are well known and extensively discussed elsewhere.