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The pressure-driven electro-dewatering (EDW) of sewage sludge was assessed using a lab device. The sludge samples were supplied from four different Wastewater Treatment Plants (WWTPs) around the metropolitan area of Milan (Italy), including both aerobically and anaerobically stabilised samples. The test results show that the EDW treatment enabled to dewater the sludge samples to a dry solids content of 18.4–31.1% (wt%), which means 2.0–12.7% improvement as compared to the conventional mechanical dewatering treatment used in these WWTPs. A follow-up test was carried out with the sample giving the best dewatering performance. A dry solids content of 39.3% (wt%) was achieved. Apart from the technological performance, the economic feasibility of EDW was evaluated. The energy consumption and sludge treatment cost associated with the EDW process were compared with the reference case (the corresponding WWTP currently operating with mechanical dewatering line). It was found that for the best performance case, technology upgrade from the conventional mechanical dewatering to the EDW dewatering will enable the WWTP to reduce its sludge management cost up to 35% per year. [ABSTRACT FROM AUTHOR]

The sewage sludge dewatering produced by wastewater treatment plants (WWTP) is a multifaceted process due to the presence of colloid fractions. Electro-osmosis could be a suitable technique to reduce the water content of the final sludge. Electric fields of 10, 15, and 20 V/cm have been studied for electro-osmosis tests under the pressure of a static or rotating piston, obtaining a dry solids content up to 40–45%, with respect to 25–30% obtained by mechanical methods. In order to optimize the process, the corrosion behavior and the wear of the anodic material appear to be the main critical aspects, due to the high circulating current density and the use of a rotating electrode. We compared the efficiency and the corrosion resistance of dimensionally stable anodes (DSA) with respect to bare stainless steel (AISI 304) and stainless steel coated by PVD technique with TiN, AlTiN, and DLC. Characterization of the anode surfaces by SEM and potentiodynamic tests show that DSA is the most suitable material for our application. However, efficiencies of the electro-osmosis processes have been found comparable, in terms of developed current densities and total energy consumptions, for short-test duration. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

To tackle the issue of phosphorus (P) supply, Sewage Sludge Ash (SSA) is a promising secondary source. The goal of this research is the optimization of the wet P extraction process in the view of providing valuable insights for the process scale-up. While most of the studies relied on the "one-variable-changed-at-a-time" approach, this work applied a statistical optimization model based on the Design of Experiments technique for investigating the influence of most relevant operating conditions of extraction process on Phosphorus Extraction Efficiency (PEE) with two types of SSA characterized by different levels of alkalinity. Experimental results highlighted the importance of ash characteristics, making some SSA not suitable for cost-effective phosphorus recovery due to the high acid dosage required in extraction process. Type of acid and contact time become significant factors only for Ca-rich ashes, especially when using H 2 SO 4 as extracting agent. Optimal operating conditions (C H 2 SO4 = 1.3 N, L/S = 20, t = 2 h and C HCl = 2.0 N, L/S = 10, t = 2 h for Ash#1 and C H2SO4/HCl = 0.8 N, L/S = 10 for Ash#2) resulting in high PEE (80–94%) were identified for extraction performed with H 2 SO 4 and HCl as a function of ash characteristics. [Display omitted] • pH and ash alkalinity significantly affect acid dosage in P extraction process. • Reduced order models clarified the effects of factors and their interaction on PEE. • HCl was slightly (5%) more effective than H 2 SO 4 for Ca-rich ash. • The selection of optimal operating conditions is dependent on ash characteristics. • P, Fe and Al dissolution is a quick process when dealing with ash with low alkalinity. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to evaluate the feasibility of implementing electro-dewatering (EDW) as an add-on unit to the existing conventional dewatering units with the aim of increasing the final dry solids content and reducing the subsequent handling and energy costs of sewage sludge management. The assessment was carried out by focusing on a case study, a small wastewater treatment plant (WWTP) in the Milan metropolitan area. Various indicators were used to evaluate the environmental impact and economic performance. Primary data, such as operating data from the case study WWTP and economic data from an EDW equipment manufacturer, were extracted and used in the modelling. Four scenarios were set up and compared, which address the current and future sludge management schemes in Italy. The results suggest that it is environmentally and economically feasible to implement the EDW upgrade if the sludge disposal follows the incineration route. More specifically, when small WWTPs deliver their EDW-dewatered sludge to a centralised incineration facility, this will enable to reduce the global warming impact of the system up to 135 kg CO2-eq. per dry tonne of sludge. In addition, good profitability (incremental return on investment > 15.1%) can be obtained when the market disposal cost is above 30.5–39.6 € per wet tonne of sludge. Based on our recent market survey, the sludge disposal price is well above the break-even values. Highlights • A case study was carried out by focusing on a small WWTP in Italy. • The EDW upgrade enables significant reduction in global warming in one scenario. • Good economic profitability can be attained for the case study WWTP. • EDW upgrade is recommended for small WWTPs disposing sludge to incineration. [ABSTRACT FROM AUTHOR]

The feasibility of pressure-driven electro-dewatering (EDW) on sludge samples taken after different biological processes, stabilisation methods or mechanical dewatering techniques was assessed. First, the influence of potential values on EDW of anaerobically and aerobically stabilised, mechanically dewatered, sludge samples was investigated. Preliminary tests carried out by applying a constant potential (10, 15 and 20 V) in a lab-scale device confirmed the possibility to reach a dry solid (DS) content of up to 42.9%, which corresponds to an increase of 15% of the dry content in dewatered sludge without the application of the electrical field. Dewatering increased with the applied potential but at the expense of a higher energy consumption. A potential equal to 15 V was chosen as the best compromise for EDW performance, in terms of DS content and energy consumption. Then, the influence of the mechanical dewatering was studied on aerobically stabilised sludge samples with a lower initial DS content: the higher initial water content led to a lower final DS content but with a considerable reduction of energy consumption. Finally, the biological process, studied by comparing sludge samples from conventional activated sludge and membrane bioreactor processes, didn’t evidence any influence on EDW. Experimental results shown that DS obtained after mechanical dewatering, volatile solids and conductivity are the main factors influencing EDW. Anaerobically digested sludge reached the highest DS content, thanks to lower organic fraction. [ABSTRACT FROM AUTHOR]

Waste activated sludge requires effective dewatering, high biological stability and retention of nutrients prior to disposal for agricultural application. The study was conducted to evaluate the impact of pressure-driven electro-dewatering (EDW) on improving sludge characteristics related to disposal in agriculture, including biological stability, pathogen availability, heavy metals concentrations and nutrients content. Thickened conditioned and mechanically dewatered sludge samples were collected from two wastewater treatment plants (WWTPs), characterized by different stabilization processes, and treated by a lab-scale device at 5, 15 and 25 V. EDW increased significantly the dry solid (DS) content, up to 43–45%, starting from 2 to 3% of raw sludge. The endogenous value of specific oxygen uptake rate (SOUR), monitored as indicator of biological stability, increased up to 56% and 39% after EDW tests for sludge from two WWTPs. On the other hand, the exogenous SOUR decreased, indicating a significant drop in the active bacterial population. Likewise, a 1–2 log unit reduction was observed for E. coli after EDW tests at 15 and 25 V. However, no remarkable removal of heavy metals, namely chromium, nickel, lead, copper and zinc, was achieved. Finally, the concentration of nutrients for soil, such as carbon, nitrogen, phosphorus and sulfur, was not affected by the EDW process. In conclusion, EDW exerts considerable effects on the biological characteristics of sludge, which should be considered in a proper design of sludge management to ensure safe and sustainable resource recovery. Image 1 • Sewage sludge was treated by a lab-scale electro-dewatering (EDW) setup. • The impact of EDW for promoting resource recovery in agriculture was assessed. • EDW resulted in a significant reduction of viable bacteria, including pathogens. • Relevant detrimental effects of EDW on sludge biological stability were observed. • The availability of nutrients for plants in sludge was not modified by EDW. [ABSTRACT FROM AUTHOR]