Spectroscopic and multivariate analysis insights into the DOM composition and distribution in a full-scale...

With the global expansion of the photovoltaic (PV) industry, zero-liquid discharge (ZLD) is a crucial approach for sustainable wastewater management. The dynamics of dissolved organic matter (DOM) remain underexplained across the long ZLD treatment train. In this study, the DOM decomposition and distribution in a full-scale PV wastewater ZLD system were investigated via simple and engineering-feasible spectroscopic techniques and multivariate data analysis. Three DOM components were identified: the N-heterocyclic organic compound was the dominant component (accounting for 70%) and was effectively removed within the pretreatment stage. The terrestrial humic/fulvic acids were less influenced during pretreatment and were preferentially rejected in the membrane processes. The tyrosine-like and soluble microbial products were formed in the microbial and oxidation processes. The significant DOM distribution pattern was revealed in the ZLD system; the A/O, ozonation, and RO units were the hotspots for DOM transformation. Seasonal differences were also demonstrated, with the decline in biological degradation as the main driving factor. DOM is characterized by high biodegradability and autochthonous sources in summer, while exhibiting higher humification and structural stability in winter. Particularly, TN and TP were the key drivers of DOM transformation in summer, whereas membrane separation and salinity dominated in winter. This study advances the mechanistic understanding of DOM composition and distribution in a full-scale ZLD process, providing a theoretical basis for the operation optimization of PV wastewater treatment.