Interfacial solar evaporation toward efficient recovery of clean water and concentration of nutrients from urine with polypyrrole-based photothermal conversion films
Graphical abstract
Introduction
Human urine consists of a mixture of water (90∼95%) and nutrients. Specifically, about 80% of the nitrogen, 56% of the phosphorus, and 63% of the potassium in domestic wastewater were originated from urine, which is known as the liquid gold of wastewater (Larsen et al., 2021; Randall and Naidoo, 2018). With the intensification of the freshwater resource crisis and water pollution (Li et al., 2020; Tunuguntla Ramya et al., 2017; You et al., 2022; Zhang et al., 2020), numerous researchers have proposed separating human fecal urine from domestic miscellaneous drainage water to recover energy and resources (Li et al., 2021; Lin et al., 2021; Randall and Naidoo, 2018). Current technologies for nutrient recovery include membrane separation (Yu et al., 2021), ion exchange adsorption (Tarpeh et al., 2017), precipitation and crystallization (Gao et al., 2018), blow-off absorption (Chipako and Randall, 2020), electrochemical and biological treatment (Nazari et al., 2020; Yang et al., 2022), etc. Nevertheless, the aforementioned treatment technologies are chemical, energy, and operation intensive, which are highly unsuitable for the recovery of energy and resources in rural areas of developing countries (Antonini et al., 2012; Wu et al., 2022). Under the condition of ensuring minimum ammonia volatilization in urine, concentration and dehydration technologies can be used to concentrate the salt in urine and obtain crystalline products to achieve the complete recovery of nitrogen, phosphorus, and potassium elements, while at the same time recovering a large amount of clean water (Martin et al., 2022; Patel et al., 2020). Among the concentration and dewatering technologies, interfacial solar evaporation is simple to operate, easy to manage, and economically feasible to replace traditional energy sources with solar energy, making it ideal for use in less developed areas or rural areas (Antonini et al., 2012; Pronk and Koné, 2009). With the rapid development of interfacial solar evaporation technology, the important applications related to this technology have gradually gained the attention of researchers (Li et al., 2018; Zhao et al., 2021). At present, the application of this technology is mainly focused on seawater desalination (Wang, Z. et al., 2019), sewage treatment (Tao et al., 2018), power generation (Wang, W. et al., 2019; Xu et al., 2022), photothermal catalysis (Zhou et al., 2018), disinfection and sterilization (Zha et al., 2019), etc. In contrast, research applying interfacial solar evaporation technology to the treatment of urine is rare. This technology not only enables urine reduction and recovery of fresh water and nutrients, but this recovery method is also green and economical (Chen et al., 2019), thereby reducing the consumption of material energy and reducing the nitrogen and phosphorus load of wastewater treatment plants. The fresh water produced can be reused as flushing water or even drinking water, the reduced urine is easy to transport and collect, and the concentrated salt fraction can be further treated and reused in agricultural fields, which can lead to great practical application value (Antonini et al., 2012; Singh et al., 2020).
In practical applications, photothermal conversion materials highly influence the performance of interfacial solar evaporation. To achieve high efficiency and economy, photothermal conversion materials are required to have the following characteristics: good solar absorption, low mid-infrared light absorption (to avoid heat dissipation), efficient photothermal conversion performance, good thermal regulation (ensuring thermal conduction, thermal radiation, and thermal convection are as low as possible), low cost, good recyclability and scalability, and long-term stability (Chen et al., 2019; Gao et al., 2019; Razaqpur et al., 2021; Zhang et al., 2019). In recent years, a rising number of scholars have developed a variety of photothermal conversion materials, which are mainly divided into four major categories (Razaqpur et al., 2021): metal plasma materials (Song et al., 2019), inorganic semiconductor materials (Wu et al., 2019), carbon-based materials (Yao et al., 2022; Zhu, L. et al., 2019), and organic polymer materials (Wang, X. et al., 2019). In contrast, polypyrrole is a typical conductive organic polymer material that is simple to prepare, has a low-cost, possesses a high light absorption in the near-infrared region due to the inclusion of a large conjugated system within its molecule, and it is environmentally friendly (Yang et al., 2021). With its excellent photothermal properties and low thermal conductivity, polypyrrole is considered an ideal candidate for solar-thermal energy conversion (Li et al., 2019).
Based on this, a series of polypyrrole-based photothermal conversion films were prepared by chemical polymerization. Through the indoor solar water evaporation experiments, the best operating conditions were selected for the further indoor solar urine evaporation experiments. The solution with high stability, excellent evaporation performance and low cost was selected for further outdoor solar urine evaporation experiment, with the aim of obtaining more clean water and concentrating of nutrients from the urine evaporation process. Specifically, indoor solar water evaporation experiments were first conducted to determine the evaporation performance and stability of CCF (cotton cloth photothermal conversion film) and PWF (paulownia wood photothermal conversion film). Moreover, the effects of light intensity and evaporation systems were investigated. Subsequently, the most suitable photothermal conversion film and the most economical evaporation system for outdoor solar urine evaporation were selected for indoor solar urine evaporation experiments. Finally, CCF-MHLC (CCF-monolithic hydrophobic-large-scale) was applied to an independently designed system of evaporation, condensation, and collection units integrated into one device for outdoor solar urine evaporation. More importantly, this work provides new ideas and data support for exploring other photothermal conversion materials for small-scale treatment of urine wastewater under laboratory conditions, especially for the large-scale treatment of urine wastewater under outdoor conditions.
Section snippets
Materials and equipment
The materials and equipment used in the experiments are provided in Text S1. In addition, the composition of synthetic hydrolyzed urine is given in Table S1.
Hydrophilic photothermal conversion films fabrication
Initially, the above two substrate materials (cotton cloth (CC) and paulownia wood (PW), 2 cm in diameter) were completely immersed in 0.02 M of 10 mL FeCl3 solution at 4°C, ensuring the substrate materials were fully wetted. Two h later, the same volume and concentration of pyrrole solution were added drop by drop to the above FeCl3
Indoor solar water evaporation performance
Fabrication of photothermal conversion films exhibit a high light absorption capacity on the surface of the substrate materials (CC and PW) is essential to drive high solar evaporation efficiency. Herein, the light absorbance, SEM images and digital photos of CC, PW, CCF, and PWF, as well as the AFM images of CC and PW were measured and displayed in Fig. 2. The polypyrrole coatings on the CC and PW surfaces remarkably improved the light absorption capacity to 96.19% and 97.44, respectively (
Conclusions
In summary, a series of polypyrrole-based photothermal conversion films were developed using ferric chloride and pyrrole as raw materials with CC and PW utilized as substrates. The indoor solar water evaporation experiments revealed that the PWF and CCF exhibited a high evaporation performance and stability of photothermal conversion materials in an imitation tree structure evaporation system under 1.0kW·m−2 illumination, which could be further used in later experiments. The indoor solar urine
CRediT authorship contribution statement
Lei Zhang: Investigation, Methodology, Software, Visualization, Writing – original draft. Jie Liu: Investigation, Methodology, Software, Visualization, Writing – original draft. Libin Yang: Conceptualization, Formal analysis, Funding acquisition, Writing – review & editing. Zhenjiang Yu: Investigation, Methodology, Software. Jiabin Chen: Conceptualization, Formal analysis, Writing – review & editing. Huaqiang Chu: Conceptualization, Formal analysis, Writing – review & editing. Yalei Zhang:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was supported by the National Key R&D Program of China (2018YFD1100500) and National Natural Science Foundation of China (U21A20322, 51878465, and 42006139).
References (51)
- et al.
Solar thermal evaporation of human urine for nitrogen and phosphorus recovery in Vietnam
Sci. Total Environ.
(2012) - et al.
Challenges and opportunities for solar evaporation
Joule
(2019) - et al.
Plasmonic wooden flower for highly efficient solar vapor generation
Nano Energy
(2020) - et al.
Urine treatment technologies and the importance of pH
J. Environ. Chem. Eng.
(2020) - et al.
An experimental study on the recovery of potassium (K) and phosphorous (P) from synthetic urine by crystallization of magnesium potassium phosphate
Chem. Eng. J.
(2018) - et al.
State of the art of urine treatment technologies: a critical review
Water Res. X
(2021) - et al.
Enhancement of interfacial solar vapor generation by environmental energy
Joule
(2018) - et al.
Adsorption of Congo red and methylene blue dyes on an ashitaba waste and a walnut shell-based activated carbon from aqueous solutions: Experiments, characterization and physical interpretations
Chem. Eng. J.
(2020) - et al.
Mining resources from water
Resour. Conserv. Recycl.
(2021) - et al.
Waste or gold? Bioelectrochemical resource recovery in source-separated urine
Trends Biotechnol
(2020)
Technologies for the recovery of nutrients, water and energy from human urine: a review
Chemosphere
Options for urine treatment in developing countries
Desalination
Urine: The liquid gold of wastewater
J. Environ. Chem. Eng.
Progress of photothermal membrane distillation for decentralized desalination: A review
Water Res
Solar steam generation through bio-inspired interface heating of broadband-absorbing plasmonic membranes
Appl. Energy
Towards sustainable saline agriculture: Interfacial solar evaporation for simultaneous seawater desalination and saline soil remediation
Water Res.
A flexible photothermal cotton-CuS nanocage-agarose aerogel towards portable solar steam generation
Nano Energy
All-in-one polymer sponge composite 3D evaporators for simultaneous high-flux solar-thermal desalination and electricity generation
Nano Energy
Valorization of livestock manure for bioenergy production: A perspective on the fates and conversion of antibiotics
Resour. Conserv. Recycl.
Sustainability and carbon neutrality trends for microalgae-based wastewater treatment: a review
Environ. Res.
Interfacial solar vapor generation for desalination and brine treatment: Evaluating current strategies of solving scaling
Water Res
Adsorption of dyes brilliant blue, sunset yellow and tartrazine from aqueous solution on chitosan: Analytical interpretation via multilayer statistical physics model
Chem. Eng. J.
Adsorption of SO2 and NH3 onto copper/graphene nanosheets composites: Statistical physics interpretations, thermodynamic investigations, and site energy distribution analyses
Chem. Eng. J.
Solar absorber material and system designs for photothermal water vaporization towards clean water and energy production
Energy Environ. Sci.
Concentrating human urine by evaporation. Master’s Thesis
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These authors contributed equally to this work.