Enhanced aerobic granulation at low temperature by stepwise increasing of salinity

Comparison of nitrification performance in SBR and SBBR with response to NaCl salinity shock: Microbial structure and functional genes

Ammonia removal by nitrifiers at the extremely high salinity poses a great challenge for saline wastewater treatment. Sequencing batch reactor (SBR) was conducted with a stepwise increase of salinity from 10 to 40 g-NaCl·L-1, while sequencing batch biofilm reactor (SBBR) with one-step salinity enhancement, their nitrification performance, microbial structure and interaction were evaluated. Both SBR and SBBR can achieve high-efficiency nitrification (98% ammonia removal) at 40 g-NaCl·L-1. However, SBBR showed more stable nitrification performance than SBR at 40 g-NaCl·L-1 after a shorter adaptation period of 4-15 d compared to previous studies. High-throughput sequencing and metagenomic analysis demonstrated that the abundance and capability of conventional ammonia-oxidizing bacteria (Nitrosomonas) were suppressed in SBBR relative to SBR. Gelidibacter, Anaerolineales were the predominant genus in SBBR, which were not found in SBR. NorB and nosZ responsible for reducing NO to N2O and reducing N2O to N2 respectively had s strong synergistic effect in SBBR. This study will provide a valuable reference for the startup of nitrification process within a short period of time under the extremely high NaCl salinity.

Beyond feast and famine: Cultivating hydrodynamic oxygenic photogranules with better performances under permanent feast regime

Oxygenic photogranules (OPGs) are currently obtained in permanent famine or cyclic feast-famine regimes. Whether photogranulation occurs under a permanent feast regime and how these regimes impact OPGs are unknown. Herein, the three regimes, each applied in two replicate hydrodynamic reactors, were established by different feeding frequencies. Results showed that OPGs were successfully cultivated in all regimes after 24-36 days of photogranulation phases with similar microbial community functions, including filamentous gliding, extracellular polymeric substances production, and carbon/nitrogen metabolism. The OPGs were then operated under the same sequencing batch mode and all achieved efficient removal of chemical oxygen demand (>91 %), ammonium (>96 %), and total nitrogen (>76 %) after different adaptation periods (19-41 days). Notably, the permanent feast regime obtained OPGs with the best physicochemical properties, the shortest adaptation period, and the lowest effluent turbidity, thus representing a novel means of hydrodynamic cultivating OPGs with better performances for sustainable wastewater treatment.

Effects of enhanced biological phosphorus removal on rapid control of sludge bulking and fast formation of aerobic granular sludge

This study investigated the effects of enhanced biological phosphorus removal (EBPR) on rapid sludge bulking control and fast aerobic granular sludge (AGS) formation by adding 20 % of EBPR activated sludge to the bulking activated sludge (BAS) reactor. The results indicate that activating EBPR activity swiftly improved BAS settleability within 16 days, thus resolving sludge bulking issues. Subsequently, a settling time-based selection was employed, resulting in the BAS granulation within another 16 days. The rapid achievement of EBPR activity improved the BAS settleability and facilitated the formation of sludge aggregates, thereby expediting BAS granulation. Inhibition of filamentous bacteria and enrichment of slow-growing organisms contributed to both sludge bulking control and aerobic granulation. Furthermore, the increase in proteins/polysaccharides ratio facilitated the granulation process. Additionally, total nitrogen removal increased from 59.4 % to 71.7 % because of the mature AGS formation. This study provided an approach to simultaneously control sludge bulking and promote aerobic granulation.

Revealing bioresponses of biofilm and flocs to salinity gradient in halophilic biofilm reactor

Understanding the different biological responses to salinity gradient between coexisting biofilm and flocs is crucial for regulating the ecological function of biofilm system. This study investigated performance, dynamics, and community assembly of biofilm system under 3 %-7% salinity gradient. The removal efficiency of NH4+-N remained stable and exceeded 93 % at 3 %-6% salinity, but decreased to below 80 % at 7 % salinity. The elevated salinity promoted the synthesis of extracellular polymer substrates, inhibited microbial respiration, and significantly regulated the microbial community structure. Compared to flocs, biofilm exhibited greater species diversity and richer Nitrosomonas. It was found diffusion limitations dominated the microbial community assembly under the salinity gradient. And microbial network revealed positive interactions predominated the microbial relationships, designating norank Spirochaetaceae, unclassified Micrococcales, Corynebacterium, and Pusillimonas as keystone species. Moreover, distinct salinity preferences in nitrogen transformation-related genes were observed. This study can improve the understanding to the regulation of biofilm systems to salt stresses.

Enhanced biological phosphorus removal sustained by aeration-free filamentous microalgal-bacterial granular sludge

The microalgal-bacterial granular sludge (MBGS) based enhanced biological phosphorus removal (EBPR) (MBGS-EBPR) was recently proposed as a sustainable wastewater treatment process. Previous work showed the possibility of obtaining an MBGS-EBPR process starting from mature MBGS and phosphate-accumulating organisms (PAOs) enriched aerobic granular sludge (AGS) and validated the effectiveness of removing carbon/nitrogen/phosphorus with mechanical aeration. The present work evaluated whether the same could be achieved starting from conventional activated sludge and operating under aeration-free conditions in an alternating dark/light photo-sequencing batch reactor (PSBR). We successfully cultivated filamentous MBGS with a high settling rate (34.5 m/h) and fast solid-liquid separation performance, which could be attributed to the proliferation of filamentous cyanobacteria and stimulation of extracellular polymeric substances (EPS) production. The process achieved near-complete steady-state removal of carbon (97.2 ± 1.9 %), nitrogen (93.9 ± 0.7 %), and phosphorus (97.7 ± 1.7 %). Moreover, improved phosphorus release/uptake driven by photosynthetic oxygenation under dark/light cycles suggests the enrichment of PAOs and the establishment of MBGS-EBPR. Batch tests showed similar phosphorus release rates in the dark but significantly lower phosphorus uptake rates in the presence of light when the filamentous granules were disrupted. This indicates that the filamentous structure of MBGS has minor limitations on substrate mass transfer while exerting protective effects on PAOs, thus playing an important role in sustaining the function of aeration-free EBPR. Microbial assays further indicated that the enrichment of filamentous cyanobacteria (Synechocystis, Leptoolybya, and Nodosilinea), putative PAOs and EPS producers (Hydrogenophaga, Thauera, Flavobacterium, and Bdellovibrio) promoted the development of filamentous MBGS and enabled the high-efficient pollutant removal. This work provides a feasible and cost-effective strategy for the startup and operation of this innovative process.

Deciphering the Role of WWTPs in Cold Environments as Hotspots for the Dissemination of Antibiotic Resistance Genes

Cold environments are the most widespread extreme habitats in the world. However, the role of wastewater treatment plants (WWTPs) in the cryosphere as hotspots in antibiotic resistance dissemination has not been well established. Hence, a snapshot of the resistomes of WWTPs in cold environments, below 5 °C, was provided to elucidate their role in disseminating antibiotic resistance genes (ARGs) to the receiving waterbodies. The resistomes of two natural environments from the cold biosphere were also determined. Quantitative PCR analysis of the aadA, aadB, ampC, blaSHV, blaTEM, dfrA1, ermB, fosA, mecA, qnrS, and tetA(A) genes indicated strong prevalences of these genetic determinants in the selected environments, except for the mecA gene, which was not found in any of the samples. Notably, high abundances of the aadA, ermB, and tetA(A) genes were found in the influents and activated sludge, highlighting that WWTPs of the cryosphere are critical hotspots for disseminating ARGs, potentially worsening the resistance of bacteria to some of the most commonly prescribed antibiotics. Besides, the samples from non-disturbed cold environments had large quantities of ARGs, although their ARG profiles were highly dissimilar. Hence, the high prevalences of ARGs lend support to the fact that antibiotic resistance is a common issue worldwide, including environmentally fragile cold ecosystems.

The acceleration of aerobic sludge granulation by alternating organic loading rate: Performance and mechanism

As a highly promising treatment technology for wastewater, long start-up time is one of the bottlenecks hindering the widespread application of aerobic granular sludge (AGS). This study focused on exploring the possibility of alternating organic loading rate (OLR) in promoting AGS granulation. Under alternating OLR (3.6-14.4 kgCOD/m3·d), AGS granulation was significantly accelerated. The mean granule size under alternating load reached 234.6 μm at 17 d, while under constant OLR (7.2 kgCOD/m3·d), the mean granule size was only 179.2 μm. Moreover, the granule size maintained continuous growth even when the alternating OLR was changed to constant OLR. Alternating load significantly increased the content of extracellular polymeric substances (EPS), especially proteins (PN) in tightly bound EPS (TB-EPS), which was likely the main reason for accelerating AGS granulation. Moreover, alternating load reduced the hydrophilicity of EPS and promoted the content of proteins secondary structures that favored aggregation in TB-EPS, which were also beneficial for granulation. Microbial community results showed that alternating load might promote the enrichment of EPS producing bacteria, such as Thauera, Brevundimonas and Shinella. Meanwhile, the content of enzymes that regulated amino acids metabolism also increased under alternating load, which might be related to the increase of PN in EPS. These results further demonstrated that alternating load promoted granulation through EPS.

Difference of high-salinity-induced inhibition of ammonia-oxidising bacteria and nitrite-oxidising bacteria and its applications

The difficulty in achieving stable partial nitritation (PN) is a challenge that limits the application of mainstream anaerobic ammonium oxidation (anammox). This study proposes high-salinity treatment as a novel strategy for inactivating nitrite-oxidising bacteria (NOB). The study indicated that NOB are more sensitive to high salinity than ammonia-oxidising bacteria (AOB). The inhibitory effect on the nitrifier gradually increased with increasing salinity from 0 to 100 g NaCl/L. After 24 h and 35 g NaCl/L inhibition, the AOB and NOB activities were 36.65% and 7.15% of their original activities, respectively. After one high-salinity treatment, nitrite accumulation rate (NAR) was above 33% during nitrification. Moreover, the sludge characteristics remained almost unchanged after suppression. A novel process for achieving mainstream PN was proposed and evaluated based on the results. An energy consumption analysis showed that mainstream PN/anammox based on the ex situ high-salinity treatment can achieve higher energy self-sufficiency compared with activated sludge.

Aerobic granular sludge treating hypersaline wastewater: Impact of pH on granulation and long-term operation at different organic loading rates

pH is one of the major parameters that influence the granulation and long-term operation of aerobic granular sludge (AGS). In hypersaline wastewater, the impact of pH on granulation and the extent of organic loading rate (OLR) that AGS can withstand under different pH are still not clear. In this study, AGS was cultivated at 3% salinity in three sequencing batch reactors with influent pH values of 5.0, 7.0, and 9.0, respectively, and the OLR was stepwise increased from 2.4 to 16.8 kg COD/m³·d after the granules maturation. The results showed the satisfactory granulation and organic removal under different influent pH conditions, in which the granulation was completed on day 43, 23, and 23, respectively. Neutral influent was the most appropriate for development of salt-tolerant aerobic granular sludge (SAGS), while acidic environment induced the formation of fluffy filamentous granules, and alkaline environment weakened the granule stability. Metagenomic analysis revealed the similar microbial community of neutral and alkaline conditions, with the predominance of genus Paracoccus_f__Rhodobacteraceae. While in acidic environment, fungus Fusarium formed the skeleton of filamentous granules and functioned as the carrier of bacteria including Azoarcus and Pararhodobacter. With the elevation of OLR, SAGSs were found to maintain the compact structure under OLRs of 2.4, 7.2, and 2.4 kg COD/m³·d, and obtain high TOC removal (>95.0%) under OLRs of 7.2, 14.4, and 14.4 kg COD/m³·d, respectively. For hypersaline high-strength organic wastewater, satisfactory TOC removal could also be obtained at broad pH ranges (5.0-9.0), in which neutral environment was the most suitable and acidic environment was the worst. This study contributed to a better understanding of SAGS granulation and treatment of hypersaline high-strength organic wastewater with different pH values.

Low salinity enhances azo dyes degradation in aerobic granular sludge systems: Performance and mechanism analysis

The biodegradation performance of azo dyes can be enhanced under low salinity conditions, but the internal biodegradation mechanism is still unclear. Aerobic granular sludge (AGS), a salt-tolerant biological wastewater treatment technology, was used in this study to explore the enhancement mechanism of acid orange 7 (AO7) degradation at low salinity level (1.0 %). Results indicated that the AGS structure and reactor performance were almost unaffected by different AO7 concentrations (5-10 mg/L). Compared with salt-free conditions, the AO7 removal efficiency was elevated by 9.9 %-19.0 % at 1.0 % salinity level, owing to the enrichment of AO7 decolorizing bacteria (e.g. Acinetobacter) and functional enzymes (e.g. FMN-dependent azoreductase). The up-regulated genes involving in the key metabolic functions (e.g. carbon metabolism and oxidative phosphorylation) promoted the electron and energy production, thereby facilitating the AO7 decolorization and degradation. These results aid understanding of the enhancement mechanism of AO7 biodegradation under low salinity conditions from macroscopic and microscopic perspectives.

Performance and Bacterial Characteristics of Aerobic Granular Sludge in Treatment of Ultra-Hypersaline Mustard Tuber Wastewater

Mustard tuber wastewater (MTW) is an ultra-hypersaline high-strength acid organic wastewater. Aerobic granular sludge (AGS) has been demonstrated to have high tolerance to high organic loading rate (OLR), high salinity, and broad pH ranges. However, most studies were conducted under single stress, and the performance of AGS under multiple stresses (high salinity, high OLR, and low pH) was still unclear. Herein, mature AGS was used to try to treat the real MTW at 9% salinity, pH of 4.1–6.7, and OLR of 1.8–7.2 kg COD/m3·d. The OLR was increased, and the results showed that the upper OLR boundary of AGS was 5.4 kg COD/m3·d (pH of 4.2) with relatively compact structure and high removal of TOC (~93.1%), NH4+-N (~88.2%), and TP (~50.6%). Under 7.2 kg COD/m3·d (pH of 4.1), most of the AGS was fragmented, primarily due to the multiple stresses. 16S rRNA sequencing indicated that Halomonas dominated the reactor during the whole process with the presence of unclassified-f-Flavobacteriaceae, Aequorivita, Paracoccus, Bradymonas, and Cryomorpha, which played key roles in the removal of TOC, nitrogen, and phosphorus. This study investigated the performance of AGS under multiple stresses, and also brought a new route for highly-efficient simultaneous nitrification–denitrifying phosphorus removal of real MTW.

Resistance and adaptation of mature algal-bacterial granular sludge under salinity stress

The study investigated the response characteristics of algal-bacterial granular sludge (ABGS) under salinity stress (0 % → 2 %). At 1 % salinity, the sludge performance was inhibited, while recovered rapidly, indicating the ABGS exhibited resistance. However, at 2 % salinity, the suppressed performances did not recover until the stress was eliminated. Under salinity stress, the nutrient removal capacity of the system and the composition and chemical characteristics of extracellular polymers substances also changed. Meanwhile, the ABGS formed adaptation to salinity stress in the early coping process. As a result, the effect of the second 2 % salinity on ABGS was significantly weakened. High-throughput sequencing results showed that the microbial community in ABGS shifted under salinity stress, and the halophilic bacteria genera Arcobacter, Denitromonas, Azoarcus, etc. were enriched, which might be the genetic basis of the adaptation.

Characterization of a novel micro-pressure double-cycle reactor for low temperature municipal wastewater treatment

To solve the deterioration of effluent caused by low temperature in urban sewage treatment plant in cold areas, a new type of reactor was proposed, the biochemical environmental and low-temperature operating characteristics of the reactor were studied. Through analysis of flow simulation and dissolved oxygen (DO) distribution when the aeration rate was 0.6 m³/h, it showed that there were many different DO environments in the reactor at the same time, which provided favourable conditions for various biochemical reactions. The operation test showed that the average effluent removal rate of COD, TN, NH₄⁺-N and TP was 92.53%, 74.57%, 89.61% and 96.04%, respectively. And there were a variety of functional bacteria related to nitrogen and phosphorus removal in the system, most of them with strong adaptability at low temperatures. Among the dominant microorganisms, Flavobacterium and Rhodobacter were related to denitrification, Aeromonas and Thiothrix were related to phosphorous removal. Denitrifying phosphorus removal was the main way of phosphorus removal. Picrust2 results showed that the reactor operated well at low temperature, and the regional difference distribution of nitrification genes further confirmed the existence of functional zones in the reactor. The results showed that the Micro-pressure Double-cycle reactor worked well at low temperature, which provided a new idea and way for the upgrading of urban sewage treatment plants in cold areas.

Performance enhancement and population structure of denitrifying phosphorus removal system over redox mediator at low temperature

The development of denitrifying polyphosphate accumulating organisms (DPAOs) presents a strategy to carbon competition between denitrifying bacteria and phosphorus removing bacteria. However, low temperature inhibits the rate of enzyme-catalyzed and substrate diffusion during denitrifying phosphorus removal (DPR). Therefore, the present study assessed the addition of NQS (100 μmol/L) for enhancing the removal of TP and TN in DPR reactors operated at alternating anaerobic and anoxic phases and different influent phosphate concentrations. The results showed that the removal efficiency of TP and TN in NQS-DPR system at 10 °C were 99.9% and 42.0%, respectively, which were 2.1 and 2.0 times higher than that of DPR system. Adding NQS significantly alleviated the increase of pH under anoxic condition and decreased the ORP value of the reactor, which in turn enhanced the PHAs accumulation process. The determination of functional genes (nirK, narG and phoD) showed that Dechloromonas, Lentimicrobium, and Terrimonas were the dominant functional bacteria in NQS-DPR system at 10 °C with the relative abundance of 3.09%, 2.99% and 2.28%, respectively. This study can provide valuable information for the effects of the addition of the redox mediator on denitrifying phosphorus removal technology.

Laboratory-scale study of a biodegradable microplastic polylactic acid stabilizing aerobic granular sludge system

The effects of microplastics on aerobic granular sludge technology are an emerging issue, although the impact of degradable microplastics (DMPs) on the aerobic granular system is still unexplored. In this study, degradable microplastic polylactic acid (DMP-PLA) was added at three concentrations (5, 15, 40 mg/L), which strengthened the granular stability and consequently stabilized pollutant removal compared to the control (without DMP-PLA). The experiment showed that adding DMP-PLA made cells secrete more extracellular polymeric substances [64.8 mg/g MLVSS (mixed liquor suspended solids)], particularly retaining β-D-glucopyranose polysaccharides in experimental group. In addition, abundant hydrogen bonds were also maintained. The reactor under the stress of DMP-PLA exhibited high pollutant removal efficiency (COD>88%, TP>91%, TIN>86%), indicating high performance of the microbes. Microbial analysis at the genus level indicated that Defuviicoccus and Candidatus_Competibacter were dominant after DMP-PLA addition, which identified denitrifying glycogen-accumulating organisms as beneficial for nitrogenous compound removal. Redundancy analysis showed that the abundance of Candidatus_Competibacter was positively related to the addition of DMP-PLA. This study demonstrated that DMP-PLA was feasibly employed in the aerobic granular water treatment process, and presents a new method to optimize the stability and extracellular secretion of the microbial community.

The effect of salinity on ammonium-assimilating biosystems in hypersaline wastewater treatment

The ammonium-assimilating biosystem is a promising solution to improve the susceptible biological nitrogen removal (BNR) and to achieve nitrogen recovery in saline wastewater treatment. However, the treatment performance and functional stability of ammonium-assimilating biosystems have not been fully illuminated in hypersaline wastewater. In this study, although the dramatic decrease of removal efficiency of NH₄⁺-N and PO₄^3--P was observed in ammonium-assimilating biosystems under the salinity from 3% to 7%, the direction of nitrogen conversions through assimilation was insusceptible to high salinity. The extremely low concentrations of nitrite and nitrate accumulation and abundances of nitrification functional genes confirmed that the process of nitrification was negligible in all biosystems. Ammonium-assimilating biosystems maintained robustness and functional stability in hypersaline wastewater. The increase of salinity stimulated the production of EPS and changed the microbial community by enriching Proteobacteria and halophilic genera. We anticipate that the ammonium-assimilating biosystem could be a promising strategy for hypersaline wastewater treatment and future practical applications.

Enhanced aerobic granular sludge by static magnetic field to treat saline wastewater via simultaneous partial nitrification and denitrification (SPND) process

Saline wastewater poses a threat to biological nitrogen removal. This study investigated whether and how static magnetic field (SMF) can improve the salt-tolerance of aerobic granular sludge (AGS) in two simultaneous partial nitrification and denitrification (SPND) reactors. Results confirmed that the SMF improved the mean size and settleability of granules, stimulated secretion of extracellular polymeric substances with high protein content, in turn enhancing the aerobic granulation. Although high salt stress inhibited functional microorganisms, the SMF maintained better SPND performance with average COD removal, TN removal and nitrite accumulation ratio finally recovering to 100%, 72.9% and 91.1% respectively. High throughput sequencing revealed that functional bacteria evolved from Paracoccus to halotolerant genera Xanthomarina, Thauera, Pseudofulvimonas and Azoarcus with stepwise increasing salinity. The enhanced salt-tolerance may be because the SMF promoted the activity of these halotolerant bacteria. Therefore, this study proposes an economic, effective and environmental biotechnology for saline wastewater treatment.

Phosphorus deficiency leads to the loosening of activated sludge: The role of exopolysaccharides in aggregation

Whether phosphorus deficiency in influent will affect the aggregation and sedimentation of activated sludge needs to be further clarified. This paper systematically studied the structure, aggregation and settlement of activated sludge, and the composition, properties and chemical structure of extracellular polymers and microbial community structure of sludge under different influent phosphorus contents to determine the causes of sludge aggregation and structural deterioration. The results show that phosphorus deficiency in influent leads to a decrease in the aggregation capacity and a loose structure of activated sludge, and the reduction of hydrophobic interactions is the main factor of sludge aggregation and structural deterioration. The content, functional groups and protein secondary structure of extracellular protein were almost unchanged. An increase in the content and hydrophilicity of extracellular polysaccharide (PS) results in a decrease in sludge hydrophobicity. Under phosphorus deficiency, the changes in microbial species related to PS secretion were the reasons for the increase in PS content and hydrophilicity. The negative effects of PS content and hydrophilicity on sludge aggregation and structure are important findings of this work and are expected to be useful for better understanding the restoration of activated sludge performance in the treatment of phosphorus-deficient wastewater.

Recovery of structure and activity of disintegrated aerobic granular sludge after long-term storage: Effect of exogenous N-acyl-homoserine lactones

Long-term storage of aerobic granular sludge (AGS) may lead to granule inactivation and disintegration. Granule recovery in both structure and activity is important for scale-up and stability of AGS, but information about the structure recovery of stored AGS is limited. In addition, whether short-term exogenous N-acyl-homoserine lactones (AHLs) regulations could accelerate the granule recovery and sustain positive effects on AGS is unknown. Herein, the recovery of 33-month stored AGS was performed in three reactors for 38 days (phase I) at different exogenous AHLs concentrations (0, 50 and 500 nM of AHL-mixtures in R0, R1 and R2, respectively) and for an extended 45 days without exogenous AHLs (phase II). Results demonstrated successful recovery of disintegrated AGS in all reactors, although it was relatively time-consuming in R0. The treatment performance was similar among the reactors and steady-state removal of COD (90%) and NH₄⁺-N (94%) could be recovered within 7 and 21 days, respectively. However, exogenous AHLs regulation (especially in R1) obviously accelerated bioactivity recovery of heterotrophs and nitrifiers and improved granule characteristics, including biomass, density, hydrophobicity and extracellular polymeric substance (EPS). During phase II, sustainable positive effects remained in R1, but granule characteristics deteriorated in R2. The abundance of functional genera Thauera, Nitrosomonas and Candidatus_Nitrotoga, contributed to the rapid recovery and helped maintain the structure and activity of AGS. The predictive functional profiling of bacterial communities also demonstrated sustainably higher activities of metabolism, growth and signal sensing under exogenous AHLs regulation at an appropriate content.

Dynamic characteristics of microbial community and soluble microbial products in partial nitrification biofilm system developed from marine sediments treating high salinity wastewater

High salinity wastewater generally resulted in microorganism death and low treatment efficiency of nutrient in conventional activity sludge system. Marine sediments, containing a huge amount of natural salt-tolerant microorganisms, provide a feasible option for the rapid construction of halophilic biological treatment system. However, the dynamic of native microorganisms and the fate of soluble microbial products (SMP) in halophilic biofilm system developed from marine sediments needs to be further studied. In this study, a partial nitrification system was successfully established by inoculation of marine sediments in sequential batch biofilm reactor. Satisfactory chemical oxygen demand (COD) and NH₄⁺-N removal efficiency (95% and 99%) and nitrite accumulation rate (NAR) (>90%) was achieved for treatment of synthetic seawater blackwater. High cell surface hydrophobicity (CSH) and proteins to polysaccharide ratio of extracellular polymeric substance (EPS) were beneficial to the initial biofilm formation. High-throughput sequencing results revealed Nitrosomonas halophila was the sole ammonia oxidizing bacteria (AOB). Thauera and Paracoccus were the main denitrifying bacteria in three biofilm samples. Excitation emission matrix (EEM) spectroscopy coupled with parallel factor analysis (PARAFAC) clarified that proteins were significantly degraded than the other two components (humic-like and fulvic acid-like substance). This study will provide a feasible approach for developing halophilic biological treatment system and present an in-depth insight of the dynamic characteristics of SMP in partial nitrification biofilm system.

Response and recovery of mature algal-bacterial aerobic granular sludge to sudden salinity disturbance in influent wastewater: Granule characteristics and nutrients removal/accumulation

The impact of sudden salinity (1-3%) disturbance in influent wastewater on mature algal-bacterial aerobic granular sludge (AGS) was investigated, in addition to its recovery possibility when salinity disturbance was removed. Results show that the mature algal-bacterial AGS with less filamentous could maintain its good settleability with sludge volume index below 41 mL/g when wastewater salinity was increased to 3%, in which loosely bound extracellular polymeric substances might play an important role. Under this condition, the granule system achieved slightly lower dissolved organic carbon removal (from 97% to 94%), while the removals of ammonia nitrogen, total nitrogen and total phosphorus were remarkably decreased from ~100%, 66% and 70% to 23%, 16% and 38%, respectively. However, the organics and nutrients removals could be recovered immediately when the salinity disturbance was removed from the influent. P bioavailability, on the other hand, kept almost stable (93-97%) in the AGS during the examination period.

Importance of exopolysaccharide branched chains in determining the aggregation ability of anammox sludge

The high aggregation ability of anammox granular sludge is an issue of wide concern; however, the mechanism needs to be further clarified. In this study, selective hydrolysis experiments were performed to determine the role of exopolysaccharide (PS) branched chains and proteins for the aggregation mechanism of anammox granular sludge. The results revealed that selective hydrolysis of proteins hardly affected the granular aggregation while the hydrolysis of PS branched chains led to a decrease in the sludge zeta potential by 17.3% (β-amylase group) and 24.1% (isoamylase group), a decrease of hydrophobicity by 11.6% (β-amylase group) and 17.7% (isoamylase group), an increase of surface free energy by 36.8% (β-amylase group) and 55.1% (isoamylase group) and the deterioration of the PS self-assembly ability. In addition, FTIR and XPS spectra analysis showed that the disruption of PS branched chains resulted in a higher proportion of hydrophilic and electronegative groups, which hindered bacterial aggregation, which was further confirmed by XDLVO theory. The key role of the PS chain structure in sludge aggregation is a critical finding of this work that provides helpful insights for the application of anammox process.