Nitrogen removal performance of high ammonium and high salt wastewater by adding carbon source from food waste fermentation with different acidogenic metabolic pathways

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.

Tofu wastewater as a carbon source flowing into municipal wastewater treatment plants for reductions of costs and greenhouse gas emissions

Wastewater treatment processes significantly contribute to greenhouse gas (GHG) emissions. Municipal wastewater treatment also faces challenges related to low strength and a low carbon-to-nitrogen (C/N) ratio. This study investigates the high-carbon tofu wastewater flowing into municipal sewers for co-treatment at a wastewater treatment plant (WWTP) directly, with the goal of enhancing nitrogen removal and reduce GHG emissions. Within the framework of a circular economy for wastewater treatment, tofu wastewater serves as an external carbon source for sustainable solutions. The concentrated tofu wastewater had an average chemical oxygen demand (CODCr) of 21,894 ± 11,485 mg/L, total nitrogen (TN) of 591.8 ± 238.2 mg/L, and a C/N ratio of 36.9 ± 7.4. The denitrification rate reached 3.05 mg NO3--N/(g MLVSS·h). Therefore, tofu wastewater is a suitable alternative carbon source. A full-scale WWTP with a capacity of 20,000 m³/day was monitored from 2017 to 2022 to evaluate the co-treatment effects of municipal wastewater and tofu wastewater. The results showed an increase in 53.3% in the average CODCr concentration of the influent wastewater, while the total nitrogen and total phosphorus removal efficiencies were enhanced to 75.8% and 95.2%, respectively. In addition, the study quantified GHG emissions from tofu wastewater and municipal wastewater treatment. Compared to separate treatment processes, the co-treatment reduced GHG emissions by 337.9 t CO2-eq., approximately 15.8% of the total emissions of WWTP, and achieved a cost saving of 7-10% of the total operational costs. These findings demonstrate the environmental and economic advantages of integrating high-carbon industrial wastewater treatment directly into wastewater treatment plants.

Microplastics enhance nitrogen loss from a black paddy soil by shifting nitrate reduction from DNRA to denitrification and Anammox

Microplastics (MPs) are frequently detected emerging pollutants in soil that can endanger farmland ecosystems; however, little is known about their impacts on dissimilatory nitrate reduction processes in paddy soil. Here, using the 15N-tracer and microbial molecular techniques, we investigated the effects of MPs (200-400 μm) made of polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE) on denitrification, anaerobic ammonium oxidation (Anammox), and dissimilatory nitrate reduction to ammonium (DNRA) and the associated microbial community in a black paddy soil. All MPs increased the Anammox rate by 6.6 %-745 % and decreased the DNRA rate by 15.1 %-74.2 %, while MPs of PS and PE significantly increased the denitrification rate by 79.3 %-102.3 % and 34.8 %-62.1 %, respectively. The MPs promoted the partitioning of NO3- towards denitrification and Anammox while inhibiting DNRA, as suggested by the decreased relative contributions of DNRA from 24.1 % to 5.4 %-14.2 % following MPs amendment. This was attributed to the increased denitrification gene abundance and the enriched specific denitrifier taxa, as well as the decreased DNRA gene abundance. Our findings suggest that the stimulated denitrification and Anammox by MPs, accompanied by the suppression of DNRA, may lead to substantial nitrogen loss in paddy fields, underscoring the need to further evaluate the environmental behaviors of MPs in agricultural ecosystems.

Enhanced nitrogen removal in sewage treatment is achieved by using kitchen waste hydrolysate without a significant increase in nitrous oxide emissions

Kitchen waste hydrolysate (KWH) is an effective replacement for commonly used carbon sources such as sodium acetate (NaAc) and glucose (Glu), in wastewater treatment plants (WWTPs) to enhance the total nitrogen (TN) removal efficiency in sewage and reduce the operating cost of WWTPs. However, KWH utilization introduces complex organic matter that may lead to increased nitrous oxide (N2O) emissions, compared with that of NaAc and Glu, causing significant damage to the atmosphere. Therefore, this study aims to compare the effects of KWH, Glu, and NaAc on N2O emissions in sewage treatment. The results indicated that KWH introduction did not lead to a significant increase in N2O emissions, with a conversion rate of only 5.61 %. Compared with raw sludge, the addition of only Glu and NaAc significantly increased the abundance of the nar G gene, indicating that the readily degradable carbon sources initiated denitrification at a faster rate than KWH. When KWH was added, there was a notable increase in the abundance of genes associated with partial nitrification and denitrification (nir K, hzo, and nos Z). In contrast, Glu and NaAc did not have a significant effect on the nos Z gene. The results suggested that KWH supplementation was more effective to reduce N2O to N2. Moreover, the KWH addition significantly increased the microbial diversity in the sludge and promoted the presence of shortcut nitrification and denitrification bacteria (Comamonadaceae) and denitrification bacteria (Rhodobacteraceae), further indicating the potential of KWH for enhanced denitrification and reduced N2O emissions. Overall, to the best of our knowledge, this is the first study that demonstrated KWH, as a novel and complex organic carbon source, can be safely used in sewage treatment processes to improve the pollutant removal efficiency without causing a significant increase in N2O emissions.

A review of microbial nitrogen transformations and microbiome engineering for biological nitrogen removal under salinity stress

The osmotic stress caused by salinity exerts severe inhibition on the process of biological nitrogen removal (BNR), leading to the deterioration of biosystems and the discharge of nitrogen with saline wastewater. Feasible strategies to solve the bottleneck in saline wastewater treatment have attracted great attention, but relevant studies to improve nitrogen transformations and enhance the salt-tolerance of biosystems in terms of microbiome engineering have not been systematically reviewed and discussed. This work attempted to provide a more comprehensive explanation of both BNR and microbiome engineering approaches for saline wastewater treatment. The effect of salinity on conventional BNR pathways, nitrification-denitrification and anammox, was summarized at cellular and metabolic levels, including the nitrogen metabolic pathways, the functional microorganisms, and the inhibition threshold of salinity. Promising nitrogen transformations, such as heterotrophic nitrification-aerobic denitrification, ammonium assimilation and the coupling of conventional pathways, were introduced and compared based on advantages and challenges in detail. Strategies to improve the salt tolerance of biosystems were proposed and evaluated from the perspective of microbiome engineering. Finally, prospects of future investigation and applications on halophilic microbiomes in saline wastewater treatment were discussed.

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.

Electrokinetic-Enhanced Bioremediation of Trichloroethylene-Contaminated Low-Permeability Soils: Mechanistic Insight from Spatio-Temporal Variations of Indigenous Microbial Community and Biodehalogenation Activity

Electrokinetic-enhanced bioremediation (EK-Bio), particularly bioaugmentation with injection of biodehalogenation functional microbes such as Dehalococcoides, has been documented to be effective in treating a low-permeability subsurface matrix contaminated with chlorinated ethenes. However, the spatio-temporal variations of indigenous microbial community and biodehalogenation activity of the background matrix, a fundamental aspect for understanding EK-Bio, remain unclear. To fill this gap, we investigated the variation of trichloroethylene (TCE) biodehalogenation activity in response to indigenous microbial community succession in EK-Bio by both column and batch experiments. For a 195 day EK-Bio column (∼1 V/cm, electrolyte circulation, lactate addition), biodehalogenation activity occurred first near the cathode (<60 days) and then spread to the anode (>90 days), which was controlled by electron acceptor (i.e., Fe(III)) competition and microbe succession. Amplicon sequencing and metagenome analysis revealed that iron-reducing bacteria (Geobacter, Anaeromyxobacter, Geothrix) were enriched within initial 60 d and were gradually replaced by organohalide-respiring bacteria (versatile Geobacter and obligate Dehalobacter) afterward. Iron-reducing bacteria required an initial long time to consume the competitive electron acceptors so that an appropriate reductive condition could be developed for the enrichment of organohalide-respiring bacteria and the enhancement of TCE biodehalogenation activity.

Influence of COD in Toxic Industrial Wastewater from a Chemical Concern on Nitrification Efficiency

COD is an arbitrary indicator of the content of organic and inorganic compounds in wastewater. The aim of this research was to determine the effect of COD of industrial wastewater on the nitrification process. This research covered wastewater from acrylonitrile and styrene-butadiene rubbers, emulsifiers, polyvinyl acetate, styrene, solvents (butyl acetate, ethyl acetate) and owipian^® (self-extinguishing polystyrene intended for expansion) production. The volume of the analyzed wastewater reflected the active sludge load in the real biological treatment system. This research was carried out by the method of short-term tests. The nitrification process was inhibited to the greatest extent by wastewater from the production of acrylonitrile (approx. 51%) and styrene-butadiene (approx. 60%) rubbers. In these wastewaters, nitrification inhibition occurred due to the high COD load and the presence of inhibitors. Four-fold dilution of the samples resulted in a two-fold reduction in the inhibition of nitrification. On the other hand, in the wastewater from the production of emulsifiers and polyvinyl acetate, a two-fold reduction in COD (to the values of 226.4 mgO₂·dm^-3 and 329.8 mgO₂·dm^-3, respectively) resulted in a significant decrease in nitrification inhibition. Wastewater from the production of styrene, solvents (butyl acetate, ethyl acetate) and owipian^® inhibited nitrification under the influence of strong inhibitors. Lowering the COD value of these wastewaters did not significantly reduce the inhibition of nitrification.

Fungal mash enzymatic pretreatment combined with pH adjusting approach facilitates volatile fatty acids yield via a short-term anaerobic fermentation of food waste

As an alternative for commercial enzyme, crude enzyme of fungal mash could promote food waste (FW) hydrolysis, but its specific effects coupled pH adjusting on the production of volatile fatty acids (VFAs) remains unknown. The crude enzyme produced from an Aspergillus awamori, named complex-amylase (CA), was added to short-term anaerobic system of FW fermentation. Results showed that adding CA significantly improved the solubility and degradability of biodegradable and non-biodegradable organics in FW, where the SCOD concentration with adding CA increased by 116.9% relative to the control but a marginal enhancement on VFAs yield. In contrast, adding CA combined with adjusting pH 8 markedly increased the VFAs production to 32.0 g COD/L, almost 10 times as much as the control. Besides, pH adjusting altered the metabolic pathway from lactate-type to butyrate-type. Adding CA coupled pH adjusting significant increase the component of butyrate compared with pH adjusting alone. Moreover, microbial community analysis indicated that adding CA reinforced proportion of the butyrate-producing bacteria (e.g., Dialister) under basic conditions, thus enhancing the butyrate metabolic pathways. This study demonstrated that fungal mash pretreatment coupled pH conditioning could be an economical way to enhance VFAs yield for FW valorization during anaerobic fermentation.

Food waste hydrolysate as a carbon source to improve nitrogen removal performance of high ammonium and high salt wastewater in a sequencing batch reactor

The high ammonium and high salt (HAHS) wastewater generated from the anaerobic digestate of food waste is usually difficult to be treated by biological process because of its low C/N ratio. Herein, food waste hydrolysate (FWH) is rich in readily biodegradable organic matter, was utilized as carbon source to enhance the nitrogen removal of HAHS in the activated-sludge system. Results showed that compared with the control average total nitrogen removal efficiency increased from 73.4% to 94.9% and effluent declined from 281.4 mg/L to 53.9 mg/L by adding FWH at the C/N ratio of 6, satisfying the sewage discharge standard regulated by China. Besides, FWH utilization led to higher selectivity of the species responsible for nitrogen removal in related to glucose-adding group, which were dominated by Flavobacteriaceae, Melioribacteraceae, PHOS-HE36, and Rhodobacteraceae after a long-term operation. In general, FWH is an alternative carbon source to enhance nitrogen removal in HAHS wastewater treatment.