Bacterial community succession in aerobic-anaerobic-coupled and aerobic composting with mown hay affected C and N losses

The primary objective of this work was to investigate how the dominant microbial species change and affect C and N losses under aerobic and aerobic-anaerobic-coupled composting of mown hay (MH, ryegrass) and corn stover (CS) mix. Results showed that C and N losses in aerobic compost of MH-CS were significantly decreased by 19.57-31.47% and 29.04-41.18%, respectively. 16S rRNA gene sequencing indicated that the bacterial microbiota showed significant differences in aerobic and aerobic-anaerobic-coupled composting. LEfSe analyses showed that aerobic composting promoted the growth of bacteria related to lignocellulosic degradation and nitrogen fixation, while aerobic-anaerobic-coupled composting promoted the growth of bacteria related to denitrification. Correlation analysis between bacterial community and environmental factors indicated that moisture content (MC) was the most important environmental factor influencing the differentiation of bacterial growth. KEGG analysis showed that aerobic composting enhanced the amino acid, carbohydrate, and other advantageous metabolic functions compared to that of aerobic-anaerobic-coupled composting. As a conclusion, the addition of 10-20% corn stover (w/w) to new-mown hay (ryegrass) appeared to inhibit anaerobic composting and prompt aerobic composting in MH-CS mix, which led to the effective utilization of mown hay as a resource for composting.

Cyanide treatment of mining tailings using suspended biomass and moving bed biomass reactors

Mexico is the top producer of silver and is on the eighth place from producing gold in the world. For instance, the hydrometallurgical extraction process produces wastewater (mining tailing) characterized by being composed with varying concentrations of cyanide and heavy metals. The purpose of this research was to study the biodegradation of cyanide contained in mining tailings by means of a bacterial consortium isolated from a tailings dam. For this purpose, three types of Eckendfelder reactors were used, one with suspended biomass (BS) and two moving bed biofilter reactors, one with biomass immobilized on Kaldnes (BK) supports, and the other on polyurethane cubes (BCP). Three experimental stages were worked; in each of them, the concentrations of total cyanide were varied. In the first one, it was 26 ± 2 mg·L^-1; in the second one 40 ± 4 mg·L^-1; and the third one 55 ± 4 mg·L^-1. During the whole operation, the pH and temperature were maintained at 9.5 units and 25 °C. After 141 days of operation, biodegradation of the total cyanide contained in the mining tailings was 69% (17 mg·L^-1) in the BS reactor, while in the BK reactor, it was 93% (3.9 mg·L^-1) and in the BCP reactor 95% (2.5 mg·L^-1). The predominant families in each of the reactors, as well as their respective relative abundances, were for the BS and for the BK of Cyclobacteriaceae (20.65% and 24.64%) and Rhizobiaceae (18.48% and 14.01%) and Halomonadaceae (46.97%) and Hyphomonadaceae (24.94%) in the BCP.