A novel electrochemical process for the recovery and recycling of ferric chloride from precipitation sludge

During wastewater treatment and drinking water production, significant amounts of ferric sludge (comprising ferric oxy-hydroxides and FePO4) are generated that require disposal. This practice has a major impact on the overall treatment cost as a result of both chemical addition and the disposal of the generated chemical sludge. Iron sulfide (FeS) precipitation via sulfide addition to ferric phosphate (FePO4) sludge has been proven as an effective process for phosphate recovery. In turn, iron and sulfide could potentially be recovered from the FeS sludge, and recycled back to the process. In this work, a novel process was investigated at lab scale for the recovery of soluble iron and sulfide from FeS sludge. Soluble iron is regenerated electrochemically at a graphite anode, while sulfide is recovered at the cathode of the same electrochemical cell. Up to 60±18% soluble Fe and 46±11% sulfide were recovered on graphite granules for up-stream reuse. Peak current densities of 9.5±4.2Am-2 and minimum power requirements of 2.4±0.5kWhkgFe-1 were reached with real full strength FeS suspensions. Multiple consecutive runs of the electrochemical process were performed, leading to the successful demonstration of an integrated process, comprising FeS formation/separation and ferric/sulfide electrochemical regeneration

A novel carbon nanotube modified scaffold as an efficient biocathode material for improved microbial electrosynthesis

We report on a novel biocompatible, highly conductive three-dimensional cathode manufactured by direct growth of flexible multiwalled carbon nanotubes on reticulated vitreous carbon (NanoWeb-RVC) for the improvement of microbial bioelectrosynthesis (MES). NanoWeb-RVC allows for an enhanced bacterial attachment and biofilm development within its hierarchical porous structure. 1.7 and 2.6 fold higher current density and acetate bioproduction rate normalized to total surface area were reached on NanoWeb-RVC versus a carbon plate control for the microbial reduction of carbon dioxide by mixed cultures. This is the first study showing better intrinsic efficiency as biocathode material of a three-dimensional electrode versus a flat electrode: this comparison has been made considering the total surface area of the porous electrode, and not just the projected surface area. Therefore, the improved performance is attributed to the nanostructure of the electrode and not to an increase in surface area. Unmodified reticulated vitreous carbon electrodes lacking the nanostructure were found unsuitable for MES, with no biofilm development and no acetate production detected. The high surface area to volume ratio of the macroporous RVC maximizes the available biofilm area while ensuring effective mass transfer to and from the biofilm. The nanostructure enhances the bacteria-electrode interaction and microbial extracellular electron transfer. When normalized to projected surface area, current densities and acetate production rates of 3.7 mA cm-2 and 1.3 mM cm-2 d-1, respectively, were reached, making the NanoWeb-RVC an extremely efficient material from an engineering perspective as well. These values are the highest reported for any MES system to date

Study of absorber intercooling in solvent-based CO2 capture based on rotating packed bed technology

Application of process intensification (PI) technologies such as rotating packed beds (RPBs) to replace packed beds (PBs) in solvent-based CO2 capture could reduce plant footprint. Concentrated monoethanolamine (MEA) solvents are generally expected to be used in RPBs. Under this circumstance, expected temperature rise during CO2 absorption should be estimated to determine whether or not intercooling is necessary for RPBs. In this study, we demonstrated that intercooling is inevitable with RPBs using 40-70 wt% monoethanolamine (MEA) solvent through liquid phase energy balance for a hypothetical scenario. Our analysis showed that liquid phase temperature rise could be as high as 80°C in some cases and this will significantly reduce absorption rate without intercooling

Modelling and techno-economic assessment of (bio)electrochemical nitrogen removal and recovery from reject water at full WWTP scale

At conventional wastewater treatment plants (WWTPs), reject waters originating from the dewatering of anaerobically digested sludge contain the highest nitrogen concentrations within the plant and thereby have potential for realising nitrogen recovery in a reusable form. At the same time, nitrogen removal from reject waters has potential to reduce the energetic and chemical demands of the WWTP due to a reduced nutrient load to the activated sludge process. In recent years, (bio)electrochemical methods have been extensively studied for nitrogen recovery from reject waters in laboratory-scale but not yet implemented in real WWTP environments, particularly due to concerns about the need for large capital investments. This study assessed the techno-economic feasibility of retrofitting a (bio)electrochemical nitrogen removal and recovery (NRR) unit into the reject water circulation line of a full-scale WWTP through modelling. Data from laboratory-scale (bio)electroconcentration ((B)EC) experiments was used to construct a simple, semi-empirical model block integrated into the Benchmark Simulation Model No. 2 (BSM2) simulating a generalised WWTP. The effects of nitrogen removal from the reject water on both the effluent quality and operational costs of the WWTP were assessed and compared to the BSM2 performance without an NRR unit. In all studied scenarios, the effluent quality index was improved by 4–11%, while both the aeration (7–19% decrease) and carbon (24–71%) requirements were reduced. The additional energy consumed by the NRR unit increased the total operational cost index by >18%, but the revenue assumed for the generated nutrient product (20 EUR kgN−1) was enough to make the BEC-NRR scenarios at realistically low current densities (1 and 5 A m−2) economically attractive compared to the control. A sensitivity analysis revealed that electricity price and nutrient product value had the most notable effects on the feasibility of the NRR unit. The results suggest a key factor in making (bio)electrochemical NRR economically viable is to reduce its electricity consumption further, while the anticipated increases in nitrogen fertiliser prices can help accelerate the adoption of these methods in larger scale.publishedVersionPeer reviewe

Fate of pharmaceuticals and PFASs during the electrochemical generation of a nitrogen-rich nutrient product from real reject water

Recycling vital macronutrients, such as nitrogen, from wastewaters back to fertiliser use is becoming essential to ensure sustainable agricultural practices. Technologies developed for such purposes are typically evaluated for their capacity to recover nutrients; however, the presence of contaminants of emerging concern (CECs) in these waste-derived nutrient products must not be overlooked. In this study, nitrogen was recovered from real anaerobically digested municipal sewage sludge reject water using a novel set-up combining membrane-based electroconcentration (EC) with electrochemical advanced oxidation processes (EAOPs). Simultaneously, the fate of five spiked pharmaceuticals (carbamazepine, ciprofloxacin, diclofenac, erythromycin and metoprolol) as well as ten indigenous perfluoroalkyl substances (PFASs) was investigated. The EC-EAOP system was effective in up-concentrating nitrogen ca. 13 times to a final concentration of 12.7 ± 0.8 g L−1 in the nutrient product. At the same time, no up-concentration was observed for the pharmaceuticals and their concentrations in the recovered concentrated remained at ≤ 3.4 ± 1.3 µg L−1. The EAOPs were the main transformation mechanism for all the pharmaceuticals at 33–88% efficiency, while diclofenac also notably adsorbed in the system (30 ± 1.4%). Out of the ten studied PFASs, only three were found in the recovered nutrient concentrate, albeit at very limited concentrations of ≤ 0.024 ± 0.013 µg L−1. The EAOPs were found to degrade longer-chain PFASs into their shorter-chain counterparts. The low contaminant concentrations in the nutrient product pose a reduced risk for soil contamination compared to, e.g., biosolids that are more typically used as fertilisers.publishedVersionPeer reviewe

Sampling location of the inoculum is crucial in designing anodes for microbial fuel cells

A Kraft pulp mill effluent was used as the inoculum to form microbial bioanodes under controlled potential at +0.4 V/SCE. Samples were collected at the inlet and outlet of the aerated lagoon of the treatment line. The outlet sample allowed efficient bioanodes to be designed (5.1 A/m²), which included Geobacter and Desulfuromonas sp. in their microbial community. In contrast, the bioanodes formed with the inlet sample did not contain directly connecting anode-respiring bacteria and led to lower currents. It was necessary to reform this bioanode at lower applied potential (-0.2 V/SCE) to select more efficient electroactive species and increase the current density to 5 A/m²

Intermittent load implementation in microbial fuel cells improves power performance

© 2014 Elsevier Ltd. This study reports on the response of small-scale MFCs to intermittent loading, in terms of power output over time. The aim was to understand the evolution with time of power output under different duty cycles, in conditions close to practical implementation. Inexpensive ceramic membranes were compared to cation exchange membranes, under continuous flow and with a pre-digester connected. Results show that at the minute-scale, all the duty cycles investigated, produced 78% higher power bursts from the MFCs (500. μW) than when under continuous loading (280. μW). These results were recorded from MFCs employing ceramic membranes, whereas the difference in performance for MFCs employing commercially available cation-exchange-membranes was insignificant. When normalising to daily energy production, only specific duty cycles produced more power than continuous loading. Furthermore, the introduction of a pre-digester increased the MFC power outputs 10-fold, thus confirming that separating fermentation from electro-active respiration, significantly enhances the system performance

Biomimetic Peptide Nanowires Designed for Conductivity

The filamentous peptide-based nanowires produced by some dissimilatory metal-reducing bacteria, such as Geobacter sulfurreducens, display excellent natural conductivity. Their mechanism of conduction is assumed to be a combination of delocalized electrons through closely aligned aromatic amino acids and hopping/charge transfer. The proteins that form these microbial nanowires are structured from a coiled-coil, for which the design rules have been reported in the literature. Furthermore, at least one biomimetic system using related synthetic peptides has shown that the incorporation of aromatic residues can be used to enhance conductivity of peptide fibers. Herein, the de novo design of peptide sequences is used to enhance the conductivity of peptide gels, as inspired by microbial nanowires. A critical factor hampering investigations in both microbiology and materials development is inconsistent reporting of biomaterial conductivity measurements, with consistent methodologies needed for such investigations. We have reported a method herein to analyze non-Ohmic behavior using existing parameters, which is a statistically insightful approach for detecting small changes in biologically based samples. Aromatic residues were found to contribute to peptide gel conductivity, with the importance of the peptide confirmation and fibril assembly demonstrated both experimentally and computationally. This is a small step (in combination with parallel research under way by other researchers) toward developing effective peptide-based conducting nanowires, opening the door to the use of electronics in water and physiological environments for bioelectronic and bioenergy applications