Environmental and economic sustainability of the novel photovoltaic industrial wastewater treatment systems from life cycle perspective.

The photovoltaic (PV) industry is advancing in tandem with the global green energy revolution. Within the PV industry’s production cycle, the manufacture of solar cells necessitates extensive chemical usage and results in the generation of high-pollution and high-risk wastewater, such as fluorinated wastewater, ammonia-nitrogen wastewater, silica-rich wastewater and acid-base wastewater (Gao et al., 2024). On average, producing 1 GW of solar cell capacity generates approximately 1,000 tons of wastewater daily (Fadila et al., 2018). Among the challenges in photovoltaic wastewater treatment (PVWT) are managing wastewater with high concentrations of fluoride and ammonia nitrogen. Fluoride poses significant toxicological threats to both animal and plant health (Nadjib et al., 2013; Zuo et al., 2018), while ammonia nitrogen is a critical factor in water body eutrophication and ecosystem degradation (Xue et al., 2021; Yafan et al., 2022). Consequently, the safe management of wastewater from solar cell production is crucial for ensuring the green and sustainable development of the PV industry.

Currently, PV enterprises typically treat fluorinated and ammonia-nitrogenated wastewater through separate processes before combining the emissions. For fluorinated wastewater, the combined chemical precipitation-coagulation process is widely used due to its simplicity and cost-effectiveness. However, this method often generates large amounts of chemical sludge and results in significant wastage of fluorine resources. Alternative methods like adsorption, ion exchange, electrocoagulation, and membrane processes are only suitable for the deep removal of low concentrations of fluorine. It is not effective at treating high-concentration fluorinated wastewater. (Chen et al., 2023; Da Conceição et al., 2021; Ewadh et al., 2021). In contrast, the treatment of ammonia-nitrogenated wastewater primarily relies on biochemical processes, with traditional anaerobic-anoxic-oxic (A²/O) and anaerobic ammonia oxidation (ANAMMOX) being commonly used for ammonia nitrogen removal (A., 2023; Mingdong et al., 2022; Weißbach et al., 2018). However, these traditional biochemical processes lose their advantages when treating high ammonia-nitrogenated wastewater due to high chemical input, high energy consumption, and substantial sludge production (Zhou et al., 2023).

Furthermore, fluorine and ammonia nitrogen in wastewater possess dual properties as both pollutants and valuable resources, making their recovery a crucial focus given the rapid depletion of primary resources. The crystalline precipitation method offers a viable solution for recovering fluorine resources from highly fluorinated wastewater (Aldaco et al., 2008). This involves the crystallization and precipitation of calcium, aluminum, and sodium salts with fluorine under specific conditions, producing high-value-added products such as calcium fluoride or cryolite. Calcium fluoride is a primary raw material for the production of hydrofluoric acid and serves as the starting material for the synthesis of most fluorine-containing compounds. It has broad applications across various industries, including metallurgy, glass, ceramics, optics, medicine, and environmental protection. Cryolite has also a variety of applications across different industries. It is widely used as a flux in aluminum electrolysis, where it significantly lowers the melting point of alumina, allowing the electrolysis process to occur at a reduced temperature. Additionally, it serves as a wear-resistant filler in rubber and grinding wheels, a milky-white agent in enamel production, a shading agent in glass manufacturing, and an insecticide for agricultural purposes, among other uses (Shao et al., 2021; T et al., 2016; You et al., 2023). For instance, there was a study, which successfully recovered ceramic-grade calcium fluoride (85.6%-87.9% purity) from fluoridated wastewater through crystallization precipitation, achieving a 99% fluorine recovery rate (Tran and Lin, 2022). Research has demonstrated the recovery of high-molecular-weight cryolite from highly fluorinated wastewater, with optimal conditions for cryolite formation being higher pH, higher influent fluoride ion concentration, and lower reaction temperature (Ke and Kanggen, 2017). Additionally, Qiu employed the ultrafiltration-bipolar membrane electrodialysis (RCUF-BMED) system to recover wastewater rich in fluoride and silica, converting it into sodium silicofluoride (Na₂SiF₆). This process achieved a recovery rate of approximately 72% and a purity of 99.1% (Qiu et al., 2022). Similarly, the alkalization-blow-off method effectively recovers ammonia nitrogen, converting it into valuable products like ammonium chloride, ammonium sulfate, and ammonium phosphate. Ammonium salts are widely utilized across several industries, including agriculture, pharmaceuticals, and food production. Notably, ammonium nitrate and ammonium sulfate serve as essential raw materials for nitrogen fertilizers, which enhance plant growth and development. Ammonium chloride, on the one hand, plays a key role in drug synthesis and acts as a sustained-release agent for medications. On the other hand, it is also employed as a food additive to improve the nutritional value, color, and flavor of food products (Bahad?rl? et al., 2025; Al-Shareef et al., 2016; Geisseler and Scow, 2014). For example, ammonium phosphate was recovered from waste leachate using the blow-off method, achieving a recovery rate of approximately 92% (Pereira et al., 2020). Although many studies have demonstrated the synergy between resource recovery and pollutant control for fluorine and ammonia nitrogen, most of the resource recovery efforts are still at the laboratory stage, lacking large-scale pilot tests to verify the resource recovery process feasibility. Additionally, resource recovery processes often involve significant chemical and energy inputs, raising concerns about their environmental impact and sustainability, which are not always systematically evaluated. Therefore, further research and development are necessary to optimize these processes for industrial-scale application while ensuring environmental friendliness.

Life cycle assessment (LCA) and life cycle cost (LCC) are essential instrument for the holistic appraisal of the environmental repercussions and economic efficacy of wastewater treatment systems (Yahong et al., 2022; Zhou et al., 2021). Thus far, there is a lack of comprehensive evaluation of the whole life cycle of PVWT and resource utilization from the perspectives of technology, economy, and environment. Consequently, the overarching aim of this investigation is to amass meticulous data pertaining to the material influx and efflux across diverse PVWT and resource exploitation routes, predicated upon laboratory refinements, pilot-scale validations, and scholarly literature. Through the elucidation of material and energy trajectories, the compilation of a life cycle inventory, and the execution of a thoroughgoing evaluation of the environmental footprint and technical economic viability of processing routes, this study endeavors to furnish the requisite insights for the refinement and judicious selection of PVWT methodologies.

ABSTRACT ONLINE AT https://www.sciencedirect.com/science/article/abs/pii/S0013935125004086