Formation and characterisation of fungal and bacterial granules under different feeding alkalinity and pH conditions

Anticancer drugs drive changes in the performance, abundance, diversity, and composition of eukaryotic communities of an aerobic granular sludge system

Anticancer drugs are emerging contaminants that are being increasingly detected in urban wastewater. However, there is limited knowledge on the use of biological wastewater treatments, such as granular sludge systems (AGSs), to remove these substances and on their impacts on the general performance of the system and the eukaryotic communities in the granules. We investigated the impacts of three anticancer drugs commonly found in wastewater treatment plants and applied at three different concentrations on the removal efficiency of anticancer drugs, physicochemical parameters, and the eukaryotic microbiome of an AGS operated in a sequential batch reactor (SBR). Anticancer drugs applied at medium and high concentrations significantly decreased the removal efficiency of total nitrogen, the granular biomass concentration, and the size and setting velocity of granules. However, these effects disappeared after not adding the drugs for about a month thus showing the plasticity of the system to return to original levels. Regardless of the concentration of anticancer drugs tested, the AGS technology was effective in removing these substances, with removal rates in the range of 68.5%-100%. The presence of anticancer drugs at medium and high concentrations significantly decreased the abundance of total fungi, an effect that was linked to changes in the physicochemical parameters. Anticancer drugs also induced decreases in the diversity of the eukaryotic community, altered the community composition, and reduced the network complexity when applied at medium and high concentrations. Taxa responsive to the presence of anticancer drugs were identified. The diversity and composition of the eukaryotic microbiome returned to original diversity levels after not adding the drugs for about a month. Overall, this study increases our understanding of the impacts of anticancer drugs on the performance and eukaryotic microbiome of an AGS and highlights the need for monitoring these substances.

Granule formation mechanism, key influencing factors, and resource recycling in aerobic granular sludge (AGS) wastewater treatment: A review

The high-efficiency and additionally economic benefits generated from aerobic granular sludge (AGS) wastewater treatment have led to its increasing popularity among academics and industrial players. The AGS process can recycle high value-added biomaterials including extracellular polymeric substances (EPS), sodium alginate-like external polymer (ALE), polyhydroxyfatty acid (PHA), and phosphorus (P), etc., which can serve various fields including agriculture, construction, and chemical while removing pollutants from wastewaters. The effects of various key operation parameters on formation and structural stability of AGS are comprehensively summarized. The degradable metabolism of typical pollutants and corresponding microbial diversity and succession in the AGS wastewater treatment system are also discussed, especially with a focus on emerging contaminants removal. In addition, recent attempts for potentially effective production of high value-added biomaterials from AGS are proposed, particularly concerning improving the yield, quality, and application of these biomaterials. This review aims to provide a reference for in-depth research on the AGS process, suggesting a new alternative for wastewater treatment recycling.

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.

Challenges of aerobic granular sludge utilization: Fast start-up strategies and cationic pollutant removal

Aerobic granular sludge (AGS) is a self-aggregated microorganism consortium with pollutant removal properties. The aim of this work is to study and review the application of aerobic granules for water treatment with special focus on new applications and methodologies. Carbon-nitrogen containing pollutants are the classic targets of AGS technology. Carbon and nitrogen removal of AGS are classified as a biodegradation process. More recently, the AGS granules have been studied as sorbent materials for wastewater treatment. In particular, the sorption of cationic pollutants has been studied through biosorption and bioaccumulation mechanisms without distinguishing when one or the other process is involved. AGS conformation made them suitable for complex wastewater treatment. Indeed, several studies have demonstrated the removal of polyvalent cationic pollutants even with higher capacity than conventional sorbent materials. However, this was achieved almost exclusively for synthetic substrates, with single cation evaluation and using in some cases only qualitative measures. For successful industrial AGS application in complex substrates, it is necessary to evaluate and demonstrate the technology in real industrial conditions and reduce the currently long start-up times which limits its utility. Two new strategies have been proposed: autoinducer molecules and the production of artificial granular from common active sludge with commercial alginate. Finally, the increase of research on AGS cations assimilation properties will allow a new point of view, where granules will be materials for the recovery of valuable metals from industrial wastewater streams.

Formation, application, and storage-reactivation of aerobic granular sludge: A review

It was an important discovery in wastewater treatment that the microorganisms in the traditional activated sludge can form aerobic granular sludge (AGS) by self-aggregation under appropriate water quality and operation conditions. With a typical three-dimensional spherical structure, AGS has high sludge-water separation efficiency, great treatment capacity, and strong tolerance to toxic and harmful substances, so it has been considered to be one of the most promising wastewater treatment technologies. This paper comprehensively reviewed AGS from multiple perspectives over the past two decades, including the culture conditions, granulation mechanisms, metabolic and structural stability, storage, and its diverse applications. Some important issues, such as the reproducibility of culture conditions and the structural and functional stability during application and storage, were also summarized, and the research prospects were put forward. The aggregation behavior of microorganisms in AGS was explained from the perspectives of physiology and ecology of complex populations. The storage of AGS is considered to have large commercial potential value with the increase of large-scale applications. The purpose of this paper is to provide a reference for the systematic and in-depth study on the sludge aerobic granulation process.

Medium-chain fatty acids production from carbohydrates-rich wastewater through two-stage yeast biofilm processes without external electron donor addition: Biofilm development and pH impact

The production of medium-chain fatty acids (MCFAs) is considered promising for carbon resource recovery from waste streams. However, a large quantity of external electron donors are often required, causing great cost and environmental impact. Therefore, in this study, a two-stage technology was developed to produce MCFAs from carbohydrate-rich wastewater without external electron donor addition, with the biofilm development and pH impact being explored. Stage I aimed at converting organics into ethanol and a yeast biofilm reactor is innovatively applied. The results showed that the yeast biofilm could quickly form on carriers with steady-state thickness reaching 50-200 μm. However, the attachment of yeast biofilm was weak at the initial stage so that the violent turbulence should be avoided during operation. The polyurethane foam was the most suitable for yeast biofilm development among the tested carriers, as evidenced by the highest ethanol production, accounting for 74.2% of soluble organics. The Nakaseomyces was the main fungal genus in the steady-state biofilm, while lactic acid bacteria were also developed, resulting in lactate and acetate production. In Stage II, the yeast biofilm reactor effluent was applied for MCFA production at different pH (5-8). However, the MCFA production selectivity was significantly affected by pH, with 65.2% at pH of 5 but decreasing substantially to 3.0% at pH of 8. Both the microbial and electron transfer efficiency analysis suggested that mildly acidic pH can promote the electron transfer from ethanol toward the chain elongation process instead of its excessive oxidation. Thus, if conditions of online extraction or microbial tolerance permit, a lower pH should be recommended for Stage II in the developed technology as well as other ethanol-based MCFA production process. This is a conceptual study that eliminated external electron donor addition in MCFAs production and provide a sustainable and reliable way in carbon resources recovery.

Alternating nitrogen feeding strategy induced aerobic granulation: Influencing conditions and mechanism

Effective cultivation of stable aerobic granular sludge (AGS) is a crucial step in the successful application of this technology, and the formation of AGS could be facilitated by some environmental stress conditions. Four identical sequencing batch reactors (SBRs) were established to investigate the aerobic granulation process under the same alternating ammonia nitrogen feeding strategy superimposed with different environmental conditions (inorganic carbon source, temperature, N/COD). Although various superimposed conditions induced a significant difference in the size, settling velocity, mechanic strength of AGS, mature aerobic granules could be successfully obtained in all four reactors after 70 days' operation, indicating the alternating ammonia nitrogen feeding strategy was the most critical factor for AGS formation. Based on the results of redundancy analysis, the presence of an inorganic carbon source could facilitate the cultivation of AGS with nitrification function, while the moderate temperature and fluctuant N/COD might benefit the cultivation of more stable AGS. In addition, superimposed stress conditions could result in the difference in the microbial population between four reactors, but the population diversity and abundance of microorganisms were not the determinants of AGS formation. This study provided an effective method for the cultivation of AGS by using alternating ammonia nitrogen feeding strategy.

The Role of Melanin in the Biology and Ecology of Nematophagous Fungi

Melanin is a heteropolymer formed by the polymerization of phenolic and indolic compounds. It occurs in organisms across all biological kingdoms and has a range different of functions, thus indicating its important evolutionary role. The presence of melanin offers several protective advantages, including against ultraviolet radiation, traumatic damage, oxidative stress, extreme temperatures, and pressure. For many species of fungi, melanin also participates directly in the process of virulence and pathogenicity. These organisms can synthesize melanin in two main ways: using a substrate of endogenous origin, involving 1,8-dihydroxynaphthalene (DHN); alternatively, in an exogenous manner with the addition of L-3, 4-dihydroxyphenylalanine (L-DOPA or levodopa). As melanin is an amorphous and complex substance, its study requires expensive and inaccessible technologies and analyses are often difficult to perform with conventional biochemical techniques. As such, details about its chemical structure are not yet fully understood, particularly for nematophagous fungi that remain poorly studied. Thus, this review presents an overview of the different types of melanin, with an emphasis on fungi, and discusses the role of melanin in the biology and ecology of nematophagous fungi.

Understanding the dependence of start-up and stability of aerobic granule on pH from the perspective of adhesion behavior and properties of extracellular polymeric substances

The start-up and stability of aerobic granular sludge (AGS) could be greatly influenced by pH variation. The inner core in the aerobic granules provided adhesion sites for microbes by extracellular polymeric substances (EPS) adhesion, the adhesion behavior of EPS and the properties of adhesion layer formed by EPS with pH changes might directly affect the start-up efficiency and stability of AGS. In this study, the adhesion behavior of EPS at an inorganic surface and the viscoelasticity of the EPS adhesion layer with pH variation was investigated by quartz crystal microbalance with dissipation monitoring, and the response of functional groups and intermolecular interactions to pH changes was explored. Based on the interaction energy calculation, it was found that the charge repulsion between substances dominated the interactions between EPS components and between EPS and the surface by regulating protonation and deprotonation of the functional groups of EPS with pH variation. A lower energy barrier between EPS and the surface at a lower pH value could facilitate the adhesion of EPS at the surface, which favored the rapid start-up of AGS. Moreover, the high ratio of both α-helix and intermolecular hydrogen bond at an acid condition could enhance the gel-strength of EPS, which provide AGS the resistance ability against external disturbance. This study revealed the mechanism of the interactions in EPS adhesion process with the variation of pH and provided useful information for a better understanding of the stability of the AGS.

Pool choice in a vertical landscape: Tadpole-rearing site flexibility in phytotelm-breeding frogs

Many species of Neotropical frogs have evolved to deposit their tadpoles in small water bodies inside plant structures called phytotelmata. These pools are small enough to exclude large predators but have limited nutrients and high desiccation risk. Here, we explore phytotelm use by three common Neotropical species: Osteocephalus oophagus, an arboreal frog that periodically feeds eggs to its tadpoles; Dendrobates tinctorius, a tadpole-transporting poison frog with cannibalistic tadpoles; and Allobates femoralis, a terrestrial tadpole-transporting poison frog with omnivorous tadpoles. We found that D. tinctorius occupies pools across the chemical and vertical gradient, whereas A. femoralis and O. oophagus appear to have narrower deposition options that are restricted primarily by pool height, water capacity, alkalinity, and salinity. Dendrobates tinctorius tadpoles are particularly flexible and can survive in a wide range of chemical, physical, and biological conditions, whereas O. oophagus seems to prefer small, clear pools and A. femoralis occupies medium-sized pools with abundant leaf litter and low salinity. Together, these results show the possible niche partitioning of phytotelmata among frogs and provide insight into stressors and resilience of phytotelm breeders.

Factors affecting aerobic granule sludge formation in leachate treatment - a systematic review

The biological treatment of landfill leachate due to high concentration of Chemical Oxygen Demand (COD), ammonia, and other toxic compounds is so difficult. One of the leachate treatment technology is the sludge biogranulation, that containing the two aerobic and anaerobic process. The aim of this study was conducted for determining the main factors affecting aerobic granule sludge formation in leachate treatment. In this study, all related papers in international databases were evaluated including Google Scholar, Science Direct, and PubMed, Also Open Access Journal Directory from 1990 until 2020 were investigated. The keywords used included Aerobic Granule Sludge (AGS), leachate treatment, Wastewater treatment, Granular Sequential Batch Reactors (GSBR), Formation Extracellular polymeric substance (EPS). Overall, 2,658 articles were retrieved of which 71 were selected after revising the titles and abstracts. Aerobic granulation has been only lately studied and a limited number of studies have been devoted to identification aspects of the process such as the organic source, and other factor affecting on formation granules. Some factors as shear stress, settling time, and the effluent discharge site have direct effect on the efficiency of aerobic granules reactor and other factors such as divalent metal ions, dissolved oxygen concentration, the ratio of height to diameter of the reactor, temperature affecting on the granulation process. If suitable conditions provide, the aerobic granule sludge process can be useful for leachate treatment.

Effect of operational strategies on the rapid start-up of nitrogen removal aerobic granular system with dewatered sludge as inoculant

In both sequencing batch reactors with dewatering sludge as inoculant, the strategies by step-feeding (R1) or step-feeding combined with low aeration (R2) were performed under alternating anoxic/aerobic condition to discover superior methods launching nitrogen removal aerobic granule system. Interestingly, two reactors accomplished granulation at day 0, two days later, possessed prominent settling performance (SVI < 45 ml/g. MLSS) and denitrifying ability (TIN > 80%). Thereinto, R2 had lower crushing rate, larger granules, higher biomass and better pollutant removal performance owing to low aeration and more filamentous bacteria on AGS surface. Moreover, effluent NH₄⁺-N was used as indicator of excess filaments due to its quick response for the filaments. After effluent NH₄⁺-N exceeded 5 mg/L, causative filaments Sphaerotilus were effectively inhibited and eliminated by enhancing pH value to 8.0 ± 0.2. As a result, this study provides a new insight into rapid start-up nitrogen removal granule system by promoting and limiting filaments in proper period.

The effect of Np-magnetite on the granulation process of an SBR reactor used for domestic wastewater treatment

This study investigated the effect of magnetite nanoparticles (Np-magnetite) added to a pilot-scale sequencing batch reactor (SBR) treating domestic wastewater, to improve aerobic granular sludge (AGS) formation and the effects of granule disintegration. Np-magnetite additions (75 mg L^-1) were made during the start-up of the reactor and repeated after 100 and 170 days, when granule disintegration was observed. From the first Np-magnetite addition, SVI₅ was reduced from 1315 to 85 mL g^-1. The granular biomass was observed on the 56th day, when 57% of the granules presented diameters bigger than 212 µm. The 100-day disintegration episode disturbed the granular biomass, reducing the volatile suspended solids by 51%, increasing the SVI values to above 200 mL g^-1. Np-magnetite addition recovered all the granular biomass parameters to the values observed before disintegration. The treatment efficiency was stable during operation of the reactor for nutrients (52.8 ± 23.4% NH₄⁺-N; 54.5 ± 12.2% PO₄^3--P) and carbonaceous organic matter (71.7 ± 12.7% BOD₅; 77.5 ± 10.0% COD_t). Np-magnetite addition changed the microbial community of the granular sludge, analysed via high-throughput 16S RNA sequencing, and recovered the treatment efficiency previously disturbed by the disintegration processes. These results indicate the potential of Np-magnetite as an agent for sludge aggregation in an aerobic granular reactor.

Effect of transient pH variation on microbial activity and physical characteristics of aerobic granules treating 4-chlorophenol

Chlorophenols are inhibitory compounds that can be biodegraded by aerobic granules in discontinuous processes. Many industrial wastewaters are characterized by transient pH variation over time. These pH changes could affect the overall granule structure and microbial activity during the chlorophenol biodegradation. The objective of this research was to evaluate the effects of transient pH variation on the specific degradation rate (q), granule integrity coefficient (IC), and size in sequencing batch reactors treating 4-chlorophenol (4-CP). First, aerobic granules were acclimated for efficient 4-CP degradation (>99%). The acclimated granules consisted of 55.7% of the phyla Proteobacteria and 40.6% of Bacteroidetes. The main bacteria belong to the order Sphingobacteriales (24%), as well as Amaricoccus, Acidovorax, Shinella, Rhizobium, and Flavobacterium, some of which are new genera reported in acclimated granules degrading 4-CP. Then, pH changes were applied to the acclimated aerobic granules, observing that acid pHs decreased to a greater extent the specific degradation rate (67% to 99%) than basic pHs (34% to 80%). These pH changes caused the granule disaggregation but with lower effects on the IC. The effects of pH change were mainly on the microbial activity more than the physical characteristics of aerobic granules degrading 4-CP.

Metagenomics revealed the phase-related characteristics during rapid development of halotolerant aerobic granular sludge

Efforts to produce aerobic granular sludge (AGS) for high-efficient and stable nutrient removal in high saline wastewaters have gained much attention recently. This study was undertaken to describe the phase-related characteristics of the rapid formation of glucose-fed salt-tolerant AGS (SAGS) generated from common municipal activated sludge using metagenomic approaches. The time needed for SAGS formation is about 11 days in a multi-ion matrix salinity of 3%. There were three distinct developmental phases during sludge maturation which were designated: I) the salinity adaptation phase (days 1-2), II) the particle-size transition phase (days 3-5) and III) the maturation and steady-state phase (days 6-11), respectively. Genome-based analysis revealed that during the phase I, members of the genus Mangrovibacter, which has the potential to secrete extracellular polymeric substances (EPS), dominated during the formation of initial SAGS aggregates. During phase II, fungi of the class Saccharomycetes, in particular the genus Geotrichum, became dominant and provided a matrix for bacterial attachment. This mutualistic interaction supported the rapid development and maintenance of mature SAGS. This work characterizes a robust approach for the rapid development of SAGS for efficient saline sewage treatment and provides unique insight into the granulation mechanism occurring during the development process.

The viscosity behaviors of bacterial suspensions or extracellular polymeric substances and their effects on aerobic granular sludge

Although the viscosity behavior of bacteria and extracellular polymeric substances (EPS) in flocculent activated sludge (FAS) and aerobic granular sludge (AGS) has been investigated, no studies have explored the role of viscosity in microbial attachment in pure culture. This study investigated the viscosity behavior of bacteria and EPS. The results showed that bacteria and their EPS exhibited non-Newtonian fluid and shear-thinning behavior. The viscosity of bacteria and EPS was 1.55-3.80 cP and 1.10-2.40 cP, respectively, while the attachment of bacteria (optical density at 600 nm) was 0.1426-3.1015. Bacteria with high attachment secreted EPS with a higher viscosity (2.40 cP), whereas those with weak attachment expressed EPS with a lower viscosity (1.10 cP). Viscosity and microbial attachment or extracellular polysaccharide (PS) content were significantly positively correlated. PS content was the source of bacterial viscosity, and β-polysaccharide played a more important role in viscosity and microbial attachment than α-polysaccharide. Thus, viscosity plays a critical role in microbial attachment, and high viscosity and PS content result in high microbial attachment, which is beneficial to the granulation process of AGS.

Microbial community dynamics during aerobic granulation in a sequencing batch reactor (SBR)

Microorganisms in aerobic granules formed in sequencing batch reactors (SBR) remove contaminants, such as xenobiotics or dyes, from wastewater. The granules, however, are not stable over time, decreasing the removal of the pollutant. A better understanding of the granule formation and the dynamics of the microorganisms involved will help to optimize the removal of contaminants from wastewater in a SBR. Sequencing the 16S rRNA gene and internal transcribed spacer PCR amplicons revealed that during the acclimation phase the relative abundance of Acinetobacter reached 70.8%. At the start of the granulation phase the relative abundance of Agrobacterium reached 35.9% and that of Dipodascus 89.7% during the mature granule phase. Fluffy granules were detected on day 43. The granules with filamentous overgrowth were not stable and they lysed on day 46 resulting in biomass wash-out. It was found that the reactor operation strategy resulted in stable aerobic granules for 46 days. As the reactor operations remained the same from the mature granule phase to the end of the experiment, the disintegration of the granules after day 46 was due to changes in the microbial community structure and not by the reactor operation.

Organic loading rate (OLR) regulation for enhancement of aerobic sludge granulation: Role of key microorganism and their function

According to unique growth characteristics of various environmental microorganism specially with different substrates and their levels, aerobic sludge granulation are studied under different operation mode of influent organic loading rate (OLR), and the EPS component, sludge surface characters and functional microbes are analyzed to achieve a novel process for stable sludge granulation. Results showed that activated sludge cultivated under gradient influent OLR decreasing from 5.5 to 3.5 kgCOD m^-3 d^-1 achieved complete granulation with average size of 438 μm and exopolysaccharide (PS) to protein (PN) ratio over 2.0. Meanwhile, these granules had excellent flocculability and hydrophobicity with Zeta potential and contact angle of -15 mV and 110°, respectively. Principal component analysis (PCA) illustrated that microbes with function of EPS secretion enriched with decreased OLR regulation for their suitable specific growth characteristics, then promoted other microbes aggregation and sludge granulation along with the improvement of cellular surface characters and microbial niche.

Aerobic granular sludge: Cultivation parameters and removal mechanisms

Aerobic granular sludge (AGS) has been the focus of many investigations, and the main parameters responsible for AGS formation are hydrodynamic shear force, short periods and feast-famine cycles. However, some other parameters are associated with AGS maintenance after long periods of operation. This review evaluates the parameters responsible for AGS formation and maintenance and some reference values are proposed. In addition, some discussions are addressed about the main metabolic pathways that AGS uses for the removal of some compounds, such as nutrients, organic matter, dyes, recalcitrant compounds, among others. Finally, the main microbial groups present in the AGS and their respective functions are discussed. It is also highlighted that many parameters that are taken as reference currently for AGS cultivation and maintenance can be optimized for energy savings, implementation costs, among others, as well as a greater recovery of resources during wastewater treatment, within the scope of the biorefinery concept.

Advanced phosphorus recovery using a novel SBR system with granular sludge in simultaneous nitrification, denitrification and phosphorus removal process

In this study, a novel process for phosphorus (P) recovery without excess sludge production from granular sludge in simultaneous nitrification-denitrification and P removal (SNDPR) system is presented. Aerobic microbial granules were successfully cultivated in an alternating aerobic-anaerobic sequencing batch reactor (SBR) for removing P and nitrogen (N). Dense and stable granular sludge was created, and the SBR system showed good performance in terms of P and N removal. The removal efficiency was approximately 65.22 % for N, and P was completely removed under stable operating conditions. Afterward, new operating conditions were applied in order to enhance P recovering without excess sludge production. The initial SBR system was equipped with a batch reactor and a non-woven cloth filter, and 1.37 g of CH3COONa·3H2O was added to the batch reactor after mixing it with 1 L of sludge derived from the SBR reactor to enhance P release in the liquid fraction, this comprises the new system configuration. Under the new operating conditions, 93.19 % of the P contained in wastewater was released in the liquid fraction as concentrated orthophosphate from part of granular sludge. This amount of P could be efficiently recovered in the form of struvite. Meanwhile, a deterioration of the denitrification efficiency was observed and the granules were disintegrated into smaller particles. The biomass concentration in the system increased firstly and then maintained at 4.0 ± 0.15 gVSS/L afterward. These results indicate that this P recovery operating (PRO) mode is a promising method to recover P in a SNDPR system with granular sludge. In addition, new insights into the granule transformation when confronted with high chemical oxygen demand (COD) load were provided.

Rapid start-up and improvement of granulation in SBR

BACKGROUND

The aim of this study is to accelerate and improve aerobic granulation within a Sequencing Batch Reactor (SBR) by cationic polymer addition.

METHODS

To identify whether the polymer additive is capable of enhancing granule formation, two SBRs (R1 and R2, each 0.15 m in diameter and 2 m in height) are used by feeding synthetic wastewater. The cationic polymer with concentration of 30 to 2 ppm is added to R2, while no cationic polymer is added to R1.

RESULTS

Results show that the cationic polymer addition causes faster granule formation and consequently shorter reactor start-up period. The polymer-amended reactor contains higher concentration of biomass with better settling ability (23% reduction in SVI15) and larger and denser granules (112% increase of granular diameter). In addition, the results demonstrate that the cationic polymer improve the sludge granulation process by 31% increase in Extracellular Polymer Substance(EPS) concentration, 7% increase in Specific Oxygen Uptake Rate(SOUR), 18% increase in hydrophobicity, and 17% reduction in effluent Mixed Liquor Suspended Solid(MLSS) concentration.

CONCLUSIONS

Concludingly, it is found that using the cationic polymer to an aerobic granular system has the potential to enhance the sludge granulation process.

Impact of influent COD/N ratio on disintegration of aerobic granular sludge

Disintegration of aerobic granular sludge (AGS) is a challenging issue in the long-term operation of an AGS system. Chemical oxygen demand (COD)-to-nitrogen (N) ratio (COD/N), often variable in industrial wastewaters, could be a destabilizing factor causing granule disintegration. This study investigates the impact of this ratio on AGS disintegration and identifies the key causes, through close monitoring of AGS changes in its physical and chemical characteristics, microbial community and treatment performance. For specific comparison, two lab-scale air-lift type sequencing batch reactors, one for aerobic granular and the other for flocculent sludge, were operated in parallel with three COD/N ratios (4, 2, 1) applied in the influent of each reactor. The decreased COD/N ratios of 2 and 1 strongly influenced the stability of AGS with regard to physical properties and nitrification efficiency, leading to AGS disintegration when the ratio was decreased to 1. Comparatively the flocculent sludge maintained relatively stable structure and nitrification efficiency under all tested COD/N ratios. The lowest COD/N ratio resulted in a large microbial community shift and extracellular polymeric substances (EPS) reduction in both flocculent and granular sludges. The disintegration of AGS was associated with two possible causes: 1) reduction in net tyrosine production in the EPS and 2) a major microbial community shift including reduction in filamentous bacteria leading to the collapse of granule structure.

Degradation of azo dye acid orange 7 in a membrane bioreactor by pellets and attached growth of Coriolus versicolour

The aim of this study was to systematically compare the degradation of azo dye acid orange 7 by spongy pellets and attached biofilm of Coriolus versicolour (NBRC 9791) in a membrane bioreactor (MBR) under non-sterile conditions. Mild stirring (35 rpm) resulted in spherical (φ=0.5 cm), spongy pellets and concomitantly triggered high enzymatic activity of the fungus, allowing for excellent decolouration (>99%) of a synthetic wastewater containing the dye. However, bacterial contamination eventually damaged the fungus pellets, leading to decreased decolouration efficiency. Promotion of attached growth on a plastic support along with formation of spherical spongy pellets allowed maintenance of high enzymatic activity and decolouration/degradation for an extended period. Hydraulic retention time (HRT) could influence the level of enzymatic activity and decolouration; however, even at the shortest HRT (1 day) examined, the MBR could accomplish >95% decolouration.

Effects of the cycle distribution on the performance of SBRs with aerobic granular biomass

The aerobic granular systems are mainly sequencing batch reactors where the biomass is submitted to feast-famine regimes to promote its aggregation in the form of granules. In these systems, different cycle distributions can be applied for the simultaneous removal of organic matter, nitrogen and phosphorus. In this work two strategies were followed in order to evaluate the effects of the cycle distribution. In the first experiment, the length of the operational cycle was decreased in order to maximize the treatment capacity and consequently the famine/feast ratio was also decreased. In the second experiment, an initial anoxic phase was implemented to improve nitrogen removal efficiency. The results obtained showed that to reduce the famine/feast ratio from 10 to 5 was possible by increasing the treated organic and nitrogen loading rates in the system to 33%, without affecting the removal efficiencies of organic matter (97%) and nitrogen (64%) and producing a slight detriment of the granules characteristics. On the other hand, the implementation of an anoxic phase of 30 min previous to the aerobic one with a pulse-fed mode increased the nitrogen removal of pig manure from 20 to 60%, while the cycle configuration comprising a continuous feeding simultaneous with an anoxic phase of 60 min did not enhance the nitrogen removal and even worsen the ammonia oxidation.

Change in the fouling propensity of sludge in membrane bioreactors (MBR) in relation to the accumulation of biopolymer clusters

A membrane bioreactor (MBR) and an activated sludge process (ASP) were operated side by side to evaluate the change of sludge supernatant characteristics and the evolution of the sludge fouling propensity. The MBR sludge had a higher organic concentration and more biopolymer clusters (BPC) in the supernatant compared with ASP. BPC increased in both concentration and size in the MBR. The results show that the change in the liquid-phase property had a profound effect on the sludge fouling propensity. MBR operation transformed typical activated sludge to MBR sludge with a higher fouling propensity. Distinct from the ASP, membrane filtration retained soluble microbial products (SMP) within the MBR, and the vast membrane surface provided a unique environment for the transformation of SMP to large size BPC, leading to further sludge deposition on the membrane surface. Thus, membrane filtration is the crucial cause of the inevitable fouling problem in submerged MBRs.

Impact of extracellular polymeric substances on the settlement ability of aerobic granular sludge

Instability of aerobic granular sludge (AGS), which is mainly caused by filamentous outgrowth, is a bottleneck in applying this technology to treat wastewater. In order to reduce the effect of filamentous outgrowth on settlement ability of AGS, the role of the distribution of extracellular polymeric substances (EPS) in settlement ability was investigated in this study. Chemical oxygen demand (COD) of influent increased gradually from 1000 mg L(-1) to 2000 mg L(-1) to 4000 mg L(-1) as organic loading rate (OLR) changed from 2 to 4 to 8 kg COD m(-3) d(-1) in the synthetic influent. The relationship between settlement ability and EPS was investigated. The sharp increase in loosely bound EPS (LB-EPS) content reduced the settlement ability, whereas the highest content of tightly bound EPS (TB-EPS) was observed in the sludge with best settlement ability. The TB-EPS plays an important role in maintaining the matrix structure of AGS. Abundance of LB-EPS did not favour the settlement ability of AGS. These results would provide useful information for improvement of stability of AGS.

Microscale hydrodynamic analysis of aerobic granules in the mass transfer process

The internal structure of aerobic granules has a significant impact on the hydrodynamic performance and mass transfer process, and severely affects the efficiency and stability of granules-based reactors for wastewater treatment. In this study, for the first time the granule complex structure was correlated with the hydrodynamic performance and substrates reactions process. First, a series of multiple fluorescence stained confocal laser scanning microscopy images of aerobic granules were obtained. Then, the form and structure of the entire granule was reconstructed. A three-dimensional computational fluid dynamics study was carried out for the hydrodynamic analysis. Two different models were developed on the basis of different fluorescence stained confocal laser scanning microscopy images to elucidate the roles of the granule structure in the hydrodynamic and mass transfer processes of aerobic granules. The fluid flow behavior, such as the velocity profiles, the pathlines and hence the hydrodynamic drag force, exerted on the granule in a Newtonian fluid, was studied by varying the Reynolds number. Furthermore, the spatial distribution of dissolved nutrients (e.g., oxygen) was acquired by solving the convection-diffusion equations on the basis of the reconstructed granule structure. This study demonstrates that the reconstructed granule model could offer a better understanding to the mass transfer process of aerobic granules than simply considering the granule structure to be homogeneous.

Fate of aerobic bacterial granules with fungal contamination under different organic loading conditions

Aerobic sludge granulation is an attractive new technology for biological wastewater treatment. However, the instability of aerobic granules caused by fungal growth is still one of the main problems encountered in granular bioreactors. In this study, laboratory experiments were conducted to investigate the fate and transformation of aerobic granules under different organic loading conditions. Bacterial granules (2-3mm) in a poor condition with fungi-like black filamentous growth were seeded into two 1L batch reactors. After more than 100d of cultivation, the small seed granules in the two reactors had grown into two different types of large granules (>20mm) with different and unique morphological features. In reactor R1 with a high organic loading rate of 2.0g COD L(-1)d(-1), the black filaments mostly disappeared from the granules, and the dominance of rod-shaped bacteria was recovered. In contrast, at a low loading of 0.5g COD L(-1)d(-1) in reactor R2, the filaments eventually became dominant in the black fungal granules. The bacteria in R1 granules had a unique web-like structure with large pores of a few hundred microm in size, which would allow for effective substrate and oxygen transport into the interior of the granules. DNA-based molecular analysis indicated the evolution of the bacterial population in R1 and that of the eukaryal community in R2. The experimental results suggest that a high loading rate can be an effective means of helping to control fungal bloom, recover bacterial domination and restore the stability of aerobic granules that suffer from fungal contamination.

Granulation of filamentous microorganisms in a sequencing batch reactor with saline wastewater

Proliferation of filamentous microorganisms frequently leads to operational failure for activate sludge systems. In this study, it was found that filamentous microorganisms could grow in compact granular structure with 5% sodium chloride in the substrate. In the early period of experiment, coccoid and rode-like bacteria predominated in the yellowish-brown granules, and later the white and the black granules were developed by filamentous microorganisms. The filamentous granules exhibited low porosity and fast settling velocity, and were more compact even than bacteria granules. It was hypothesized that the elevated pH in the later period might be a possible reason for the compact growth of filamentous granules. However, the bacteria granules showed the high bioactivity in terms of specific oxygen utilizing rate, and comprised of a wider diversity of compounds based on the thermogravimetric evaluation. The findings in this study demonstrated that filamentous microbes could form compact granular structure, which may encourage the utilization of filamentous microorganisms rather than the inhibition of their growth, as the latter is frequently used for sludge bulking control.