TP Removal Research Articles

The operating performance of Modified Basalt Fibers (MBF) bio-nest reactor exposed to nano-plastics

Biological nests made of Modified Basalt Fiber (MBF bio-nests) serve as effective carriers for enhancing wastewater treatment. However, little is known about their performance when exposed to nano-plastics. This study investigates the decontamination efficiency and microbial functionality of four types of MBF and traditional Basalt Fibers (BF) as carriers in contact oxidation reactors. Compared to BF, MBF demonstrated superior growth effects and biocompatibility within the bio-nest. Ca-MBF and Mn-MBF bio-nests exhibited the highest and most uniform absorption capacities, respectively, alongside increased secretion of total Extracellular Polymeric Substances (EPS) and higher Protein to Sugar (PN/PS) ratios. In sewage environments, all MBF groups displayed stable performance in removing NH4+-N and COD. Significant removal of TN and TP was notably observed in Mn-MBF treatments. Mn and Ca treatments predominantly influenced the Proteobacteria and Bacteroidetes phyla, crucial for nitrogen and phosphorus removal. Following exposure to nano-plastics, Mn-MBF and Ca-MBF treatments maintained high decontamination efficiency, particularly for TP and COD (48.64 % to 57.78 % and 90.91 % to 92.89 %, respectively). The significant removal of NH4+-N and TP only occurred in Mn-MBF and Ca-MBF treatments, which stimulated the growth of bacteria resistant to nano-plastics. Key genera such as Zoogloea and Meganema were identified as dominant, contributing to organic matter decomposition, EPS secretion, biofilm condensation, and enhanced microbial attachment. The findings underscore the structural stability enhancement of Mn-MBF and Ca-MBF bio-nests in contact oxidation reactors, demonstrating their resilience against nano-plastic pollution.

Innovative Treatment of Urban Wastewater by Flocculation Combined with Ozone Pre-Oxidation and Denitrification

In this study, urban wastewater was treated by flocculation, ozone pre-oxidation and denitrification for efficient purification. Polymeric aluminum chloride (PAC) and polymeric aluminum ferric sulfate (PAFS) were added to the wastewater at different levels to remove the COD, turbidity, TP and TN of the wastewater. A better flocculant was selected and its optimum ozone pre-oxidation concentration was determined by changing the ozone concentration and measuring the effluent quality. Denitrification was further enhanced by varying the C/N ratio of the wastewater. The results show that, with the increase in flocculant dosage, the removal rates of COD, turbidity, TP and TN by PAC and PAFS were improved. The purification effect of PAC was better than that of PAFS and the optimum removal of COD, turbidity, TP and TN was obtained at a dosage of 80 mg L−1 by PAC, at 55.9%, 55.6%, 90.0% and 13.3%, respectively. Ozone pre-oxidation enhanced the removal of COD, turbidity and TN by PAC, and the optimal ozone dosage was 1.2 mg L−1, which resulted in 64.8%, 57.1% and 24.8% removal of COD, turbidity and TN, respectively. With the increase in the C/N ratio from 2.0 to 4.0, the NO3−-N concentration of PAC-treated water gradually decreased, but when the C/N ratio was 4.0, the COD concentration increased, so the optimal C/N ratio should be 3.5. Overall, the combination of ozone pre-oxidation, denitrification and flocculation was an effective method to treat urban wastewater, which has a strong application prospect.

Synergistic phosphorus removal mechanism of Tetrasphaera enrichment in a micro-pressure swirl reactor

To investigate the effect of Tetrasphaera’s enrichment on phosphorus removal mechanism, three micro-pressure swirl reactor (MPSR) groups were used to experiment on sewage treatment under different SRT (17.2, 50.8, and 68.2 d). Results showed that Tetrasphaera enrichment in the MPSR system was promoted by extending the SRT. After extending the SRT from 17.2 to 68.2 d, the relative abundance of Tetrasphaera increased from 3.1% to 12.1%, and the TP removal efficiency maintained above 92%. The internal circulation results indicated that after extending the SRT, glycogen and polyhydroxybutyrate were co-synthesized during the anaerobic stage, which enhanced the driving force of nutrient removal. Analysis of the microbial composition and functional gene prediction indicated that efficient phosphorus removal can be attributed to the enrichment of Tetrasphaera at long SRT. Overall, the synergistic mechanisms of Tetrasphaera in the organic matter degradation and phosphorus removal processes were integrated into the MPSR.

Performance evaluation of modified Living Wall garden for treating septic tank effluent.

The Living Wall (LW) garden system has been employed as a post-treatment system to improve the effluent quality of septic tanks. This improvement primarily involves reducing nutrient levels, as well as facilitating the removal of organic matter and solids in accordance with effluent discharge guidelines. The objective of this study was to investigate the treatment performance of the LW system connected to a septic tank, along with an examination of the microbial communities within the LW units. A laboratory-scale LW system, comprising LW1, LW2, and LW3 units, was employed. The system was fed with effluent obtained from septic tanks and varied by theoretical hydraulic retention time (HRT) of 6, 12, and 24h. The TCOD, SCOD, TSS, TVS, TKN, and TP removal efficiencies of the LWs were achieved at 62 ± 24, 42 ± 19, 72 ± 21, 66 ± 15, 80 ± 15, and 58 ± 21%, respectively. To classify microbial communities in the soil and gravels collected from each LW unit, the Illumina MiSeq System Sequencer was employed. Nitrospirota was consistently found in all LW units, aiding in the conversion of nitrogen. Fusobacteriota were detected in specific layers of the LW units, indicating varying oxygen levels in the LW system.

Electrode-based floating treatment wetlands: Insights into design operation factors influencing bioenergy generation and treatment performance

Exponential increases in energy consumption and wastewater have often irreversible environmental impacts. As a result, bio-electrochemical devices like microbial fuel cells (MFCs), which convert chemical energy in organic matter to electricity using exoelectrogenic bacteria, have gained interest. However, operational factors affecting efficiency and energy output need further study. This research investigated bioenergy production and COD, TN, and TP removal in mesoscale floating treatment wetlands (FTW-MFC) using Phragmites australis, Iris pseudacorus, and a mix of both. The Iris FTW-MFC achieved a high voltage peak of 2100 mV. The maximum power densities of 484 mW/m2, 1196 mW/m2, and 441 mW/m2 were observed for Phragmites, Iris, and mixed FTW-MFCs, respectively. Despite promising bioenergy yields, pollutant removal was unsatisfactory. A low area/height ratio (0.38 m2/0.8 m) and high loading rate (18.1 g/m2·d COD) boosted bioenergy output but hindered treatment performance and stressed plants, causing root decay. No significant pollutant removal differences were found between FTW-MFC and FTW. Higher relative plant growth rates occurred in the FTW-MFC. Microbial analysis shown that representatives of Pseudomonas and Clostridium species were consistently found across all samples, involved in both organic compound transformation and electricity generation, contributed to successful microscale results. A supporting microscale MFC experiment showed wastewater composition's impact on bioenergy yield and pollutant removal. Pre-inoculated reactors improved organic matter transformation and electricity generation, while aeration increased voltage and treatment performance. The role of plants requires further verification in future experiments.

Sulfoaluminate cement-modified loess as bioretention cell filler for nutrient removal from stormwater runoff

In order to reduce the consumption of sand and gravel resources, the use of loess can reduce transportation costs and realize the in-situ construction of spongy in areas with rich loess resources. But the collapsibility and low permeability of loess make it unable to be directly used as the filler of bioretention cells. In this study, sulfoaluminate cement (SAC) mixed with a small amount of basalt fiber was considered to be used for loess modification, and the physicochemical properties and nutrient removal effect of SAC-modified loess as filler in bioretention cells were comprehensively evaluated. The results showed that when the SAC dosage was 15% and the basalt fiber addition was 0% (S15B0) and 0.6% (S15B6) and the curing time was 14 days, the stability and appropriate permeability can be exhibited, which can preliminarily satisfy the requirements of bioretention cell. SAC made the maximum adsorption capacity of S15B0 and S15B6 for ammonia nitrogen (NH4+-N) and phosphate higher than that of sand by 10.96%–31.51% and 45.92%–76.72%, respectively. The hydration products in SAC modified loess can fill the internal pores of loess particles and provide structural support, and ultimately reduce the accumulated pores, mesoporous pore size (20%) and surface homogeneity. Both S15B0 and S15B6 showed good removal effects of NH4+-N and COD. The TP removal efficiency was stable at 95.43%∼99.95%. Both the antecedent drying days and the submerged zone have an effect on the nitrogen removal in the bioretention cells, where a longer antecedent drying days is detrimental to the nitrogen removal, and the installation of a submerged zone improves the nitrogen removal. The basalt fiber can enhance the transformation process from nitrate-nitrogen to nitrite-nitrogen in the bioretention cell. Therefore, the modification of SAC can provide a certain idea for the in-situ use of loess as the filler of the bioretention cell.

Ecological threshold effect mediates the long-term synergistic management of mega-city runoff nutrients in large-scale hybrid constructed wetlands

Constructed wetlands (CWs), as nature-based solutions for pollutant control, have been widely applied globally. The functionality of CW ecosystems begins to degrade when certain ecological thresholds are exceeded, where the ecosystem’s response and functions stay within a 'safe ecological limit'. However, the sustainability of these functions and their ecological thresholds have not yet been quantitatively assessed. This gap limits our understanding of the sustainability of CWs and the “safe operating space” for environmental management. Here, we evaluate whether and how the nitrogen and phosphorus removal functions in large-scale hybrid CWs (HCWs) of a mega-city change over time, as well as how they respond to changes in pollutant loads, stoichiometric characteristics, hydrology, and environmental conditions. Though it has been running stably for 6 years, the large HCWs achieved average total nitrogen (TN) and phosphorus (TP) removal efficiencies of 81.0 % and 55.8 % from 2017 to 2020, respectively, with widespread synergistic relationships. This indicates that CWs have a long-term effect of removing nitrogen and phosphorus pollutants for over 10 years. A decrease in the stoichiometric characteristic TN:TP from inflow to outflow was a signal for preferential nitrogen removal (35 vs. 6.8, mass based). Importantly, the TN and TP removal efficiencies and their synergistic relationship change over operation time, with threshold points occurring at 378 days, 259 days, 1040 days, and 647 days, respectively. TN and TP removal efficiencies and their synergistic relationship were controlled by the thresholds of nitrogen (9.6–12.1 mg/L) and phosphorus (0.6–0.8 mg/L) loads, TN:TP (7.59), water levels (25.5–25.6 m), water replenishment (0.14 m), dissolved oxygen (5.8–9.0 mg/L), temperature (9.3–13.9 °C), and pH (8.8–10.1) levels. The thresholds of cross-attribute driving factors significantly affect the sustainability of nutrient removal functions. Our findings provide new insights into the threshold effects of pollutant loads and their stoichiometric characteristics, hydrology, and environmental conditions on the water purification functions of CWs. This offers critical support for defining the safe operating space in the sustainable management of CWs in mega-cities.

Comparative analysis of operating efficiency for two sewage treatment processes

To decrease pollutant effluent levels in sewage plants, in order to improve the pollutant control capacity, the removal efficiencies for COD, TP, TN, and NH3-N in two sewage plants located in Guangzhou were compared and analyzed. The correlation among influent carbon and nitrogen ratios, water loading rate, and total nitrogen removal rate were examined to enhance the nitrogen removal. The CASS process in Plant I had slightly higher TN (81.85%) and TP (98.38%) removal rates than those in Plant II (80%). Plants I and II achieved COD removal rates of 95.51% and 96.44%, respectively, and NH3-N removal rates of 99.08% and 99.34%, respectively. Correlation analysis showed that only the influent loading rate of Plant I had a moderate correlation with the total nitrogen removal rate, while the other factors only had a weak correlation. Therefore, the total nitrogen removal rate is influenced by multiple factors.

Removal of Nitrogen and Phosphorus in Low Polluted Wastewater by Aquatic Plants: Impact of Monochromatic Light Radiation

Plant absorption via aquatic plants is vital for the deep purification of treated wastewater. This study aimed to determine the removal efficiencies of nitrogen and phosphorus for different aquatic plants and the effect of monochromatic light as compared to white light. Five plants (i.e., Iris pseudacorus, Oenanthe javanica, Zantedeschia aethiopica, Ipomoea aquatica Forssk. and Sagittaria trifolia) were cultured in prepared wastewater and radiated by white, red, green and blue LED lamps with 8 h radiation per day, respectively. After 4 d of cultivation, the O. javanica and S. trifolia exhibited relatively better growth status and higher TP removal rates (90%). The blue light radiation played a key role in the TP uptake of the tested plants. The N removal rates of plants were relatively lower (10–40%), limited by the low COD content. The S. trifolia exhibited the highest efficiency, and red light promoted the removal of TN and NO3−-N, whereas NH4+-N removal was driven by blue light radiation. So, O. javanica and S. trifolia coupled with blue and red lamps as supplementary light were suggested for the deep purification of municipal treated wastewater. The effect of intensity and ratio of monochromatic lights could be a direction for further research.

Modification of polyvinylidene fluoride membrane with ciprofloxacin to improve the bacteriostatic performance

The common polyvinylidene fluoride (PVDF) membrane itself is susceptible to membrane fouling, especially biofouling, which is a serious threat. In this study, PVDF membrane was modified with ciprofloxacin (CIP) through co-blending to investigate the filtration properties, bacterial inhibition and fouling resistance. Modified membranes were prepared by adding 0.3 g (MC0.3), 0.6 g (MC0.6), 0.9 g (MC0.9) and 1.2 g (MC1.2) CIP per 100 g casting solution. Among these modified membranes, MC0.6 showed the best filtration performances, with the pure water flux stabilized at about 416.67 L/(m2·h) and bovine serum albumin (BSA) rejection of 92.0% at a trans-membrane pressure of 0.1 MPa. The pore size was reduced, the average roughness was reduced to 29.4 nm, the contact angle was lowered to 68.9°, and the hydrophilicity was greatly improved. The width of the inhibition circle produced by MC0.6 was 0.35–0.45 mm, and the modified membrane showed good inhibition of non-specific bacteria and algal removal during urban river water filtration. The rejection of BSA was increased by 16.32% compared to the base membrane and the adsorption rate for BSA was reduced by 68.45%. In addition, the removal of conventional pollutants in urban river water by the modified membranes for was also improved. Compared with that of the base membrane, the removal of TN, NH3–N, TP and COD by MC0.6 was increased by 10.58%, 12.45%, 15.44% and 13.53%. The results showed that CIP co-blending modified PVDF membrane could effectively improve membrane performances and has good value for water treatment.

Enhancing effects and mechanisms by reductive iron on constructed wetland with perfluorooctanoic acid exposure: Comparison between zero-valent and ferrous iron

Reductive iron caused efficient enhancement of constructed wetlands (CWs) under toxic stress like perfluorooctanoic acid (PFOA), while effects and mechanisms brought by different iron have not been illustrated. In this study, impacts of zero-valent (Fe(0)) and ferrous iron (Fe(II)) on CW systems with PFOA exposure were compared. Higher ammonium removal above 98 % was discovered with Fe(0) addition than Fe(II), according with more expression of hydroxylamine dehydrogenase [EC:1.7.2.6]. On the contrary, Fe(II) was more prone to stimulate activities of ammonia monooxygenase and nitrite oxidoreductase, consisting with higher abundance of Nitrosomonas and Nitrospira than Fe(0). Fe(II) had more potential to improve denitrification, with total nitrogen removal 2.64–6.83 % higher compared to Fe(0) group. It was aligned with boost of dominant denitrifying bacteria like Zoogloea (53.48 %), which probably resulted from promotion of metabolism pathways related to nitrite reduction. Phosphorus removal with Fe(II) addition was 4.59–19.04 % higher than Fe(0). Higher TP removal in Fe(II) group could result from more enhancement of physicochemical processes, compared with Fe(0). Moreover, decrease of reactive oxygen species production by citrate and activation of mitochondrial metabolism was explanation for alleviation of PFOA stress with reductive iron introduction, particularly Fe(II). As for plants, Fe(0) led to higher chlorophyll contents and lower activity of antioxidant enzymes like catalase and malondialdehyde. Current work offered new information about comparative effects of reductive iron on CWs under PFOA exposure.

Evaluating the effect of antibiotics on aerobic granular sludge treatment of pharmaceutical wastewater.

Aerobic granular sludge (AGS) has been widely applied in pharmaceutical wastewater treatment due to its advantages such as high biomass and excellent settling performance. However, the influence of commonly found antibiotics in pharmaceutical wastewater on the operational efficiency of AGS has been poorly explored. This study investigated the effects of tetracycline (TE) on AGS treating pharmaceutical wastewater at room temperature and analyzed the related mechanisms. The results demonstrate a dose-dependent relationship between TE's effects on AGS. At concentrations below the threshold of 0.1 mg/L, the effects are considered trivial. In contrast, TE with more than 2.0 mg/L reduces the performance of AGS. In the 6.0 mg/L TE group, COD, TN, and TP removal efficiencies decreased to 72.6-75.5, 54.6-58.9, and 71.6-75.8%, respectively. High concentrations of TE reduced sludge concentration and the proportion of organic matter in AGS, leading to a decline in sludge settling performance. Elevated TE concentrations stimulated extracellular polymeric substance secretion, increasing polymeric nitrogen and polymeric phosphorus content. Intracellular polymer analysis revealed that high TE concentrations reduced polyhydroxyalkanoates but enhanced glycogen metabolism. Enzyme activity analysis disclosed that high TE concentrations decreased the activity of key enzymes associated with nutrient removal.

Study Filter Materials for Vertical Subsurface Flow Constructed Wetland to Treat Wastewater from the Da Mai Noodle Handicraft Village in Bac Giang Province

Vertical subsurface flow-constructed wetlands (VSF CW) are evaluated in this research as a potentially effective and cost-efficient solution for treating wastewater from Da Mai noodle handicraft village in Bac Giang province. Due to the high pollution load in this type of wastewater, there are concerns about clogging and the stability of the technology. In this study, we explored different sizes of limestone and gravel for the five medium composition formulas in the VSF CW system. The experiments were conducted over a period of three months. We used ANOVA, one-sample T-test, and Pearson correlation analysis methods to evaluate the experimental results, with statistical significance set at 0.05. The results showed a linear correlation between medium size, hydraulic conductivity, and treatment efficiency (p < 0.05). Smaller medium sizes had higher pollutant removal efficiency but lower porosity and hydraulic conductivity. For the same sizes, limestone demonstrated higher treatment efficiency compared to gravel (p < 0.05). The Cp5 formula (comprising sand, 1×2 cm limestone, and 3×5 cm gravel) was selected as the best filter medium for VSF CW, achieving COD, TSS, TN, and TP removal efficiencies of 86.02 ± 1.71%, 81.15 ± 2.24%, 64.46 ± 2.23%, and 69.76 ± 2.68%, respectively. After three months of operation, the treated wastewater consistently met QCVN 40:2011/BTNMT Column B standards, and there were no significant differences in hydraulic conductivity (p > 0.05), indicating stable operation of the VSF CW.

Aerobic granular sludge sequencing batch reactor for high strength domestic wastewater treatment: Assessing kinetic models and microbial community dynamics

The study aims to treat high strength domestic wastewater (HSDW) and cultivate microbial granular sludge in a sequencing batch reactor (SBR). A bench-scale bioreactor was used for startup. Response surface methodology (RSM) was used to determine the ideal parameters for removing organic materials from HSDW. Organic loading rate (OLR) and cycle time were the independent variables taken into consideration, while the response variable was COD removal. Results from RSM revealed that the optimal conditions for achieving > 98 % COD and TP (>80) removal were a cycle length of 6 h and an OLR of 1.5 kgCOD/m3d. The Modified-Kincannon and the Grau second-order kinetic models were compared to the COD removal rate for the SBR system. The saturation rate constant (Ni) and maximal substrate removal rate (Vc) were proposed to be 6.8 g L−1 d−1 and 0.83 g L−1 d−1, respectively, based on the modified Stover-Kincannon model. The modified Stover-Kincannon (R2 = 0.93673) and Grau second order (R2 = 0.99219) models high correlation coefficient values show that the experimental results and the prediction for the microbial aerobic granular based SBR system accord well. It was discovered that the modified Stover-Kincannon model was less suitable than the Grau second order model. The system microbial community changed because of the granulation process, as the reactor design operation had a big impact on the community structure. Decreased filamentous bacteria favoured several taxa that have been found to exist in granular biomass that is appropriate for treating wastewater. This study sheds important light on the complex interactions that occur between microbial populations and operational variables all through the granulation process in SBR.

Granular sludge characterization and microbial response in a hydroxyapatite (HAP)- anammox coupled process at different nitrogen loading rates

To enhance the treatment capacity and operational stability of the anammox process for nutrient-rich wastewater disposal, a hydroxyapatite (HAP)-anammox coupled process was developed in a granular sludge-based upflow bioreactor. The impact of nitrogen loading rate (NLR) on process performance was investigated by gradually increasing the NLR from 1 to 1.5, 3, and 5 kgN/m3/d for 264 days continuous operation. TN and TP removal rates of 82.51 ± 3.58 % and 60.49 ± 2.82 % were achieved at the NLR of 5 kgN/m3/d. The precipitation of Ca and phosphorus resulted in HAP crystals formation evidenced by sludge morphology and component analysis, which enhanced sludge settling properties and facilitated biomass enrichment. The HAP-anammox granular sludge was characterized by the outer layer HAP crystals formed on inner anammox granules, while highly mineralized granular sludge with higher density distributed at the bottom of the reactor is conducive to HAP-based phosphorus recovery. After a long-term accumulation, the abundance of Planctomycetota phylum gradually increased (from 7.7 % to 14.1 %), consisting of three species of anammox bacteria, namely Candidatus_Brocadia_sapporoensis, Candidatus_Brocadia_sinica and Candidatus_Kuenenia_stuttgartiensis. Nitrogen metabolic pathway analysis illustrated that denitrification was also present except the anammox reaction, synergistically contributing to superior nitrogen removal in the HAP-anammox process.

Synergistically enhancing the remediation of low C/N slightly black-odorous water body using pretreated stalk in-situ loaded with sulfidated nano zero-valent iron

Sulfidated nano zero-valent iron (S-NZVI) as reductants coupled with organic carbon are promising in enhancing denitrification which is crucial for remediation of low C/N water body. Nevertheless, the dearth of research on the effectiveness of these materials in actual water remediation limits their application. Additionally, most of the studies utilizes industrial chemical-derived organic carbon, which exacerbates environmental and economic burdens. This study proposes employing pretreated stalks in-situ loaded S/Fe (SS-S/Fe) to remediate the low C/N slightly black-odorous water body. The pretreated stalk acts as carbon source replacing the industrial chemicals. The pretreatment process was carried out by using H2O2 and acetic acid to decrease the lignin content. The 2, 4-dichlorophenol was utilized as a target pollutant for optimization of materials. The sediment from the water body was remediated, the impact of SS-S/Fe on water body and microbial community structure were clarified. The lignin residues in the stalk were found to enhance the dispersity, O2 resistance, and reduction performance toward 2, 4-dichlorophenol of S/Fe. S/Fe facilitates 2, 4-dichlorophenol degradation via reduction and TP removal via forming Fe-P precipitation. SS plays a significant role in TN removal, assisting in enhancing the 2, 4-dichlorophenol and TP removal performance of S/Fe. Crucially, SS and S/Fe synergistically boost sediment microbial activity, conferring resistance to the subsequent pollution shock. The decisive role of SS in enhancing denitrification by cultivating Anaeromyxobacter, unclassified_f_Comamonadaceae, norank_f_norank_o_norank_c_Anaerolineae and Thiobacillus has been demonstrated. This study improves S-NZVI applicability in actual low C/N water bodies and provides new methods for utilizing stalk resources.

The growth and nutrient removal properties of heterotrophic microalgae Chlorella sorokiniana in simulated wastewater containing volatile fatty acids

To reduce the high cost of organic carbon sources in waste resource utilization in the cultivation of microalgae, volatile fatty acids (VFAs) derived from activated sludge were used as the sole carbon source to culture Chlorella sorokiniana under the heterotrophic cultivation. The addition of VFAs in the heterotrophic condition enhanced the total nitrogen (TN) and phosphorus (TP) removal of C. sorokiniana, which proved the advantageous microalgae in using VFAs in the heterotrophic culture after screening in the previous study. To discover the possible mechanism of nitrogen and phosphorus adsorption in heterotrophic conditions by microalgae, the effect of different ratios of VFAs (acetic acid (AA): propionic acid (PA): butyric acid (BA)) on the nutrient removal and growth properties of C. sorokiniana was studied. In the 8:1:1 group, the highest efficiency (77.19%) of VFAs assimilation, the highest biomass (0.80 g L−1) and lipid content (31.35%) were achieved, with the highest TN and TP removal efficiencies of 97.44 % and 91.02 %, respectively. Moreover, an aerobic denitrifying bacterium, Pseudomonas, was determined to be the dominant genus under this heterotrophic condition. This suggested that besides nitrate uptake and utilization by C. sorokiniana under the heterotrophy, the conduct of the denitrification process was also the main reason for obtaining high nitrogen removal efficiency.

High capacities of carbon capture and photosynthesis of a novel organic carbon-fixing microalgae in municipal wastewater: From mutagenesis, screening, ability evaluation to mechanism analysis

The development of wastewater treatment processes capable of reducing and fixing carbon is currently a hot topic in the wastewater treatment field. Microalgae possess a natural carbon-fixing advantage, and microalgae that can symbiotically coexist with indigenous bacteria in actual wastewater attract more significant attention. Ultraviolet (UV) mutagenesis and dissolved organic carbon (DOC) acclimation were applied to strengthen the carbon-fixing performance of microalgae in this study. The mechanisms associated with microalgal water purification ability, gene regulation at the molecular level and photosynthetic potential under different trophic modes resulting from carbon fixation and transformation were disclosed. The superior performance of Chlorella sp. MHQ2 was eventually screened out among a large number of mutants generated from 3 wild-type Chlorella strains. Results indicated that the dry cell weight of the optimal species Chlorella sp. HQ mutant MHQ2 was 1.91 times that of the wild strain in the pure algal system, more carbon from municipal wastewater (MW) were transferred to the microalgae and re-entered into the biological cycle through resource utilization. In addition, COD, NH3-N and TP removal efficiencies of MW by Chlorella sp. MHQ2 were found to increase to 95.8% (1.1-times), 96.4% (1.4-times), and 92.9% (1.2-times), respectively, under the extra DOC supply and the assistance of indigenous bacteria in the MW. In the transcriptome analysis of the logarithmic phase, the glycolytic pathway was inhibited, and the pentose phosphate pathway was mainly carried out for microalgal life activities, further promoting efficient energy utilization. Upon analysis of carbon capture capacity and photosynthetic potential in trophic mode, the addition of NaHCO3 increased the photosynthetic rate of Chlorella sp. MHQ2 in mixotrophy whereas it was attenuated in autotrophy. This study could provide a new perspective for the study of resource utilization and microalgae carbon- fixing mechanisms in the actual wastewater treatment process.

Synergistic degradation efficiency of nitrogen, phosphorus and microbial dynamic succession driven by a novel strain Gordonia sp. D4 during synthetic wastewater treatment

Nitrogen (N) and phosphorus (P) coexist in the industrial and domestic wastewater posed a pressing challenge for synergistic removal of N and P by bioenhancement. In this study, a novel denitrifying phosphorus-accumulating organism (DPAO) of Gordonia sp. D4, exhibited peak NO3--N, NO2--N, NH4+-N and TP removal efficiencies of 98.11%, 65.02%, 85.34% and 100%, corresponding to 9.30 mg/(L·h), 6.08 mg/(L·h), 3.63 mg/(L·h) and 0.47 mg/(L·h) removal rates, respectively. Strain D4 contained the nitrogen cycling genes narK, narI, narJ, narH, narG, nirB and nirD, as well as the phosphorus cycling genes ppk1, ppk2 and ppx-gppA, which contributes to its excellent simultaneous removal of N and P. More importantly, the addition of D4 into the sequencing batch reactor (SBR) significantly improved the P, TN and NO3--N removal efficiencies by 18.91%, 7.35%, and 18.55%, respectively. This was closely related to the clear enrichment of Gordonia and its contribution to the increasing abundances of Pararhodobacter, unclassified_f_Cyclobacteriaceae, unclassified_o_Rhodospirillales, Thauera and Candidatus Promineofilum and their associated functional genes that drive P or N removal, thereby enhancing the N and P synergistic degradation efficiency. This study provides a valuable strain resource and process reference for the simultaneously removing N and P from the wastewater.

Enhancing wastewater treatment with a novel separated algae membrane oxygenated activated sludge reactor

In this investigation, a separated algae membrane oxygenated activated sludge wastewater treatment reactor was developed. During the phase of aeration pump absence, the system, featuring a separated algae biofilm oxygenation activated sludge mechanism with an internal reflux ratio of 5 and a C/N ratio of 10, demonstrated remarkable efficiency in pollutant removal. Specifically, it achieved COD, TN, NH4+-N, and TP removal rates of 96.6 %, 81.9 %, 98.6 %, and 95.5 %, respectively. Despite a decline in dissolved oxygen (DO) during the transition of wastewater from the algae membrane reactor to the aerobic tank, the internal circulation reflux ratio of 5 ensured that the oxygen-enriched effluent from the algae membrane photoreactor maintained a stable DO level in the aerobic tank, ranging from 1.5 to 2.0 mg/L, thus meeting the oxygen demand of the activated sludge. Alterations in the aeration method had a notable impact on the diversity of the microbial community. Notably, the community shifted from bacteria adapted to intermittent aeration to those acclimated to internal recirculation for oxygen supply. The dominant microbial position was reinforced, with the Patescibacteria phylum and the norank_f__norank_o __ Saccharimonadales genus emerging as the dominant entities within the community. Under internal circulation reflux aeration, filamentous green algae persisted, resulting in a significant increase in biomass and chlorophyll content by 3.07 and 2.93 times, respectively. Furthermore, microalgae exhibited elevated protein and polysaccharide content, which increased by 3.14 and 3.16 times, respectively, due to the influence of the internal circulation reflux process, promoting the maturation of the algae membrane.