High Sludge Retention Time Research Articles

Increasing the energy production in an urban wastewater treatment plant using a high-rate activated sludge: Pilot plant demonstration and energy balance

The use of high-rate activated sludge (HRAS) reactors for the removal of COD in urban wastewater treatment plants (WWTPs) has been investigated because its potential contribution to energy generating WWTPs. A one-year operation period of a pilot plant treating the effluent of the primary settler of a full-scale WWTP was analyzed. The HRAS pilot plant operated without iron salts addition at temperatures between 12 and 28 °C at an average organic loading rate 2.8 ± 0.5 kg COD m−3 d−1 and with an average inflow COD concentration of 330 ± 86 mg O2 L−1. The influence of sludge retention time (SRT) on COD recovery and biomethane potential of the produced sludge was investigated and compared to the full scale WWTP performance. The highest observed sludge yield coefficient and biomethane potential of the sludge were achieved at SRT of 0.6 days. The weak point of the HRAS performance at STR of 0.6 days is the high loss of organic matter in the effluent due to the limited efficiency of the solids separation in the secondary settler. At higher SRT (in the range 1.0–2.1 days), the secondary settler efficiency and the COD recovery are higher than those achieved at SRT of 0.6 days but part of the inlet ammonium can be nitrified in the HRAS system at temperatures above 20 °C. A detailed energy balance indicated that two-thirds reduction of aeration requirements and one-third increase of biogas production could be achieved in a plant configuration in which HRAS is coupled to autotrophic biological nitrogen removal (BNR) compared to the heterotrophic BNR configuration, yielding a net energy production of ca. 0.1 kWh m−3 of treated water.

Kinetics of Pulp and Paper Wastewater Treatment by High Sludge Retention Time Activated Sludge Process

Paper and pulp industrial processes lead to the discharge of wastewater that contains high pollutants concentrations into the environment, which subsequently contaminate freshwater. Thus, it necessitates a sustainable treatment approach. This study focused on the start-up of the bench-scale activated sludge system fed with pulp and paper wastewater to verify the influence of HRT, wastewater concentration, and sugarcane bagasse on COD and ammonia removal efficiencies during the treatment process. An activated sludge process was operated at a flow rate of 5 L/day, while the reactor kept running at 72 h, 48 h, and 24 h HRT, respectively. Wastewater concentrations were set at 1039, 3158, 5248 mgCOD//L and 13.74, 40.37, 67.04 mgNH4+-N/L corresponding to 10, 50 and 100% respectively. Findings revealed high removal efficiencies up to 98.11% and 92.67% for COD and ammonia, respectively. After treatment, effluent concentrations for both parameters have satisfactorily met the Standard "A" standard limits for industrial discharge at 48 hours HRT. Therefore, further testing is not required. The First order and Modified Stover-Kincannon models evaluated substrate removal rates. In the Modified Stover–Kincannon model, high correlation coefficients R2 of 0.9999 and 0.9998 were obtained for COD and ammonia, respectively. Unfortunately, the activated sludge process in the bioreactor could not be described by the first-order kinetic model. The modified Stover-Kincannon model proved to best suit the experimental data.

Influence of volatile solids and pH for the production of volatile fatty acids: Batch fermentation tests using sewage sludge

The aim of this work was to study the effect of volatile suspended solid (VSS) and pH on volatile fatty acids (VFA) production from waste activated sludge (WAS) fermentation by means of batch tests. The final goal was to gain insights to enhance VFA stream quality, with the novelty of using WAS with high sludge retention time. Results revealed that the optimum conditions to maximize VFAs and minimize nutrients and non-VFA sCOD are a VSS concentration of 5.9 g/L and initial pH adjustment to pH 10. The WAS bacterial community structures were analysed according to Next Generation Sequencing (NGS) of 16S rDNA amplicons. The results revealed changes of bacterial phyla abundance in comparison with the batch test starting condition.

An innovative biofilter technology for reducing environmental spreading of emerging pollutants and odour emissions during municipal sewage treatment

Wastewater treatment plants (WWTPs) are known sources of contaminants of emerging concern (CECs) spreading into the environment, as well as, of unpleasant odors. CECs represent a potential hazard for human health and the environment being pharmaceutical or biologically active compounds and they are acquiring relevance in European directives. Similarly, the public concern about odour emissions from WWTPs is also increasing due to the decreasing distance between WWTP and residential areas. This study focuses on the effectiveness of the recently developed MULESL technology (MUch LEss SLudge; WO2019097463) in removing CECs and limiting odour emissions from WWTPs. MULESL technology has been developed for its ability to reduce up to 80% the sludge production from WWTPs. However, it is ought to evaluate if the benefits coming from sludge production reduction do not invalidate CECs removal or negatively affect odour emissions. Thus, the performances of a MULESL and a conventional WWTP (flow rate of 375 m3/d and 3600 m3/d, respectively) were compared while treating the same municipal sewage.Whereas both plants succeeded in removing the traditional gross parameters characterizing wastewaters (e.g. chemical oxygen demand, nitrogen), the MULESL was much more effective than the conventional one in terms of CECs removal for about 60% of the identified compounds showing, however, the same or lower effectiveness for about 30% and 10% of them, respectively. This result was attributed to the high sludge retention time and biomass concentration in the MULESL (enabling enrichment of slow growing microorganisms and forcing biomass to use unusual substrates, respectively), and to the biomass feature to grow in the form of biofilm and granules (favoring micropollutants absorption on biomass).Furthermore, odour impact analysis has shown that the MULESL was characterized by a much lower impact, i.e. 45% lower than that of primary and secondary treatments of the conventional WWTP.

Development of aerobic granulation system for simultaneous removal of C, N, and P in sequencing batch airlift reactor

Conventional biological nutrient removal techniques often have disadvantages like low removal efficiencies, requirement of large footprint, and excess sludge production. Ever increasing stringent discharge standards demand for alternative technologies. In this context aerobic granular sludge (AGS) has evolved as a promising technology for complete nutrient removal. However, degradation of structural integrity of aerobic granules in long run is a prime concern of this technology. This work attempts to develop stable aerobic granules in an automated sequential batch airlift reactor (SBAR) for simultaneous C, N, and P removals under alternating aerobic and anoxic conditions. The reactor was operated at high sludge retention time (SRT). Combined operating strategies of varying dissolved oxygen (DO) concentration and feed cycle times were followed to optimize the conditions for effective granulation and subsequent removal efficiencies. Profiles of extracellular polymeric substances (EPS) and sludge volume index (SVI) were monitored. Optimum removal efficiencies of NH4+-N (92.7%), TN (90.6%), COD (90.1%), and PO43--P (83.2%), and granules of size 1.3–8 mm were achieved in phase IV at operational DO of 1–2 mg/L, and feeding intervals of 15 h and 9 h. NH4+-N (R2 = 0.97, k = 0.5093/h) and PO43--P (R2 = 0.95, k = 0.2574/h) removals were fitted well with first order kinetic model and that of COD (R2 = 0.97, k = 0.0032 L/mg/h) followed second order kinetics. This process is economical as effective biological nutrient and organics removal occurs in a single reactor without requirement of alkalinity supply, and negligible excess sludge production. The process requires small foot print and applicable for decentralized wastewater management in University campuses/tourist resorts/apartment complexes.

Fate of pharmaceutically active compounds in a pilot-scale A2O integrated fixed-film activated sludge (IFAS) process treating municipal wastewater

The goal of this research was to study the operation of an integrated fixed-film activated sludge system (IFAS), in anaerobic/anoxic/aerobic (A2O) configuration for the elimination of emerging pollutants, in particular of 27 pharmaceutical active compounds (PhACs) (eight anti-inflammatory and/or analgesic pharmaceuticals (AIAPs), six antibiotics, four b-blockers, two antihypertensives/diuretics, three lipid regulators-bezafibrate and four psychiatric medications). Different operational conditions were analyzed in the biological reactor, controlling at all times both the amount of suspended and fixed biomass present. The A2O-IFAS system has obtained similar or higher removal efficiency (RE) in the elimination of organic matter, and especially of nutrients, nitrogen (N) and phosphorous (P), with respect to the conventional A2O system, working however with very low values of the sludge retention time (SRT) (4.0 days) and mix liquid suspended solid (MLSS) in the reactor (1822 mg L-1). In general, conventional activated sludge (CAS) and IFAS processes show the importance of operating at high SRT and MLSS concentration, that give low food/microorganisms (F/M) ratio, to increase the RE of several PhACs. However, the A2O-IFAS system, operating with low mixed liquor SRT and MLSS has achieved similar or better RE of PhACs, obtaining the highest average REs values (>80%) for fenofibrate, acetaminophen, ibuprofen, naproxen, clarithromycin and atenolol. According to the results obtained, due to the affordable cost and well-demonstrated performance, IFAS systems become one of the most promising technology for conventional wastewater treatment plants (WWTP) upgrading.

Steady-State Methodology for Activated Sludge Model 1 (ASM1) State Variable Calculation in MBR

The complexity of Activated Sludge Model No. 1 (ASM1) is one of the main obstacles slowing its widespread use, particularly among wastewater treatment plant (WWTP) professionals. In this paper, a simplification procedure based on steady-state mass balances is proposed for the conventional activated sludge process (ASP) configuration, consisting of an aerated bioreactor and a perfect settler (without particular compounds in the outlet). The results do, in fact, show perfect suitability to a membrane bioreactor process (MBR). Both organic carbon and nitrogen removal were investigated. The proposed approach was applied to ASM1, and simple analytical expressions of the state variables were obtained. These analytical expressions were then validated by comparison to simulations given by the original ASM1 (implemented in GPS-X software). A strong match (less than 4% of error overall) was obtained between both results in the steady-state; consequently, these analytical expressions may be useful as tools for quickly estimating the main state variables, feeding the filtration models, or identifying the interaction between operating parameters. Moreover, this enables a sensitivity analysis, covering relevant factors such as kinetics or operating parameters. For instance, the sludge retention time (SRT) effect is lower on XBH and XS at high SRT (˃20 days), while it is more pronounced on XP and XI as their variations with SRT are linear.

Investigation of micropollutants removal from landfill leachate in a full-scale advanced treatment plant in Istanbul city, Turkey

Although the levels of micropollutants in landfill leachate and municipal wastewater are well-established, the individual removal mechanisms and the fate of micropollutants throughout a landfill leachate treatment plant (LTP) were seldom investigated. Therefore, the determination of the removal efficiencies and the fates of micropollutants in a full-scale leachate treatment plant located in the largest city of Turkey were aimed in this study. Some important processes, such as equalization pond, bioreactor, ultrafiltration (UF) and nanofiltration (NF), are being operated in the treatment plant. Landfill leachate was characterized as an intense pollution source of macro and micropollutants compared to other water types. Chemical oxygen demand (COD), NH3, suspended solids (SS) and electrical conductivity (EC) values of the landfill leachate (and their removal efficiencies in the treatment plant) were determined as 18,656 ± 12,098 mg/L (98%), 3090 ± 845 mg/L (99%), 4175 ± 1832 mg/L (95%) and 31 ± 2 mS/cm (51%), respectively. Within the scope of the study, the most frequently and abundantly detected micropollutants in the treatment plant were found as heavy metals (8 ± 1.7 mg/L), VOCs (38 ± 2 μg/L), alkylphenols (9 ± 3 μg/L) and phthalates (8 ± 3 μg/L) and the overall removal efficiencies of these micropollutants ranged from −11% to 100% in the treatment processes. The main removal mechanism of VOCs in the aerobic treatment process has been found as the volatilization due to Henry constants greater than 100 Pa·m3/mol. However, the molecular weight cut off restriction of UF membrane has caused to less or negative removal efficiencies for some VOCs. The biological treatment unit which consists of sequential anoxic and oxic units (A/O) was found effective on the removal of PAHs (62%) and alkylphenols (87%). It was inferred that both NO3 accumulation in anoxic reactor, high hydraulic retention time (HRT) and sludge retention time (SRT) in aerobic reactor provide higher biodegradation and volatilization efficiencies as compared to the literature. Membrane processes were more effective on the removal of alkylphenols (60–80%) and pesticides (59–74%) in terms of influent and effluent loads of each unit. Removal efficiencies for Cu, Ni and Cr, which were the dominant heavy metals, were determined as 92, 91 and 51%, respectively and the main removal mechanism for heavy metals has thought to be coprecipitation of suspended solids by microbial biopolymers in the bioreactor and the separation of colloids during membrane filtration. Total effluent loads of the LTP for VOCs, semi volatiles and heavy metals were 1.0 g/day, 5.2 g/day and 1.5 kg/day, respectively. It has been concluded that the LTP was effectively removing both conventional pollutants and micropollutants with the specific operation costs of 0.27 $/(kg of removed COD), 0.13 $/(g of removed VOCs), 0.35 $/(g of removed SVOCs) and 2.6 $/(kg of removed metals).

Efficient carbon, nitrogen and phosphorus removal from low C/N real domestic wastewater with aerobic granular sludge

This work reports on simultaneous nitrification, denitrification and phosphorus removal treating real domestic wastewater with low carbon/nitrogen (C/N) ratio by aerobic granular sludge (AGS). Operations at high sludge retention time (SRT = 61 ± 24 days) resulted in low biomass yield per chemical oxygen demand removed (CODrem) (0.21 ± 0.01 gCODx/gCODrem), lower COD demand for denitrification as well as high effluent quality in terms of total suspended solids (TSS) (22 ± 7 mgTSS/L). The average ratio between the biodegradable soluble COD stored anaerobically as polyhydroxyalkanoates (PHAs) and the N removed was 3.1 ± 0.6 gCODsto/gNrem, suggesting that nitrification/denitrification occurred partly via the nitrite pathway. Results revealed that stable AGS process with high C/N/P removal efficiency of 84/71/96% can be obtained besides a low organic loading rate (0.43 ± 0.11 g COD/L/d) and influent C/N ratio (3.8 ± 1.6 g/g), resulting in a high effluent quality characterized by 25 ± 6 mg sCOD/L, 0.09 ± 0.07 mgPO4-P/L, 9 ± 2 mgTIN/L (10 ± 2 mgTN/L) and 22 ± 7 mgTSS/L.

Long-term acclimatization of sludge microbiome for treatment of high-strength organic solid waste in anaerobic membrane bioreactor

In this study, anaerobic membrane bioreactor (AnMBR) was applied for the treatment of a model slurry of high-strength organic solid waste. Continuous monitoring of reactor performances by chemical analyses and fine-scale tracing of the AnMBR sludge microbiome by high-throughput 16S rRNA gene sequencing were conducted during the long-term operation with increased organic loading rates (OLRs) up to 5.26 kgCOD m−3 day−1. Stable treatment was achieved at the highest OLR for over 170 days. The chemical oxygen demand removal rate of around 99%, membrane flux of 3.31 ± 0.40 L m−2 h−1, and biogas production rate of 31.1 ± 4.8 L day−1 were observed. The latter two parameters were improved after the sludge retention time (SRT) control, showing 4.76 ± 0.25 L m−2 h−1 and 34.5 ± 6.9 L day−1, respectively. The principal coordinate and taxonomic analyses of the sequence data showed that the sludge microbiome was changed drastically in response to both the OLR increase and SRT control. The species-level characterization showed that the relative abundances of aceticlastic methanogens, e.g., Methanosaeta concilii, decreased at high OLRs, whereas those of hydrogenotrophic methanogens, such as Methanolinea mesophila, as well as a syntrophic bacterium Smithella propionica, increased under the high OLRs and SRT control conditions. These results strongly suggest that the effective treatment of the high-strength organic solid waste slurry was mediated via the syntrophic methanogenesis pathway in the AnMBR.

Coupling ammonia nitrogen adsorption and regeneration unit with a high-load anoxic/aerobic process to achieve rapid and efficient pollutants removal for wastewater treatment

In this study, an ammonium nitrogen (NH4+-N) adsorption and regeneration (AAR) was constructed by a zeolite-packed column and NaClO–NaCl regeneration unit, and coupled with an anoxic/aerobic (AO) system to achieve efficient removal of carbon, nitrogen and phosphorus under short hydraulic retention time (HRT) and sludge retention time (SRT). Compared to conventional anaerobic/anoxic/aerobic (AAO) process, the proposed AO-AAR process achieved more efficient and stable nitrogen removal with greatly shorter HRT (5.6 h) and SRT (8 d) at 10.4 °C, with NH4+-N and total nitrogen in the effluent below 1.5 and 8.0 mg/L, respectively. The AO-AAR also obtained efficient phosphorus removal (<0.5 mg/L) by dosing aluminum in aerobic tank. High load and short SRT deteriorated sludge settleability and dewaterability, but enhanced methane production by improving sludge biodegradability. Dosing aluminum made the AO operating module more stable with improved settleability and dewaterability, and further enhanced methane production. Short HRT and SRT also resulted in the thriving of filamentous bacteria (Thiothrix) and heterotrophic nitrifiers (Acinetobacter, Pseudomonas and Rhodobacter) in the AO module, which helped in enhancing denitrification potential and nitrification efficiency under low temperature. Long-term operation showed that exchange capacity and physicochemical properties of zeolite were unchanged under NaClO–NaCl regeneration by introducing the tail gas from aerobic tank into the used regenerant to remove Ca2+ and Mg2+ exchanged from effluent of the AO module. Techno-economic analysis showed that the AO-AAR process is attractive and sustainable for municipal wastewater treatment by significantly improving nitrogen removal, greatly reducing land occupancy, enhancing methane production and achieving efficient reduction of carbon dioxide emission.

Biological Treatment of a Synthetic Musk in a Raw Hospital Wastewater Under Different Sludge Retention Times

Pharmaceuticals and personal care products (PPCPs) are the problem of our age and hospital wastewaters are one of the main sources of PPCPs having a concentration range of ng L-1 to µg L-1 Hospital wastewaters are almost untreated before being discharged into municipal/urban wastewater treatment plants (WWTPs) via wastewater networks in Turkey. These WWTPs are not designed to remove complex compounds such as PPCPs, however, a sizeable amount is released into the environment. Some of the PPCPs present a considerable threat for aquatic organisms even at very low concentrations. This study presents the biological treatability of a synthetic musk namely musk tonalide (AHMT) from a raw hospital wastewater under different sludge retention times (SRTs). The treatability of this PPCP was investigated using an anaerobic UASB/aerobic CSTR sequential biological reactor system in laboratory conditions for the first time in Turkey. Effect of different sludge retention times (5; 30; 45 and 55 days) on the removal of AHMT was researched at mesophilic temperature conditions for the biological reactors. COD, SCOD and AHMT yields were determined. Methane gas (CH4) productions and VFA concentrations were also monitored in anaerobic UASB reactor. pH changes, dissolved oxygen (DO) variations and redox potentials (ORPs) were monitored in anaerobic UASB and aerobic CSTR reactors. As a result of the study, increasing of the SRT has a positive effect on COD (94.1%) and SCOD (91.1%) yields at 55 days of SRT in the biological reactor system. Also, biodegradation (in the supernatant) and adsorption (onto biological sludge) removal efficiencies of AHMT were increased at higher SRTs. AHMT was removed 42.3% with biodegradation from the supernatant while adsorption removal efficiency reached 57.5% in the biological sludge at 55 days of SRT for the anaerobic UASB/aerobic CSTR sequential biological reactor system. Keywords: Biological treatment; Musk tonalide; Raw hospital wastewater; Sludge retention time

EFFECT OF FLUX CONDITION ON POLLUTANTS REMOVAL OF SPONGE MEMBRANE BIOREACTOR TREATING HOSPITAL WASTEWATER

Nowadays, membrane bioreactor (MBR) is an advanced available technology for wastewater treatment due to technical innovations and cost reduction. Especially, the high biomass concentration and long sludge retention time are favourable for the biodegradation of organic pollutants and nitrification. This research aims to study on the treatment performance of two lab-scale submerged membrane bioreactors treating hospital wastewater. One was operated at low fluxes (2, 4, 6 LMH) and the other at higher fluxes (10, 15, 20 LMH). Polyester-urethane cube sponge media (20 % v/v) was added into both reactors for fouling control and simultaneous nitrification denitrification (SND). The results showed that organic removal efficiencies were improved with an increase in flux. The removal efficiencies of COD and total nitrogen were 85-89 % and 26-42 % at low fluxes and 96-97 %, 53-65 % at higher fluxes, respectively. The treated water quality complied with Vietnam National Technical Regulation on health care wastewater, class A.

Enhanced retention of deammonification microorganisms for the treatment of psycrophilic anaerobic digestate

This study focused on the treatment of psychrophilic anaerobic digestate from pig slurry digestion through a single-stage Sequencing Batch Reactor (SBR) accomplishing the autotrophic nitrogen removal (ANR). In period 1, the combination of the high sludge retention time (>50 days) and the presence of significant concentrations of biodegradable organic carbon favoured the uncontrolled growth of the denitrifying bacteria (HDB) and the nitrite oxidizing bacteria (NOB), affecting negatively the deammonification (DAM) activity from 14 to 15 mgN/gMLVSS·h to only 2.2 mgN/gMLVSS·h. In Period 2, the sieving of the suspended biomass at 125 µm was evaluated to enhance the retention time of DAM microrganisms in granular sludge into the SBR. This strategy allowed the recovery of 60% of the initial specific deammonification activity (sDAA) and to promote the wash-out of the NOB, obtaining a nitrogen removal efficiency of 81%. This method was never applied to increase the robustness and reliability of ANR during the treatment of livestock streams, so it could be considered after optimization as a potential option to increase the sustainability of smaller and local farms.

Understanding the performance of an AnMBR treating urban wastewater and food waste via model simulation and characterization of the microbial population dynamics

Abstract An anaerobic membrane bioreactor (AnMBR) pilot plant treating kitchen food waste (FW) jointly with urban wastewater was run for 536 days. Different operational conditions were tested varying the sludge retention time (SRT), the hydraulic retention time (HRT) and the penetration factor (PF) of food waste disposers. COD removal efficiency exceeded 90% in all tested conditions. The joint treatment resulted in an almost 3-fold increase in methane production (at 70 days of SRT, 24 h HRT and 80% PF) in comparison with the treatment of urban wastewater only. Mathematical model simulations and Illumina technology were used to obtain in-depth information of this outstanding process performance. Both the PF and SRT factors increased influent biodegradability. The experimental results were accurately reproduced via model simulations modifying only the influent biodegradability. The high SRT and the presence of ground FW in the influent resulted in higher hydrolytic activity. Not only did the Archaea population increase 3-fold but Levilinea genera was also significantly raised. Three new genera characterised by anaerobic fermentation of amino acids (Leptolinea, Aminomonas and Aminobacterium) were among the ten most abundant of the total sequences identified during the joint treatment, indicating an improvement in the hydrolysis step of anaerobic degradation. Influent biodegradability remained at high values when FW addition stopped.

Application of Oxygen Limited Autotrophic Nitritation/Denitrification (OLAND) for anaerobic latex processing wastewater treatment

The study aimed to remove nitrogenous compounds from anaerobic latex processing wastewater by using Oxygen Limited Autotrophic Nitritation/Denitrification (OLAND) process in a single reactor with rotating bio-carrier and sequencing batch regime. The anaerobic latex processing effluent, of which suspended solids (SS) and biodegradable COD (bCOD) were removed by latex scum trap, coagulation-flocculation and followed by Upflow Anaerobic Sludge Blanket Reactor (UASB), contained 100–200 mg l−1 NH4+-N, 150–250 mg l−1 total nitrogen (TN) and 50–80 mg l−1 COD. Dissolved oxygen (DO) in the experiment was maintained at different concentration ranges of 0.4–0.8 mg l−1; 0.2–0.4 mg l−1 and 0.1–0.2 mg l−1. The highest performance (TN and COD removals, 94% and 61%, respectively) obtained at DO range of 0.10–0.20 mg l−1. Moreover, the low effluent nitrate (8.5 ± 3.1 mg l−1 NO3−-N), which was less than that of theoretical reaction of OLAND, shown that, in the single reactor, co-existence of denitrifiers using the remaining bCOD (less than 50 mg l−1) in the feed wastewater or carbon source from cell lysis at high sludge retention time (about 90 days). Analysis of bacteria community showed that Candidatus Kuenenia, anammox bacteria, was dominant species in the sludge mixture of biofilm and bioflocs (4.8%) with 99% of sequence identities. AOB species, nitrifying bacteria, had 6.6% with 98% of sequence identities. Besides, denitrifying Proteobacterium E4-1 was found in the reactor.

Behaviour of the main nonsteroidal anti-inflammatory drugs in a membrane bioreactor treating urban wastewater at high hydraulic- and sludge-retention time

The behaviour and removal efficiency of ibuprofen (IBU), diclofenac (DCF), ketoprofen (KPF), and naproxen (NPX) during the real urban wastewater treatment by an experimental full-scale MBR working at high sludge and hydraulic retention time (SRT, HRT) were determined. The MBR worked in denitrification/nitrification conformation at 35.4h of HRT (Q=0.45m3/h), 37 d of SRT and a recirculation flow rate of 4Q. The experiments were made under steady-state conditions, reaching a biodegradable organic matter removal higher than 99.5%. The MBR system showed similar removal capacity for IBU, NPX, and KTP (>95%), whose main transformation occurred in the aerobic reactor with a low contribution from the anoxic reactor. The system worked with complete nitrification, also achieving an effective retention of the unbiodegradable organic matter due to recirculation. DCF removal was low with negative removal yields for several samplings. Both removal and increase transformation of DCF also occurred in the aerobic reactor, this not being observed in the anoxic one. DCF tends to accumulate in the system and to be recirculated. Thus, during the sampling in which DCF influent concentration decreases, removal yields turn negative. The increase of DCF concentration in the aerobic bioreactor also contributes to the negative removal yields.

Effect of sludge retention time on continuous-flow system with enhanced biological phosphorus removal granules at different COD loading

The effect of sludge retention time (SRT) on the continuous-flow system with enhanced biological phosphorus removal (EBPR) granules at different COD loading was investigated during the operation of more than 220days. And the results showed that when the system operated at long SRT (30days) and low COD loading (200mg·L−1), it could maintain excellent performance. However, long SRT and high COD loading (300mg·L−1) deteriorated the settling ability of granules and the performance of system and resulted in the overgrowth of filamentous bacteria. Meanwhile, the transformation of poly-β-hydroxyalkanoates (PHAs) and glycogen in metabolism process was inhibited. Moreover, the results of pyrosequencing indicated that filamentous bacteria had a competitive advantage over polyphosphate-accumulating organisms (PAOs) at high COD loading and long SRT. The PAOs specious of Candidatus_Accumlibater and system performance increased obviously when the SRT was reduced to 20days at high COD loading.

Carbamazepine behaviour and effects in an urban wastewater MBR working with high sludge and hydraulic retention time

ABSTRACTThe behaviour and fate of carbamazepine (CBZ) in urban wastewater treatment by a membrane bioreactor (MBR) and its possible effects on the system's efficiency, and on mixed microbial communities, has been studied. The experimental microfiltration MBR system, with capacity to treat 10.8 m3 d−1 of urban wastewater, operated with a pre-denitrification configuration with high sludge and hydraulic retention time. The CBZ concentration assayed was higher than in the usual urban wastewater, in order to provoke a strong biomass reaction. Influent, effluent, and all bioreactors of the MBR system were analysed in order to calculate a CBZ balance. Bench-scale experiments and respirometric analyses were performed, with and without the presence of CBZ, to evaluate its influence on the bacterial activity. The respirometric assays showed variations in the oxygen uptake rate (OUR) in the presence of CBZ. Negative effects were detected in the MBR bacterial community during the initial period of dosing. However, the effects were not permanent and the biomass spiked with CBZ had behaviour similar to that of the biomass without CBZ after a few hours. Biodegradation was not detected during the MBR treatment. The system showed an inefficient elimination of CBZ (less than 10%) with a high concentration in the effluent. The small percentage of CBZ removal was associated with the sludge retention and eliminated by the purge. All CBZ present in the influent was accounted for, and even an increase in the total amount of CBZ was registered in the permeate. During and after the experimental process, CBZ did not significantly affect the efficiency of the MBR system, and the quality of the effluent was not affected by the dosing of CBZ in terms of COD and nitrogen removal.

Treatment performance and microbial diversity under dissolved oxygen stress conditions: Insights from a single stage IFAS reactor treating municipal wastewater

In the present study, assessment of a single stage integrated fixed film activated sludge (IFAS) reactor treating municipal wastewater and subjected to various dissolved oxygen (DO) stresses, is done in terms of treatment performance and changes in bio-chemical characteristics of activated sludge. Results obtained from experimental revealed that the DO concentrations of 0.5, 2.5, and 4.5mgL−1 affected significantly the performance of IFAS reactor. The optimal DO concentrations for the efficient removals of organics, nitrification, denitrification, and total nitrogen were recorded as 4.5, 4.5, 2.5, and 2.5mgL−1, respectively. Biological phosphorus removal (BPR) efficiency of pilot deteriorated significantly at high DO (4.5mgL−1) levels. Insignificant variation in SVI values (190–245mLg−1) was observed at different DO phase experiments. The macromolecular composition) of activated sludge was also determined in terms of lipids, proteins and polysaccharides content. Moreover, activated sludge characterization results revealed that the dominance of micro fauna (ciliated protozoa) and microorganisms (gram characteristics) was different at different DO levels. Overall, the optimal DO concentration was suggested as 4.5mgL−1 for the IFAS system as it not only achieved high organics removal efficiency and but also minimized the sludge production with high sludge retention time.