Aerobic hydrogen-oxidizing bacteria, commonly referred to as Knallgas bacteria, are chemoautotrophic microorganisms that oxidize molecular hydrogen (H₂) while fixing carbon dioxide (CO₂) into cellular material. Historically studied as model systems for lithoautotrophic metabolism, these organisms have regained attention due to their potential for renewable H₂ utilization, land-independent biomass production, and electrochemically coupled CO₂ conversion. Among them, Cupriavidus necator has emerged as a promising industrial platform, while thermophilic and high-affinity H₂-oxidizers such as Kyrpidia spormannii are increasingly explored in bioelectrochemical systems. Despite growing interest, substantial gaps remain between laboratory demonstrations and scalable industrial performance. This review analyzes the physiological characteristics of Knallgas bacteria, including growth kinetics and H₂ oxidation parameters, and evaluates their translation into gas fermentation and oxic microbial electrosynthesis systems. Particular emphasis is placed on key engineering limitations, including H₂ mass transfer, electron partitioning during aerobic metabolism, reactor safety constraints, and electrochemical surface scaling.
Recent advances in chemical recycling have moved innovative pathways from laboratory research toward commercial deployment. However, upstream challenges, including feedstock collection, preprocessing, contaminant removal, and solids handling, remain underappreciated despite major impacts on cost, reliability, and scalability. In this review, we highlight key upstream challenges in feedstock acquisition, quality, and transport that may limit the growth of chemical recycling technologies. Using flexible film packaging, textiles, and electronic waste as case studies, we show how feedstock-specific logistics and pretreatment requirements influence process operability. We also highlight key considerations for heterogeneous solids processing. We argue that achieving cost competitiveness with virgin production will require innovations beyond deconstruction chemistry, including modular process architectures, distributed preprocessing strategies, and reactor systems designed to accommodate variable and contaminated solid feedstocks.
The continued accumulation of post-consumer plastic waste underscores the limitations of current recycling technologies, particularly when applied to heterogeneous and contaminated waste. These challenges are amplified in geographically isolated economies such as New Zealand, where centralised recycling infrastructure is often impractical. This review examines recent developments in reactive extrusion (REX) as a versatile, intermediate strategy that bridges conventional mechanical and energy-intensive chemical recycling approaches. Four REX-enabled strategies are highlighted: (1) dry-chemical approaches, (2) dynamic networks and structure control, (3) universal compatibilisers for multi-component blends and (4) partial depolymerisation and reconstruction. Together, these approaches provide pathways to recycle immiscible and contaminated plastic waste into economically valuable materials without requiring complete separation. As a next step, achieving industrial viability necessitates transitioning from laboratory-scale to pilot-scale demonstrations with real-world feedstocks containing additives and multi-phase polymer mixtures. Such targeted approaches are significant for aligning with market realities and ensuring the retention of material resources locally.
The environmental persistence of extracellular antibiotic resistance genes (eARGs) after wastewater effluent discharge raises significant ecological and public health concerns. Photochemical degradation is considered as a key mechanism for natural attenuation of eARGs, however, its effectiveness is highly variable depending on the composition of dissolved organic matter (DOM) in aquatic systems. This perspective highlights that disinfection applied in wastewater treatment plants could be an important process that fundamentally reprograms the photochemical reactivity of DOM toward eARGs, in particular in wastewater effluent-receiving aquatic environments. Such reprogramming reshapes both the photosensitizing capacity and antioxidant properties of DOM, thereby altering the balance between photochemical damage and repair of eARGs. This perspective outlines a mechanistic framework linking DOM composition, disinfection mechanism, and photochemical fate of eARGs. Also, key knowledge gaps towards photodegradation of eARGs in wastewater-impacted environments are identified for future studies.
Photocatalytic (PC) and photoelectrocatalytic (PEC) disinfection are promising technologies for inactivating antibiotic-resistant bacteria (ARB) and degrading antibiotic resistance genes (ARGs). However, their role in the spread of antimicrobial resistance (AMR) is complex and ambiguous. This review provides a comprehensive summary of the dual role of PC/PEC technologies in controlling AMR dissemination. The significant effect of PC/PEC in eliminating ARB and destroying ARGs through mechanisms such as oxidative damage to cell membranes, proteins, and genetic material is first summarized. Furthermore, although optimal lethal treatment can inhibit horizontal gene transfer by inactivating donor/recipient cells and degrading genetic vectors, sub-lethal or non-optimal PC/PEC exposures may enhance ARGs transfer. Finally, key future research perspectives are highlighted, with emphasis on enhancing reactive oxygen species efficiency, mitigating dissolved organic matter fouling and mass-transfer constraints, and developing integrated strategies to ensure these technologies mitigate rather than exacerbate AMR spread.
