Denitrification performance and bacterial flora analysis of immobilized denitrification filler in industrial wastewater

Reason and control strategy for denitrification and anammox sludge flotation in nitrogen removal process: Mechanisms, strategies and perspectives

Anaerobic biological treatment technology, especially denitrification and anaerobic ammonia oxidation (anammox) technology as mainstream process, played dominant role in the field of biological wastewater treatment. However, the above process was prone to sludge floating during high load operation and thereby affecting the efficient and stable operation of the system. Excessive production of extracellular polymeric substance (EPS) was considered to be the main reason for anaerobic granular sludge flotation, but the summaries in this area were not comprehensive enough. In this review, the potential mechanisms of denitrification and anammox sludge floatation were discussed from the perspective of granular sludge structural characteristics, nutrient transfer, and microbial flora change respectively, and the corresponding control strategies were also summarized. Finally, this paper indicated that future research on sludge flotation should focus on reducing the negative effects of EPS in sludge particles.

Bio-promoter mediated denitrification recovery from Cd(II) stress: Microbial activity resilience, electron behavior enhancement and microbial community evolution

Denitrification is fragile to toxic substances, while currently there are few regulation strategies for toxic substance-stressed denitrification. This study proposed a combined bio-promoter composed of basic bio-promoter (cytokinin, biotin, L-cysteine, and flavin adenine dinucleotide) and phosphomolybdic acid (PMo12) to recover cadmium(II) (Cd(II)) stressed denitrification. By inhibiting 58.02% and 48.84% of nitrate reductase and nitrite reductase activities, Cd(II) caused all the influent nitrogen to accumulate as NO3--N and NO2--N. Combined bio-promoter shortened the recovery time by 21 cycles and improved nitrogen removal efficiency by 10% as the synergistic effect of basic bio-promoter and PMo12. Basic bio-promoter enhanced antioxidant enzyme activities for reactive oxygen species clearance and recovered 23.30% of nicotinamide adenine dinucleotide for sufficient electron donors. Meanwhile, PMo12 recovered electron carriers contents, increasing the electron transfer activity by 60.81% compared with self-recovery. Bio-promoters enhanced the abundance of denitrifiers Seminibacterium and Dechloromonas, which was positively correlated with rapid recovery of denitrification performance.

Mechanism of quinone mediators modified polyurethane foam for enhanced nitrobenzene reduction and denitrification

The nitrobenzene (NB) reduction and denitrification performance of the immobilized biofilm (I-BF) reactors based on 9,10-anthraquinone-2-sulfonyl chloride (ASC) modified polyurethane foam (PUF-ASC) carriers were investigated. Experiments demonstrated that the quinone mediators enhanced NB reduction and denitrification performance. The NB reduction rates increased by 1.46, while the NO3--N removal rates increased by 1.55 times in the PUF-0.1ASC system. The quinone mediators promote extracellular polymeric substances (EPS) secretion. Electrochemical tests indicated that quinone mediators enhanced the electron transfer of biofilm systems. NADH generation was accelerated and microbial electron transport system activity (ETSA) was promoted. The abundance of genera with electrochemical activity, NB degradation and denitrification ability (Pseudomonas sp., Diaphorobate sp., and Acinetobacter sp.) increased. Metabolic pathways relating to NO3--N and NB reduction were uploaded. In conclusion, electron acquisition by NO3--N and NB was facilitated, bacterial community structure and metabolic pathways were affected by the quinone mediators.

Retrospect and prospect of aerobic biodegradation of aniline: Overcome existing bottlenecks and follow future trends

Aniline is a highly bio-toxic industrial product, even at low concentrations, whose related wastewater has been flowing out worldwide on a large scale along with human production. As a green technology, aerobic biological treatment has been widely applied in industrial wastewater and exhibited various characteristics in the field of aniline wastewater. Meanwhile, this technology has shown its potential of synchronous nitrogen removal, but it still consumes energy badly. In the face of resource scarcity, this review comprehensively discusses the existing research in aerobic biodegradation of aniline wastewater to find out the developmental dawn of aerobic biological treatment. Primarily, it put forward the evolution history details of aniline biodegradation from pure culture to mixed culture and then to simultaneous nitrogen removal. On this basis, it presented the existing challenges to further expand the application of aerobic biotechnology, including the confusions of aniline metabolic mechanism, the development of co-degradation of multiple pollutants and the lack of practical experience of bioreactor operation for aniline and nitrogen removal. Additionally, the prospects of the technological shift to meet the needs of an energy-conserving society was described according to existing experiences and feasibility. Including but not limiting to the development of multifunctional bacteria, the reduction of greenhouse gases and the combination of green technologies.

Simultaneous removal of COD and NH4+-N from domestic sewage by a single-stage up-flow anaerobic biological filter based on Feammox

In recent years, Feammox has made it possible to remove NH₄⁺-N under anaerobic conditions; however, its application in practical wastewater treatment processes has not been extensively reported. In this study, an up-flow anaerobic biological filter based on limonite (Lim-UAF) was developed to facilitate long-term and stable treatment of domestic sewage. Lim-UAF achieved the highest removal efficiency of chemical oxygen demand (COD) and NH₄⁺-N at a hydraulic retention time (HRT) of 24 h (Stage II). Specifically, the COD and NH₄⁺-N content decreased from 240.8 and 30.0 mg/L to about 7.5 and 0.35 mg/L, respectively. To analyze the potential nitrogen removal mechanism, the Lim-UAF was divided into three layers according to the height of the reactor. The results showed that COD and NH₄⁺-N removal had remarkable characteristics in Lim-UAF. More than 55.0% of influent COD was removed in the lower layer (0-30 cm) of Lim-UAF, while 60.2% of NH₄⁺-N was removed in the middle layer (30-60 cm). Microbial community analysis showed that the community structure in the middle and upper layers (60-90 cm) was relatively similar, but quite different from that of the lower layer. Heterotrophic bacteria were dominant in the lower layer, whereas iron-reducing and iron-oxidizing bacteria were enriched in the upper and middle layers. The formation of secondary minerals (siderite and Fe(OH)₃) indicated that the Fe(III)/Fe(II) redox cycle occurred in Lim-UAF, which was triggered by the Feammox and NDFO processes. In summary, limonite was used to develop a single-stage wastewater treatment process for simultaneously removing organic matter and NH₄⁺-N, which has excellent application prospects in domestic sewage treatment.

Synergistic removal of fluoride, calcium, and nitrate in a biofilm reactor based on anaerobic microbially induced calcium precipitation

Fluoride (F^-) and calcium (Ca²⁺) are primary causes of skeleton fluorosis and scaling, posing a grievous threat to aquatic lives and public health. Therefore, a novel strategy for polluted groundwater in immobilized biofilm reactor based on the anaerobic microbial induced calcium precipitation (MICP) was proposed, in which loofah was used as a multifunctional strain Cupriavidus sp. W12 growth carrier. Effects of different hydraulic retention time (HRT), initial F^-concentration, and pH on the synchronous removal of pollutants were examined. Under stable operation conditions, the highest efficiencies for Ca²⁺, F^-, and nitrate (NO₃^--N) reached 76.73%, 94.92%, and 100%, respectively. Furthermore, gas chromatography (GC), Fluorescence excitation-emission matrix (EEM), X-ray diffraction (XRD), Scanning electron microscope-energy dispersive spectroscope (SEM-EDS), and Fourier transform infrared spectrometer (FTIR) comprehensively clarified the mechanism of pollutants removal. The results elucidated that the removal of various pollutants was achieved through a combination of anaerobic MICP, adsorption, and co-precipitation. Besides, high-throughput sequencing analysis showed that Cupriavidus had a predominant proportion of 42.36% in the reactor and had stability against pH impact. As the first application of a biofilm reactor based on anaerobic MICP, it put forward a new insight for efficient defluorination and decalcification.

Nitrate removal under low carbon to nitrogen ratio by modified corn straw bioreactor: Optimization and possible mechanism

ABSTRACTThe removal of nitrate (NO₃^--N) from water bodies under the conditions of poor nutrition and low carbon to nitrogen (C/N) ratio is a widespread problem. In this study, modified corn stalk (CS) was used to immobilize Burkholderia sp. CF6 with cellulose-degrading and denitrifying abilities. The optimal operating parameters of the bioreactor were explored. The results showed that under the hydraulic retention time (HRT) of 3 h and the C/N ratio of 2.0, the maximum nitrate removal efficiency was 96.75%. In addition, the organic substances in the bioreactor under different C/N ratios and HRT were analyzed by three-dimensional fluorescence excitation-emission mass spectrometry (3D-EEM), and it was found that the microorganisms have high metabolic activity. Scanning electron microscope (SEM) showed that the new material has excellent immobilization effects. Fourier transform infrared spectrometer (FTIR) showed that it has potential as a solid carbon source. Through high-throughput sequencing analysis, Burkholderia sp. CF6 was observed as the main bacteria present in the bioreactor. These research results showed that the use of waste corn stalks waste provides a theoretical basis for the advanced treatment of low C/N ratio wastewater.

Release Mechanism, Secondary Pollutants and Denitrification Performance Comparison of Six Kinds of Agricultural Wastes as Solid Carbon Sources for Nitrate Removal

Agricultural wastes used as denitrification carbon sources have some drawbacks such as excessive organic carbon release and unclear release characteristics of nitrogen, phosphorus, and chromatic substances, which can cause adverse effects on the effluent quality during the denitrification process. The composition and surface characteristics, carbon release mechanisms, and secondary pollutant release properties of six kinds of agricultural wastes, i.e., rice straw (RS), wheat straw (WS), corn stalk (CS), corncob (CC), soybean stalk (SS), and soybean hull (SH) were studied and analyzed in this research. The denitrification performance of these agricultural wastes was also investigated extensively by batch experiments. The results showed that the carbon release basically followed the second-order reaction kinetic equation and Ritger-Peppas equation in the 120 h reaction, and it was mainly controlled by the diffusion process. The kinetic equation fitting results and bioavailability test suggested that the potential risk of excessive effluent COD of CC was the lowest due to the appropriate amount and degradability of its released carbon. The NH₄⁺-N, TN, and TP in the leachate of RS were higher than those of the other five agriculture wastes, and the chroma in the leachate of WS and CS was heavier than that of the others. CC released the lowest pollutants, which resulted in slight fluctuations of effluent quality in the start-up period (1-11 d), and it had the best nitrogen removal capacity in the denitrification experiment. The average NO₃^--N removal of CC was 5.12 mg for each batch in the stable period (11-27 d), which was higher than that of others, and less NO₂^--N, NH₄⁺-N, and COD were accumulated in the CC effluent during the whole denitrification process.