PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison.

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

The anaerobic exposure time (AET) as a novel process parameter in the anaerobic side-stream reactor (ASSR)-based process for excess sludge minimization.

Minimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields. To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Yobs) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10-60 %) with the increase of the AET (7.9-13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Yobs reduction reported in previous studies, also indicating a linear relationship (R2 = 0.92) between these parameters. Contrarily, the correlation between the Yobs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=-0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process.

Combined recovery of polyhydroxyalkanoates and reclaimed water in the mainstream of a WWTP for agro-food industrial wastewater valorisation by membrane bioreactor technology.

The present study investigated the combined production of reclaimed water for reuse purposes and polyhydroxyalkanoates (PHA) from an agro-food industrial wastewater. A pilot plant implementing a two-stage process for PHA production was studied. It consisted of a mainstream sequencing batch membrane bioreactor (SBMBR) in which selection of PHA-accumulating organisms and wastewater treatment were carried out in, and a side-stream fed-batch reactor (FBR) where the excess sludge from the SBMBR was used for PHA accumulation. The performance of the SBMBR was compared with that of a conventional sequencing batch reactor (SBR) treating the same wastewater under different food to microorganisms' ratios (F/M) ranging between 0.125 and 0.650 kgCOD kgTSS-3 d-1. The SBMBR enabled to obtain very high-quality effluent in compliance with the relevant national (Italy) and European regulations (Italian DM 185/03 and EU, 2020/741) in the field of wastewater reclamation, whereas the performances in the SBR collapsed at F/M higher than 0.50 kgCOD kgTSS-1d-1. A maximum intracellular storage of 45% (w/w) and a production yield of 0.63 gPHA L-1h-1 were achieved when the SBMBR system was operated with a F/M ratio close to 0.50 kgCOD kgTSS-1d-1. This resulted approximately 35% higher than those observed in the SBR, since the ultrafiltration membrane avoided the washout of dispersed and filamentous bacteria capable of storing PHA. Furthermore, while maximizing PHA productivity in conventional SBR systems led to process dysfunctions, in the SBMBR system it helped mitigate these issues by reducing membrane fouling behaviour. The results of this study supported the possibility to achieve combined recovery of reclaimed water and high-value added bioproducts using membrane technology, leading the way for agro-food industrial wastewater valorization in the frame of a circular economy model.

Insights on mechanisms of excess sludge minimization in an oxic-settling-anaerobic process under different operating conditions and plant configurations.

In the present research, insights about the mechanisms of excess sludge minimization occurring in an oxic-settling-anaerobic (OSA) were provided. The investigation involved two systems operating in parallel. In particular, a conventional activated sludge (CAS) system as control and a system implementing the OSA process both having a pre-denitrification scheme were considered. Five periods (P1-P5) were studied, during which several operating conditions and configurations were tested. Specifically, the hydraulic retention time (HRT) in the anaerobic reactor of the OSA system (P1 8 h, P2-P3 12 h, P4 8 h, P5 12 h) and the return sludge from the anaerobic to the anoxic (scheme A) (P1-P2) or aerobic (scheme B) mainstream reactors (P3-P5) were investigated. The results highlighted that the excess sludge production in the OSA was lower in all the configurations (12-41%). In more detail, the observed yield (Yobs) was reduced from 0.50-0.89 gTSS gCOD-1 (control) to 0.22 -0.34 gTSS gCOD-1 in the OSA process. The highest excess sludge reduction (40%) was achieved when the OSA was operated according to scheme B and HRT of 12 h in the anaerobic reactor (P3). Generally, scheme A enabled the establishment of cell lysis and extracellular polymeric substances (EPS) destructuration, leading to a worsening of process performances when high anaerobic HRT (>8 h) was imposed. In contrast, scheme B enabled the establishment of maintenance metabolism in addition to the uncoupling metabolism, while cell lysis and EPS destruction were minimized. This allowed obtaining higher sludge reduction yield without compromising the effluent quality.

Challenges and opportunities for citrus wastewater management and valorisation: A review.

Citrus wastewaters (CWWs) are by-products of the citrus fruit transformation process. Currently, more than 700 million of m³ of CWWs per year are produced worldwide. Until nowadays, the management of CWWs is based on a take-make-use-dispose model. Indeed, after being produced within a citrus processing industry, CWWs are subjected to treatment and then discharged into the environment. Now, the European Union is pushing towards a take-make-use-reuse management model, which suggests to provide for the minimization of residual pollutants simultaneously with their exploitation through a biorefinery concept. Indeed, the recovery of energy nutrients and other value-added products held by CWWs may promote environmental sustainability and close the nutrient cycles in line with the circular bio-economy perspective. Unfortunately, knowledge about the benefits and disadvantages of available technologies for the management and valorisation of CWWs are very fragmentary, thus not providing to the scientific community and stakeholders an appropriate approach. Moreover, available studies focus on a specific treatment/valorisation pathway of CWWs and an overall vision is still missing. This review aims to provide an integrated approach for the sustainable management of CWWs to be proposed to company managers and other stakeholders within the legislative boundaries and in line with the circular bio-economy perspective. To this aim, firstly, a concise analysis of citrus wastewater characteristics and the main current regulations on CWWs are reported and discussed. Then, the main technologies with a general comparison of their pros and cons, and alternative pathways for CWWs utilization are presented and discussed. Finally, a focus was paid to the economic feasibility of the solutions proposed to date relating to the recovery of the CWWs for the production of both value-added compounds and agricultural reuse. Based on literature analysis an integrated approach for a sustainable CWWs management is proposed. Such an approach suggests that after chemicals recovery by biorefinery, wastewaters should be directly used for crop irrigation if allowed by regulations or addressed to treatment plant. The latter way should be preferred when CWWs cannot be directly applied to soil due to lack of concomitance between CWWs production and crop needs. In such a way, treated wastewater should be reused after tertiary treatments for crop irrigation, whereas produced sludges should be undergone to dewatering treatment before being reused as organic amendment to improve soil fertility. Finally, this review invite European institutions and each Member State to promote common and specific legislations to overcome the fragmentation of the regulatory framework regarding CWWs reuse.

Membrane Fouling Mitigation in MBR via the Feast-Famine Strategy to Enhance PHA Production by Activated Sludge.

Fouling is considered one of the main drawbacks of membrane bioreactor (MBR) technology. Among the main fouling agents, extracellular polymeric substances (EPS) are considered one of the most impactful since they cause the decrease of sludge filterability and decline of membrane flux in the long term. The present study investigated a biological strategy to reduce the membrane-fouling tendency in MBR systems. This consisted of seeding the reactor with activated sludge enriched in microorganisms with polyhydroxyalkanoate (PHA) storage ability and by imposing proper operating conditions to drive the carbon toward intracellular (PHA) rather than extracellular (EPS) accumulation. For that purpose, an MBR lab-scale plant was operated for 175 days, divided into four periods (1-4) according to different food to microorganisms' ratios (F/M) (0.80 kg COD kg TSS-1 d-1 (Period 1), 0.13 kg COD kg TSS-1 d-1 (Period 2), 0.28 kg COD kg TSS-1 d-1 (Period 3), and 0.38 kg COD kg TSS-1 d-1 (Period 4)). The application of the feast/famine strategy favored the accumulation of intracellular polymers by bacteria. The increase of the PHA accumulation inside the cells corresponded to the decrease of EPS and an F/M of 0.40-0.50 kg COD kg TSS-1 d-1 was found as optimum to maximize the PHA production, while minimizing EPS. The lowest EPS content in the sludge (18% of total suspended solids) that corresponded to the maximum content of PHA (9.3%) was found in Period 4 and determined significant mitigation of the fouling rate, whose value was close to 0.10 × 1011 m-1 h-1. Thus, by imposing proper operating conditions, it was possible to drive the organic matter toward PHA accumulation. Moreover, a lower EPS content corresponded to a decrease in the irreversible fouling mechanism, which would imply a lower frequency of the extraordinary cleaning operations. This study highlighted the possibility of obtaining a double benefit by applying an MBR system in the frame of wastewater valorization: minimizing the fouling tendency of the membrane and recovery precursors of bioplastics from wastewater in line with the circular economy model.

Occurrence of Microplastics in Waste Sludge of Wastewater Treatment Plants: Comparison between Membrane Bioreactor (MBR) and Conventional Activated Sludge (CAS) Technologies.

In this study, the presence of microplastics in the sludge of three wastewater treatment plants (WWTPs) was examined. The investigated WWTPs operated based on a conventional activated sludge (CAS) process, with (W1) or without (W2) primary clarification, and a membrane bioreactor process (MBR) (W3). The microplastics (MPs) concentration in the samples of W3 was approximately 81.1 ± 4.2 × 103 particles/kg dry sludge, whereas MPs concentrations in W1 and W2 were 46.0 ± 14.8 × 103 particles/kg dry sludge and 36.0 ± 5.2 × 103 particles/kg dry sludge, respectively. Moreover, MPs mainly consisted of fragments (66-68%) in the CAS plants, whereas the fractions of MPs shapes in the MBR sludge were more evenly distributed, although fiber (47%) was the most abundant fraction. Furthermore, samples from the MBR showed a greater diversity in MPs composition. Indeed, all the main polyesters (i.e., textile fibers and polyethylene terephthalate), polyolefins (i.e., polyethylene and polypropylene) and rubber (i.e., polybutadiene) were observed, whereas only polybutadiene, cellulose acetate and polyester were detected in the CAS plants. These findings confirmed that MPs from wastewater are transferred and concentrated in the waste sludge. This is a critical finding since sludge disposal could become a new pathway for microplastic release into the environment and because MPs might affect the fouling behavior of the membrane.

Biomethane Production from Anaerobic Co-Digestion of Selected Organic Fraction of Municipal Solid Waste (OFMSW) with Sewage Sludge: Effect of the Inoculum to Substrate Ratio (ISR) and Mixture Composition on Process Performances.

The aim of this study was to evaluate the effect of the inoculum to substrate ratio (ISR) and the mixture ratio between organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) on the methane production potential achievable from anaerobic co-digestion (AcoD). Biochemical Methane Potential (BMP) assays at mesophilic temperature were used to determine the best AcoD configuration for maximizing methane yield and production rate, as well as to address possible synergistic effects. The maximum methane yield was observed at ISR of 1 and 60% OFMSW: 40% SS as co-digestion mixture, whereas the highest methane production rate was achieved at ISR of 2 with the same mixture ratio (207 mL/gVS/d). Synergistic effects were highlighted in the mixtures having OFMSW below 60%, determining an increase of approximately 40% in methane production than the OFMSW and SS digestion as a sole substrate. The experimental data demonstrated that co-digestion of OFMSW and SS resulted in an increase in the productivity of methane than anaerobic digestion using the sole substrates, producing higher yields or production rates while depending on the ISR and the mixture ratio.

Aerobic granular sludge treating anaerobically pretreated brewery wastewater at different loading rates.

In this study, three different aerobic granular sludge (AGS) reactors fed with anaerobically pre-treated brewery wastewater were studied. The AGS reactors were operated under different conditions including organic loading rates (OLR) between 0.8 and 4.1 kg COD m-3 d-1, C:N:P ratios (100:10:1 and 100:6:1) and food to microorganism ratios (F/M) between 0.8 ± 0.6 and 1.2 ± 0.5 and 0.9 ± 0.3 kg-TCOD kg-VSS-1d-1. Stable granulation was achieved within two weeks and the size of the granules increased according to the OLR applied. The results indicated that low C:N:P and F/M ratios were favorable to achieve stable aerobic granules in the long term. The carbon removal rate was load-independent in the range examined (TCOD removal >80%), whereas TN removals were inversely proportional to the OLRs. Overall, a longer aeration reaction time with a lower OLR was beneficial to granular structure, which exhibited a compact and defined architecture. Performance results within the other conditions studied further indicated that the microbial community and its complex functionality in nutrient removal was efficient at operational parameters of OLR at 0.8 ± 0.2 kg-TCOD m-3d-1 and F/M ratio at 0.5 ± 0.2 kg-TCOD VSS-1d-1. Moreover, the protein to polysaccharide ratio increased as OLR decreased, leading to a stable granular structure.

Simultaneous sludge minimization, biological phosphorous removal and membrane fouling mitigation in a novel plant layout for MBR.

The integration of one anaerobic reactor in the mainstream (AMSR) of a pre-denitritication-MBR was evaluated with the aim to achieve simultaneous sludge minimization and phosphorous removal. The excess sludge production was reduced by 64% when the AMSR was operated under 8 h of hydraulic retention time (HRT). The highest nutrients removal performances referred to organic carbon (98%), nitrogen (90%) and phosphorous (97%) were obtained under 8 h of HRT. In contrast, prolonged anaerobic-endogenous conditions were found to be detrimental for all nutrients removal performances. Similarly, the lowest membrane fouling tendency (FR = 0.65∙1011 m-1 d-1) was achieved under 8 h of HRT, whereas it significantly increased under higher HRT. The highest polyphosphate accumulating organisms kinetics were achieved under HRT of 8 h, showing very high exogenous P-release (46.67 mgPO4-P gVSS-1 h-1) and P-uptake rates (48.6 mgPO4-P gVSS-1 h-1), as well as a not negligible P-release rate under endogenous conditions at low COD/P ratio (≈1).

Combination of the OSA process with thermal treatment at moderate temperature for excess sludge minimization.

This study investigated the chance to couple the conventional Oxic Settling Anaerobic (OSA) process with a thermic treatment at moderate temperature (35 °C). The maximum excess sludge reduction rate (80%) was achieved when the plant was operated under 3 h of hydraulic retention time (HRT). Compared with the conventional OSA system, the thermic treatment enabled a further improvement in excess sludge minimization of 35%. The observed yield coefficient decreased from 0.25 gTSS gCOD-1 to 0.10 gTSS gCOD-1 when the temperature in the anaerobic reactor was increased to 35 °C, despite the lower HRT (3 h vs 6 h). Moreover, the thermic treatment enabled the decrease of filamentous bacteria, thereby improving the sludge settling properties. The thermic treatment enhanced the destruction of extracellular polymeric substances and the increase of endogenous decay rate (from 0.64 d-1 to 1.16 d-1) that reduced the biomass active fraction (from 22% to 4%).

Assessment of landfill leachate biodegradability and treatability by means of allochthonous and autochthonous biomasses.

The biodegradability and treatability of a young (3 years old) municipal landfill leachate was evaluated by means of chemical oxygen demand (COD) fractionation tests, based on respirometric techniques. The tests were performed using two different biomasses: one cultivated from the raw leachate (autochthonous biomass) and the other collected from a conventional municipal wastewater treatment plant after its acclimation to leachate (allochthonous biomass). The long term performances of the two biomasses were also studied. The results demonstrated that the amount of biodegradable COD in the leachate was strictly dependent on the biomass that was used to perform the fractionation tests. Using the autochthonous biomass, the amount of biodegradable organic substrate resulted in approximately 75% of the total COD, whereas it was close to 40% in the case of the allochthonous biomass, indicating the capacity of the autochthonous biomass to degrade a higher amount of organic compounds present in the leachate. The autochthonous biomass was characterized by higher biological activity and heterotrophic active fraction (14% vs 7%), whereas the activity of the allochthonous biomass was significantly affected by inhibitory compounds in the leachate, resulting in a lower respiration rate (SOUR = 13 mg O2 gVSS-1 h-1vs 37 mg O2 gVSS-1 h-1). The long-term performance of the autochthonous and allochthonous biomasses indicated that the former was more suitable for the treatment of raw landfill leachate, ensuring higher removal performance towards the organic pollutants.

Comparison between kinetics of autochthonous marine bacteria in activated sludge and granular sludge systems at different salinity and SRTs.

Biological nutrient removal performances and kinetics of autochthonous marine biomass in forms of activated sludge and aerobic granular sludge were investigated under different salinity and sludge retention time (SRT). Both the biomasses, cultivated from a fish-canning wastewater, were subjected to stepwise increases in salinity (+2 gNaCl L-1), from 30 gNaCl L-1 up to 50 gNaCl L-1 with the aim to evaluate the maximum potential in withstanding salinity by the autochthonous marine biomass. Microbial marine species belonging to the genus of Cryomorphaceae and of Rhodobacteraceae were found dominant in both the systems at the maximum salinity tested (50 gNaCl L-1). The organic carbon was removed with a yield of approximately 98%, irrespective of the salinity. Similarly, nitrogen removal occurred via nitritation-denitritation and was not affected by salinity. The ammonium utilization rate and the nitrite utilization rate were approximately of 3.60 mgNH4-N gVSS-1h-1 and 10.0 mgNO2-N gVSS-1h-1, respectively, indicating a high activity of nitrifying and denitrifying bacteria. The granulation process did not provide significant improvements in the nutrients removal process likely due to the stepwise salinity increase strategy. Biomass activity and performances resulted affected by long SRT (27 days) due to salt accumulation within the activated sludge flocs and granules. In contrast, a lower SRT (14 days) favoured the discharge of the granules and flocs with higher inert content, thereby enhancing the biomass renewing. The obtained results demonstrated that the use of autochthonous-halophilic bacteria represents a valuable solution for the treatment of high-strength carbon and nitrogen saline wastewater in a wide range of salinity. Besides, the stepwise increase in salinity and the operation at low SRT enabled high metabolic activity and to avoid excessive accumulation of salt within the biomass aggregates, limiting their physical destructuration due to the increase in loosely-bound exopolymers.

Biological minimization of excess sludge in a membrane bioreactor: Effect of plant configuration on sludge production, nutrient removal efficiency and membrane fouling tendency.

Excess sludge minimization was studied in a MBR with pre-denitrification scheme. Sludge minimization, nitrogen removal performance and membrane fouling tendency were investigated in two configurations, characterized by a different position of the sludge retention reactor (SRR). In particular, the SRR was placed: i) in the return activated sludge line (Anaerobic Side-Stream Reactor - ASSR configuration) and ii) in the mainstream between the anoxic and aerobic reactor (Anaerobic Main-Stream Reactor - AMSR configuration). The achieved results demonstrated that the ASSR enabled a higher excess sludge reduction (74% vs 32%), while achieving lower biological nitrogen removal (BNR) (TN = 63% vs 78%) and membrane fouling tendency (FR = 2.1 ·â€¯1012 m-1 d-1vs 4.0 ·â€¯1011 m-1 d-1) than the AMSR. It was found that metabolism uncoupling, destruction of EPS and endogenous decay simultaneously occurred in the ASSR. Conversely, selective enrichment of bacteria population with low biomass yield was found the main mechanism affecting sludge minimization in the AMSR.

Aerobic granular sludge treating high strength citrus wastewater: Analysis of pH and organic loading rate effect on kinetics, performance and stability.

In the present paper, the feasibility of citrus wastewater treatment with aerobic granular sludge sequencing batch reactors (AGSBR) was investigated. Two AGSBRs (named R1 and R2, respectively) were operated for 90 days under different organic loading rates (OLR) and pH in two experimental periods. The OLR ranged approximately between 3.0 kg TCOD m-3d-1 and 7 kg TCOD m-3d-1 during Period I, whereas between 7 kg TCOD m-3d-1 and 15 kg TCOD m-3d-1 during Period II. pH was maintained at 7.0 and 5.5 in R1 and R2, respectively. The results revealed that under high OLR and unbalanced feast/famine regime (Period I), the development of fast-growing microorganisms (fungi and filamentous bacteria) was favoured in both reactors, resulting in granular sludge instability. An extended famine phase and a proper balancing between feast and famine periods (Period II) were favourable for the development of bacteria with low growth rates (0.05 d-1) thus enhancing the granules stability. To the benefit of granular sludge stability and effluent quality, the length of the feast period should not exceed 25% of cycle length. Moreover, under OLR lower than 7 kg TCOD m-3d-1 the removal efficiency of total chemical oxygen demand (TCOD) was approximately 90% in R1 and R2 and no side effects on the organic carbon removal performance related to the pH were observed. In contrast, at higher OLR a significant decrease in the removal efficiency (from 90% to less than 75%) was observed in R2. Results revealed also that under low pH, hydrolysis of proteins occurred and a decrease in the biological kinetic rates proportionally to the applied OLR was observed.

Shortcut nitrification-denitrification by means of autochthonous halophilic biomass in an SBR treating fish-canning wastewater.

Autochthonous halophilic biomass was cultivated in a sequencing batch reactor (SBR) aimed at analyzing the potential use of autochthonous halophilic activated sludge in treating saline industrial wastewater. Despite the high salt concentration (30 g NaCl L-1), biological oxygen demand (BOD) and total suspended solids (TSS), removal efficiencies were higher than 90%. More than 95% of the nitrogen was removed via a shortcut nitrification-denitrification process. Both the autotrophic and heterotrophic biomass samples exhibited high biological activity. The use of autochthonous halophilic biomass led to high-quality effluent and helped to manage the issues related to nitrogen removal in saline wastewater treatment.

Physical properties and Extracellular Polymeric Substances pattern of aerobic granular sludge treating hypersaline wastewater.

The modification of the physical properties of aerobic granular sludge treating fish-canning wastewater is discussed in this paper. The structure and composition of the Extracellular Polymeric Substances (EPSs) were analyzed at different salinity levels and related to granules stability. Results outlined that the total EPSs content increased with salinity, despite the EPSs increment was not proportional to the salt concentration. Moreover, the EPSs structure was significantly modified by salinity, leading to a gradual increase of the not-bound EPSs fraction, which was close to the 50% of the total EPSs content at 75gNaClL-1. The increasing salt concentration modified also the EPSs composition, causing the gradual reduction of protein content resulting in a decrease of granule hydrophobicity. The results pointed out that the granules stability significantly reduced above 50gNaClL-1, suggesting the existence of a salinity threshold above which granules stability is compromised.

Effect of extended famine conditions on aerobic granular sludge stability in the treatment of brewery wastewater.

Results obtained from three aerobic granular sludge reactors treating brewery wastewater are presented. Reactors were operated for 60d days in each of the two periods under different cycle duration: (Period I) short 6h cycle, and (Period II) long 12h cycle. Organic loading rates (OLR) varying from 0.7kgCODm-3d-1 to 4.1kgCODm-3d-1 were tested. During Period I, granules successfully developed in all reactors, however, results revealed that the feast and famine periods were not balanced and the granular structure deteriorated and became irregular. During Period II at decreased 12h cycle time, granules were observed to develop again with superior structural stability compared to the short 6h cycle time, suggesting that a longer starvation phase enhanced production of proteinaceous EPS. Overall, the extended famine conditions encouraged granule stability, likely because long starvation period favours bacteria capable of storage of energy compounds.

Fate of aerobic granular sludge in the long-term: The role of EPSs on the clogging of granular sludge porosity.

This work aims to investigate the stability of aerobic granular sludge in the long term, focusing on the clogging of the granular sludge porosity exerted by the extracellular polymeric substances (EPSs). The effects of different cycle lengths (short and long-term cycle) on the granular sludge stability were investigated. Results obtained outlined that during the short duration cycle, the formation and breakage of the aerobic granules were continuously observed. During this period, the excess of EPS production contributed to the clogging of the granules porosity, causing their breakage in the long run. During the long-duration cycle, the extended famine period entailed a greater EPSs consumption by bacteria, thus limiting the clogging of the porosity, and allowed obtaining stable aerobic granules. Reported results demonstrated that an excess in EPSs content could be detrimental to the stability of aerobic granular sludge in the long-term.

Simultaneous nitritation-denitritation for the treatment of high-strength nitrogen in hypersaline wastewater by aerobic granular sludge.

Fish processing industries produce wastewater containing high amounts of salt, organic matter and nitrogen. Biological treatment of such wastewaters could be problematic due to inhibitory effects exerted by high salinity levels. In detail, high salt concentrations lead to the accumulation of nitrite due to the inhibition of nitrite-oxidizing bacteria. The feasibility of performing simultaneous nitritation and denitritation in the treatment of fish canning wastewater by aerobic granular sludge was evaluated, and simultaneous nitritation-denitritation was successfully sustained at salinities up to 50 gNaCl L(-1), with a yield of over 90%. The total nitrogen concentration in the effluent was less than 10 mg L(-1) at salinities up to 50 gNaCl L(-1). Nitritation collapsed above 50 gNaCl L(-1), and then, the only nitrogen removal mechanism was represented by heterotrophic synthesis. In contrast, organic matter removal was not affected by salinity but was instead affected by the organic loading rate (OLR). Both COD and BOD removal efficiencies were over 90%. The COD fractionation analysis indicated that aerobic granules were able to remove more than 95% of the particulate organic matter. Finally, results obtained in this work noted that aerobic granular sludge had an excellent ability to adapt under adverse environmental conditions.