Influent Loading Rate Research Articles

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.

Enhanced biodegradation of 2, 4-dichlorophenol in packed bed biofilm reactor by impregnation of polyurethane foam with Fe3O4 nanoparticles: Bio-kinetics, process optimization, performance evaluation and toxicity assessment

In this work, an effort has been made to enhance the efficacy of biological process for the effective degradation of 2, 4-dichlorophenol (2, 4-DCP) from wastewater. The polyurethane foam was modified with Fe3O4 nanoparticles and combined with polyvinyl alcohol, sodium alginate, and bacterial consortium for biodegradation of 2, 4-DCP in a packed bed biofilm reactor. The maximum removal efficiency of 2, 4-DCP chemical oxygen demand, and total organic carbon were found to be 92.51 ± 0.83 %, 86.85 ± 1.32, and 91.78 ± 1.24 %, respectively, in 4 days and 100 mg L−1 of 2, 4-DCP concentration at an influent loading rate of 2 mg L−1h−1 and hydraulic retention time of 50 h. Packed bed biofilm reactor was effective for up to four cycles to remove 2, 4-DCP. Growth inhibition kinetics were evaluated using the Edward model, yielding maximum growth rate of 0.45 day−1, inhibition constant of 110.6 mg L−1, and saturation constant of 62.3 mg L−1.

Investigating the biodesulfurization potential of isolated microbial consortia: Impact of sulfide loading, pH and oxidation-reduction potential on sulfur recovery

Acid rain is regarded as one of the major concerns due to the release of sulfur-containing wastewaters from petrochemical and other allied industries. Biological desulfurization, an ecofriendly process offers no secondary pollution and allows for the recovery of elemental sulfur as a valuable product in a useable form as fertilizer and can be used as raw material in various industries. Therefore, this work explores the bio desulfurization potential of mixed microbial consortia that was isolated from various sources for the removal of sulfur containing compounds from synthetic wastewater at varying influent sulfide loading rate. Further, this study focused on optimizing the critical process parameters such as influent sulfide loading rate, ORP and pH to achieve maximum sulfur recovery. The experiments were performed at varying sulfide loading of 3000, 4000, 5000 and 6000 mg/L using the isolated mixed consortia at an ORP of −300 ± 20 mV and −360 ± 20 mV for an incubation period of 70 h. Results revealed that the isolated microbial consortia belong to the genera 73% Pseudomonas, 24% Alishewanella and 3% Zobellella. The maximum sulfide conversion efficiency to sulfite 309 mg/L, elemental sulfur 1152 mg/L and sulfate 1813 mg/L was exhibited by microbial consortia at an initial sulfide load of 6000 mg/L and ORP of −360 ± 20 mV.

Microbial interactions facilitating efficient methane driven denitrification via in-situ utilization of short chain fatty acids

High nitrate pollution in agriculture and industry poses a challenge to emerging methane oxidation coupled denitrification. In this study, an efficient nitrate removal efficiency of 100 % was achieved at an influent loading rate of 400 mg-N/L·d, accompanied by the production of short chain fatty acids (SCFAs) with a maximum value of 80.9 mg/L. Batch tests confirmed that methane was initially converted to acetate, which then served as a carbon source for denitrification. Microbial community characterization revealed the dominance of heterotrophic denitrifiers, including Simplicispira (22.8 %), Stappia (4.9 %), and the high‑nitrogen-tolerant heterotrophic denitrifier Diaphorobacter (19.0 %), at the nitrate removal rate of 400 mg-N/L·d. Notably, the low abundance of methanotrophs ranging from 0.24 % to 3.75 % across all operational stages does not fully align with the abundance of pmoA genes, suggesting the presence of other functional microorganisms capable of methane oxidation and SCFAs production. These findings could facilitate highly efficient denitrification driven by methane and contributed to the development of denitrification using methane as an electron donor.

Increasing specific biomass nitrogen load facilitated nitrite accumulation in mainstream wastewater treatment

By regulating influent nitrogen loading rate (NLR) and solids retention time (SRT), the effect of specific biomass nitrogen load (BNL) on the start-up of mainstream partial nitrification (PN) was investigated in five parallel sequencing batch reactors inoculated with ordinary nitrification sludge. The results showed that increasing BNL by both methods could achieve nitrite accumulation. Moreover, a high initial activity of ammonium oxidizing bacteria (AOB) accelerated nitrite accumulation. Increasing influent NLR (ammonium: 55–70 mg N/L) achieved only 30%–40% of nitrite accumulation ratio (NAR) and gradually decreased with reactor operation. By increasing BNL via controlling SRT (30 days), desirable PN with an average NAR of 81.7 ± 4.4% (effluent nitrite: ∼10 mg N/L) was obtained. Nitrite oxidizing bacteria (NOB) were effectively inhibited, and the AOB to NOB activity ratio increased from 1.5 to 7.8, promoting efficient nitrite accumulation. Overall, increasing BNL by regulating SRT was a potential method for start-up of mainstream PN.

Fate of biofilm activity in cascade aerating trickling filter for wastewater treatment: Comparison of two types of indigenous support media

Cascade aerating trickling filters (CATF) with two indigenous and novel support media [date palm fiber, (DPF) and maize cob (MC)] were operated to treat domestic wastewater. The biomass, nitrification rate (NR), oxygen uptake rate (OUR) and cultural characteristics of biofilms were measured to investigate microorganism activity and biodiversity. However, the attached biomass on MC (4760 gVSS/m3) was obviously found more than the DPF (1460 gVSS/m3). Huge biomass may decrease the activity of biofilm in CATF. It was also observed that the nitrifying bacteria grow easily on MC surface due to its lower NR (4.2 mg N gVSS/m3) than DPF (5.3 mg N gVSS/m3). Similarly, the OUR of MC media was found higher than DPF media that indicated the improved metabolic activities and microbial growth in the biofilm. At filtration velocities of 4, 8, and 12 m/hr, the biofilm biomass increased with increasing filtration velocity, reaching 2105, 4817, and 6247 mgVSS/m2 respectively. At a filtration velocity of 12 m/hr, the highest biofilm density was 39 mg/cm3. Biomass and thickness of Biofilm were lowest at the filtration velocity of 8 m/hr due to the low influent loading rate. Both the CATFs showed good capability of COD removal, nitrification and denitrification.

Integration of Zeolite Membrane Bioreactor With Granular Sludge-Based Anammox in High-Efficiency Nitrogen Removal From Iron Oxide Red Wastewater.

Acquisition of stable nitritation and efficient anammox play a crucial role in partial nitritation (PN) combined with anammox for nitrogen removal from ammonium-rich wastewater. Due to the limitation of ammonia-oxidizing bacteria (AOB) enrichment and nitrite-oxidizing bacteria (NOB) control in traditional membrane biological reactor (MBR), it can result in a lower nitrite production rate (NPR) and unstable PN, eventually reducing the nitrogen removal rate (NRR) via PN-anammox. In this study, we developed a zeolite membrane biological reactor (ZMBR) to enhance the PN of iron oxide red wastewater (IORW), in which the biofilm derived from the zeolite surface can provide free ammonia (FA)-containing microenvironment for AOB enrichment and NOB inhibition. The results showed that ZMBR can tolerate a higher influent nitrogen loading rate (NLR) of 2.78 kg/(m3⋅day) in comparison to the traditional MBR [2.02 kg/(m3⋅day)] and the NPR in ZMBR and traditional MBR were 1.39 and 0.96 kg/(m3⋅day), respectively. The mass concentration ratio of -N/-N ranged from 1.05 to 1.33 in ZMBR, suggesting a suitable condition for nitrogen removal via anammox. Subsequently, the domesticated granular sludge obtained from a paper-making wastewater treatment was used as the carrier of anammox bacteria to remove nitrogen. After 93 days of operation, the NRR was observed to be 2.33 kg/(m3⋅day) and high-throughput sequencing indicated that the relatively higher abundance (45.0%) of Candidatus Kuenenia stuttgartiensis was detected in the granular sludge of the bottom part of the reactor, which can produce more proteins and lipids, suggesting a good settleability. Overall, this study provides a high-efficient method to control PN and domesticate anammox for nitrogen removal from IORW.

Long-term phosphorus sorption and leaching in sand filters for onsite treatment systems

The sorption capacities of sand filters used for onsite wastewater treatment and their associated risks of phosphorus (P) leaching on contact with rainwater were investigated in column experiments and with modelling tool for over 300 days. Columns packed with sand were exposed to real domestic wastewater of different characteristics and hydraulic loading modes. The wastewater fed into the columns was effluent collected from three different treatment units in the field: a septic tank (ST), biofiltration tank (BF) and Polonite® filter bag (PO). The risk of P leaching to groundwater and surface water was also assessed, by exposing the same sand columns to natural rainwater. Overall results indicated that sand soils can exhibit different adsorption and desorption capacities for electrical conductivity (EC), Total-P, phosphate-P and total suspended solids, depending on the characteristics of influent wastewater, loading rate and total operation time. The removal efficiencies of the sand columns increased in the order ST (98.16%) > PO (93.36%) > BF (81.57%) for PO4-P and slightly decreased ST (97.11%) > PO (92.06%) > BF (76.76%) for Total-P columns. All sand columns loaded with actual wastewater solutions from septic tanks and biofiltration tank have demonstrated high risks of phosphorus leaching (>99.99%) to the groundwater. The modelling was successful captured behavior of EC tracer and adsorption of PO4-P with acceptable prediction uncertainty in the PO < 8% columns. The modelling results indicated that the decrease of loading rate from 83.3 mL d-1 to 20.83 mL d-1 led to an average increase of removal efficiency and prolong operational lifetime and mass of adsorbed Total-P in the sand soil. This study concludes that sand is a valuable filter medium at low loading rate for phosphorus removal in full-scale operations of onsite treatment systems, however very vulnerable for leaching P when in contact with rainwater.

Recovery of ammonium nitrate solution from urine wastewater via novel free nitrous acid (FNA)-mediated two-stage processes

Nitrogen (N) recovery from urine wastewater has been an important route to overcome intensive energy consumption in the conventional N-removal process. Hereby, this study reports a new process for recovering N in the form of ammonium nitrate (AN, i.e. NH4NO3), a common, stabilized type of fertilizer in agriculture. The process is achieved through two-stage biological–chemical reactions by using free nitrous acid (FNA) as an intermediate. In the first stage, a biological reactor was operated for 170 days, with ammonium-rich human urine wastewater as influent and gradually increased influent ammonium loading rates. Then a closed chemical reactor was designed to generate AN from the effluent of the biological reactor. Experimental results demonstrate that the two-stage biological-chemical process is technically and economically viable. Comprehensive modelling analyses show that FNA is the key to maintain stable partial nitritation in the biological reactor, and also critically affects the reaction rate of the chemical nitrite oxidation. pH adjustment of the bioreactor effluent is needed to increase an FNA concentration up to 250 mg HNO2-N/L in the biological reactor effluent. As such, chemical nitrite oxidation can reach a substantially high rate, i.e. at 15 kg N/(m3·d), compared with the nitrite production rate of ∼0.5 kg N/(m3·d) achieved in the biological reactor. This result also indicates that the biological stage is a rate-limiting step in the overall process. Overall, the proposed FNA-based approach provides a promising option for nitrogen recovery from urine wastewater.

Impacts of bioreactor operating parameters on removal efficiency, biodegradation rate, molecular distribution, and toxicity of commercial naphthenic acids.

Effects of naphthenic acids (NAs) concentration (50-200mg NA L-1; 35-140mg TOC L-1) and loading rate (1.4-1249mg NA L-1h-1; 1-874mg TOC L-1h-1) on removal efficiency, removal rate, and molecular distribution of NAs, and effluent toxicity were evaluated for biodegradation of commercial NAs mixture in circulating packed bed bioreactors (CPBBs). Increase of NAs concentration and loading rate (shorter residence times) increased the removal rate, while removal efficiency initially declined and then stabilized. The maximum biodegradation rates for 50, 100, 150, and 200mg NA L-1 were 128.0, 321.7, 430.2, and 630.0mg TOC L-1h-1 at loading rates of 218.5, 455.6, 673.5 and 874.0mg TOC L-1h-1, respectively, with removal efficiencies of 58.6, 70.6, 63.9 and 72.1%. Analysis of influent and treated effluents with gas chromatography-mass spectrometry showed that molecular weight and cyclicity (C and Z numbers) affected the biodegradation, with low molecular weight acyclic NAs (C = 6-12) were the most amenable to biodegradation and those with intermediate and high molecular weights (C = 13-22) and moderate cyclicity (Z = -4, -6) were the most recalcitrant. In the biofilm, Proteobacteria and Actinobacteria were the most abundant phyla, and Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria were the dominant classes. Toxicity analyses with Artemia salina and Vibrio fischeri (Microtox) showed that high influent concentrations and loading rates (short residence times) led to higher NAs residual concentration and effluent toxicity. To design and operate large-scale CPBBs, intermediate loading rates and residence times that result in high removal efficiency, reasonable removal rates, and low toxicity are recommended.

Achieving high-rate partial nitritation with aerobic granular sludge at low temperatures.

Partial nitritation is necessary for the implementation of the mainstream anammox (anaerobic ammonium oxidation) process in wastewater treatment plants. However, the difficulty in outcompeting nitrite-oxidizing bacteria (NOB) at mainstream conditions hinders the performance of partial nitritation. The present work aimed to develop a high-rate partial nitritation process for low-ammonium wastewater treatment at low temperatures by seeding aerobic granules. Experimental results suggested that both stratified structure of nitrifiers developed in the granules and sufficient residual ammonium concentration (18-35mgN L-1) in the bulk liquid contributed to efficient NOB repression. With the hydraulic retention time progressively shortened from 1.0 to 0.17h, the influent nitrogen loading rate of the partial nitritation process reached 6.8 ± 0.4kgN m-3 d-1 even at 10-15°C. The high concentration (7.5 gVSS L-1) and activity (0.48gN g-1 VSS d-1 at 11°C) of granular sludge made the reactor possess an overcapacity evaluated by the ratio between the actual ammonium oxidation rate of the granules and their maximum potential. The overcapacity helped the reactor to face the adverse effect of decreasing temperatures. Overall, this work indicated the great potential of applying aerobic granules to achieve high-rate partial nitritation at mainstream conditions. Moreover, anammox bacteria with a relative abundance of 2.8% was also identified in the partial nitritation granules at the end of this study, suggesting that the granules provided a habitable niche for anammox bacteria growth. Note that these results cannot fully relate to the treatment of real domestic/municipal wastewater, they are a source of important information increasing the knowledge about low temperature partial nitrification.

The impact of a seasonal change in loading rate on the nitrous oxide emissions at the WWTP of a tourist region

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) whose production and emission must be minimised from wastewater treatment plants (WWTPs) to avoid undesirable impacts to climate change and the ozone layer. WWTPs operated in tourist regions undergo large seasonal changes to the influent loading rates of organic matter, nitrogen and phosphorus, which operators must respond to by changing their operational conditions. This study examines the impact of a change in low to high season on the N2O emissions of an activated sludge WWTP in a well-known tourist region in the Algarve, Portugal. While literature studies have suggested that increases in the nitrogen and organic loading rates can promote increased N2O emissions, we have found higher N2O emissions in the low season (7.4% kgN2O-N·kgNH4-N−1), where these loading rates were lower. It was found that the impact of accompanying operational changes to the WWTP outweighed any change caused by the increased loading rate, where the aeration rate showed a significant correlation with N2O emission dynamics. The location of the N2O fluxes observed as well as the dissolved vs gaseous N2O levels suggested that the hydroxylamine oxidation pathway was likely to be of higher relevance towards N2O production as compared to nitrifier denitrification. This study contributes towards the understanding of operational factors impacting N2O emissions at full-scale WWTPs and potential mitigation strategies.

Insights into complete nitrate removal in one-stage nitritation-anammox by coupling heterotrophic denitrification

Nitritation-anammox has been considered to be the most promising process for nitrogen (N) removal from wastewater. However, the anammox reaction still produces an amount of nitrate, which cannot be removed further. This study hypothesizes that heterotrophic denitrification can be an appealing option to remove the residual nitrate in the one-stage nitritation-anammox process. Through monitoring N-removal performance and microbial community succession of a laboratory microaerobic reactor, the effect of four different levels of oxygen supply on nitrate removal was investigated. The reactor was continuously fed with real manure-free piggery wastewater containing ~240 mg NH4+-N/L and chemical oxygen demand (COD)/total nitrogen (TN) ratio of less than 1 for 180 days. With a high influent loading rate of 0.7 kg N/(m3·d), efficient total nitrogen removal (>80 %) was achieved during stable operation of dissolved oxygen (DO) concentrations between 0.3 and 0.6 mg O2/L, indicating N-removal via the nitritation-anammox pathway in the low-carbon wastewater treatment. At the same time, the effluent nitrate reduced with decreased oxygen supply and completely depleted at DO of 0.3 ± 0.1 mg O2/L. In addition to oxygen, preventing ammonia nitrogen from falling to very low levels (<10 mg/L) could be also useful for the complete nitrate removal and stable nitritation-anammox. 16S rRNA gene-based analyses confirmed a complex microbial community including nitrifiers, denitrifiers and anammox bacteria in the biomass of the reactor. Collectively, this study provides new insights into high-level N-removal of a nitritation-anammox process by complete nitrate depletion.

Influence of substrates concentrations on the dynamics of oxygen demand and aeration performance in ideal bioreactors

The effect of bioreactor configurations on the dynamics of aeration modelling was investigated by incorporating three different correlations from the literature to estimate α-factors into the aeration model. Estimated air flow rates using the three correlations were then validated against experimental data obtained from pilot sequencing batch reactors (SBRs). Two identical SBRs were operated in parallel; one received raw wastewater and the other received primary treated wastewater. The validated aeration model was then used to evaluate aeration dynamics in different bioreactor configurations, both for nitrification only and nitrification/denitrification, with the three different correlations. The current study is the first to investigate the validity of the aforementioned correlations using various bioreactor configurations and to establish that the bioreactor configuration not only impacts spatial and temporal biological oxygen demands as currently understood but also oxygen transfer efficiency. The first correlation based on the real-time bioreactor soluble chemical oxygen demand (sCOD) was able to predict the temporal measured air flow rate in the pilot SBRs. The second correlation based on the influent COD overestimated the air flow rates as it considered the impact of the influent loading rates on the α-factor and overlooked the improvement in α-factor due to biodegradation. The third correlation based on MLSS concentrations underestimated the air flow rates at the beginning of the aeration cycle as it ignored the impact of influent loading rates on the α-factor and considered only the insignificant change in MLSS during the aeration cycle. In terms of bioreactor configuration, the model-based analysis showed that the first correlation is suitable for designing SBR, plug flow reactor (PFR), step-feed PFR, and completely mixed stirred reactor (CSTR) systems, and the third correlation is suitable for designing CSTRs and membrane bioreactors (MBRs), while the second correlation was not accurate in any of the reactors modelled. When nitrification was targeted, the CSTR reduced aeration energy by 44 %–49 % compared to the PFR, and 41 %–43 % when both nitrification and denitrification were targeted. Compared to the plug-flow reactor, the step-feed PFR reduced aeration energy by 9% when nitrification only was targeted. However, when pre-denitrification was added, both systems showed the same aeration energy consumption. Pre-denitrification reduced organic loadings to aeration tanks and decreased aeration energy by 22 %, 11 %, 15 %, and 14 % in PFR, CSTR, PFR step feed and MBR systems, respectively.

Simultaneous Carbon and Nitrogen Removal from Domestic Wastewater using High Rate Vermifilter.

Being a cost-effective and environmentally benign technology, vermifiltration has significantly replaced the available conventional wastewater remediation methods in many cases over the last few decades. The present work emphasizes on the investigation of the nitrogen transformation dynamics, in addition to the organic carbon abatement in the designed high rate hybrid vermifilter. Moreover, the economical sustainability of the vermifiltration technology has also been enlightened by creating a bridge with the concept of circular bio-economy. The designed high rate macrophyte-assisted vermifilter (MAVF) ascertained significant high nitrogen and organic carbon removal efficiencies from the real domestic sewage, considering the chemical oxygen demand (COD) of the influent and hydraulic loading rate (HLR) as the input variables. The designed MAVF facilitated the maximum ammonium nitrogen (NH4 +-N), organic nitrogen, and total kjeldahl nitrogen removal efficiencies up to 98.2 ± 0.70%, 100%, and 99 ± 0.47%, respectively when COD of the influent and HLR were 200 ± 25mg/L and 3 ± 0.1 m3/m2-d, respectively. On the other hand, substantial enhancement in the nitrate nitrogen (NO3 --N) in the effluent (73 ± 10.55 times its influent concentration) was observed with influent COD of 200 ± 25mg/L and HLR of 7 ± 0.2 m3/m2-d. When the influent COD and HLR were maintained at 700 ± 45mg/L and 3 ± 0.1 m3/m2-d, respectively, the highest total nitrogen removal of 87 ± 2.25% was obtained. Alternatively, the influent COD of 200 ± 25mg/L and HLR of 3 ± 0.1 m3/m2-d yielded the highest COD removal efficiency of 77 ± 1.59%. Hence, the outcome of the present research work strengthens the suitability of the vermifiltration technology as an economically and ecologically sound natural wastewater bio-remediation technology for the treatment of domestic wastewater.

A novel denitrifying phosphorus removal and partial nitrification, anammox (DPR-PNA) process for advanced nutrients removal from high-strength wastewater

This study developed a novel DPR-PNA (denitrifying phosphorus removal, partial nitrification and anammox) process for sustaining high-strength wastewater treatment in a modified continuous flow reactor without external carbon source. After 259-days operation, a synchronous highly-efficient total inorganic nitrogen, PO43--P and CODcr removal efficiencies of 88.5%, 89.5% and 90.1% were obtained, respectively even influent nitrogen loading rate up to 3.2 kg m−3 d−1. Batch tests revealed that denitrifying phosphorus accumulating organisms (DPAOs) using NO3−-N as electron acceptors significantly enriched (74% in total PAOs), which emerged remarkable positive impacts on deep-level nutrient removal as the key limiting factor. Furthermore, the NO2−-N inhibitory threshold value (∼20.0 mg L−1) for DPAOs was identified, which demonstrated as an inhibitory component in excessive recycling NOx−-N. From the molecular biology perspective, Dechloromonas-DPAOs group (18.59%) dominated the excellent dephosphatation performance, while Nitrosomonas-AOB (ammonia oxidizing bacteria) group (16.26%) and Candidatus_Brocadia-AnAOB (anammox bacteria) group (15.12%) were responsible for the desirable nitrogen loss process. Overall, the present work highlighted the novel DPR-PNA process for nutrients removal is a promising alternation for wastewater of high nitrogen but low carbon.

Treatment of high-strength sewage by textile fibers-based sequencing batch biofilm reactor for simultaneous removal of organics and nutrients

This study investigates the effectiveness of SBBR with low-cost textile fibers-based bio-carrier namely polypropylene fibers for the treatment of real sewage. The influent loading rates of COD, TN, and TP were averaged at 0.2780, 0.0170, and 0.0077 kg/m3.d, respectively. The removal efficiencies of BOD, COD, TN, and TP recorded in SBBR were 98%, 93%, 82%, and 44%, respectively at an aeration time of 4 h. The TN and TP removal achieved in SBBR were 2.05 and 2.75 times, respectively higher than SBR. The COD removal efficiency was more than 90% under all SRT conditions (10, 14, 18, 22, and 26 d) in SBBR, and the highest efficiency of 93% was obtained at an SRT of 22 days. As the SRT increased, the nitrogen and phosphorus removal decreased, because the denitrification rate and phosphorus release and uptake rate decreased at longer SRT. Simultaneous nitrification and denitrification (SND) efficiency was 85% in SBBR and 44% in SBR, indicating the co-existence of aerobic nitrifiers and anoxic denitrifiers in the biofilm reactor. In SBBR, the nitrogen mass balance showed 74% of nitrogen removed by denitrification, 9% was removed through sludge wasting process, and 13% was removed in effluent at an SRT of 22 days and DO concentration of 3 mg/L. The t-test results suggest that the performance of SBBR was better than SBR in nitrogen and phosphorus removal at a 95% confidence interval.

Start-up and Optimization of Denitrifying Phosphorus Removal in ABR-MBR Coupling Process

The feasibility of the denitrifying phosphorus removal process in the ABR-MBR system with no sludge reflux and high concentration of seeding activated sludge (25 g ·L-1, in MLSS) in the ABR was investigated. The characteristics of the microbial community in the denitrifying phosphorus removal compartment were also evaluated. The denitrifying phosphorus removal function was achieved by gradually increasing the reflux ratio (R) from 0% to 200%. During the stable operation, the average removal rates of COD, PO43--P, and TN in the system were 88.28%, 54.45%, and 61.93%, respectively. When the influent loading rate, NOx--N reflux ratio, and hydraulic retention time (HRT) of ABR and MBR were 0.8 kg ·(m3 ·d)-1, 150%, and 9 h and 3.3 h, respectively, the average VFA concentration of 80.58 mg ·L-1, ρ(NO2--N)/ρ(NO3--N) reflux ratio of 1.68, and PO43--P and TN removal rates of 64.94% and 62.95% were obtained. The short-cut nitrification denitrifying phosphorus removal was achieved in the ABR-MBR system. Batch tests showed that denitrifying phosphorus removal bacteria (DPAOs) were the main functional bacteria in the ABR, with anaerobic phosphorus release and anoxic phosphorus uptake of 3.73 mg ·L-1 and 10.22 mg ·L-1, respectively. High throughput sequencing results showed that Proteobacteria and Bacteroidetes were the dominant phyla in the phosphorus removal compartment, accounting for 23.49%-53.66% and 16.55%-21.78% of the total phyla, respectively. Thauera, Thiothrix, Pseudomonas, norank_ f_Rhodocyclaceae, and unclassification_ f_Rhodocyclaceae in Proteobacteria, and Sphingobacteriales in Bacteroidetes were the potential denitrifying phosphorus removal microorganisms.

Fast start-up of PN/A process in a single-stage packed bed and mechanism of nitrogen removal.

The single-stage partial nitritation-anammox (PN/A) process is severely limited by a long start-up time and unstable removal efficiency. In this study, PN/A was developed in 67days in a novel packed bed equipped with porous bio-carriers by gradually increasing the influent nitrogen loading rate (0.15-0.73kg-Nm-3·d-1) and controlling the dissolved oxygen (< 1.2mgL-1). An average ammonium nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TNR) of 87.01 and 72.41%, respectively, were obtained. This represents a reliable alternative method of achieving rapid PN/A start-up. The results of 16S rRNA sequencing showed that Proteobacteria and Planctomycetes, with which ammonia-oxidizing bacteria and anammox bacteria were affiliated, accounted for 38.8%, representing the dominant phylum in the system after acclimation. The abundance of Nitrosomonas and Candidatus Brocadia increased by 16 and 1.79%, respectively. The results of metagenomics and metatranscriptomics revealed that the nitrite oxidation process was blocked by the transcriptional suppression of nitrite oxidoreductase and the entire nitrogen metabolism process was dominated by the partial nitritation and anammox process. Moreover, a high abundance of heterotrophic bacteria with potential for nitrogen removal was detected. In the nitrogen cycle, a widespread nitrite-accumulated denitrification helps to form a nitrite loop, which promotes the efficiency of total nitrogen removal. This is crucial for further improving the nitrogen removal mechanism in the PN/A system.

Start-up of single-stage partial nitritation-anammox micro-granules system: Performance and microbial community dynamics

By manipulating influent nitrogen load and DO concentration in bulk liquid, the start-up and performance of a new micro-granule based partial nitritation-anammox process was investigated in a continuous stirred tank reactor (CSTR). Under the condition of nitrogen loadings from 0.3 to 1.4 kgN /m³/d and DO <0.21mg/L, the single-stage partial nitritation-anammox (SPNA) system was successfully started, with a nitrogen removal of 76.2%. Meanwhile, the oxygen utilization efficiency by ammonium oxidizing bacteria (AOB) increased in the system with the increase of influent ammonia loading rate. Micro-granules with an average diameter of 0.25 mm were formed. Sludge granulation was promoted by increasing influent nitrogen load, and there was a positive correlation between nitrogen load, extracellular polymeric substances (EPS) content and sludge particle size. Ca. Kuenenia became the dominant anaerobic ammonium oxidizing bacteria (AnAOB) in the SPNA system. As the dominant AOB genera, Nitrosomonas coexist with Ca. Kuenenia in the micro-granules.