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Caproic acid has broad applications and can be produced from activated sludge via fermentation, but its quality is hindered by ammonia (NH 4 + -N) and reactive phosphorus (RP) in the fermentation broth. However, flow-electrode capacitive deionization (FCDI), a novel ion separation technology that operates continuously without secondary pollution seems to be an efficient process that separates the ions. The results showed that at pH 5.0, the majority of N and P presented as NH 4 + and H 2 PO 4 - , with removal efficiencies of 59.5 % for NH 4 + -N, 49.5 % for RP, and 17.4 % for caproate. Higher caproate concentrations increased boundary layer thickness, thereby promoting caproate transport to compensate for the ions consumed. The anion exchange membrane exhibited stronger rejection of divalent phosphate than acetate and caproate, resulting in lower HPO 4 2- selectivity. The FCDI holds potential as a viable technology for resource recovery from fermentation broth, offering an alternative method in bioprocessing applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Ltd. All rights reserved.)

Energy-efficient wastewater treatment plants (WWTPs) utilize systems like high-rate activated sludge (A-stage) system to redirect organics from wastewater are redirected into energy-rich sludge (A-sludge). Anaerobic membrane bioreactors (AnMBRs) offer lower footprint and higher effluent quality compared to conventional digesters. In this study, the biological treatment and the filtration performances of AnMBRs for A-sludge digestion under mesophilic and thermophilic conditions were comparatively evaluated through lab-scale experiments, mass balancing and dynamic modeling. Under thermophilic conditions, a higher COD fraction of the influent sludge was converted into methane gas than under mesophilic conditions (65% versus 57%). The energy balance indicated that the surplus energy recovery under thermophilic conditions was less than the additional energy required for heating the AnMBR, resulting in a more than three-fold higher net energy recovery under mesophilic conditions. Therefore, operating an AnMBR for sludge digestion under mesophilic conditions has a higher potential to improve the energy balance in WWTPs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The disintegration of raw sludge is of importance for enhancing biogas production and facilitates the degradation of substrates for microorganisms so that the efficiency of digestion can be increased. In this study, the effect of hydrodynamic cavitation (HC) as a pretreatment approach for waste activated sludge (WAS) was investigated at two upstream pressures (0.83 and 1.72 MPa) by using a milli-scale apparatus which makes sludge pass through an orifice with a restriction at the cross section of the flow. The HC probe made of polyether ether ketone (PEEK) material was tested using potassium iodide solution and it was made sure that cavitation occurred at the selected pressures. The analysis on chemical effects of HC bubbles collapse suggested that not only cavitation occurred at low upstream pressure, i.e., 0.83 MPa, but it also had high intensity at this pressure. The pretreatment results of HC implementation on WAS were also in agreement with the chemical characterization of HC collapse. Release of soluble organics and ammonium was observed in the treated samples, which proved the efficiency of the HC pretreatment. The methane production was improved during the digestion of the treated samples compared to the control one. The digestion of treated WAS sample at lower upstream pressure (0.83 MPa) resulted in higher methane production (128.4 mL CH 4 /g VS) compared to the treated sample at higher upstream pressure (119.1 mL CH 4 /g VS) and control sample (98.3 mL CH 4 /g VS). Thus, these results showed that the HC pretreatment for WAS led to a significant increase in methane production (up to 30.6%), which reveals the potential of HC in full-scale applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Recently, one of the main purposes of wastewater treatment plants is to achieve a neutral or positive energy balance while meeting the discharge criteria. Aerobic granular sludge (AGS) technology is a promising technology that has low energy and footprint requirements as well as high treatment performance. The effect of co-treatment of municipal wastewater and food waste (FW) on the treatment performance, granule morphology, and settling behavior of the granules was investigated in the study. A biochemical methane potential (BMP) test was also performed to assess the methane potential of mono- and co-digestion of the excess sludge from the AGS process. The addition of FW into wastewater enhanced the nutrient treatment efficiency in the AGS process. BMP of the excess sludge from the AGS process fed with the mixture of wastewater and FW (195 ± 17 mL CH 4 /g VS) was slightly higher than BMP of excess sludge from the AGS process fed with solely wastewater (173 ± 16 mL CH 4 /g VS). The highest methane yield was observed for co-digestion of excess sludge from the AGS process and FW, which was 312 ± 8 mL CH 4 /g VS. Integration of FW as a co-substrate in the AGS process would potentially enhance energy recovery and the quality of effluent in municipal wastewater treatment., (© 2024. The Author(s).)

Coagulants such as aluminum sulfate (Al 2 (SO 4 ) 3 (alum)) and ferric chloride (FeCl 3 ) used in water treatment plants (WTPs) led to the generation of sludge that is usually disposed to landfills. However, the utilization of WTP sludge is being encouraged by authorities to achieve sustainable development. This study aims to investigate WTP sludge utilization in a pilot-scale high-rate activated sludge (HRAS) system as a substitute for conventional coagulants. Based on jar tests, the iron sludge was selected for pilot-scale testing due to its superior ability to enhance the treatment efficiency of the HRAS process compared to alum sludge. Iron sludge addition (20.1 ± 1.6 mg dry sludge/L wastewater) slightly improved the removal efficiency of particulate chemical oxygen demand (pCOD) from 74 % to 81 % (p-value: 0.014). Iron sludge addition had a distinct effect on the sludge characteristics of the HRAS process. The average median particle size (d 50 ) increased from 96 ± 3 to 163 ± 14 μm (p-value<0.00) with the addition of iron sludge, which improved the settleability of the HRAS process sludge. However, the biochemical methane potential (BMP) of the HRAS process sludge decreased by 8.9 % (p-value<0.00) after iron sludge addition. In a scenario analysis of WTP sludge use in a hypothetical HRAS plant, the effluent quality index (EQI), an indicator of environmental impact, was calculated and the cost related to the operation (the transfer and landfill disposal of WTP and HRAS process sludge, energy and chemical consumption of the HRAS plant) was estimated. As a result, using WTP sludge in the HRAS plant did not significantly affect the EQI of the plant but decreased overall cost by 11 %. The results showed that the use of WTP sludge as a coagulant in wastewater treatment could achieve mutual benefits for WTPs and WWTPs and have the potential to realize the circular economy model., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Biogas production from anaerobic sludge digestion plays a central role for wastewater treatment plants to become more energy-efficient or even energy-neutral. Dedicated configurations have been developed to maximize the diversion of soluble and suspended organic matter to sludge streams for energy production through anaerobic digestion, such as A-stage treatment or chemically enhanced primary treatment (CEPT) instead of primary clarifiers. Still, it remains to be investigated to what extent these different treatment steps affect the sludge characteristics and digestibility, which may also impact the economic feasibility of the integrated systems. In this study, a detailed characterization has been performed for sludge obtained from primary clarification (primary sludge), A-stage treatment (A-sludge) and CEPT. The characteristics of all sludges differed significantly from each other. The organic compounds in primary sludge consisted mainly of 40% of carbohydrates, 23% of lipids, and 21% of proteins. A-sludge was characterized by a high amount of proteins (40%) and a moderate amount of carbohydrates (23%), and lipids (16%), while in CEPT sludge, organic compounds were mainly 26% of proteins, 18% of carbohydrates, 18% of lignin, and 12% of lipids. The highest methane yield was obtained from anaerobic digestion of primary sludge (347 ± 16 mL CH 4 /g VS) and A-sludge (333 ± 6 mL CH 4 /g VS), while it was lower for CEPT sludge (245 ± 5 mL CH 4 /g VS). Furthermore, an economic evaluation has been carried out for the three systems, considering energy consumption and recovery, as well as effluent quality and chemical costs. Energy consumption of A-stage was the highest among the three configurations due to aeration energy demand, while CEPT had the highest operational costs due to chemical use. Energy surplus was the highest by the use of CEPT, resulting from the highest fraction of recovered organic matter. By considering the effluent quality of the three systems, CEPT had the highest benefits, followed by A-stage. Integration of CEPT or A-stage, instead of primary clarification in existing wastewater treatment plants, would potentially improve the effluent quality and energy recovery., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Medium chain fatty acids (MCFAs) production from excess sludge have recently received great research interest due to higher energy densities, easy-separation capability and high economic benefits. Here, the addition of chain elongation (CE) enrichments with ethanol as electron donor was used to enhance caproate production from one-stage sludge fermentation. Compared with 0.20 g/L of controls, caproate production reached 9.00 g/L by supplementing CE enrichments with ethanol/acetate ratio of 3:1 after 7 days of acidification of organic matter in pretreated sludge fermentation. Clostridium&#95;sensu&#95;stricto&#95;12, that refers to CE, was enriched in the first and second transfer of the sludge microbial consortium. Maintaining the stability of the microbial consortium would be the key that enables stable and efficient caproate production from sludge fermentation by supplementing CE enrichments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Achieving a neutral/positive energy balance without compromising discharge standards is one of the main goals of wastewater treatment plants (WWTPs) in terms of sustainability. Aerobic granular sludge (AGS) technology promises high treatment performance with low energy and footprint requirement. In this study, high-rate activated sludge (HRAS) process was coupled to AGS process as an energy-efficient pre-treatment option in order to increase energy recovery from municipal wastewater and decrease the particulate matter load of AGS process. Three different feeding strategies were applied throughout the study. AGS system was fed with raw municipal wastewater, with the effluent of HRAS process, and with the mixture of the effluent of HRAS process and raw municipal wastewater at Stage 1, Stage 2 and Stage 3, respectively. Total suspended solids (TSS), chemical oxygen demand (COD), ammonia nitrogen (NH 4 + -N), and total phosphorus (TP) concentrations in the effluent were less than 10 mg/L, 60 mg/L, 0.4 mg/L, and 1.3 mg/L respectively at all stages. Fluctuations were observed in the denitrification performance due to changes in the influent COD/total nitrogen (TN) ratio. This study showed that coupling HRAS process with AGS process by feeding the AGS process with the mixture of HRAS process effluent and raw municipal wastewater could be an appropriate option for both increasing the energy recovery potential of WWTPs and enabling high effluent quality., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Aerobic granules contain microorganisms that are responsible for carbon, nitrogen, and phosphorus removal in aerobic granular sludge (AGS) process in which aerobic/anoxic/anaerobic layers (from surface to core) occur in a single granule. Optimizing the aerobic granular sludge (AGS) process for granulation and efficient nutrient removal can be challenging. The aim of this study was to examine the impact of settling prior to AGS process on granulation and treatment performance of the process. For this purpose, synthetic wastewater mimicking municipal wastewater was fed directly (Stage 1), and after primary sedimentation (Stage 2) to a laboratory-scale AGS system. In full-scale wastewater treatment plants, primary sedimentation is used to remove particulate organic matter and produce primary sludge which is sent to anaerobic digesters to produce biogas. Performances obtained in both stages were compared in terms of treatment efficiency, granule settling behavior, and granule morphology. Granulation was achieved in both stages with more than 92% chemical oxygen demand (COD) removal efficiencies in each stage. High nutrient removal was obtained in Stage 1 since anaerobic phase was long enough (i.e., 50 min) to hydrolyze particulate matter to become available for PAOs. Primary sedimentation caused a decrease in influent organic load and COD/N ratio, as a result, low nitrogen and phosphorus removal efficiencies were observed in Stage 2 compared to Stage 1. With this study, the effect of the primary sedimentation on the biological removal performance of AGS process was revealed. COD requirement for nutrient removal in AGS systems should be assessed by considering energy generation via biogas production from primary sedimentation sludge., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Anaerobic digestion is one of the most commonly accepted processes applied for the stabilization and treatment of primary sludge generated in municipal wastewater treatment plants enabling energy recovery via biogas production. Understanding and optimizing anaerobic sludge digesters play a key role in sustainability of wastewater treatment plants. Mathematical modeling of biological treatment systems provides several advantages such as better understanding of biochemical processes, interrelations of different biomass types, and impact of environmental conditions on the treatment plant performance. This research presents the modeling of a full-scale anaerobic sludge digester by implementing Anaerobic Digestion Model No. 1 with a limited number of monitored parameters. Model calibration was carried out using a long-term data set. The accuracy of the optimized parameter sets was assessed against measured data obtained from the full-scale sludge digester. The model could predict the methane flow and effluent chemical oxygen demand concentration in good agreement with the measured data. Therefore, the validated model can be used to predict full-scale sludge digester performance under dynamic loadings, and to optimize methane production at different operation conditions.

The objective of this study was to assess the operational feasibility of an anaerobic membrane bioreactor (AnMBR), consisting of an upflow anaerobic sludge blanket (UASB) reactor coupled to an ultrafiltration membrane unit, at two operational temperatures (25°C and 15°C) for the treatment of municipal wastewater. The results showed that membrane fouling at 15°C was more severe than that at 25°C. Higher chemical oxygen demand (COD) and soluble microbial products (SMP) concentrations, lower mean particle diameter, and higher turbidity in the UASB effluent at lower temperature aggravated membrane fouling compared to the 25°C operation. However, the overall AnMBR treatment performance was not significantly affected by temperature, which was attributed to the physical membrane barrier. Cake resistance was found responsible for over 40% of the total fouling in both cases. However, an increase was observed in the contribution of pore blocking resistance at 15°C related to the larger amount of fine particles in the UASB effluent compared to 25°C. Based on the overall results, it is concluded that an AnMBR, consisting of a UASB coupled membrane unit, is not found technically feasible for the treatment of municipal wastewater at 15°C, considering the rapid deterioration of the filtration performance., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This study investigated the effect of upflow velocity (Vup) on biological removal efficiency and effluent filterability in a laboratory scale upflow anaerobic sludge blanket (UASB) reactor. Upflow velocities of 1.2, 0.6 and 1.2m/h were applied in three successive stages over a total operation period of 116 days. Filterability tests were carried out during each stage in order to assess the effect of Vup on subsequent membrane performance. Results indicated a significant impact of Vup on both biological performance and physicochemical effluent characteristics. The observed differences in protein/carbohydrate ratio and particle size distribution (PSD), which play important roles in membrane fouling, lead to the hypothesis that Vup is a critical parameter for effluent filterability in membrane coupled UASB reactors. Results showed that filterability of the effluent during the operation at 0.6m/h was better than that during the operation at 1.2m/h., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Co-digestion of the organic fraction of municipal solid waste (OFMSW) and sewage sludge may be an attractive alternative for sustainable management of two separate waste streams produced in large amounts in all countries. This study evaluates calculation-based results of an anaerobic co-digestion process for primary sludge (PS) together with the OFMSW. The calculations were carried out for the anaerobic digester of Kayseri municipal wastewater treatment plant (in Turkey) presently digesting only PS. Two alternatives were proposed using different solid waste contents in co-digesters. For achieving the optimal solids content, some treated wastewater should be recycled to the inlet of the digesters. The municipal solid waste collection method characterized as mechanically sorted (MS-OFMSW; Option 1) is evaluated as well as a source sorted (SS-OFMSW) alternative (Option 2). Utilizing the energy produced by the existing sludge digester, only 30% of the internal energy demand at the wastewater treatment plant can be covered. The aim of this study is to evaluate how energy production would be increased by co-digestion of OFMSW and PS. The best operational condition considering organic loading rate, hydraulic retention time and energy generation could be attained at 10% digester solids content for both options. According to Option 1, almost 77% of the energy demand could be covered by co-digestion of MS-OFMSW and PS. Results indicated that almost 100% energy coverage can be obtained when co-digestion (Option 2) was performed according to SS-OFMSW and PS.

Today, the transition to renewable energy from conventional energy practices is more important than ever to establish energy security and mitigate climate change. The wastewater treatment plants (WWTP) consume a remarkable amount of energy and cause significant greenhouse gas emissions. The energy balance of WWTP can be improved by implementing energy-efficient applications such as anaerobic digestion. However, most of the existing WWTPs utilize only sewage sludge in conventional anaerobic digesters (CAD) which results in low biogas generation. Generally, co-digestion is indicated as an effective solution for the low biogas generation faced in mono-digestion. Moreover, recently, anaerobic membrane bioreactors (AnMBR) have been promoted as a prominent alternative to CADs. This paper overviews the current situation of co-digestion applications by AnMBRs for municipal WWTPs. Furthermore, the environmental and economic aspects of these applications were reviewed. Lastly, challenges and future perspectives related to the co-digestion applications by AnMBR were thoroughly discussed. [ABSTRACT FROM AUTHOR]

Industries use reclaimed water for their makeup water requirements of cooling towers to decrease their water footprints. Makeup water quality depends on the type of cooling tower design; however, total suspended solids (TSS), biological oxygen demand (BOD 5), fecal coliform, pH, total dissolved solids (TDS), some ions (sulphate, chloride, ammonium) and heavy metals (aluminum, silica, manganese, iron) are important parameters to prevent contamination, scaling, and corrosion. In the first part of this study, cooling water production from municipal wastewater was experimentally investigated, in the second part of this study cost of treatment alternatives was estimated. Six different treatment configurations (C1: microfiltration (MF)+nanofiltration (NF); C2: ultrafiltration (UF)+NF; C3: high-rate activated sludge (HRAS)+NF; C4: MF+reverse osmosis (RO); S5: UF+RO; C6: HRAS+RO) were analyzed. Thanks to the high treatment performances of NF and RO membranes, reclaimed water in each scenario met the suggested cooling water quality. The effluent of the HRAS process showed the worst effluent quality in terms of turbidity (42.1 ± 2.6 NTU of turbidity) compared to MF and UF direct filtration (turbidity of DMF permeates were below 5 NTU). However, since HRAS process is less costly than direct membrane filtration (DMF) via MF or UF membranes, the lowest treatment cost was achieved with the C3 (HRAS+NF) treatment configuration (0.52 €/m3 reclaimed water). This study demonstrates that the HRAS+NF configuration can produce water suitable for cooling tower makeup, highlighting its potential as a sustainable solution to reduce water footprints and promote water circularity in industries. • HRAS process effluent had the highest turbidity (42.1 ± 2.6 NTU) compared to direct membrane filtration (DMF). • HRAS effluent reduced nanofiltration (NF) flux by 10 % compared to ultrafiltration (UF) permeate. • HRAS process effluent led to 22 % reverse osmosis (RO) flux reductions compared to UF permeate. • All of six treatment configurations' reclaimed water met makeup water quality standards. • HRAS+NF configuration achieved the lowest treatment cost: 0.52 €/m3 reclaimed water. [ABSTRACT FROM AUTHOR]

Abstract Excess sludge from a pilot-scale high-rate activated sludge (HRAS) system was digested anaerobically under mesophilic conditions. The pilot-scale HRAS system was initially fed with only wastewater and following that, fed with wastewater together with food waste. Impact of food waste inclusion on anaerobic digestion performance was investigated. Thereafter, a feasibility study was carried out using the performance data obtained from the experimental studies. The results showed that digestion of HRAS sludge could be a preferable option unless excellent biomass-liquid separation could be employed and mineralization of influent chemical oxygen demand (COD) could be suppressed. Additionally, co-treatment of wastewater and food waste increased the methane yield and improved the energy balance of the wastewater treatment plants (WWTPs). Thus, WWTPs can have a surplus in the energy budget. Highlights • Food waste addition to wastewater increased methane yield of excess sludge by ∼50%. • Food waste addition to wastewater raised actual methane conversion from 36% to 52%. • Superior water-solid separation processes can enhance energy recovery of the WWTPs. • An energy surplus of 70% can be obtained under ideal conditions in an HRAS plant. [ABSTRACT FROM AUTHOR]

Conventional activated sludge (CAS) process is one of the most commonly applied processes for municipal wastewater treatment. However, it requires a high energy input and does not promote energy recovery. Currently, high-rate activated sludge (HRAS) process is gaining importance as a good option to reduce the energy demand of wastewater treatment and to capture organic matter for valorizing through anaerobic digestion (AD). Besides, food waste addition to wastewater can help to increase the organic matter content of wastewater and thus, energy recovery in AD. The objective of this study is to evaluate the applicability of co-treatment of municipal wastewater and food waste in a pilot-scale HRAS system as well as to test the minimal hydraulic retention times (HRTs) such as 60 and 30 min. Food waste addition to the wastewater resulted in a 10% increase in chemical oxygen demand (COD) concentration of influent. In the following stages of the study, the pilot-scale system was operated with wastewater solely under the HRTs of 60 and 30 min. With the decrease of HRT, particulate COD removal increased; however, soluble COD removal decreased. The results demonstrated that if the settling process is optimized, more particulate matter can be diverted to sludge stream. [ABSTRACT FROM AUTHOR]

Membrane bioreactors (MBRs) are commonly used in municipal and industrial wastewater treatment. However, membrane fouling problem limits the performance of MBRs. The objective of this study was to determine the impact of vibration on membrane fouling. Long-term filtration experiments were conducted to compare treatment and filtration performance of vibrated (magnetically induced) and non-vibrated modules in an MBR treating synthetic municipal wastewater. Results showed that vibration did not have any remarkable effect on treatment performance. However, filtration performance and thus, membrane fouling were significantly affected by the vibration. Magnetically induced vibration system achieved better filtration performance than the non-vibrated module. Cake layer formation found in the magnetically induced vibrating system resulted in low potential for pore clogging. The results suggest that magnetically induced vibration is a promising alternative for reducing membrane fouling problem in MBR systems. [ABSTRACT FROM AUTHOR]

In this study, fate of micropollutants was investigated in a membrane bioreactor (MBR) having dynamic membrane (DM) and ultrafiltration (UF) membrane for the treatment of raw municipal wastewater. Removal efficiencies of different micropollutants including sulfamethoxazole, ciprofloxacin, trimethoprim, caffeine and acetaminophen were assessed. A commercial hollow fiber UF membrane was used in parallel with a DM that was formed on a low-cost hollow fiber support material, made of polyester. MBR was operated at a flux of 10 L/m2·h. High total suspended solids (>99%) and chemical oxygen demand (>91%) removal efficiencies were achieved with each membrane. Besides, high removal efficiencies of micropollutants (>68.3->99.7%) were achieved. Morphological analyses were conducted for each membrane in order to get insight to the cake (dynamic) layer that was accumulated on the membrane. DM technology provides an effective alternative to the conventional membrane systems for micropollutant removal from municipal wastewater. • Hollow fiber dynamic membrane (DM) and a commercial ultrafiltration membrane (UF) were compared. • The two membranes were operated at a flux of 10 L/m2·h in the same reactor. • Similar micropollutant removal efficiencies were obtained with both membranes. • Higher transmembrane pressure was observed for DM, because of dynamic layer formation. [ABSTRACT FROM AUTHOR]