Simultaneous multi-pollutant removal from photovoltaic wastewater by aluminum-modified biochar-enhanced partial nitritation-anammox process.

Photovoltaic (PV) wastewater features high ammonium (NH4+-N) and multiple pollutants such as silica (SiO2), fluoride ions (F-), and aluminum (Al), creating barriers to autotrophic nitrogen removal. An aluminum-modified sludge biochar (Al-SBC) supplemented single-stage sludge-biofilm coupled partial nitritation/anammox (PN/A) reactor was established in this work for real PV wastewater treatment. Experimental findings illustrated that Al‑SBC markedly boosted the PN/A reactor's treatment performance for PV wastewater. Under low PV wastewater proportion conditions, Al-SBC rapidly promoted biofilm formation and sludge granulation. Under 100% PV wastewater conditions, the Al-SBC enhanced system still maintained excellent nitrogen removal performance, together with good removal of SiO2, F-, and total Al (TAl). In contrast, the control system lost its nitrogen removal function and exhibited virtually no removal capacity for SiO2, F-, and TAl. These outcomes stemmed from Al‑SBC's strong sequestration of SiO2, F- and TAl, promotion of robust biofilm and compact small sludge granule formation, and modulation of hydrophobic amino acid (HAA) synthesis within tightly bound extracellular polymeric substances. Furthermore, in the Al-SBC-enhanced system, Candidatus Brocadia dominated the biofilm (30%), while Nitrosomonas was the predominant genus in the granular sludge (28%), indicating that Al-SBC facilitated functional microbial niche differentiation between aggregates. Metatranscriptomic analysis showed that Al-SBC upregulated the transcriptional activity of key pathways such as nitrogen metabolism and HAA biosynthesis, and the transcription of functional genes. This study facilitates the application and advancement of PN/A processes for photovoltaic wastewater treatment.