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Abstract Heterogeneous photocatalysis is an emerging area of catalysis increasingly fraught with pains caused by the battle between hype and real‐ world application. Inspired by abundant yet diffuse solar energy and applications such as clean water and energy, ample motivation has provided the background for this situation. However, substantial fundamental (e. g., charge transfer, recombination), engineering (e. g., observed rates, photon management), and practical barriers (e. g., use of precious metals, competing technologies) have limited implementation. In this review, these are all outlined, in conjunction with typical strategies for improvements, with an emphasis on the use of semiconductor photocatalysts for the degradation of emerging forever chemical contaminants in water. The selected classes of forever chemical contaminants are (micro)‐plastics, per‐ and polyfluoroalkyl substances (PFAs), siloxanes, and dioxanes. Each has been identified as a key or emerging contaminant and often travel widely while accumulating in the atmosphere due to the lack of natural remediation processes. Recommendations to the field and opportunities for contributions are highlighted throughout and as part of the outlook to the future. 

Conventional biological nitrogen removal (BNR) processes for mainstream municipal wastewater (MMW) treatment have high energy and chemical costs. Partial nitritation/anammox (PN/A) has the potential to reduce the carbon footprint of BNR; however, its implementation for MMW treatment has been limited by the low ammonium and high organic matter concentrations in MMW, which prevent suppression nitrite oxidizing bacteria (NOB) and heterotrophic denitrifiers. In this study, after organic carbon diversion, ammonium was separated from MMW in a novel bench-scale sequencing batch biofilm reactor (SBBR) containing chabazite, a natural zeolite mineral with a high ammonium ion exchange (IX) capacity. After breakthrough, chabazite was bioregenerated by PN/A biofilms. Recirculation was applied from the bottom to the top of the column to create an aerobic zone (top) for ammonia-oxidizing microorganisms (AOM) and an anoxic zone (bottom) for anammox bacteria. Rapid IX-PN/A SBBR startup was observed after inoculation with PN/A enrichments. The time required for bioregeneration decreased with increasing recirculation rate, with high total inorganic nitrogen (TIN) removal efficiency (81 %) and ammonium removal rate (0.11 g N/L/day) achieved at recirculation velocity of 1.43 m/h. The core microbiome of the IX-PN/A SBBR contained a high abundance of bacteria of the phylum Pseudomonadota (15.27–20.62 %), Patescibacteria (12.38–20.05 %), Chloroflexota (9.36–14.23 %), and Planctomycetota (7.55–12.82 %), while quantitative PCR showed the highest ammonia monooxygenase (amoA, 2.0 × 102) and anammox copy numbers (amx, 1.0 × 104) in the top layers. The single-stage IX-PN/A SBBR achieved stable BNR for >two years without chemical inputs, media replacement or brine waste production.