Insight into the effects of regulating denitrification on composting: Strategies to simultaneously reduce environmental pollution risk and promote aromatic humic substance formation

Denitrification during composting is a hidden danger that causes environmental pollution risk and aromatic humic substance damage, which needs to be better regulate urgently. In this study, two denitrification regulation methods, moisture and biochar amendment, were conducted during chicken manure composting. Denitrification performance data showed two regulation methods obviously reduced NO₃^--N, NO₂^--N and N₂ contents. Humic substance increased by 25.3 % and 29.1 % under two regulations. Microbiological analysis indicated that two regulation methods could decreasing denitrifying functional microbes with aroma degradation capability. Subsequently, denitrification gene narG, nirS, nosZ were significantly inhibited (p < 0.05) and the aromatic degradation metabolism pathways were down-regulated. Correlation analysis further revealed the important influence of interspecific interactions and non-biological characteristics on functional microbes. These results provided important scientific basis to denitrification regulation in the practice of composting, which achieved the purpose of simultaneously controlling environmental pollution risk and conducing end-product formation.

Environmental Pollution Index and economic growth: evidence from OECD countries

The increase in economic growth and production has caused some environmental risks. Factors such as global climate changes and global warming have raised awareness against environmental pollution. In this context, the environmental Kuznets curve (EKC) hypothesis, developed to explain the relationship between economic growth and environmental pollution, has become one of the most researched topics in the literature. In this research, the relationship is investigated between economic growth and environmental pollution for 28 OECD countries with data from the period 1995-2015. Initially, the Environmental Pollution Index was calculated using some standardized values. In addition, the relationship is examined between the Environmental Pollution Index, per capita income, environmentally related tax revenues, and urban population using Driscoll-Kraay standard errors and system generalized moments method estimators. According to the study's findings, there is an inverted U-shaped relationship between the Environmental Pollution Index and per capita income. This result supports the environmental Kuznets curve hypothesis for the OECD countries. This research is aimed to contribute to improving awareness of environmental pollution risk, which has a vital impact on sustainability besides contributing to literature.

An improved method used for evaluating potential environmental pollution risk based on spatial distribution and density of farms

The livestock manure nitrogen load on farmland (LMNLF) is often used to assess the potential environmental pollution risk of livestock manure nitrogen nutrient (LMN) in a target region. First, the LMNLF of Wuhan city is calculated, and the potential environmental pollution risk of LMN is mainly concentrated in Jiangxia District, Xinzhou District, and Huangpi District, but does not exceed the European Union (EU) standards. Heat map results also certificate this conclusion. Therefore, these three districts are the research emphases. Second, considering spatial distribution of farms, an improved LMNLF method is proposed combining the previous LMNLF and density-based spatial clustering of applications with noise (DBSCAN) methods. Several regions with pollution risks including seven regions in Jiangxia District, one in Xinzhou District, and one in Huangpi District are found out using the improved LMNLF method. Third, to evaluate the carrying capacity of the intensive breeding areas more reasonably, 2 km is taken as the farthest transportation distance of manure; there is still one region in Huangpi District which has serious pollution risk on the environment. These above results can help evaluate the pollution degree of livestock manure to the surrounding environment more precisely.