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Excessive organic matter in the anaerobic ammonia oxidation (Anammox) leads to the growth of a large number of heterotrophic bacteria, which disrupts the anaerobic ammonia oxidation. The adsorption-anaerobic ammonia oxidation process can effectively reduce excessive organic matter, capturing it instead of consuming it, which is a sustainable development technology. In this study, utilizing the excellent adsorption performance of aerobic granular sludge (AGS), an adsorption-regeneration process was employed to remove organic matter at the front end of the Anammox process through bio-adsorption in an artificial simulated domestic sewage environment, and it was successfully used for denitrification. Stirring rate is a key factor affecting sludge granulation. As a parallel experiment of sludge granulation, two Sequencing Batch Reactors (SBRs) (R1 and R2) were operated simultaneously at different stirring rates. After 153 days, the particle size of the two reactors was analyzed, revealing that the proportion of particles larger than 200 μm was over 50%, and granular sludge was successfully formed in both reactors. Long-term operational results indicate that at a temperature of 16.5 ± 1 °C, varying initial pH levels (6.5, 6.7, 7.2, and 8.5) significantly affect the removal efficiency of chemical oxygen demand (COD). COD is rapidly adsorbed and removed within a short period. Among the tested initial pH values, a pH of 6.7 yielded the best total chemical oxygen demand (tCOD) removal efficiency, achieving up to 95%. Additionally, the study examined the effects of different carbon sources on denitrification, revealing that under carbon-rich conditions, the denitrification rate was highest, reaching 1.44 mg N/(g VSS·h). Compared to endogenous denitrification, the denitrification rate increased by 40%, and the nitrate (NO₃⁻-N) removal efficiency reached 100%., 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.)

An interesting and potential property of extracellular polymeric substances (EPS) is the hydrogel formation with calcium ions. Aiming at understanding the significant difference in the hydrogel formed between EPS from flocculent and granular sludge, a targeted investigation of the lipopolysaccharides (LPS), one of the important EPS components, was performed. LPS was isolated from the EPS of flocculent and granular sludge, and both the glycan and the lipid A parts of LPS were characterized and compared. The morphology of LPS-calcium (LPS-Ca) aggregates were visualized by the polymyxin B-based fluorescent probe. The LPS constituted about 25 % and 15 % of the EPS from flocculent and granular sludge, respectively. The flocculent sludge LPS showed a lower amount of glycans, shorter glycan chain length, lower molecular weight, and higher possibility of containing unsaturated lipids than the granular sludge EPS. The flocculent sludge LPS-Ca aggregates demonstrated invert structures with the water phase in between, contributing to the fluid-like property of the respect EPS-Ca. In contrast, with the remarkably different chemical structure, LPS-Ca aggregates from granular sludge displayed bilaminar multilayered morphology, contributing to the solid, self-standing hydrogel of EPS-Ca., 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 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Phosphorus (P) recovered from sludge-incinerated ash (SIA) could be applied to synthesize highly added-value products (FePO 4 and LiFePO 4 ) with in situ Fe in SIA. Indeed, LiFePO 4 is a future of rechargeable batteries, which makes lithium (Li) highly needed. Alternatively, Li could also be extracted from concentrated brines to face a potential crisis of Li depletion on lands. Based on H 3 PO 4 and Fe 3+ co-extracted from the acidic leachate of SIA by tributyl phosphate (TBP), FePO 4 (31.2 wt% Fe, 17.6 wt% P and the molar ratio of Fe/P = 0.98) was easily formed only adjusting pH of the stripping solution to 1.6. Interestingly, the organic phase from the first-stage co-extraction process of Fe 3+ and H 3 PO 4 could be utilized for Li-extraction from salt-lake brine, based on the TBP-FeCl 3 -kerosene system, and a good performance (78.7%) of Li-extraction and separation factors (β) (186.0-217.4) were obtained. Furthermore, the compounds with Li-extraction are complex, possibly LiFeCl 4 ∙2TBP, in which Li + could be stripped to form Li 2 CO 3 by 4.0 M HCl (with a stripping rate up to 83%). Besides, Li 2 CO 3 could also be obtained from desalinated brine by adsorption with manganese oxide ion sieve (HMO) and desorption with HCl. In the two cases, almost pure Li 2 CO 3 products were obtained, up to 99.7 and 99.5 wt% Li 2 CO 3 respectively, after further purification and concentration. Finally, recovered FePO 4 and extracted Li 2 CO 3 were synthesized for producing LiFePO 4 that had a similar electrochemical property (69.5 and 77.8 mAh/g of the initial discharge capacity) to those synthesized from commercial raw materials., 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 high-rate contact stabilization (HiCS) process, a variant of high-rate activated sludge, has gained attention for its superior energy recovery and enhanced biosorption capabilities. The need for efficient energy recovery in HiCS necessitates a high settling efficiency to minimize resource loss due to endogenous sludge consumption. However, the low sludge retention time (SRT) required for HiCS can significantly affect sludge floc stability and flocculation performance, warranting a deeper analysis of the factors influencing these characteristics. This study investigates the impact of SRT reduction on sludge performance, focusing on energy potential, viscoelasticity, and critical pressure. The analysis was conducted using rheological tests, contact angle measurements, zeta potential analysis, Fourier transform infrared spectroscopy, XDLVO theory, and the PARAFAC model. Results indicate that due to the contribution of hydrophobicity, the HiCS system maintained the large flocs morphology of the sludge even when the SRT was maintained for 2d. However, a combination of aerobic microbial activity, high concentrations of loosely bound extracellular polymeric substances, and the presence of the filamentous bacterium Thiothrix contributed to reduced flocculation performance., 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 interaction between extracellular polymeric substances (EPS) in municipal sludge and antibiotics in wastewater is critical in wastewater treatment, resource recovery, and sludge management. Therefore, it is increasingly urgent to investigate the distribution coefficient (Log K) of sulfonamide antibiotics (SAs) in EPS, particularly in sludge-derived dissolved organic carbon (DOC) and aqueous phase systems. Herein, through balance experiments, the concentrations of SAs were determined using alkaline extraction EPS (AEPS) and alginate-like extracellular polymer (ALE) systems, and the Log K DOC values were determined. The results showed that the Log K DOC of AEPS was higher than that of ALE, which exhibited a negative K DOC value, indicating an inhibitory effect on dissolution. For the three SAs studied, the Log K DOC values were in the following order: sulfamethoxazole > sulfapyridine > sulfadiazine. This order can be attributed to the differing physicochemical properties, such as polarity, of the SAs. Three-dimensional excitation-emission matrix fluorescence spectra and fitting results indicated a lack of aromatic proteins dominated by tryptophan and humus-like substances in ALE. Meanwhile, the hydrophobic interaction of aromatic proteins dominated by tryptophan was the main driving force in the binding process between AEPS and SAs., 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. Published by Elsevier Inc.)

Nitrospira is a common genus of nitrite-oxidising bacteria (NOB) found in wastewater treatment plants (WWTPs). To identify the key factors influencing the composition of NOB communities, research was conducted using both sequencing batch reactor (SBR) and continuous flow reactor under different conditions. High-throughput 16S rRNA gene sequencing revealed that Nitrospira (18.79% in R1 and 25.77% in R3) was the dominant NOB under low dissolved oxygen (DO) and low nitrite ( NO 2 - -N) concentrations, while Nitrobacter (21.26% in R2) was the dominant NOB under high DO and high NO 2 - -N concentrations. Flocculent and granule sludge were cultivated with Nitrospira as the dominant genus. Compared to Nitrospira flocculent sludge, Nitrospira granule sludge had higher inhibition threshold concentrations for free ammonia (FA) and free nitrous acid (FNA). It was more likely to resist adverse environmental disturbances. Furthermore, the effects of environmental factors such as temperature, pH, and DO on the activity of Nitrospira granular sludge were also studied. The results showed that the optimum temperature and pH for Nitrospira granular sludge were 36°C and 7.0, respectively. Additionally, Nitrospira granular sludge showed a higher dissolved oxygen half-saturation constant ( K o) of 3.67 ± 0.71 mg/L due to its morphological characteristics. However, the majority of WWTPs conditions do not meet the conditions for the Nitrospira granular sludge. Thus, it can be speculated that future development of aerobic partial nitrification granular sludge may automatically eliminate the influence of Nitrospira . This study provides a theoretical basis for a deeper understanding of Nitrospira and the development of future water treatment processes.

The recovery of biopolymers, particularly alginate-like extracellular polymers, from municipal sludge represents a promising step toward sustainable sludge treatment practices. Originating from wastewater plants in complexly polluted environments, alginate-like extracellular polymers carry potential environmental risks concerning their reuse. This study employs ultrahigh-performance liquid chromatography-tandem mass spectrometry to investigate the distribution coefficients and occurrence of alginate-like extracellular polymers and sulfamethoxazole. Results demonstrate a negative distribution coefficient, suggesting an inhibitory effect on sulfamethoxazole dissolution. The ethanol-extracted alginate-like extracellular polymers exhibits higher sulfamethoxazole levels (approximately 52%) than those obtained via dialysis extraction. Three-dimensional excitation-emission matrix analysis and adsorption studies indicate the absence of tyrosine-like substances in the alginate-like extracellular polymers, unlike in other extracellular polymeric substances. This absence diminishes hydrophobic interactions, highlighting that electrostatic interactions play a more important role. These insights are crucial for understanding the adsorption behavior of alginate-like extracellular polymers and optimizing their large-scale extraction processes., 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.)

This study investigated the effect of high DO concentrations on PN. The experimental setup involved operating at high DO concentrations (1.5-2.5 mg/L) and environmental temperatures (15-20 °C) over a period of 180 days. Through a sludge enrichment process, the kinetic parameters of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were determined. Surprisingly, contrary to conventional reports, it was observed that NOB exhibited a stronger affinity for DO compared to AOB. As a result, high DO concentrations were necessary to provide favorable conditions for the growth of AOB. In order to establish PN, strategies including intermittent aeration, free ammonia (FA), and controlled sludge retention time (SRT) were employed. The successful PN was achieved with a specific ammonia oxidation rate of 24 mg N/g MLVSS/h and a specific nitrite oxidation rate below 0.10 mg N/g MLVSS/h. The nitrite accumulation rate (NAR) was maintained at 100% during stable operation. The abundance of Nitrosomonas, a typical genus of AOB, was found to be 68.62%, which surpasses previous studies in similar research. A slightly higher DO concentrations may increase energy consumption, but achieve higher efficiency and stability in PN. This study provided new insights into the application of PN in wastewater treatment., Competing Interests: Declaration of competing interest No potential conflict of interest was reported by the author(s)., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Extracellular polymeric substances (EPS) are biopolymers contained in both aerobic and anaerobic sludge. In EPS, alginate like extracellular polymers (ALE) is thought as a highly valued material, which have been widely studied with aerobic sludge. Nevertheless, a curiosity on ALE remains in anaerobic digested sludge (ADS). With 5 different sludge sources, anaerobic digestion of excess sludge was conducted in a batch mode, and then ADS was used to extract ALE and to analyze its physicochemical properties for potential applications. The yield of ALE extracted from ADS (ALE-ADS) ranged from 119.4 to 179.4 mg/g VSS. The compositional characteristics of ALE-ADS observed by FT-IR, 3D-EEM and UV-Vis spectroscopy revealed that there were minor differences in the composition and property of ALE-ADS but a similarity of 62 %-70 % to a commercial alginate remained in terms of chemical functional groups. Moreover, ALE-ADS composed of 1,4-linked β-d-mannuronic acid (M) and 1,4 α-l-guluronic acid (G) residues that form blocks of GG (20.8 %-33.8 %), MG (12.8 %-30.1 %) and MM (6.6 %-15.1 %), respectively. Based on the gel-forming capacity, film-forming property, adsorbility, and amphiphilicity, ALE-ADS seems potential as a water-proof coating with even a better performance than the commercial alginate, as a seed coating with an increased germination rate, and as a bio-adsorbent with a similar performance to the commercial alginate and ALE from aerobic sludge., 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.)

A high moisture content of waste activated sludge (WAS) associated with a low calorific value needs to be deeply dried towards self-supporting incineration. On the other hand, thermal energy with low temperature exchanged from treated effluent has great potential for drying sludge. Unfortunately, low-temperature drying of sludge seems to be low in efficiency and long in drying time. For this reason, some agricultural biomass was added into WAS to improve the drying efficiency. The drying performance and sludge properties were analyzed and evaluated with this study. Experimental results demonstrated that wheat straw was the best in enhancing the drying performance. With only 20 % (DS/DS) of crushed wheat straw added, the average drying rate achieved up to 0.20 g water/g DS·min, much higher than 0.13 g water/g DS·min of the raw WAS. The drying time to the targeted moisture content (63 %) (for self-supporting incineration) was shortened to only 12 min, much lower than 21 min of the raw WAS. The analysis revealed that wheat straw could reduce the specific resistance of filtration (SRF) and increase the sludge filterability (X). Also, the sludge rheology, particle size distribution and SEM images could conclude that agricultural biomass played a positive role in skeleton builders, forming a mesh-like structure in sludge flocs. These special channels could obviously improve the transfer capacities of heat and water inside the sludge matrix and thus greatly increase the drying performance of WAS., 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.)

As a highly added value material, alginate-like extracellular polymers (ALE) can be extracted from extracellular polymeric substances (EPS) from aerobic granular sludge (AGS). In fact, conventional activated sludge (CAS) also contains a certain amount of ALE. As CAS is widely used everywhere, waste activated sludge (WAS) from CAS is huge in its absolute amount. Although the ALE property of CAS was identified not so good as that from AGS, the mechanisms remains unclear. For this reason, it is necessary to unravel the chemically compositional blocks of ALE. Referring to natural alginate, ALE can be separated into three compositional blocks: GGL, GML and MML (like units containing guluronate or mannuronate), associated with other compositions including protein (PN), polysaccharide (PS), phosphorus (P), humic acid (HA). With real WAS from CAS, ALE was extracted and three blocks were separated: GGL = 54 %, GML = 42 % and MML = 4 % in weight, which is similar to the previous study. Moreover, the GGL blocks in CAS were obviously lower than AGS, down to by 1/3-1/2. And the GML and MML blocks in CAS were much higher than AGS, by more than 1/2. Different compositional blocks of ALE in AGS and CAS should be the reason forming different properties in applications. For this reason, a further study will be initiated to dispense/reorganize three blocks of ALE from CAS for expanding its potential applications, based on the compositional blocks of ALE from AGS., Competing Interests: Declaration of competing interest We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Wet-chemical approach is widely applied for phosphate recovery from incinerated ash of waste activated sludge (WAS), along with metals removed/recovered. The high contents of both aluminum (Al) and iron (Fe) in WAS-incinerated ash should be suitable for producing coagulants with some waste anions like Cl - and SO 4 2- With acid (HCl) leaching and metals' removing, approximately 88 wt% of phosphorus (P) in the ash could be recovered as hydroxylapatite (HAP: Ca 5 (PO 4 ) 3 OH); Fe 3+ in the acidic leachate could be selectively removed/recovered by extraction with an organic solvent of tributyl phosphate (TBP), and thus a FeCl 3 -based coagulant could be synthesized by stripping the raffinate with the original brine (containing abundant Cl - and SO 4 2- ). Furthermore, a liquid poly-aluminum chloride (PAC)-based coagulant could also be synthesized with Al 3+ removed from the ash and the brine, which behaved almost the same in the coagulation performance as a commercial coagulant on both phosphate and turbidity removals. Both P-recovery from the ash and coagulant production associated with the brine would enlarge the markets of both 'blue' phosphate and 'green' coagulants., 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.)

Sludge incineration and seawater desalination are two approaches that can be used in the disposal of waste activated sludge (WAS) and for obtaining fresh water. As resource recovery from wastewater treatment and water purification is a topic of particular interest in these times, "water mining" has become a focus of research, with phosphate/P-recovery from WAS incineration ash, and extraction of useful elements from the brine of desalination being important steps in the pursuit of a circular/blue economy. However, P-recovery from ash involves removing metals, which need to be disposed of carefully, as does the brine collected. If cations in the ash and anions in the brine could be combined in order to produce coagulants/flocculants, a new circular model would be established. A preliminary experiment for this purpose has demonstrated that a liquid poly‑aluminum chloride (PAC) could be synthesized from the aluminum ion/Al 3+ removed from the ash and the original brine. With this work, we synthesized the liquid PAC by a hydrothermal method, and the results from infrared spectrometer demonstrated that the synthesized PAC was similar to a commercial PAC. Moreover, the synthesized PAC was able to efficiently reduce the effluent turbidity of wastewater treatment plants (WWTPs), especially when compared with the commercial PAC. It is therefore important that research in this area be continued in order to improve the quality of synthesized coagulants and to produce different coagulants based on cations and anions in ash and brine., 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 B.V. All rights reserved.)

Alginate like extracellular polymers (ALE) recovered from flocculent sludge has been identified as a kind of highly valuable biomaterials. However, the extraction protocols limit the production of biopolymers as ALE extracted from flocculent sludge is at a lower level, around 90-190 mg/g VSS. Under this circumstance, the eco-friendly and effective optimizations for the ALE extraction protocols are expected, and thus surfactants have gained an attention to enhancing the ALE extraction. With this study, different surfactants with different structures and chemical characteristics, such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and octyl phenyl polyoxyethylene ether (Triton X-100), were experimented to improve the ALE extraction, and in turn the optimal conditions and the associated mechanisms were evaluated and figured out. The experimental results indicated that surfactants could enhance the ALE extraction but also improve the alginate purification of ALE. With the optimal dosage of surfactants, the ALE extraction increased from 124.1 mg/g VSS to about 222.8-281.9 mg/g VSS, and the alginate purify was at around 54%-70%, in which the efficiency of the ALE extraction was improved by 79.5%-127.2%. Among others, Triton X-100 had the best performance on improving the ALE extraction, followed by CTAB and SDS. The mechanisms of surfactants on enhancing the ALE extraction and improving the alginate purify can be attributed to: i) surfactants micelles, which can solubilize flocs and extracellular biopolymers; ii) similar structures of surfactants and ALE, which follows the rule of "like dissolves like"; iii) functional groups adsorption, which facilitates the ALE release from matrixes. In a word, the optimized extraction protocol by using surfactants can be effectively applied to extract ALE from flocculent sludge., 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 B.V. All rights reserved.)

As a product of phosphorous recovery from anaerobic digestion (AD) of waste activated sludge (WAS), vivianite has received increasing attention. However, key factors controlling vivianite formation have not yet been fully addressed. Thus, this study was initiated to ascertain key factors controlling vivianite formation. A simulation of chemical equilibriums indicates that interfering ions such as metallic ions and inorganic compounds may affect vivianite formation, especially at a PO 4 3- concentration lower than 3 mM. The experiments demonstrated that the rate of ferric bio-reduction conducted by dissimilatory metal-reducing bacteria (DMRB) and the competition of methane-producing bacteria (MPB) with DMRB for VFAs (acetate) were not the key factors controlling vivianite formation, and that ferric bio-reduction of DMRB can proceed when a sufficient amount of Fe 3+ exists in WAS. The determined affinity constants (K s ) of both DMRB and MPB on acetate revealed that the K HAc constant (4.2 mmol/g VSS) of DMRB was almost 4 times lower than that of MPB (15.67 mmol/g VSS) and thus MPB could not seriously compete for VFAs (acetate) with DMRB. As a result, vivianite formation was controlled mainly by the amount of Fe 3+ in WAS. In practice, a Fe/P molar ratio of 2:1 should be enough for vivianite formation in AD of WAS. Otherwise, exogenously dosing Fe 3+ or Fe 2+ into AD must be applied in AD., 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. Published by Elsevier Ltd.)

Entropy is a concept defined by the second law of thermodynamics. Applying this concept to the world we live in, entropy production must be minimized and negentropy (negative entropy production) should be accelerated, in order to produce a healthy and stable ecological system. The present wastewater treatment, however, contributes to entropy production. This means that conventional wastewater treatment, without recovery of resource and energy, will gradually but inevitably contribute to a deteriorating ecological balance. When the self-cleaning ability of the natural ecological system is limited, the need to develop sustainable wastewater treatment in order to delay entropy production and accelerate negentropy becomes urgent. Resource and energy recovery from wastewater should be the first priority, as they can contribute significantly towards minimizing entropy production and accelerating negentropy. Sustainable wastewater treatment must focus on recovering recyclable high value-added organic chemicals from wastewater and/or excess sludge to minimize entropy production caused by methane (CH 4 , once combusted, is converted into CO 2 - an even higher substance in entropy) via anaerobic digestion. Instead of CH 4 , thermal energy present in the effluent can be utilized for heating/cooling buildings and also for drying excess sludge towards incineration to recover more energy. Overall, this can lead to a carbon-neutral operation and even creating a "carbon sink" could be possible for wastewater treatment., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The recovery of polymeric substances from excess sludge is gaining significant research interest in future wastewater treatment technologies. We present a surfactant-enhanced ultrasonic method to extract mixed polymeric substances with typical functional groups from excess sludge. Four potential reasons were revealed for the higher efficiency upon ultrasonication with surfactant: low surface tension, damage of non-covalent bonds between extracellular polymeric substances and cells, enhanced dissolution of polymeric substances, and release of intracellular polymeric substances caused by cell lysis. The increase in extraction efficiency after the addition of cetyltrimethylammonium bromide and sodium dodecyl sulfate reached the maximum of 76.5% and 53.1%, respectively. The contents of polysaccharides, proteins, and DNA were approximately 50% of the total polymeric substances, and the content of protein was higher than that of polysaccharide; the concentration change of the surfactant had a minimal effect on these contents. For the polymeric substances extracted via ultrasonication with surfactant, the size was smaller than that for the non-surfactant extraction; moreover, the contents of metals decreased significantly (Al: 0.18% → 0%; Na: 0.15% → 0%; Ca: 0.24% → 0.11%), which was probably caused by the interaction between the surfactant and metal ions in the excess sludge. The surfactant had a negligible effect on the properties of polymeric substances, adsorption capacity of polymeric substances for heavy metal ions, and dewatering performance of sludge. The recycled polymeric substances may be used as a substitute for commercial adsorbents of heavy metal ions. Thus, the obtained results provide further insight into the recovery of polymeric substances from excess sludge via the surfactant-enhanced ultrasonic method., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Extracellular polymeric substances (EPS) are biopolymers that can be recovered from excess sludge, which could contribute to a more sustainable wastewater treatment plant (WWTP) operation. An example is alginate like extracellular polymers (ALE) contained in the biopolymers could be a potential resource with a highly-added value. EPS extraction for ALE from aerobic granules sludge (AGS) has already been well studied and applied in the Netherlands. On the other hand, there is little attention to the recovery of biopolymers from conventional activated sludge (CAS). In this study, flocculent sludge from eight CAS-WWTPs in China was collected and their EPS/biopolymers were extracted to investigate their recovery potential, chemical & physical properties and limiting factors. The results revealed that the biopolymers extracted and purified from CAS ranged from 90 to 190 mg/g VSS. The compositional characteristics of the biopolymers were observed by FT-IR, 3D-EEM and UV-Visible spectra, demonstrating some differences in the composition and property of the biopolymers from the different WWTPs. The biopolymers had a similarity of about 60% to a commercial alginate with respect to chemical functional groups and the alginate equivalent was >400 mg/g biopolymers. Moreover, the biopolymers consisted of poly (guluronic acid) blocks (20%-30%) and poly (guluronic acid-mannuronic acid) blocks (8%-28%), and the ionic hydrogel formation tests indicated that condensed beads were immediately formed once the drops of the biopolymers came in contact with CaCl 2 solution. These results demonstrated that the biopolymers extracted had a relatively high gel-forming capacity and might also have a potential application as commercial biopolymers. Furthermore, the factors influencing the biopolymers' formation such as influent substrate, nutrient content and microbial community and the related mechanisms were investigated. Among them, increasing soluble organics (SCOD) content and low nutrient content (C/N/P) in the influent could promote the biopolymers' formation. Also, different bacteria in BNR processes might have positive or negative effects on the biopolymers' formation. In conclusion, the diversity and abundance of bacteria were identified to be a crucial and decisive factor controlling biopolymers' extraction and composition., (Copyright © 2021. Published by Elsevier Ltd.)

Anaerobic digestion (AD) is an effective approach to recovering chemical (organic) energy from excess sludge, but the conversion efficiency for energy is usually not very high. One of the obstacles comes from the severe inhibition of humic acid (HA) on both hydrolytic and methanogenic process on the AD. Therefore, it is necessary to ascertain some effective approaches to relieving the inhibition of HA for obtaining a high methane (CH 4 ) yield. With the "clean" sludge (cultured by synthetic wastewater) containing almost no HA and metal ions, the inhibition of HA on the AD process was designed by dosing HA at 15% VSS, and relieving the inhibition by metal ions was also designed by dosing the different amounts of Ca 2+ and Al 3+ . Based on the batch AD experiments, solo Ca 2+ =100 mg /L or Al 3+ =70 mg/L added realized the highest relieved efficiency of 65%, respectively. Interestingly, dual metal ions added at the low concentrations (Ca 2+ =50 mg/L and Al 3+ =10 mg/L) could reach up to 80 % of the relieved efficiency, which was attributed to the synergistic effect of 1+1>2. The mechanisms behind the phenomena could be that metal ions might interact with HA via electrostatic force, cation exchange and sweep flocculation. Thus, some key hydrolytic and methanogenic enzymes could indirectly be reactivated and degradation of organic substances could be enhanced in the AD process. In wastewater treatment plants, metal ions contained in excess sludge would "inherently" relieve the inhibition of HA to an extent, which depends on the effective and/or optimal concentration of metal ions at a free (unabsorbed and/or unwrapped) state., 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 © 2020 Elsevier Ltd. All rights reserved.)

Handling excess sludge produced by wastewater treatment is a common problem worldwide. Due to limited space available in landfills, as well as difficulties involved in using excess sludge in agriculture, there is a need for alternative disposal methods. Although anaerobic digestion (AD) is widely used in processing sludge, only partial energy recovery from methane and sludge volume reduction can be achieved, resulting in a substantial amount of sludge remaining, which needs to be disposed of. Direct incineration after sludge drying is one possible option, a practice that is already in place in some cities in China. A comparison between direct incineration and conventional AD (with or without pretreatment by thermal hydrolysis) has to be made with respect to the energy balance and investment & operational (I & O) costs. This comparison reveals direct incineration to have the lowest energy deficit and I & O costs. Therefore, it is expected that direct incineration without AD will become the preferred sustainable approach to handling sludge., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Anaerobic digestion (AD) is a technology for recovering chemical energy as methane from excess sludge/waste. Unfortunately, humic acids (HA) contained in excess sludge can have the effects of inhibiting the efficiency of energy conversion. Based on a batch experiment, the impact of HA on a semi-continuous AD process was sequentially investigated, with the impact on the associated enzymes and microorganisms being measured. The results of this semi-continuous experiment indicate that the inhibition of the microbial community increased with an increased HA:VSS ratio. Long-term cultivation did not result in the adaption of methane production to the presence of HA. Moreover, at HA:VSS = 20%, the strongest inhibition (74.3%) on energy conversion efficiency was observed in the semi-continuous experiment, which was two-fold higher than that recorded in the batch experiment. This is attributed to serious and irreversible inhibition of both acidogenic and methanogenic microorganisms, as well as the physical-chemical reactions between HA and the associated enzymes which, it was concluded, were the dominant mechanisms of inhibition in the batch experiment., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Sulfite has been widely employed as a key agent in many industrial processes, leading to a large amount of sulfite-laden wastes generated. Given its antimicrobial function and destructive ability on cell walls, detailed mechanisms for impacts of sulfite on waste activated sludge (WAS) and outcomes of methane production after the sulfite-pretreatment have not been clear so far. In this study, the feasibility of methane production from sulfite pretreated WAS was verified and investigated. Biochemical methane potential tests demonstrated that methane production from WAS after the pretreatment at 800 mg S/L of sulfite (a typical level in sulfite-laden wastes) increased by up to 25%. Kinetic analysis of the test results indicated that sulfite pretreatment increased the sludge hydrolysis rate (k hyd ) by 1.71 times while the ultimate biochemical methane potential (B u ) by 1.20 times. Further study investigated the effects of sulfite on WAS from the macro-scale (i.e. sludge physicochemical properties) to the micro-scale (i.e. bacterial viability, microbial community). Sulfite concentrations of up to 800 mg S/L substantially enhanced WAS disintegration and solubilization, reducing the particle size by up to 39%, boosting substrate release by 87% and improving cell lysis by 43% through the direct destruction of gram-positive microorganisms (e.g., norank_p_Saccharibacteria) in WAS. Adverse impact on anaerobic digestion by introduction of sulfite was not observed in this study, though a long-term evaluation is needed in the future work. Based on the findings of the present study, sulfite-laden by-products or wastes from industrial processes may be co-treated with WAS when overall cost-effectiveness is concerned., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Anaerobic digestion (AD) is a sustainable pathway towards recovering chemical energy from excess sludge, and humic substances (HSs) contained in sludge can inhibit energy (methane/CH 4 ) conversion efficiency. This study aims to investigate the impact of humic acids (HA) on the various processes in a batch anaerobic digestion process. For this purpose, "clean" sludge was cultivated in a laboratory to avoid HSs presence. The cultivated sludge was used in a series of batch experiments, with humic acids added at different levels. A complete AD test, as well as three sub-phase tests (hydrolytic phase; acidogenic phase; methanogenic phase) was performed and analyzed with and without HA dosing. In the single-phase AD system, dosing with HA inhibited the methanogenic efficiency by 35.1% at HA:VSS = 15%. However, the effects of HA on the three sub-phases revealed something very different. HA inhibited hydrolytic efficiency by 38.2%, promoted acidogenic efficiency by 101.5%, and finally inhibited methanogenic efficiency by 52.2%. The combined efficiency of the three sub-phases without HA dosing is calculated at 15.7%; and with HA dosing (HA:VSS = 15%) at 10.2%. Overall, the combined inhibition efficiency of the three sub-phases is equal to 35.0%, which is almost identical (35.1%) to the result observed in the single-phase AD process. The possible mechanisms behind the phenomena were analyzed and summarized in the context., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In biological wastewater treatment, the bacteria starvation always challenges the stability of system operation. Yet, the effects of starvation and possibility of reactivation are less understood for anaerobic sulfidogenic system. Sulfidogenic systems use sulfate as electron acceptor for organic chemical oxygen demand (COD) degradation, so it will encounter two kind of starvations: (i) complete stoppage of wastewater flow (named complete food starvation) and (ii) remaining organic COD but with very low level sulfate in the influent (named sulfate starvation). In this study, the relative long-term starvation (over 30-day) and subsequent reactivation were studied in two lab-scale continuous gas recirculation sulfate-reducing upflow sludge bed (CGR-SRUSB) reactors. It was observed that the complete food starvation and sulfate starvation decreased the COD removal rate (in the similar range of 60-65%) and the specific sulfidogenic activity (about 45% and 61% respectively), as well as increasing the sludge flotation potential (SFP) from <15% to 58% and 35% respectively. Moreover, the following restoration experiments proved that the perturbed systems could be reactivated within 10-15 days for both cases. The results of investigating the mechanisms showed the performance deterioration were highly attributed to the starvation-induced granular sludge transitions, with respect to the changing of sludge physico-chemical properties (permeability, porosity, hydrophobicity and viscocity) and microbial stuctures (sulfate-reducting bacteria and extracellular polymeric substances). The outcomes of this study can provide useful information for dealing with the prolonged starvation problems in sulfidogenesis-based systems in industrial and municipal wastewater treatment., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

To Explore a suitable C/N ratio for efficient nitrogen removal and simultaneously achieving N 2 O release reduction, ammonia-rich wastewater with sodium acetate as an organic carbon source in a granular sludge completely autotrophic nitrogen removal over nitrite (CANON) reactor under different C/N water conditions were studied to determine the reactor's nitrogen removal performance and N 2 O release. The results showed that the total nitrogen (TN) removal rate and the removal load tended to increase gradually with the increase of C/N, ranging from 0 to 2.0. When C/N=0, the TN removal rate was 56.50 mg·L -1 in 7 h; the highest TN removal efficiency was 49%. When C/N=2.0, the highest TN removal rate was 71.42 mg·L -1 in 7 h; the highest TN removal efficiency was 59.52%, and the contribution of CANON to nitrogen removal gradually decreased, whereas the denitrification contribution gradually increased. When △NO 3 - -N/△TN=0.086, the contribution of CANON nitrogen removal was only 51.48% and that of denitrification was 48.52%. The N 2 O release volume and release ratio decreased with increasing C/N. When C/N=0, the N 2 O release volume and rate were the highest, namely 3.60 mg and 2.13%, respectively. The lowest N 2 O release volume and rate were 1.61 mg and 0.75%, respectively, when C/N=2.0.

Carbon-neutral operation of wastewater treatment plants (WWTPs) requires enhancing anaerobic digestion (AD) of excess sludge for a higher energy conversion efficiency. Among others, iron has been identified to function on enhancing methane production in AD. As an industrial residual, waste iron scraps (WISs) have been reported as potentially enhancing CH 4 production in AD. With this study, the mechanisms of AD enhanced by WISs are analysed in a two-phase process: acidogenic phase (AP) and methanogenic phase (MP). Semi-continuous tests substantially excluded ORP reduction and hydrogen-evolution corrosion induced by WISs in enhancing CH 4 production, although WISs (10 g Fe/L) could indeed increase CH 4 production by 10.1% and 21.4% when added in AP and MP respectively. Detection on both FISH and enzymatic activities of involved microorganisms revealed that the stimulating effects of WISs on anaerobes (both catabolism and anabolism) could play an important (96.3%) role in enhancing CH 4 production, which would facilitate hydrolysis of refractory organics and improvement of electron transport rate (ETR)., (Copyright © 2017 Elsevier Ltd. All rights reserved.)