Sludge Solubilization Research Articles

Effect of varying hydrothermal temperature, time, and sludge pH on sludge solubilisation

In recent years, hydrothermal treatment has been considered as among the most promising option for sludge solubilisation and carbon recovery in terms of sludge management. In this study, the effect of different individual hydrothermal operating conditions like temperature (110–250 °C), sludge pH (6–13) and reaction time (0.5–3 h) were varied to understand their influence on sludge solubilisation. The most effective hydrothermal conditions (severity factor of 9.7) were found to be at 200 °C, sludge pH of 12 and reaction time of 1 h which solubilised about 1743 mg/g and 131 mg/g of COD and carbohydrates respectively into the aqueous phase. Also, gas chromatography- mass spectrometry (GC–MS) analysis was done that identified the organic compounds in the treated liquid phase to be mainly carboxylic acids, phenols, esters, and their derivatives. Although further studies are required to efficiently separate and recover the different organic compounds present, this work provides more insights for future valorisation of the organic rich hydrothermally treated liquid phase.

A novel strategy and mechanism for high-quality volatile fatty acids production from primary sludge: Peroxymonosulfate pretreatment combined with alkaline fermentation

To obtain high-quality VFAs production from primary sludge, a novel strategy that combined peroxymonosulfate (PMS) pretreatment and alkaline fermentation (i.e., PMS & pH9) was proposed in the study. The results showed that PMS & pH9 was efficient in sludge solubilization and hydrolysis, resulting in a maximal VFAs yield of 401.2 mg COD/g VSS, which was 7.3-, 2.1-, and 8.8-fold higher than the sole PMS, sole pH9, and control, respectively. Acetate comprised 87.6% of VFAs in this integration system. Mechanism investigations revealed that sulfate and free radicals produced by PMS play roles in improving VFAs yield under alkaline conditions. Besides, sulfate also aided in C3∼C5 VFAs converting to acetate under alkaline conditions depending on the increase of incomplete-oxidative sulfate-reducing bacteria (iso-SRB) (i.e., Desulfobulbus and Desulfobotulus). Moreover, the relative abundances of acid-forming characteristic genera (i.e., Proteiniborus, Proteinilcasticum, and Acetoanaerobium) were higher in PMS & pH9.

Insights into the role of chitosan in hydrogen production by dark fermentation of waste activated sludge

Chitosan is widely used as a dewatering flocculant, but whether it affects hydrogen production from sludge anaerobic fermentation is unclear. This study aimed to elucidate the role of chitosan in the dark fermentation of waste activated sludge for hydrogen production. The results showed that chitosan had a negative effect on hydrogen production from sludge. Chitosan at 30 g/kg total suspended solids reduced hydrogen accumulation by 56.70 ± 1.22 % from 3.94 ± 0.12 to 1.71 ± 0.10 mL/g volatile suspended solids. Chitosan hindered the solubilization of sludge by flocculation, which reduced the available substrate for anaerobic fermentation. In addition, chitosan interfered with the electron transport system by reducing cytochrome C and caused lipid peroxidation by inducing reactive oxygen species, thereby inhibiting the activity of enzymes involved in anaerobic fermentation. Hydrogen production was reduced because hydrogen-producing processes (i.e., hydrolysis, acidification, and acetification) were inhibited more strongly than hydrogen-consuming processes (i.e., methanogenesis, sulfate reduction, and homoacetogenesis). Furthermore, chitosan enriched the abundance of Spirochaetaceae sp. and Holophagaceae sp., which occupied the survival space of hydrogen-producing microorganisms. This study reveals the potential impact of chitosan on hydrogen production in dark fermentation of sludge and provide direct evidence that chitosan triggers oxidative stress in anaerobic fermentation.

Differential impact of acidic and alkaline conditions on hydrothermal pretreatment, fermentation and anaerobic digestion of sludge.

Anaerobic digestion and fermentation processes in wastewater sludge treatment are limited by several factors, including the slow breakdown of complex organic matter and solubilization of solids. In this study, thermochemical pretreatment of thickened waste activated sludge using high temperature (>170 °C) was investigated to understand the impact of the pretreatment on the volatile fatty acids (VFA) production and its fractions during the fermentation process. Furthermore, the influence the thermochemical pretreatment on sludge disintegration and methane recovery was investigated. A range of acidic and alkaline conditions over the pH range of 4.5-10 was examined. Sludge (pH adjusted) was exposed to hydrothermal pretreatment (HTP) at a temperature of 170 °C for 30 min. Pretreated samples were then subjected to batch fermentation and methane potential tests which revealed that acidic and alkaline conditions resulted in increased sludge solubilization during HTP. Acidic conditions were associated with a higher VFA production yield of up to 185 mg chemical oxygen demand/g total chemical oxygen demand. Alkaline conditions led to a higher methane production yield where the maximum yield (276 mL CH4/g total chemical oxygen demandadded) was found to occur at pH 10. Therefore, alkaline sludge used for fermentation has shown technical and economic feasibility for sludge carbon recovery.

Calcium peroxide and freezing co-pretreatment enhancing short-chain fatty acids production from waste activated sludge towards carbon–neutral sludge treatment

Short-chain fatty acids (SCFAs) recovery through anaerobic fermentation is a promising technology to achieve carbon–neutral in waste activated sludge (WAS) management. After 0.15 g CaO2/g volatile suspended solids (VSS) addition and three-cycle freezing co-pretreatments, the maximal SCFAs production of 438.5 mg COD/g VSS was achieved within 4 days fermentation, and more than 70 % of SCFAs was composed of acetate and propionate, which achieved a higher level than reported in previous studies. Mechanism explorations elucidated that co-pretreatment triggered sludge solubilization, promoting the release of biodegradable organics, providing more biodegradable substrates for SCFAs generation. Further microbial community analysis indicated that the abundances of hydrolytic microorganisms and acidogens were enriched, whereas methanogens were inhibited. Besides, environmental analysis suggested that co-pretreatment could achieve carbon reduction benefits of 0.116–0.291 ton CO2/ton WAS, demonstrating its huge carbon–neutral potential benefits.

Synergic role of ferrate and nitrite for triggering waste activated sludge solubilisation and acidogenic fermentation: Effectiveness evaluation and mechanism elucidation

Enhancing anaerobic treatment efficiency of waste activated sludge (WAS) toward preferable resource recovery would be an important requirement for achieving carbon-emission reduction, biosolids minimization, stabilization and security concurrently. This study demonstrated the synergic effect of potassium ferrate (PF) and nitrite on prompting WAS solubilisation and acidogenic fermentation toward harvesting volatile fatty acids (VFAs). The results indicated the PF+NaNO2 co-pretreatment boosted 7.44 times and 1.32 times higher WAS solubilisation [peak soluble chemical oxygen demand (SCOD) of 2680 ± 52 mg/L] than that by the single nitrite- and PF-pretreatment, respectively, while about 2.77 times and 2.11 times higher VFAs production were achieved (maximum VFAs accumulation of 3536.25 ± 115.24 mg COD/L) as compared with the single pretreatment (nitrite and PF)-fermentations. Afterwards the WAS dewaterability was improved simultaneously after acidogenic fermentation. Moreover, a schematic diagram was established for illustrating mechanisms of the co-pretreatment of PF and nitrite for enhancing the VFAs generation via increasing key hydrolytic enzymes, metabolic functional genes expression, shifting microbial biotransformation pathways and elevating abundances of key microbes in acidogenic fermentation. Furthermore, the mechanistic investigations suggested that the PF addition was conducive to form a relatively conductive fermentation environment for enhancing electron transfer (ET) efficiency, which contributed to the VFAs biotransformation positively. This study provided an effective strategy for enhancing the biodegradation/bioconversion efficiency of WAS organic matters with potential profitable economic returns.

Synergistic effect of yeast integrated with alkyl polyglucose for short-chain fatty acids production from sludge anaerobic fermentation

An efficient strategy for short-chain fatty acid (SCFA) production from sludge anaerobic fermentation was proposed with the combination of yeast and alkyl polyglucose (APG). It revealed that the synergetic effect of yeast and APG could boost the SCFA concentration to the maximum value of 2800.34 mg COD/L within 9 days at 0.20 g/g suspended solids (SS) yeast and 0.20 g/g SS APG, which was significantly higher than that of its counterparts. Interestingly, the sludge solubilization, the biodegradability of fermentation substrate, as well as the acidification of hydrolyzed products, was evidently improved in the coexistence of APG and yeast. The activities of hydrolytic enzymes and acetate kinase were also stimulated, whereas the coenzyme F420 was inhibited. The synergetic effect of yeast and APG used in this work enriches the study of carbon resource recovery from sludge anaerobic fermentation.

New insights into microbial fuel cells for saline wastewater treatment: Bioelectrogenesis evaluation, microbial interactions and salinity resource reuse

This first-attempted study displayed the multi-skilling performance of microbial fuel cells (MFCs) for treating saline wastewater in terms of soluble organics biodegradation, bioelectricity conversion, redox-mediators obtainment and salinity reuse. Results indicated that a bioelectricity conversion efficiency of ca. 0.865–0.960 kWh/kg CODMn with over 90% organics removal in 10.0–20.0 g NaCl/L conditions could be realized. Meanwhile, the redox mediators-like substances could be enriched from saline wastewater via MFCs treatment, which exhibited relatively high redox properties as electron shuttles. Moreover, the dominant members of Bacteroides, Azospirillum, Dyella, Sphingomonas, Ignavibacteriales and Clostridium cooperated together for completing bioelectrogenesis effectively with high capabilities of salinity tolerance. Higher salinity (ca. 30.0–40.0 g NaCl/L) impaired key hydrolase activities, reduce microbial metabolic functions and weaken anodic microbial diversity, which negatively reduce MFCs’ running properties. Finally, the harvested salinity from saline wastewater through MFCs could be used effectively as a promising way of achieving waste sludge solubilization. This study could help to re-shape the thinking about future saline wastewater and excess sludge treatment/management toward resource recovery and cost minimization.

BOF slag as a new alkalizing agent for the stabilization of sewage sludge

This study assessed, for the first time ever, the use of basic oxygen furnace (BOF) slag as alkalinizing material during the sludge conditioning, as an environmentally-friendly alternative to CaO and other conventional alkalis. Its effects on the dewatering, solubilisation and stabilization of sewage sludge were studied, testing increasing dosages of BOF from 0 to 6 gBOF/gTSS0 at room temperature and under constant mechanical agitation was evaluated. Results revealed that the addition of BOF slag to sewage sludge produced similar degrees of solubilisation to those obtained using lime, reaching a maximum of 34% of total COD for 3.00 gBOF/gTSS0. The use of BOF slag also involved a low solubilisation of either nitrogen, carbon or phosphorous, a negligible mobilization of heavy metals and a positive effect on its biological hygienisation. A Class A biosolid for doses of 4.50gBOF/gTSS0 or higher was achieved, which can be applied directly to the soil for agricultural purposes in accordance with current legislation.

Ultrasound-sodium percarbonate effectively promotes short-chain carboxylic acids production from sewage sludge through anaerobic fermentation

Short-chain carboxylic acids (SCCAs) production from sewage sludge via anaerobic fermentation is usually restricted by low substrates availability and rapid products consumption. Therefore, the ultrasound (US)-sodium percarbonate (SPC) technique was proposed to effectively break the bottlenecks. Results showed the total SCCAs yield, acetate yield and particulate organics reduction respectively attained 392.8 mg COD/g VSS, 204.6 mg COD/g VSS and 47.4 % under the optimal condition. Mechanistic explorations disclosed that US + SPC largely reduced biodegradation resistances of particulate organics and improved sludge biodegradability. The destruction of spatial structure was the inherent mechanisms for initial solubilization and further degradation of solid-phase sludge. Besides, US + SCP up-regulated hydrolytic and SCCAs-forming enzymes, but downregulated the key enzyme for methanation. Meanwhile, US + SPC altered the microbial structure and stimulated functional microorganism enrichment, well correlated with substrate biotransformation and products output. Overall, this strategy could effectively enhance SCCAs production from WAS and reduce the environmental risk for subsequent sludge disposal.

Impact of divalent cations on lysozyme-induced solubilisation of waste-activated sludge: Perspectives of extracellular polymeric substances and surface electronegativity

Lysozyme hydrolysis can accelerate waste-activated sludge (WAS) solubilisation, which can significantly shorten the process and promote the efficiency of anaerobic digestion. This study investigated the impact of divalent cations on lysozyme-induced solubilisation of WAS. The performance of lysozyme pretreatment was dramatically inhibited by Mg2+ and Ca2+. Compared to the control group, the amount of net SCOD, protein, and polysaccharides released to the supernatant were reduced by 36.6%, 44.7%, and 35.8%, respectively, in the presence of divalent cations. The extracellular polymeric substance (EPS) matrix became tightly bound, resulting in fewer proteins and polysaccharides being extracted from loosely-bound EPS (LB-EPS) with divalent cations, which was detrimental to the solubilisation of WAS. Divalent cations decreased the surface electronegativity of sludge particles and prolonged the adsorption of lysozymes by sludge flocs. More than 16.6% of total lysozymes remained in the liquid phase of WAS after 240min Mg2+ and Ca2+ strengthened the binding among proteins and polysaccharides and promoted the intermolecular cross-linking of polysaccharides. The EPS matrix formed a dense spatial reticular structure that blocked the transfer of lysozymes from the EPS matrix to the pellet. As a result, the lysozymes accumulated in LB-EPS rather than hydrolysing the microorganism's cell wall. This study provides a new perspective on the restriction of WAS pretreatment with lysozymes and optimises the method of lysozyme-induced solubilisation of WAS.

Combining high pressure homogenization with free nitrous acid pretreatment to improve anaerobic digestion of sewage sludge.

Single pretreatment of sewage sludge, either physical, chemical or biological, has its own drawbacks in term of poor sanitization, energy intensity and high operational and capital cost. To tackle these drawbacks, combined high pressure homogenization (HPH) and free nitrous acid (FNA) pretreatment for sludge solubilization and further biodegradation in anaerobic digestion was investigated. Synergistic effect of combined HPH (40MPa) and FNA (2.49mg/L) pretreatment (HPH-FNA) for improving anaerobic digestion was evaluated, and its effect on archaeal and bacterial community structure was analyzed. Compared with single HPH and FNA pretreatments, HPH-FNA pretreatment efficiently solubilized wasted activated sludge (WAS), subsequently improved anaerobic digestion. Cumulative biogas production from sewage sludge pretreated with HPH-FNA was 154%, 108% and 284% more than that with single pretreatment of FNA, HPH and raw sludge, respectively. In addition, volumetric biogas production of combined pretreatment system (815ml) was more than the sum from single pretreatment (710ml). Methane content in biogas for raw sludge, FNA, HPH and HPH-FNA pretreated sludge was 45%, 51%, 55% and 65%, respectively. Illumina MiSeq sequencing analysis revealed that HPH-FNA pretreatment promoted bacterial growth of phyla Bacteroidetes, Firmicutes and Synergistetes and archaeal genera Methanospirillum and Methanosaeta. Overall, combined HPH-FNA pretreatment of sewage sludge, prior to anaerobic digestion, is an environmentally-friendly and potentially economic technology.

Elucidating the role of solids content in low-temperature thermal hydrolysis and anaerobic digestion of sewage sludge

The role of total solids content in low-temperature thermal hydrolysis and anaerobic digestion of sewage sludge was investigated. Increasing total solids from 2% to 6% improved thermal hydrolysis and anaerobic digestion performance, while increasing it further to 12% decreased methane production. Maximum sludge solubility (22.9% ± 0.6%) and methane production (320 ± 7 mL/g volatile solids) were achieved at 6% solids. The increase in solids content from 2% to 6% improved heating efficiency and volatile fraction content, which facilitated sludge solubilization and enrichment of methanogens. However, further increases in solids content resulted in a stable floc structure with excess ammonia nitrogen and volatile fatty acids, which limited the release of substrates and reduced the abundance of acidifying bacteria and methanogens, ultimately leading to reduced methane production. An in-depth understanding of the role of solids content opens up new avenues for improved low-temperature thermal hydrolysis of sludge.

Improved methane production from the two-phase anaerobic digestion and dewaterability of anaerobically digested sludge by β-cyclodextrin pretreatment

Cyclodextrin-based technologies have drawn worldwide attention for wastewater and sludge treatment due to its extraordinary solubilization of hydrophobic organics. β-cyclodextrin (β-CD) has been applied for enhancing sludge solubilization for production of volatile fatty acids. However, the impact of β-CD on methane production in the anaerobic digestion seemingly was unnoticed in the past, which was likely due to its inhibition effect on the methanogenesis in single-phase digestion system. Herein, a new pretreatment strategy using β-CD was firstly explored to enhance methane yield in two-phase anaerobic digestion of waste activated sludge (WAS) and simultaneously improve anaerobically digested sludge (ADS) dewaterability. Results illustrated that the total methane yield in the two phase increased from 101.43 to 277.67 mL/g VS with β-CD level raising from 0 to 0.3 g/g TS. A better ADS dewaterability was also obtained (24.14% capillary suction time increase). Mechanism investigations suggested that WAS solubilization and acidification were significantly enhanced in the first phase (i.e., acidogenic phase), with 8.97-fold soluble chemical oxygen demand (SCOD) and 17.37-fold short-chain fatty acids (SCFAs) increases. This implied that more available substrates after β-CD pretreatment could be used for methanogenesis. Further calculation indicated the utilization of β-CD was not the main reason for the enhanced methane. Model-based explorations revealed hydrolysis rate and methane potential were improved by 153.17% and 175.36% after β-CD pretreatment. The activities of enzymes associated with hydrolysis/acidification/methanogenesis in methanogenic phase were improved even if those were suppressed in acidogenic phase. Moreover, β-CD increased the abundance of key hydrolysis-acidification microbes and strengthened both the hydrogenotrophic and aceticlastic methanogenesis pathways. Finally, a “multifaceted benefits” operation concept based on β-CD treatment was proposed, providing an implication for wastewater treatment and sludge disposal.

Effect of ferrate pretreatment on anaerobic digestibility of primary sludge spiked with resin acids.

Resin acids are mixtures of high molecular weight carboxylic acids found in tree resins. Due to higher hydrophobicity and low solubility, they tend to adsorb on the suspended solids in pulp and paper (P&P) mill wastewater and accumulate in primary sludge through settling. Anaerobic digestion (AD) is a common practice stabilizing sludge; however, high concentration of resin acids affects the AD process. The aim of this research was mainly to determine the impact of ferrate (Fe (VI)) oxidation on selected resin acids and anaerobic digestibility of ferrate-treated primary sludge (PS) spiked with the resin acids. First, batch control oxidation of model resin acids with Fe (VI) was conducted to identify an optimum dosage, pH and contact time using a Box-Behnken design approach. Thereafter, anaerobic treatability studies of primary sludge spiked with resin acids both under control condition and optimum ferrate pretreatment were conducted. Up to 97% oxidation of resin acids occurred in pure water, while only 44%-62% oxidation of resin acids occurred in PS with an increasing Fe (VI) dosage from 0.034 to 0.137mg Fe (VI)/mg tCODfed. The pretreatment did not affect the anaerobic biodegradability of resin acids; however, it lowered their negative influences on the PS digestibility. About 0.076mg Fe (VI) dosage/mg tCODfed solubilized the sludge increasing the methane production by 40% compared to the untreated digester. The potential benefits of ferrate pretreatment of P&P primary sludge include resin acids oxidation and subsequent toxicity reduction, higher sludge solubilization enhancing methane production and enabling anaerobic digestion at higher COD loading.

Effects of hydrothermal treatment on organic compositions, structural properties, dewatering and biogas production of raw and digested sludge

The effects of hydrothermal treatment (HTT) under different temperatures and time (120 °C to 250 °C, 10 min to 60 min) on organic matter solubilization and structure changes of secondary sludge (SS) and digested sludge (DS), as well as downstream dewatering and anaerobic digestion were investigated. The results showed that organic matter solubilization increased significantly at 120 °C to 170 °C, then decreased at 200 °C to 250 °C. The organic matter solubilization during HTT showed no obvious difference for two sludge, but for the different organic components. The polysaccharides are easier to be dissolved than protein, which was manifested by the higher dissolution rate at low temperature. The protein was the main soluble component for both of hydrothermal SS and DS, which accounted for 44 % to 64 % of soluble chemical oxygen demand (SCOD). The decrease of residual extracellular polymeric substances (EPS) content and increase of N-acetylglucosamine and DNA concentrations indicated that sludge EPS and cell wall structure were damaged at 170 °C, which contributed to the high organic matter solubilization. Nitrogen balance and molecular weight distribution indicated the concentrations of soluble organic components were the combined result of dissolution and hydrolysis reaction. The hydrolysis and polymerization reaction were intensified at 170 °C to 250 °C, which was verified by the COD balance and molecular weight transformation. The hydrothermal time could further facilitate the organics dissolution and hydrolysis based on the effect of hydrothermal temperature. The EPS structure damage also contributed to the high percentage of free moisture, resulting in enhanced dewaterability. The highest methane production was 298.1 mL CH4/g VSadd for DS hydrothermally treated at 170 °C, which were 125 % and 9.8 % higher than SS and SS-HTT, respectively. This study provided an insight into the general mechanism of HTT and the application of different HTT and AD configurations.

Bioreactor-scale production of rhamnolipids from food waste digestate and its recirculation into anaerobic digestion for enhanced process performance: Creating closed-loop integrated biorefinery framework

Reaching industrially relevant productivities in bioprocesses and their efficient integration in the existing industrial infrastructure remain as important challenges in the circular economy to create closed loop sustainability framework. Using anaerobic digestion (AD) biorefinery as a model, the present work addressed these problems via integration of next-generation rhamnolipids production with AD. A high rhamnolipids concentration of 10.25 ± 1.34 g/L was obtained by fed-batch fermentation using food waste digestate as medium. Digestate-derived rhamnolipids contained Rha-C10-C10 and Rha-Rha-C10-C10 as the predominant congeners. These were used back in single-phase AD to demonstrate their effect on sludge solubilization and digestion efficiency. A dosage of 0.02 g rhamnolipids/g total suspended solids was found to be optimal which enhanced the hydrolysis-acidogenesis reactions to up to 27% over control. It however retarded methane production which could be overcome by the prolongation of digestion time. Finally, the value chain appreciation by the proposed process was demonstrated by a feasibility analysis.

The effects of sulfite pretreatment on the biodegradability and solubilization of primary sludge: Biochemical methane potential, kinetics, and potential implications

Sulfite is effective in the waste activated sludge (WAS) pretreatment for enhancing its solubilization, disintegration, and biodegradability. Given the various structures and constituents of the WAS and primary sludge (PS), how sulfite pretreatment affects the characteristics of the PS remains unclear. This study is the first to consider the application of the sulfite pretreatment to a full-scale-plant-derived PS treatment to reveal the changes in sludge properties. The methane production from the PS, pretreated with 500 mg SO32−-S/L of sulfite, was reduced by up to 37%. However, the solubilization of the PS was enhanced by the sulfite pretreatment, leading to substantial substrates being released from the PS, namely soluble polysaccharides, by 96%, and soluble proteins, by 304%. Sulfite directly reduced the concentration of the aromatic amino acid tryptophan in the PS, while the functional groups of key substances in the PS were destroyed by sulfite. Moreover, the dewaterability and degradation extents of the PS were enhanced following the sulfite pretreatment with a low capillary suction time and high solid reduction. The findings of this study suggest that the sulfite-based technology is viable for PS pretreatment prior to the dewatering and final disposal stages towards efficient post sludge treatment.

Antimicrobial PCMX facilitates the volatile fatty acids production during sludge anaerobic fermentation: Insights of the interactive principles, microbial metabolic profiles and adaptation mechanisms

Para-chloro-meta-xylenol (PCMX), as a massively used antimicrobial agent, exhibited dose-dependent effects on the sludge fermentation for volatile fatty acids (VFAs). The presence of PMCX at environmental levels (10–20 mg/g TSS) promoted the VFAs production by 2.5–3.0 folds but caused evident inhibition at high level (100 mg/g TSS). PCMX synchronously promoted the sludge solubilization, hydrolysis, and acidification but inhibited methanogenesis. Mechanistic investigations revealed that PCMX could interact with the extracellular polymeric substances (EPS) in sludge and cause the release of biodegradable substrates (especially proteins) by altering the WAS structures. Moreover, the functional fermentative bacteria (i.e., Firmicutes and Chloroflexi) were enriched while those VFAs consumers (i.e., Methanothrix and Methanomassiliicoccus) were reduced with low level of PCMX exposure. The microbial enzymatic activities (i.e., protease) and critical genes relevant to the substrates transport (i.e., gluC and lhpN) and metabolisms (especially the proteins, i.e., pckA), and VFAs biosynthesis (i.e., fabG) were all upregulated with the low PCMX stimulus. The microbial response and adaptation to PCMX toxicity were mainly attributed to the regulation of two-component and quorum sensing systems. Overall, PCMX contributed to the VFAs accumulation during sludge fermentation by mainly interacting and disrupting the sludge structures, and improving the microbial metabolic function traits. This work provided new insights into exogenous pollutants’ interactions, potential influences, and reaction mechanisms in the complicated sludge matrix.

Application of CaO2-enhanced peroxone process to adjust waste activated sludge characteristics for dewaterability amelioration: Molecular transformation of dissolved organic matters and realized mechanism of deep-dewatering

Sludge dewaterability is commonly poor due to the hydrophilic biopolymeric substances. The highly efficient oxidation process is of great significance for extracellular biopolymers disintegration and bound water discharge. This work investigated the novel CaO2-enhanced peroxone (CaO2/O3) process to adjust sludge characteristics for dewaterability enhancement and focused on the molecular composition and transformation of dissolved organic matters (DOM). CaO2/O3 (60/40 mg/gTS (total solid)) treatment showed more powerful sludge solubilization of 57.8% and cell death proportion of 46.1% over single CaO2 or O3 treatment. Hydrophilic extracellular polymeric substances, especially protein-like substances, were substantially degraded, and their conformation turned to be more hydrophobic, and carbohydrate-like, aminosugars-like, and lignins-like substances increased in CaO2/O3 process. Meanwhile, CaO2/O3 handling resulted in more decomposition of CHO-containing compounds than N-containing or S-containing compounds. Subsequently, 60 mg/gTS PFS (polyferric sulfate) reflocculation exerted a strengthened role in eliminating proteins & lipids-like, lignins-like, and unsaturated hydrocarbons-like substances, and especially S-containing compounds, which compensated for the unsatisfactory removal effects of these substances in the CaO2/O3 oxidation process. Therefore, the CaO2/O3-PFS treated sludge with less hydrated DOM easily harvested deep-dewatering in pressure filtration. Furthermore, it was noteworthy that the presence of CaO2 created an alkaline environment and served as the source of sustained-release H2O2, which accelerated O3 decomposition and greatly improved •OH generation. These findings provided molecular insight into a novel sludge conditioning approach for ideal dewaterability based on the CaO2-enhanced peroxone process in sludge treatment.