SARS-CoV-2 shedding sources in wastewater and implications for wastewater-based epidemiology

Wastewater-based epidemiology (WBE) approach for COVID-19 surveillance is largely based on the assumption of SARS-CoV-2 RNA shedding into sewers by infected individuals. Recent studies found that SARS-CoV-2 RNA concentration in wastewater (C_RNA) could not be accounted by the fecal shedding alone. This study aimed to determine potential major shedding sources based on literature data of C_RNA, along with the COVID-19 prevalence in the catchment area through a systematic literature review. Theoretical C_RNA under a certain prevalence was estimated using Monte Carlo simulations, with eight scenarios accommodating feces alone, and both feces and sputum as shedding sources. With feces alone, none of the WBE data was in the confidence interval of theoretical C_RNA estimated with the mean feces shedding magnitude and probability, and 63% of C_RNA in WBE reports were higher than the maximum theoretical concentration. With both sputum and feces, 91% of the WBE data were below the simulated maximum C_RNA in wastewater. The inclusion of sputum as a major shedding source led to more comparable theoretical C_RNA to the literature WBE data. Sputum discharging behavior of patients also resulted in great fluctuations of C_RNA under a certain prevalence. Thus, sputum is a potential critical shedding source for COVID-19 WBE surveillance.

Data-driven estimation of COVID-19 community prevalence through wastewater-based epidemiology

Wastewater-based epidemiology (WBE) has been regarded as a potential tool for the prevalence estimation of coronavirus disease 2019 (COVID-19) in the community. However, the application of the conventional back-estimation approach is currently limited due to the methodological challenges and various uncertainties. This study systematically performed meta-analysis for WBE datasets and investigated the use of data-driven models for the COVID-19 community prevalence in lieu of the conventional WBE back-estimation approach. Three different data-driven models, i.e. multiple linear regression (MLR), artificial neural network (ANN), and adaptive neuro fuzzy inference system (ANFIS) were applied to the multi-national WBE dataset. To evaluate the robustness of these models, predictions for sixteen scenarios with partial inputs were compared against the actual prevalence reports from clinical testing. The performance of models was further validated using unseen data (data sets not included for establishing the model) from different stages of the COVID-19 outbreak. Generally, ANN and ANFIS models showed better accuracy and robustness over MLR models. Air and wastewater temperature played a critical role in the prevalence estimation by data-driven models, especially MLR models. With unseen datasets, ANN model reasonably estimated the prevalence of COVID-19 (cumulative cases) at the initial phase and forecasted the upcoming new cases in 2-4 days at the post-peak phase of the COVID-19 outbreak. This study provided essential information about the feasibility and accuracy of data-driven estimation of COVID-19 prevalence through the WBE approach.

Co-digestion of primary sewage sludge with drinking water treatment sludge: A comprehensive evaluation of benefits

Anaerobic co-digestion of primary sludge with two types of drinking water treatment sludge (DWTS), namely iron- or aluminum-rich DWTS (Fe- or Al-DWTS) were systematically evaluated by biochemical methane potential tests, kinetic modelling, downstream process parameters and microbial community analysis. Specific methane yields decreased approximately 19% to 123 mL·g^-1 VS, while the hydrolysis constant k_h decreased from 0.21 d^-1 to 0.18 d^-1 for Fe-DWTS at 10% to 40% dosages. On the contrary, specific methane yields decreased 45-55% for Al-DWTS, and k_h decreased to 0.14 d^-1 at 40% dosage. Significant removals (>95%) of phosphate and hydrogen sulfide were observed for Fe- and Al-DWTS additions at 40% dosage. Microbial community analysis revealed that Al-DWTS increased the abundance of most hydrogenotrophic methanogens, while Fe-DWTS increased the abundance of acetoclastic methanogens. Kinetic modelling further revealed that Fe- and Al-DWTS additions affected the hydrolysis and methanogenesis process kinetics and the methane yield differently.

Enhanced anaerobic digestion of primary sludge with additives: Performance and mechanisms

Anaerobic digestion of primary sludge with different additives, namely nano magnetite, graphite powder, activated carbon powder and NiCl₂/CoCl_2, were evaluated by biomethane potential tests, kinetics modelling and microbial community analysis. Specific methane yields increased from 136 mL/g VS for primary sludge to 146 mL/g VS, 151 mL/g VS, and 152 mL/g VS for the addition of nano magnetite, graphite powder, and activated carbon powder at optimal dosages, respectively. The first order hydrolysis constant k_h increased from 0.488 d^-1 to 0.526 d^-1, 0.622 d^-1, and 0.724 d^-1, respectively. Microbial community analysis revealed that the abundance of key bacterial and archaeal populations was positively correlated with hydrolysis and methane production. The enhanced methane production with activated carbon powder was due to shifting methane formation pathway from acetoclastic to hydrogenotrophic methanogenesis. In contrast, nano magnetite and graphite powder additives enhanced the direct interspecies electron transfer evidenced by increased abundance of Methanosaeta and Methanolinea.

Revealing the variations in physicochemical, morphological, fractal, and rheological properties of digestate during the mesophilic anaerobic digestion of iron-rich waste activated sludge

Dosing of iron (Fe)-salts in sewers to control odour and corrosion problems have proven to be effective on phosphate and sulfide removal in downstream treatment units. However, the interaction of Fe with sludge may impact the sludge properties during wastewater treatment and sludge digestion. Herein, we investigated the downstream impacts of sewer-dosed Fe-salt on key digestate properties including digestate dewaterability. For this, Fe-salt was dosed to a sewer reactor and resultant iron-rich waste activated sludge (Fe-WAS) was digested in an anaerobic digester (AD) in the experimental line of integrated laboratory system running in parallel to a control system. Iron containing and non-iron containing digestates were sourced from the respective AD reactors of experimental and control lines. Results showed improved dewaterability in iron containing digestate than non-iron containing digestate, which was attributed to the variations in key digestate properties. Compared to non-iron containing digestate, iron containing digestate exhibited the decreased contents of bound water, soluble extracellular polymeric substances (S-EPS), protein, polysaccharide, and monovalent-to-divalent (M⁺/D⁺⁺) cations ratio. Likewise, we observed the increased mean particle size (D_v50) for iron containing digestate than the non-iron containing digestate, but fractal dimension (D_f) values were comparable. Besides, iron containing digestate exhibited a reduced degree of thixotropy, relative sludge network strength, viscosity, yield stress, flow stress, and storage/loss/complex (G'/G''/G∗) moduli but increased creep compliance and shear strain (%) than non-iron containing digestate. The combined synergistic effects of such favorable changes amongst the key properties of iron containing digestate, might have been responsible for improving it's dewaterability.

Rebar corrosion and its interaction with concrete degradation in reinforced concrete sewers

Concrete corrosion, as a major issue in sewer management, has attracted considerable research. In comparison, the corrosion of reinforcing steel bar (rebar) is not well understood. Particularly, fundamental knowledge of rebar corrosion and its interactions with concrete corrosion/cracking is largely lacking. This study investigated rebar corrosion and concrete degradation using reinforced concrete coupons exposed in a pilot sewer system. The physical-chemical corrosion characteristics were investigated in local regions; the nature of rebar rusts was analyzed using the advanced mineral analytical techniques, including Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD); further, the interactions between rebar corrosion and concrete corrosion/cracking were elucidated by characterizing the microstructure and element distribution in interfacial areas using Mineral Liberation Analysis (MLA). The rebar corrosion products were found to be iron oxides, oxyhydroxides, chlorides, sulfides and sulfates. The predominant rebar corrosion reactions varied with exposure time and the development of concrete corrosion. When concrete corrosion reached rebar surface, the cracking of the concrete cover was influenced by multiple effects, including the macro-cracking induced by the corrosion products expansion, and the micro-cracking accelerated by the dissolution, diffusion and deposition of Fe derived from rebar rusts at the concrete corrosion front. A conceptual model elucidating rebar corrosion and the complex interactions between rebar corrosion and concrete degradation is proposed to support the development of corrosion prevention and refurbishment strategies for reinforced concrete sewers.

Assessing the removal of organic micropollutants from wastewater by discharging drinking water sludge to sewers

Discharging drinking water treatment sludge (DWTS) to sewers could be an efficient waste management strategy with the potential to replace chemical dosing for pollutant control. This study for the first time investigated the fate of 28 different organic micropollutants (MPs) due to the dosing of iron-rich and aluminum-rich DWTS in a pilot rising main sewer. Nine MPs had an initial rapid removal within 1-hr (i.e., 10-80%) due to Fe-DWTS dosing. The formation of FeS particles due to Fe-DWTS dosing was responsible for the removal of dissolved sulfides (80% reduction comparing to control sewer). Further particle characterization using SEM-EDS, XRD and ATR-FTIR confirmed that FeS particles formation played an important role in the removal of MPs from wastewater. Adsorption of MPs onto the FeS particles was likely the possible mechanism for their rapid removal. In comparison to iron-rich DWTS, aluminum-rich DWTS had very limited beneficial effects in removing MPs from wastewater. The degradability of degradable MPs, including caffeine, paraxanthine, paracetamol, metformin, cyclamate, cephalexin, and MIAA were not affected by the DWTS dosing. Some non-degradable MPs, including cotinine, hydroxycotinine, tramadol, gabapentin, desvenlafaxine, hydrochlorothiazide, carbamazepine, fluconazole, sulfamethoxazole, acesulfame, saccharin and sucralose were also not impacted by the DWTS dosing. This study systematically assessed the additional benefits of discharging Fe-DWTS to the sewer network i.e., the removal of MPs from the liquid phase thereby reducing its load to the treatment plant. The results corroborate the discharge of Fe-rich DWTS in sewers as an effective and beneficial way of managing the waste by-product.

Full-scale investigation of ferrous dosing in sewers and a wastewater treatment plant for multiple benefits

This study demonstrates the full scale application of iron dosing in a metropolitan wastewater treatment plant (WWTP) and the upstream sewer system for multiple benefits. Two different dosing locations, i.e., the WWTP inlet works (Trial-1) and upstream sewer network (Trial-2) were tested in this study. Both dosing trials achieved multiple benefits such as sulfide control, phosphate removal and improved sludge dewaterability. During Trial-1, a sulfide reduction of >90% was achieved at high dosing rates (>19 kgFe ML^-1) of ferrous chloride in the inlet works and in Trial-2 the in-sewer ferrous dosing had significant gas phase hydrogen sulfide (H₂S) concentration reduction in the sewer network. The ferrous dosing enhanced the phosphate removal in the bioreactor up to 76% and 53 ± 2% during Trial-1 & 2, respectively. The iron ending up in the anaerobic sludge digester reduced the biogas H₂S concentration by up to 36% and 45%, respectively. The dewaterability of the digested sludge was improved, with relative increases of 9.7% and 9.8%, respectively. The presence of primary clarifier showed limited impact on the downstream availability of iron for achieving the afore-mentioned multiple benefits. The iron dosing enhanced the total chemical oxygen demand removal in the primary clarifier reaching up to 49% at the high dose rates during Trial-1 and 42 ± 1% during Trial-2. This study demonstrated that multiple benefits could be achieved independent of the iron dosing location (i.e., at the WWTP inlet or in the network). Further, iron dosing at both locations enhances primary settling, beneficial for bioenergy recovery from wastewater.

Effects of in-sewer dosing of iron-rich drinking water sludge on wastewater collection and treatment systems

The use of coagulants and flocculants in the water and wastewater industry is predicted to increase further in the coming years. Alum is the most widely used coagulant, however, the use of ferric chloride (FeCl₃) is gaining popularity. Drinking water production that uses FeCl₃ as coagulant produces waste sludge rich in iron. We hypothesised that the iron-rich drinking water sludge (DWS) can potentially be used in the urban wastewater system to reduce dissolved sulfide in sewer systems, aid phosphate removal in wastewater treatment and reduce hydrogen sulfide in the anaerobic digester biogas. This hypothesis was investigated using two laboratory-scale urban wastewater systems, one as an experimental system and the other as a control, each comprising sewer reactors, a sequencing batch reactor (SBR) for wastewater treatment, sludge thickeners and anaerobic digestion reactors. Both were fed with domestic wastewater. The experimental system received in-sewer DWS-dosing at 10 mgFe L^-1 while the control had none. The sulfide concentration in the experimental sewer effluent decreased by 3.5 ± 0.2 mgS L^-1 as compared with the control, while the phosphate concentration decreased by 3.6 ± 0.3 mgP L^-1 after biological wastewater treatment in the experimental SBR. The dissolved sulfide concentration in the experimental anaerobic digester also decreased by 15.9 ± 0.9 mgS L^-1 following the DWS-dosing to the sewer reactors. The DWS-doing also enhanced the settleability of the mixed liquor suspended sludge (MLSS) (SVI decreased from 193.2 ± 22.2 to 108.0 ± 7.7 ml g^-1), and the dewaterability of the anaerobically digested sludge (the cake solids concentration increased from 15.7 ± 0.3% to 19.1 ± 1.8%). The introduction of DWS into the experimental system significantly increased the COD and TSS concentrations in the wastewater, and consequently the MLSS concentration in the SBR, however, this did not affect normal operation. The results demonstrated that iron-rich waste sludge from drinking water production can be used in the urban wastewater system achieving multiple benefits. Therefore, an integrated approach to urban water and wastewater management should be considered to maximise the benefits of iron use in the system.

Opportunities for reducing coagulants usage in urban water management: The Oxley Creek Sewage Collection and Treatment System as an example

Iron and aluminium based coagulants are used in enormous amounts and play an essential role in urban water management globally. They are dosed at drinking water production facilities for the removal of natural organic matter. Iron salts are also dosed to sewers for corrosion and odour control, and at wastewater treatment plants (WWTPs) for phosphate removal from wastewater and hydrogen sulfide removal from biogas. A recent laboratory study revealed that iron dosed to sewers is available for phosphate and hydrogen sulfide removal in the downstream WWTP. This study demonstrates for the first time under real-life conditions the practical feasibility and effectiveness of the strategy through a year-long full-scale investigation. Over a period of 5 months, alum dosing at ∼190 kg Al/day to the bioreactor in a full-scale WWTP was stopped, while FeCl₂ dosing at ∼160 kg Fe/day in the upstream network was commenced. Extensive sampling campaigns were conducted over the baseline, trial and recovery periods to investigate sulfide control in sewers and its flow-on effects on phosphate in WWTP effluent, H₂S in biogas, as well as on the WWTP effluent hypochlorite disinfection process. A plant-wide mass balance analysis showed that the Fe²⁺ dosed upstream was effectively used for P removal in the activated sludge tanks, with an effluent phosphate concentration comparable to that in the baseline period (i.e. with alum dosing to the bioreactor). Simultaneously, hydrogen sulfide concentration in biogas decreased ∼43%, from 495 ± 10 to 283 ± 4 ppm. No effects on biological nitrogen removal and disinfection processes were observed. Both effluent phosphate and H₂S in biogas increased in the recovery period, when in-sewer dosing of FeCl₂ was stopped. X-ray diffraction failed to reveal the presence of vivianite in the digested sludge, providing strong evidence that thermal hydrolysis prevented the formation of vivianite during anaerobic digestion. The latter limits the potential for selective recovery of Fe and P through magnetic separation. Overall, our study clearly demonstrates the multiple beneficial reuse of iron in a real urban wastewater system and urges water utilities to adopt an integrated approach to coagulant use in urban water management.

Removal of Pharmaceuticals and Illicit Drugs from Wastewater Due to Ferric Dosing in Sewers

Ferric (Fe³⁺) salt dosing is an efficient sulfide control strategy in the sewer network, with potential for multiple benefits including phosphorus removal in the biological reactors and sulfide emission control in the anaerobic digesters of wastewater treatment plant (WWTP). This paper extends the knowledge on the benefit of iron dosing by exploring its impact on the fate of organic micropollutants (MPs) in the wastewater using sewer reactors simulating a rising main sewer pipe. The sulfide produced by the sewer biofilms reacted with Fe³⁺ forming black colored iron sulfide (FeS). Among the selected MPs, morphine, methadone, and atenolol had >90% initial rapid removal within 5 min of ferric dosing in the sewer reactor. The ultimate removal after 6 h of retention time in the reactor reached 93-97%. Other compounds, ketamine, codeine, carbamazepine, and acesulfame had 30-70% concentration decrease. The ultimate removal varied between 35 and 70% depending on the biodegradability of those MPs. In contrast, paracetamol had no initial removal. The rapid removal of MPs was likely due to adsorption to the FeS surface, which is further confirmed by batch tests with different FeS concentrations. The results showed a direct relationship between the removal of MPs and FeS concentration. The transformation kinetics of these compounds in the reactor without Fe³⁺ dosing is in good agreement with biodegradation associated with the sewer biofilms in the reactor. This study revealed a significant additional benefit of dosing ferric salts in sewers, that is, the removal of MPs before the sewage enters the WWTP.