Achieving partial denitrification using organic matter in brewery wastewater as carbon source

From acetate-driven partial denitrification (PD) to N-Methylpyrrolidone-driven PD: Microbial community, metabolic pathway and functional genes

With the rapid development of the new energy industry, the wastewater discharged from battery production industries has increased significantly, in which N-Methylpyrrolidone (NMP) have aroused widespread attention. It is valuable to develop low-cost biological methods for NMP containing wastewater treatment. In this study, an NMP-driven PD system was acclimated in an sequencing batch reactor (SBR) by gradually replacing the sodium acetate with NMP. The nitrate-to-nitrite transformation ratio (NTR) of the acclimated PD sludge was stabilized around 60 % and reached up to 68.1 %.The TOC removal was maintained above 90 %, and the NO-3-N reduction reached up to 96.7 %. The relative abundance of denitrifying bacterium Paracoccus increased during domestication (from 0.11 % to 9.38 %), and the abundance of NMP metabolism-related genes (hyuA, hyuB, mao, and gabD) also increased significantly. Moreover, the contribution of Paracoccus to NMP metabolism-related genes gradually increased. It suggests that Paracoccus may play a major role in this system. In conclusion, this study verified the feasibility of NMP as a carbon source to drive PD process to achieve NO-2-N accumulation, and provided a novel strategy for nitrogen removal of battery wastewater.

Integrating network and in-silico simulation insights into the ecological interactions shaped by carbon sources in partial denitrification and anammox system

The underlying ecological mechanism of microbial communities shaped by carbon source in partial denitrification and anammox (PDA) systems remains poorly understood, despite the potential of multiple carbon sources to support the partial denitrification process. Herein, the integrated network and in-silico simulation methods were used to evaluate the considerable impact of carbon sources on the dynamics of ecological interactions. The fluctuation of carbon source (from acetate to glucose and ethanol) significantly destabilized the performance of PDA system (total nitrogen removal efficiency decreased from 96.8% to 69.1%). Glucose simultaneously altered the composition of denitrifying bacteria, resulting in a significant enrichment of the genus Elstera (from 0% to 12.7%). By contrast, genus Thauera re-dominated for partial denitrification with ethanol as carbon source. Importantly, heterotrophic bacteria (e.g., genus Calditrichia) gradually enriched by utilizing ethanol. The presence of acetate in phase IV further enhanced the competitive advantage of heterotrophic bacteria over denitrifying bacteria, thereby resulting in the deteriorated performance of the PDA system. The in-silico simulation of co-culture further revealed that the overgrowth of auxotrophic species Calditrichia utilized amounts of nutrients and limited other functional bacteria. Additionally, the whole co-occurrence network indicated that positive interactions likely improved the adaptability of anammox bacteria under the unsteady conditions. This study provides profound insights into the ecological interactions shaped by carbon sources in PDA systems and underscores the necessity of comprehensive review of the external carbon source to ensure optimal performance.

Inorganic bioelectric system for nitrate removal with low N2O production at cold temperatures of 4 and 10 °C

Groundwater, essential for ecological stability and freshwater supply, faces escalating nitrate contamination. Traditional biological methods struggle with organic carbon scarcity and low temperatures, leading to an urgent need to explore efficient approaches for groundwater remediation. In this work, we proposed an inorganic bioelectric system designed to confront these challenges. At 10 and 4 °C, the system achieved total nitrogen (TN) removal efficiencies of 95.4 ± 2.7% and 90.9 ± 1.9% at 2 h hydraulic retention time (HRT), while maximum TN removal rates were recorded as 206.0 ± 6.3 and 178.3 ± 9.4 g N·m-3·d-1 at 1 h HRT. The microbial analysis uncovered shifts in dominant genera across temperatures, with Dechloromonas prevalent at 10 °C and Chryseobacterium at 4 °C, highlighting adaptability to cold-tolerant species. Gene analysis on narG, napA, nirS, nirK, norB, nosZI, nosZII, and nifA examined the nitrate reduction processes, and analysis on mtrC and omcA hinted at electrotrophic processes. Additionally, we demonstrated system resilience to disruptions of power outage and short periods without flow through. These findings establish a foundational understanding of electricity-driven nitrate bioreduction in cold environments, crucial in groundwater remediation strategies and paving the way for future optimization and upscaling efforts.

Achieving rapid start-up and efficient nitrogen removal of partial-denitrification/anammox process using organic matter in brewery wastewater as carbon source

To find a cost-efficient carbon source for the partial denitrification/anaerobic ammonium oxidation (anammox) (PD/A) process, the practicability of using the organic matter contained in brewery wastewater as carbon source was investigated. Quick self-enrichment of denitrifying bacteria was achieved by supplying brewery wastewater as organic carbon source and using the mature anammox sludge as the seeding sludge. The PD/A process was successfully established after 33-day operation and then the average total nitrogen removal efficiency reached 92.29% when the influent CODCr: NO3--N: NH4+-N ratio was around 2.5: 1.0: 0.67. The relative abundance of Thauera increased from 0.03% in the seeding sludge to 54.29% on day 110, whereas Candidatus brocadia decreased from 30.66% to 2.08%. The metagenomic analysis indicated that the sludge on day 110 contained more nar and napA (total of 41.24%) than nirK and nirS (total of 11.93%). Thus NO2--N was accumulated efficiently in the process of denitrification and sufficient NO2--N was supplied for anammox bacteria in the PD/A process. Using brewery wastewater as carbon source not only saved the cost of nitrogen removal but also converted waste into resource and reduced the treatment expense of brewery wastewater.

Machine Learning-Assisted Optimization of Mixed Carbon Source Compositions for High-Performance Denitrification

Appropriate mixed carbon sources have great potential to enhance denitrification efficiency and reduce operational costs in municipal wastewater treatment plants (WWTPs). However, traditional methods struggle to efficiently select the optimal mixture due to the variety of compositions. Herein, we developed a machine learning-assisted high-throughput method enabling WWTPs to rapidly identify and optimize mixed carbon sources. Taking a local WWTP as an example, a mixed carbon source denitrification data set was established via a high-throughput method and employed to train a machine learning model. The composition of carbon sources and the types of inoculated sludge served as input variables. The XGBoost algorithm was employed to predict the total nitrogen removal rate and microbial growth, thereby aiding in the assessment of the denitrification potential. The predicted carbon sources exhibited an enhanced denitrification potential over single carbon sources in both kinetic experiments and long-term reactor operations. Model feature analysis shows that the cumulative effect and interaction among individual carbon sources in a mixture significantly enhance the overall denitrification potential. Metagenomic analysis reveals that the mixed carbon sources increased the diversity and complexity of denitrifying bacterial ecological networks in WWTPs. This work offers an efficient method for WWTPs to optimize mixed carbon source compositions and provides new insights into the mechanism behind enhanced denitrification under a supply of multiple carbon sources.

Selective genes expression and metabolites transformation drive a robust nitrite accumulation during nitrate reduction under alternating feast-famine condition

Nitrite production via denitrification has been regarded as a key approach for survival of anaerobic ammonium oxidation (anammox) bacteria. Despite the important carbon substrate, little is known about the role of differential genes expression and extracellular metabolite regulation among diverse microbial communities. In this study, a novel alternating feast-famine strategy was proposed and demonstrated to efficiently accumulate nitrite in a low-nitrogen loading rate (NLR) (0.2∼0.8 kg N/m3/d) denitrification system. Highly selective expression of denitrifying genes was revealed as key regulators. Interestingly, in absence of carbon source (ACS) condition, the expression of narG and narI/V genes responsible for reduction of nitrate to nitrite jumped to 2.5 and 5.1 times higher than that in presence of carbon source (PCS) condition with carbon to nitrate ratio of 3.0. This fortunately facilitated a rapid nitrite accumulation once acetate was added, despite a significantly down-regulated narG and narI/narV and up-regulated nirS/nirK. This strategy selected Thauera as the most dominant denitrifier (50.2 %) with the highest contribution to narG and narI/narV genes, responsible for the high nitrite accumulation. Additionally, extracellular xylose, pyruvate, and glucose jointly promoted carbon-central metabolic pathway of key denitrifiers in ACS stage, playing an important role in the process of self-growth and selective enrichment of functional bacteria. The relatively rapid establishment and robust performance obtained in this study shows an engineering-feasible and economically-favorable solution for the regulation of partial denitrification in practical application.

Nitrogen and nitrous oxides emission characteristics of anoxic/oxic wastewater treatment process under different oxygen regulation strategies

Nitrous oxide (N2O) and nitrogen oxides (NOx) (i.e., nitric oxide (NO) and nitrogen dioxide (NO2)), which could be produced in wastewater treatment process and result in greenhouse effect and atmospheric pollution, respectively, have been studied limitedly in their emission characteristics and transformation mechanisms. In this study, intelligent oxygen regulation was applied in anoxic/oxic wastewater treatment process (I-A/O), and its effects on regulating NOx and N2O transformations were extensively explored by comparing it with conventional A/O process (C-A/O). Results showed that the average emission amounts of N2O and NOx in I-A/O were 7.45 ± 0.66 mg and 1.88 ± 0.10 mg, respectively. Satisfactory reduction of N2O by 29.28 %-45.08 % was achieved in I-A/O compared to that of C-A/O, but together with increased NOx emission by 83.19 %-120.57 %. Pearson correlation and transcriptional analysis suggested that NO2--N reduction in the anoxic phase dominated N2O production, while no significant N2O production in the oxic phase was found. Hence, the reduced N2O production in I-A/O was mainly attributed to its efficient denitrification process. On the other hand, both the anoxic and oxic phases played important roles in NO production. More importantly, sufficient oxygen in I-A/O promoted the ammonia oxidation process, resulting in higher NO emission in I-A/O in the oxic phase. The imbalance in NO and N2O emissions was then amplified by the NOR enzyme, which mediates the conversion of NO to N2O in both the anoxic and oxic phases. Besides, carbon emission reduction by 31.32 %-36.50 % was obtained in I-A/O due to aeration consumption savings and greenhouse gas emissions reduction compared to C-A/O. Overall, intelligent oxygen regulation optimized the nitrogen transformation and achieved carbon emission reduction in A/O process, but special attention should be paid to the associated risk caused by increased NO emissions.

Effect of streptomycin sulphate on the nitrification system in activated sludge: insight into nitrification characteristic, antibiotic resistance gene and microbial community

Wastewater with residual streptomycin sulphate usually contains high content of ammonia-nitrogen. However, the biological removal process of ammonia-nitrogen under streptomycin sulphate circumstance was unclear. In this study, short-term and long-term effects of streptomycin sulphate on biological nitrification systems, including AOB, NOB, SAOR, SNOR and SNPR, were evaluated comprehensively. The results indicated IC50 for AOB and NOB were 7.5 and 6.6 mg/L. SAOR and SNPR could be decreased to 3.43 ± 0.52 mg N/(g MLSS·h) and 0.24 ± 0.03 mg N/(g MLSS·h) while the addition of streptomycin sulphate was 10 mg/L. When streptomycin sulphate addition was stopped, nitrification ability recovered slightly, SAOR and SNPR increased to 9.37 ± 0.36 mg N/(g MLSS·h) and 1.66 ± 0.49 mg N/(g MLSS·h), respectively. The protein of EPS increased gradually during the acclimatization process, and the maximal protein value was 68.24 mg/g MLSS on the 100th day, however, no significant change of polysaccharose was observed during the acclimatization process. High abundance of ARGs and intI1 was detected in effluent and sludge of the biological treatment system. The maximal relative abundance of aadA1 in the sludge appeared on the 140th day, and increased by 0.99 orders of magnitude. Biological diversity decreased significantly during the acclimatization process, relative abundance of nitrosomonas was changed from 9.07% to 38.68% on the 61st day, while relative abundance of nitrobacter was changed from 1.30% to 0.64%. It should be noted that relative abundances of nitrosomonas and nitrobacter were reduced to 16.17% and 0.25% on the 140th day. This study would be helpful for nitrogen removal in wastewater with antibiotic.

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.

Novel nitrogen removal process in marine aquaculture wastewater treatment using Enteromorpha ferment liquid as carbon

The process performance of partial denitrification of a novel anaerobic fermentation integrated fixed-film activated sludge (IFAS-AFPD) of Enteromorpha was studied. The response surface method was used to determine the optimal reaction conditions, and the operation experiment was carried out under the optimal conditions. The results showed that the nitrogen removal effect was the best when the salinity was 12.2 g•L^-1, the Carbon-Nitrogen ratio (C/N) was 4, the pH was 8.5, and the Nitrite Accumulation Rate, Nitrate Removal Rate, Chemical Oxygen Demand Utilization Rate could reach 77%, 89% and 51%. Experimental results have shown that the NAR of the Enteromorpha ferment liquid system could be maintained at about 74%, which was noteworthy higher than that of the sodium acetate (CH₃COONa) system at 42%; Microbial community analysis showed that Enteromorpha ferment liquid was more beneficial to the growth of Bacteroidetes than CH₃COONa.

Effect of COD/ NO3−-N ratio on nitrite accumulation and microbial behavior in glucose-driven partial denitrification system

COD/NO₃ ^--N ratio was considered to be one of the key factors achieving effective nitrite accumulation during partial denitrification. In two parallel reactors incubated with glucose as carbon source at COD/NO₃ ^--N of 3 and 5, respectively, the microbial community structure shift and the nitrite accumulation performance during long-term operation were investigated. The maximum nitrite accumulation ratios at COD/NO₃ ^--N of 3 and 5 were 17.9% and 47.04%, respectively. Thauera was the dominant genus in both reactors on day 220 with the relative abundance of 18.67% and 64.01%, respectively. Batch experiments with different electron acceptors suggested that the distinction in nitrite accumulation at COD/NO₃ ^--N of 3 and 5 might be caused by the differences in the abundance of Thauera.

Highly efficient transformation of slowly-biodegradable organic matter into endogenous polymers during hydrolytic fermentation for achieving effective nitrite production by endogenous partial denitrification

The utilization of slowly-biodegradable organic matter (SBOM) to provide nitrite efficiently for anaerobic ammonia oxidation (anammox) process is an essential topic. High nitrite concentration without inhibition of exogenous organic matter is optimal condition for anammox process. In this study, hydrolytic fermentation (HF) of SBOM was applied to drive an endogenous partial denitrification (EPD) process (nitrate to nitrite) during an anaerobic-anoxic operation in a starch-fed system. With a limited production of exogenous organic matter (22.3 ± 4.9 mg COD/L), 79.0% of SBOM was transformed into poly-hydroxyalkanoates (PHA) through a pathway of simultaneous HF-absorption and endogenous polymer synthesis, corresponding to a hydrolytic fermentation ratio of 86.0%. A high nitrate to nitrite transformation ratio of 85.4% was achieved under an influent carbon to nitrogen ratio of 4.8. Denitrifying glycogen-accumulating organisms (DGAOs) was enriched from 0.6% to 10.9%, with an increase from 0.7 to 1.0 of nitrate reductase genes to nitrite reductase genes ratio. Subsequently, nitrate reduction rate was 5.6-fold higher than the nitrate reduction rate. A prominent migration of exogenous complete denitrification to EPD was accomplished. Furthermore, the starch-fed system exhibited performance with significant adaptability and stability in the presence of different SBOMs (dissolved protein and primary sludge). Therefore, the HF-EPD system achieved efficient nitrite production through EPD with the addition of various SBOMs, providing a potential alternative to anammox systems for the treatment of SBOM-rich wastewater.

Effects of salinity on nitrite and elemental sulfur accumulation in a double short-cut sulfur autotrophic denitrification process

Double short-cut sulfur autotrophic denitrification (DSSADN) coupled with Anammox is of great significance in the low-carbon treatment of nitrogen-containing wastewater. In order to achieve high salinity autotrophic nitrogen removal, the effects of different salinities on the accumulation characteristics of NO₂^--N and S⁰ and microorganisms in DSSADN process were studied. The results showed that the effect of salinity on the DSSADN process could be categorized into the stimulation, stable, and inhibition. When the salinity gradually increased to 2.5 %, the highest NO₂^--N production rate (NiPR) and S⁰ production rate (S⁰PR) of DSSADN were 0.54 kg/(m³·d) and 1.1 kg/(m³·d) respectively. NiPR and S⁰PR gradually decreased as the salinity increased to more than 3 %. However, salinity had a relatively low impact on nitrite accumulation efficiency and S⁰ accumulation efficiency, which were 80 % and 81.5 %, respectively, when the salinity reached 5 %. Salinity has a great influence on the structure and abundance of microbial communities in the system.

Disintegration of waste sludge as an element bio-circular economy in waste water treatment plant towards carbon recovery for biological nutrient removal

The goal of the study was to evaluate the possibility of use of disintegrated excess sludge to enhance combined biological nutrient removal from wastewater. In the experiment lasting 295 days four runs were performed. Effectiveness of contaminants removal in sequencing batch reactor without and with applying sludge subjected previously to hydrodynamic disintegration at three energy density (Ɛ_L) levels was analysed. It was shown that Ɛ_L is a crucial parameters responsible for the characteristics of disintegrated sludge applied as a carbon source for biological nutrient removal. Using sludge disintegrated at 70 and 210 kJ/L the increase in effectiveness of N and P removal was noted, averagely by 16.1 % (N removal) and 70.3 % (P removal) at Ɛ_L = 70 kJ/L and by 17.8 % and 63.1 % at Ɛ_L = 210 kJ/L. On the contrary, use of sludge disintegrated at Ɛ_L = 280 kJ/L caused decline in N removal by averagely 12.8 %, what was a consequence of nitrification failure.