Characteristics of nitrate removal in a bio-ceramsite reactor by aerobic denitrification

Accelerated humification and alteration of microbial communities by distillers' grains addition during rice straw composting

This research explored the influence of distillers' grains amendment on the humification performance and microbial communities during rice straw composting. The composition of dissolved organic matter and maturity index were analyzed by the fluorescence excitation emission matrix spectroscopy and parallel factor analysis. High-throughput sequencing and redundancy analysis were employed for revealing the structure dynamics for microbial community and their shaping factors, respectively. Results indicated that addition of distillers' grains effectively increased the microbial activity, which was beneficial to the organic matter degradation and nitrogen conservation. Microbial community structures were significantly changed with different amendment strategies. Nitrate, water soluble carbon, organic matter, ammonium were the key parameters influencing the variation of bacterial community in different treatments. Water soluble carbon significantly affected the dominant fungal community dynamics. These results showed that addition of distillers' grains effectively improved the nutritional status and changed the microbial communities during rice straw composting.

Evaluation of NOx removal from flue gas and Fe(II)EDTA regeneration using a novel BTF-ABR integrated system

A promising process is under development for the removal of NOx and regeneration of Fe(II)EDTA in a novel biotrickling filter-anaerobic baffled reactor (BTF-ABR) integrated system at 50 ± 0.5 ℃. In this work, we investigated the NOx removal capacity of a BTF under different O₂ concentrations (7.0 vol%, 5.25 vol% and 3.5 vol%), and tested the effect of an ABR on NOx removal and regeneration of Fe(II)EDTA. The results showed that the NOx removal capacity was significantly increased with the O₂ concentration reduced from 7.0% to 3.5%. The microoxygen environment produced by the BTF-ABR integrated system was more conducive to the removal of NOx and regeneration of Fe(II)EDTA compared with that in the BTF. Real-time polymerase chain reaction (PCR) analysis showed that the coordinated expression of denitrification genes was the major reason for no N₂O emission, along with no nitrate and nitrite accumulation. The 16S rRNA gene amplicon sequencing analysis showed that the cooperation of denitrifying bacteria (Klebsiella, Petrimonas, Rhodococcus and Ochrobactium) and iron-reducing bacteria (Klebsiella, Geobacter and Petrimonas) in the system was the key to the stable and efficient removal of NOx and the regeneration of Fe(II)EDTA simultaneously.

Effect of Denitrifying Bacterial Biomass and Carbon Sources on Nitrate Removal

Denitrification based on immobilized microbial cellulose may offer an economical replacement for conventional treatment for nitrate removal. The environmental and bacterial biomass may influence the rate of biological denitrification processes. This study aimed to investigate the factors that affect denitrification rates, including carbon sources, pH, and bacterial inoculum. Different inoculum biomass of Pseudomonas aeruginosa and various carbon sources of glucose, sucrose, and cellulose with different concentrations were tested to assimilate 100 mg/L of KNO3 as nitrate source. Additionally, five additional inoculations, five different incubation time, and seven different pH levels were studied. The Pseudomonas aeruginosa isolates used different mineral media with three carbon sources, glucose, sucrose, and cellulose, with different concentrations at different rates to denitrify nitrate. The highest denitrification rate was with glucose after 18 hrs and was after 24 hrs when sucrose and cellulose were used, respectively. The bacterial biomass denitrification level was the highest, between 0.8% and 1% of OD600=1. Nitrate removal by Pseudomonas aeruginosa was the highest at pH 7, 8, and 9. This report suggests that when glucose is used as a carbon source, at neutral to alkaline pH, and 1% of denitrifying bacterial biomass, the highest level of biological denitrification process may be achieved.

A critical review of aerobic denitrification: Insights into the intracellular electron transfer

Aerobic denitrification is a novel biological nitrogen removal technology, which has been widely investigated as an alternative to the conventional denitrification and for its unique advantages. To fully comprehend aerobic denitrification, it is essential to clarify the regulatory mechanisms of intracellular electron transfer during aerobic denitrification. However, reports on intracellular electron transfer during aerobic denitrification are rather limited. Thus, the purpose of this review is to discuss the molecular mechanism of aerobic denitrification from the perspective of electron transfer, by summarizing the advancements in current research on electron transfer based on conventional denitrification. Firstly, the implication of aerobic denitrification is briefly discussed, and the status of current research on aerobic denitrification is summarized. Then, the occurring foundation and significance of aerobic denitrification are discussed based on a brief review of the key components involved in the electron transfer of denitrifying enzymes. Moreover, a strategy for enhancing the efficiency of aerobic denitrification is proposed on the basis of the regulatory mechanisms of denitrification enzymes. Finally, scientific outlooks are given for further investigation on aerobic denitrification in the future. This review could help clarify the mechanism of aerobic denitrification from the perspective of electron transfer.

Experimental investigation and simulation of nitrogen transport in a subsurface infiltration system under saturated and unsaturated conditions

The nitrogen dynamics in a subsurface infiltration system (SIS) are affected by many factors, including temperature, system design, and feed water quality, which are not easily quantified. In this study, a column experiment was conducted to simulate an SIS. The HYDRUS-1D software package was used to investigate and quantify the factors that affect nitrate transport in an SIS. Three treatments were carried out based on different hydraulic conditions, including continuous wetting (CW), wetting/drying (WD), and a specific hydraulic loading rate (SH). The effects of hydraulic conditions and temperature on nitrate transformation were investigated. The model was calibrated and validated using two-year experimental data. Simulations of cumulative outflow volume and nitrate concentration fitted well with the observations. Among the three SISs, the denitrification rate was greatest under unsaturated conditions at high water temperature. The denitrification rate constant had an exponential relationship with temperature. An empirical formula describing this relationship was developed and validated in the SIS. The results showed that the SH column attained the greatest nitrate removal efficiency, mainly due to its low hydraulic loading and long retention time. Overall, the results showed that HYDRUS-1D adequately simulated nitrate transport through the soil column under different temperature and hydraulic conditions in an SIS. The fate of nitrate was directly controlled by the water temperature and hydraulic conditions.

Long-term pollutant removal performance and mitigation of rainwater quality deterioration with ceramsite and Cyperus alternifolius in mountainous cities of China

Rainwater harvesting brings various desired environmental and social benefits in urban development. Tanks in rainwater harvesting systems need low-maintenance and low-cost approaches to manage water quality, especially for scattered small rainwater tanks associated with complex terrains in mountainous cities. Four rain barrels were set up to store roof runoff at the campus of Chongqing University, Chongqing, China. Barrel 1 (B1) and barrel 2 (B2) stored the first-flush water and the roof runoff with first-flush water diverted, respectively, while barrel 3 (B3) was loaded with a biological ceramsite and barrel 4 (B4) used biological ceramsite as a substrate media and planted with Cyperus alternifolius (C. alternifolius) to treat the first-flush water. The performances of the rain barrels were evaluated as well as the variations in water quality parameters were examined. The removal efficiency of B3 was 48.2%, 76.0%, 44.3%, and 24.6% for COD, NH₄⁺-N, TN, and TP, respectively, while B4 had removal efficiencies of 93.4%, 71.0%, 75.0%, and 76.5% for COD, NH₄⁺-N, TN, and TP, respectively. B4 had BOD, NH₄⁺-N, TN, and TP concentrations within the class III Chinese Standard requirement after a storage period of about 240 days. Furthermore, the turbidity in B4 kept dropping. Thus, B4 is a more promising alternative for water quality management in mountainous cities of China.