Electro-dewatering treatment of sludge: Assessment of the influence on relevant indicators for disposal in agriculture.

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.

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

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 20V) 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 15V 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.

Modeling the adsorption behavior of linear end-functionalized poly(ethylene glycol) on an ionic substrate by a coarse-grained Monte Carlo approach.

The rheology of cement pastes can be controlled by polymeric dispersants such as branched polyelectrolytes that adsorb on the surfaces of silicate particles. In the present work, we analyze the adsorption behavior of ad hoc-prepared end-carboxylated poly(ethylene glycol), or PEG, on CaCO(3) particles as a model of cement in an early hydration stage. The experimental adsorption isotherms form the base of a theoretical study aimed at unraveling polymer conformational aspects of adsorption. The study was carried out with Monte Carlo simulations using a coarse-grained bead-and-spring model of linear end-charged polymer chains adsorbing on a flat, continuous, uniformly charged surface. The adsorption driving force was introduced by a Debye-Hückel electrostatic screened potential to describe the interaction between the negatively charged end group of PEG and the positively charged CaCO(3) surface empirically. With a suitable length-scale conversion between real PEG and the coarse-grained model, the calculated and experimental adsorption isotherms can be semiquantitatively compared. The theoretical results reproduce the fundamental aspects of polymer adsorption, in essential agreement with analytical approaches relating the isotherm shape to the polymer conformational properties. The conformational transition mushroom-brush of the adsorbed polymer is located on the isotherm and is related to the molecular shape. The solvent quality effect and the solution ionic strength are also considered, and their implications on the isotherms are discussed.