1,721,084 research outputs found
Biopolymer Recovery from Aerobic Granular Sludge and Conventional Flocculent Sludge in Treating Industrial Wastewater: Preliminary Analysis of Different Carbon Routes for Organic Carbon Utilization
Full text linkThe 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
Effect of long-term salinity increase on nitritation and denitritation kinetics in activated sludge and granular sludge reactors
No full textThe aim of this work was to investigate the effects of moderate and drastic long-termincrease of salinity.Particularly, the study was aimed at assessing the shock effecton nitritationand denitritation kineticsof halophilic biomass inboth forms:flocculent activated sludge and granular sludge
Biological Stability of Organic Fraction of Municipal Solid Wastes During Composting Processes
No full textThe 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 2,650mgO(2)/(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
The anaerobic exposure time (AET) as a novel process parameter in the anaerobic side-stream reactor (ASSR)-based process for excess sludge minimization
No full textMinimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields. To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Yobs) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10-60 %) with the increase of the AET (7.9-13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Yobs reduction reported in previous studies, also indicating a linear relationship (R-2 = 0.92) between these parameters. Contrarily, the correlation between the Yobs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=-0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process
The role of extracellular polymeric substances on aerobic granulation with stepwise increase of salinity
Full text linkA 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
Influence of the Oxic-Settling-Anaerobic (OSA) Process on Methane Production by Anaerobic Digestion of Sewage Sludge
Full text linkThe 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 (31%) was obtained. Operating conditions in scheme A caused the occurrence of cell lysis and EPS hydrolysis, thereby increasing the biodegradability of sludge. In contrast, scheme B favoured the occurrence of uncoupling and a maintenance metabolism that did not involve sludge hydrolysis. Consequently, despite a higher reduction of excess sludge (82%), a significant decrease in methane productivity in the OSA (4 mLCH4 gVSS−1d−1, −41%) was observed. Based on the results, implementing the OSA process may allow high levels of methane production by anaerobic digestion to be maintained if specific sludge-reduction mechanisms are triggered in the waterline, also raising the possibility of co-digestion with other feedstocks
Shortcut nitrification-denitrification by means of autochthonous halophilic biomass in an SBR treating fish-canning wastewater
No full textAutochthonous 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 Lâ1), 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
Combination of the OSA process with thermal treatment at moderate temperature for excess sludge minimization
Full text linkThis 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%)
A comprehensive comparison between halophilic granular and flocculent sludge in withstanding short and long-term salinity fluctuations
No full textThe 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. Nitritation activity collapsed from approximately 3.8 mgNH4-N gVSSâ1hâ1to 0.73 mgNH4-N gVSSâ1hâ1and from 4.5 mgNH4-N gVSSâ1hâ1to 0.24 mgNH4-N gVSSâ1hâ1in the AGS-R1 and FAS-R1, respectively, even if the ammonium oxidation capacity did not completely disappeared. Denitritation activity decreased from 11.44 mgNO2-N gVSSâ1hâ1to 3.93 mgNO2-N gVSSâ1hâ1in the AGS-R1 at steady state, whereas in the FAS-R1, it decreased from 12.53 mgNO2-N gVSSâ1hâ1to 2.09 mgNO2-N gVSSâ1hâ1. Nitritation and denitritation were completely restored 5 days after ST shock. No significant effects were observed after the moderate shock. The changes in the total EPS content were lower than 10%, therefore, it was considered negligible. Only drastic shocks caused significant changes in the EPS structure, with an increase of the loosely-bound by 45% in the AGS and 55% in the FAS
- …
