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 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…

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 purpos…

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…

Effect of biomass features on oxygen transfer in conventional activated sludge and membrane bioreactor systems

Abstract 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 conve…

Preliminary evaluation of biopolymers production by mixed microbial culture from citrus wastewater in a MBR system using respirometric techniques

Abstract This preliminary study was aimed at evaluating the feasibility to produce biopolymers (BP) from citrus wastewater by mixed microbial culture in an anaerobic/aerobic membrane bioreactor (A/O-MBR). The activated sludge of the A/O-MBR was successfully enriched in microorganisms having a good capacity in producing intracellular biopolymers. The production of BP was found to be about 0.55 mgCOD mgCOD−1 using pure acetate at a concentration of 1000 mgCOD L−1. When using fermented wastewater, the conversion of acetate into BP product was 0.56 mgCOD mgCOD−1 in the test performed with C/N equal to 1000:1, whereas it was only 0.12 mgCOD mgCOD−1 in the test with C/N of 100:5. The results achi…

Biopolymer Recovery from Aerobic Granular Sludge and Conventional Flocculent Sludge in Treating Industrial Wastewater: Preliminary Analysis of Different Carbon Routes for Organic Carbon Utilization

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…

Sequential biological and photocatalysis based treatments for shipboard slop purification: A pilot plant investigation

This study investigated the treatment of a shipboard slop containing commercial gasoline in a pilot plant scale consisting of a membrane biological reactor (MBR) and photocatalytic reactor (PCR) acting in series. The MBR contributed for approximately 70% to the overall slop purification. More precisely, the biological process was able to remove approximately 40%, on average, of the organic pollution in the slop. Nevertheless, the membrane was capable to retain a large amount of organic molecules within the system, amounting for a further 30% of the influent total organic content removal. However, this affected the membrane fouling, thus resulting in the increase of the pore blocking mechani…

Aerobic granular sludge treating shipboard slop: Analysis of total petroleum hydrocarbons loading rates on performances and stability

Abstract 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…

Treatment of high strength industrial wastewater with membrane bioreactors for water reuse: Effect of pre-treatment with aerobic granular sludge on system performance and fouling tendency

Abstract In this study, the treatment of citrus wastewater with membrane bioreactors (MBRs) under different configurations was investigated for water reuse. In particular, one MBR and one aerobic granular sludge MBR (AGS + MBR) bench scale plants were operated for 60 days. The experimental campaign was divided into two periods. In Phase I, a conventional hollow fiber MBR was employed for the treatment of the raw high strength wastewater, whereas in Phase II a combination of in-series reactors (AGS + MBR) was adopted for the treatment of the high strength citrus wastewater The results demonstrated that both plant configurations enabled very high COD removal, with average values close to 99%.…

Achievement of partial nitrification under different carbon-to-nitrogen ratio and ammonia loading rate for the co-treatment of landfill leachate with municipal wastewater

Abstract Partial nitrification (PN) is a technically and economically effective solution for the treatment of wastewater featuring low C/N ratio, allowing to achieve approximately 25% energy saving and 40% carbon source for denitrification. This study investigated the effect of different carbon to nitrogen ratio (C/N) and ammonia loading rate (ALR) on PN performances in a sequencing batch reactor (SBR) treating landfill leachate with municipal wastewater. The aim was to find an optimum range for C/N and ALR to maximize PN performances. Results demonstrated that a proper balancing between ALR and C/N is crucial to achieve high PN efficiency. The results highlighted the existence of an optimu…

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

Abstract 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,…

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 m…

Study of aerobic granular sludge stability in a continuous-flow membrane bioreactor.

A granular continuous-flow membrane bioreactor with a novel hydrodynamic configuration was developed to evaluate the stability of aerobic granular sludge (AGS). Under continuous-flow operation (Period I), AGS rapidly lost their structural integrity resulting in loose and fluffy microbial aggregates in which filamentous bacteria were dominant. The intermittent feeding (Period II) allowed obtaining the succession of feast and famine conditions that favored the increase in AGS stability. Although no further breakage occurred, the formation of new granules was very limited, owing to the absence of the hydraulic selection pressure. These results noted the necessity to ensure, on the one hand the…

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

Abstract 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 bacte…

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 fra…

The role of extracellular polymeric substances on aerobic granulation with stepwise increase of salinity

Abstract 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. Th…

Respirometric assessment of heterotrophic and autotrophic biomass activity in alternate oxic-anoxic MBR pilot plant

The paper reports the main results of an experimental study carried out on a Membrane Biological Reactor (MBR) pilot plant characterized by intermittent aeration. The effect of different aeration/non aeration ratio (TA/TNA) on biomass behavior, in terms of heterotrophic and autotrophic kinetic parameters and active biomass fraction, was studied. Moreover was proposed a method to evaluate the autotrophic active fraction, derived by a combination of the ASM1 model and biokinetic parameters directly evaluated by means of respirometry. The experimental observation outlined that TA/TNA in the cycle didn’t affect heterotrophic biomass kinetic and active fraction. This one instead, resulted strong…

Effect of a co-substrate supply in a MBR treating shipboard slop: Analysis of hydrocarbon removal, biomass activity and membrane fouling tendency

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…

Biokinetic Behaviour of Autochthonous Halophilic Biomass at Different Salinity: Comparison Between Activated Sludge and Granular Sludge Systems

The main goal of this study was the evaluation of the impact of increasing salinity on halophilic biomass in forms of flocculent and granular sludge for the treatment of hypersaline fish-canning wastewater, focusing on the metabolic behavior of autotrophic biomass. For this purpose, two sequencing batch reactors, one with aerobic granular sludge (GSBR) and the other with flocculent activated sludge (SBR) were monitored. In both reactors, a halophilic biomass was cultivated from a real saline wastewater collected from a fish-canning industry. The salt concentration was stepwise increased (2 gNaCl L-1) from 30 gNaCl L-1 to 50 gNaCl L-1. Therefore, ammonia and nitrite uptake rates for granular…

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

Small and medium breweries discharging to municipal sewers without treatment generate significant loads with typical concentrations reported by Valta et al. (2014) as 2-6 g COD L-1, 25-80 mg TN L-1, 10-50 mg TP L-1, with pH between 4.5 and 12. Treatment of the high-strength wastewater requires specialized low footprint processes, such as aerobic granular sludge (AGS), capable of high-rate degradation, as well as simultaneous nitrogen and phosphorous removal (Wang et al., 2007). The objective of this study was to evaluate the start-up period of AGS receiving brewery wastewater after initial anaerobic pretreatment.

Optimization of acetate production from citrus wastewater fermentation

Abstract Citrus wastewater is a sugar-rich waste stream suitable for the recovery of energy of material from its treatment. In this study, fermentation of citrus wastewater was carried out to assess the optimal conditions to maximize the bioconversion of the organic substrate into acetate. Unbalanced nutrient (C: N: P 200:0.1:0.1) enabled the highest acetate production. The presence of the particulate organic fraction enabled to obtain a higher acetate concentration regardless the initial COD concentration. Initial pH values higher than 5 did not cause substantial differences on the maximum bioconversion of COD into acetate in Trial 3, whereas pH lower than 5 hindered the hydrolysis process…

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 consump…

The management of sewage sludge: technologies, critical issue and perspectives

The management of sludge produced by urban wastewater treatment plants has long been a problem for plant managers. This is due both to the growing costs for their disposal, and to the possible consequences that incorrect management may have on the performance of the wastewater treatment plant and on the environment. Further difficulties arose following the evolution of the European and national legislations, which regulates the management of sludge and its possible agronomic uses that introduced further checks and restrictions for this use. Several studies have been underway since last decades to reduce the extent of the problem. These focus on alternative objectives being aimed on the one …

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 remove…

Integrated production of biopolymers with industrial wastewater treatment: Effects of OLR on process yields, biopolymers characteristics and mixed microbial community enrichment

The production of polyhydroxyalkanoates (PHA) using industrial wastewaters as feedstocks is a current and challenging topic. This study investigated the production of biopolymers by a mixed microbial culture under different OLRs equal to 1 kgCOD m-3d-1 (Period 1), 2 kgCOD m-3d-1 (Period 2) and 3 kgCOD m-3d-1 (Period 3). The maximum PHA content was achieved in Period 2 (0.38 gPHA gTSS-1), whereas lower values were obtained in Period 1 (0.13 gPHA gTSS-1) and Period 3 (0.26 gPHA gTSS-1). Overall, the maximum PHA productivity resulted equal to 0.08 gPHA L-1h-1 (P2), 0.05 gPHA L-1h-1 (P1) and 0.04 gPHA L-1h-1 (P3), respectively. The molecular weight of the PHA increased from Period 1 (250 kDa) t…

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

Abstract 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…

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

Abstract 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 = …

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

Abstract 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…

RIMOZIONE COMBINATA DI CARBONIO E NUTRIENTI IN DUE REATTORI SBR GRANULARI: EFFETTO DELLA DIMENSIONE DEI GRANULI

Sono state investigate le performance di due impianti SBR (Sequencing Batch Reactor), alimentati con refluo sintetico a base di acetato di sodio e funzionanti con due differenti tipi di fango aerobico granulare, in termini di dimensione media dei granuli. In particolare, è stato analizzato l’impatto della differente dimensione dei granuli sul processo di nitrificazione e denitrificazione simultanea (Simultaneous Nitrification Denitrification, SND) e sulla rimozione biologica del fosforo. Allo scopo di valutare l’efficienza di tale tipo di processo, sono state applicate differenti strategie di coltivazione e condizioni operative, in termini di carico organico (COD 600-1200 mg/L) e azoto (60-…

An innovative respirometric method to assess the autotrophic active fraction: Application to an alternate oxic-anoxic MBR pilot plant

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 ni…

Analisi Sperimentali su impianti MBR ad aerazione intermittente

Cultivation of granular sludge with hypersaline oily wastewater

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 …

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

Abstract 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, where…

The role of extracellular polymeric substances (EPS) on aerobic granules formation: comparison between a case of synthetic wastewater supply and another of industrial wastewater

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, …

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 75 g NaCl L-1. The increasing salt concentration modified also the EPSs compos…

Application of the Oxic-Settling-Anaerobic Process in a Membrane Bioreactor for Excess Sludge Reduction

The main goal of this study was the evaluation of the excess sludge reduction in a MBR for biological nitrogen removal (BNR) through the implementation of the Oxic-Settling-Anaerobic (OSA) process. For this purpose, a MBR pilot plant (42 L volume) was realized according to a pre-denitrification scheme. The whole experimentation was divided into two periods, named Period 1 and Period 2, respectively. In Period 1 the pilot plant was started-up and the excess sludge production was evaluated. In Period 2 the plant configuration was partially modified by inserting an anaerobic reactor into the return activated sludge (RAS) line to realize an OSA configuration. In Period 1, the Yobs resulted equa…

Influence of the Oxic-Settling-Anaerobic (OSA) Process on Methane Production by Anaerobic Digestion of Sewage Sludge

The present study evaluated different sludge-reduction mechanisms in the oxic-settling-anaerobic (OSA) process in terms of their effects on methane productivity by anaerobic digestion of sewage sludge. Two different layouts were investigated for the sludge return from an anaerobic side-stream reactor (ASSR) to the anoxic (scheme A) or the aerobic (scheme B) reactor of a pre-denitrification plant. Biochemical methane-potential (BMP) assays performed on the excess sludge revealed that scheme A promoted an overall increase of methane production in the OSA (20 mLCH4 gVSS−1d−1, +19%), although compared with a control CAS plant a significant decrease in the excess sludge production (3…

A comprehensive comparison between halophilic granular and flocculent sludge in withstanding short and long-term salinity fluctuations

The effects of salinity fluctuations on the activity of autochthonous halophilic bacteria in aerobic granular sludge (AGS) and flocculent activated sludge (FAS) reactors were investigated. The response of nitrifiers and denitrifiers activity to drastic and moderate salinity shocks in the short-term (ST) and long-term (LT) was examined. The BOD5removal efficiency decreased only in the reactors subjected to the drastic LT salinity increase. Nevertheless, stable performances were achieved 18 days after the shock in the AGS-R1 (90%), whereas after 27 days in the FAS-R1 (82%). The loss in nitritation efficiency was higher in the FAS reactors and was proportional to the shock intensity. Nitritati…

Enhanced Sewage Sludge Drying with a Modified Solar Greenhouse

This work reports the results obtained with an innovative configuration of a closed-static solar greenhouse for sludge drying. The novelty of the solar greenhouse configuration consisted in using a forced ventilation system to provide hot air for sludge drying and the utilization of solar irradiation for energy supply. Wet sewage sludge (97% humidity) was successfully dried up to a residual humidity close to 5% after 25 days during wintertime. The increase of the airflow rate supplied under the sludge bed improved the sludge drying rate. Moreover, the fraction of volatile suspended solids decreased from 70% to 41% after 13 days, indicating that air supply promoted the simultaneous stabiliza…

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

Abstract 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 efflu…

The role of extracellular polymeric substances (EPS) on aerobic granules formation: comparison between a case of synthetic wastewater supply and another of industrial wastewater

The paper focused on the evolution of extracellular polymeric substances (EPSs) content during the granulation process in two Granular Sequencing Batch Airlift Reactors (GSBAR) (3,5 L) fed with synthetic and industrial wastewater. Results showed that EPSs, in particular proteins (PN) were mainly produced during the feast phase because of high substrate availability, especially under conditions of metabolic stress. Than EPSs content reduced during the famine period. More in detail, during the granulation process, a greater polysaccharides (PS) consumption occurred in both reactors, while PN content reduced significantly only in R2. As a result PN/PS ratio increased significantly during granu…

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 aero…