Enhanced •Cl generation by introducing electrophilic Cu(II) in Co3O4 anode for efficient total nitrogen removal with hydrogen recovery in urine treatment

Urine is a nitrogen-containing waste, but can be used as an attractive alternative substrate for H2 recovery. However, conventional urea oxidation reaction is subject to complex six-electron transfer kinetics and requires alkaline conditions. Herein, an efficient method of enhancing •Cl generation by introducing electrophilic Cu(II) into Co3O4 nanowires anode was proposed, which realized the highly efficient TN removal and H2 production in urine treatment under neutral conditions. The key mechanism is that the electrophilic effect of Cu(II) attracts electrons from the oxygen atom, which causes the oxygen atom to further attract electrons from Co(II), reducing the charge density of Co(II). Electrophilic Cu(II) accelerates the difficult conversion step of Co(II) to Co(III), which enhances the generation of •Cl. The generated •Cl efficiently converts urea to N2, while the electron transport promotes H2 production on the CuO@CF nanowires cathode. Results showed that the steady-state concentration of •Cl was increased to about 1.5 times by the Cu(II) introduction. TN removal and H2 production reached 94.7% and 642.1 μmol after 50 min, which was 1.6 times and 1.5 times that of Co3O4 system, respectively. It was also 2.3 times and 2.1 times of RuO2, and 3.3 times and 2.5 times of Pt, respectively. Moreover, TN removal was 11.0 times higher than that of without •Cl mediation, and H2 production was 4.3 times higher. More importantly, excellent TN removal and H2 production were also observed in the actual urine treatment. This work provides a practical possibility for efficient total nitrogen removal and hydrogen recovery in urine wastewater treatment.

[STUDY OF URINATION TREATMENT AFTER BCG INTRAVESICAL INSTILLATION THERAPY]

(Background and methods) Bacillus Calmette-Guérin (BCG) intravesical instillation therapy is used to treat non-muscle invasive bladder cancer. Instilled BCG is typically collected at the time of initial urination and disposed of after sterilization with 10% sodium hypochlorite or household bleach, however, these methods can have unpleasant effects, such as pungent odor, rapid foaming and fever. We investigated whether isopropanol be used to sterilize and dispose of urine after BCG intravesical instillation therapy, because isopropanol at a concentration of 33% or higher (70% isopropanol was used in this study) has the same disinfectant and bactericidal effects against Mycobacterium tuberculosis as 10% sodium hypochlorite or household bleach. (Results) Use of isopropanol eliminated the unpleasant effects experienced with sodium hypochlorite and no growth of Mycobacterium tuberculosis was observed in culture tests. (Conclusion) Isopropanol is safer than sodium hypochlorite, and should be considered for sterilizing and disposing of urine after BCG intravesical instillation therapy in the future. However, fire and ventilation precautions are required.

Superior selectivity of high-frequency ultrasound toward chorine containing-pharmaceuticals elimination in urine: A comparative study with other oxidation processes through the elucidation of the degradation pathways

This work considered the sonochemical degradation (using a bath-type reactor, at 375 kHz and 106.3 W L^-1, 250 mL of sample) of three representative halogenated pharmaceuticals (cloxacillin, diclofenac, and losartan) in urine matrices. The action route of the process was initially established. Then, the selectivity of the sonochemical system, to degrade the target pharmaceuticals in simulated fresh urine was compared with electrochemical oxidation (using a BDD anode, at 1.88 mA cm^-2), and UVC/H₂O₂ (at 60 W of light and 500 mol L^-1 of H₂O₂). Also, the treatment of cloxacillin in an actual urine sample by ultrasound and UVC/H₂O₂ was evaluated. More than 90% of the target compounds concentration, in the simulated matrix, was removed after 60 min of sonication. However, the sono-treatment of cloxacillin in the real sample was less efficient than in the synthetic urine. The ultrasonic process achieved 43% of degradation after 90 min of treatment in the actual matrix. In the sonochemical system, hydroxyl radicals in the interfacial zone were the main degrading agents. Meanwhile, in the electrochemical process, electrogenerated HOCl was responsible for the elimination of pharmaceuticals. In turn, in UVC/H₂O₂ both direct photolysis and hydroxyl radicals degraded the target pollutants. Interestingly, the degradation by ultrasound of the pharmaceuticals in synthetic fresh urine was very close to the observed in distilled water. Indeed, the sonodegradation had a higher selectivity than the other two processes. Despite the sono-treatment of cloxacillin was affected by the actual matrix components, this contrasts with the UVC/H₂O₂, which was completely inhibited in the real urine. The sonochemical process led to 100% of antimicrobial activity (AA) elimination after 75 min sonication in the synthetic urine, and ∼ 20% of AA was diminished after 90 min of treatment in the real matrix. The AA decreasing was linked to the transformations of the penicillin nucleus on cloxacillin, the region most prone to electrophilic attacks by radicals according to a density theory functional analysis. Finally, predictions of biological activity confirmed that the sono-treatment decreased the activity associated with cloxacillin, diclofenac, and losartan, highlighting the positive environmental impact of degradation of chlorinated pharmaceuticals in urine.

Effect of microbial fuel cell operation time on the disinfection efficacy of electrochemically synthesised catholyte from urine

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The MFC with the thickest ceramic membrane produced the best quality catholyte.

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MFC operation time contributes to the catholyte quality and killing properties.

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Catholyte from ceramic MFC (10 mm) reached pH 11 at day 42 and eradicated E. coli.

Microbial fuel cells (MFCs) offer an excellent solution to tackle some of the major challenges currently faced by humankind: sustainable energy sources, waste management and water stress. Besides treating wastewater and producing useful electricity from urine, ceramic MFCs can also generate biocidal catholyte in-situ. It has been proved that the electricity generation from the MFCs has a high impact in the catholyte composition. Therefore, the catholyte composition constantly changes while electricity is generated. However, these changes in catholyte composition with time has not yet been studied and that could highly contribute to the disinfection efficacy. In this work, the evolution of the catholyte generation and composition with the MFC operation time has been chemically and microbiologically evaluated, during 42 days. The results show an increase in pH and conductivity with the operation time, reaching pH 11.5. Flow cytometry and luminometer analyses of bioluminescent pathogenic E. coli exposed to the synthesised catholyte revealed killing properties against bacterial cells. A bio-electrochemical system, capable of electricity generation and simultaneous production of bactericidal catholyte from human urine is presented. The possibility to electrochemically generate in-situ a bacterial killing agent from urine, offers a great opportunity for water reuse and resource recovery for practical implementations.

From the lab to the field: Self-stratifying microbial fuel cells stacks directly powering lights

The microbial fuel cell (MFC) technology relies on energy storage and harvesting circuitry to deliver stable power outputs. This increases costs, and for wider deployment into society, these should be kept minimal. The present study reports how a MFC system was developed to continuously power public toilet lighting, with for the first time no energy storage nor harvesting circuitry. Two different stacks, one consisting of 15 and the other 18 membrane-less MFC modules, were operated for 6 days and fuelled by the urine of festival goers at the 2019 Glastonbury Music Festival. The 15-module stack was directly connected to 2 spotlights each comprising 6 LEDs. The 18-module stack was connected to 2 identical LED spotlights but going through 2 LED electronic controller/drivers. Twenty hours after inoculation the stacks were able to directly power the bespoke lighting system. The electrical energy produced by the 15-module stack evolved with usage from ≈280 mW (≈2.650 V at ≈105 mA) at the beginning to ≈860 mW (≈2.750 V at ≈300 mA) by the end of the festival. The electrical energy produced by the LED-driven 18-module stack increased from ≈490 mW at the beginning to ≈680 mW toward the end of the festival. During this period, illumination was above the legal standards for outdoor public areas, with the 15-module stack reaching a maximum of ≈89 Lx at 220 cm. These results demonstrate for the first time that the MFC technology can be deployed as a direct energy source in decentralised area (e.g. refugee camps).

Dataset on the degradation of losartan by TiO2-photocatalysis and UVC/persulfate processes

Losartan is a highly consumed antihypertensive worldwide and commonly found in effluents of municipal wastewater treatment plants. In the environment, losartan can promote harmful effects on organisms. Thus, an option to face this pollutant is the treatment by photochemical advanced oxidation processes. This dataset has two main components: 1) theoretical calculations on reactivity indexes for losartan, and 2) degradation of the pollutant throughout TiO2-photocatalysis and UVC/persulfate (UVC/PS). The first part of the work presents the data about HOMO and LUMO energies, optimized geometry, dipolar moment, HOMO/LUMO energy gap and total density distribution, in addition to ionization energy, electron affinity, chemical potential, hardness, softness and electrophilicity for losartan. Meanwhile, the second one depicts information on the routes involved in the degradation of the pharmaceutical by the oxidation processes, mineralization, toxicity evolution and losartan removal from a complex matrix (synthetic fresh urine). The data reported herein may be utilized for further researches related to elimination of pharmaceuticals in primary pollution sources such as urine. Moreover, this work also provides experimental and theoretical data useful for the understanding of the response of losartan to oxidative and photochemical processes.

Scalability and stacking of self-stratifying microbial fuel cells treating urine

The scalability of Microbial fuel cells (MFCs) is key to the development of stacks. A recent study has shown that self-stratifying membraneless MFCs (S-MFCs) could be scaled down to 2 cm without performance deterioration. However, the scaling-up limit of S-MFC is yet unknown. Here the study evaluates the scale-up height of S-MFCs treating urine, from 2 cm, 4 cm to 12 cm high electrodes. The electrochemical properties of the S-MFCs were investigated after steady-states were established, following a 70-days longevity study. The electrochemical properties of the 2 cm and 4 cm conditions were similar (5.45 ± 0.32 mW per cascade). Conversely, the 12 cm conditions had much lower power output (1.48 ± 0.15 mW). The biofilm on the 12 cm cathodes only developed on the upper 5-6 cm of the immersed part of the electrode suggesting that the cathodic reactions were the limiting factor. This hypothesis was confirmed by the cathode polarisations showing that the 12 cm S-MFC had low current density (1.64 ± 9.53 µA cm-2, at 0 mV) compared to the other two conditions taht had similar current densities (192.73 ± 20.35 µA cm-2, at 0 mV). These results indicate that S-MFC treating urine can only be scaled-up to an electrode height of around 5-6 cm before the performance is negatively affected.

Reduction in energy for electrochemical disinfection of E. coli in urine simulant

ABSTRACT

We report the development of novel modes of operation for electrochemical disinfection of E. coli in human urine simulant with an aim to minimize the energy required for disinfection. The system employs boron-doped diamond electrodes and will be part of an energy neutral, water and additive free outdoor toilet being developed for use in developing countries. Disinfection had been previously demonstrated with voltage being continuously applied to the electrode until disinfection was achieved. In the present study, a new pulsed mode of operation is investigated. This includes a continuous on mode, where oxidants are generated until disinfection is achieved, a single cycle mode, where oxidants are generated for a fixed time and the water is circulated so allow already generated oxidants to disinfect, and a pulsed mode with different duty cycles, which is like the single cycle mode but with multiple cycles. Disinfection was achieved with pulsed mode operation with a 68% energy reduction compared to the continuous on mode. Energy saving was most likely achieved by lengthening the contact time of the disinfectant with the bacteria and increased generation of non-chlorine disinfecting oxidants.

GRAPHICAL ABSTRACT

Techno-economic feasibility of recovering phosphorus, nitrogen and water from dilute human urine via forward osmosis

Due to high phosphorus (P) and nitrogen (N) content, human urine has often proven to suitable raw material for fertiliser production. However, most of the urine diverting toilets or male urinals dilute the urine 2 to 10 times. This decreases the efficiency in the precipitation of P and stripping of N. In this work, a commercial fertiliser blend was used as forward osmosis (FO) draw solution (DS) to concentrate real diluted urine. During the concentration, the urea in the urine is recovered as it diffuses to the fertiliser. Additionally, the combination of concentrate PO₄^3-, reverse Mg²⁺ flux from the DS and the Mg²⁺ presents in the flushing water, was able to recover the PO₄^3- as struvite. With 50% concentrated urine, 93% P recovery was achieved without the addition of an external Mg²⁺. Concurrently, 50% of the N was recovered in the diluted fertiliser DS. An economic analysis was performed to understand the feasibility of this process. It was found that the revenue from the produced fertilisers could potentially offset the operational and capital costs of the system. Additionally, if the reduction in the downstream nutrients load is accounted for, the total revenue of the process would be over 5.3 times of the associated costs.

Scalability of self-stratifying microbial fuel cell: Towards height miniaturisation

The scalability of bioelectrochemical systems is a key parameter for their practical implementation in the real-world. Up until now, only urine-fed self-stratifying microbial fuel cells (SSM-MFCs) have been shown to be scalable in width and length with limited power density losses. For practical reasons, the present work focuses on the scalability of SSM-MFCs in the one dimension that has not yet been investigated, namely height. Three different height conditions were considered (1 cm, 2 cm and 3 cm tall electrodes). The normalised power density of the 2 cm and 3 cm conditions were similar either during the durability test under a hydraulic retention time of ≈39 h (i.e. 15.74 ± 0.99 μW.cm^-3) and during the polarisation experiments (i.e. 27.79 ± 0.92 μW.cm^-3). Conversely, the 1 cm condition had lower power densities of 11.23 ± 0.07 μW.cm^-3 and 17.73 ± 3.94 μW.cm^-3 both during the durability test and the polarisation experiment, respectively. These results confirm that SSM-MFCs can be scaled in all 3 dimensions with minimal power density losses, with a minimum height threshold for the electrode comprised between 1 cm and 2 cm.

Urine microbial fuel cells in a semi-controlled environment for onsite urine pre-treatment and electricity production

Microbial fuel cell (MFC) systems have the ability to oxidize organic matter and transfer electrons to an external circuit as electricity at voltage levels of <1 V. Urine has been shown to be an excellent feedstock for various MFC systems, particularly MFCs inoculated with activated sludge and with a terracotta ceramic membrane separating carbon-based electrodes. In this article, we studied a MFC system composed of two stacks of 32 individual cells each sharing the same anolyte. By combining the current produced by the 32 cells connected in parallel and by adding the potential of both stacks connected in series, an average power density of 23 mW m^-2 was produced at an effective current density of 65 mA m^-2 for more than 120 days. [NH₃], TIC, COD, and TOC levels were monitored frequently to understand the chemical energy conversion to electricity as well as to determine the best electrical configuration of the stacks. Archaeal and bacterial populations on selected anode felts and in the anolyte of both stacks were investigated as well. Indicator microorganisms for bacterial waterborne diseases were measured in anolyte and catholyte compartments to evaluate the risk of reusing the catholyte in a non-regulated environment.

Simultaneous phosphorous and nitrogen recovery from source-separated urine: A novel application for fertiliser drawn forward osmosis

Re-thinking our approach to dealing with waste is one of the major challenges in achieving a more sustainable society. However, it could also generate numerous opportunities. Specifically, in the context of wastewater, nutrients, energy and water could be mined from it. Because of its exceptionally high nitrogen (N) and phosphorous (P) concentration, human urine is particularly suitable to be processed for fertiliser production. In the present study, forward osmosis (FO) was employed to mine the P and N from human urine. Two Mg²⁺-fertilisers, i.e. MgSO₄ and Mg(NO₃)₂ were selected as draw solution (DS) to dewater synthetic non-hydrolysed urine. In this process, the Mg²⁺ reverse salt flux (RSF) were used to recover P as struvite. Simultaneously, the urea was recovered in the DS as it is poorly rejected by the FO membrane. The results showed that, after concentrating the urine by 60%, about 40% of the P and 50% of the N were recovered. XRD and SEM - EDX analysis confirmed that P was precipitated as mineral struvite. If successfully tested on real urine, this process could be applied to treat the urine collected in urban areas e.g., high-rise building. After the filtration, the solid struvite could be sold for inland applications whereas the diluted fertiliser used for direct fertigation of green walls, parks or for urban farming. Finally, reduction in the load of N, P to the downstream wastewater treatment plant would also ensure a more sustainable urban water cycle.

Load ratio determines the ammonia recovery and energy input of an electrochemical system

Complete removal and recovery of total ammonia nitrogen (TAN) from wastewaters in (bio)electrochemical systems has proven to be a challenge. The system performance depends on several factors, such as current density, TAN loading rate and pH. The interdependence among these factors is not well understood yet: insight is needed to achieve maximum ammonium recovery at minimal energy input. The aim of this study was to investigate the influence of current density and TAN loading rate on the recovery efficiency and energy input of an electrochemical cell (EC). We therefore defined the load ratio, which is the ratio between the applied current and the TAN loading rate. The system consisted of an EC coupled to a membrane unit for the recovery of ammonia. Synthetic wastewater, with TAN concentration similar to urine, was used to develop a simple model to predict the system performance based on the load ratio, and urine was later used to evaluate TAN transport in a more complex wastewater. High fluxes (up to 433 gN m^-2 d^-1) and recovery efficiencies (up to 100%) were obtained. The simple model presented here is also suited to predict the performance of similar systems for TAN recovery, and can be used to optimize their operation.

Enhanced MFC power production and struvite recovery by the addition of sea salts to urine

Urine is an excellent fuel for electricity generation in Microbial Fuel Cells (MFCs), especially with practical implementations in mind. Moreover, urine has a high content in nutrients which can be easily recovered. Struvite (MgNH₄PO₄·6H₂O) crystals naturally precipitate in urine, but this reaction can be enhanced by the introduction of additional magnesium. In this work, the effect of magnesium additives on the power output of the MFCs and on the catholyte generation is evaluated. Several magnesium sources including MgCl₂, artificial sea water and a commercially available sea salts mixture for seawater preparation (SeaMix) were mixed with real fresh human urine in order to enhance struvite precipitation. The supernatant of each mixture was tested as a feedstock for the MFCs and it was evaluated in terms of power output and catholyte generation. The commercial SeaMix showed the best performance in terms of struvite precipitation, increasing the amount of struvite in the solid collected from 21% to 94%. Moreover, the SeaMix increased the maximum power performance of the MFCs by over 10% and it also changed the properties of the catholyte collected by increasing the pH, conductivity and the concentration of chloride ions. These results demonstrate that the addition of sea-salts to real urine is beneficial for both struvite recovery and electricity generation in MFCs.

Integrated forward osmosis-membrane distillation process for human urine treatment

This study demonstrated a forward osmosis-membrane distillation (FO-MD) hybrid system for real human urine treatment. A series of NaCl solutions at different concentrations were adopted for draw solutions in FO process, which were also the feed solutions of MD process. To establish a stable and continuous integrated FO-MD system, individual FO process with different NaCl concentrations and individual direct contact membrane distillation (DCMD) process with different feed temperatures were firstly investigated separately. Four stable equilibrium conditions were obtained from matching the water transfer rates of individual FO and MD processes. It was found that the integrated system is stable and sustainable when the water transfer rate of FO subsystem is equal to that of MD subsystem. The rejections to main contaminants in human urine were also investigated. Although individual FO process had relatively high rejection to Total Organic Carbon (TOC), Total Nitrogen (TN) and Ammonium Nitrogen (NH4(+)-N) in human urine, these contaminants could also accumulate in draw solution after long term performance. The MD process provided an effective rejection to contaminants in draw solution after FO process and the integrated system revealed nearly complete rejection to TOC, TN and NH4(+)-N. This work provided a potential treatment process for human urine in some fields such as water regeneration in space station and water or nutrient recovery from source-separated urine.