Pilot-scale Activated Sludge System Research Articles

Effects of pH on extracellular polymeric substances compositions of biofilm in Integrated Fixed Film Activated Sludge process

Integrated fixed film activated sludge system typically integrates biofilm in the aerobic zone. The proteins-to-polysaccharides ratio of extracellular polymeric substances in the biofilm matrix is related to the strength of biofilm and, thereby, involves with the reliability and performance of this system. This study evaluated the effects of pH on proportions of both components in the extracellular polymeric substances of biofilm installed in the aerobic zone of this system. The experiments were conducted in four identical pilot-scale activated sludge systems, by which three systems were installed with Bioweb® media in the aerobic zones and fed with different wastewater pH values of 6.5, 7.5 and 8.5, respectively. Another system without fixed film media installed was fed with influent pH of 7.5 and then used as a control system. It was found that the proteins-to-polysaccharides ratios of the extracellular polymeric substances in biofilm were 0.12, 0.10 and 0.08 (w/w) at the influent pH values of 6.5, 7.5 and 8.5, respectively. The ratios decreased as the influent pH increased from 6.5 to 8.5, suggesting that extracellular polymeric substances were loosely structured in biofilm layers. Less proteins with more polysaccharides were found at high pH of 8.5, leading to resulting in the easily detachment of biofilm and viscous bulking of suspended flocs. Loosely structured biofilm decreased the mass transfer resistances, resulting in higher denitrification and nitratation in aerobic zones; therefore, the highest biological nitrogen removal was achieved at the pH of 8.5.

Clustering, morphology, and treatment resistance of Bacillus globigii spores recovered from a pilot-scale activated sludge system

This study examines the organization and morphology of Bacillus globigii (BG) spores, a common surrogate for Bacillus anthracis, which were seeded and then recovered at various times from several points within a conventional, pilot-scale activated sludge system. Recovered BG spores were enumerated, microscopically examined, and tested for resistance to chemical (i.e. 5% H2O2 for 8 min), thermal (80 °C for 30 min), and ultraviolet light (8 W, 254 nm UV for 1 min) inactivation. Spores exposed to activated sludge germinated, sporulated, and exhibited unique multilayer clustering patterns and statistically significant changes (p < 0.005) in dimensional morphology. Spores collected in the later experimental stages (i.e., during weeks 6 and 7) were significantly more resistant (p ≤ 0.05) to inactivation than those collected on the first day of testing. These results have direct consequences for sludge treatment requirements at wastewater treatment plants that receive spore-containing waste streams.

Influence of hydraulic retention time, food-to-microorganism ratio and influent biodegradability on the performance of an aerobic selector treating petrochemical wastewater

Selectors have been widely recognized as a solution to control filamentous bulking and consequently enhance sludge settling. However, to guarantee the selector’s effectiveness (Sludge Volumetric Index<100mLg−1 during 90% of the time) in a full-scale installation, it is compulsory to find the proper design and operational parameters, according to the quality of the wastewater treated. In order to identify the key parameters to optimize the selector’s performance, petrochemical wastewater was tested in a pilot-scale activated sludge system including an aerobic selector. The optimum conditions in the selector were an hydraulic retention time (HRT) of 30min and a food-to-microorganism ratio (F/M) from 30 to 35g CODg−1 VSS day−1. They corresponded to the selector’s maximum COD (37.4%) and BOD5 (95.1%) removal efficiency and the dominance of the storage mechanism in front of replicative growth (ratio Nitrogen assimilation-to-Volatile Suspended Solid production of 0.07g NH4+-N assimilated g−1 VSS produced). Feeding a more biodegradable influent to the selector (up to 45g BODg−1 VSS day−1) enhanced its effectiveness, whereas increasing the supply of particulate matter (up to 139.6g CODg−1 VSS day−1) showed a negative effect on sludge settling. The inclusion of the aerobic selector in the activated sludge system, operated at the optimum parameters, resulted in an older aged sludge. Increasing the selector’s F/M above the optimum value or reducing the influent BOD5 produced a progressive loss of efficiency of the activated sludge system and higher oxygen requirements.

Sludge settling enhancement in a pilot scale activated sludge process treating petrochemical wastewater by implementing aerobic or anoxic selectors

Industrial Continuous Stirred Tank aerobic biological Reactors (CSTR) often suffer from low F/M filamentous bulking, which results in deficient sludge settling. In order to find solutions to this issue, a pilot-scale Activated Sludge System treating petrochemical wastewater was operated under three different conditions: i) Increasing the F/M supplied to the CSTR ii) Including an anoxic selector iii) Including an aerobic selector. The initial sludge quality, characterized by DSVI values of 500mLg−1, open floc structure and bridging filaments was slightly improved by increasing the F/M from 0.10 up to 0.40g COD g−1VSS day−1. However, the Diluted Sludge Volumetric Index (DSVI) didn't reach values lower than 100mL g−1 until a selector was implemented. Anoxic and aerobic selectors were effective to improve sludge settling, reducing DSVI to average values of 80 and 45mLg−1, respectively. However, whereas the anoxic selector produced lots of short filaments, the aerobic selector reduced significantly the number of filaments, obtained a more compact floc structure and leaded to a more reliable operation. Biomass and nitrogen balances suggested that production of new biomass cells and substrate uptake for storage occurred in both selectors. The aerobic selector system, compared to the CSTR, also leaded to a slightly higher soluble COD removal efficiency, as well as lower observed ammonia assimilation and lower observed volatile suspended solid production per unit of COD, in the main reactor. The last factor indicated that including a selector resulted in an older sludge, susceptible of experiencing nitrification issues.

Pilot-scale verification of efficient nitrifier backseeding in a combined activated sludge-biofilm system

Purpose of the paper is to experimentally verify that a downstream nitrifying fixed-film reactor may effectively backseed an activated sludge (AS) system. The experiment was carried out at the Southpest Wastewater Treatment Plant in Budapest, Hungary, with two pilot-scale AS systems connected directly to the preclarified influent and to the stream recirculated from the nitrifying fixed-film reactor of the full-scale plant ensuring both the nitrate and the backwashed biomass recirculation. Effluent NH 4 -N level dropped down to near zero in the experimental systems whereas no significant nitrification occurred in the fullscale plant being operated at lower aeration intensity. Simulation model developed for describing the combined system supported that backseeding was the cause of the high nitrification efficiency having been limited by inadequate oxygen supply in the full scale system.

Water Treatment Plant Sludge Discharge to Wastewater Treatment Works: Effects on the Operation of Upflow Anaerobic Sludge Blanket Reactor and Activated Sludge Systems

This experiment examined the effects of the discharge of water treatment plant (WTP) sludge into the following three types of wastewater treatment systems: a pilot-scale upflow anaerobic sludge blanket (UASB) reactor, a pilot-scale activated sludge system, and a full-scale activated sludge sequencing batch reactor (SBR). The UASB reactor received 50 mg of suspended solids (SS) of WTP sludge per liter of wastewater in the first phase, and, in the second phase, it received 75 mg SS/L. The pilot-scale activated sludge system received 25 and 50 mg SS/L in the first and second phases, respectively. The full-scale WWTP (SBR) received approximately 74 mg SS/L. The results of the experiments showed that, despite some negative effects on nitrification, there were positive effects on phosphorus removal, and, furthermore, there was the addition of solids in all systems.

The influence and mechanism of influent pH on anaerobic co-digestion of sewage sludge and printing and dyeing wastewater

Two pilot-scale activated sludge systems consisting of an anaerobic baffled reactor (ABR) and an aerobic plug flow reactor (PFR) were operated with the aim of minimising excess sludge output of the activated sludge process through coupled alkaline hydrolysis and anaerobic digestion. Variations in the effluent of total chemical oxygen demand (TCOD), NH4 +-N and TP concentration proved that the recirculation ratio of aerobic excess biomass recirculated to ABR could obtain 60% of theoretically total aerobic excess sludge production, under aerobic conditions with effluent TCOD concentration well below the discharge limit of 150 mg/ℓ. After hydrochloric acid addition in the influent to neutralise high influent pH, the solubilisation of alkaline hydrolysis was obviously damaged and the effluent concentrations exceeded the discharging limit. High influent pH could promote the reduction efficiency of excess sludge production during co-digestion of printing and dyeing wastewater and sewage sludge. A possible mechanism of influent pH acting on anaerobic co-digestion was put forward.Keywords:&nbsp; alkaline hydrolysis, anaerobic co-digestion, influent pH, printing and dyeing wastewater, sludge

The influence of aerobic sludge retention time on anaerobic co-digestion of dyeing and printing wastewater and sewage sludge

Two pilot-scale activated sludge systems comprising anaerobic baffled reactor (ABR) and aerobic plug flow reactor (PFR) were operated aiming to minimize excess sludge output of the activated sludge process through coupled alkaline hydrolysis and anaerobic digestion. Variations in the effluent total chemical oxygen demand (TCOD) and NH4 +-N concentration proved that the process not only could minimize excess sludge production but also guarantee the effluent TCOD well below the discharging limit (150 mg/l) if the inverse ratio of the aerobic sludge recirculation to anaerobic reactor did not exceed 60% for system A with 10 d aerobic sludge retention time (SRT) and 40% for system B (SRT was 25 d). The sludge activity at aerobic SRT of 25 d was evidently lower than aerobic SRT of 10 d. Those differences of sludge characteristics affected the inverse sludge ratio obviously. Aerobic bacteria after internal and external decay were converted to anoxic or anaerobic biomass. The distinct differences in sludge yield of aerobic and anaerobic/anoxic processes could explain how aerobic SRT decided excess sludge activity which consequently affected anaerobic codigestion of printing and dyeing wastewater and sewage sludge.

Utilization of an Activated Sludge for the Improvement of an Existing Thermophilic Wastewater Treatment System

A pilot-scale activated sludge system was started to determine its effectiveness in treating the thermophilic biological effluent from an existing organic chemical industrial wastewater treatment system. Preliminary results demonstrated that an additional 95% biological oxygen demand and 65% dissolved organic carbon removal was achieved. In addition, significant biodegradation of the volatile organic compounds and organic nitrogen was observed.

Operational strategies for an activated sludge process in conjunction with ozone oxidation for zero excess sludge production during winter season

A pilot-scale activated sludge system coupled with sludge ozonation process was operated for 112 days of a winter season without excess sludge wasting. The concept of this process is that the excess sludge produced is first disintegrated by ozone oxidation and then recirculated to a bioreactor in order to mineralize the particulate and soluble organic compounds. The basis of operation was to determine either the optimal amount of sludge in kg SS ozonated each day (SO) or the optimal ozonation frequency under the variable influent chemical oxygen demand (COD) loading and temperature conditions, since the ozone supply consumes costly energy. The optimal SO was obtained using the theoretically estimated sludge production rate (SP) and experimentally obtained ozonation frequency (n). While the SP was mainly subject to the COD loadings, sludge concentration was affected by the temperature changes in winter season. The optimal n was observed between 2.5 and 2.7 at around 15 degrees C, but it was doubled at 10 degrees C. Mixed liquor suspended solids (MLSS) concentration was leveled off at around 5000 mg/L in bioreactor at 15 degrees C, but the volatile fraction of MLSS was fixed around 0.7 indicating that there was no significant inorganic accumulation. Suspended solids (SS) and soluble COD in effluents kept always a satisfactory level of 10 and 15 mg/L with sufficient biodegradation. It was recommended to apply a dynamic SO under variable influent COD loadings and temperature conditions to the activated sludge system without excess sludge production for saving energy as well as system stabilization.

Effect of low ORP in anoxic sludge zone on excess sludge production in oxic-settling-anoxic activated sludge process

This paper studied the effect of oxidation–reduction potential (ORP) in the anoxic sludge zone on the excess sludge production in the oxic-settling-anoxic process (OSA process), a modified activated sludge process. Two pilot-scale activated sludge systems were employed in this study: (1) an OSA process that was modified from a conventional activated sludge process by inserting a sludge holding tank or namely the “anoxic” tank in the sludge return line; and (2) a conventional process used as the reference system. Each was composed of a membrane bioreactor to serve the aeration tank and solid/liquid separator. Both systems were operated with synthetic wastewater for 9 months. During the operation, the OSA system was operated with different ORP levels (+100 to −250 mV) in its anoxic tank. It has been confirmed that the OSA system produced much less excess sludge than the reference system. A lower ORP level than +100 mV in the anoxic tank is in favor of the excess sludge reduction. When the ORP level decreased from +100 to −250 mV the sludge reduction efficiency was increased from 23% to 58%. It has also been found that the OSA system performed better than the reference system with respect to the chemical oxygen demand removal efficiency and sludge settleability. The OSA process may present a potential low-cost solution to the excess sludge problem in an activated sludge process because addition of a sludge holding tank is only needed.

Fate of selected RCRA compounds in a pilot-scale activated sludge system

Water Environment ResearchVolume 68, Issue 7 p. 1194-1214 Discussion Fate of selected RCRA compounds in a pilot-scale activated sludge system Gregory M. Adams, Gregory M. AdamsSearch for more papers by this author Gregory M. Adams, Gregory M. AdamsSearch for more papers by this author First published: 01 November 1996 https://doi.org/10.2175/106143096X128649AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume68, Issue7November-December 1996Pages 1194-1214 RelatedInformation

Dependence of the heat resistance of bacterial spores on the calcium: Dipicolinic acid ratio

This study examines the organization and morphology of Bacillus globigii (BG) spores, a common surrogate for Bacillus anthracis, which were seeded and then recovered at various times from several points within a conventional, pilot-scale activated sludge system. Recovered BG spores were enumerated, microscopically examined, and tested for resistance to chemical (i.e. 5% H2O2 for 8 min), thermal (80 °C for 30 min), and ultraviolet light (8 W, 254 nm UV for 1 min) inactivation. Spores exposed to activated sludge germinated, sporulated, and exhibited unique multilayer clustering patterns and statistically significant changes (p < 0.005) in dimensional morphology. Spores collected in the later experimental stages (i.e., during weeks 6 and 7) were significantly more resistant (p ≤ 0.05) to inactivation than those collected on the first day of testing. These results have direct consequences for sludge treatment requirements at wastewater treatment plants that receive spore-containing waste streams.