There is an unmet need for a low-cost instrumented technology for detecting sanitation-related malodor as an alert for maintenance around shared toilets and emerging technologies for onsite waste treatment. In this article, our approach to an electronic nose for sanitation-related malodor is based on the use of electrochemical gas sensors, and machine-learning techniques for sensor selection and odor classification. We screened 10 sensors from different vendors with specific target gases and recorded their response to malodor from fecal specimens and urine specimens, and confounding good odors such as popcorn. The analysis of 180 odor exposures data by two feature-selection methods based on mutual information indicates that, for malodor detection, the decision tree (DT) classifier with seven features from four sensors provides 88.0% balanced accuracy and 85.1% macro F1 score. However, the k-nearest-neighbors (KNN) classifier with only three features (from two sensors) obtains 83.3% balanced accuracy and 81.3% macro F1 score. For classification of urine against feces malodor, a balanced accuracy of 94.0% and a macro F1 score of 92.9% are achieved using only four features from three sensors and a logistic regression (LR) classifier.

Platinum electrodes are commonly used in devices such as fuel cells, neurostimulators, and sensors. Device performance can be improved by increasing the electrochemically active surface area of the platinum, which increases the charge storage capacitance, oxygen reduction reaction (ORR) rates, and catalytic activity. Therefore, there is significant motivation to fabricate platinum 3D structures, but it is challenging to accomplish successfully. In this study, graphenated carbon nanotubes (gCNTs), a type of carbon nanotube with leaf-like graphene foliates, were decorated with platinum nanoparticles to fabricate a 3D structure with increased Pt surface area. The carbon nanotubes act as a conductive scaffold and the foliates provide increased surface area and highly reactive edge sites.The development of gCNTs was accomplished by systematically adjusting growth parameters in a microwave plasma enhanced chemical vapor deposition system. The primary growth parameters were growth temperature, growth time, process gas composition (methane flow rate vs ammonia flow rate), and microwave power. gCNTs were characterized to obtain the best relevant electrochemical properties, i.e., impedance, voltage window, stability, and charge storage capacity. Compared to platinum, typical gCNT electrodes had lower impedance at 100 Hz at 230 Ω vs 375 Ω for Pt. The electrochemical properties of the gCNTs were compared to scanning electron microscope images (Fig. 1) and it was found that a medium foliate density (3.0 CH4: 1 NH3) had the best electrochemical properties.Next, the gCNTs electrodes can be further enhanced by decoration with nanoparticles of platinum via atomic layer deposition (ALD). Atomic layer deposition alternates two reagents so that the first adsorbs on the surface in a monolayer and the second reacts with the monolayer. The most reactive sides tend to nucleate first, so that at low deposition density, particles preferentially deposit at the edges of the graphene foliates. A major advantage of ALD is that it produces much more monodispersed nanoparticles, which yields more uniform properties. The combined electrodes will have the larger electrochemical surface area of gCNTs and the catalytic and charge storage properties of platinum electrodes. Electrochemical properties of Pt-gCNTs will be compared to gCNTs and planar Pt electrodes. Figure 1

Inadequately treated wastewater exiting from on-site water treatment systems (OWTS) contains high levels of ammonium and phosphate, which contribute to environmental nutrient pollution. Nutrient removal in small-scale OWTS can be challenging because the most effective known methods are designed for large-scale systems and rely on biological processes. This work focuses on the implementation of two natural silicate-based minerals, clinoptilolite and Polonite, as non-biological sorptive media for nutrient removal in an OWTS. Lab-scale batch sorption experiments showed that Polonite performance is maximized after suspended solids have been removed from blackwater via ultrafiltration. In contrast, clinoptilolite shows robust performance even with untreated blackwater. With both minerals installed in our full-scale OWTS prototype, nutrient removal performance increased from 47.5 ± 15.0% to 84.1 ± 6.3% removal for total N and from 32.3 ± 2.3% to 78.9 ± 5.9% removal for total P. Nevertheless, the target removal performance (>80%) for total P was only achieved with high Polonite loading, which increased effluent pH outside the target range of 6 < pH < 9. Additionally, no loss in nutrient removal performance was observed when the OWTS was restarted after a 150-day idle period. To investigate the potential for media reuse and nutrient recovery, various media regeneration solutions were evaluated. For clinoptilolite, 1 M HCl, NaCl, and KCl all showed good regeneration ability at 2 h contact time, with KCl showing the highest (>86%) ammonium recovery. For the first time, we demonstrated that a minor fraction (30–40%) of binding sites in Polonite can be regenerated using 1 M NaOH or KOH. We also found that the same 1 M HCl regeneration solution could be reused for four clinoptilolite regeneration cycles with no loss in performance. From these results, we discuss opportunities and limitations for implementing these materials in small-scale OWTS.

p-Cresol modulation was for the first time evaluated as an alternative option for odor control in sanitation facilities. Results indicate that the oxidation of p-cresol can generate 4-hydroxybenzaldehyde (4-HB), a molecule with a sweet-woody odor, following the introduction of chloride ions into the supporting electrolyte. In an attempt to impede electrode fouling, pulsed chronoamperometry (CA) was implemented and resulted in ∼10% higher p-cresol removal compared to CA at constant potential. Boron doped diamond (BDD) was also explored as an alternative working electrode. p-Cresol oxidation on the diamond surface resulted in higher removal percentages, but the desired oxidation product was not detected by Liquid chromatography–mass spectrometry (LC-MS) likely due to complete combustion.