Structural integrity affects nitrogen removal activity of granules in semi-continuous reactors

Research progress of novel bio-denitrification technology in deep wastewater treatment

Excessive nitrogen emissions are a major contributor to water pollution, posing a threat not only to the environment but also to human health. Therefore, achieving deep denitrification of wastewater is of significant importance. Traditional biological denitrification methods have some drawbacks, including long processing times, substantial land requirements, high energy consumption, and high investment and operational costs. In contrast, the novel bio-denitrification technology reduces the traditional processing time and lowers operational and maintenance costs while improving denitrification efficiency. This technology falls within the category of environmentally friendly, low-energy deep denitrification methods. This paper introduces several innovative bio-denitrification technologies and their combinations, conducts a comparative analysis of their denitrification efficiency across various wastewater types, and concludes by outlining the future prospects for the development of these novel bio-denitrification technologies.

Multivariate and Multiscale Approaches for Interpreting the Mechanisms of Nitrous Oxide Emission during Pig Manure-Wheat Straw Aerobic Composting

Nitrous oxide (N₂O) emission during composting causes nitrogen loss and air pollution. The interpretation of N₂O emission mechanisms will help to customize composting strategies that mitigate climate change. At pile and particle scales, this study characterized N₂O emission-related variables (gases, ions, and microbes) and their correlations during pig manure-wheat straw aerobic composting. Pile-scale results showed that N₂O emission mainly occurred in mesophilic, thermophilic, and cooling phases; the nitrification by ammonia-oxidizing bacteria ( AOB) and nitrite-oxidizing bacteria ( NOB) coexisted with the denitrification by denitrificans ( DEN); the major NOB and DEN were Nitrobacter ( NOB_Nba) and Thiobacillus denitrificans ( DEN_Tb), respectively. The mechanisms of nitrification, nitrifier denitrification, and anaerobic denitrification in composting particles were initially visualized by confocal laser scanning microscopy: Betaproteobacteria ( AOB_ Beta) sporadically distributed on the outer area of the particles, NOB_Nba internally attached to AOB_ Beta, and Nitrosomonas europea/ Nitrosomonas eutropha ( AOB_eu) and DEN_Tb concentrated in the interior. Correlation analysis of the variables showed that the distribution area of AOB_eu was proportional to N₂O emission ( R² = 0.84); AOB not only participated in nitrification but also nitrifier denitrification, and N₂O formation was mainly from nitrifier denitrification by AOB_eu during the mesophilic-thermophilic phase and from denitrification by AOB_eu and DEN during the cooling phase.