Conventional Activated Sludge Research Articles

Microbiome structure and function in parallel full-scale aerobic granular sludge and activated sludge processes

Aerobic granular sludge (AGS) and conventional activated sludge (CAS) are two different biological wastewater treatment processes. AGS consists of self-immobilised microorganisms that are transformed into spherical biofilms, whereas CAS has floccular sludge of lower density. In this study, we investigated the treatment performance and microbiome dynamics of two full-scale AGS reactors and a parallel CAS system at a municipal WWTP in Sweden. Both systems produced low effluent concentrations, with some fluctuations in phosphate and nitrate mainly due to variations in organic substrate availability. The microbial diversity was slightly higher in the AGS, with different dynamics in the microbiome over time. Seasonal periodicity was observed in both sludge types, with a larger shift in the CAS microbiome compared to the AGS. Groups important for reactor function, such as ammonia-oxidising bacteria (AOB), nitrite-oxidising bacteria (NOB), polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs), followed similar trends in both systems, with higher relative abundances of PAOs and GAOs in the AGS. However, microbial composition and dynamics differed between the two systems at the genus level. For instance, among PAOs, Tetrasphaera was more prevalent in the AGS, while Dechloromonas was more common in the CAS. Among NOB, Ca. Nitrotoga had a higher relative abundance in the AGS, while Nitrospira was the main nitrifier in the CAS. Furthermore, network analysis revealed the clustering of the various genera within the guilds to modules with different temporal patterns, suggesting functional redundancy in both AGS and CAS.Key points• Microbial community succession in parallel full-scale aerobic granular sludge (AGS) and conventional activated sludge (CAS) processes.• Higher periodicity in microbial community structure in CAS compared to in AGS.• Similar functional groups between AGS and CAS but different composition and dynamics at genus level.Graphical abstract

Micropollutant biotransformation under different redox conditions in PhoRedox conventional activated sludge systems

The ecotoxicological safety of the water bodies relies on the reduction of micropollutant emissions from wastewater treatment plants (WWTP). The ecotoxicological safety of the water bodies relies on the reduction of micropollutant emissions from wastewater treatment plants (WWTP). Quantification of micropollutant removal at full-scale WWTP is scarce. To our knowledge, the anaerobic conversion rates determined at conventional activated sludge processes are, so far, scarcely available in the literature for most of the micropollutants. In this research, we quantified the biotransformation rate constants and the removal efficiencies of 16 micropollutants (4,5-methylbenzotriazole, azithromycin, benzotriazole, candesartan, carbamazepine, clarithromycin, diclofenac, gabapentin, hydrochlorothiazide, irbesartan, metoprolol, propranolol, sotalol, sulfamethoxazole, trimethoprim, and venlafaxine), under aerobic, anoxic, and anaerobic redox conditions; using as inoculum wastewater and biomass from a full-scale conventional activated sludge (CAS) system in the Netherlands. Clarithromycin was the compound that exhibited the highest aerobic (76%) and anaerobic (78%) removal efficiencies, while gabapentin showed the highest removal under anoxic conditions (91%). A preference for cometabolic biotransformation of the targeted micropollutants was observed. The highest biotransformation rate constants obtained were: at aerobic conditions clarithromycin with 1.46 L.gSS−1.d−1; at anoxic conditions, gabapentin with 2.36 L.gSS−1.d−1; and at anaerobic redox conditions clarithromycin with 1.87 L.gSS−1.d−1. The obtained results of biotransformation rates will allow further modelling of micropollutant removal in CAS systems, under various redox conditions. These biotransformation rates can be added to extended ASM models to predict effluent concentration and optimize targeted advanced oxidation processes allowing savings in the operational costs and increasing the process viability.

Extracellular Polymeric Substance Composition Effects on Biosorption for Primary Carbon Diversion

This paper characterizes the composition of extracellular polymeric substances (EPSs) in different types of activated sludge (AS) processes and analyzes the biosorption of soluble organics when waste AS (WAS) is mixed with raw wastewater for primary carbon diversion. The fraction of AS organics identified as EPSs was 26% in a membrane bioreactor (MBR), 54% in conventional AS (CAS), and 51% in a trickling filter/solids contact (TF/SC) process. EPSs were found to be approximately 15% carbohydrates, 40% proteins, 40% humics, and 5% uronics in CAS and MBR AS. Biosorption was not correlated to the organic portion (VSS) of the WAS; however, statistically significant correlations were found for the total amount of EPSs (for TF/SC and CAS) and the protein fraction (for TF/SC and MBR) in the VSS. EPSs from different types of AS biosorbed the same amount of soluble organics, removing 1.43 ± 0.15 (n = 16) mg of soluble chemical oxygen demand (sCOD), and 1.20 ± 0.18 (n = 16) mg of truly soluble COD (ffCOD), per mg of cation exchange resin (CER) total extracted EPSs. Utilizing multiple extraction methods in series (CER–base–sulfide) increased EPS extraction yields by nearly 100% relative to CER alone and indicated different EPS fractionization for CAS (a smaller fraction of carbohydrates and a larger fraction of humics).

Optimized process intensification through dynamic performance simulation and evaluation of treatment alternatives for a wastewater treatment plant in Toronto

In this study, a comprehensive plant-wide model of the North Toronto Treatment Plant (NTTP) was developed, focusing on improving operational efficiency and capacity utilization. NTTP, with a rated capacity of 45 MLD, is currently operating at about 18 MLD with treatment processes including physical units (incorporating four primary settling tanks), chemical precipitation (for phosphorus removal using ferrous chloride), and biological processes (utilizing eight plug-flow conventional activated sludge (CAS) aeration tanks), and two sets of final clarifiers. Utilizing Biowin 6.2, the study constructed and calibrated a mechanistic model based on historical plant records and extensive sampling campaign data gathered from July to August 2022. The performance of various process configurations under different operational and seasonal conditions was evaluated. It was observed that the Ludzack-Ettinger (L-E) configuration demonstrated enhanced performance in terms of Environmental Compliance Approval (ECA) objectives and cost-efficiency compared to the CAS process. However, the L-E configuration posed challenges related to the final clarifier loading. The State Point Analysis (SPA) conducted within the study emphasized the effectiveness of the Membrane Aerated Bioreactor (MABR) in producing high-quality effluent, while also reducing the burden on the final clarifiers. This research provides a foundation for potential upgrades to NTTP, leveraging existing infrastructure to approach its full rated capacity while maintaining adherence to current ECA objectives.

Performance and life cycle assessment of moving-bed biofilm and integrated fixed-film reactors to upgrade activated sludge systems

Upgrading the capacity of existing wastewater treatment plants (WWTPs) is hindered by the limited space for extension. This matter is particularly crucial in developing countries where dense urban areas experience unexpectedly growing populations. Herein, we study the capacity upgrading of a WWTP working by a conventional activated sludge (CAS) system from 180,000 m3/d to 240,000 and 300,000 m3/d. The WWTP case study focuses on a large plant in Mansoura, Egypt, requiring capacity upgrades to accommodate population growth. For this purpose, we used mathematical modeling to simulate current and suggested WWTP designs. Moving bed biofilm reactor (MBBR) and integrated fixed film-activated sludge (IFAS) systems were designed to increase the WWTP capacity to 240,000 and 300,000 m3/d by the addition of plastic biofilm carrier to 25% and 50% of the aeration basins, respectively. IFAS outperformed conventional and MBBR systems in terms of BOD, COD, TSS, NH4, TP, and PO4, in addition to increased capacity. We moreover used life cycle assessment (LCA) to comprehend the environmental favorability of upgrading scenarios. The most affected environmental categories are global warming and eutrophication due to the operation stage (especially electricity). Global warming potential for CAS, MBBR, and IFAS (300,000 m3/d) are 2.19, 1.69, and 1.73 kg CO2 eq respectively. Eutrophication potential for CAS, MBBR, and IFAS (300,000 m3/d) are 0.0025, 0.0022, and 0.0017 kg PO4- eq respectively. We also estimated the amortization and running costs for various upgrading scenarios, providing an integrated analysis for decision-making purposes.

The effect of aeration mode (intermittent vs. continuous) on nutrient removal and greenhouse gas emissions in the wastewater treatment plant of Corleone (Italy)

The paper reports the results of an experimental study aimed at comparing two configurations of a full-scale wastewater treatment plant (WWTP): conventional activated sludge (CAS) and oxic-settling-anaerobic process (OSA) with intermittent aeration (IA). A comprehensive monitoring campaign was carried out to assess multiple parameters for comparing the two configurations: carbon and nutrient removal, greenhouse gas emissions, respirometric analysis, and sludge production. A holistic approach has been adopted in the study with the novelty of including the carbon footprint (CF) contribution (as direct, indirect and derivative emissions) in comparing the two configurations. Results showed that the OSA-IA configuration performed better in total chemical oxygen demand (TCOD) and ortho-phosphate (PO4-P) removal. CAS performed better for Total Suspended Solids (TSS) removal showing a worsening of settling properties for OSA-IA. The heterotrophic yield coefficient and maximum growth rate decreased, suggesting a shift to sludge reduction metabolism in the OSA-IA configuration. Autotrophic biomass showed a reduced yield coefficient and maximum growth yield due to the negative effects of the sludge holding tank in the OSA-IA configuration on nitrification. The OSA-IA configuration had higher indirect emissions (30.5 % vs 21.3 % in CAS) from additional energy consumption due to additional mixers and sludge recirculation pumps. The CF value was lower for OSA-IA than for CAS configuration (0.36 kgCO2/m3 vs 0.39 kgCO2/m3 in CAS).

Evaluation of virus removal in membrane bioreactor (MBR) and conventional activated sludge (CAS) processes based on long-term monitoring at two wastewater treatment plants

The membrane bioreactor (MBR) process always offers better wastewater treatment than conventional activated sludge (CAS) treatment. However, the difference in their efficacy of virus reduction remains unknown. To investigate this, we monitored virus concentrations before and after MBR and CAS processes over 2 years. Concentrations of norovirus genotypes I and II (NoV GI and GII), aichivirus (AiV), F-specific RNA phage genotypes I, II, and III (GI-, GII-, and GIII-FRNAPHs), and pepper mild mottle virus (PMMoV) were measured by a quantitative polymerase chain reaction (qPCR) method at two municipal wastewater treatment plants (WWTPs A and B) in Japan. Virus concentration datasets containing left-censored data were estimated by using both maximum likelihood estimation (MLE) and robust regression on order statistics (rROS) approaches. PMMoV was the most prevalent at both WWTPs, with median concentrations of 7.5 to 8.8 log10 copies/L before treatment. Log10 removal values (LRVs) of all viruses based on means and standard deviations of concentrations before and after treatment were consistently higher following MBR than following CAS. We used NoV GII as a model pathogen in a quantitative microbial risk assessment of the treated water, and we estimated the additional reductions required following MBR and CAS processes to meet the guideline of 10−6 DALYs pppy for safe wastewater reuse.

Pilot-scale investigation of performance and microbial community in a novel system combining fixed and suspended activated sludge

The conventional activated sludge (CAS) process is a widely used method for wastewater treatment due to its effectiveness and affordability. However, it can be prone to sludge abnormalities such as sludge bulking/foaming and sludge loss, which can lead to a decrease in treatment efficiency. To address these issues, a novel bag-based fixed activated sludge (BBFAS) system utilizing mesh bags to contain the sludge was developed for low carbon/nitrogen ratio wastewater treatment. Pilot-scale experiments demonstrated that the BBFAS system could successfully avoid the sludge abnormalities. Moreover, it was not affected by mass transfer resistance and exhibited significantly higher nitrogen removal efficiency, surpassing that of the CAS system by up to 78%. Additionally, the BBFAS system demonstrated comparable organic matter removal efficiency to CAS system. 16S rRNA gene high-throughput sequencing revealed that the bacterial community structure within the BBFAS system was significantly different from that of the CAS system. The bacteria associated with ammonium removal were more abundant in the BBFAS system than in the CAS system. The abundance of Nitrospira in the BBFAS could reach up to 6% and significantly higher than that in the CAS system, and they were likely responsible for both ammonia-oxidizing and nitrite-oxidizing functions. Clear stratification of microbial communities was observed from the outer to inner layers of the bag components due to the gradients of dissolved oxygen and other substrates. Overall, this study presents a promising approach for avoiding activated sludge abnormalities while maintaining high pollutant removal performance.

Differential biotransformation of micropollutants in conventional activated sludge and up-flow anaerobic sludge blanket processes

We report differential micropollutant biotransformations in a conventional activated sludge (CAS) process and a pilot-scale up-flow anaerobic sludge blanket (UASB) process operating in parallel at the same wastewater treatment plant.

Coupling of augmented PAN membranes by surface immobilization of pincer ligands with an activated sludge to treat a real wastewater

In the present study, industrial estate wastewater was subjected to treat with a conventional activated sludge (CAS) bioreactor and then purified using a highly efficient surface-modified PAN ultrafiltration membrane. Response surface methodology (RSM) has been employed to analytically design, carry out, and optimize biological experiments using two independent operating variables, MLSS (6,000–14,000 mg/L) and HRT (5–15 h). This resulted in an effluent that was optimally stabilized before ultrafiltration due to the consequent responses of COD removal (90 %), effluent turbidity (1 NTU), and SVI (82 mL/g). To rationally tailor the antifouling PAN UF membranes for this intended purpose, novel hydrophilic pincer ligands were formed by covalent binding of cyanuric chloride (CC) activated membrane surfaces with various loadings of (1.0, 3.0, and 5.0 wt%) 5-amino-1, 3, 4-thiadiazol-2-thiol (AMT). In terms of hydrophilicity, surface roughness, antifouling characteristics, and permeate flux, the optimum membrane surface-modified with 3.0 wt% pincer ligand loading outperformed the others, leading to a low WCA of 42.75°, smoother surface (Sa = 14.77 nm), FRR of 97.1 %, and PWF of 56.07 kg/m2.h. The operated CAS followed by surface-modified Pincer/PAN membranes is therefore an appealing proposal for generating high-quality effluent from industrial wastewaters.

Ecotoxicological mixture risk assessment of 35 pharmaceuticals in wastewater effluents following post-treatment with ozone and/or granulated activated carbon

Reducing the risk posed by mixtures of pharmaceuticals is a goal of current initiatives such as the European Green Deal to reduce anthropological environmental impacts. Wastewater effluent typically contains large numbers of active pharmaceutical ingredients (APIs). For some APIs, existing technology such as conventional activated sludge (CAS) wastewater treatment plants (WWTPs) have removal rates below 20 %, thus the WWTP discharges are adding to the toxic burden of receiving waters.We present an environmental risk assessment of mixtures of 35 APIs in effluent samples from 82 Northern European WWTPs using the concentration addition model, and identify the respective risk-driving APIs. This is then compared to a corresponding mixture risk assessment of effluent samples from the Danish Hillerød WWTP subjected to post-treatment with varying specific ozone doses (0.15–1.05 mgO3/mgDOC) and/or granulated activated carbon (GAC).All 82 WWTP effluent samples exceeded risk thresholds by at least a factor of 30, with a median RQSUM of 92.9, highlighting the need for effluent post-treatment and/or a substantial dilution in the recipient waters. Antibiotics, analgesics and anti-depressants were among the top risk drivers with 99 % of the average mixture risk attributable to azithromycin, diclofenac, venlafaxine, clarithromycin and mycophenolic acid. Effluent mixture risk was reduced by ozonation in a concentration-dependent manner, decreasing below threshold levels to a median RQSUM of 0.83 following treatment with 0.65 mgO3/mg DOC. Fresh GAC was also effective at reducing the mixture risk both alone and with ozone treatment, with median RQSUM of 0.04 and 0.07 respectively.To our knowledge, this is the first study to present a risk assessment of pharmaceutical mixtures in effluent comparing “conventional” WWTP processes with additional post-treatment with ozone and/or GAC for reducing the joint risks of pharmaceutical mixtures for recipient waters. We demonstrate the need for additional WWTP treatment technologies, and the efficacy of GAC and ozonation in decreasing the risk to the aquatic environment from pharmaceutical mixtures to below acceptable threshold limits.

SARS-CoV-2 removal in municipal wastewater treatment plants: Focus on conventional activated sludge, membrane bioreactor and anaerobic digestion

This work focuses on the removal of SARS-CoV-2 RNA in the various stages of a full-scale municipal WWTP characterised by two biological processes in parallel: (i) conventional activated sludge (CAS) and (ii) membrane bioreactor (MBR). The monitoring was carried out during the Omicron wave in 2022, a period characterised by a high concentration of SARS-CoV-2 in influent wastewater. The average concentration of SARS-CoV-2 in influent wastewater was 3.7 × 104 GU/L. In the primary sedimentation, the removal of SARS-CoV-2 was not appreciable. The largest log removal value of SARs-CoV-2 occurred in the biological stages, with 1.8 ± 0.9 and 2.2 ± 0.7 logs in CAS and MBR systems. The mean concentrations of SARS-CoV-2 in the CAS and MBR effluents were 6.8 × 102 GU/L and 6.4 × 102 GU/L, respectively. The MBR effluent showed more negative samples, because small particles are retained by membrane and cake layer.The analysis of the different types of sludge confirmed the accumulation of SARS-CoV-2 in primary (5.2 × 104 GU/L) and secondary sludge (3.5 × 104 GU/L), due to the affinity of enveloped viruses towards biosolids. A SARS-CoV-2 concentration in the digested sludge equal to 4.8 × 104 GU/L denotes a negligible reduction in the mesophilic anaerobic digester at temperature of 31–33 °C.

Microaerophilic Activated Sludge System for Ammonia Retention toward Recovery from High-Strength Nitrogenous Wastewater: Performance and Microbial Communities.

A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia and organic carbon removal is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is based on conventional activated sludge (CAS) with aerobic and settling compartments. Low dissolved oxygen (DO) concentrations (<0.2 mg/L) and short solids retention times (SRTs) (<5 days) eliminated nitrifying bacteria. The two parallel MASs were successfully operated for 300 days and had ammonia retention of 101.7 ± 24.9% and organic carbon removal of 85.5 ± 8.9%. The MASs mitigated N2O emissions with an emission factor of <0.23%, much lower than the default value of CAS (1.6%). A short-term step-change test demonstrated that N2O indicated the initiation of nitrification and the completion of denitrification in the MAS. The parallel MASs had comparable microbial diversity, promoting organic carbon oxidation while inhibiting ammonia-oxidizing microorganisms (AOMs), as revealed by 16S rRNA gene amplicon sequencing, the quantitative polymerase chain reaction of functional genes, and fluorescence in situ hybridization of β-proteobacteria AOB. The microbial analyses also uncovered that filamentous bacteria were positively correlated with effluent turbidity. Together, controlling DO and SRT achieved organic carbon removal and successful ammonia retention, mainly by suppressing AOM activity. This process represents a new nitrogen management paradigm.

Impact of Influent Composition and Operating Conditions on Carbon and Nitrogen Removal from Urban Wastewater in a Continuous-Upflow (Micro)Aerobic Granular Sludge Blanket Reactor

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L−1), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L−1, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH4+, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system.

In-depth insight on microbial electrochemical systems coupled with membrane bioreactors for performance enhancement: a review.

A conventional activated sludge (CAS) system has traditionally been used for secondary treatment in wastewater treatment plants. Due to the high cost of aeration and the problem of sludge treatment, researchers are developing alternatives to the CAS system. A membrane bioreactor (MBR) is a technology with higher solid-liquid separation efficiency. However, the use of MBR is limited due to inevitable membrane fouling and high energy consumption. Membrane fouling requires frequent cleaning, and MBR components must be replaced, which reduces membrane lifetime and operating costs. To overcome the limitations of the MBR system, a microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system has attracted the interest of researchers. The design of the novel bioelectrochemical membrane reactor (BEMR) can effectively couple microbial degradation in the microbial electrochemical system (MES) and generate a microelectric field to reduce and alleviate membrane fouling in the MBR system. In addition, the coupling system combining an MES and an MBR can improve the efficiency of COD and ammonium removal while generating electricity to balance the energy consumption of the system. However, several obstacles must be overcome before the MFC-MBR coupling system can be commercialised. The aim of this study is to provide critical studies of the MBR, MES and MFC-MBR coupling system for wastewater treatment. This paper begins with a critical discussion of the unresolved MBR fouling problem. There are detailed past and current studies of the MES-MBR coupling system with comparison of performances of the system. Finally, the challenges faced in developing the coupling system on a large scale were discussed.

Sustainable treatment of municipal secondary effluent from UASB systems by solar photo-Fenton: CECs removal and toxicity control

Upflow Anaerobic Sludge Blanket (UASB) systems are vastly implemented for municipal wastewater treatment in developing tropical countries. Despite that, efforts related to the removal of contaminants of emerging concern (CECs) from municipal secondary effluents (MSE) via post-treatment by solar photo-Fenton are mainly conducted with MSE from Conventional Activated Sludge (CAS). Hence, it is critical to investigate the efficiency of solar photo-Fenton to treat MSE from UASB systems. This is the first study to evaluate the performance of solar photo-Fenton and dark Fenton conducted with intermittent additions of Fe2+ and at circumneutral pH for the removal of CEC from UASB followed by Trickling Filter (UASB+TF) and UASB effluent. Acute and chronic ecotoxicity to Aliivibrio fischeri and Raphidocelis subcapitata, respectively, and phytotoxicity to Lactuca sativa were also evaluated for both matrixes. Solar photo-Fenton removed 83% of ΣCECs from UASB+TF effluent and resulted in non-toxic samples. Solar photo-Fenton performed in MSE from UASB system alone showed 65% ΣCECs removal and reduced chronic effect to R. subcapitata (growth inhibition) from 11% to 26%. In addition, no acute toxicity was verified for A. fischeri nor L. sativa. This work shows the feasibility of applying solar photo-Fenton at circumneutral pH to improve the quality of MSE resulting from UASB systems prior to wastewater discharge or reuse in agriculture.

Daily Monitoring at a Full-Scale Wastewater Treatment Plant Reveals Temporally Variable Micropollutant Biotransformations.

Despite decades of micropollutant (MP) monitoring at wastewater treatment plants (WWTPs), we lack a fundamental understanding of the time-varying metabolic processes driving MP biotransformations. To address this knowledge gap, we collected 24-h composite samples from the influent and effluent of the conventional activated sludge (CAS) process at a WWTP over 14 consecutive days. We used liquid chromatography and high-resolution mass spectrometry to (i) quantify 184 MPs in the influent and effluent of the CAS process; (ii) characterize temporal dynamics of MP removal and biotransformation rate constants; and (iii) discover biotransformations linked to temporally variable MP biotransformation rate constants. We measured 120 MPs in at least one sample and 66 MPs in every sample. There were 24 MPs exhibiting temporally variable removal throughout the sampling campaign. We used hierarchical clustering analysis to reveal four temporal trends in biotransformation rate constants and found MPs with specific structural features co-located in the four clusters. We screened our HRMS acquisitions for evidence of specific biotransformations linked to structural features among the 24 MPs. Our analyses reveal that alcohol oxidations, monohydroxylations at secondary or tertiary aliphatic carbons, dihydroxylations of vic-unsubstituted rings, and monohydroxylations at unsubstituted rings are biotransformations that exhibit variability on daily timescales.

Reduction of SARS-CoV-2 by biological nutrient removal and disinfection processes in full-scale wastewater treatment plants

Detection of SARS-CoV-2 RNA in wastewater poses people's concerns regarding the potential risk in water bodies receiving wastewater treatment effluent, despite the infectious risk of SARS-CoV-2 in wastewater being speculated to be low. Unlike well-studied nonenveloped viruses, SARS-CoV-2 in wastewater is present abundantly in both solid and liquid fractions of wastewater. Reduction of SARS-CoV-2 in past studies were likely underestimated, as SARS-CoV-2 in influent wastewater were quantified in either solid or liquid fraction only. The objectives of this study were (i) to clarify the reduction in SARS-CoV-2 RNA during biological nutrient removal and disinfection processes in full-scale WWTPs, considering the SARS-CoV-2 present in both solid and liquid fractions of wastewater, and (ii) to evaluate applicability of pepper mild mottle virus (PMMoV) as a performance indicator for reduction of SARS-CoV-2 in WWTPs. Accordingly, large amount of SARS-CoV-2 RNA were partitioned in the solid fraction of influent wastewater for composite sampling than grab sampling. When SARS-CoV-2 RNA in the both solid and liquid fractions were considered, log reduction values (LRVs) of SARS-CoV-2 during step-feed multistage biological nitrogen removal (SM-BNR) and enhanced biological phosphorus removal (EBPR) processes ranged between>2.1–4.4 log and did not differ significantly from those in conventional activated sludge (CAS). The LRVs of SARS-CoV-2 RNA in disinfection processes by ozonation and chlorination did not differ significantly. PMMoV is a promising performance indicator to secure reduction of SARS-CoV-2 in WWTPs, because of its higher persistence in wastewater treatment processes and abundance at a detectable concentration even in the final effluent after disinfection.

Anaerobic fermentation of aerobic granular sludge: Insight into the effect of granule size and sludge structure on hydrolysis and acidification

Aerobic granular sludge (AGS) has different physicochemical properties and microbial communities compared to conventional activated sludge (CAS), which may result in different behaviors during anaerobic fermentation and require further investigation. This study investigated the effect of granule size and sludge structure on the hydrolysis and acidification of AGS. Experimental results show that AGS exhibited significantly higher soluble chemical oxygen demand (SCOD) dissolution and total volatile fatty acids (TVFA) production (330.6–430.3 mg/gVSS and 231.0–312.5 mgCOD/gVSS) compared to conventional activated sludge (CAS) (167.0 mg/gVSS and 133.3 mgCOD/gVSS). This is because AGS (90.6–96.9 mg/gVSS) had higher extracellular polymeric substances (EPS) content than CAS (81.2 mg/gVSS). EPS can not only serve as substrates but also release the trapped hydrolases. Moreover, the relative abundances of hydrolytic/acidogenic bacteria and genes were higher in AGS (0.46%–3.60% and 3.01 × 10−3%-4.04 × 10−3%) than in CAS (0.30% and 1.23 × 10−3%). The optimal granule size for AGS fermentation was found to be 500–1600 μm. The crushing of granule structure promoted the dissolution of small amounts of EPS and the release of some trapped hydrolases, thereby potentially enhancing the enzyme-substrate contacts and bacteria-substrate interactions. Therefore, the highest SCOD dissolution (510.6 mg/gVSS) and TVFA production (352.1 mgCOD/gVSS) from crushed 500–1600 μm AGS were observed. Overall, the findings of this study provide valuable insights into the recovery of organic carbon from AGS via anaerobic fermentation.

Water-Energy Nexus in the Antofagasta Mining District: Options for Municipal Wastewater Reuse from a Nearly Energy-Neutral WWTP

The region of Antofagasta is the mining hearth of Chile. The water requirement of the local mining sector is 65% of the total water uses, with a water consumption of approx. 9 m3/s in the year 2020. That determines an important pressure onto freshwater, which can only be alleviated by resorting to desalination or reuse of treated wastewater. At present, an amount equal to 90% of the wastewater generated in the city of Antofagasta is discharged into the ocean, after undergoing only preliminary treatments. The wastewater treatment plant (WWTP), which includes a conventional activated sludge (CAS) process, has a very low treatment capacity, insufficient to serve the whole population. A new WWTP will be built with the twofold aim of (i) purifying the totality of the wastewater generated from the city (approx. 320,000 equivalent inhabitants, e.i.), and (ii) allowing the reuse of 100% of the treated wastewater in the local mining sector, in agreement with the goals of the Chilean government. The new Antofagasta WWTP will include preliminary treatments and a conventional activated sludge (CAS) process with a higher treatment capacity. This study integrates a number of modeling tools, namely the Activated Sludge Model n.3 (ASM3), the Takacs model, and some stoichiometric and energy balances, to assess the impact that some changes, possibly introduced into the project of the new WWTP, could determine on its energy and environmental sustainability. Specifically, through an energy-economic-environmental (3-E) analysis, the original scheme of the planned WWTP was compared with three scenarios, of which Scenario 1 introduces anaerobic digestion (AD) of secondary sludge, Scenario 2 concerns primary sedimentation and AD of both primary and secondary sludge, and, finally, Scenario 3, other than primary sedimentation and AD, also includes a pre-denitrification process. The results of the study demonstrated that all the changes introduced by Scenario 3 were of capital importance to promote the transformation of the WWTP into a nearly energy-neutral water resource recovery facility (WRRF). Specifically, the processes/operations introduced with Scenario 3 can reduce the electric energy demand from external sources to only 20% of that of the original scheme, and consequently avoid the emission of 4390 tons CO2-equivalent/y.