Enhancement of denitrification efficiency using municipal and industrial waste fermentation liquids as external carbon sources

Utilizing waste-derived carbon source for partial denitrification-anammox process: Wastewater- and sludge-derived organics

The partial denitrification-anammox (PDA) process is a promising and sustainable technology for nitrogen removal in wastewater treatment. It is well-suited for mainstream nitrogen removal from municipal wastewater, polishing of anammox for ammonia-rich wastewater treatment, and simultaneous treatment of nitrate and ammonia containing wastewater. While the PDA process reduces external carbon source consumption by over 40 %, it still requires additional carbon input. Wastewater treatment systems inherently contain organics in both wastewater and sludge, but these sources are often inaccessible to denitrifiers. Efficient utilization of these organics is essential for advancing energy-efficient wastewater treatment. This review provides a comprehensive overview of recent advances in utilizing organics derived from wastewater and waste-sludge. Key developments in hydrolytic acidification and Fe-C micro-electrolysis are highlighted for enhancing the biodegradability and conversion of refractory organics. Strategies such as extended hydraulic retention time, functional microbial enrichment, enzymatic pretreatment, and microbial co-cultures are also discussed to improve readily biodegradable organics supply and nitrogen removal. This review further explores emerging applications of PDA process that leverage carbon sources from wastewater treatment systems. Future research should prioritize the efficient integration of these organics throughout PDA process and develop cost-effective methods to address by-products like ammonia-nitrogen. Moreover, a practical roadmap is proposed, outlining optimization of fermentation conditions, system integration, stability under real-world conditions, and techno-economic evaluations. This review aims to provide a comprehensive framework to unlock the full-scale application of PDA using waste-derived carbon, advancing toward carbon-neutral and cost-effective wastewater treatment.

Optimizing denitrification with volatile fatty acids from hydrolysis acidification-treated domestic wastewater: Comparative effects of nitrate and nitrite using immobilized biofiller

By embedding immobilized biofiller, 100% denitrification efficiency was achieved with nitrate or nitrite as electron acceptors utilizing volatile fatty acids (VFAs) from domestic wastewater after hydrolysis acidification. The consumption patterns of VFAs by functional bacteria and differences in nitrogen metabolic gene expression were thoroughly analyzed. Total consumption of acetic and propionic acids with >95% VFAs utilization was achieved utilizing nitrate, whereas the consumption of butyric and valeric acids was enhanced utilizing nitrite. Denitrification-related genes were all upregulated, particularly nosZ, indicating systemic N2O emission reduction potential. Electron acceptor changes dynamically shifted microbial dominance from Thauera (19.4%) to Thiobacillus (7.2%). These results provide valuable insights into the adaptability and ecological niche characterization of denitrifying bacteria, contributing to improving nitrogen removal efficiency, optimizing carbon source utilization, and reducing sludge production.

Effect of root exudation on community structure of rhizosphere microorganism of three macrophytes during treating swine wastewater

Macrophytes not only directly absorb nitrogen (N) from wastewater, but also influence N removal processes. They were achieved by microorganisms in rhizosphere through root exudations and oxygen secretion. However, changes of root exudes and rhizosphere microbial community structure in macrophytes in high N wastewater are still unclear. Objectives of this study were to investigate effects of dissolved organic carbon (DOC) and organic acids (OA) on composition and diversity of microbial communities across three macrophytes during treating swine wastewater. Result showed that secretion rates of DOC and total organic acid (TOA) displayed an increasing trend with extended experimental times in Pontederia cordata and Iris pseudacorus rhizosphere, while it presented a decline trend in Canna indica rhizosphere. Preponderant phyla in rhizosphere were Proteobacteria, Bacteroidetes, Firmicutes and Acidobacteria. Genera Geobacter enriched in I. pseudacorus rhizosphere, while unidentified_Cyanobacteria enriched in P. cordata rhizosphere. Diversity and richness of microbial communities in C. indica and P. cordata rhizosphere at different experimental periods showed no significant differences (P > 0.05). However, diversity of microbial community increased in I. pseudacorus rhizosphere. Although interactions among microorganisms reduced, they became more mutualistic after treating swine wastewater. Concentration of NH4+-N and total nitrogen (TN), pH, dissolved oxygen (DO) in swine wastewater, malonic acid and succinic acid released by roots enhanced N cycle functions of microbial community. The results contribute to further comprehension of the mechanism of N removal in rhizosphere during treating swine wastewater.

Characterisation and anaerobic digestion of fat, oil and grease (FOG) waste from wastewater treatment plants

The materials removed in the oil separation units of wastewater treatment plants can be referred to as fat, oil and grease (FOG) waste. FOG waste accumulation in treatment plants can cause clogging of pipes, production of excessive scums and foams, and negatively affect air/liquid oxygen transfer. While conventional disposal routes of this material can be limited by its water and organic content, FOG can represent a source of bio-energy other than bio-diesel production. This research determined the chemical and physical characteristics of FOG waste collected at four different wastewater treatment plants and defined the potential for energy recovery via dark fermentation and anaerobic digestion as treatment options for final disposal. The FOG samples featured markedly distinct physical aspects in connection with the oil separation technologies: solid agglomerate with a high content of lipids from vortex-type separation and semi-solid agglomerate with a low content of oils and fats from horizontal-flow chambers. All FOG waste presented high potential for methane production with values ranging from 460 to 865 Nm3CH4/tVS but low yields of biological hydrogen via dark fermentation. This study addresses a knowledge gap in the scientific literature on the characteristics of FOG waste from treatment plants and defines possible routes for sustainable management via bio-energy recovery.

Use of embedding immobilized biofillers to improve hydrolysis acidification efficiency in domestic wastewater treatment

This study evaluated the effectiveness of embedding immobilization technology in wastewater treatment and its capacity to enhance the hydrolysis acidification process. Based on this technology, a stable anaerobic environment has been maintained. Results showed that the rates of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) conversion both exceeded 98 % under short hydraulic retention time (HRT = 2h) and ambient temperature. Notably, acetic acid and propionic acid comprised up to 90.9 % of the total volatile fatty acids in the effluent, providing suitable carbon sources for downstream denitrification. 16S rRNA gene sequencing indicated that biofillers effectively enriched and retained functional bacteria, causing norank_Anaerolineaceae (11.6 %-29.7 %) and norank_Bacteroidetes_vadinHA17 (10.8 %-14.9 %) as the dominant genera in the reactor, which were crucial for refractory organic matter degradation. Immobilized biofillers effectively improved wastewater biodegradability, supporting a stable microbial community with high DON and DOP conversion rates as well as increased VFA accumulation.

Enhanced nitrogen removal for low C/N wastewater via preventing futile carbon oxidation and augmenting anammox

Efficient carbon use is crucial for biological nitrogen removal. Traditional aerobic processes can waste carbon sources, exacerbating carbon deficiency. This study explores an anaerobic/oxic/anoxic system with sludge double recirculation to improve nitrogen removal in low C/N wastewater. This system integrated aerobic nitrification after the carbon intracellular storage, separating carbon and nitrogen by denitrifying glycogen-accumulating organisms (DGAOs) with endogenous partial denitrification and Anammox within the anoxic units. A significant efficiency of 91.02±7.01% chemical oxygen demand (COD) was converted into intracellular carbon in anaerobic units, significantly reducing carbon futile oxidation in the aerobic units by effectively separating COD from ammonia. Intracellular storage of carbon sources and microbial adaptation to carbon scarcity prevent futile oxidation of COD in the aerobic units even with short-term high dissolved oxygen (DO), thereby enhancing nitrogen removal under anoxic conditions with sufficient intracellular carbon source. The microbial analysis identified Candidatus Brocadia as the dominant anammox bacteria, in combination with the activity of DGAOs and other related microbial communities, accounting for 37.0% of the TN removal. Consequently, the system demonstrated remarkable nitrogen removal efficiencies, achieving 81.3±3.3% for total nitrogen (TN) and 98.5±0.9% for ammonia nitrogen while maintaining an effluent COD concentration of 17.2±9.1 mg/L, treating the low C/N of 4.18 in the influent wastewater. The findings in this study provide a sustainable and energy-saving technique for conventional WWTPs to meet strict discharge standards by avoiding futile oxidation of COD and encouraging anammox contributions.

Optimizing nitrogen removal in constructed wetlands for low C/N ratio wastewater treatment: Insights from fermentation liquid utilization

The inefficient nitrogen removal in constructed wetlands (CWs) can be attributed to insufficient carbon sources for low carbon-to-nitrogen (C/N) ratio wastewater. In this study, sugarcane bagasse fermentation liquid (SBFL) was used as a supplemental carbon source in intermittently aerated CWs to enhance nitrogen removal. The impact of different regulated influent C/N ratios on nitrogen removal and greenhouse gas (GHG) emissions was investigated. Results demonstrated that SBFL addition significantly enhanced the denitrification capacity, resulting in faster NO3--N removal compared to sucrose. Moreover, intermittently aerated CWs significantly improved NH4+-N removal efficiency compared to non-aerated CWs. The highest total nitrogen removal efficiency (98.3 %) was achieved at an influent C/N ratio of 5 in intermittently aerated CWs with SBFL addition. The addition of SBFL resulted in a reduction of N2O emissions by 17.8 %-43.7 % compared to sucrose. All CWs exhibited low CH4 emissions, with SBFL addition (0.035-0.066 mg·m-2h-1) resulting in lower emissions compared to sucrose. Additionally, higher abundance of denitrification (nirK, nirS and nosZ) genes as well as more abundant denitrifying bacteria were shown in CWs of SBFL inputs. The results of this study provide a feasible strategy for applying SBFL as a carbon source to improve nitrogen removal efficiency and mitigate GHG emissions in CWs.

Enhanced wastewater treatment with an AnF-AAO system for improved internal carbon source utilization

The main challenge in removing nutrients from municipal wastewater in China is the lack of available carbon sources. While hydrolysis acidification tanks can improve wastewater biodegradability by effectively utilizing internal carbon sources, high sludge concentrations are difficult to control in traditional tank variants. In this study, an innovative anaerobic filter (AnF) hydrolysis acidification reactor composed of a continuously stirred tank reactor (CSTR) and cloth media filter was designed to regulate and maintain high sludge concentrations in the hydrolysis acidifier. The reactor was used as a pretreatment unit for the anaerobic/anoxic/oxic (AAO) units and combined into an AnF-AAO system to explore the effectiveness of internal carbon source utilization in wastewater. The results indicate that as the sludge concentration in the hydrolysis acidifier increased, the hydrolysis and acidification processes became more efficient. The optimal sludge concentration was 40 g/L, which significantly increased the production of soluble chemical oxygen demand and volatile fatty acids. Above this concentration, the efficiency decreased. Compared to traditional AAO processes, the AnF-AAO system achieved superior total nitrogen and phosphorus removal with shorter hydraulic retention times and reduced sludge production by a significant amount of 35%. Due to its capacity for enhancing internal carbon source utilization, the AnF-AAO system constitutes a promising approach for sustainable urban wastewater treatment.

Mitigating nitrous oxide emissions from low carbon to nitrogen ratio wastewater treatment: Utilizing sugarcane bagasse fermentation liquid for constructed wetlands

Sugarcane bagasse was recycled to produce fermentation liquid (FL) as a supplementary carbon source that was added to constructed wetlands (CWs) for regulating influent carbon to nitrogen ratio (C/N), and then being applied to investigate nitrogen transformations and greenhouse gas emissions. Results showed that this FL achieved faster NO3--N removal and lower N2O fluxes than sucrose did, and the lowest N2O flux (67.6 μg m-2h-1) was achieved when FL was added to CWs in a C/N of 3. In contrast, CH4 emissions were higher by the FL addition than by the sucrose addition, although the fluxes under both additions were in a lower range of 0.06-0.17 mg m-2h-1. The utilization of FL also induced significant variations in microbial communities and increased the abundance of denitrification genes. Results showed the application of FL from sugarcane bagasse can be an effective strategy for improving nitrogen removal and mitigating N2O emissions in CWs.

Mixotrophic denitrification of waste activated sludge fermentation liquid as an alternative carbon source for nitrogen removal: Reducing N2O emissions and costs

Heterotrophic-sulfur autotrophic denitrification (HAD) has been proposed to be a prospective nitrogen removal process. In this work, the potential of fermentation liquid (FL) from waste-activated sludge (WAS) as the electron donor for denitrification in the HAD system was explored and compared with other conventional carbon sources. Results showed that when FL was used as a carbon source, over 99% of NO3--N was removed and its removal rate exceeded 14.00 mg N/g MLSS/h, which was significantly higher than that of methanol and propionic acid. The produced sulfate was below the limit value and the emission of N2O was low (1.38% of the NO3--N). Microbial community analysis showed that autotrophic denitrifiers were predominated in the HAD system, in which Thiobacillus (16.4%) was the dominant genus. The economic analysis showed the cost of the FL was 0.062 €/m3, which was 30% lower than that in the group dosed with methanol. Our results demonstrated the FL was a promising carbon source for the HAD system, which could reduce carbon emission and cost, and offer a creative approach for waste-activated sludge resource reuse.

Exploratory study on the metabolic similarity of denitrifying carbon sources

Mixed carbon sources have been developed for denitrification to eliminate the "carbon dependency" problem of single carbon. The metabolic correlation between different carbon sources is significant as guidance for the development of novel mixed carbon sources. In this study, to explore the metabolic similarity of denitrifying carbon sources, we selected alcohols (methanol, ethanol, and glycerol) and saccharide carbon sources (glucose, sucrose, and starch). Batch denitrification experiments revealed that methanol-acclimated sludge improved the denitrification rate of both methanol (14.42 mg-N/gMLVSS*h) and ethanol (9.65 mg-N/gMLVSS*h), whereas ethanol-acclimated sludge improved the denitrification rate of both methanol (7.80 mg-N/gMLVSS*h) and ethanol (22.23 mg-N/gMLVSS*h). In addition, the glucose-acclimated sludge and sucrose-acclimated sludge possibly improved the denitrification rate of glucose and sucrose, and the glycerol-acclimated sludge improved the denitrification rate of volatile fatty acids (VFAs), alcohols, and saccharide carbon sources. Functional gene analysis revealed that methanol, ethanol, and glycerol exhibited active alcohol oxidation and glyoxylate metabolism, and glycerol, glucose, and sucrose exhibited active glycolysis metabolism. This indicated that the similarity in the denitrification metabolism of these carbon sources was based on functional gene similarity, and glycerol-acclimated sludge exhibited the most diverse metabolism, which ensured its good denitrification effect with other carbon sources.

Application of a hybrid-fruit-peel (HFP) coagulant in low carbon source wastewater treatment as an external carbon source

The application of a hybrid-fruit-peel (HFP) coagulant used as an external carbon source (ECS) in both simulated water and real sewage having a low carbon source treated with sequencing batch reactor (SBR) was studied, compared with that of sodium acetate (NaAc). The impact of HFP on sludge properties (such as extracellular polymer substance (EPS), dehydrogenase activity (DHA), charged property, size, microscopic images and bacteria phase) was characterized. The results showed that as an ECS, HFP basically gave similar nitrogen removal to NaAc and also gave a similar developing trend of both dissolved oxygen (DO) and pH. HFP promoted more proliferation of microorganisms and posed higher levels of protein (PN) and polysaccharide (PS) than NaAc, but gave slightly lower DHA than NaAc. After HFP was added as an ECS, the types and quantities of microorganisms increased significantly, the effluent qualities were improved and the sludge size and extensibility became larger, which was conducive to direct contact and remove pollutants. HFP played a similar role to NaAc as ECS and can be used as a quality and slow-releasing ECS for low carbon source wastewaters.

Step-feeding food waste fermentation liquid as supplementary carbon source for low C/N municipal wastewater treatment: Bench scale performance and response of microbial community

Municipal wastewater treatment often lacks carbon source, while carbon-rich organics in food waste are deficiently utilized. In this study, the food waste fermentation liquid (FWFL) was step-fed into a bench-scale step-feed three-stage anoxic/aerobic system (SFTS-A/O), to investigate its performance in nutrients removal and the response of microbial community as a supplementary carbon source. The results showed that the total nitrogen (TN) removal rate increased by 21.8-109.3% after step-feeding FWFL. However, the biomass of the SFTS-A/O system was increased by 14.6% and 11.9% in the two phases of the experiment, respectively. Proteobacteria was found to be the dominant functional phyla induced by FWFL, and the increase of its abundance attributed to the enrichment of denitrifying bacteria and carbohydrate-metabolizing bacteria was responsible for the biomass increase. Azospira belonged to Proteobacteria phylum was the dominant denitrifying genera when step-fed with FWFL, its abundance was increased from 2.7% in series 1 (S1) to 18.6% in series 2 (S2) and became the keystone species in the microbial networks. Metagenomics analysis revealed that step-feeding FWFL enhanced the abundance of denitrification and carbohydrates-metabolism genes, which were encode mainly by Proteobacteria. This study constitutes a key step towards the application of FWFL as a supplementary carbon source for low C/N municipal wastewater treatment.

Deammonification Potential of Pig Slurries and Vapor Condensates from Sewage Sludge Drying-Substrate Quality and Inhibition

Deammonification is a well-established process for sludge liquor treatment and promising for wastewaters with high nitrogen loads because of its low energy demand compared to nitrification/denitrification. Two wastewaters with high NH4-N concentrations and a rising significance in Germany-pig slurry (12 samples) and condensates from sewage sludge drying (6 samples)-were studied for their deammonification potential. Furthermore, a comprehensive quality assessment is presented. Both wastewaters show a wide range in terms of CODt, CODs, TN and NH4-N, whereby condensates show a greater variability with no direct relation to dryer type or temperature. In the slurries, CODt shows a relative standard deviation of 106% (mean 21.1 g/L) and NH4-N of 33% (mean 2.29 g/L), while in condensates it reaches 148% for CODt (mean 2.0 g/L) and 122% for NH4-N (mean 0.7 g/L). No inhibition of ammonium-oxidizing-bacteria was detected in the slurries, while two out of five condensates showed an inhibition of >40%, one of >10% and two showed no inhibition at all. Since the inhibition could be avoided by mixing, deammonification can be recommended for condensate treatment. For slurry treatment, the importance of employing some form of solid-liquid-separation as a pretreatment was noted due to the associated COD.

A municipal wastewater treatment plant "drinking beer" for reduction of cost and carbon emission

In wastewater treatment plants (WWTPs), external carbon sources are often required due to low C/N influent. However, the use of external carbon sources can increase treatment costs and cause large carbon emissions. Beer wastewater, which contains a substantial amount of carbon, is often treated separately in China, consuming significant energy and cost. However, most studies using beer wastewater as an external carbon source are still on a laboratory scale. To address this issue, this study proposes using beer wastewater as an external carbon source in an actual WWTP to reduce operating costs and carbon emissions while achieving a win-win situation. The denitrification rate of beer wastewater was found to be higher than that of sodium acetate , resulting in improved treatment efficiency of the WWTP. Specifically, COD, BOD₅, TN, NH₄⁺-N and TP increased by 3.4%, 1.6%, 10.8%, 1.1%, and 1.7%, respectively. Additionally, the treatment cost and carbon emission per 10 000 tons of wastewater treated were reduced by 537.31 yuan and 2.27 t CO₂, respectively. These results indicate that beer wastewater has significant utilization potential and provide a reference for using different types of production wastewater in WWTPs. This study's findings demonstrate the feasibility of implementing this approach in an actual WWTP setting.

Mitigation of N2O emissions via enhanced denitrification in a biological landfill leachate treatment using external carbon from fermented sludge

The effects of an external carbon source (C-source) on the mitigation of N₂O gas (N₂O_(g)) emissions from landfill leachate were investigated via enhanced denitrification using anaerobically fermented sewage sludge. Anaerobic fermentation of sewage sludge was conducted under thermophilic conditions with progressively increasing organic loading rates (OLR). Optimal conditions for fermentation were determined based on the efficiency of hydrolysis and the concentrations of sCOD and volatile fatty acids (VFAs) as follows: at an OLR of 40.48 ± 0.77 g COD/L·d with 1.5 days of solid retention time (SRT), 14.68 ± 0.59% of efficiency of hydrolysis, 14.42 ± 0.30 g sCOD/L and 7.85 ± 0.18 g COD/L of VFAs. Analysis of the microbial community in the anaerobic fermentation reactor revealed that degradation of sewage sludge might be potentially affected by proteolytic microorganisms producing VFAs from proteinaceous materials. Sludge-fermentate (SF) retrieved from the anaerobic fermentation reactor was used as the external C-source for denitrification testing. The specific nitrate removal rate (K_NR) of the SF-added condition was 7.54 mg NO₃^-N/g VSS·hr, which was 5.42 and 2.43 times higher than that of raw landfill leachate (LL) and a methanol-added condition, respectively. In the N₂O_(g) emission test, the liquid phase N₂O (N₂O-^N_(l)) of 20.15 mg N/L was emitted as N₂O_(g) of 19.64 ppmv under only LL-added condition. On the other hand, SF led to the specific N₂O_(l) reduction rate (K_N2O) of 6.70 mg N/g VSS hr, resulting in mitigation of 1.72 times the N₂O_(g) emission compared to under the only-LL-added condition. The present study revealed that N₂O_(g) emissions from biological landfill leachate treatment plants can be attenuated by simultaneous reduction of NO₃^-N and N₂O_(l) during enhanced denitrification via a stable supply of an external C-source retrieved from anaerobically fermented organic waste.

Construction and function of a high-efficient synthetic bacterial consortium to degrade aromatic VOCs

Aromatic volatile organic compounds (VOCs) are a type of common pollution form in chemical contaminated sites. In this study, seven aromatic VOCs such as benzene, toluene, ethylbenzene, chlorobenzene, m-xylene, p-chlorotoluene and p-chlorotrifluorotoluene were used as the only carbon source, and four strains of highly efficient degrading bacteria were screened from the soil of chemical contaminated sites, then the synthetic bacterial consortium was constructed after mixing with an existing functional strain (Bacillus benzoevorans) preserved in the laboratory. After that, the synthetic bacterial consortium was used to explore the degradation effect of simulated aromatic VOCs polluted wastewater. The results showed that the functional bacterium could metabolize with aromatic VOCs as the only carbon source and energy. Meanwhile, the growth of the synthetic bacterial consortium increased with the additional carbon resources and the alternative of organic nitrogen source. Ultimately, the applicability of the synthetic bacterial consortium in organic contaminated sites was explored through the study of broad-spectrum activity.

Comparing VFA Composition, Biomethane Potential, and Methane Production Kinetics of Different Substrates for Anaerobic Fermentation and Digestion

Solid waste is one of the largest sources of greenhouse gases (GHGs) today. The carbon footprint of landfills also has a large impact on global warming. Therefore, it is becoming more urgent to study the possibility of better environmentally friendly approaches for solid waste management and its safe disposal. The digestion of solid waste is a biological process that breaks down the organic content of the solid waste and thus stabilizes it. It also allows the recovery of valuable resources (such as biogas) and the utilization of stabilized waste in various industries. In this study, six substrates were studied to determine their biomethane potential (BMP) in anaerobic digestion. The substrates were fermented and digested anaerobically, and the biogas production was measured. The methane yield of food waste substrates had a higher methane yield between 354 and 347 mL/g-TCOD, and a biodegradability of 89–87%. Wastewater sludge substrates yielded between 324 and 288 mL/g-TCOD with a biodegradability of 81–73%. A kinetics analysis using first-order and Gompertz models was performed for biodegradation and methane production.

Molecular mechanisms through which different carbon sources affect denitrification by Thauera linaloolentis: Electron generation, transfer, and competition

Characterizing the molecular mechanism through which different carbon sources affect the denitrification process would provide a basis for the proper selection of carbon sources, thus avoiding excessive carbon source dosing and secondary pollution while also improving denitrification efficiency. Here, we selected Thauera linaloolentis as a model organism of denitrification, whose genomic information was elucidated by draft genome sequencing and KEGG annotations, to investigate the growth kinetics, denitrification performances and characteristics of metabolic pathways under diverse carbon source conditions. We reconstructed a metabolic network of Thauera linaloolentis based on genomic analysis to help develop a systematic method of researching electron pathways. Our findings indicated that carbon sources with simple metabolic pathways (e.g., ethanol and sodium acetate) promoted the reproduction of Thauera linaloolentis, and its maximum growth density reached OD₆₀₀ = 0.36 and maximum specific growth rate reached 0.145 h^-1. These carbon sources also accelerated the denitrification process without the accumulation of intermediates. Nitrate could be reduced completely under any carbon source condition; but in the "glucose group", the maximum accumulation of nitrite was 117.00 mg/L (1.51 times more than that in the "ethanol group", which was 77.41 mg/L), the maximum accumulation of nitric oxide was 363.02 μg/L (7.35 times more than that in the "ethanol group", which was 49.40 μg/L), and the maximum accumulation of nitrous oxide was 22.58 mg/L (26.56 times more than that in the "ethanol group", which was 0.85 mg/L). Molecular biological analyses demonstrated that diverse types of carbon sources directly induced different carbon metabolic activities, resulting in variations in electron generation efficiency. Furthermore, the activities of the electron transport system were positively correlated with different carbon metabolic activities. Finally, these differences were reflected in the phenomenon of electronic competition between denitrifying reductases. Thus we concluded that this was the main molecular mechanism through which the carbon source type affected the denitrification process. In brief, carbon sources with simple metabolic pathways induced higher efficiency of electron generation, transfer, and competition, which promoted rapid proliferation and complete denitrification; otherwise Thauera linaloolentis would grow slowly and intermediate products would accumulate seriously. Our study established a method to evaluate and optimize carbon source utilization efficiency based on confirmed molecular mechanisms.

Potential of food waste-derived volatile fatty acids as alternative carbon source for denitrifying moving bed biofilm reactors

Fossil-based materials such as methanol are frequently used in the denitrification process of advanced biological wastewater treatment as external carbon source. Volatile fatty acids (VFAs) produced by anaerobic digestion of food waste, are sustainable compounds with the potential to act as carbon sources for denitrification, reducing carbon footprint and material costs. In this study, the effectiveness of food waste-derived VFAs (AD-VFA) was investigated in the post-denitrification process in comparison with synthetic VFA and methanol as carbon sources. Acetic acid had the highest rate of disappearance among single tested VFAs with a denitrification rate of 0.44 g NOx-N removed/m2/day, indicating a preferential utilization pattern. While AD-VFA had a denitrification rate of 0.61 mg NOx-N removed/m2/day, sVFA had a rate of 0.57 mg NOx-N removed/m2/day, indicating that impurities in AD-VFA did not play substantial role in denitrification. AD-VFA proved to be promising carbon source alternative for denitrification in wastewater treatment plants.

A new LDH based sustained-release carbon source filter media to achieve advanced denitrogenation of low C/N wastewater at low temperature

Advanced denitrogenation of wastewater is now facing major challenges brought by low C/N ratio and low temperature. The development of sustained-release materials with good and stable carbon release properties was an effective countermeasure. FeNi-Layered double-metal hydroxides (LDH)- sodium carboxymethyl cellulose (CMC) filter media and its potential use in heterotrophic and sulfur-based mixotrophic denitrification biological filter (DNBF), was firstly reported. It demonstrated stable structure and good carbon release performance with a mass transfer coefficient (K) of 4.40 mg·L^-1·s^-1. When the influent NO₃^--N of 50 mg/L with the C/N ratio of 3 at 10 °C, the maximum nitrogen loading rate of 0.22 kg·N/(m³·d) and effluent TN close to 5 mg/L (nitrogen removal of almost 90 %) could be achieved. The slowly released carbon source and the leached iron increased the abundance of denitrifying bacteria and functional genes, and the augmentation of Sulfuritalea and the secretion of biofilm protein stimulated by sulfur also played a synergistic role. This study provided a new potentially effective strategy to enhance advanced denitrification of wastewater of low C/N wastewater at low temperature.

Comparison of primary and secondary sludge carbon sources derived from hydrolysis or acidogenesis for nitrate reduction and denitrification kinetics: Organics utilization and microbial community shift

Seeking available and economical carbon sources for denitrification process is an intractable issue for wastewater treatment. However, no study compared different types of waste sludge as carbon source from denitrification mechanism, organics utilization and microbial community aspects. In this study, primary and secondary sludge were pretreated by thermophilic bacteria (TB), and its hydrolysis or acidogenic liquid were prepared as carbon sources for denitrification. At C/N of 8-3, the variations of NO₃^--N and NO₂^--N were profiled in typical cycles and denitrification kinetics was analyzed. Primary sludge achieved a competitive NO_X-N removal efficiency with less dosage than secondary sludge. Fourier transform infrared (FTIR) spectroscopy was introduced to analyze organic composition from functional-group perspective and the utilization of organic matters in different sludge carbon sources was investigated. To further analyze the microbial community shift in different denitrification systems, high-throughput sequencing technology was applied. Results showed that denitrifier Thauera, belonging to Proteobacteria, was predominant, and primary sludge acidogenic liquid enriched Thauera most intensively with relative abundance of 47.3%.

Recent advances in waste-derived functional materials for wastewater remediation

Water pollution is a major concern for public health and a sustainable future. It is urgent to purify wastewater with effective methods to ensure a clean water supply. Most wastewater remediation techniques rely heavily on functional materials, and cost-effective materials are thus highly favorable. Of great environmental and economic significance, developing waste-derived materials for wastewater remediation has undergone explosive growth recently. Herein, the applications of waste (e.g., biowastes, electronic wastes, and industrial wastes)-derived materials for wastewater purification are comprehensively reviewed. Sophisticated strategies for turning wastes into functional materials are firstly summarized, including pyrolysis and combustion, hydrothermal synthesis, sol-gel method, co-precipitation, and ball milling. Moreover, critical experimental parameters within different design strategies are discussed. Afterward, recent applications of waste-derived functional materials in adsorption, photocatalytic degradation, electrochemical treatment, and advanced oxidation processes (AOPs) are analyzed. We mainly focus on the development of efficient functional materials via regulating the internal and external characteristics of waste-derived materials, and the material's property-performance correlation is also emphasized. Finally, the key future perspectives in the field of waste-derived materials-driven water remediation are highlighted.