Sludge Stabilization Research Articles

High-Rate Nitrite Production by Stable Denitrification Granular Sludge in a Reinforced-Mixing Up-Flow System: Shift in Spatiotemporal Characteristics of Functional Bacteria and Metagenomic Mechanisms

High-Rate Nitrite Production by Stable Denitrification Granular Sludge in a Reinforced-Mixing Up-Flow System: Shift in Spatiotemporal Characteristics of Functional Bacteria and Metagenomic Mechanisms

Enhancing Sewage Sludge Stabilization, Pathogen Removal, and Biomass Production through Indigenous Microalgae Promoting Growth: A Sustainable Approach for Sewage Sludge Treatment

Sewage sludge (SS), a byproduct of wastewater treatment plants, poses significant environmental and health risks if not properly handled. Conventional approaches for SS stabilization often involve costly and energy-consuming processes. This study investigated the effect of promoting native microalgae growth in SS on its stabilization, pathogen bacteria removal, and valuable biomass production. The effect on settleability, filterability, and extracellular polymeric substances (EPSs) was examined as well. Experiments were conducted in photobioreactors (PBRs) without O2 supply and CO2 release under controlled parameters. The results show a significant improvement in SS stabilization, with a reduction of volatile solids (VSs) by 47.55%. Additionally, fecal coliforms and E. coli were efficiently removed by 2.25 log and 6.72 log, respectively. Moreover, Salmonella spp. was not detected after 15 days of treatment. The settleability was improved by 71.42%. However, a worsening of the sludge filterability properties was observed, likely due to a decrease in floc size following the reduction of protein content in the tightly bound EPS fraction. Microalgae biomass production was 16.56 mg/L/day, with a mean biomass of 0.35 g/L at the end of the batch treatment, representing 10.35% of the total final biomass. These findings suggest that promoting native microalgal growth in SS could be sustainable and cost-effective for SS stabilization, microalgal biomass production, and the enhancement of sludge-settling characteristics, notwithstanding potential filtration-related considerations.

Feasibility study of electrodialysis as an ammonium reuse process for covering the nitrogen demand of an industrial wastewater treatment plant

Electrodialysis (ED) is a cost-effective membrane technology used is a variety of fields for desalination and concentration. This feasibility study explores the potential of ED as an NH4-N recovery technology from anaerobic digestate liquor (ADL), and the use of the concentrate as a nitrogen source in an industrial wastewater treatment plant (WWTP). Three neighboring WWTPs were the focus of this study: Two municipal WWTPs A and B, operating anaerobic sludge stabilization, and a pulp & paper WWTP C, utilizing urea as a nitrogen source. Two-stage bench-scale experiments with the municipal ADL from WWTP A and WWTP B were conducted, and performance indicators were determined. A concentration of approximately 10 g NH4-N/L and 15 g NH4-N/L was obtained in stages 1 and 2, respectively. The NH4-N removal was above 85 % in all experiment, while recovery varied between 25 and 95 %. The specific energy consumption (SEC) was on average 12.9 kWh/kg NH4-N. Moreover, mass and energy balances in a model WWTP demonstrated that an ED side-stream treatment for NH4-N removal coupled with microfiltration (MF) pre-treatment results in a net energy gain, also without the added benefit of the ED concentrate as a nitrogen source.

Revealing the interplay of dissolved organic matters variation with microbial symbiotic network in lime-treated sludge landscaping

Lime pretreatment is commonly used for sludge hygienization. Appropriate lime dosage is crucial for achieving both sludge stabilization (lime dosage >0.2 g/g-TS) and promoting plant and soil health during subsequent landscaping (lime dosage <0.8 g/g-TS). While much research has been conducted on sludge lime treatment, few studies have examined the effects of lime dosing on integrating sludge stabilization and plant growth promotion during landscaping. In this study, we investigated microbial dynamics and dissolved organic matter (DOM) transformation during sludge landscaping with five lime dosage gradients (0, 0.2, 0.4, 0.6, 0.8 g lime/g-TS) over 90 days. Our results showed that a lime dosage of 0.4 g/g-TS is the lower threshold for achieving waste activated sludge (WAS) stabilization during landscaping, leading to maximum humic substance formation and minimal phytotoxicity. Specifically, at 0.4 g/g-TS lime dosage, protein degradation and decarboxylation-induced humification were significantly enhanced. The predominant microbial genera shifted from Aromatoleum to Exiguobacterium and Romboutsia (both affiliated with the phylum Firmicutes). Reactomics analysis further indicated that a 0.4 g/g-TS lime dosage promoted the hydrolysis of proteins (lyase reactions on C-C, C-O, and C-N bonds), amino acid metabolism, and decarboxylation-induced humification (e.g., C1H2O2, C2H4O2, C5H4O2, C6H4O2). The co-occurrence network analysis suggested that the phyla Firmicutes, Proteobacteria, and Bacteroidetes were key players in DOM transformation. This study provides an in-depth understanding of microbe-mediated DOM transformation during sludge landscaping and identifies the optimal lime dosage for improving sludge landscaping efficiency.

Stabilization of Sewage Sludge from North Moroccan Wastewater Treatment Plants Using Convective Indirect Solar Drying

Stabilization of Sewage Sludge from North Moroccan Wastewater Treatment Plants Using Convective Indirect Solar Drying

Synchronous reinforcement azo dyes decolorization and anaerobic granular sludge stability by Fe, N co-modified biochar: enhancement based on extracellular electron transfer

Anaerobic digestion (AD) treatment of azo dyes wastewater often suffers from low decolorization efficiency and poor stability of anaerobic granular sludge (AnGS). In this study, iron and nitrogen co-modified biochar (FNC) was synthesized based on the secondary calcination method, and the feasibility of this material for enhanced AD treatment of azo dye wastewater and its mechanism were investigated. FNC not only formed richer conducting functional groups, but also generated Fe2+/Fe3+ redox pairs. The decolorization efficiency of Congo red and AD properties (e.g., methane production) were enhanced by FNC. After adding FNC, the content of extracellular polymeric substances (EPS) and the ratio of proteins remained stable under the impact of Congo red, which greatly protected the internal microbial community. This was mainly contributed to the excellent electrochemical properties of FNC, which strengthened the microbial extracellular electron transfer and realized the coupled mechanism of action: On the one hand, an electron transfer bridge between decolorizing bacteria and dyes was constructed to achieve rapid decolorization of azo dyes and mitigate the impact on methanogenic bacteria; On the other hand, the stability of AnGS was enhanced based on enhanced extracellular polymeric substances secretion, microbial community and direct interspecies electron transfer (DIET) process. This study provides a new idea for enhanced AD treatment of azo dyes wastewater.

Enhanced aerobic granular sludge by thermally-treated dredged sediment in wastewater treatment under low superficial gas velocity

The positive contributions of carriers to aerobic granulation have been wildly appreciated. In this study, as a way resource utilization, the dredged sediment was thermally-treated to prepared as carriers to promote aerobic granular sludge (AGS) formation and stability. The system was started under low superficial gas velocity (SGV, 0.6 cm/s)for a lower energy consumption. Two sequencing batch reactors (SBR) labeled R1 (no added carriers) and R2 (carriers added), were used in the experiment. R2 had excellent performance of granulation time (shortened nearly 43%). The maximum mean particle size at the maturity stage of AGS in R2 (0.545 mm) was larger compared to R1 (0.296 mm). The sludge settling performance in R2 was better. The reactors exhibited high chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal rates. The total phosphorus (TP) removal rate in R2 was higher than R1 (almost 15% higher) on stage II (93-175d). R2 had a higher microbial abundance and dominant bacteria content. The relative abundance of dominant species was mainly affected by the carrier. However, the enrichment of dominant microorganisms and the evolution of subdominant species were more influenced by the increase of SGV. The results indicated that the addition of carriers induced the secretion of extracellular polymeric substances (EPS) by microorganisms and accelerated the rapid formation of initial microbial aggregates. This work provided a low-cost method and condition to enhance aerobic granulation, which may be helpful in optimizing wastewater treatment processes.

Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances

Microplastics (MPs) and nanoplastics (NPs) present in wastewater can pose a negative impact to aerobic granular sludge (AGS). Herein, this study found that MPs and NPs (20 mg/L) deteriorated the sludge settleability and granule integrity, resulting in a 15.7 % and 21.9 % decrease in the total nitrogen removal efficiency of the AGS system, respectively. This was possibly due to the reduction of the extracellular polymeric substances (EPS) content. The subsequent analysis revealed that tyrosine, tryptophan, and humic acid-like substances in EPS exhibited a higher propensity for chemisorption and inhomogeneous multilayer adsorption onto NPs compared to MPs. The binding of EPS onto the surface of plastic particles increased the electronegativity of the MPs, but facilitated the aggregation of NPs through reducing the electrostatic repulsion, thereby mitigating the adverse effects of MPs/NPs on the AGS stability. Additionally, comprehensive analysis of the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the suppressed aggregation of microorganisms was the internal mechanisms contributing to the inadequate stability of AGS induced by MPs/NPs. This study provides novel insights into the detrimental mechanisms of MPs/NPs on the AGS stability, highlighting the key role of EPS in maintaining the structural stability of AGS when exposed to MPs/NPs.

Sulfur-driven microbial fuel cells denitrification system for targeted treatment of nitrate-containing groundwater: Performance and mechanism

Sulfur (S0)-driven autotrophic denitrification system has obvious advantages in economy and performance in treating the low carbon/nitrogen groundwater. However, the by-products produced from S0 oxidation will cause disturbance to the water quality. In this study, a dual-chamber microbial fuel cell was driven by S0 (S0-MFC) to separate the S0 and nitrate, the electrons generated by the oxidation of S0 in the anodic chamber transferred to the cathode for nitrate reduction. Under the action of the anode microorganisms, the S0 was directly oxidized to sulfate. The maximum nitrate removal rate (NRR) in the cathodic chamber was 2.31 ± 0.03 mg N/L/h, and the anode electron utilization rate could reached to 19.69 %. Electrochemical results showed that flavin and c-type cytochrome could acted as electron mediators promote the electron transfer processes. The presence of loop current contributed to the enhancement of microbial metabolic activity, thus improving the stability of sludge and NRR. The denitrifiers (Thiobacillus and Denitratisoma) and sulfur autotrophs (Desulfocapsa and Acidithiobacillus) played an important role in the high NRR. A low-cost and pollution-free method for removing nitrate from groundwater was realized in this study.

Changes in the operation of the aerobic stabilisation chamber to increase the reliability of Nutrient pollution removal in a multi-phase biological reactor

The objective of the study was to optimise the operation of the aerobic stabilisation chamber so as to increase the efficiency of elimination of nitrogen and phosphorus compounds at the collective wastewater treatment plant in Dąbrowa Tarnowska. To demonstrate positive optimisation measures, the study was carried out in two periods, pre-modernisation and post-modernisation. The first part of the study took place from January 2016 to May 2020, with the latter from June 2020 to December 2023. The reliability of biogenic compounds removal in the treatment process was carried out using the Weibull method. The modernisation of the operation of the aerobic sludge stabilisation chamber resulted in the stabilisation and increased efficiency of the nitrification and denitrification processes in this treatment plant. The reliability of removal of nitrogen compounds in the post-modernisation period was 79 % compared to the pre-change period, which was 47 %. In the case of phosphorus compounds, no significant changes were found in the concentration in the treated effluent in either of the analysed periods.

Microbial Selection for the Densification of Activated Sludge Treating Variable and High-Strength Industrial Wastewater

This study investigates the densification/granulation of activated sludge with poor settleability, treating real industrial wastewater from a tank truck cleaning company. The wastewater is low in nutrients, acidic in nature, and high and variable in chemical oxygen demand (COD, ranging from 2770 mg·L−1 to 14,050 mg·L−1). A microbial selection strategy was applied to promote slow-growing glycogen-accumulating microorganisms (GAO) by the implementation of an anaerobic feast/aerobic famine strategy in a sequencing batch reactor (SBR). After 60 to 70 days, the uptake of carbon during the anaerobic phase exceeded 80%, the sludge morphology improved, and the sludge volume index (SVI) dropped below 50 mL·g−1. 16S rRNA gene sequencing showed the enrichment of the GAOs Defluviicoccus and Candidatus Competibacter. Stable sludge densification was maintained when using a constant organic loading rate (OLR) of 0.85 ± 0.05 gCOD·(L·d)−1, but the sludge quality deteriorated when switching to a variable OLR. In view of the integration of densified/granular sludge in a membrane bioreactor configuration, the filtration properties of the densified SBR sludge were compared to the seed sludge from the full-scale plant. The densified sludge showed a significantly lower resistance due to pore blockage and a significantly higher sustainable flux (45 vs. 15 L·(m2·h)−1).

Synergetic effect of biochar and intermittent electricity stimulation on mitigating the adverse effects of tannic acid on anaerobic granular sludge in wastewater

Tannic acid (TA), a common industrial contaminant in sectors such as papermaking and leather production, affects the anaerobic treatment of wastewater by forming complexes with proteins in sludge granules, thereby inhibiting microbial efficiency and promoting sludge deflocculation. Although techniques such as intermittent electricity can promote microbial growth, they do not effectively resolve sludge deflocculation. Additionally, although biochar (BC) enhances the abundance of microbes, it does not significantly improve microbial activity or treatment performance. This study aimed to alleviate the adverse effects of TA on anaerobic granular sludge (AnGS) by synergistically applying intermittent electrical stimulation and BC. Co-treatment with 1 h-on/off intermittent electricity and 3 g/L BC notably reduced granular sludge deflocculation. Consequently, the chemical oxygen demand (COD) removal efficiency in wastewater reached 91.73 %, with a maximum methane production per cycle of 230.59 mL/g COD, 16.95 % higher than that of the control reactor (197.17 mL/g COD). This improvement was attributed to the synergistic action of intermittent electricity and BC, which enriched the functional microorganisms and stimulated their activity, thereby facilitating direct interspecies electron transfer. Additionally, enhancing the polysaccharide and protein levels in extracellular polymeric substances improved the stability of granular sludge, ultimately mitigating the adverse effects of TA on AnGS.

Valorization of Fecal Sludge Stabilization via Vermicomposting in Microcosm-Enriched Substrates Using Organic Plant-Derived Materials and Agricultural Soil for Compost Production

The enormous generation of fecal sludge without proper treatment is a major sanitation problem. Vermicomposting of fecal sludge is an innovative way of producing value added compost called vermicompost. A vermicomposting technique that involves augmenting vermibed substrates with organic rich materials to provide additional nutrients and underlying layers needed for microcosm development to produce desirable vermicompost is mostly referred to as substrate enrichment. This study investigated the substrate enrichment of using plant-derived materials, which include coconut coir, palm coir and saw dust, combined with agricultural soil for the production of vermicompost from fecal sludge. Enriched substrates were prepared with 80 g of agricultural soil as amending material, 120 g of fecal matter (65-70% dry matter) and 160 g of the plant-derived materials. The treatments were labeled T1-T3, thus, T1 contained coconut coir, T2 contained palm coir and T3 contained saw dust, followed by a control treatment (T4) that had no plant-derived material. Treatments were triplicated and about 3-week-old 20 clitellated, E. fetida (live weight ∼255–275 mg) were used in the vermicomposting for 12 wk. Physicochemical parameters such as pH, Organic Carbon (Corg), Total Nitrogen (Ntot), Available Phosphorus (Pavail), Exchangeable Calcium (Caexch), Iron (Fe), Lead (Pb) and Aluminum (Al) test were performed. Vermicompost at T1 had the most Corg mineralization, most enhancement in Ntot, Pavail, Caexch, and least concentration of Fe, Pb and Al. Less than 20% earthworm mortality was recorded in all treatments except T4 (28.38 ± 8.71%). The enriched substrates were suitable for vermiculture with a worm weight ranged from 593.77 to 569.39 ± 2.30 mg and the vermicompost recorded high nutrient contents. The nutritious nature and the reduced metal concentration of the produced vermicompost might be safe and productive for agricultural use. However, further studies on the effectiveness of the vermicompost on plants growth and yield needs to be investigated.

Treatment of high ammonia anaerobically digested molasses wastewater using aerobic granular sludge reactor

This study addressed the treatment of high ammonia, low biodegradable chemical oxygen demand (bCOD) anaerobically digested molasses wastewater, utilizing an aerobic granular sludge (AGS) reactor. The AGS achieved 99 % ammonia removal regardless of the bCOD supplementation. By adding low ammonia (<60 mg/L), high bCOD raw molasses wastewater (before anaerobic digestion) as a carbon source, enhanced nitrogen removal, increasing from 10 % to 97 %, and improved sludge settleability via bio-induced calcite precipitation were observed. Functional genes prediction suggested two potential denitrification pathways, including heterotrophic denitrification by Paracoccus and Thauera, and autotrophic denitrification, specifically sulfide-oxidizing autotrophic denitrification by Thiobacillus. An increase in the relative abundance of microorganisms involved in heterotrophic denitrification was observed with the addition of high bCOD raw molasses wastewater. Consequently, incorporating raw molasses wastewater into the AGS presents a sustainable approach to achieve mixotrophic denitrification, maintain stable granular sludge and ensure stable treatment performance when treating anaerobically digested molasses wastewater.

Calcium carbide residue-based material for the stabilization of dredged sludge and its use in road subgrade construction

Addressing the dual environmental challenges of dredged sludge disposal and the repurposing of industrial by-products, this study pioneers the application of Calcium Carbide Residue (CCR)-based materials for stabilizing dredged sludge in road subgrade construction. The proliferation of dredged sludge, characterized by high moisture content and pollutants, presents a significant environmental hazard, while CCR, a by-product of acetylene production, poses disposal and pollution challenges. This research endeavors to mitigate these issues by exploring the stabilization potential of CCR when mixed with dredged sludge, aiming to enhance the mechanical properties of materials used in road subgrade construction. Through comprehensive laboratory testing, including unconfined compressive strength assessments, scanning electron microscope analyses, and X-ray diffraction examinations, the study reveals the intricate physicochemical interactions between CCR and sludge. These interactions lead to notable improvements in material strength and moisture reduction, substantiating the efficacy of CCR-based binders in sludge stabilization. The CCR-based binder can make the strength of the stabilized sludge reach 215.4kPa and the water content drop to 32 %. Field tests conducted to assess real-world applicability confirm the laboratory results, demonstrating the treated material's suitability for road construction as per secondary road design criteria and its environmental safety. The research highlights the environmental and engineering benefits of using CCR-based materials for sludge stabilization, offering a sustainable solution to the challenges of dredged sludge management and industrial waste utilization. The findings represent a step forward in waste-to-resource conversion, promoting environmental sustainability in civil engineering practices.

Impact of truncated modified basalt fibers on aerobic granular sludge stability and pollutant removal in piggery wastewater treatment

Modified basalt fibers (MBF) and carbon fibers (CF) are effective bio-carrier materials that enhance wastewater treatment performance. This study explored the use of two lengths of truncated MBF and CF (0.1 and 0.4 mm) in a sequencing batch reactor to support activated sludge treatment, facilitating the formation of aerobic granular sludge (AGS). This approach aimed to enhance the stability and pollutant removal efficiency of AGS, particularly for treating piggery wastewater (PWW). The study further assessed the impact of adding truncated fibers on AGS formation, stability, and its chemical oxygen demand (COD) and total nitrogen (TN) removal capabilities. Results indicate that truncated MBF notably enhanced sludge activity, promoting the secretion of extracellular polymeric substances (EPS) within AGS. This process further increased the protein/polysaccharide ratio and bolstered AGS stability. Specifically, the addition of 0.1 mm MBF boosted PWW treatment efficiency. Fluorescence in situ hybridization (FISH) revealed that the addition of fibers had a minimal impact on the distribution of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) within AGS, although truncated MBF enriched the population of AOB. Microbial community analysis showed that the addition of MBF favored the enrichment of bacteria associated with nitrogen removal, upregulating the tricarboxylic acid cycle, nitrogen and amino acid metabolism. Overall, truncated MBF significantly improved AGS stability and its effectiveness in PWW treatment.

Rapid formation mechanism of SAD granular sludge: From flocculated activated sludge to granular sludge

The SAD (Simultaneous Anammox and Denitrification) process combines anammox with denitrification to achieve nitrogen removal and carbon reduction. In this study, the flocculent activated sludge in the secondary sedimentation tank of the traditional sewage treatment plant was used as the research object. Under the action of high NH4+, adding reflux, and adjusting HRT in the UASB reactor, the transformation from flocculent sludge to SAD granular sludge was quickly realized. The results showed that a relatively stable SAD granular sludge system could be formed after 250 days of operation, and the system with reflux was more resistant to changes in the external environment than the system without reflux. In the SAD system, TN Removal Rate (TNRE) ≈ 90 %, Carbon Removal Rate (CRR) ≈ 90 %. After 3D-EEM, FTIR, and analysis of protein secondary structure, it was found that the particle stability and aggregation of the SAD stage were significantly improved compared with the previous two stages. The bacterial community structure had obvious vertical heterogeneity, mainly AnAOB (Ca. Kuenenia≈30 %) and denitrifying bacteria (Comamonas≈20 %). When the temperature drops sharply, the performance of SAD can be effectively restored by adding reflux and reducing the carbon source.

Ozonation for improved sludge reduction, cytotoxicity and estrogenicity control in anaerobic digestion

Anaerobic digestion (AD) is a common treatment for sludge reduction and stabilization. Simultaneously reductions in sludge chemical oxygen demand (COD), cytotoxicity, and estrogenicity are desired for safer handling and reuse. We investigated the impact, mechanism, and control strategy of ozonation (common sludge biodegradability method) on AD, methane production, and sludge cytotoxicity and estrogenicity modulations. Results revealed that ozone treatment could boost the methane production potential and rate by up to 36.5 and 69.2 %, respectively, but only after partial sludge digestion. Ozone modulated sludge cytotoxicity and estrogenicity, significantly improving this effect (maximum reductions of 28 and 23 %, respectively) by introducing anaerobically digested sludge to the ozonation module due to lowered volatile solids (VS) compared to raw sludge and less competition from the abundant biodegradable organics. Results support introducing ozone during AD for simultaneous COD reduction, and cytotoxicity and estrogenicity control.

Advances in aerobic granular sludge stabilization in wastewater

This study provides a comprehensive overview of the advancements made in the research concerning the stability of aerobic granular sludge, and succinctly outlines the development mechanisms of aerobic granular sludge, encompassing the "filamentous bacteria theory" and the "extracellular polymer theory", "selective pressure driven hypothesis", and "self coagulation hypothesis"; The primary elements influencing the stability of aerobic granular sludge include temperature, pH levels, the rate of organic loading, and concentrations of ammonia nitrogen, dissolved oxygen and particle size, satiety hunger period, hydraulic shear force, sludge age and toxic and harmful substances; It is discussed in detail that measures such as inhibiting filamentous bulking, promoting the secretion of extracellular polymers, enhancing the growth of slow-growing microorganisms and fortifying the central structure of granules can improve the stability of aerobic granular sludge. It is suggested that future studies should prioritize exploring the formation mechanisms and functional microbial communities associated with aerobic granular sludge. Such investigations will lay the groundwork for its broader industrial applications.

Stabilization of Arsenic Sulfide Sludge to Form Stable Johnbaumite by Alkaline-Oxidative Hydrothermal Treatment

Stabilization of Arsenic Sulfide Sludge to Form Stable Johnbaumite by Alkaline-Oxidative Hydrothermal Treatment