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To achieve efficient and cost-effective treatment for the rural wastewater, a novel humus biochemical system (HBS) process derived from humus bio-functional material was proposed to treat rural wastewater under low dissolved oxygen (DO) conditions, and the operational performance, sludge characteristics, and microbial community in HBS were systematically investigated in this study. The results indicated that the HBS reactor could be operated stably under low DO levels of 0.2–0.8 mg/L, and maintained high removal efficiencies of 96.4%, 96.0%, and 88.2% for chemical oxygen demand, ammonia nitrogen, and total nitrogen, with corresponding effluent concentrations of 11.0, 1.7, and 5.1 mg/L, respectively. The sludge produced from HBS was characterized by relatively large particle size, complex structural morphology, and abundant humic substances, which favorably improved the system stability. Illumina sequencing demonstrated that HBS reactor possessed high microbial abundance and diversity and was enriched with plenty of nitrifying and denitrifying bacteria, which synergistically intensified the whole biological nitrogen removal process in this system. The study presented the feasibility and adaptability of HBS for energy-efficient rural wastewater treatment. [Display omitted] • Novel HBS process with low energy consumption was proposed to treat rural wastewater. • HBS sludge was characterized by large particle size and complex structural morphology. • Distinctive microbial community with high abundance and diversity were cultured in HBS. • HBS bioreactor achieved efficient removal for N and COD under low DO conditions. [ABSTRACT FROM AUTHOR]

Abstract Quaternary Mg 2 Si 0.25 Ge 0.05 Sn 0.7 based solid solutions were synthesized by B 2 O 3 flux method combined with spark plasma sintering (SPS) technique. The carrier concentration was tuned by adjustment of the SPS temperature. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured in the temperature range from 320 to 820 K. The results show that the density, carrier concentration and lattice thermal conductivity monotonically increase with sintering temperature. With increasing carrier concentration the electron effective mass increases due to band convergence, while the electron mobility drops dramatically from 70.5 cm2 V−1 s−1 to 7.5 cm2 V−1 s−1. The phonon scattering mechanism in the quaternary solid solutions was analyzed using the Abeles model. The calculation shows that mass fluctuation scattering plays a crucial role in reducing the lattice thermal conductivity. Owing to band convergence combined with scattering of the phonons by point defects, a ZT max of 1.1 at 700 K was obtained for Mg 2 (Si 0.2 Ge 0.1 Sn 0.7) 0.99 Sb 0.01. Graphical abstract Band convergence combined with point defect scattering of phonons leads to a high ZT of 1.1 at 700 K in Mg 2 (Si 0.2 Ge 0.1 Sn 0.7) 0.99 Sb 0.01. fx1 Highlights • Mg 2 (Si,Ge,Sn) solid solutions have been successfully prepared by B 2 O 3 flux method. • Band convergence markedly enhances the Seebeck coefficient. • Mass fluctuation scattering effectively reduces the lattice thermal conductivity. • A ZT max of 1.1 at 700 K was obtained for Mg 2 (Si 0.2 Ge 0.1 Sn 0.7) 0.99 Sb 0.01. [ABSTRACT FROM AUTHOR]