Average Removal Rates Of TN Research Articles

Efficacy and power production performance of constructed wetlands coupled with microbial fuel cells for the advanced treatment of saline tailwater from wastewater treatment plants

In this study, the effects of different electrode materials and salt-tolerant plants on the efficacy and power production performance of constructed wetlands coupled microbial fuel cells (CW-MFCs) were analyzed for the advanced treatment of saline tailwater from wastewater treatment plants (WWTPs). The results showed that when carbon felt was used as the cathode material, the voltage was 165.45 ± 14.90 mV after system stabilization, the maximum power density was 3.20 mW/m2 when the current density was 25.58 mA/m2, and the power production performance of carbon felt was better than that of common titanium mesh and granular activated carbon-stainless steel mesh cathode materials (p < 0.05). When the two groups of systems were operated and stabilized, the average removal rates of TN, TP, NH4+-N and COD in RS-CW-MFC were 86.48 %, 88.1 %, 82.67 % and 88.96 %, respectively, and those of TN, TP, NH4+-N and COD in RN-CW-MFC were 84.33 %, 87.34 %, 81.63 % and 87.64 %, respectively. Salinity enhanced the power production efficiency by increasing ionic strength and decreasing the internal resistance of the system. The microbial community in the saline tailwater systems gradually evolved toward salt-tolerant species, which enhanced the power production efficiency of the system without affecting the treatment of traditional pollutants in the CW-MFC systems.

Inducing root redundant development to release oxygen: An efficient natural oxygenation approach for subsurface flow constructed wetland

Dissolved oxygen (DO) is a limiting factor affecting the purification efficiency of subsurface flow (SSF) constructed wetlands (CWs). To clarify the causes of oxygen environments and the response characteristics of plant oxygen release (POR) in SSF CWs, this study set three oxygen source treatments by limiting atmospheric reaeration (AR) and influent oxygen (IO) and compared the differences in plant physiological metabolism, DO distribution characteristics, and the purification effect of the SSF CWs at different depths. The results showed that limiting exogenous oxygen stimulated root redundancy of the wetland plants. The root volume and proportion of fibrous roots of the wetland plants increased significantly (p < 0.05). When only the POR existed, the root zone DO increased significantly to 2.05–4.37 mg/L (p < 0.05), and was positively correlated with the TN and TP removal rates (p < 0.05). Additionally, in the presence of POR only, the average removal rates of TN and TP in the top layer were 86.5% and 76.9%, respectively. The proportion of fibrous roots, root zone DO, and root-shoot ratio were key factors promoting the purification effect of the SSF CWs under limited exogenous oxygen sources. Enhancing POR by inducing root redundancy enhanced nitrification (hao, pmoABC-amoABC), plant absorption, and assimilation-related functional genes (nrtABC, nifKDH), and enriched nitrogen and phosphorus removal bacteria, such as Flavobacterium and Zoogloea. This consequently improved pollutant removal efficiency. Inducing root redundancy to strengthen POR produced an aerobic environment in the SSF CWs. This ensures the efficient and stable operation of the SSF CW and is an effective approach for natural oxygenation.

Effects of freeze-thaw intensities on N2O release from subsurface wastewater infiltration system

Subsurface wastewater infiltration system (SWIS) is a low-investment and cost-effective wastewater treatment technology. Nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, is a major by-product of biological denitrification processes within SWIS. Although SWIS has been widely applied in varying zones, until now, whether and how periodical freeze-thaw cycles (FTCs) occurring in aerobic layers affect N2O release still remain unclear? In this study, two runs were arranged, which covered two freeze-thaw (FT) intensities of − 5 °C/5 °C and − 15 °C/5 °C, respectively. An in-situ simulation system of SWIS was carried out to monitor N2O release and microbial community structure in different profiles. The result revealed that raising FT intensity decreased the rate of nitrogen removal of SWIS. Average removal rate of TN under strong FTCs was 88.65–88.97%, which was 1.32–2.47% lower than that under weak FTCs conditions. In addition, a positive correlation was found between FT numbers and N2O release. The contribution of anaerobic zone increased from 29.24% to 75.16% with extending the FT cycles from 1 to 9. High-throughput sequencing results showed that different FT intensities had distinct effects on microbial communities. Euryarchaeota abundance increased significantly under strong FT treatment, while Proteobacteria abundance sharply decreased from 49.5% to 7.6% at day 27 of stable operation. PCA analysis shows that bacterial community composition of samples treated with weak FT and CK is similar. While significant differences in sample composition were found between strong and weak FT treatments, which was the main reason resulting in different N2O release patterns.

Sewage treatment effect of AOA-SBR under different C/P value and its mechanism of nitrogen and phosphorus removal

Aiming at the practical problem of difficulty in nitrogen and phosphorus removal in WWTPs due to low influent C/P value, five groups of AOA-SBR were used to carry out the experiment on the treatment of sewage with different C/P values (120, 40, 24, 17, 13). The results showed that when the C/P value decreased from 120 to 40, the average removal rates of TN and TP in the AOA-SBR system increased from 70.36% and 90.90% to 79.31% and 99.22%. The analysis showed that the difference in denitrification of each system mainly occurred in the anoxic period, and the reduction of TN in the anoxic period reached the maximum when the C/P value was 40. Moreover, the concentration of orthophosphate entered the anoxic period was more suitable at this time, which promoted the DPR of the system. Phosphorus forms analysis showed that when the influent C/P value was further reduced (24, 17, 13), the accumulation of AP content in the activated sludge inhibited the activity of PAOs (including DPAOs), and finally decreased the denitrification and phosphorus removal effects. Based on metabolic composition and pathway analysis, the enrichment of DPAOs (Dechloromonas, Pseudomonas, Rhodobacter) and higher relative abundances of nas+nap and phbC/phaC+phaZ were the key to improve the nitrogen and phosphorus removal efficiency of AOA-SBR system at low C/P value.

Responses of simultaneous anammox and denitrification (SAD) process to nitrogen loading variation: Start-up, performance, sludge morphology and microbial community dynamics

The effects of loading variation on the efficiency, EPS, sludge morphology and microbial population of simultaneous anammox and denitrification (SAD) were thoroughly investigated with the low-abundance SAD sludge. Results indicated that the first stage lasted the longest (33d), and the average removal rate of TN can be maintained above 95%. The specific anammox activity (SAA), specific denitrification activity and PN/PS continued to increase, but the excessive loading caused the effluent to deteriorate rapidly, and SAA and PN/PS also decreased slightly, but it could be recovered quickly. The contribution rate of anammox and denitrification to N removal reached 87.6% and 12.4% eventually, respectively. The abundance of AnAOB was 10.68%–18.01%, 9.01%–15.54%, 5.74%–12.88% in the upper, middle and lower layers, respectively. Candidatus Kuenenia was always the dominant AnAOB, especially after high loading inhibition. The abundance of denitrifying bacteria (mainly Bacillus, Comamonas and Denitratisoma) gradually became the highest.

Aerobic Granular Sludge Operation and Nutrient Removal Mechanism from Domestic Sewage in an Anaerobic/Aerobic Alternating Continuous Flow System

Mature aerobic granular sludge was inoculated at room temperature in an anaerobic/aerobic alternating continuous flow system. The system consisted of two independent anaerobic and aerobic tanks. Actual domestic sewage was used as the influent to explore the influence of the gas intensity and hydraulic residence time on the continuous flow system. The results revealed that the conditions of a reflux ratio of 2, lower aeration intensity (0.6 mL·min-1), and proper hydraulic residence time (9 h) were more conducive to the removal of pollutants. Under such conditions, the average removal rate of TP was 80.43%, the average removal rate of TN was 83.6%, the average removal rate of COD was 90.39%, the sludge concentration was approximately 2100 mg·L-1, the sludge volume index was maintained below 50 mL·g-1, and the particle size was 700-800 nm. The EEM-PARAFAC model was used to characterize and analyze the EPS at different stages. The results revealed that changing the parameters could change the composition of EPS. The hydraulic residence time had a greater impact on the continuous flow system than the aeration intensity. In addition, a preliminary conceptual reaction process model in the anaerobic/aerobic alternating continuous flow system was built using high-throughput pyrosequencing and phylogenetic assignment. Eleven major functional bacteria related to nitrogen and phosphorus removal were found in the system.

Long-term performance of nutrient removal in an integrated constructed wetland.

Constructed wetlands (CWs) have been regarded as efficient technologies for both wastewater treatment and reuse of water resources. Most studies on CW treatment efficiency are limited to a short-term perspective, and there are still many unknowns about the long-term performance of CWs. Here we evaluated the performance of an integrated CW that has been in operation for more than ten years. The average removal rates of TN and TP were maintained at 53.6% and 67.3% over 10years, respectively. The annual mass reductions in TN and TP reached 937.5kgha-1yr-1 and 303.2kgha-1yr-1, respectively. In addition, TN removal rate was significantly higher in summer and autumn than those in spring, yet there was no seasonal difference in TP removal. The bacterial richness and diversity in summer and autumn were higher than those in spring. TN and TOC not only determine the bacterial community structure, but also affect the removal efficiency of CW. Denitrification and dephosphorization microorganisms were enriched and accounted for a considerable proportion (21.14-52.85%) in the bacterial community. In addition, the relative abundance of Pseudomonas was significantly positively related with the rate of TN and TP removal.

Characteristics of Nutrient Removal in a Pilot-scale A2/O with Mixture of Sludge Fermentation Liquor and Tail Water as External Carbon Source

To resolve the issue of sewage fluctuation and discontinuity in a rural district of China, a new operation mode of replenishing the mixture of fermentation liquor and tail water during the off-flow period was proposed, and the nutrient removal performance of a pilot-scale A2/O system with this operation mode was investigated. The results of beaker experiments found that the mixture of tail water and fermentation liquor at a ratio of 12:1 had better denitrification and phosphorus release/absorption characteristics than the raw water, and theoretically had the function of enhancing denitrification and phosphorus removal performances. The results of a 97 d pilot test showed that the removal efficiency of TN and TP was improved after the system was adjusted from the constant flow mode to this new operation mode, and the average removal rate of TN and TP increased from 69.27% and 86.94% to 73.34% and 89.94%, respectively. The corresponding average effluent concentration decreased from 15.77 mg·L-1 and 0.80 mg·L-1 to 13.76 mg·L-1 and 0.64 mg·L-1. The sequencing results of the 16S rRNA gene showed that this new operation mode was beneficial to the enrichment of five common hydrolytic acidizing bacteria genera, six phosphorus-accumulating organisms genera, and four denitrifying bacteria genera. This was also the main reason for the improved nutrient removal performance. According to the long-term monitoring of the characteristics of activated sludge, this new operating mode will degrade the sedimentation performance of activated sludge in the system, and the average SVI increased from 106 mL·g-1 to 131 mL·g-1. However, this degree of deterioration did not adversely affect the sludge activity and nutrients removal performance of the system, and there was no sludge bulking in the entire experiment. The results of this study have shown that the A2/O system can maintain and improve the performance of nutrients removal by replenishing the mixture of tail water and sludge fermentation liquor when the flow is cut off. This will provide new ideas for the design and operation of sewage treatment plants in rural areas in the future.

Nitrogen and Phosphorus Removal from Domestic Sewage Aerobic Granular Sludge Under Intermittent Gradient Aeration

In this study, three SBR reactors R1, R2, and R3 were set up and operated using (A/O)3-SBR gradient aeration, (A/O)3-SBR constant aeration, and the conventional (A/O)-SBR mode, respectively. The nutrient removal performance and aerobic granular sludge characteristics under these aeration modes were explored using real municipal wastewater as the influent matrix. The experimental results revealed that for the R1, R2, and R3 particles during the stable period, the average removal rate of COD was 88.68%, 89.05%, and 88.96%, respectively, the average removal rate of TN was 76.97%, 71.99%, and 64.92%, respectively, the average removal rate of TP was 96.28%, 85.05%, and 78.97%, respectively, and the proportion of denitrifying phosphorus accumulating bacteria to phosphorus accumulating bacteria was 25.52%, 19.60%, and 12.77%, respectively. The results showed that the operation mode of anaerobic, aerobic, and anoxic was more conducive to the enrichment of denitrifying phosphorus accumulating bacteria (DPAOs), and that the gradient aeration was more enriched than the constant aeration mode, which is of great significance to low-intensity municipal domestic sewage treatment with an insufficient carbon source. At the same time, the dissolved oxygen in the aeration section of R1 was reduced step-by-step, which improved the simultaneous nitrification and denitrification rates of particles and the utilization rate of the internal carbon source, which was beneficial for the efficient removal of TN. The particle size of the three groups of reactors was 727.368, 815.072, and 895.041 μm respectively. As the transfer rate of the matrix decreased with particle size, the microorganisms in R2 and R3 may have caused anaerobic respiration to release harmful gas, thus damaging the particle structure, such that the particles in R2 and R3 were less dense than those in R1. In addition, the PN/PS values of R1, R2, and R3 were 6.31, 5.63, and 4.83, respectively, and the EPS content (in terms of VSS) was 103.97, 92.22, and 76.98 mg·g-1, respectively, at the time of particle stabilization, which revealed that the mode of intermittent gradient aeration was beneficial to stimulate the secretion of EPS. This was especially the case for the secretion of PN, which increased the PN/PS value, enhanced the cell hydrophobicity, and made the particles dense and stable.

Study on the purification of aquaculture wastewater by the compound wetland ecosystem

Traditional freshwater aquaculture can easily cause serious environmental problems and waste of water resources. Thus, ecological bioremediation techniques for freshwater pond environments are more attractive. In this study, a set of compound wetland ecological system with ecological ditch, constructed wetland and multi-functional ecological pond was constructed, and its purification effect was also evaluated. Our results showed that the compound wetland ecosystem has high removal efficiency for aquaculture wastewater. The concentration of total nitrogen, ammonia nitrogen, Nitrite Nitrogen, total phosphorus, and chlorophyll-a in each treatment unit gradually decreased after the system was stabilized. The annual average removal rates of TN, NH4 +-N, NO2 −-N, TP and Chl-a can reach 73.03%, 74.27%, 91.89%, 64.29% and 83.02%. We found ammonia nitrogen concentration was significantly biodegraded (p <0.05) by the ecological ditch, as well as constructed wetland and multi-functional ecological purification pond had obvious removal effect on TN, TP, NH4 +-N, NO2 −-N, and Chl-a (p <0.05). Moreover, the concentrations of pollutants after purification were lower than the standard value of fishery aquaculture water quality in China, and the purified water was recycled to fish ponds for reuse. Therefore, the compound wetland ecosystem can be adopted by the water shortage area to develop water-saving fisheries in the future.

Practical application of domestic sewage in a new compound biological filter

The application of a new composite biofilter with a batch-type mud membrane composite biofilter (CSBF) series deep treatment filter (EBF) combination in urban domestic sewage was studied. The results of 20-day operation data show that the new filter process has good removal effect on COD, NH3-N, TN and TP. The average removal rate of COD during operation is 94.63%, the average removal rate of NH3-N is 99.02%, and the average removal rate of TN is 77.89%. The average removal rate of TP is 97.99%, and each index is stable to the first-class A standard of GB8978-1996, in which COD, NH3-N and TP can reach the surface water class IV standard.

New Solution To Apply Constructed Wetland Technology In Cold Climate

Due to the influence of low temperature in winter, the removal effect of pollutants in constructed wetlands in winter is greatly reduced. In order to improve the removal effect of wetland on pollutants such as nitrogen and phosphorus, this paper proposes a new insulation method that uses the residual heat of bathroom bath waste water to supply heat to the constructed wetland. In the proposed new wetland system, the average removal rates of TN, TP and NH4 +-N in wetlands reached 61.09%, 85.03% and 33.85%, respectively. The application of residual heat energy to the construction of constructed wetland can realize the recovery and utilization of energy, which is conducive to the promotion and application of constructed wetland in the cold regions of the north. A post-publication change was made to this article on 29 May 2020 to correct an author name on the webpage.

Strengthening Effect of Different Cattail Pretreatment Methods on the Denitrification of Horizontal Subsurface Flow in a Constructed Wetland

Nitrogen removal in constructed wetlands (CWs) is highly affected by the supply of organic carbon. Thus, to enhance nitrogen removal in the horizontal subsurface flow of CWs, plant carbon sources were added during the downstream portion of the wetland. Moreover, the characteristics of static release and the denitrification potential of Typha were evaluated using three different pretreatment methods (i.e., minced, acid-heated, and alkali-heated). The average concentrations of COD released and the nitrate removal rate with the alkali-heated, acid-heated, and minced Typha were 89.57 mg·L-1 and 75.2%, 67.27 mg·L-1 and 67.2%, and 54.45 mg·L-1 and 23.5%, respectively. The results showed that different pretreatment methods resulted in the release of different amounts of acetic acid, and the alkali-heated Typha performed much better than the other pretreatments. Therefore, the alkali-heated Typha was selected and added to the middle of the horizontal subsurface flow CW, which improved the nitrogen-removal rate significantly; the average removal rate of TN and TP was higher than that of a control CW by 30.3% and 33.9%, respectively. However, the COD concentration of the CW with the alkali-heated Typha was not significantly increased.

Comparison of operational strategies for nitrogen removal in aerobic granule sludge sequential batch reactor (AGS-SBR): A model-based evaluation

The nitrogen removal in the aerobic granule sludge sequential batch reactor (AGS-SBR) could be operated as two modes: the simultaneous nitrification and denitrification (SND) mode and the denitrification-nitrification reaction in serials mode. It is not clear which mode deliver better nitrogen removal performance. In this study, the performance of the two operation modes and their control strategies were evaluated in three operation scenarios (A, B and C) based on mathematical model simulation. The control strategy for the SND in AGS-SBR involved the dissolved oxygen (DO) concentration control, in which the DO was manipulated to optimize nitrogen removal (scenario A). The denitrification-nitrification AGS-SBR was achieved by pre-denitrification, high DO nitrification and low DO SND configuration. In the operation scenario B, the duration of high DO nitrification was manipulated to produce optimized nitrogen removal. The duration for pre-denitrification, high DO nitrification and low DO SND were fixed for the operation scenario C, without using control strategies. The results indicated that operation scenario B and C produced better performance than scenario A in terms of nitrogen removal. The average TN removal rate was 84.4%, 95% and 92% for the scenario A, B and C respectively. The DO control strategy used in scenario A could not cope with the dynamic influent feeding condition. The pre-denitrification, high DO nitrification and low DO SND operation scenarios demonstrated satisfactory nitrogen removal even without using control strategies.

Nitrogen Removal Efficiencies from Road Runoff by Dry Grass Swales with a Shallow Substrate Layer

To investigate nitrogen removal efficiencies and mechanisms from road runoff by dry grass swales with a shallow substrate layer, we constructed six dry grass swale columns with different structures and media composition. In order to enhance the nitrogen removal efficiencies during the whole process, fermented woodchips were added into the substrate layer, and saturated zones were established. Semi-synthetic road runoff was used as the influent water. The influent and effluent quality were analyzed, and the change in volumetric water content and ORP of the media were monitored. The results showed significant nitrogen removal by these columns under unfavorable conditions. The range of the average removal rate of TN by the dry grass swales with saturated zones was 67%-78%. The nitrogen removal process mainly occurred during the wet period of the substrate layer. The saturated zones enhanced nitrogen removal efficiencies during the dry period, and also promoted the quick establishment of anoxic conditions in the substrate layer during the wet period. The water-holding transition layer with organic matter was effective at providing a carbon source for denitrification in the saturated zone, and for avoiding the leaching of pollutants caused by organic decomposition.

Profile of organic carbon and nitrogen removal by a continuous flowing conventional activated sludge reactor with pulse aeration

Abstract This study aimed to investigate the effect of pulse aeration (on/off time 5/10 min) on the pollutants removal efficiencies and on the evolution of the denitrifying bacteria communities of a continuous flowing completely mixed activated sludge reactor. Organic matters and nitrogen removal were evaluated and the denitrifying bacteria community structure was analyzed by MiSeq sequencing technology. Results showed that the TOC removal rates were steadily above 81.6% and the NH4+-N removal rates were 92.1% ± 0.5% when the pulse aerated activated sludge reactor was operated with the optimized pulse aeration cycle (PAC) of 5/10 min. There was no significant impact on both TOC and NH4+-N removal efficiencies, while the average TN removal rate of the pulse aerated reactor (58.4%) was significantly higher than that of the constantly aerated one (30.6%). The removal efficiencies of both organics and nitrogen were stable during the 60-day acclimation period regardless of the changing DO concentration fluctuated in pulse mode. Although the denitrifier bacterial compositions varied between the pulse aerated group and the constantly aerated group, the denitrifier community richness and diversity were similar. Boost of the TN removal was mainly due to the anoxic denitrifying environment provided by the non-aerated phase in each PAC.

Mechanism on Enhanced Nitrogen Removal in Municipal Secondary Effluent via Internal-Electrolysis Constructed Wetlands at Low Temperature in Winter

Aiming at the low pollutant removal efficiency of constructed wetlands (CWs) at low temperature in winter, three laboratory-scale vertical-flow CWs, namely unplanted CWs, ordinary CWs, and internal-electrolysis CWs, were used to investigate the nitrogen removal efficiency of municipal secondary effluent when the water temperature was 3-12℃. Moreover, the mechanism of enhanced denitrification of the new wetland was revealed through analysis of the microbial community diversity and community structure. The results showed that the internal-electrolysis CWs could make better use of the carbon sources in the municipal secondary effluent and had a higher removal rate. The effluent TN concentration was maintained at about (9±0.29) mg·L-1. The average TN removal rate was 42.27%, which was 17.91% and 17.33% higher than those of the unplanted CWs and ordinary CWs, respectively. The microbial activity was detected using fluorescein diacetate (FDA), and the result revealed that the microbial activity of the internal-electrolysis CWs could reach 0.224 mg·g-1, which was 2.6 times and 3.4 times of that of the unplanted CWs and ordinary CWs, respectively. The microbial denitrification intensity of the internal-electrolysis CWs was 2.8 times and 3.3 times of that of the unplanted and ordinary CWs, respectively. The results of high-throughput sequencing showed that the microbial community diversity of the internal electrolysis CWs was higher than those of the unplanted and ordinary CWs. Denitrification microorganisms were detected, mainly Dechloromonas, Rhizobium, Hyphomicrobium, and Rhodobacter, as well as Thiobacillus, which is an autotrophic denitrifying bacterium. There were obvious advantages in the total amount of denitrifying microorganisms in the internal-electrolysis CWs, as the denitrification microorganisms accounted for 7.13% of the total microbial biomass, which was 3.8 times and 8.7 times of that of the unplanted CWs and ordinary CWs, respectively.

Nitrogen removal from urban stormwater runoff by stepped bioretention systems

Nitrogen excess is a key trigger for the eutrophication of water bodies. Stormwater is an important nitrogen source in urban environments and thus requires effective treatment, especially in mountainous cities due to their stronger runoff flushing. However, the design method of bioretention systems focusing on mountainous cities is still rare in China and nitrogen is often released due to the lack of denitrification environments. In this study, the stepped bioretention systems were designed based on the terrain characteristics in mountainous cities by two columns in the stair-stepping connection. From 2015–2016, 18 replicates of stepped bioretention systems, which included a 400mm deep planting layer, a 200mm deep transition layer and a 200mm gravel layer planted with Radermachera hainanensis (Merr.), Juncus effusus (L.), Vetiveria zizanioides (L.), Ophiopogon japonicus (Linn. f.) and Medicago sativa (L.)., respectively, were tested under certain operational conditions (e.g., the simulated rainfall intensity was 3.5, 5.3 and 14mm/h, respectively.). The stepped columns planted with Medicago sativa (L.). showed poor nitrogen removal (e.g., the RRTN (removal rate of TN) was from − 29.8% to − 123.0%), while those planted with Radermachera hainanensis (Merr.), Juncus effusus (L.), Ophiopogon japonicus (Linn. f.) or Vetiveria zizanioides (L.) performed well without additional carbon sources (e.g., the RRTN was from 52.8% to 84.2%). Nitrogen would be released from the systems (e.g., the average RRTN was −178.0%) when peat soil was mixed in the planting layer at a ratio of 20%. After retrofitting the flow pattern within the stepped columns, U flow pattern was more advantageous for the improvement of nitrogen removal. In the 1st, 2nd, 4th, 5th, 10th and 11th systems, the average RRTN and RRNO3N (removal rate of NO3N) in the systems with U flow pattern were 1.2 − 7.0% and 5.0 − 5.8%, both higher than those with W flow pattern. Through leaching dynamics analysis, NH3NC (NH3N Concentration) of all effluent samples was <0.5mg/L, but the concentrations of TN and NO3N were increased with the duration of rainfall events. Generally, RRTN was significantly correlated to TNC (TN Concentration), NH3NC, NO3NC (NO3N Concentration) and D (Depth of saturated zone), while RRNH3N (Removal Rate of NH3N) was associated with ID (Interval Days between rainfall events). Our results suggested that the stepped bioretention systems should be recommended in mountainous cities if nitrogen discharges posed a potential threat to the receiving environments.

Advantages of intermittently aerated SBR over conventional SBR on nitrogen removal for the treatment of digested piggery wastewater

An intermittently aerated sequencing batch reactor (IASBR) and a traditional sequencing batch reactor (SBR) were parallelly constructed to treat digested piggery wastewater, which was in high NH 4 + -N concentration but in a low COD/TN ratio. Their pollutant removal performance was compared under COD/TN ratios of 1.6–3.4 d and hydraulic retention times of 5–3 d. The results showed that the IASBR removed TN, NH 4 + -N and TOC more efficiently than the SBR. The average removal rates of TN, NH 4 + -N and TOC were 83.1%, 96.5%, and 89.0%, respectively, in the IASBR, significantly higher than the corresponding values of 74.8%, 82.0%, and 86.2% in the SBR. Mass balance of organic carbon revealed that the higher TN removal in the IASBR might be attributed to its efficient utilization of the organic carbon for denitrification, since that 48.7%–52.2% of COD was used for denitrification in the IASBR, higher than the corresponding proportion of 43.1%–47.4% in the SBR. A pre-anoxic process in the IASBR would enhance the ammonium oxidation while restrict the nitrite oxidation. Anoxic duration of 40–80 min should be beneficial for achieving stable nitritation.

Effects of Temperature on the Characteristics of Nitrogen and Phosphorus Removal and Microbial Community in SCSC-S/Fe

In order to investigate the effect of temperature on the cellulose-degrading bacteria and denitrifying bacteria, the denitrification and phosphorus removal of solid carbon source of cellulose corncob+sulfur/sponge iron nitrogen and phosphorus removal composite system, abbreviated as SCSC-S/Fe, was analyzed under different temperature conditions, and the surface structure and microbial properties of corncob before and after reaction were analyzed by scanning electron microscope (SEM) and MiSeq high-throughput sequencing technologies. The results indicated that when temperature increased from 15, 20, 25 to 30℃, the average TN removal rate of the system increased from 78.88% to 92.70%, the average removal rate of TP increased from 82.58% to 89.15%;microbial properties showed that the surface reaction after corncob was dominated by spherical and rod-shaped microorganisms; the proportion of cellulose-degrading bacteria was 11.01% higher at 30℃ than 20℃, and the proportion of denitrifying bacteria decreased by 21.26%. It can be seen that the cellulose -degrading bacteria were more sensitive to the temperature than the denitrification bacteria, and more obviously affected by the temperature.