Higher TN Removal Efficiency Research Articles

Evaluating the role of carbon sources on the development of algal-bacterial granular sludge: From sludge characteristics, extracellular polymer properties, quorum sensing, and microbial communities

This study investigated the effect of dissolved organic matter (DOM) and particulate organic matter (POM) on the formation process of algal-bacterial granular sludge (ABGS). The results showed that compared with DOM, POM accelerated biomass growth and improved the settling performance of the sludge. However, concerning pollutant removal, ABGS cultured with DOM exhibited high TN and TP removal efficiency. The analysis of extracellular polymeric substances (EPS), indicated that the presence of POM primarily facilitated the production of loosely bound EPS (LB-EPS), whereas the presence of DOM promoted the secretion of tightly bound EPS (TB-EPS). Notably, carbon sources influenced the secretion of different signal molecules. ABGS cultured with POM exhibited higher concentrations of 3-oxo-C8-HSL than that cultivated with DOM, while DOM resulted in the production of more C8-HSL and C6-HSL. Microbial communities analysis revealed that the dominant bacteria in the mature ABGS cultured with different carbon sources were Plasticicumulans, while the predominant algal genus displayed notable diversity. Further investigations into functional genes suggested that the nitrification process (hao) and the denitrification process (nir, nar) were greatly enhanced in the presence of DOM. This study reveals the mechanism of carbon source types and ABGS formation, providing valuable guidance for the treatment of municipal wastewater with high POM proportion.

Different in root exudates and rhizosphere microorganisms effect on nitrogen removal between three emergent aquatic plants in surface flow constructed wetlands

Swine wastewater contains high concentration of nitrogen (N), causing pollution of surrounding water bodies. Constructed wetlands (CWs) are considered as an effective ecological treatment measure to remove nitrogen. Some emergent aquatic plants could tolerate high ammonia, and play a crucial part in CWs to treat high concentration N wastewater. However, the mechanism of root exudates and rhizosphere microorganisms of emergent plants on nitrogen removal is still unclear. Effects of organic and amino acids on rhizosphere N cycle microorganisms and environmental factors across three emergent plants were investigated in this study. The highest TN removal efficiency were 81.20% in surface flow constructed wetlands (SFCWs) plant with Pontederia cordata. The root exudation rates results showed that organic and amino acids were higher in 56 d than that in 0 d in SFCWs plants with Iris pseudacorus and P. cordata. The highest ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) gene copy numbers were found in I. pseudacorus rhizosphere soil, while the highest nirS, nirK, hzsB and 16S rRNA gene copy numbers were detected in P. cordata rhizosphere soil. Regression analysis results demonstrated that organic and amino acids exudation rates were positive related to rhizosphere microorganisms. These results indicated that organic and amino acids secretion could stimulate growth of emergent plants rhizosphere microorganisms in SFCWs for swine wastewater treatment. In addition, the EC, TN, NH4+-N and NO3−-N were negatively correlated with organic and amino acids exudation rates, and abundances of rhizosphere microorganisms via Pearson correlation analysis. These results imply that organic and amino acids, and rhizosphere microorganisms synergically affected on the nitrogen removal in SFCWs.

Characterization of Achromobacter denitrificans QHR-5 for heterotrophic nitrification-aerobic denitrification with iron oxidation function isolated from BSIS：Nitrogen removal performance and enhanced SND capability of BSIS

Strain QHR-5, a heterotrophic nitrification-aerobic denitrification bacterium (HNADB) with iron oxidation function, was isolated from biological sponge iron system (BSIS) and identified as Achromobacter denitrificans. The carbon source suitable for growth and nitrogen removal by the strain from the denitrification medium 1(DM1) was investigated. Maximum growth and total inorganic nitrogen (TIN) removal were observed when Seignette salt was the carbon source. Single-factor experiments showed that the highest NO3--N removal performance was achieved when C/N ratio was 17, the shaking speed was 120 rpm, the temperature was 30 ℃, and the pH was 7.0. The heterotrophic nitrification and aerobic denitrification activity with different nitrogen sources (NH4+-N, NO3--N, and NO2--N) showed removal efficiencies of 90.84%, 98.37%, and 60.37%, respectively. With NH4+-N, NO3--N or NH4+-N, NO2--N as mixed nitrogen sources, Strain QHR-5 still showed good denitrification activity. Runs R1 (BSIS) and R2 (BSIS + Strain QHR-5) showed that with higher concentration NO3--N (981.12 mg/L), the TN removal efficiency of R2 increased by 18.32%. Higher TN removal efficiency could be attributed to the aerobic denitrification capability of Strain QHR-5 and the accelerated dissolution of Fe2+ in BSIS due to the iron oxidation function of Strain QHR-5.

Evaluation of an anaerobic baffled reactor (ABR) – downflow hanging sponge (DHS) system in treatment of black wastewater from a closed recirculating aquaculture system

This study focused on evaluating the nitrogen and solids removal performance of a laboratory-scale anaerobic baffled reactor (ABR) – downflow hanging sponge (DHS) system for treating black wastewater from a closed recirculating aquaculture system (RAS) under a salinity of 15‰. The system was investigated under a controlled temperature (35 °C) with total organic carbon/total nitrogen (TOC/TN) ratios of 1.8, 2.5, 0.3, and 3.0, which corresponded to Phases 1, 2, 3, and 4, respectively, for 500 days. The ABR achieved a nitrate removal efficiency of 95–99 % at TOC/TN ratios higher than 1.8. The nitrate removal efficiency significantly decreased from 98 % to 12 % when the TOC/TN ratio decreased from 3.0 to 0.3. The highest TN removal efficiency (94 ± 4 %) was achieved with a TOC/TN ratio of 3.0. The ABR could remove 97 ± 6 % of the suspended solids during the entire experimental period. The DHS reactor achieved a nitrification efficiency of 70 % with short hydraulic retention times of 0.11–0.28 min. Total ammonia nitrogen in the DHS effluent was less than 1.0 mg N/L in the stable condition. The denitrifying Thauera genera predominant in the ABR reactor led to a high degree of denitrification. Methanogenic organisms such as Methanobacterium and Methanosaeta contributed to methane production of 0.8 ± 0.4 L/d in the ABR at a TOC/TN ratio of 3.0. Microbial community structure analysis showed that nitrifying microorganisms, such as Nitrosomonas, Nitrospira, and Candidatus Nitrosopumilus, were detected in the DHS-retained sludge. These results indicate that the ABR–DHS system evaluated could be applied for the removal of nitrogen and solids from RAS derived black wastewater to meet the water quality level needed for production-scale RAS.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) μm on day 80. The excellent removal performance of COD (92%) and NH4+-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO2−-N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Investigation on the improved electrochemical and bio-electrochemical treatment processes of soilless cultivation drainage (SCD)

The soilless crop cultivation under cover generates wastewater called soilless cultivation drainage (SCD), being a nutrient-rich overflow. The average concentration of phosphorus- and nitrogen-based pollutants from soilless tomato cultivation usually ranges from 35.4 to 104.0 mg P/L and from 270.0 to 614.9 mg N/L, respectively. In bio-electrochemical reactors, nitrogen and phosphorus are removed via biological denitrification, electrochemical nitrate reduction, bio-electrochemical reduction, and electrocoagulation. The novelty of this study is due to the use of alternating current (AC), which can both mitigate the corrosion on the anode and solve the issue of insoluble oxide build-up on the cathode. Additionally, and crucially, it promotes bacterial growth and activity. The aim of the present study was to determine (1) the effectiveness of soilless cultivation drainage treatment methods that employ biological and electrochemical processes, with consideration given to (2) the quantity and quality of the produced sludge as a potential nutrient-rich product. The bio-electrochemical reactor proved more effective than the electrochemical one and ensured a high TP and TN removal efficiency exceeding 97% and 66%, respectively. The resulting sludge was rich in such elements as calcium, potassium, carbon, phosphorus, and nitrogen, and as such may serve as a viable alternative to conventional mineral fertilizers.

Effects of substrate combinations on greenhouse gas emissions and wastewater treatment performance in vertical subsurface flow constructed wetlands

Climate warming would be generally influenced by the quantity and component of greenhouse gases during the carbon and nitrogen removal in constructed wetlands (CWs). In this study, the impacts of the combinations by walnut shell (organic-rich substrate improving denitrification), manganese (Mn) ore (electron-exchange substrate transferring CH4 to CO2) and activated alumina (phosphorus-adsorption substrate) on global warming potentials (GWPs) were investigated to propose a strategy for both mitigating GWPs and performing well in wastewater treatment. During hybrid CWs, the highest COD and TP removal efficiencies were respectively 89.4% and 98.1% in CWs with the substrate combination of Mn ore and activated alumina, and the highest TN removal efficiency was in CWs with walnut shell and Mn ore. The substrate combination of walnut shell and Mn ore would simultaneously strengthen the nitrification and denitrification process resulting in the lowest N2O flux in CWs. The combinations of Mn ore with walnut shell or activated alumina could significantly decrease the GWPs through promoting the conversion of CH4 to CO2 due to the better redox potential environment favorable for methanotrophs (pmoA) instead of methanogenesis (mcrA) provided by Mn ore. This study provided a feasible way to mitigate climate warming during wastewater treatment in CWs by using substrate combination of Mn ore and walnut shell.

Long-term effects of N-acyl-homoserine lactone-based quorum sensing on the characteristics of ANAMMOX granules in high-loaded reactors

Laboratory experiments were carried out to determine the long-term effects of N-acyl-homoserine lactone (AHL)-based quorum sensing on the characteristics of ANAMMOX granules in high-loaded reactors. Results clearly showed that adding 30 mg L−1 N-octanoyl-DL-homoserinelactone (C8-HSL) at the initial stage (1–40 d) of the experiment had long-term positive effects on the settleability of granules and controlled the sludge floatation effectively. C8-HSL decreased the content of bound extracellular polymeric substances (B-EPS) and the ratio of protein to carbohydrate (PN/PS) by 17% and 48%, respectively and increased the relative hydrophobicity (RH) of the granules by 28%. The results of batch tests indicated that C8-HSL significantly reduced the content of loosely-bound EPS (LB-EPS) in the B-EPS, which was responsible for variations in granule settleability and stability. Thus, the settleability of the granules was improved significantly due to addition of C8-HSL, contributing to operational stability and the high TN removal efficiency of the reactor. On day 150, when the nitrogen loading rates of all reactors were 13.4 kg TN m−3 d−1, the nitrogen removal rate and nitrogen removal efficiency of the reactor with C8-HSL (R3) were up to 11.2 kg TN m−3 d−1 and 88%, respectively. N-hexanoyl-DL-homoserine lactone (C6-HSL) improved activity of the granules, while N-dodecanoyl-DL-homoserine lactone (C12-HSL) had no effect on the characteristics of the granules. The long-term effects of C8-HSL on the settleability of granules may be attributed to sustainable release of endogenous signals induced by exogenous signal.

Determining the effects of aeration intensity and reactor height to diameter (H/D) ratio on granule stability based on bubble behavior analysis.

Aerobic granular sludge was considered as a leading wastewater technology in the next century. However, the loss of granule stability limited the application of this promising biotechnology. Increasing aeration intensity and height to diameter (H/D) ratio were conventional strategies to enhance granule stability. In this study, hydraulic effects of aeration intensity and H/D ratio were explored basing on bubble behavior analysis. However, results revealed that due to viscous resistance, increasing aeration intensity and H/D ratio had limited effects on enhancing hydraulic shear stress, not to mention the extra operation and construction cost. A deflector component was further applied to regulate hydraulic shear stress on large granules under low aeration intensity and H/D ratio. Hydraulic shear stress of large granules was constantly around 3.0 times higher than that in the conventional reactor, resulting in higher percentage of granules within optimal size range (81.95 ± 5.13%). A high abundance of denitrifying bacteria was observed in reactors, which led to high TN removal efficiency of 88.6 ± 3.8%.

Influence of Biological Activated Carbon on Simultaneous Nitrification and Denitrification in Inflow with Different C/N Ratios

Influence of biological activated carbon (BAC) on simultaneous nitrification and denitrification (SND) in inflow with different C/N ratios was investigated with continuous operation of BAC reactor and SBR. Methanol was added as carbon source and the inflow C/N ratio was set to 3, 5, 8 and 10 to run for about 120 cycles, under conditions of indoor temperature (15-27℃), initial DO 2-3mg·L-1. The TN removal efficiency and stability of two reactors were compared. The results showed that, BAC reactor had a higher TN removal efficiency than SBR at different C/N ratios. TN removal rate of BAC reactor was 44.88%, 58.07% and 66.64%, when the C/N ratio was 3, 5 and 8 respectively. After increasing the C/N ratio to 10, the BAC reactor could maintain TN removal rate of 63.65%, but the SBR showed sludge bulking. BAC provided various DO environments for microorganisms in a vessel, which was beneficial to SND. BAC could reduce the influence of excessive carbon source on the nitrification system, enlarge the application range and improve the stability of reactor at different C/N ratios, and increase the nitrogen removal capacity of organic matter. BAC provided condition for efficient nitrogen removal.

Systematic design of membership functions for fuzzy-logic control: A case study on one-stage partial nitritation/anammox treatment systems

A methodology is developed to systematically design the membership functions of fuzzy-logic controllers for multivariable systems. The methodology consists of a systematic derivation of the critical points of the membership functions as a function of predefined control objectives. Several constrained optimization problems corresponding to different qualitative operation states of the system are defined and solved to identify, in a consistent manner, the critical points of the membership functions for the input variables. The consistently identified critical points, together with the linguistic rules, determine the long term reachability of the control objectives by the fuzzy logic controller. The methodology is highlighted using a single-stage side-stream partial nitritation/Anammox reactor as a case study. As a result, a new fuzzy-logic controller for high and stable total nitrogen removal efficiency is designed. Rigorous simulations are carried out to evaluate and benchmark the performance of the controller. The results demonstrate that the novel control strategy is capable of rejecting the long-term influent disturbances, and can achieve a stable and high TN removal efficiency. Additionally, the controller was tested, and showed robustness, against measurement noise levels typical for wastewater sensors. A feedforward-feedback configuration using the present controller would give even better performance. In comparison, a previously developed fuzzy-logic controller using merely expert and intuitive knowledge performed worse. This proved the importance of using a systematic methodology for the derivation of the membership functions for multivariable systems. These results are promising for future applications of the controller in real full-scale plants. Furthermore, the methodology can be used as a tool to help systematically design fuzzy logic control applications for other biological processes.

Anaerobic/anoxic/oxic configuration in hybrid moving bed biofilm reactor-membrane bioreactor for nutrient removal from municipal wastewater

A membrane bioreactor (MBRp), a hybrid moving bed biofilm reactor-membrane bioreactor containing carriers in the anaerobic, anoxic and aerobic zones (hybrid MBBR-MBRap) and a hybrid moving bed biofilm reactor-membrane bioreactor which contained carriers only in the anaerobic and anoxic compartments (hybrid MBBR-MBRbp) were used in parallel and compared regarding the nutrient and organic matter removal from municipal wastewater. The hydraulic retention time (HRT) was 18h. A kinetic study for the heterotrophic and autotrophic bacteria, mainly nitrite-oxidizing bacteria (NOB), was carried out and related to the nutrient and organic matter removal. The hybrid MBBR-MBRap performed best regarding chemical oxygen demand (COD) and total phosphorus (TP) removals, with values of 85.82±2.12% and 81.42±3.85%, respectively. This system had a higher phosphorus release under anaerobic conditions and a higher phosphorus uptake under aerobic conditions. The highest TN removal efficiency was obtained for the hybrid MBBR-MBRbp, with a value of 61.39±10.71%.

改良ICEAS工艺提高污水厂脱氮效率的方法研究

为进一步提高ICEAS工艺污水处理厂的总氮去除率，本文研究了如何通过对ICEAS工艺的改良提高其脱氮效率，并最终应用于城镇污水处理厂ICEAS工艺高效脱氮升级改造。研究结果表明，连续进水方式限制了总氮去除率的提高，将连续进水方式变为间歇进水方式，系统的脱氮效率明显提高。运行模式为搅拌56 min、曝气112 min、沉淀50 min，滗水70 min，运行周期为4.8 h时，可明显提高总氮的去除率。 In order to improve the total nitrogen removal rate, this paper studied the ways to improve the nitrogen removal efficiency through the improvement of ICEAS process, which was finally applied to the urban wastewater treatment plant. The results showed that the traditional ICEAS process limits the improvement of total nitrogen removal rate, and the step-feed ICEAS process always has a higher TN removal efficiency than the traditional ICEAS process. Operation mode consisted of 56 min agitation, 112 min aeration, 50 min precipitation, and 70 min decanting; when operation cycle was 4.8 h, the removal rate of total nitrogen could be significantly improved.

A new step aeration approach towards the improvement of nitrogen removal in a full scale Carrousel oxidation ditch

Two aeration modes, step aeration and point aeration, were used in a full-scale Carrousel oxidation ditch with microporous aeration. The nitrogen removal performance and mechanism were analyzed. With the same total aeration input, both aeration modes demonstrated good nitrification outcomes with the average efficiency in removing NH4+-N of more than 98%. However, the average removal efficiencies for total nitrogen were 89.3% and 77.6% under step aeration and point aeration, respectively. The results indicated that an extended aerobic zone followed the aeration zones could affect the proportion of anoxic and oxic zones. The step aeration with larger anoxic zones indicated better TN removal efficiency. More importantly, step aeration provided the suitable environment for both nitrifiers and denitrifiers. The diversity and relative abundance of denitrifying bacteria under the step aeration (1.55%) was higher than that under the point aeration (1.12%), which resulted in an overall higher TN removal efficiency.

Optimization of the operating parameters for online ultrasonic on controlling membrane fouling in SMBR

In this study, bi-frequency online ultrasound was applied to a submerged membrane bioreactor (SMBR–US) to mitigate the membrane fouling. The transmembrane pressure (TMP) was used as an indicator of membrane fouling, and it was observed at different ultrasound parameters to investigate the alleviating effect of membrane fouling. The wastewater treatment experiments were then carried out to explore the effects of online ultrasound on effluent quality and activated sludge concentrations in SMBR system. The results show that the TMP were relatively low when the ultrasonic cleaning time continued for three minutes with an ultrasonic frequency at 50 kHz, or bi-frequency of 25–50 kHz, or tri-frequency of 25–50–90 kHz and an ultrasonic power of 200 or 300 W. The results of wastewater treatment experiments show that both the SMBR–US and the SMBR-Control system had high COD, ammonia, and TN removal efficiency, indicating that the ultrasound did not have a negative influence on the properties of activated sludge and effluent quality. The mixed liquor suspended solids (MLSS) in SMBR–US system decreased apparently, about 7.1% when comparing to the SMBR-Control system, after 40-day operation, which suggested that the ultrasound can reduce extra sludge production.

Effects of Aeration on Nitrogen and Phosphate Removal with A<sup>2</sup>O Process

A2O process is shortened form Anaerobic-Anoxic-Aerobic process, which can achieve carbon, nitrogen and phosphate removal, is widely used for its low cost and high efficiency. The Experiment using a 52.15 L anaerobic-anoxic- aerobic (A2O) reactor with simulate synthetic wastewater, by adjusting the aeration of Aerobic units, observing the performance of nitrogen and phosphorus removal under different dissolved oxygen(DO). The result of the whole operation show that the system can not keep a high TN removal efficiency under high aeration, and the low aeration made the system a significant decline in nitrogen and phosphorus removal.

Studies on Effects of Several Wetland Plants on Eutrophic Water Purification

Effectiveness of combinations of seven different ecotypes of wetland plants including Thalia dealbata, Iris tectorum, Acorus calamus,Zizania aquatica, Nymphaea tetragona,Georgi, Myriophyllum aquaticum, Thalia dealbata purifying water was investigated by hydrostatic simulation experiment method. The research showed that combinations of various wetland plants had significant purification effects on eutrophic water body, plant community was stable, and plants grew well. Chemical Oxygen Demand (COD) removal efficiencies of various combinations were higher than 97%, and 25.9% higher than that of the blank control group; the average highest total phosphorus (TP) removal efficiency of plant combinations was 97.6%. Compared with COD and TP, Total nitrogen( TN)removal efficiency was lower, ranging from 90.4% to 83.1%.Different wetland plants had different purification effectiveness for different pollutant. The combination N+Z+A+ZI had the highest TNremoval efficiency, reaching 90.4%. Combinations N+Z+A+ZI and N+Z respectively won the first and second place in the disposal of TP,reaching 99.68%, 99.34%. For Chemical Oxygen Demand COD removal, the combination N+Z+C+T did the best and the highest removal efficiency reached 97.6%. Fuzzy comprehensive evaluation method is used to select the following combinations with stronger capacities of removing N and P in sewage: N+Z+A+ZI, N+Z, N+Z+C+T. They can be promoted and applied in purification of eutrophic water body in ecological projects.