We present a fully-printable method to embed interactive information inside 3D printed objects. The information is invisible to the human eye and can be read using thermal imaging after temperature transfer through interaction with the objects. Prior methods either modify the surface appearance, require customized devices or not commonly used materials, or embed components that are not fully 3D printable. Such limitations restrict the design space for 3D prints, or cannot be readily applied to the already deployed 3D printing setups. In this paper, we present an information embedding technique using low-cost off-the-shelf dual extruder FDM (Fused Deposition Modeling) 3D printers, common materials (e.g., generic PLA), and a mobile thermal device (e.g., a thermal smartphone), by leveraging the thermal properties of common 3D print materials. In addition, we show our method can also be generalized to conventional near-infrared imaging scenarios. We evaluate our technique against multiple design and fabrication parameters and propose a design guideline for different use cases. Finally, we demonstrate various everyday applications enabled by our method, such as interactive thermal displays, user-activated augmented reality, automating thermal triggered events, and hidden tokens for social activities.

The Paris Climate Treaty implies the coming of a new era towards carbon-neutral operation in wastewater treatment plants (WWTPs), and thus energy self-sufficiency from biosolids and/or heat in the form of wastewater temperature has to be considered. In this regard, anaerobic digestion (AD) of sludge should be paid renewed attention to resolve a low conversion efficiency of biosolids. As a potential way to energy positive operation, exogenous iron has been proposed to enhance methane production in recent years. In this review, the authors provided a deep insight into the feasibility of iron-enhanced AD system. Hydrogen evolution from iron corrosion and its effects on CH₄ production is firstly reviewed; then the roles of iron in reducing ORP was illustrated with regard to its impact on fermentation type; serving as an essential element and potential electron donor, the stimulating effects of iron on microorganisms and enzyme activities were also elaborated, and thus the technical feasibility of iron-based AD could be evaluated. In regards of the environmental and economic impacts of iron-based AD, life cycle assessment (LCA) was employed to calculate its economic feasibility, and the results revealed that iron-based AD system could reduce both operational costs and carbon emissions. Conclusion was drawn that iron-based anaerobic digestion is promising on technical level as well as economic perspective, and is expected to contribute to carbon-neutral operation of WWTPs. Iron-based anaerobic digestion is such a promising and sustainable strategy towards circular economy that it could be applied to many cross-disciplinary fields.

Carbon-neutral operation of wastewater treatment plants (WWTPs) requires enhancing anaerobic digestion (AD) of excess sludge for a higher energy conversion efficiency. Among others, iron has been identified to function on enhancing methane production in AD. As an industrial residual, waste iron scraps (WISs) have been reported as potentially enhancing CH₄ production in AD. With this study, the mechanisms of AD enhanced by WISs are analysed in a two-phase process: acidogenic phase (AP) and methanogenic phase (MP). Semi-continuous tests substantially excluded ORP reduction and hydrogen-evolution corrosion induced by WISs in enhancing CH₄ production, although WISs (10 g Fe/L) could indeed increase CH₄ production by 10.1% and 21.4% when added in AP and MP respectively. Detection on both FISH and enzymatic activities of involved microorganisms revealed that the stimulating effects of WISs on anaerobes (both catabolism and anabolism) could play an important (96.3%) role in enhancing CH₄ production, which would facilitate hydrolysis of refractory organics and improvement of electron transport rate (ETR).