Electro-Dewatering of Anaerobically Digested and Activated Sludges: An Energy Aspect Analysis

Olivier, Jérémy; Mahmoud, Akrama; Vaxelaire, Jean; Conrardy, Jean-Baptiste; Citeau, Morgane; Vorobiev, Eugène

doi:10.1080/07373937.2014.884133

Cited by 61 publications

(35 citation statements)

References 35 publications

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“…Considering that the Italian energy conversion efficiency is equal to 0.47 (Caputo and Sarti, 2015), the total equivalent thermal energy consumption is 616-871 Wh/kg H2O , lower than the maximum energy needed for thermal drying (1200 Wh/ kg evaporated water ) (Olivier et al, 2014), but not economically feasible with respect to conventional mechanical methods.…”

Section: Considerations On Energy Consumptionmentioning

confidence: 99%

“…The high sludge dryness that is reached by the EDW process is a promising alternative to the thermal drying technique, thanks to the lower energy consumption involved. Sludge thermal drying indeed requires, at industrial scale, energies ranging from 617 Wh/kg evaporated water (the enthalpy of water vaporization) to as high as 1200 Wh/ kg evaporated water (Olivier et al, 2014). On the contrary, depending on the potential and pressure values applied, EDW process is capable to reduce the energy consumption by 10-25% of the theoretical thermal drying energy (Mahmoud et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

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Performance of electro-osmotic dewatering on different types of sewage sludge

Visigalli

Turolla

Gronchi

et al. 2017

Environmental Research

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A B S T R A C TThe 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.

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Section: Considerations On Energy Consumptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Performance of electro-osmotic dewatering on different types of sewage sludge

Visigalli

Turolla

Gronchi

et al. 2017

Environmental Research

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“…After preliminary tests, we set the initial cake thickness at 1 cm, in order to have a thin insulating [20].…”

Section: Resultsmentioning

confidence: 99%

Electrode surface treatments in sludge electro-osmosis dewatering

Gronchi

Canziani

Brenna

et al. 2017

Materials and Manufacturing Processes

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The sewage sludge dewatering produced by Wastewater Treatment Plants 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 V/cm, 15 V/cm 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 optimise the process, the corrosion behaviour and the wear of the anodic material appear 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.Keywords: electro-osmosis; dewatering; sludge; DSA; anode; corrosion. IntroductionThe so-called "activated sludge process" is adopted by almost the totality of urban and industrial wastewater treatment plants to achieve the concentration limits of biodegradable pollutants stated by the law to allow the discharge of treated effluents to natural water bodies (rivers, lakes and the sea).About half of the organic pollution load treated by the activated sludge process is oxidised and converted into water and carbon dioxide, while the remaining is converted into biomass, called "excess biological sludge" or "waste sludge". After reducing both the content of biodegradable matter and the water content through mechanical dewatering or thermal drying, the sludge becomes a product suitable for its final disposal.When compared with thermal (evaporative) processes for water reduction, mechanical dewatering is often selected due to its low energy requirement. The processes of mechanical dewatering are largely developed on the industrial scale and can produce sludge with 20-25% of dry solid (DS) content and, in some cases, up to 30%. However, the high DS values demanded for thermal valorisation of sludge cannot be achieved by mechanical dewatering techniques. , and Tuan et al. [10] reported that the pH drop relates to the reduction of the absolute value of the zeta potential, thus the decrease in pH (specifically at the anode) reduced the electro-osmotic flow during direct current application [1, 5,8,11].The oxidation of the anode material, due to oxygen evolution, ohmic heating and pH decrease, reduces the process efficiency [12] and can cause in some applications the contamination of the filter cake or filtrate, increasing the operating cost. Anodes such as stainless steel will be subject to

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“…After that, the samples reached a DS content (DS CFG ) of 7.5-13.9% (wt%) and then they were fed into the EDW cell. The EDW treatment is composed of two successive phases [16,18]: (i) filtration under mechanical pressure (duration of 10 min), (ii) application of a constant electric potential in the presence of mechanical pressure (duration of 25 min). As already observed by Visigalli et al [27,34], a polarisation phase of 15 min is enough to reach a DS content higher than that achieved by mechanical dewatering.…”

Section: Procedures For Edw Testsmentioning

confidence: 99%

“…The process has been investigated in many publications, with a focus on the process performance and various operating parameters, such as pressure, electric potential, current, treatment time, delaying the application of the electric field, chemical conditioning dosage and cake thickness in the EDW cell [6,7,12,[15][16][17][18][19][20][21][22][23]. Citeau et al have shown that the use of a DC power supply at constant electric potential, instead of constant electric current, allows to achieve a higher DS content [20] and a better control of the temperature at the end of the tests, preventing from ohmic heating [17].…”

Section: Introductionmentioning

confidence: 99%