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Membrane bioreactors (MBRs) represent by now a well established alternative for wastewater treatment. Their increasing development is undoubtedly related to the several advantages that such technology is able to guarantee. Nevertheless, this technology is not exempt from operational problems; among them the foaming still represents an “open challenge” of the MBR field, due to the high complexity of phenomenon. Unfortunately, very little work has been done on the foaming in MBRs and further studies are required. Actually, there is not a distinct difference between conventional activated system and MBR: the main difference is that the MBR plants can retain most Extracellular Polymeric Substances (EPSs) in the bioreactor. For these reason, unlike conventional activated sludge systems, MBRs have experienced foaming in the absence of foam-forming micro-organisms. Nevertheless, the actual mechanisms of EPS production and the role of bacteria in producing foam in activated sludge in MBRs are still unclear. In this paper, the authors investigated the roles of EPS and foam-forming filamentous bacteria by analyzing samples from different pilot plants using MBRs. In particular, in order to define the macroscopic features and the role of EPS and filamentous bacteria, a Modified Scum Index (MSI) test was applied and proposed. Based on the MSI and the foam power test, the causes of biological foaming were identified in terms of the potential for foaming, the quality and the quantity of the foam. The results indicated that the MBR foaming was influenced significantly by the concentration of bound EPSs in the sludge. In addition, the quantity and stability of MBR scum increased when both bound EPSs and foam-forming filamentous bacteria were present in the activated sludge. [Copyright &y& Elsevier]

Highlights: [•] The study offers information about the carbon and nitrogen removal in granular SBR. [•] The SND process was discussed under high dissolved oxygen concentration conditions. [•] Different organic and nitrogen loading rate have been applied. [•] Results show that even with high DO concentration N and C can be removed. [ABSTRACT FROM AUTHOR]

The excess biomass produced during biological treatment of municipal wastewater represents a major issue worldwide, as its disposal implies environmental, economic and social impacts. Therefore, there has been a growing interest in developing technologies to reduce sludge production. The main proposed strategies can be categorized according to the place inside the wastewater treatment plant (WWTP) where the reduction takes place. In particular, sludge minimization can be achieved in the wastewater line as well as in the sludge line. This paper presents the results of two pilot scale systems, to evaluate their feasibility for sludge reduction and to understand their effect on biomass activity: (1) a pilot plant with an ozone contactor in the return activated sludge (RAS) stream for the exposition of sludge to a low ozone dosage; and (2) an oxicsettling-anaerobic (OSA) process with high retention time in the anaerobic sludge holding tank have been studied. The results showed that both technologies enabled significant excess sludge reduction but produced a slight decrease of biomass respiratory activity. [ABSTRACT FROM AUTHOR]

Abstract: Foaming in Membrane BioReactor (MBR) is a frequently discussed topic. Some authors reported that the phenomenon is due to filamentous organisms, like at Conventional Activated Sludge (CAS) plants. However, in recent years, other authors reported that the Extra-cellular Polymer Substances (EPSs) concentration is an important factor for controlling foam as well. Nevertheless, even if a number of MBR plants are affected by foaming, presently there are no suitable methods to evaluate the phenomenon. To facilitate the study of this controversial phenomenon in an MBR system, certain foam tests proposed in the past for CASPs were investigated. The results of the tests were able to adequately measure quantity, stability and quality of the foam. In particular, the Scum Index increased proportionally with the EPS concentration and mixed liquor viscosity; Foam Power was mainly correlated with the protein concentration of in the EPS; Foam Rating was also correlated with the EPS concentration. [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]

Graphical abstract Highlights • The effect of a co-substrate addition in TPH removal was studied in a MBR. • A novel hydrocarbons extraction method from complex mixture was developed. • A lower co-substrate supply enabled approximately 98% of biological TPH removal. • Bacteria able to grow on hydrocarbons as primary substrate were selected. • The membrane fouling increased under lower co-substrate supply. Abstract The paper reports the main results of an experiment carried out on a membrane bioreactor (MBR) plant designed for the treatment of shipboard slops. With a view of a co-treatment process of the slop with other wastewaters, sodium acetate, as external co-substrate, was supplied (high dosage – Period 1, low dosage – Period 2) to evaluate its effects on hydrocarbons removal. The MBR pilot plant enabled approximately 99% of total petroleum hydrocarbon (TPH) removal during the entire experiment, confirming the robustness of the MBR technology for the treatment of slops. The chromatography/mass spectrometry analysis showed that the removal efficiency for each alkane was close to the value observed for total mixture removal (>99%) and the hydrocarbons removal was mostly due to the microorganism-mediated biodegradation. The biological contribution to TPH removal increased from approximately 85% to 98% when the co-substrate was decreased. Biomass kinetics revealed that a lower co-substrate dosage enhanced the growth of bacterial groups able to use hydrocarbons as primary substrate. A clear predominance of Microthrix Parvicella under low co-substrate dosage was observed. However, the lower co-substrate addition caused a significant worsening in the physical properties of the activated sludge, which resulted enriched in soluble exopolymers (>70%), more hydrophobic (>90%) and with small and dispersed flocs (<30 μm). Consequently, the membrane permeability reduced because of the irreversible fouling increase. [ABSTRACT FROM AUTHOR]

The article shows results of monitoring of a Sicilian composting plant (southern Italy). In particular, the biological stability of the organic fraction of municipal solid wastes has been monitored. Two experimental periods have been carried out: (1) plant start-up and (2) first operation period. The biological stability has been evaluated throughout the dynamic respiration index (DRI). This index was determined at different stages of process, for each phase. To our knowledge, no work has been previously published on the monitoring of composting plants in southern Italy. This work has the originality of using the DRI measured data for improving operation of a full-scale composting plant, rarely adopted in literature. Results show that storage time of the untreated matrix strongly influences performance of the composting process in terms of biological stability. At high value of storage time (>4 to 5 days) the pH decreased due to acetic acid production. Consequently, inhibition of the aerobic stabilization process takes place. Indeed, after treatment the DRI value was still quite high: 1,709 and 2,650 mgO2/(kgVS·h) during start-up and start-up and first operation period, respectively. Results also reveal the need of using all operational parameters as reference for regulation of ventilation systems. [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]

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. [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]

• The AET was studied as a novel parameter affecting excess sludge minimization. • Sludge minimization efficiency was statistically dependent on the AET. • Cell lysis and EPS destruction were enhanced by operating at high AET in the ASSR. • AET was better correlated to YOBS reduction than other parameters like ASLR and HRT. • Sludge minimization mechanisms showed a clear dependence on AET. 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 (Y obs) 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 Y obs reduction reported in previous studies, also indicating a linear relationship (R2 = 0.92) between these parameters. Contrarily, the correlation between the Y obs 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined a MBR pilot plant under high strength and saline wastewater. [•] Significant influence of salinity increase on nitrifying activity. [•] Membrane fouling mainly due to irreversible cake deposition. [•] Changes of biomass characteristics affected filtration properties. [Copyright &y& Elsevier]

Highlights: [•] We examined a hybrid activated/biofilm pilot plant working in cold climate region. [•] High COD and ammonium removal efficiencies in the whole period. [•] It is possible to sustain nitrification at quite low SRT values of mixed liquor. [•] Seeding effect of nitrifiers from the detached biofilm to the mixed liquor. [Copyright &y& Elsevier]

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. [Display omitted] • A mainstream SBMBR was used for the combined recovery of treated water and PHA. • SBMBR effluent complied with reuse limits set by the current European regulations. • PHA performance (45% w/w and 0.63 gPHA L−1h−1) were higher in the SBMBR than the SBR. • Competitive reactions to PHA accumulation (EPS synthesis) were limited in the SBMBR. • PHA accumulation significantly reduced the membrane fouling tendency. [ABSTRACT FROM AUTHOR]

Abstract: This study analysed a submerged membrane bioreactor (SMBR) start-up with the purpose of determining the best conditions to carry it out. In order to do this, a hollow fibre membrane module was installed in a submerged configuration in a pilot aerobic reactor. The experiment was then divided in two phases, lasting 65days each. During phase 1, the pilot plant was started-up without inoculum of activated sludge and no sludge, withdrawal was performed. Conversely, in phase 2, the MBR pilot plant was started-up with sludge inoculum and the sludge concentration was kept constant. In both phases, the volumetric loading rate applied to the pilot plant was kept constant. The authors analysed the difference in carbon removal performances, the evolution of floc sizes and the fouling rate in both phases. The results confirmed that MBRs can be quickly and easily started-up, but the initial start-up strategy can influence membrane fouling. More specifically, the carbon removal performances were similar in both phases, while the fouling rate increased faster during the start-up without inoculum, especially in terms of irreversible deposition of soluble compost on the membrane surface and into membrane pores. [Copyright &y& Elsevier]

Over the last decade new technologies are emerging even more for wastewater treatment. Among the new technologies, a recent possible solution regards Moving Bed Biofilm Reactors (MBBRs) that represent an effective alternative to conventional processes. More specifically such systems consist in the introduction of plastic elements inside the aerobic reactor as carrier material for the growth of attached biomass. Recently, one of the mostly used alternatives is to couple the Moving Bed Biofilm Reactor (MBBR) process with the conventional activated sludge process, and the resulting process is usually called HMBBR (Hybrid MBBR). In the MBBR process the biofilm grows attached on small plastic elements that are kept in constant motion throughout the entire volume of the reactor. Indeed, in such a system, a competition between the two biomasses, suspended and attached, can arise for the availability of the substrates, leading, as a consequence, to a modification in the biokinetic parameters of the two biomasses, compared to that of a pure suspended or attached biomass process. This paper presents the first results of a study aimed at estimating the kinetic heterotrophic constants in a HMBBR pilot plant using respirometric techniques. The pilot plant was built at the Acqua dei Corsari (Palermo) wastewater treatment plant and consisted of two parallel lines realized in a pre-anoxic scheme, in one of which the carrier material was added to the aerobic reactor with a filling ratio of 30%. [ABSTRACT FROM AUTHOR]

The paper presents the comparison between the traditional activated sludge system (AS) and a hybrid moving bed biofilm reactor (HMBBR). In particular, an experimental campaign has been carried out at the WWTP in Palermo (Italy), on a pilot plant consisting of two pre-anoxic schemes. The aerated tank of the HMBBR line was filled with suspended carriers (AnoxKaldnes® K1), with a 30% filling ratio. The hydraulic load of the HMBBR line was increased up to two times the AS one. Further, in order to distinguish the additional contribution of the attached biomass for the HMBBR system, in the two lines the Mixed Liquor Suspended Solids (MLSS) was maintained as equal as possible. The monitoring period lasted three months during which several parameters were monitored. The obtained results showed a good treatment ability of the HMBBR system, referring to the organic matter removal as well as to the ammonium removal. In particular, in spite of the increase of the hydraulic load for the HMBBR line, the two systems showed a similar performance in terms of both organic and nitrogen removal. The results demonstrate the higher treatment capacity of the HMBBR addressing such system as an effective technology for the upgrading of overloaded wastewater treatment plants. [ABSTRACT FROM AUTHOR]

• Leachate biodegradability was assessed for autochthonous and allochthonous biomasses. • Leachate biodegradability strongly depended on the biomass used to perform the tests. • Autochthonous biomass enabled a higher biodegradation capacity (75% vs 40%). • Autochthonous biomass exhibited a higher resistance to inhibitory leachate compounds. • Allochthonous biomass required the supply of an organic co-substrate. 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 O 2 gVSS−1 h-1 vs 37 mg O 2 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. [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]

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 · 10 12  m −1  d −1 vs 4.0 · 10 11  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. [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]

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 (Y obs) 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. [Display omitted] • An OSA process with a novel plant layout enabled excess sludge reduction up to 40%. • Cell lysis and EPS destruction were enhanced by operating under prolonged anaerobiosis. • Cell lysis and EPS hydrolysis impaired effluent quality and sludge settling features. • Maintenance and uncoupling metabolism enabled higher sludge reduction (26–40%). • Nitrifiers were affected by prolonged starvation under not aerobic conditions. [ABSTRACT FROM AUTHOR]

This work investigates the causes of foaming and fouling in an Intermittent Aerated – Membrane BioReactor (IA-MBR) used for wastewater treatment. The experiment was divided into three periods with different aerated regimes expressed with different t aeration /t cycle ratio (Period I: 60 min/180 min, Period II: 80 min/180 min, Period III: 30 min/90 min). The advanced foaming tests used allow the study of the role of extracellular polymeric substances (EPSs) on foaming and fouling. In general, in the Periods I and II, good correlations between the EPSs and the Modified Scum Index without purification (MSI 0 ) and the Foam Power were observed. The results shown that the filamentous microorganisms, which mainly grew in the Period III, play also a key factor in the foaming and fouling. In particular, when a net proliferation of filamentous bacteria occurred (during period III with a higher number of cycles per day) both EPSs concentration and filamentous abundance influence the modified scum index obtained after two purification steps (MSI 2 ). Finally, the processing data show that the EPSs hampered also the membrane filtration but improve the pre-filtration action of cake layer. On the other hand, the co-presence of EPSs and filamentous bacteria reduced the effect o cake layer as pre-filter. [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]

An innovative respirometric method was applied to evaluate the autotrophic active fraction in an alternate anoxic/oxic membrane bioreactor (MBR) pilot plant. The alternate cycle (AC) produces a complex microbiological environment that allows the development of both autotrophic and heterotrophic species in one reactor. The present study aimed to evaluate autotrophic and heterotrophic active fractions and highlight the effect of different aeration/non aeration ratios in a AC-MBR pilot plant using respirometry. The results outlined that the autotrophic active fraction values were consistent with the nitrification efficiency and FISH analyses, which suggests its usefulness for estimating the nitrifying population. Intermittent aeration did not significantly affect the heterotrophic metabolic activity but significantly affected the autotrophic biomass development. Finally, the heterotrophic active biomass was strongly affected by the wastewater characteristics, whereas the resultant autotrophic biomass was considerably affected by the duration of the aerated phase. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Sustainable management of CWWs is achievable by implementing biorefinery concepts. • Characteristics of CWWs would require advanced treatments properly integrated. • Biological treatments of CWWs could be coupled for exploiting synergistic effects. • Reuse of CWWs and sludges for agriculture purpose promote circular bioeconomy. • Efforts to promote common and specific legislations for CWWs reuse are needed. [ABSTRACT FROM AUTHOR]

A collection of forty-two (42) strains was obtained during microbiological screening of a Membrane Bioreactor (MBR) system developed for the treatment of saline oily waste originated from marine transportation. The diversity of the bacterial collection was analyzed by amplification and sequencing of the 16S rRNA gene. Taxonomic analysis showed high level of identity with recognized sequences of seven (7) distinct bacterial genera (Alcanivorax , Erythrobacter , Marinobacter , Microbacterium , Muricauda , Rhodococcus and Rheinheimera ). The biotechnological potential of the isolates was screened considering an important factor such as the biosurfactant production. In particular fourteen (14) biosurfactant producing bacteria were selected and further tested, for growth on crude oil and hydrocarbon degradation. Data obtained from this study confirmed the high activity of bacteria related to genera Alcanivorax (isolates MBR-B11 and MBR-G10), Rheinheimera (isolates MBR-H02 and MBR-H05), Rhodococcus (isolates MBR-F04 and MBR-G05) and Muricauda (isolate MBR-G04) and underline the possible application of these bacteria in remediation of saline oily waste water. [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]

In order to prevent hydrocarbon discharge at sea from ships, the International Maritime Organization (IMO) enacted the MARPOL 73/78 convention in which any oil and oil residue discharged in wastewater streams must contain less than 5 ppm hydrocarbons. Effective treatment of this petroleum-contaminated water is essential prior to its release into the environment, in order to prevent pollution problem for marine ecosystems as well as for human health. Therefore, two bench scale membrane bioreactors (MBRs) were investigated for hydrocarbon biodegradation. The two plants were initially fed with synthetic wastewater characterised by an increasing salinity, in order to enhance biomass acclimation to salinity. Subsequently, they were fed with a mixture of synthetic wastewater and real shipboard slops (with an increasing slops percentage up to 50% by volume). The results indicated a satisfactory biomass acclimation level in both plants with regards to salinity, providing significant removal efficiencies. The real slops exerted an inhibitory effect on the biomass, partially due to hydrocarbons as well as to other concomitant influences from other compounds contained in the real slops difficult to evaluate a priori . Nevertheless, a slight adaptation of the biomass to the new conditions was observed, with increasing removal efficiencies, despite the significant slops percentage. [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]

The effect of a sharp variation of C/N ratio in a moving bed membrane bioreactor (MB-MBR) pilot plant treating high strength wastewater has been investigated. The experimental campaign was divided into two periods, each characterized by a different C/N ratio (namely, 2.5 and 15, Period 1 and Period 2, respectively). The MB-MBR system was analyzed in terms of organic carbon removal, nitrification efficiency, biokinetic activity and fouling behavior. The results showed that the nitrification process was severely affected by lower C/N value and by high concentration of ammonia. It was noticed an extensive stress effect on the autotrophic bacteria. Furthermore, it was observed an increase of the resistance related to particle deposition into membrane pores, likely due to a worsening of the cake layer features, with a reduction of the “pre-filter” effect, also related to the increase of the total Extracellular Polymeric Substances production with the C/N ratio. [ABSTRACT FROM AUTHOR]

A bench-scale MBR unit was operated, under stressing condition, with the aim of stimulating the onset of foaming in the activated sludge. Possible synergies between synthetic surfactants in the wastewater and biological surfactants (Extra-Cellular Polymeric Substances, EPSs) were investigated by changing C/N ratio. The growth of filamentous bacteria was also discussed. The MBR unit provided satisfactory overall carbon removal overall efficiencies: in particular, synthetic surfactants were removed with efficiency higher than 90% and 95% for non-ionic and ionic surfactants, respectively. Lab investigation suggested also the importance to reduce synthetic surfactants presence entering into mixed liquor: otherwise, their presence can significantly worsen the natural foaming caused by biological surfactants (EPSs) produced by bacteria. Finally, a new analytic method based on “ink test” has been proposed as a useful tool to achieve a valuation of EPSs bound fraction. [ABSTRACT FROM AUTHOR]

Highlights: [•] MBR and MB-MBR pilot plants under gradual salinity increase were compared. [•] Respirometry showed that the biomass activity was not significantly affected by the salinity. [•] Membrane fouling was mainly due to irreversible cake deposition. [•] Biofilm detachment phenomena affected the irreversible cake deposition. [•] Pore fouling tendency was more pronounced for the MBR pilot plant. [Copyright &y& Elsevier]

Highlights: [•] Low content of foam-formation microorganisms was found. [•] There is a possible transfer of the EPS from the mixed liquor to the foam. [•] We found a good correlation between fouling and EPS and foaming and bound EPSs. [•] Fouling rate decreases with the foam formation. [•] In UCT-MBR plants the foam can be formed even without foam-former bacteria. [Copyright &y& Elsevier]

The behavior of a University of Cape Town (UCT) membrane bioreactor (MBR) system was investigated for use in biological nutrient removal from real wastewater. The pilot plant was in operation for a period of 165 days, during which an extensive data gathering campaign was conducted. The pilot plant was started up by inoculating it with activated sludge from a nearby wastewater treatment plant, and it was fed by real municipal wastewater characterized by high organic nitrogen concentrations attributable to discharges from industrial wastewater and sporadic landfill leachate. Carbon and biological nutrient removal processes, a sludge production process, and a membrane fouling mechanism were analyzed and discussed. The organic nitrogen levels, which were higher than typical values for municipal wastewater, caused ammonification phenomena. This led to intense nitrification and denitrification activities. The pilot plant showed satisfactory efficiency in terms of average removal efficiencies for both carbon and nitrogen. However, lower efficiencies were recorded for phosphorus removal as an indirect effect of the intense denitrifying activity of the phosphorus-accumulating organisms in the anoxic tank. Membrane fouling was mainly of reversible nature, and low values of soluble microbial product were measured. [ABSTRACT FROM AUTHOR]

Abstract: Over the last two decades, Membrane Bioreactors (MBRs) emerged even more for wastewater treatment, ensuring high removal efficiencies as well as very small footprint requirements. Indeed, in this kind of process, a modification in biomass activity and viability can exist compared to that of a CAS process. In this context, respirometric analysis represents a reliable tool in order to evaluate the actual biomass kinetic parameters, to insert in mathematical models in the design phase, as well as to monitor the biomass viability, especially when these processes are operated with high SRT values. The paper presents some results of respirometric techniques applied for the characterisation of wastewater and biomass activity in a pilot UCT-MBR plant for nutrient removal, operating with high SRT. In particular, the respirometric tests were specifically aimed at investigating heterotrophic and autotrophic bacterial activity. The pilot plant was built at Palermo WWTP and consisted of three reactors: anaerobic, anoxic and aerobic, followed by an aerobic compartment containing two submerged hollow fibre membrane modules with typical recycling lines. The kinetic parameters for heterotrophic bacteria resulted lower respect to the CAS; regarding the nitrifying bacteria, the kinetic constants were in the range of CAS, suggesting a good nitrification activity. [Copyright &y& Elsevier]

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 mgPO 4 -P gVSS−1 h−1) and P-uptake rates (48.6 mgPO 4 -P gVSS−1 h−1), as well as a not negligible P-release rate under endogenous conditions at low COD/P ratio (≈1). Image 1 • HRT of 8 h in the AMSR enabled the maximum excess sludge minimization (64%). • AMSR (HRT = 8 h) improved phosphorous removal (97%) and reduced the membrane fouling. • P-release was observed under anaerobic/endogenous conditions at low C/P ratio (≈1). • Cryptic growth favored the simultaneous excess sludge minimization and P removal. • Long anaerobic/endogenous HRTs worsen effluent quality and membrane permeability. [ABSTRACT FROM AUTHOR]

• A thermic-OSA process at low temperature for excess sludge minimization was studied. • Thermic-OSA enabled 80% of sludge reduction at HRT lower than conventional OSA. • The abundance of filamentous bacteria decreased when the thermic-OSA was implemented. • The thermic-OSA process produced an increase of the bacterial endogenous decay. 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%). [ABSTRACT FROM AUTHOR]

The aim of the present study was to compare the oxygen transfer efficiency in a conventional activated sludge and a membrane bioreactor system. The oxygen transfer was evaluated by means of the oxygen transfer coefficient and α-factor calculation, under different total suspended solids concentration, extracellular polymeric substances, sludge apparent viscosity and size of the flocs. The oxygen transfer coefficient and α-factor showed an exponential decreasing trend with total suspended solid, with a stronger oxygen transfer coefficient dependence in the conventional activated sludge compared to the membrane bioreactor. It was noted that the oxygen transfer coefficient in the conventional activated sludge become comparable to that in membrane bioreactor when the total suspended solid concentration in the conventional activated sludge was higher than 5 g L−1. Operating under high carbon to nitrogen ratio, the oxygen transfer coefficient increased in both conventional activated sludge and membrane bioreactor because of sludge deflocculation and it was noticed a weaker dependence of the oxygen transfer coefficient with total suspended solid. The results indicated that the most important parameters on the oxygen transfer efficiency were in order: the total suspended solid concentration, flocs size, sludge apparent viscosity and extracellular polymeric substances content. Based on the influence of the main biomass features affecting the oxygen transfer coefficient and considering the typical operating conditions in both systems, those of membrane bioreactor appeared to be more favorable to oxygen transfer efficiency. The paper provides a useful insight about some peculiarities of oxygen transfer in a conventional activated sludge and a membrane reactor system, highlighting new and useful information in the light of a more sustainable management of these systems. Image 1 • A comparison between the oxygen transfer in CAS and MBR bench plant was carried out. • (k L a) 20 and α-factor showed exponential trends with TSS for both CAS and MBR. • (k L a) 20 values higher in MBR within a TSS range between 4 gTSS L−1 and 6 gTSS L−1. • Under similar conditions features of sludge in MBR more favorable to oxygen transfer. • TSS, EPS and viscosity should be controlled to optimize aeration efficiency. [ABSTRACT FROM AUTHOR]