Long-term, selective production of caproate in an anaerobic membrane bioreactor.

Fermentative caproate production from wastewater is attractive but is currently limited by the low product purity and concentration. In this work, continuous, selective production of caproate from acetate and ethanol, the common products of wastewater anaerobic fermentation, was achieved in an anaerobic membrane bioreactor (AnMBR). The reactor was continuously operated for over 522 days without need for chemical cleaning. With an ethanol-to-acetate ratio of 3.0, the effluent caproate concentration was 2.62 g/L on average and the caproate ratio in liquid products reached 74%. Further raising the influent ethanol content slightly increased the effluent caproate level but lowered the product selectivity and resulted in microbial inhibition. The Clostridia (the major caproate-producing bacteria) and Methanobacterium species (which consume hydrogen to alleviate microbial inhibition) was significantly enriched in the acclimated sludge. Our results imply a great potential of utilizing AnMBR to recover caproate from the effluent of wastewater acidogenic fermentation process.

Sulfate-Functionalized Nickel Hydroxide Nanobelts for Sustained Oxygen Evolution.

Nickel hydroxide (Ni(OH)2)-based electrocatalysts are promising for the oxygen evolution reaction (OER) due to their low cost, but their activity and durability still need substantial improvement to meet practical application. Here, we report a sulfate-functionalized Ni(OH)2 nanobelt (S-Ni(OH)2) electrocatalyst, which exhibited self-enhanced OER activity due to its self-renewed surface during anodic oxidation. The S-Ni(OH)2 was in situ grown on the nickel foam (NF) surface in potassium peroxydisulfate solution through one-step hydrothermal treatment. This material outperformed all the existing electrocatalysts in the intensity and duration of the OER activity enhancement. An overpotential drop of 70 mV is shown by the S-Ni(OH)2/NF electrode during 110 h reaction at a current density of 100 mA cm-2, and the overpotential remains as low as 358 mV at a current density of 200 mA cm-2. Such activity enhancement during OER is mainly ascribed to the formation of a highly active NiOOH/Ni(SO4)0.3(OH)1.4 composite on the S-Ni(OH)2 surface as a result of gradual sulfate release. Given the facile and environmentally benign fabrication process (without external addition of a Ni source and surfactant) and good electrochemical properties (high activity and long lifetime), the S-Ni(OH)2 holds great potential for practical OER application. The surface self-renewal strategy developed here might also be expanded to other electrocatalysts and electrochemical processes.