Matteo Canato

Techno-economic and environmental assessment of sewage sludge wet oxidation.

Today, several technologies and management strategies are proposed and applied in wastewater treatment plants (WWTPs) to minimise sludge production and contamination. In order to avoid a shifting of burdens between different areas, their techno-economic and environmental performance has to be carefully evaluated. Wet oxidation (WO) is an alternative solution to incineration for recovering energy in sewage sludge while converting it to mostly inorganic residues. This paper deals with an experimentation carried out within the EU project “ROUTES”. A mass balance was made for a WWTP (500,000 person equivalents) in which a WO stage for sludge minimisation was considered to be installed. Both bench- and full-scale test results were used. Design of treatment units and estimation of capital and operational costs were then performed. Subsequently, technical and economic aspects were evaluated by means of a detailed methodology which was developed within the ROUTES project. Finally, an assessment of environmental impacts from a life cycle perspective was performed. The integrated assessment showed that for the specific upgrade considered in this study, WO technology, although requiring a certain increase of technical complexity at the WWTP, may contribute to environmental and economic advantages. The paper provides guidance in terms of which aspects need a more thorough evaluation in relation to the specific case in which an upgrade with WO is considered.

How can sludge dewatering devices be assessed? Development of a new DSS and its application to real case studies.

A key issue in biological Waste Water Treatment Plants (WWTPs) operation is represented by the sludge management. Mechanical dewatering is a crucial stage for sludge volume reduction; though, being a costly operation, its optimization is required. We developed an original experimental methodology to evaluate the technical (dewatering efficiency) and financial (total treatment costs) performance of dewatering devices, which might be used as a DSS (Decision Support System) for WWTP managers. This tool was then applied to two real case studies for comparing, respectively, three industrial size centrifuges, and two different operation modes of the same machine (fixed installation vs. outsourcing service). In both the cases, the best option was identified, based jointly on economic and (site-specific) technical evaluations.

Methodology for technical and economic assessment of advanced routes for sludge processing and disposal

In order to meet the environmental legislative framework in force in Europe and reduce sludge processing and disposal costs, several sludge treatment technologies and management strategies have been proposed in the last two decades. The evaluation of their technical and economic suitability, case by case, may be a challenge, since many aspects are involved, so that a robust decision support system should be used. Within the ROUTES project (founded within the EU Seventh Framework Programme), the authors have developed an assessment procedure which allows rating several technical factors (such as system reliability, complexity, safety aspects, modularity, etc.) and estimating capital and operating costs, in case a plant is being upgraded. The comparison between the original (reference) plant and the modified configuration informs about technical hot spots (which are expressed by a traffic light-type colour code) and cost gaps resulting from the implementation of the new solution.

Method for technical, economic and environmental assessment of advanced sludge processing routes

The legislative framework in force in Europe entails restrictive effluent standards for sensitive areas, and quite severe restrictions on the properties of residual sewage sludge, both for landfill disposal and for agricultural use. Several technologies and management strategies have been proposed and applied in wastewater treatment plants to minimise sludge production and contamination. However, their techno-economic and environmental performance has to be carefully evaluated. The ROUTES project, funded within the EU Seventh Framework programme, aims to find new routes for wastewater treatment and sludge management and thereby guide EU members in their future choices. Within this project, the authors have developed and applied a procedure for techno-economic-environmental assessment of new wastewater and sludge processing lines in comparison to reference plants. The reference plants are model conventional plants that experience different types of problems and the new plants are modified plants in which different innovative technologies have been added to solve these problems. The procedure involves a rating of selected technical issues, estimates of operating costs and an assessment of environmental impacts from a life cycle perspective. This paper reports on the procedure and shows examples of results.

Enhanced versus conventional sludge anaerobic processes: performances and techno-economic assessment.

Sewage sludge processing is a key issue in water resource recovery facilities due to the inefficacy of conventional treatments to produce high quality biosolids to be safely used in agriculture. Under this framework, the performances of several enhanced stabilization processes, namely ultrasound-pretreated Mesophilic Anaerobic Digestion (US+MAD), thermophilic anaerobic digestion (TAD), thermal-pretreated TAD (TH+TAD) and ultrasound-pretreated inverse Temperature Phased Anaerobic Digestion (US+iTPAD) have been investigated. Such enhanced processes resulted in higher biogas yields and higher destruction of pathogens with respect to conventional MAD process, thus suggesting their feasibility in full-scale implementation perspectives. A procedure for technical-economic comparison of new sludge processing lines against conventional ones (benchmarking) was developed, based on the definition of technical issues (e.g. reliability, complexity, etc.) which are rated for each situation. Moreover, capital and operating costs were estimated. The enhanced processes analyzed in this work showed some potentially critical items, mainly related to energy balance and reagent consumption.

Sewage sludge minimisation by means of wet oxidation: process performance and economic sustainability

Today, several technologies and management strategies are proposed and applied in WWTPs to minimise sludge production and contamination and their techno-economic feasibility has to be carefully evaluated. In this work (which is being conducted within the European Union project ‘ROUTES’), based on bench results, a mass balance was drawn for a WWTP (500,000 PE), where it was supposed to install a wet oxidation (WO) stage for sludge minimisation. The design of treatment units and the estimation of capital and operation costs were then performed. Subsequently, a procedure for technical-economic assessment was developed. Basically, this procedure consists in the definition and ranking of several technical (e.g., reliability of the technology, complexity and integration with the existing facilities, amount of residues to be disposed of or recovered, etc.) and economic aspects. Preliminary results have shown WO to be a suitable solution for sludge minimisation.