Electro-concentration for chemical-free nitrogen capture as solid ammonium bicarbonate

Source-separated urine is a promising stream for nutrient capture using electrochemical technologies. It contains the majority of macronutrients present in municipal wastewater in a concentrated, high ionic conductivity liquid and in N:P:K ratios suitable for agricultural application. The purpose of this study was to recover nutrients from urine, and particularly nitrogen as a solid without any chemical addition. Simulated source-separated urine was concentrated using a three-compartment electrochemical system, applying a range of current densities and feed compositions. Electro-concentration into a liquid concentrate reached maximum recovery of 72:61:79% for N:P:K, respectively, from a synthetic feed simulating ureolysed and digested urine, with a specific electrical energy consumption of 47 MJ/kg N and current efficiency of 67% for ammonium. Cooling the concentrate to −18 °C resulted in solid ammonium bicarbonate crystal formation in samples with high ammonium bicarbonate ionic product and high relative ammonium bicarbonate ionic strength. Precipitation started to occur when ammonium bicarbonate ionic product was higher than 2.25 M and ammonium bicarbonate accounted for more than 62% of the total ionic strength of the feed. The maximum observed nitrogen recovery into solid ammonium bicarbonate reached 17% using a current density of 100 A m. Based on these results, electro-concentration is a promising technology for urine nutrient capture. However, capture as solid ammonium bicarbonate is feasible only if higher recovery efficiencies are achieved by removing competing ions

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

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

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

Redox-Polymers Enable Uninterrupted Day/Night Photo-Driven Electricity Generation in Biophotovoltaic Devices

Biophotovoltaic devices modified with immobilized polymeric osmium/azine redox-mediators exhibited a considerable electrical output enhancement (64/43-fold under light/dark conditions, respectively). More importantly, the systems exhibited uninterrupted current generation at same magnitude levels during day/night cycles, paving the way toward solar energy conversion bio-panels that will not require energy storage peripherals

Urine Treatment on the International Space Station: Current Practice and Novel Approaches

A reliable, robust, and resilient water recovery system is of paramount importance on board the International Space Station (ISS). Such a system must be able to treat all sources of water, thereby reducing resupply costs and allowing for longer-term space missions. As such, technologies able to dewater urine in microgravity have been investigated by different space agencies. However, despite over 50 years of research and advancements on water extraction from human urine, the Urine Processing Assembly (UPA) and the Water Processor Assembly (WPA) now operating on the ISS still achieve suboptimal water recovery rates and require periodic consumables resupply. Additionally, urine brine from the treatment is collected for disposal and not yet reused. These factors, combined with the need for a life support system capable of tolerating even dormant periods of up to one year, make the research in this field ever more critical. As such, in the last decade, extensive research was conducted on the adaptation of existing or emerging technologies for the ISS context. In virtue of having a strong chemical resistance, small footprint, tuneable selectivity and versatility, novel membrane-based processes have been in focus for treating human urine. Their hybridisation with thermal and biological processes as well as the combination with new nanomaterials have been particularly investigated. This article critically reviews the UPA and WPA processes currently in operation on the ISS, summarising the research directions and needs, highlighted by major space agencies, necessary for allowing life support for missions outside the Low Earth Orbit (LEO). Additionally, it reviews the technologies recently proposed to improve the performance of the system as well as new concepts to allow for the valorisation of the nutrients in urine or the brine after urine dewatering