Biological treatment of N-methylpyrrolidone, cyclopentanone, and diethylene glycol monobutyl ether distilled residues and their effects on nitrogen removal in a full-scale wastewater treatment plant

Manufacturing processes in semiconductor and photonics industries involve the use of a significant amount of organic solvents. Recycle and reuse of these solvents produce distillate residues and require treatment before being discharged. This study aimed to evaluate the performance of the biological treatment system in a full-scale wastewater treatment plant that treats wastewater containing distillate residues from the recycling of electronic chemicals. Batch experiments were conducted to investigate the optimal operational conditions for the full-scale wastewater treatment plant. To achieve good nitrogen removal efficiency with effluent ammonia and nitrate concentrations below 20 mg N/L and 50 mg N/L, respectively, it was suggested to control the ammonia concentration and pH of the influent below 500 mg N/L and 8.0, respectively. In addition, the biodegradability of N-methylpyrrolidone, diethylene glycol monobutyl ether, and cyclopentanone distillate residues from the electronic chemicals manufacturing process were evaluated under aerobic, anoxic, and anaerobic conditions. N-methylpyrrolidone and cyclopentanone distillate residues were suggested to be treated under anoxic condition. However, substrate inhibition occurred when using cyclopentanone distillate residue as a carbon source with chemical oxygen demand (COD) levels higher than 866 mg/L and nitrate levels higher than 415 mg N/L. Under aerobic condition, the COD from both N-methylpyrrolidone and cyclopentanone distillate residues could be easily degraded. Nevertheless, a negative effect on nitrification was observed, with a prolonged lag time for ammonia oxidation as the initial COD concentration increased. The specific ammonia oxidation rate and nitrate production rate decreased under high COD concentration contributed by N-methylpyrrolidone and cyclopentanone distillate residues. Furthermore, the biodegradability of diethylene glycol monobutyl ether distillate residue was found to be low under aerobic, anoxic, and anaerobic conditions. With respect to the abundance of nitrogen removal microorganisms in the wastewater treatment plant, results showed that Comammox may have an advantage over ammonia oxidizing bacteria under high pH conditions. In addition, Comammox may have higher resistance to environmental changes. Dominance of Comammox over ammonia oxidizing bacteria under high ammonia condition was first reported in this study.

Unveiling the power of COD/N on constructed wetlands in a short-term experiment: Exploring microbiota co-occurrence patterns and assembly dynamics

Constructed wetlands (CWs) are a cost-effective and environmentally friendly wastewater treatment technology. The influent chemical oxygen demand (COD)/nitrogen (N) ratio (CNR) plays a crucial role in microbial activity and purification performance. However, the effects of CNR changes on microbial diversity, interactions, and assembly processes in CWs are not well understood. In this study, we conducted comprehensive mechanistic experiments to investigate the response of CWs to changes in influent CNR, focusing on the effluent, rhizosphere, and substrate microbiota. Our goal is to provide new insights into CW management by integrating microbial ecology and environmental engineering perspectives. We constructed two groups of horizontal subsurface flow constructed wetlands (HFCWs) and set up three influent CNRs to analyse the microbial responses and nutrient removal. The results indicated that increasing influent CNR led to a decrease in microbial α-diversity and niche width. Genera involved in nitrogen removal and denitrification, such as Rhodobacter, Desulfovibrio, and Zoogloea, were enriched under medium/high CNR conditions, resulting in higher nitrate (NO3--N) removal (up to 99 %) than that under lower CNR conditions (<60 %). Environmental factors, including water temperature (WT), pH, and phosphorus (P), along with CNR-induced COD and NO3--N play important roles in microbial succession in HFCWs. The genus Nitrospira, which is involved in nitrification, exhibited a significant negative correlation (p < 0.05) with WT, COD, and P. Co-occurrence network analysis revealed that increasing influent CNR reduced the complexity of the network structure and increased microbial competition. Analysis using null models demonstrated that the microbial community assembly in HFCWs was primarily driven by stochastic processes under increasing influent CNR conditions. Furthermore, HFCWs with more stochastic microbial communities exhibited better denitrification performance (NO3--N removal). Overall, this study enhances our understanding of nutrient removal, microbial co-occurrence, and assembly mechanisms in CWs under varying influent CNRs.

Effect of low-intensity ultrasound on partial nitrification: Performance, sludge characteristics, and properties of extracellular polymeric substances

Ultrasound technology, which is environment-friendly and economical, has emerged as a novel strategy that can be used to enhance the partial nitrification process. However, its effect on this process remains unclear. Therefore, in this study, partial nitrification sludge was subjected to low-intensity (0.15 W/mL) ultrasound treatment for 10 min, and the effect of ultrasonic treatment on the partial nitrification process was evaluated based on changes in reactor performance, sludge characteristics, and the properties of extracellular polymeric substances (EPS). The results obtained showed that the ultrasonic treatment enhanced nitrite accumulation performance as well as the activity of ammonia-oxidizing bacteria from 3.3 to 16.6 mg O₂/g VSS,⋅while inhibiting the activity of nitrite-oxidizing bacteria. Further analysis showed that owing to the ultrasonic treatment, there was an increase in EPS contents. Particularly, there was a significant increase in loosely bound polysaccharide (PS) contents, indicating the occurrence of intracellular PS anabolics as well as PS secretion. Additionally, ultrasonic treatment induced a significant increase in carbonyl, hydroxyl, and amine functional group contents, and EPS analysis results revealed that it had a positive effect on mass transfer efficiency; thus, it enhanced the partial nitrification process. Overall, this study describes the effect of intermittent low-intensity ultrasound on the partial nitrification process as well as the associated enhancement mechanism.

Microcystis blooms aggravate the diurnal alternation of nitrification and nitrate reduction in the water column in Lake Taihu

To explore the effects of Microcystis blooms on nitrogen (N) cycling in the water column, the community structures of the Microcystis-attached and free-living bacteria in Lake Taihu were assessed and a mesocosm experiment was further conducted on the shore of Lake Taihu. The bacterial communities of Microcystis-attached and free-living bacteria were dominated by heterotrophic bacteria, such as Pseudomonas and Massilia, while the relative abundances of the genera related to traditional autotrophic nitrification were surprisingly low. However, the dramatic increase in nitrate (NO₃^-) levels at the daytime suggested that in the mesocosms nitrification did occur, during which the heterotrophic nitrifiers played a predominant role as revealed by the acetylene inhibition experiment. The ammonium (NH₄⁺) concentrations were always maintained at a low level, indicating that most of the substrates for daytime nitrification originated from organic N. The total N being removed during the experiment was much less than the sum of daily NO₃^- reduction, while the decrease in NO₃^- concentration was much higher than the increase in NH₄⁺ concentration during the night, indicating that assimilation was the main explanation for nocturnal NO₃^- reduction. Thus, the cycling of organic N (remineralization) - heterotrophic nitrification - NO₃^- assimilation (reduction) promoted by Microcystis blooms aggravates the diurnal variation of NO₃^- in the water column.

Managing biofilm growth and clogging to promote sustainability in an intermittent sand filter (ISF)

The sustainability of rural sanitation includes the long-term welfare of both rural and urban societies. As a commonly used rural sanitation technology, operation of intermittent sand filters (ISF) is impacted by biofilm clogging inside the ISF. In this study ISF performance is studied at low hydraulic loading rates (HLR) to explore the interaction between biofilm growth and wastewater treatment efficiency. CW2D/HYDRUS, a simulation model which does not include media hydraulic property changes caused by biofilm growth, is utilized as a numerical control to contrast the effects of biofilm growth inside an experimental ISF. A paired experiment with simulation demonstrate that biofilm clogging comprised dominantly of heterotrophs occurred in the top layers of the ISF. Lowered HLR slows clogging development but not final clogging extent. The biofilm clogging development zone offers adequate removal of applied biodegradable COD and NH₄⁺ - N. However, the spatial distribution of heterotrophs and biodegradable COD does not match the denitrification requirement of the resulting NO₃^- - N. A simultaneous nitrification and denitrification (SND) potential is manifested in the clogging development zone, but lowered HLR reduces media moisture level to a less favorable level for denitrification. Furthermore, slowed water movement under lower HLR aggravates the accumulation of NO₃^- - N, which can potentially result in counterproductive salt accumulation. Since biofilm growth is a natural and self-adaptive response to wastewater application, this study suggests accepting limited, managed biofilm growth and clogging in ISFs. In addition, this study calls for further research to manage biofilm growth and clogging for long-term ISF sustainability.

The Operating Characteristics of Partial Nitrification by Controlling pH and Alkalinity

In many experiments, a partial nitrification device is initiated with the use of highly active nitrating sludge because of the large number of nitrifying bacteria. Ammonia-oxidizing bacteria (AOB) are more adaptable to low-dissolved oxygen environments than nitrite-oxidizing bacteria (NOB). NOB activity was inhibited when the dissolved oxygen (DO) levels were decreased, causing the nitrate-nitrogen concentration to gradually decrease in the effluent and the nitrite-nitrogen concentration to gradually increase, achieving the accumulation of nitrous nitrogen. In this experiment, a sequencing batch reactor (SBR) was used to suppress NOB activity at a given pH while maintaining DO at a very low level so that the ammonia–water reaction mainly occurred in the device, and then the mud and water separated. Compared with other experiments, this approach can occur in 25 days, and it runs stably for more than two months until the device closes when the ammonia-nitrogen concentration is about 170 mg/L. This experiment also compared the difference between the pH change at the beginning of the device operation and after the device was stable. In order to increase the efficiency of bacterial appreciation, supplementing NaHCO3 increased the HCO3− concentration by 300 mg/L on the 25th day. It was found that some nitrification reactions still occurred, but they were not enough to destabilize the device. The nitrosate accumulation efficiency still gradually increased, and the average nitrite accumulation efficiency was 87.25% after NaHCO3 supplementation.

Numerical assessment of a soil moisture controlled wastewater SDI disposal system in Alabama Black Belt Prairie

To promote the environmental sustainability of rural sanitation, a soil moisture controlled wastewater subsurface drip irrigation (SDI) dispersal system was field tested in the Black Belt Prairie of Alabama, USA. The soil moisture control strategy was designed to regulate wastewater disposal timing according to drain field conditions to prevent hydraulic overloading and corresponding environmental hazard. CW2D/HYDRUS simulation modeling was utilized to explore difficult-to-measure aspects of system performance. While the control system successfully adapted hydraulic loading rate to changing drain field conditions, saturated field conditions during the dormant season presented practical application challenges. The paired field experiment and simulation model demonstrate that soil biofilm growth was stimulated in the vicinity of drip emitters. Although biofilm growth is critical in maintaining adequate COD and NH₄⁺-N removal efficiencies, the efficient removal of biodegradable COD itself by soil biofilm limits denitrification of formed NO₃^--N . Furthermore, stimulated soil biofilm growth can create soil clogging around drip emitters, which was discerned in the field experiment along with salt accumulation, both of which were verified by simulation. Comparable modeling of system performance in sand and clay media demonstrate that the placement of soil moisture sensors within the drain field can have pronounced impacts on system hydraulic performance, depending on the soil permeability. Overall, the soil moisture control strategy tested is shown as a viable supplemental technology to promote the environmental sustainability of rural sanitation systems.

Partial nitritation performance and microbial community in sequencing batch biofilm reactor filled with zeolite under organics oppression and its recovery strategy

Influences of organics on partial nitritation performance were investigated in a lab-scale sequencing batch biofilm reactor filled with zeolite. Significant differences in nitrite production rate (NPR) were observed between different dosages of glucose. With influent COD/N ratio from 0 to 1.5, NPR declined from 0.4 to 0.05 kg/(m3·d). Meanwhile, an appropriate NO2--N/NH4+-N ratio (1.4 ± 0.5) could be obtained for simultaneous anammox denitrification at COD/N ratio of 0.5. Increasing airflow rate was found as an effective recovery strategy. Other than competition of heterotrophs with nitrifiers for dissolved oxygen, it has been verified that addition of organics generated higher free ammonia, and then further inhibitedammonium oxidizing bacteria (AOB). Moreover, three-dimensional excitation-emission matrix (3D-EEM) results revealed that protein-like and humic acid-like substances were the main components in extracellularpolymericsubstances (EPS). And high-throughput sequencing analysis demonstrated that the relative abundance of AOB decreased.

Analysis of rapid culture of high-efficiency nitrifying bacteria and immobilized filler application for the treatment of municipal wastewater

Activated sludge from the A2/O process in a wastewater treatment plant (WWTP) was used as the seed sludge for enrichment to achieve faster growth of nitrifying bacteria and higher nitrification efficiency of the filler made by nitrifying bacteria. The bacterial community was enriched in a self-circulating bacteria culture tank by a continuous ammonia feeding mode. The study found that the nitrifying bacteria community was enriched in 38 days with the ammonia oxidation rate of approximately 275.58 mg (L h)-1. High-throughput sequencing demonstrated that Nitrosomonas belonging to ammonia-oxidizing bacteria (AOB) was predominant in the sludge after 38 days at a ratio extending from 0.43% to 61.91%. The enriched sludge was used as the bacterial source and the immobilization was carried out with polyvinyl alcohol (PVA). After the recovery culture, the ammonia oxidation rate of the filler was up to 44.61 mg (L h)-1 for the treatment of municipal wastewater, and the effluent ammonia was below 1 mg L-1, indicating that the immobilized filler is effective for municipal wastewater nitrification. Scanning electron microscope (SEM) observations showed that immobilized fillers were highly porous and bacteria adhered to the network structure, demonstrating that the filler provided a good growth microenvironment for microorganisms.

Impact of biochar on greenhouse gas emissions from constructed wetlands under various influent chemical oxygen demand to nitrogen ratios

Biochar is widely used for nutrient removal in constructed wetlands (CWs); however, its influence on greenhouse gas (GHG) emissions from CWs remains unclear. Here, biochar was used to mitigate the global warming potential (GWP) from CWs and promote the removal of contaminants from simulated domestic wastewater under different influent chemical oxygen demand to nitrogen ratios (COD/N = 3, 6, 9, 12). Results demonstrated that biochar could improve the removal of COD, NH₄⁺- N, and TN. The average N₂O and CO₂ fluxes were significantly lower and CH₄ fluxes were higher in biochar-added CWs than those in none-biochar CWs. Biochar reduced GWP values of N₂O and CH₄ from 18.5% to 24.0%. N₂O fluxes and GWP decreased, while CH₄ and CO₂ fluxes increased as COD/N ratios increased. Additionally, biochar increased the abundance of Geobacter and denitrifiers such as Hydrogenophaga. Overall, biochar could not only promote the removal of nutrients but also mitigate GWP in CWs.

Nitritation-anammox process - A realizable and satisfactory way to remove nitrogen from high saline wastewater

In this study, acclimation of freshwater nitritation-anammox sludge to remove nitrogen in high saline and hypersaline wastewater was evaluated, during which the microbes activity and microbial community revolution were revealed to understand the fate of a nitritation-anammox process (SNAP) in response to increasing salt stress. By enhanced aeration, the SNAP system can treat saline (3%) ammonium-rich (185 mg/L) wastewater after gradual adaption. Hypersalinity (5%) caused final deterioration of the SNAP system due to a severe inhibition on anammox activity. Genera Kuenenia (anammox), Nitrosomonas (AOB) and Nitrosovibrio (AOB) bacteria were salt adaptable microbes, while genus Nitrospira (NOB) bacteria were sensitive to salinity. Under the enhanced aeration, AOB bacteria could bear 3% salinity with possible enriched ammonia monooxygenase to stimulate the conversion of ammonium to nitrite by producing more intermediate-hydroxylamine, which could alleviate the negative effect of insufficient hydroxylamine oxidase members in AOB bacteria.

Effect of free ammonia inhibition on NOB activity in high nitrifying performance of sludge

The inhibition of free ammonia (FA) on nitrite-oxidizing bacteria (NOB) was investigated using an enriched NOB community with high nitrifying performance. A continuous-flow reactor was operated for the enrichment of the bacterial community. High-throughput sequencing analysis showed that Nitrospira (NOB) using in batch experiments was extended from 4.78% to 12.08% during the under continuous-flow operation for 27 days. For each batch experiments, an ammonia injection at the start-up resulted in the desired initial FA concentration (at pH = 8.1-8.2, T = 25 °C), and a continuous ammonia feeding stream allowed for a relatively stabilized FA levels as much as the initial one. Results indicated that FA inhibition on NOB was not instantaneous but occurred gradually at a certain reaction time. Low concentrations of FA (18.08-24.95 mg L-1) had a limited inhibition on NOB with increasingly high nitrate production rates, whereas high FA levels (36.06-50.66 mg L-1) exerted a significant negative impact on the NOB. Also, strong adaptation happened in these high levels of FA inhibition on NOB, which resulted in an overall low NOB activity during the whole aerobic operation.

Simultaneous improvement of waste gas purification and nitrogen removal using a novel aerated vertical flow constructed wetland

Insufficient oxygen supply is identified as one of the major factors limiting organic pollutant and nitrogen (N) removal in constructed wetlands (CWs). This study designed a novel aerated vertical flow constructed wetland (VFCW) using waste gas from biological wastewater treatment systems to improve pollutant removal in CWs, its potential in purifying waste gas was also identified. Compared with unaerated VFCW, the introduction of waste gas significantly improved NH₄⁺-N and TN removal efficiencies by 128.48 ± 3.13% and 59.09 ± 2.26%, respectively. Furthermore, the waste gas ingredients, including H₂S, NH₃, greenhouse gas (N₂O) and microbial aerosols, were remarkably reduced after passing through the VFCW. The removal efficiencies of H₂S, NH₃ and N₂O were 77.78 ± 3.46%, 52.17 ± 2.53%, and 87.40 ± 3.89%, respectively. In addition, the bacterial and fungal aerosols in waste gas were effectively removed with removal efficiencies of 42.72 ± 3.21% and 47.89 ± 2.82%, respectively. Microbial analysis results revealed that the high microbial community abundance in the VFCW, caused by the introduction of waste gas from the sequencing batch reactor (SBR), led to its optimized nitrogen transformation processes. These results suggested that the VFCW intermittently aerated with waste gas may have potential application for purifying wastewater treatment plant effluent and waste gas, simultaneously.

A novel aerated surface flow constructed wetland using exhaust gas from biological wastewater treatment: Performance and mechanisms

In this study, a novel aerated surface flow constructed wetland (SFCW) using exhaust gas from biological wastewater treatment was investigated. Compared with un-aerated SFCW, the introduction of exhaust gas into SFCW significantly improved NH₄⁺-N, TN and COD removal efficiencies by 68.30 ± 2.06%, 24.92 ± 1.13% and 73.92 ± 2.36%, respectively. The pollutants removal mechanism was related to the microbial abundance and the highest microbial abundance was observed in the SFCW with exhaust gas because of the introduction of exhaust gas from sequencing batch reactor (SBR), and thereby optimizing nitrogen transformation processes. Moreover, SFCW would significantly mitigate the risk of exhaust gas pollution. SFCW removed 20.00 ± 1.23%, 34.78 ± 1.39%, and 59.50 ± 2.33% of H₂S, NH₃ and N₂O in the exhaust gas, respectively. And 31.32 ± 2.23% and 32.02 ± 2.86% of bacterial and fungal aerosols in exhaust gas were also removed through passing SFCW, respectively.

Organic loading rate shock impact on extracellular polymeric substances and physicochemical characteristics of nitrifying sludge treating high-strength ammonia wastewater under unsteady-state conditions

Laboratory experimentation was used to investigate the impact of the organic loading rate shock on extracellular polymeric substances (EPSs) and the physicochemical characteristics of nitrifying sludge (NS) treating high-strength ammonia wastewater. The increased organic loading rates (OLRs) strongly influenced the stability of the NS with regard to nutrient removal, biomass–liquid separation, and surface properties, leading to the sludge system collapse at the OLR of 0.75 kg COD per kg MLVSS d. However, an incomplete recovery of the NS after the high OLRs shock was observed when decreasing the OLRs. In addition, the variations of OLRs resulted in relatively stable amounts of tightly bound EPS (TB-EPS), but a significant change in loosely bound EPS (LB-EPS). Both in LB-EPS and TB-EPS, the proteins (PN) contents and proteins to polysaccharides (PN/PS) ratios decreased with the increase in OLRs. Results from the excitation emission matrix spectra implied that the tryptophan PN-like substances were the major components in EPS at low OLRs, while the humic acid-like and fulvic acid-like substrates increased markedly at high OLRs. Furthermore, correlation analysis demonstrated that PN and the PN/PS ratio were the most important factors in determining the physicochemical properties of the NS. It was indicated that the PN could accurately reflect the sludge properties of the NS, and thus effectively change the surface properties of the sludge, contributing to the cohesion between the aggregates to maintain a stable structure.

Laboratory experimentation was used to investigate the impact of the organic loading rate shock on extracellular polymeric substances (EPSs) and the physicochemical characteristics of nitrifying sludge (NS) treating high-strength ammonia wastewater.

Weak magnetic field: A powerful strategy to enhance partial nitrification

Partial nitrification (PN) combined with anaerobic ammonium oxidation process has been recognized as a promising technology for the removal of nitrogenous contaminants from wastewater. This research aimed to investigate the potential of external magnetic field for enhancing the PN process in short and long term laboratory-scale experiments. Different strength magnetic fields (0, 5, 10, 15, 20 and 25 mT) were evaluated in short-term batch tests and 5 mT magnetic field was found to have better ability to increase the activities of aerobic ammonium oxidizing bacteria (AOB) of PN consortium. Long-term effect of magnetic field on PN consortium was studied with 5 mT magnetic field. The results demonstrated that the positive effect of magnetic field on PN process could also be testified at all of the four stages. Furthermore, a decrease of bacterial diversity was noted with the increase of magnetic field strength. Relative abundance of Nitrosomonadaceae decreased significantly (p < 0.01) from 13.9% in R_CK to 12.9% in R_5mT and 5.5% in R_25mT. Functional genes forecast based on KEGG database indicated that the expressions of functional genes related to signal transduction and cell motility in 5 mT environment were higher expressed compared with no magnetic field addition and high magnetic field addition. The existence of 5 mT magnetic field didn't increase the abundance of AOB but increased the activity of AOB by increasing the rate of free ammonia into the interior of microbial cells. Addition of magnetic field couldn't change the final state of PN process according to the hypothesis proposed in this article. These findings indicated that the weak magnetic field was useful and reliable for the fast start-up of PN process since it was proved as a simple and convenient approach to enhance AOB activity.

Reduction of nitrous oxide emissions from partial nitrification process by using innovative carbon source (mannitol)

The purpose of this study was to evaluate the effect of mannitol as carbon source on nitrogen removal and nitrous oxide (N2O) emission during partial nitrification (PN) process. Laboratory-scale PN sequencing batch reactors (SBRs) were operated with mannitol and sodium acetate as carbon sources, respectively. Results showed that mannitol could remarkably reduce N2O-N emission by 41.03%, without influencing the removal efficiency of NH4(+)-N. However, it has a significant influence on nitrite accumulation ratio (NAR) and TN removal, which were 19.97% and 13.59% lower than that in PN with sodium acetate, respectively. Microbial analysis showed that the introduction of mannitol could increase the abundance of bacteria encoding nosZ genes. In addition, anti-oxidant enzymes (T-SOD, POD and CAT) activities were significantly reduced and the dehydrogenase activity had an obvious increase in mannitol system, indicating that mannitol could alleviate the inhibition of N2O reductase (N2OR) activities caused by high NO2(-)-N concentration.