Effect of dissolved oxygen on nitrogen removal and process control in aerobic granular sludge reactor

A novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) for advanced nitrogen removal from domestic sewage

To achieve advanced nitrogen removal from actual municipal sewage, a novel multistage anoxic/aerobic process with sludge regeneration zone (R-MAO) was developed. The reactor was used to treat actual domestic sewage and the nitrogen removal capacity of the sludge regeneration zone (R zone) was investigated during the long-term operation. The best performance was obtained at the R zone's Oxidation-Reduction Potential (ORP) of -50±30 mV and hydraulic residence times (HRT) of 1.2 hr. The average effluent COD, TN, NH₄⁺-N and NO₃^--N of the R-MAO process were 18.0±2.3, 7.5±0.6, 1.0±0.5 and 4.6±0.4 mg/L, respectively, with the corresponding removal efficiency of COD, TN and NH₄⁺-N were 92.9%±1.0%, 84.1%±1.5% and 97.5%±1.1%. Compared to the sole MAO system, the TN removal efficiency of the R-MAO increased by 10.1%. Besides, under the optimal conditions, the contribution of the R zone in the R-MAO that removal COD, TN, NH₄⁺-N and NO₃^--N were 0.36, 0.15, 0.032 and 0.82 g/day. High-throughput sequencing results showed that uncultured_bacterium_f_Burkholderiaceae (5.20%), OLB8 (1.04%) and Ottowia (1.03%) played an important role in denitrification in the R zone. This study provided effective guidance for the design and operation of the R-MAO process in domestic sewage treatment.

Effect of flow regime on mass transfer diffusion and stability of aerobic granular sludge (AGS) in view of interfacial thermodynamic

Aerobic granular sludge (AGS) technology has been widely studied as "The Next Generation Wastewater Treatment technology". The effect of hydraulic conditions on the structural stability of AGS has been widely studied. However, the function of flow regime on the AGS stability, especially dissolved oxygen (DO) mass transfer, is still unknown. In this study, we used the Reynolds number (Re) to quantify the flow regime and selected different stages of AGS as experimental subjects. Results showed that the relatively suitable Re (Re = 150) could create lower DO mass transfer limitation (Lc = 27.4 μm) and increase protein (PN) contents and the abundance of hydrophobic functional groups in AGS. At this condition (Re = 150), the interfacial Gibbs free energy of sludge-water (ΔG_LS^a) was at a lower state (-129.75 ± 2.15 mJ·m^-2), which favored the stability of AGS. Principal component analysis (PCA) and correlation analysis indicated that the response of ΔG_LS^a was affected by Lc, PN, and hydrophobic groups. In addition, results obtained for unstable AGS further verified that suitable Re regulates the structural stability of AGS. This study deepens the understanding of Re as an important hydraulic parameter for structural stability of AGS, which is also of great significance for energy saving of sequential batch reactors (SBRs) with agitation in practical engineering.

Efficient nitrogen removal from onsite wastewater by a novel continuous flow biofilter

Soil-based passive biofiltration system is an economically feasible technology for nitrogen removal from onsite wastewater. However, the conventional design requires a large system footprint with limited treatment capacity. In this study, a novel continuous flow biofilter (CFB) with adjustable recirculation and continuous flow pattern was developed for onsite wastewater treatment with a small footprint. Efficient total nitrogen removal (80.1-97.5%) was observed at various hydraulic loadings (0.03-0.12 m³ m^-2 d^-1), nitrogen loadings (1.1-8.6 g N m^-2 d^-1) and recycle ratios (2-3) when treating septic tank effluent (STE), with low effluent TN (0.7-13.6 mg N L^-1). Nitrous oxide was observed in the denitrification effluent indicating incomplete denitrification at elevated dissolved oxygen levels (3.3-5.8 mg L^-1). Nitrogen removal rate (2.9-7.0 g N m^-2 d^-1) and ammonium removal rate (2.4-7.2 g N m^-2 d^-1) were positively correlated with nitrogen loadings increase (1.1-8.6 g N m^-2 d^-1) but were not significantly impacted by the hydraulic loading rate change (0.08-0.12 m³ m^-2 d^-1). The total biomass abundance and nitrifying microorganisms decreased significantly as the nitrification columns depth increased, while homogeneous microbial distribution was observed in the denitrification columns. The abundance of ammonium oxidizing archaea (AOA) increased significantly at increased hydraulic and nitrogen loading rate, while the ammonium oxidizing bacteria (AOB) abundance remained steady. The abundance of functional genes involved in denitrification process (nirS, nirK and nosZ) responded differently when hydraulic and nitrogen loading rate changes. Collectively, this study suggested the CFB could efficiently remove nitrogen from onsite wastewater with fluctuating influent compositions and various hydraulic loadings.

Optimization of nutrient removal performance of magnesia-containing constructed wetlands: a microcosm study

Recently, magnesia has drawn much attention for enhancing phosphorus (P) removal of constructed wetlands. However, the poor nitrogen (N) removal efficiency of magnesia-containing constructed wetlands (Mg-CWs) inherently caused by magnesia impedes its application. In this study, peat and intermittent aeration were applied to enhance N removal in a Mg-CW, identified as P-CW and A-CW, respectively. A high TP removal rate (around 90%) was achieved in all CW, and the TN removal rate in the P-CW was 91.05% higher than that in the Mg-CW, which was mainly because the carbon source provided by the peat directly promoted the growth and metabolism of microorganisms and plants. Higher fresh weight of plants was obtained in P-CW (64.94 ± 5.78 g), compared with A-CW (35.88 ± 15.25 g) and Mg-CW (46.25 ± 18.88 g), accomplished by stronger tolerance to high pH (>10). The microbial abundance (16S rRNA) in the P-CW was 15.6 and 8.12 times higher than that of Mg-CW and A-CW, respectively, resulting in lower global warming potential. Tanking all factors into consideration, addition of peat could be an effective method to optimize the nutrient removal performance of Mg-CW.

Effects of wastewater type on stability and operating conditions control strategy in relation to the formation of aerobic granular sludge - a review

Currently, research trends on aerobic granular sludge (AGS) have integrated the operating conditions of extracellular polymeric substances (EPS) towards the stability of AGS systems in various types of wastewater with different physical and biochemical characteristics. More attention is given to the stability of the AGS system for real site applications. Although recent studies have reported comprehensively the mechanism of AGS formation and stability in relation to other intermolecular interactions such as microbial distribution, shock loading and toxicity, standard operating condition control strategies for different types of wastewater have not yet been discussed. Thus, the dimensional multi-layer structural model of AGS is discussed comprehensively in the first part of this review paper, focusing on diameter size, thickness variability of each layer and diffusion factor. This can assist in facilitating the interrelation between disposition and stability of AGS structure to correspond to the changes in wastewater types, which is the main objective and novelty of this review.

Effect of carrier particle size on enrichment and shift in nitrifier community behaviors for treating increased strength wastewater

In activated sludge systems, adding carriers can improve nitrifier enrichment. Different attachment area induced by different particle sizes of carriers may result in different nitrifier community. This research investigated the effect of different particle sizes of coal ash on nitrifier enrichment treating increased strength wastewater. Results indicated efficient nitrifying coal ash was obtained with smaller coal ash. The ammonia removal rates reached over 98%, which outclassed that in negative control (63.28%), and no nitrite accumulated in these systems under high nitrogen concentration of 1123.35 mg N/L. The high-throughput sequencing assays indicated carriers changed the microbial community structure significantly, thus facilitated the nitrification capacity. Increase abundance of nitrifier has a negative correlation with particle size of carriers. Nitrosomonas became the biggest beneficiary, which maximum composed 50.29% in fillers system and only 13.69% in negative control, whereas the number of Nitrobacter (less than 3.04%) became much lower than ammonia-oxidizing bacteria (AOB). However, the shift of microbial structures, large number of Dokdonella for instance, may guarantee the complete nitrification in systems with smaller carriers. Batch experiments showed a high dissolved oxygen (DO) concentration (4 mg/L) and slightly alkaline condition (pH 8.0) had a positive effect on nitrifying coal ash. PRACTITIONER POINTS: The increase size of nitrifier has a negative correlation with particle size of coal ash. The smaller coal ash reduces the adverse effect of high nitrogen on nitrification. The ammonia removal rate reached 99.82% with influent of 1123.35 mg NH 4 + - N /L in the smallest carriers system.

Efficiency of sulfamethoxazole removal from wastewater using aerobic granular sludge: influence of environmental factors

The effects of adsorption, sulfamethoxazole (SMX) content, chemical oxygen demand (COD), and dissolved oxygen (DO) are recognized to be crucial for SMX removal in the aerobic granular sludge (AGS) system. Therefore, we investigated the impact of adsorption and these three different environmental factors on the SMX removal loading rate and removal efficiency of an AGS system, and determined the differences in microbial community composition under different environmental conditions. Adsorption was not the main SMX removal mechanism, as it only accounted for 5% of the total removal. The optimal SMX removal conditions were obtained for AGS when the COD, DO, and SMX concentrations were 600 mg/L, 8 mg/L, and 2,000 µg/L, respectively. The highest SMX removal efficiency was 93.53%. Variations in the three environmental factors promoted the diversity and changes of microbial communities in the AGS system. Flavobacterium, Thauera, and norank_f_Microscillaceae are key microorganisms in the AGS system. Thauera, and norank_f_Microscillaceae were sensitive to increases in SMX concentrations and beneficial for degrading high SMX concentrations. In particular, Flavobacterium abundances gradually decreased with increasing SMX concentrations.

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.

Enhanced nitrogen removal in an aerobic granular sequencing batch reactor under low DO concentration: Role of extracellular polymeric substances and microbial community structure

In this study, the role of extracellular polymeric substances (EPSs) in nitrogen removal and the microbial community structure of aerobic granular sludge (AGS) were analyzed under different dissolved oxygen (DO) conditions (6-7, 4-5, and 2-3 mg·L^-1). The EPSs transported and retained nitrogen in the denitrification process, and the total inorganic nitrogen (TIN) in the EPSs decreased from 6.09 to 5.54 mg·g^-1 MLSS when the DO concentration decreased from 6-7 to 2-3 mg·L^-1. The microbial community showed different core denitrifying bacterial populations involved in nitrogen removal in the AGS system under different DO conditions, with more species when they were higher relative abundances of denitrifying bacteria participating in the nitrogen removal process in AGS under low DO conditions, including Hydrogenophilaceae, Thauera, Enterobacter, Xanthomonadaceae_unclassified, Comalmonadaceae_unclassified, Nitrosomonas and Paracoccus. This study provides a more comprehensive understanding of the DO effect on the TIN removal mechanism by AGS.

Effect of Carbon to Nitrogen Ratio on Water Quality and Community Structure Evolution in Suspended Growth Bioreactors through Biofloc Technology

Application of biofloc technology could effectively treat wastewater. However, the effect of influent carbon to nitrogen ratio (C/N ratio) on water quality and microbial community structure evolution in suspended growth bioreactors (SGBRs) through biofloc technology is still unclear. Here, we show that the total ammonia nitrogen (TAN) and nitrite nitrogen in the effluent of the C/N 10 treatment was significantly higher than that in the C/N 15, C/N 20 and C/N 25 treatments (p < 0.05). Higher TAN removal efficiency was obtained in treatments of C/N 15, C/N 20 and C/N 25, and there was no accumulation of nitrite nitrogen and nitrate nitrogen. Increasing the C/N ratio strengthened the elimination ability of total phosphorus and chemical oxygen demand (COD). The concentrations of TAN and COD first dropped to the lowest level and then increased slightly within one cycle in all treatments. The accumulation of biomass in the reactors increased with the increasing C/N ratio, indicating that a higher C/N ratio was conducive to microbial proliferation. The 16S rRNA sequencing revealed that the microbial community diversity in SGBRs was significantly higher than that in the natural wastewater (P0). The predominant phylum were Proteobacteria, Bacteroidetes and Verrucomicrobia, but Saccharibacteria occupied a dominant position in the late period of the experiment. Pathogens, such as Aeromonas, Acidovorax, Flavobacterium, and Malikia were significantly decreased after high C/N ratio simulative wastewater treating natural wastewater in the reactors. In summary, the water quality and biomass concentrations in SGBRs can be improved under the conditions of influent C/N ratio, equal to or greater than 15.

Simultaneous nitrification, denitrification and phosphorus removal in an aerobic granular sludge sequencing batch reactor with high dissolved oxygen: Effects of carbon to nitrogen ratios

Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) using aerobic granules is a promising approach in water treatment. The present work investigated the effects of influent carbon to nitrogen (N) ratios (20, 10, and 4) on the SNDPR performance in aerobic granular sequencing batch reactors (AGSBR) under high aeration rate. Results revealed that granules remained long-term stability when the DO concentration was 7-8 mg/L. With the decline of COD/N ratios, the denitrification efficiency was reduced due to the accumulation of nitrate, although the removal of COD and TP remained stable with good efficiency. Rising concentration of ammonia N led to the increase of PN/PS ratio of EPS as well as the protein types according to the results of 3D-EEM fluorescence spectroscopy. MiSeq pyrosequencing technology indicated that the decreasing ratio of COD/N under high DO concentration contributed to accumulation of GAOs and DNPAOs rather than PAOs.

Carbon-nitrogen removal in a structured-bed reactor (SBRRIA) treating sewage: Operating conditions and metabolic perspectives

The present study evaluated the efficiency of a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) to promote nitrogen and carbon removal from domestic sewage. The intermittent aeration and the recycling rate of 3 keeps the desired mixing degree inside the SBRRIA. Four different operational conditions were tested by varying the hydraulic retention time (HRT) from 12 to 8 h and aerated and non-aerated periods (A/NA) from 2 h/1 h and 3 h/1 h. At the THD of 8 h and A/NA of 2 h/1 h there was a decrease in the nitrification process (77.5%) due to the increase of organic matter availability, affecting the total-N removal performance. However, by increasing the aerated period from 2 h to 3 h, the nitrification efficiency rose to 91.1%, reaching a total-N removal efficiency of 79%. The system reached a maximum total-N loading removed of 0.117 kgN.m^-3.d^-1 by applying an HRT of 8 h and an intermittent aeration cycle of 3 h, aerated and 1 h non-aerated. The simultaneous nitrification and denitrification (SND) process was related to a complex interplay among microorganisms affiliated mostly to Acidovorax sp., Comamonas sp., Dechloromonas sp., Hydrogenophaga sp., Mycobacterium sp., Rhodobacter sp., and Steroidobacter sp.

A Coordinated Revenue-Sharing Model for a Sustainable Closed-Loop Supply Chain

This study takes a sustainable closed-loop supply chain composed of one manufacturer and two price-competitive retailers as the object and considers the two-way risk aversion characteristics of manufacturers and retailers in examining the coordination mechanism in a closed-loop supply chain. Using game theory, optimal decision-making on wholesale prices, retail prices, and recycling prices are explored under decentralized and centralized decision-making scenarios, and representative expressions are established. By analyzing the effects of the risk aversion coefficient on players’ optimal strategies, we found that the manufacturer’s and retailers’ risk aversion coefficients have different effects on the wholesale price, retail price, and recycling price under decentralized decision-making, while in a centralized decision-making scenario, the effects are the same. The comparison also found that the wholesale price and recovery price under the centralized decision-making scenario are higher than those under decentralized decision-making. To achieve closed-loop supply chain coordination, we propose a revenue-sharing contract that we demonstrate by coordinating price competition with risk aversion and analyze a range of parameters that influence the revenue-sharing contract. The results show that the proposed contract can increase the profits of supply chain members by identifying the optimal revenue-sharing ratio.

Simultaneous nitrification, denitrification and phosphorus removal in aerobic granular sequencing batch reactors with high aeration intensity: Impact of aeration time

A new operating approach by reducing the aeration time while keeping high intensity was evaluated for enhanced nutrients removal and maintenance of granular stability. Three aerobic granular sequencing batch reactors (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) were run at different aeration time (120, 90, and 60 min). Aerobic granules could remain their integrity and stability over long-term operation under high aeration intensity and different time, and shorter aeration time favored the retention of biomass, better settleability, and more production of extracellular polymeric substances (EPS). Besides, efficient and stable reactor performance for carbon and phosphorus were achieved, especially, enhanced nitrogen removal was obtained due to reduction of aeration time. Further exploration revealed that the aeration time shaped the bacterial community in terms of diversity, composition, as well as the distribution of functional groups involving carbon, nitrogen and phosphorus removal.

Study on ammonium and organics removal combined with electricity generation in a continuous flow microbial fuel cell

A continuous microbial fuel cell system was constructed treating ammonium/organics rich wastewater. Operational performance of MFC system, mechanisms of ammonium removal, effect of ammonium on organics removal and energy output, C and N balance of anode chamber and microbial community analysis of anode chamber were studied. It was concluded that 0.0914kg/m³d NH₄⁺-N and 5.739kg/m³d COD were removed from anode chamber and simultaneous nitrification and denitrification (SND) occurred in cathode chamber resulting in COD, TN removal rate of 88.53%, 71.35% respectively. Excess ammonium affected energy output and the MFC system reached maximum energy output of 816.8mV and 62.94mW/m³. In anode chamber, Spirochaetes bacterium sp., Methanobacterium formicicum sp. was predominant in bacteria, archaea communities respectively which contributed to wastewater treatment and electricity generation. This study showed the potential for practical application of continuous flow MFC system treating ammonium/organics rich wastewater and achieving electricity generation simultaneously.

Poultry slaughterhouse wastewater treatment plant for high quality effluent

This paper assesses a wastewater treatment plant (WWTP) regarding the technology used, as well as organic matter and nutrient removal efficiencies aiming to optimize the treatment processes involved and wastewater reclamation. The WWTP consists of a dissolved air flotation (DAF) system, an upflow anaerobic sludge blanket (UASB) reactor, an aerated-facultative pond (AFP) and a chemical-DAF system. The removal efficiencies of chemical oxygen demand (COD) (97.9 ± 1.0%), biochemical oxygen demand (BOD) (98.6 ± 1.0%) and oil and grease (O&G) (91.1 ± 5.2%) at the WWTP, the nitrogen concentration of 17 ± 11 mg N-NH3 and phosphorus concentration of 1.34 ± 0.93 mg PO4(-3)/L in the final effluent indicate that the processes used are suitable to comply with discharge standards in water bodies. Nitrification and denitrification tests conducted using biomass collected at three AFP points indicated that nitrification and denitrification could take place in the pond.

Influence of hydraulic retention time on partial nitrification of continuous-flow aerobic granular-sludge reactor

This study investigated the effects of hydraulic retention time (HRT) at 12 h, 7.2 h and 2.4 h on partial nitrification efficiency of continuous-flow aerobic granular reactors (CFAGRs) with mature aerobic granules (500 +/- 20mg l-1). At HRT 12 h and 7.2h, the removal efficiency of both ammonia-nitrogen (NH4+ - N) and nitrite accumulation rate were exceeding 90%. At HRT 2.4 h, NH4+ - N removal efficiency was reduced but most of the conversion efficiency to nitrite was only slightly reduced. At HRT < 2.4 h, washout of aerobic granules occurred. In all tests conducted herein, the chemical oxygen demand removal efficiencies exceeded 90%. The clone library results noted the presence of ammonia-oxidizing bacteria belonged to beta-Proteobacteria subclass, including 94% of Nitrosomonas europaea and 6% of Nitrosomonas sp. The polymerase chain reaction and denaturing gradient gel electrophoresis results suggested that Alpha proteobacterium, Pseudoxanthomonas mexicana strain, Sphaerotilus natans and Uncultured gamma proteobacterium were responsible for the aerobic granular stability and processing performance. The present CFAGR successfully implemented continuous partial nitrification using aerobic granules at low HRT.

Aerobic granular sludge for simultaneous accumulation of mineral phosphorus and removal of nitrogen via nitrite in wastewater

Lab-scale experiments were conducted to investigate the aerobic granular sludge process for simultaneous phosphorus (P) accumulation by chemical precipitation and biological nitrogen removal via nitrite. The P-rich granules were successfully incubated in a sequencing batch reactor, in which simultaneous nitrification-denitrification occurred via nitrite. The average diameter of the P-rich granules was 2.47 mm and the P content in granules was much higher than that in other granular systems with enhanced biological phosphorus removal process. Filamentous bacteria (genus Thiothrix) in the granules and the long sludge retention time (30 d) of the granular system played a crucial role in accumulation of precipitated phosphate. X-ray diffraction analysis, scanning electron microscopy coupled with energy dispersive X-ray and the experimental design using response surface methodology confirmed that the main mineral patterns in P-rich granules were Ca-Mg phosphate and whitlockite.

Determination of optimum conditions for dairy wastewater treatment in UAASB reactor for removal of nutrients

In this study, the granular sludge was generated for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) and studied on a laboratory scale. Analyzing the nutrients removal percentages from wastewater were scrutinized by using an optimization of the variables, i.e., COD:N:P ratio, OLR, aeration time, MLSS, F:M and HRT. These 6 interrelated parameters were evaluated as the process response. Microscopic observations of the performance of the SNDPR process revealed that the granules included Bacillus sp. in the bacterial community. According to these results, the UAASB system produced an effluent that lends dairy wastewater suitable for land irrigation and that this an attractive process of using granular sludge is appropriate for achieving carbon, nitrogen and phosphorus removal from nutrient-rich wastewater by a biological method.

Simultaneous nitrogen and organic carbon removal in aerobic granular sludge reactors operated with high dissolved oxygen concentration

Simultaneous nitrification and denitrification (SND) together with organic removal in granules is usually carried out without Dissolved Oxygen (DO) concentration control, at "low DO" (with a DO<30-50% of the saturation value, about 3-4 mg/L) to promote anoxic conditions within the aggregates. These conditions can sometimes be in detrimental of the stability of the granules itself due to a lack of shear force. In this work, the authors achieved SND without oxygen control with big sized granules. More specifically, the paper presents a experimentation focused on the analysis of two Sequencing Batch Reactors (SBRs), in bench scale, working with different aerobic sludge granules, in terms of granule size, and high DO concentration, (with concentration varying from anoxic conditions, about DO ∼0 mg/L, to values close to those of saturation, >7-8 mg/L, during feast and famine conditions respectively). In particular, different strategies of cultivation and several organic and nitrogen loading rate have been applied, in order to evaluate the efficiencies in SND process without dissolved oxygen control. The results show that, even under conditions of high DO concentration, nitrogen and organic matter can be simultaneously removed, with efficiency >90%. Nevertheless, the biological conditions in the inner layer of the granule may change significantly between small and big granules, during the feast and famine periods. From point of view of granule stability, it is also interesting that with a particle size greater than 1.5mm, after the cultivation start-up, the granules are presented stable for a long period (about 100 days) and, despite the variations of operational conditions, the granules breaking was always negligible.

High-rate nitrogen removal and its behavior of granular sequence batch reactor under step-feed operational strategy

Alternating anoxic/oxic (A/O) combined with the step-feed granular sequence batch reactor (step-feed SBR) was operated in laboratory scale to investigate nitrogen removal. The results showed that when the total inorganic nitrogen (TIN) and chemical oxygen demand (COD) levels were 55 and 320 mg/L in the influent, the TIN removal efficiencies were 89.7-92.4% in the step-feed mode and 48.1-59.5% in the conventional alternating A/O single-feed mode within a 360 min cycle. The pH and dissolved oxygen (DO) were used to optimize the process of denitrification and nitrification in the step-feed mode. The optimized operational condition was achieved by shortening the cycle time to 207 min, resulting in a nitrogen removal rate of 0.27 kg N/m3 d, which was much higher than those achieved using activated sludge systems. The dominant community in the aerobic granules was coccus-like bacteria, and filamentous bacteria were hardly found. Granules were well maintained throughout the 90 days of continuous step-feed operation.

Treatment of high-ammonium anaerobic digester supernatant by aerobic granular sludge and ultrafiltration processes

Anaerobic sludge digester supernatant characterized by 569 mg TKN L(-1), high color and a COD/N ratio of 1.4 was treated in granular sequencing batch reactors (GSBRs) followed by post-denitrification (P-D) and ultrafiltration (UF) steps. The use of granular sludge allowed for the oxidation of ammonium in anaerobic digester supernatant at all investigated GSBR cycle lengths of 6, 8 and 12 h. The highest ammonium removal rate (15 mg N g(-1) VSS h(-1)) with removal efficiency of 99% was noted at 8 h. Since the GSBR effluent was characterized by a high concentration of nitrites, slowly-degradable substances and biomass, additional purification steps were applied. In P-D stage, the microbial activity of granular biomass in the GSBR effluent was implemented. The P-D was supported by external carbon source addition and the most advantageous variant comprised dosing of half of the theoretical acetate dose for nitrite reduction in the 3-h intervals. The use of the system consisting of the GSBR with 8 h, an optimal P-D variant and a UF for the treatment of anaerobic digester supernatant allowed for the 99%, 71% and 97% reductions of TKN, COD and color, respectively.

Aerobic sludge granulation: a tale of two polysaccharides?

Aerobic sludge granules are suspended biofilms with the potential to reduce the cost and footprint of secondary wastewater treatment. Attempts to answer how and why they form leads to a consideration of the role of their extracellular polymeric substances (EPS) in determining their physical and microbiological properties. The exopolysaccharide components of this matrix, in particular, have received attention as putative structural, gel-forming agents. Two quite different exopolysaccharides have been proposed as the gel-forming constituents, with their gel properties clearly different from those of activated sludge EPS. This review aims to address the question of whether more than one gel-forming exopolysaccharide exist in granules. Based on the available structural data, it seems likely that they are different gel-forming polymers and their differences are not artifacts of the analytical methods used. Nonetheless, both proposed structural gel polymers are extracted and purified based on procedures selecting for anionic polar polysaccharides soluble at high pH, and both contain hexuronic acids. Granulation does not result from EPS synthesis by any single microbial population, nor from production of a single exopolysaccharide. Future studies using solvents suitable for recalcitrant polysaccharides are likely to reveal important structural roles for other polysaccharides. It is hoped that this article will serve as a guide for subsequent studies into understanding the roles of exopolysaccharides in aerobic granular sludge.

Aerobic treatment of dairy wastewater in an industrial three-reactor plant: effect of aeration regime on performances and on protozoan and bacterial communities

An industrial three-reactor plant treating 45 m(3) d(-1) of dairy wastewater was monitored to investigate the effect of different aeration regimes on performance efficiency and to find relationships with bacterial and protozoan communities in the activated sludge. During the study, the plant was maintained at six different "on/off" cycles of the blower (45/15, 15/15, 15/45, 30/30, 30/45 and 30/60 min), providing between 30.2 and 90.6 kg O(2) d(-1), and the main chemical/biochemical parameters (COD, BOD, NH(4)(+), NO(2)(-), NO(3)(-), PO(4)(3-), etc.) were determined. When at least 45.4 kg O(2) d(-1) (30/45) were provided, COD removal efficiencies were always in the range 88-94% but decreased to about 70% under aeration regimes 15/45 and 30/60. Ammonium ion degradation performance was compromised only in the lowest aeration regime (15/45). Total number of protozoa and their species richness, and bacterial viable counts and denaturing gradient gel electrophoresis (DGGE) profiles were used to characterize the microbiota of the activated sludge. Cell abundances and community structures of protozoa and bacteria were very similar in the three aerated reactors but changed with the aeration regimes. In particular, the 15/45 and 30/60 regimes led to low protozoan diversity with prevalence of flagellates of the genus Trepomonas at the expense of the mobile and sessile forms and, thus, to a less efficient activated sludge as indicated by Sludge Biotic Index values (3 and 4.5 for the two regimes, respectively). The structure of the bacterial community strongly changed when the aeration regimes varied, as indicated by the low similarity values between the DGGE profiles. On the contrary, number of viable bacteria and values of the biodiversity index remained stable throughout the whole experimentation. Taken together, the results of the present study clearly indicate that aeration regime variations strongly influence the structure of both protozoan and bacterial communities and, above all, that a high biodiversity among protozoan populations in the activated sludge is prerequisite for high performances in dairy wastewater treatment.

Ammonium removal pathways and microbial community in GAC-sand dual media filter in drinking water treatment

A GAC-sand dual media filter (GSF) was devised as an alternative solution for drinking water treatment plant to tackle the raw water polluted by ammonium in place of expensive ozone-GAC processes or bio-pretreatments. The ammonium removal pathways and microbial community in the GSFs were investigated. The concentrations of ammonium, nitrite and nitrate nitrogen were monitored along the filter. Total inorganic nitrogen (TIN) loss occurred during the filtration. For 1 mg ammonium removal, the TIN loss was as high as 0.35 mg, DO consumption was 3.06 mg, and alkalinity consumption was 5.55 mg. It was assumed that both nitrification and denitrification processes occur in the filters to fit the TIN loss and low DO consumption. During the filtration, nitritation, nitrification and nitritation-anaerobic ammonium oxidation processes probably occur, while traditional nitrification and denitrification and simultaneous nitrification and denitrification processes may occur. In the GSFs, Nitrosomonas and Nitrospira are likely to be involved in nitrification processes, while Novosphingobium, Comamonadaceae and Oxalobacteraceae may be involved in denitrification processes.

A review of the impact and potential of intermittent aeration on continuous flow nitrifying activated sludge

Intermittent aeration of activated sludge plants (ASPs) is a potential strategy that may help deliver reduced operational costs while providing an adequate effluent quality. This review paper critically assesses the implications of temporary turning aeration offin continuous flow nitrifying ASPs, including impact on dissolved oxygen concentrations, process biology and operational parameters. The potential savings and pitfalls of the approach are further illustrated through an example scenario. Findings from this review indicate rapid dissolved oxygen depletion times of 1-60 minutes and a significant reduction of nitrification rates from 0.12 to less than 0.04 g NH4-N/g VSS/d. Further negative impacts include a potential increase in nitrous oxide emissions from 0.07% to 27% N2O-N per mole of NH4-N oxidized; enhanced filamentous bacteria growth; a noticeable increase in effluent turbidity developing within one hour of air supply interruption; and, if no mechanical mixing is in place, risk of mixed liquor suspended solids settling in the bioreactor within short times (23-53 min). However, the potential savings in terms of aeration costs could amount to 33%-45% if instrumentation adequacy and impact on process biology and carbon equivalent emissions are excluded from the economic analysis. Further research on the areas of nitrous oxide emissions and the use of hybrid systems to provide resilience and robustness to the intermittent operation of continuous flow nitrifying ASPs is recommended.