Evaluating river health through respirogram metrics: Insights from the Weihe River basin, China.

Human activities pose a significant threat to rivers, requiring robust assessment methods for effective river management. This study focuses on the Weihe River Basin in Shaanxi province and introduces the respirogram as an innovative assessment technique. The respirogram allows the simultaneous assessment of river health from two important aspects: pollution levels and microbial status. Specifically, the in-situ respiration ratio (Rs/t) serves as an indicator of pollution, with higher Rs/t values correlating with increased pollution levels. Conversely, the recovery index (RI) measures microbial vitality, with values below 0.15 indicating greater microbial activity and recovery potential. Using predefined thresholds of Rs/t = 0.3 and RI = 0.15, water bodies were categorized into four types. For example, rivers with Rs/t > 0.3 and RI > 0.15 were identified as receiving sewage, characterized by high pollution and low microbial vitality. Similarly, different assessment criteria delineated urban rivers, natural rivers, and wastewater treatment plants. Based on these classifications, targeted engineering measures were proposed to enhance the self-purification capabilities of rivers of different statuses.

A novel approach to estimate and control denitrification performance in activated sludge systems with respirogram technology.

Respirogram technology has been widely applied for aerobic process, however, the response of respirogram to anoxic denitrification is still unclear. To reveal such response may help to design a new method for the evaluation of the performance of denitrification. The size distribution of flocs measured at different denitrification moments demonstrated a clear expansion of flocs triggered by denitrification, during which higher specific endogenous and quasi-endogenous respiration rates (SOURe and SOURq) were also observed. Furthermore, SOURq increases exponentially with the specific denitrification rate (SDNR), suggesting that there should be a maximum SDNR in conventional activated sludge systems. Based on these findings, an index Rq/t, defined as the ratio of quasi-endogenous (OURq) to maximum respiration rate (OURt), is proposed to estimate the denitrification capacity that higher Rq/t indicates higher denitrification potential, which can be readily obtained without complex measurement or analysis, and it offers a novel and promising respirogram-based approach for denitrification estimation and control by taking measures to extend anoxic time to maintain its value at a high level within a certain range.

COD/TN ratios shift the microbial community assembly of a pilot-scale shortcut nitrification-denitrification process for biogas slurry treatment.

In this study, effects of carbon to nitrogen (COD/TN) ratios of biogas slurry on shortcut nitrification-denitrification in a pilot-scale integrated fixed film activated sludge (IFAS) system were investigated. Lowering the COD/TN ratio from 11.7 to 6.2 exerted a negative impact on shortcut nitrification-denitrification performance. Accordingly, the NH3-N and TN removal rates decreased from 94.4 to 91.2% and 92.3 to 85.9%, respectively. The dynamics of microbial assembly was analyzed by MiSeq sequencing, and the denitrifying functional genes were quantified by qPCR. The results showed that ammonia oxidizing bacteria and amoA gene were more abundant on the biofilm of oxic tank, indicating they play a key role in NH3-N removal. Autotrophic, endogenous, and fast heterotrophic kinetics denitrifiers were coexisted and enriched in the IFAS system with a decreasing of COD/TN ratio. TN removal was mainly affected by denitrifiers (including Arenimonas, Acidovorax, and Thaurea) harboring narG and nirS genes. Canonical correspondence analysis proved that COD/TN ratio was the most critical factor driving the succession of microbial community. Dissolved oxygen (DO) and pH were found positively correlated with denitrifiers at low COD/TN ratio conditions. As a result, NH3-N and TN removal were effectively enhanced when the DO level in the oxic tank of IFAS system was increased to 1.0-3.0 mg/L.

[Distribution characteristics of organic matter and total nitrogen in sediments of lake Wuliangsuhai].

Lake Wuliangsuhai is one of the representative inland freshwater lakes in grassland areas of China, and its shrinking and eutrophication is becoming more serious. The study on the ecological and environmental effects of the shrinking and eutrophication revealed that the total nitrogen (TN) content in the surface sediment of the lake had an obvious differentiation both in longitudinal and in latitudinal direction, and had a significant correlation with organic matter content. The mean C/N ratio of the sediment ranged from 12.07 to 19.95, which meant that the organic matter was mainly come from the hydrophytes of the lake, and the eutrophication of the lake was mostly caused by its internal load. Both TN and organic matter had a clear grain-size effect in different fractions of grain sizes of surface sediment, and their contents in IV (< 63 microm) were as 3.1 - 7.6 and 2.5 - 8.0 times as those in I (>250 microm), respectively.