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The recovery of biopolymers from sewage sludge could be a crucial step in implementing circular economy principles in wastewater treatment plants (WWTP). In this frame, the present study was aimed at evaluating the simultaneous production of polyhydroxyalkanoates (PHA) and extracellular polymeric substances (EPS) obtainable from the treatment of agro-industrial wastewater. Two biological enrichment systems, aerobic granular sludge (AGS) and a conventional activated sludge operating as a sequencing batch reactor (SBR), were monitored for 204 and 186 days, respectively. The maximum biopolymers accumulation capacity was close to 0.60 mgPHA-EPS gVSS−1 in the AGS when operating at 3 kgCODm−3d−1, whereas in the SBR, it was about half (0.35 mgPHA-EPS gVSS−1). Biopolymers extracted from the AGS were mainly constituted by EPS (>70%), whose percentage increased up to 95% with the OLR applied in the enrichment reactor. In contrast, SBR enabled obtaining a higher PHA production (50% of the biopolymers). Results suggested that organic carbon was mainly channeled toward metabolic pathways for extracellular storing in AGS, likely due to metabolic stressors (e.g., hydraulic selection pressure, shear forces) applied for promoting aerobic granulation. [ABSTRACT FROM AUTHOR]

The paper focused on the evolution and the comparison of the extracellular polymeric substances (EPSs) content during the granulation process in two Granular Sequencing Batch Airlift Reactors (GSBAR) (3,5 L) fed with synthetic (R1) and industrial wastewater (R2). The results showed that in both the reactors the EPSs, in particular proteins (PN), were mainly produced during the feast phase because of the high substrate availability, especially under conditions of metabolic stress. Then, the EPSs content reduced during the famine period, because of biodegradation by bacteria. More in detail, during the granulation process, a greater polysaccharides (PS) consumption occurred in both reactors, whereas the PN content reduced significantly only in R2. As a result, the PN/PS ratio increased significantly during the granules formation, confirming the key role of proteins on the granulation process. In R2, the granules produced a greater amount of PN on average, and this resulted in a more rapid granulation. Nevertheless, due to the several consumption of PN during the famine period, the granules in R2 resulted weaker and less dense compared with the granules in R1. For this reason, the granules in R2 were more susceptible to breakage. Overall, although the industrial wastewater favored a more rapid granulation, the excessive consumption of the EPSs, led to the structural weakening of the granules. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • A mainstream process for PHA production was integrated with wastewater treatment. • A comparison between AS, AGS and MBR as the enrichment/treatment stage was assessed. • MBR enabled the highest PHA production potential and effluent water eligible for reuse. • Biomass enrichment under full aerobic in AGS promoted extracellular storage pathways. • Integration of PHA production in the mainstream of a WWTP resulted feasible using MBR. [ABSTRACT FROM AUTHOR]

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 −3 d −1 and 7 kg TCOD m −3 d −1 during Period I, whereas between 7 kg TCOD m −3 d −1 and 15 kg TCOD m −3 d −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 −3 d −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. [ABSTRACT FROM AUTHOR]

A granular sequencing batch reactor (GSBR) worked for 164 days to study the effect of salinity on aerobic granulation. The feeding had an organic loading rate (OLR) of 1.6 kg COD⋅m −3 ⋅d −1 and a gradual increase of salinity (from 0.30 to 38 g NaCl − ⋅L −1 ) to promote a biological salt-adaptation. First aggregates (average diameter ≈ 0.4 mm) appeared after 14 days. Extracellular polymeric substances (EPSs) analyses revealed that proteins were mainly higher than polysaccharides, and microorganisms metabolized EPSs as additional carbon source, mostly in feast phase, to face the energy demand for salinity adaptation. No significant worsening of organic matter removal was observed. The initial decrease of nitrification (from 58% to 15%) and the subsequent increase (up to 25%), confirmed the acclimation of AOBs to saline environment, while the accumulation of nitrites suggested NOBs inhibition. The nitrogen removal initially decreased from 58% to 15%, due to the inhibitory effect of salinity, and subsequently increased up to 29% denoting a simultaneous nitrification–denitrification. The dimensions of mature granules (higher than 1 mm) probably involved PAOs growth in the inner anaerobic layers. Nitrites caused a temporary deterioration of phosphorous removal (from 60% to almost zero), that increased up to 25% when nitrites were depleted. [ABSTRACT FROM AUTHOR]

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 75 g NaCl L −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 50 g NaCl L −1 , suggesting the existence of a salinity threshold above which granules stability is compromised. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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 mgNH 4 -N gVSS−1h−1 and 10.0 mgNO 2 -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. Graphical abstract Image 1 Highlights • Autochthonous marine bacteria were cultivated as granular and activated sludge. • Biomass metabolic kinetics were evaluated at different salinity and SRT. • Salinity did not affect the biomass kinetics within the range of 30–50 gNaCl L−1. • Biomass activity and performances decreased for both system because of a long SRT. • Destructuration of the microbial bioaggragates occurred due to salt accumulation. [ABSTRACT FROM AUTHOR]

The work focuses on the feasibility of treating slop with aerobic granular sludge. For this purpose, a 3.5 L granular sequencing batch reactor was activated and it was monitored for 156 days. The experimental campaign was divided into two periods, named Period I (100 days) and Period II (56 days). Total Petroleum Hydrocarbon (TPH) concentration in the slop was, on average, equal to 6.8 ± 1.5 mg L −1 and 13 ± 1.5 mg L −1 in Period I and Period II respectively. The obtained results during the first experimental period indicated that about 80 days were required to reach steady state with mature granules, when TPHs removal efficiency was approximately 90%. The results indicated that both adsorption and biodegradation phenomena occurred. Subsequently, due to the increase in the TPH concentration in Period II, a temporary degranulation was observed, leading to the deterioration of effluent quality. When the granulation was recovered, the TPHs removal efficiencies were gradually recovered. Based on the results, the granular sludge appears able to remove hydrocarbons, in compliance the discharge limits, even if a significant deterioration in granular sludge structure was observed with the increase in TPH concentration. [ABSTRACT FROM AUTHOR]

Results obtained from three aerobic granular sludge reactors treating brewery wastewater are presented. Reactors were operated for 60 d days in each of the two periods under different cycle duration: (Period I) short 6 h cycle, and (Period II) long 12 h cycle. Organic loading rates (OLR) varying from 0.7 kg COD m −3 d −1 to 4.1 kg COD m −3 d −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 12 h cycle time, granules were observed to develop again with superior structural stability compared to the short 6 h 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The time required to stabilise mature aerobic granules is rather variable. In addition, cultivation time and the structural characteristics of granules seem to be related to the nature of wastewater influent. Granular sludge has been used for the treatment of several industrial wastewaters, but nothing has been reported about wastewater characterized by the simultaneous presence of hydrocarbons and high chloride concentration. In this work, the authors analysed the granulation process and performance as well as the physical characteristics of aerobic granules in two Granular Sequencing Batch Airlift Reactors (GSBARs), fed with acetate-based synthetic wastewater in reactor 1 (R1) and with a mixture of real and simulated slop (R2). The results obtained in 100 days show that full granulation was achieved in both reactors. The granules in R2 developed more quickly, but they appeared slightly unstable and more susceptible to breaking. Despite high salt concentration, the efficiency of phosphorous and carbon removal was satisfactory. Low nitrification activity was observed in R1, confirming that a longer time is necessary to obtain the acclimation of autotrophic biomass in aerobic granules. In R2 the combined effect of salinity and hydrocarbons caused the inhibition of the autotrophic biomass, with the consequence that nitrification was absent. Hydrocarbons were initially removed by adsorption afterwards by biological degradation with a removal efficiency of over 90%. [ABSTRACT FROM AUTHOR]