Sludge Disintegration Research Articles

Multifaceted roles of methylisothiazolinone intervention in sludge disintegration and acidogenic and methanogenic pathways for efficient carboxylate production during anaerobic fermentation

Anaerobic fermentation is a promising approach for sludge treatment, although it is frequently hindered by the tight structure of extracellular polymeric substances (EPS) and limited metabolic activities. This work firstly discovered that methylisothiazolinone (MIT, a commonly used antimicrobial agent in water treatment) effectively disintegrated the sludge structure and stimulated metabolic pathways, leading to efficient volatile fatty acids (VFAs) production. The presence of MIT (ranging from 10 to 40 mg/g TSS) contributed to the acidogenic process but strongly restrained the methanogenesis, and the distinct interfering effect is highly associated with the MIT dose. The VFAs accumulation reached a maximum of 1776.7 mg COD/L (5.2 times of control) but faced a complete inhibition of methanogenic activity at 40 mg/g TSS. Spectroscopic and molecular docking analysis revealed that MIT interacted with and disrupted the EPS (mainly proteins) structure by forming hydrogen bonds with N-H groups. This disruption facilitated the release of biodegradable organics, which served as fermentation substrates. Furthermore, the MIT-mediated improvement selectively enriched the hydrolytic-acidifying bacteria (i.e., Clostridium and Caloramator) and stimulated the associated metabolic functions, particularly in the uptake, hydrolysis, and metabolism of amino acids considering the high expressions of encoding genes (e.g., oppA, pepP, gdhA). However, methanogens' reproductive and metabolic abilities were suppressed due to their inefficient response and adaptation to MIT. This suppression was evident through downregulated genetic expressions involved in DNA replication and aminoacyl-tRNA synthesis. Consequently, a decline in methanogens abundance (e.g., Methanothrix, and Methanosarcina) and methanogenic activity occurred, impeding the consumption of VFAs. This work provided an innovative niche to promote resource recovery in the sludge anaerobic system and deciphered the underlying mechanisms at both biochemical interactive steps and microbial genetic traits.

Effect of pH on sodium citrate pretreatment to promote volatile fatty acids production during anaerobic fermentation of waste activated sludge

The efficiency of sodium citrate (SC) pretreatment in enhancing volatile fatty acids (VFAs) generation from waste activated sludge (WAS) has been demonstrated, yet the yield remains limited. Therefore, this study investigated the influence of pH regulation on the efficiency of SC pretreatment by combining different initial acid-base conditions with SC. The results indicated that the acidic environment coupled with SC led to a tighter extracellular polymeric substances (EPS) structure and hindered the organic matter solubilization or VFAs production. Conversely, the alkaline environment combined with SC demonstrated a positive synergistic effect on sludge hydrolysis and VFAs production, with the synergy becoming more pronounced as alkalinity increases. When the initial pH was 11, the sludge disintegration degree (DDSCOD) and DNA solubilization were 1.67 and 3.76 times higher than those of SC alone, respectively. Moreover, the maximum VFAs production of 759.75 mg COD/g VSS (volatile suspended solids) was achieved at day 4 of fermentation. Microbial analysis showed that acidic conditions combined with SC favored hydrogen-producing bacteria (Clostridium_sensu_stricto) enrichment, while alkaline conditions combined with SC promoted the substantial enrichment of hydrolytic acid-producing bacteria with higher tolerance and adaptability (Macellibacteroides, Proteiniclasticum, and Acetoanaerobium). This may be the fundamental reason for the improvement of VFAs production.

A novel membrane bioreactor inoculated with algal-bacterial granular sludge for sewage reuse and membrane fouling mitigation: Performance and mechanism

In this study, a novel membrane bioreactor (MBR) inoculated with algal-bacterial granular sludge (ABGMBR) was established to improve pollutant removal and alleviate membrane fouling. The ABGMBR system showed higher pollutant removal rate and longer operation time (152 day) compared to the control MBR (AGMBR). Moreover, the contents of the pollutants such as granular sludges, extracellular polymeric substances (EPS), and soluble microbial products on the membrane were remarkably reduced, leading to the formation of a porous and loose cake layer on the membrane and a slow increase in transmembrane pressure. Standard blocking was the main mechanism of membrane fouling; however, the membrane pore blockage was significantly reduced in ABGMBR. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory suggested that the aggregation and adhesion of foulants on the membrane were greatly inhibited in ABGMBR. Furthermore, correlation analysis showed significant differences in membrane fouling characteristics between AGMBR and ABGMBR. The ABGMBR system effectively retarded sludge disintegration and increased the repulsion between the sludge and membrane owing to the favorable mixed liquor characteristics. This study showcases the superior operational efficiency and anti-fouling performance of ABGMBR, offering a novel perspective on sewage reuse and membrane fouling mitigation.

An efficient strategy for improving short-chain fatty acid production from sludge anaerobic fermentation with calcium carbide residue addition

Calcium carbide residue (CCR), a industrial by-product generated by acetylene production, was introduced into sludge anaerobic fermentation as an alternative approach for improving short-chain fatty acid (SCFA) production. The maximum SCFA production increased by 13.52 times as the amount of added CCR increased from 0 to 0.16 g/g suspended solids (SS) and then decreased upon further increasing the CCR dosage. CCR accelerated sludge disintegration and hydrolysis to provide substantial organic material for SCFA generation. The activities of key acid-forming enzymes were simultaneously increased. Although the addition of CCR reduced the diversity of the microbial community, the methanogens were inhibited, whereas the bacteria responsible for hydrolysis and acidification (e.g., Bacilli, phylum Firmicutes) was enriched. However, the dewaterability of fermented sludge was dependent on the dosage of CCR, which deteriorated when CCR dosage exceeded 0.08 g/g SS. This study provides a robust method of treating waste by waste for enhancing SCFA production from anaerobic fermentation of waste activated sludge.

Study on anaerobic fermentation of waste activated sludge to produce volatile fatty acids by thermal–rhamnolipid treatment

AbstractBACKGROUNDThe extracellular polymer and cell wall of waste activated sludge serve as chemical barriers for anaerobic fermentation, limiting the recycling and utilization of organic carbon contained in the sludge. To improve the efficiency of anaerobic fermentation, this paper proposes thermal–rhamnolipid (T‐RL) pretreatment technology and systematically discusses the effect of T‐RL treatment on the anaerobic fermentation of waste activated sludge for acid production from the perspective of organic matter dissolution characteristics, total volatile fatty acid (VFA) content, composition and microbial changes.RESULTST‐RL treatment significantly promoted the dissolution of organic matter in sludge, with soluble chemical oxygen demand solubilizing to 6097.78–7375.56 mg L−1, soluble carbohydrates solubilizing to 207.38–274.74 mg L−1, and the dissolution of soluble proteins and DNA also at a high level. Both treatment factors significantly promoted the enrichment of acid‐producing microorganisms, especially acetic acid‐producing microorganisms. The best VFA production conditions of T‐RL treatment were 60 mg g−1 total solids and 70 °C, and the yield was 3294.96 mg L−1. Compared with thermal and RL treatments, the optimum yield of T‐RL treatment increased by 33.16% and 22.06%, respectively. The VFA components in the T‐RL group were mainly acetic acid and propionic acid. Under optimal conditions, the proportion of acetic acid and propionic acid reached 77%.CONCLUSIONT‐RL treatment can promote sludge disintegration and organic matter conversion through the coupling effect of thermal and RL treatments, providing sufficient and high‐quality substrate for acid‐producing microorganisms, effectively enriching VFA producers, and thus improving the efficiency of anaerobic fermentation for VFA production. This treatment technology will provide some beneficial references for the future utilization of sludge resources. © 2023 Society of Chemical Industry (SCI).

A comparative study of hydrogen peroxide oxidation and electrocoagulation using aluminum, iron, and zinc electrodes for urban sludge disintegration

ABSTRACT Municipal and industrial wastewater treatment plants produce large amounts of sludge containing high levels of organic, chemical, and microbial pollutants. Unless stabilized completely and discharged safely, they may become potential pollution sources threatening soil and water bodies. This study investigated H2O2 oxidation and electrocoagulation as pretreatments to improve stabilization of an urban sludge. The H2O2 oxidation was optimized with respect to H2O2 dosage and initial sludge pH-H2O2. Batch electrocoagulation experiments were conducted using aluminum, iron, and zinc electrodes to investigate the effect of treatment period, current density, and pH. The effectiveness was compared in terms of solubilization of sludge, disintegration degree, and reduction of total solids. Sludge settling velocity after disintegration by both H2O2 oxidation and electrocoagulation were measured with respect to the operating conditions. The obtained results indicated that the high rate of sludge disintegration (63.3%) was obtained with aluminum electrodes, which has lower operating costs than iron and zinc electrodes. The H2O2 oxidation reached a maximum disintegration degree of 50%. Additionally, with aluminum and iron electrodes, sludge settleability was enhanced with both H2O2 oxidation and electrocoagulation.

Development of a Primary Sewage Sludge Pretreatment Strategy Using a Combined Alkaline–Ultrasound Pretreatment for Enhancing Microbial Electrolysis Cell Performance

Ultrasound and combined alkaline–ultrasound pretreatment (AUP) strategies were examined for primary sewage sludge (SS) disintegration and were utilized to evaluate the degree of solubilization (DS). Further, the pretreated primary SS was operated in microbial electrolysis cells (MECs) to maximize methane production and thereby improve the reactor performance. The highest DS of 67.2% of primary SS was recorded with the AUP. MEC reactors operated with the AUP showed the highest methane production (240 ± 6.4 mL g VSin−1). VS (61.1%) and COD (72.2%) removal in the MEC ALK-US showed the best organic matter removal efficiency. In the modified Gompertz analysis, the substrate with the highest degree of solubilization (AUP) had the shortest lag phase (0.2 ± 0.1 d). This implies that forced hydrolysis via pretreatment could enhance biodegradability, thereby making it easy for microorganisms to consume and leading to improved MEC performances. Microbial analysis implicitly demonstrated that pretreatment expedited the growth of hydrolytic bacteria (Bacteroidetes and Firmicutes), and a syntrophic interaction with electroactive microorganisms (Smithella) and hydrogenotrophic methanogens (Methanoculleus) was enriched in the MECs with AUP sludge. This suggests that the AUP strategy could be useful to enhance anaerobic digestion performance and provide a new perspective on treating primary SS in an economical way.

Feasibility of membrane distillation brine assistant anaerobic fermentation for enhancing carbon migration and recovery from excess sludge: Two wastes into one resource

The carbon recovery from excess sludge has received rising attentions. This study developed an innovative membrane distillation (MD) brine assistant anaerobic fermentation. The Na+, instead of other ions in MD brine, disrupted O-H stretching and N-H/C-N stretches of amide I in proteins for loosening protein structure and reducing hydrophilic functional groups, which triggered considerable sludge disintegration and microbial cell lysis with plicated floc surface structure and organic fragment stripping. Thereby, the carbon sources of 785.90 mg/L were released, among which the tyrosine-like protein and soluble microbial by-products were identified as the crucial dissolved organic matters relating to enhancing anaerobic fermentation. As such, the volatile fatty acids (VFAs) production was improved to 1689.65 mg COD/L (55.93 mg C/g VSS) through 4-day MD brine assistant anaerobic fermentation, which was mainly composed by acetic and propionic acids (58.96–84.16%), while the acetoxylation was also facilitated by MD brine. Correspondingly, the carbon source biodegradation towards micromolecule shift was promoted, considerable carbon release and recovery rates of 18.27% and 13.31% were achievable, respectively. The VFAs and proteins were dominant soluble carbon sources, while the pretty high C/N of 10.4 was achieved in fermentation liquid, demonstrating the bio-availability of recovered carbon sources. The economic and carbon-emission reduction benefits of 167.94–412.26 CNY and 0.0726 ton CO2 were obtained by carbon recovery from each ton excess sludge solid.

Insights into biodegradation behaviors of methanolic wastewater in up-flow anaerobic sludge bed (UASB) reactor coupled with in-situ bioelectrocatalysis

Granular sludge disintegration and washing out pose a challenge to up-flow anaerobic sludge bed (UASB) reactor treating methanolic wastewater. Herein, in-situ bioelectrocatalysis (BE) was integrated into UASB (BE-UASB) reactor to alter microbial metabolic behaviors and enhance the re-granulation process. BE-UASB reactor exhibited the highest methane (CH4) production rate of 388.0 mL/Lreactor/d and chemical oxygen demand (COD) removal of 89.6 % at 0.8 V. Sludge re-granulation was strengthened with particle size over 300 µm of up to 22.4%. Bioelectrocatalysis stimulated extracellular polymeric substances (EPS) secretion and formation of granules with rigid [-EPS-cell-EPS-] matrix by enhancing the proliferation of key functional microorganisms (Acetobacterium, Methanobacterium, and Methanomethylovorans) and diversifying metabolic pathways. Particularly, a high Methanobacterium richness (10.8%) drove the electroreduction of CO2 into CH4 and reduced its emissions (52.8%). This study provides a novel bioelectrocatalytic strategy for controlling granular sludge disintegration, which will facilitate the practical application of UASB in methanolic wastewater treatment.

Optimizing waste activated sludge disintegration by investigating multiple electrochemical pretreatment conditions: Performance, mechanism and modeling

The complex and rigid floc structure often limits the reutilization of waste activated sludge (WAS). Electrochemical pretreatment (EPT) is one of the most effective technologies that can enhance WAS disintegration. But a comprehensive investigation into how multiple EPT conditions work was rarely reported. The study evaluated the effects of multiple EPT conditions, i.e., different electrolytes (NaCl, Na2SO4, and CaCl2), electrolytes dosage (0 g/L, 0.5 g/L, 1.0 g/L, and 3.0 g/L), EPT current (0 A, 0.5 A, 1.0 A, and 3.0 A) and EPT time (0 min, 30 min, 60 min, and 90 min) on WAS disintegration. The results showed that NaCl was outstanding from other electrolytes in promoting more WAS disintegration. Besides, a relatively higher NaCl dosage, a higher EPT current, and a longer EPT time promoted more reactive chlorine species (RCS), thus enhancing WAS disintegration in terms of extracellular polymeric substances (EPS) structure destruction and biodegradable organic matter release. After EPT for 60 min at NaCl dosage of 1.0 g/L and current of 1.0 A, the EPS multilayer structure destruction, biodegradable organic matters release, and soluble chemical oxygen demand (SCOD) increase in the supernatant were enhanced by 17.2 %, 130.5 %, and 238.7 %, respectively. Then a predictive quadratic model was established and the impact significance of the above EPT factors for enhancing WAS disintegration followed dosage of NaCl > current > EPT time. Furthermore, response surface methodology (RSM) suggested NaCl dosage of 2.75 g/L, current of 2.0 A, and EPT time of 30 min were the optimal EPT conditions, bringing a 42.0 % increase in the net economic benefit of WAS treatment compared to without EPT.

Characteristics of Solidified Carbon Dioxide and Perspectives for Its Sustainable Application in Sewage Sludge Management.

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO2 for dewatering, sanitization, and digestion improvement. Solidified CO2 is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO2 is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO2 in the pretreatment and management of sewage sludge. Using solidified CO2 for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO2 can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO2 cycle of biogas production-biogas upgrading-solidified CO2 production-sludge disintegration-digestion-biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO2 emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO2 generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process.

Enhanced Sewage Sludge Disintegration and Nutrients Release by Catalytic Microbubbles Ozonation Using Sewage Sludge-Based Char as Catalyst

Using microbubble ozonation (MO) technique to disintegrate sludge is a promising sludge treatment process. To enhance the lysis and reduction of sludge, the catalytic ozonation consisting of MO and sewage sludge derived char (SC) were combined. Total solids (TS), volatile solids (VS), total nitrogen and phosphate (TN and TP) were selected as main parameters for evaluating the treatment performance both in solids and supernatant. With the utilization of the catalytic MO, the ozone utilization and sludge reduction were largely improved. At a reaction time of 90 min, an ozone utilization efficiency exceeding 99% was achieved by using a MO system. The optical ozone and sludge char dosages of 150 mg/g suspended solids (SS) and 1 g/L were found for sludge lysis, respectively. TS and VS concentrations decreased by 43% and 56%, respectively, as compared to those of 16.7% and 17.9% obtained by the treatment with MO alone under the condition of sludge solution pH 4. The supernatant soluble chemical oxygen demand (SCOD), TN, TP, NH4+-N and NO3−-N increased by 1750%, 205%, 25%, 31% and 43%, respectively. A small amount of additional SC exhibited strong catalytic activity on dissolving organic matter of the sludge, demonstrating the positive effect caused by the heterogeneous catalytic ozonation on sludge disintegration.

Investigation of sludge disintegration using vortex cavitation circulating fluidised grinding technology

Waste-activated sludge (WAS) is regarded as a source of hazardous waste pollution from sewage treatment plants. To efficiently deal with WAS, vortex cavitation circulating fluidised grinding technology (VCCFGT) was proposed as a novel circulating fluidisation technology (CFT) to disintegrate WAS. To be specific, we investigated the effects of disintegration duration, pressure, and filling ratio of mill balls on sludge disintegration. The results of chemical and physical evaluation showed that the values of soluble chemical oxygen demand (SCOD), disintegration degree (DDSCOD), DNA, protein, carbohydrate, and NH4+-N increased with the increase in the filling ratio of the mill balls. Under a pressure and filling ratio of 0.30 MPa and 1.6%, respectively, the maximum effect was achieved after 60 min of treatment. Compared to those in the treatment without mill balls, the values of SCOD, DDSCOD, DNA, protein, carbohydrate, and NH4+-N in the treatment using mill balls increased by 218, 229, 230, 177, 371, and 190%, respectively. As a result of this technology, the temperature of the sludge dramatically increased, rising approximately 42.9 °C. Compared to that of the raw sludge, the sludge particle size after treatment was reduced by 83.25% at most, and the morphology of the sludge comprised smaller flocs. Compared to that of the ball-milling method, the mill balls filling ratio of VCCFGT reduced by 93.60–98.12%. Compared to that of sludge disintegration by the vortex cavitation method, VCCFGT indicating good disintegration degree (increased by 229%) and economic feasibility. VCCFGT has good application prospects for sludge disintegration. The main mechanisms of sludge disintegration and organic release include centrifugal force, grinding, shear force, cavitation, and cyclic fatigue effects, among which grinding plays a leading role. This study concluded that CFT can effectively disintegrate sludge flocs and disrupt bacterial cell walls.

Divalent cation chelation enhancing carbon migration and recovery from anaerobic fermentation of waste activated sludge

Recently, the short-chain fatty acids (SCFAs) production with carbon recovery from waste activated sludge has received increasing attention. Despite that numerous approaches have been investigated, the divalent cation chelation towards enhancing anaerobic fermentation and the carbon migration fates has been rarely reported. This work attempted to chelate structural divalent cations from sludge flocs by sodium pyrophosphate (SP) at the dosages of 0–0.6 g/g SS, facilitating sludge disintegration and hydrolysis with particulate organic matters solubilization. At the optimal SP dosage of 0.4 g/g SS, the chemical oxygen demand (COD) and carbon source content in sludge solid were reduced by 45.24 % and 35.50 % within 1-day treatment, leading to considerable sludge hydrolysis and carbon release performances with soluble COD/total COD of 23.21 % and carbon release rate of 26.94 % in 2-day anaerobic fermentation, respectively. Numerous SCFAs of 237.43 mg COD/g VSS were produced by 4-day anaerobic fermentation, with the overall carbon recovery rate of 21.19 %, which were dominantly composed by acetate and propionate. Meanwhile, the SP-inhibited biogas generation also contributed to SCFAs accumulation. The divalent cation chelation obviously improved rate constant and equilibrium performances of anaerobic fermentation process, which were 1.81–5.21 and 1.36–2.82 times higher than those without SP, respectively. The carbon migration pattern was proposed by interphase carbon source balance and the mechanism was also illustrated. The crucial novelty was to propose an innovative and economic sludge hydrolysis pattern by divalent cation chelation towards improving carbon recovery.

Ultrasonic pretreatment for Enhancing Sludge disintegration and Resource Utilization: A mini review

As a byproduct of sewage treatment plants, sludge presents dual characteristics of “resource” and “pollution”. While it enriches nutrients from wastewater, it also contains a portion of toxic substances. Moreover, when the organic matter content of sludge is low, it affects the efficiency of resource utilization and energy recovery (sludge digestion efficiency, energy consumption of incineration systems). Developing new physicochemical-biological combined pretreatment to enhance the dissolution of organic matter in sludge (sludge disintegration) and reduce the solid content of sludge is a crucial step to improve sludge dewaterability and digestibility. Ultrasonic, as a novel sludge pretreatment technology, gains the advantages of being environmentally sustainable, efficient, and easily operable. It can disrupt sludge flocs, alter microbial activity, release intracellular organic matter, and be used in combination with other pretreatment processes. This article summarizes the mechanism of ultrasonic pretreatment of sludge and its research progress in improving sludge dewaterability and digestibility, providing a new perspective for the application of ultrasound in sludge resource utilization.

Long-term effect of copper and tetracycline on the performance and sludge characteristics of anoxic-aerobic sequencing batch reactor with integrated sludge disintegration

Long-term effect of copper and tetracycline on the performance and sludge characteristics of anoxic-aerobic sequencing batch reactor with integrated sludge disintegration

Characteristics of phosphorus release from sludge with sludge disintegration

Characteristics of phosphorus release from sludge with sludge disintegration

Experimental study on the redistribution law of heavy metals in sludge disintegration

Aiming at the problems of large output of excess sludge, difficulty in treatment and disposal, and the potential toxicity of heavy metals restricting its resource utilization, this paper studies the redistribution law of heavy metals in the process of sludge disintegration. The dissertation investigates the distribution law of typical heavy metals such as Cu, Pb, Cd, Zn in the process of microwave and citric acid-microwave cracking sludge under different specific energy and fixed specific energy conditions. The Tessier five-step continuous extraction method was used to extract heavy metals, and the changes in their content and chemical forms were analyzed, which provided certain technical support for the subsequent harmless treatment and resource utilization of excess sludge. The main findings of this paper are as follows: The dissolution rate of heavy metals Cu, Pb, Cd, and Zn increased rapidly during the citric acid-microwave cracking process in the TS specific energy range of 0–45000 kJ/kg, and then gradually tended to be gradual. The maximum dissolution rates of Cu, Pb, Cd, Zn were 8.06%, 16.58%, 14.69%, and 24.11%, respectively. The concentrations of Cu, Pb, Cd, and Zn in the sludge were mainly F4; F3, F4; F2, F3. The proportions of stable states of Cu, Pb, Cd, and Zn in sludge increased to 88.6%, 55.91%, 35.7%, and 31.35%, respectively. When the specific energy was 45000 kJ/kg TS, the concentrations of Pb, Zn, and Cd in the solid phase of the sludge appeared to increase under microwave cracking alone and decrease under the combined action of citric acid and microwave. The concentration of Cu in the solid phase of the sludge increased slightly. The dissolution rates of Pb, Cd, and Zn by microwave alone and citric acid-microwave method were 14.23% and 16.58%, 10.34% and 14.69%, 17.53%, and 24.11%, respectively. The dissolution rates of Cu by both methods were lower. The steady state ratios of Pb and Zn in the citric acid-microwave method increased to 55.91% and 31.25%, respectively; the steady state ratio of Cd in the microwave alone method increased to 39.51%; both methods had no significant effect on the stability of Cu.

Calcium hypochlorite-coupled aged refuse promotes hydrogen production from sludge anaerobic fermentation

This work investigated the effect of calcium hypochlorite (CH) coupled aged refuse (AR) treatment on the enhanced hydrogen generation from sludge anaerobic dark fermentation (SADF). The enhanced mechanism was systematically revealed through sludge disintegration, organic matter biotransformation, and microbial community characteristics, etc. The experimental data showed that CH coupled AR increased the hydrogen yield to 18.1 mL/g, significantly higher than that in the AR or CH group alone. Mechanistic analysis showed that CH-coupled AR significantly promoted sludge disintegration and hydrolysis processes, providing sufficient material for hydrogen-producing bacteria. Microbiological analysis showed that CH-coupled AR increased the relative abundance of responsible hydrogen-producing microorganisms. In addition, CH-coupled AR was very effective in reducing phosphate content in the fermentation liquid and fecal coliforms in the digestate, thus facilitating the subsequent treatment of fermentation broth and digestate. CH coupled AR is an alternative strategy to increase hydrogen production from sludge.

Performance and mechanism of sodium citrate pretreatment to promote waste activated sludge disintegration and short-chain fatty acid production during anaerobic fermentation

Waste activated sludge (WAS) contains massive organic matter that can be used for resource recovery. Anaerobic fermentation to produce short-chain fatty acids (SCFAs) is recognized as an expedient and efficient measure to recycle sludge resource. Complexing agents have been reported to be effective in disintegrating extracellular polymeric substances (EPS) and increasing the rate of sludge hydrolysis. This study investigated the performance and mechanism of sodium citrate (SC) pretreatment to promote the disintegration of WAS and the production of SCFAs by anaerobic fermentation. The results showed that when SC dosage was 0.25 g/g TSS, both EPS and cell membrane were destroyed. Among them, the soluble protein and polysaccharide in the supernatant reached 1 072 ± 15 mg COD/L and 233 mg COD/L, and DNA reached 175 ± 3 mg/L at the fifth hour. Damage of EPS is mainly reflected in S-EPS and LB-EPS, while it is not obvious in TB-EPS. The SC pretreated group was much higher in SCFAs production, and the SC dosing of 0.25 g/g TSS group reached the peak acid production of 7 677 ± 350 mg COD/L on the third day, which was 8.3 times higher than that of the control group. Moreover, SC was able to increase the hydrolytic enzyme activity and inhibit the coenzyme F420 activity, which increased the production of SCFAs and decreased its consumption rate.