Advances in denitrification microorganisms and processes / 生物工程学报

Denitrification is an indispensable part of most sewage treatment systems. The biological denitrification process has attracted much attention in the past decades due to the advantages such as cost-effectiveness, process simplicity, and absence of secondary pollution. This review summarized the advances on biological denitrification processes in recent years according to the different physiological characteristics and denitrification mechanisms of denitrification microorganisms. The pros and cons of different biological denitrification processes developed based on nitrifying bacteria, denitrifying bacteria, and anaerobic ammonia-oxidizing bacteria were compared with the aim to identify the best strategy for denitrification in a complex wastewater environment. The rapid development of synthetic biology provides possibilities to develop highly-efficient denitrifying strains based on mechanistic understandings. Combined with the applications of automatic simulation to obtain the optimal denitrification conditions, cost-effective and highly-efficient denitrification processed can be envisioned in the foreseeable future.

Emisión de óxido nitroso, nitrificación, desnitrificación y mineralización de nitrógeno durante el cultivo del arroz en 2 suelos de Uruguay / Nitrous oxide emission, nitrification, denitrification and nitrogen mineralization during rice growing season in 2 soils from Uruguay

Los procesos microbianos como la mineralización, la nitrificación y la desnitrificación regulan la dinámica del nitrógeno en el suelo. Estos 2 últimos son los principales responsables de la emisión de óxido nitroso (N2O). En este trabajo se determinaron los flujos de N2O en momentos clave del ciclo de cultivo del arroz en 2 sitios que diferían principalmente en el contenido de materia orgánica del suelo (MO), en las localidades de Salto (mayor MO) y de Treinta y Tres. Dichos momentos clave fueron a la siembra, en macollaje, en primordio floral y a la madurez. También se determinó el potencial de mineralización neta de N y las actividades y los números más probables (NMP) de oxidantes de NH4+ y de desnitrificantes. El potencial de mineralización de N, así como la actividad y el NMP de oxidantes de NH4+, no variaron con el tipo de suelo. Sin embargo, la actividad y el NMP de desnitrificantes fueron mayores en el suelo con mayor contenido de MO, independiente de la etapa del cultivo. A su vez, en las etapas finales del ciclo del cultivo, el NMP de desnitrificantes aumentó coincidiendo con el mayor potencial de mineralización y el mayor contenido de N mineral del suelo. Solo se observó un incremento en el flujo de N2O en el suelo de Salto a la madurez del arroz y cuando el suelo ya había sido drenado (44,2g N-N2O/ha d, frente a 20,8g N-N2O/ha d en Treinta y Tres). Esta investigación señala la importancia de estudiar las emisiones en distintos tipos de suelos y de continuar la medición luego del drenaje del cultivo de arroz para la elaboración de los inventarios de gases de efecto invernadero.

Microbial processes such as mineralization, nitrification and denitrification regulate nitrogen dynamics in the soil. The last two processes may produce nitrous oxide (N2O). In this work N2O fluxes were quantified at four moments of the rice cycle, sowing, tillering, panicle initiation and maturity, in two sites that differed mainly in their soil organic matter (OM) content, Salto (higher OM) and Treinta y Tres. Potential net N mineralization, ammonium oxidation and denitrification as well as the most probable numbers (MPN) of ammonia oxidizers and denitrifiers were determined. Potential N mineralization did not vary with the soil type and increased at rice maturity. Neither ammonia oxidation potential nor MPN were different among the soils. However, the soil with higher OM exhibited higher activity and MPN of denitrifiers, irrespective of the rice stage. In turn, at the latest phases of the crop, the MPN of denitrifiers increased coinciding with the highest mineralization potential and mineral N content of the soil. Significant differences in N2O flux were observed in Salto, where the highest emissions were detected at rice maturity, after the soil was drained (44.2 vs 20.8g N-N2O/ha d in Treinta y Tres). This work shows the importance of considering the soil type and end-of-season drainage of the rice field to elaborate GHGs (greenhouse gases) inventories.

Immobilization of ammonia-oxidizing bacteria by polyvinyl alcohol and sodium alginate

Abstract Ammonia-oxidizing bacteria were immobilized by polyvinyl alcohol (PVA) and sodium alginate. The immobilization conditions and ammonia oxidation ability of the immobilized bacteria were investigated. The following immobilization conditions were observed to be optimal: PVA, 12%; sodium alginate, 1.1%; calcium chloride, 1.0%; inoculum concentration, 1.3 immobilized balls/mL of immobilized medium; pH, 10; and temperature, 30 °C. The immobilized ammonia-oxidizing bacteria exhibited strong ammonia oxidation ability even after being recycled four times. The ammonia nitrogen removal rate of the immobilized ammonia-oxidizing bacteria reached 90.30% under the optimal immobilization conditions. When compared with ammonia-oxidizing bacteria immobilized by sodium alginate alone, the bacteria immobilized by PVA and sodium alginate were superior with respect to pH resistance, the number of reuses, material cost, heat resistance, and ammonia oxidation ability.