Effect of food-to-microorganisms ratio on aerobic granular sludge settleability: Microbial community, potential roles and sequential responses of extracellular proteins and polysaccharides

Biofouling control strategy through denatured extracellular proteins: An empirical evidence from reclaimed water distribution systems

Biofouling remains a significant challenge in water treatment fields, leading to a decline in the hydraulic performance, increased operational costs, and potential health risks. Previous biofouling control strategies primarily focused on the removal of particulates and microorganisms, often neglecting the role of extracellular proteins. Using a reclaimed water distribution system as an example, this study proposes a strategy to inhibit biofouling formation by utilizing urea, a reported protein denaturant with fertilizer functionality. Results indicated that urea significantly slowed the accumulation of biofouling, leading to a 16.4-49.4 % decrease in biofouling weight, an 18.6-55.3 % decrease in extracellular protein content, and a 25.9-45.3 % reduction in extracellular polymer substance (EPS) content. Urea mitigated biofouling through two mechanisms: (1) disrupting protein structures, which convert tightly bound EPS to loosely bound EPS, and (2) downregulating biofilm-forming signaling proteins, thereby inhibiting biofouling formation. In the process, proteins, polysaccharides, and microorganisms exhibited clear mutual promotion relationships. Additionally, urea weakened microbial symbiotic interactions by affecting protein signaling molecules, inhibiting microbial growth and polysaccharide metabolism. The research confirms that denaturing extracellular proteins to mitigate biofouling is a feasible and efficient approach. The findings aim to provide valuable insights for the development of sustainable and effective biofouling cleaning strategies.

Unravelling the mechanism of residual sludge promoting rapid formation of microalgal-bacterial granular sludge: Enhancement of extracellular polymers substances and electron transfer efficiency

Microalgal-bacterial granular sludge (MBGS) is a sustainable biotechnology that has attracted increasing attention, but there remains limited knowledge about the utilization of residual sludge generated from MBGS. This present work proposed a promising approach to rapidly construct the MBGS system from activated sludge by inoculating residual microalgal-bacterial sludge. Compared with inoculated activated sludge, the newly formed MBGS maintained a stable structure, higher biomass content (4.51 g/L), better settleability (42 mL/g), and higher pollutant removal. The results indicated that inoculation of residual sludge resulted in higher extracellular polymeric substances (EPS) content and promoted the microbial aggregation. Besides, this increase effectively improved the electron transfer efficiency within the particle, which facilitated the granulation of MBGS. Microbial community analysis revealed that the dominant bacteria (Pseudofulvimonas and Thauera) were mainly responsible for the secretion of EPS. Furthermore, the nitrogen and phosphorus metabolic pathways were also promoted to some certain extent. In conclusion, the inoculation of residual sludge can achieve an effective reduction in granulation period. This study provides a novel insight and fills the gap in the utilization of residual sludge generated by MBGS.

Influence of saline stress in alternating pulses on aerobic granulation and resource production using different inoculum sources

Aerobic granular sludge (AGS) is a promising technology for wastewater treatment, particularly for its ability to recover valuable resources such as polyhydroxyalkanoates, alginate-like exopolysaccharide, and phosphorus. However, achieving stable granule formation remains a significant challenge. Research has shown that the addition of salt can accelerate the granulation process and enhance bioresource production. The source of the seed biomass is also critical for the system's success, with most AGS studies using activated sludge as the inoculum. This study aims to compare granulation, reactor performance, and bioresource recovery outcomes using inocula from different sources while also evaluating the impact of saline stress. Four sequential batch reactors were monitored, differing in the type of inoculum sludge (biomass from an aerated biofilter or activated sludge systems) and the presence of NaCl in the feed. The saline feed alternated between cycles containing 5 gNaCl/L and conventional feed without NaCl. Osmotic pressure was found to favor granulation and solids accumulation in both types of biomasses. Reactors inoculated with activated sludge and subjected to salt addition achieved complete granulation more rapidly. In contrast, reactors inoculated with submerged aerated biofilter sludge exhibited higher solids concentrations. All systems demonstrated excellent chemical oxygen demand removal, with activated sludge reactors showing superior performance in ammonia and total nitrogen removal and bioresources recovery. Salt addition stimulated the production of extracellular polymeric substances and amino acids such as tyrosine and tryptophan while reducing the intensity of fulvic acid-like substances, irrespective of the inoculum type.

Solids retention time (SRT) control in the co-treatment of leachate with domestic sewage in aerobic granular sludge systems: Impacts on system performance, operational stability, and bioresource production

This study investigates the co-treatment of leachate and domestic sewage in municipal wastewater treatment plants using aerobic granular sludge (AGS) systems, focusing on granule formation, system stability, and resource production in two units (R1 and R2). In R2, solids retention time (SRT) was controlled between 10 and 25 days, while R1 maintained approximately 9 days. The results show that low leachate proportions (5 %) did not affect system performance or stability. However, increasing the leachate to 10 % reduced the structural stability of extracellular polymeric substances (EPS), leading to a significant decrease in alginate-like exopolysaccharides (ALE) production in R1 (216 mgALE/gVSS) and R2 (125 mgALE/gVSS). Principal component analysis revealed that SRT was crucial for optimizing biopolymer synthesis. Furthermore, SRT control in R2 improved filamentous control, biomass retention, and total nitrogen removal. Thus, selective biomass discharge is essential for maintaining granule stability, enhancing treatment efficiency, and supporting resource production.

Inhibition of denitrification and enhancement of microbial interactions in the AGS system by high concentrations of quinoline

Quinoline represents a highly toxic and structurally stable nitrogen-containing heterocyclic compound in coking wastewater, posing a potential threat to human beings and the ecological environment. In this study, we investigated the impact of gradually elevating quinoline concentration on pollutant removal efficiency, sludge characteristics, microbial community and their interactions in the aerobic granular sludge (AGS) system. The results demonstrated that AGS was capable of effectively degrading quinoline, with a final removal rate of 90 mg/L quinoline reaching 98.54 ± 0.28%. Notably, the denitrification process was significantly impeded in the presence of 90 mg/L quinoline, with the Phase D effluent displaying a notably high NO3--N concentration of 37.09 ± 21.81 mg/L, primarily attributed to the reduced abundance of norank_f_A4b bacteria. As the quinoline concentration increased, the sludge particle size diminished from 3.46 to 2.60 mm, while the settling performance deteriorated significantly, escalating from 31.29 ± 1.63 mL/g to 62.32 ± 2.87 mL/g. Meanwhile, the protein (PN) content in EPS gradually increased (from 19.87 ± 0.88 mg/g MLVSS to 51.22 ± 3.21 mg/g MLVSS), while the polysaccharide (PS) content fluctuated. Quinoline profoundly modified microbial community composition and structure, with deterministic processes dominating community assembly. Network analysis indicated intensified and complex microbial interactions at 90 mg/L quinoline, characterized by significantly higher positive correlations. In addition, rare taxa (RT) dominated the network nodes, with 74 of 93 key species belonging to RT, highlighting their pivotal roles in sustaining system functions and strengthening microbial connections. This study provides new insights into the effects of quinoline on microbial community structure and interactions in AGS system.

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

Aerobic granulation and resource production under continuous and intermittent saline stress

Three sequential batch reactors (SBR) were operated to evaluate salt addition's impact on granulation, performance, and biopolymer production in aerobic granular sludge (AGS) systems. System R1 was fed without adding salt (control); system R2 operated with saline pulses, i.e., one cycle with salt (2.5 g NaCl/L) addition followed by another without salt; and R3 received continuous supplementation of 2.5 g NaCl/L. The results indicated that the reactors supplemented with salt presented higher concentrations of mixed liquor volatile suspended solids (MLVSS) and better settleability than R1, showing that osmotic pressure contributed to biomass growth, accelerated granulation, and improved physical characteristics. The faster granulation occurred in R2, thus proving the beneficial effects of intermittent salt addition through alternating pulses. Salt addition did not impair the simultaneous removal of carbon, nitrogen, and phosphorus. In fact, R2 showed better carbon removals. In conclusion, continuous or intermittent (pulsed) supplementation of 2.5 g NaCl/L did not lead to increased production of extracellular polymeric substances (EPS) and alginate-like exopolymers (ALE). This outcome could be attributed to the low saline concentration employed, a higher food-to-microorganism (F/M) ratio observed in R1, and possibly greater endogenous consumption of biopolymers in the famine period in R2 and R3 due to the greater solids retention time (SRT). Therefore, this study brings important results that contribute to a better understanding of the effect of salt in continuous dosing or in pulses as a selection pressure strategy to accelerate granulation, as well as the behavior of the AGS systems for saline effluents.

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.

Aerobic digestibility of waste aerobic granular sludge (AGS) assessed by respirometry, physical-chemical analyses, modeling and 16S rRNA gene sequencing

Research has evolved on aerobic granular sludge (AGS) process, but still there are very few studies on the treatment of excess AGS sludge, with almost none considering its aerobic digestion. Here therefore, the aerobic digestibility of typical AGS sludge was assessed. Granules were produced from acetate-based synthetic wastewater (WW) and were subjected to aerobic digestion for 64 d. The stabilization process was monitored over time through physical-chemical parameters, oxygen uptake rates (OUR) and 16S rRNA gene sequencing. The microbial analyses revealed that the cultivated granules were dominated by slow-growing bacteria, mainly ordinary heterotrophic organisms with potential for polyhydroxyalkanoates (PHA) aerobic storage (PHA-OHOs), polyphosphate and glycogen accumulating organisms (PAOs and GAOs), fermentative anaerobes and nitrifiers (AOB and NOB). Differential abundance analysis of the bacterial data (before versus after digestion) discriminated between the most vulnerable microbiome genera and those most resistant to aerobic digestion. Furthermore, modeling of the stabilization process determined that the endogenous decay rate constant (bH) for the heterotrophs present in the granules was notably low; bH = 0.05 d-1 (average), four times less than for common activated sludge (AS), which is rated at 0.2 d-1. For first time, the research reveals another important feature of AGS sludge, i.e. the slow-decaying character of its bacteria (along with their known slow-growing character). This results in slower stabilization, need of bigger digesters and reconsideration of the specific OUR limits in biosolids regulations (SOUR limit of 1.5 mg/gTSS.h), for waste AGS compared to conventional waste AS. The study suggests that aerobic digestion of waste AGS (fully-granulated) could differ from that of conventional AS. Future work is needed on aerobic digestibility of real AGS sludges from municipal and industrial WWs, compared to synthetic WWs.