Calcium peroxide significantly enhances volatile solids destruction in aerobic sludge digestion through improving sludge biodegradability

Mechanism Involved in Polyvinyl Chloride Nanoplastics Induced Anaerobic Granular Sludge Disintegration: Microbial Interaction Energy, EPS Molecular Structure, and Metabolism Functions

Nanoplastics (NPs) are emerging pollutants and have been reported to cause the disintegration of anaerobic granular sludge (AnGS). However, the mechanism involved in AnGS disintegration was not clear. In this study, polyvinyl chloride nanoplastics (PVC-NPs) were chosen as target NPs and their long-term impact on AnGS structure was investigated. Results showed that increasing PVC-NPs concentration resulted in the inhibition of acetoclastic methanogens, syntrophic propionate, and butyrate degradation, as well as AnGS disintegration. At the presence of 50 μg·L-1 PVC-NPs, the hydrophobic interaction was weakened with a higher energy barrier due to the relatively higher hydrophilic functional groups in extracellular polymeric substances (EPS). PVC-NPs-induced ROS inhibited quorum sensing, significantly downregulated hydrophobic amino acid synthesis, whereas it highly upregulated the genes related to the synthesis of four hydrophilic amino acids (Cys, Glu, Gly, and Lys), resulting in a higher hydrophily degree of protein secondary structure in EPS. The differential expression of genes involved in EPS biosynthesis and the resulting protein secondary structure contributed to the greater hydrophilic interaction, reducing microbial aggregation ability. The findings provided new insight into the long-term impact of PVC-NPs on AnGS when treating wastewater containing NPs and filled the knowledge gap on the mechanism involved in AnGS disintegration by PVC-NPs.

A novel remediation strategy of mixed calcium peroxide and degrading bacteria for polycyclic aromatic hydrocarbon contaminated water

Polycyclic aromatic hydrocarbons (PAHs) are a class of toxic organic pollutants commonly detected in the aqueous phase. Traditional biodegradation is inefficient and advanced oxidation technologies are expensive. In the current study, a novel strategy was developed using calcium peroxide (CP) and PAH-degrading bacteria (PDB) to effectively augment PAH degradation by 28.62-59.22%. The PDB consisted of the genera Acinetobacter, Stenotrophomonas, and Comamonas. Applying the response surface model (RSM), the most appropriate parameters were identified, and the predictive degradation rates of phenanthrene (Phe), pyrene (Pyr), and ΣPAHs were 98%, 76%, and 84%, respectively. The constructed mixed system could reduce 90% of Phe and more than 60% of ΣPAHs and will perform better at pH 5-7 and lower salinity. Because PAHs tend to bind to dissolved organic matter (DOM) with larger molecular weights, humic acid (HA) had a larger negative effect on the PAH-degradation efficiency of the CP-PDB mixed system than fulvic acid (FA). The proposed PAH-degradation pathways in the mixed system were based on the detection of intermediates at different times. The investigation constructed and optimized a novel environmental PAH-degradation strategy. The synergistic application of PDB and oxidation was extended for organic contaminant degradation in aqueous environments.

Application of calcium peroxide in promoting resource recovery from municipal sludge: A review

The harmless disposal, resource recovery, and synergistic efficiency reduction of municipal sludge have been the research focuses for the last few years. Calcium peroxide (CaO2) is a multifunctional and safe peroxide that produces an alkaline oxidation environment to promote the fermentation of municipal sludge to produce hydrogen (H2) and volatile fatty acids (VFAs), thus realizing sludge resource recovery. This review outlines the research achievements of CaO2 in sludge resource recovery, improvement of sludge dewaterability, and removal of pollutants from sludge in recent years. Meanwhile, the mechanism of CaO2 and its influencing factors have also been comprehensively summarized. Finally, the future development direction of the application of CaO2 in municipal sludge is prospected. This review would provide theoretical reference for the potential engineering applications of CaO2 in improving sludge treatment in the future.

Synergistic promotion of sludge reduction by surfactant-producing and lysozyme-producing bacteria: Optimization and effect of Na. BIORESOURCE TECHNOLOGY 2024;393:130065. [PMID: 37984671 DOI: 10.1016/j.biortech.2023.130065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

To improve the efficiency of aerobic digestion, this investigation utilized the synergistic effect of lysozyme-producing strain YH14 and surfactant-producing strain ZXY4 to promote sludge hydrolysis, and added NaCl to enhance this promoting effect. The best performance in promoting sludge hydrolysis was achieved when the inoculum of functional bacteria was 12 % (inoculum ratio of strain YH14: strain ZXY4 = 1:3) and the dosage of NaCl was 5 g L-1, which caused an increase of 19.25 % in the SS removal rate and 2588.21 mg L-1 in the SCOD release, as compared with the control. Fluorescence region integral analysis shows that the synergy of two functional bacteria and NaCl can enhance the biodegradability of sludge. Protein secondary structure analysis shows that strain ZXY4 and Na+ cause the EPS structure to loosen, increasing the chances of lysozyme lysis of bacteria. Nucleotide metabolism, metabolism of other amino acids and membrane transport enhanced in a co-processing system.

In-situ sulfite treatment promotes solid reduction during aerobic digestion of waste activated sludge: Feasibility for small-scale wastewater treatment plants

Aerobic digestion remains the preferred choice for small-scale wastewater treatment plants (WWTPs) in some developing countries, largely due to economic viability and operational simplicity. The escalating production of waste activated sludge (WAS) has prompted small-scale WWTPs to improve efficiency. To address this issue, this study employed an in-situ sulfite treatment as a non-intrusive method to augment aerobic digestion. With sulfite-enhanced solubilization and hydrolysis, a 3.6-fold increase in degradation was achieved. Both sludge dewatering properties and pathogens inactivation were improved. Microbial community analysis revealed a preferential enrichment of Actinobacteriota and Firmicutes during sulfite treatment. The desktop scaling-up estimation suggests that implementing this treatment yielded operational cost savings exceeding 40 %. In summary, in-situ sulfite treatment offers a cost-effective strategy for WAS management in small-scale WWTPs.

The synergistic regulation of sewage sludge biodrying and greenhouse gas reduction by additives

As a dewatering method of high moisture solid waste sludge, biodrying still faces environmental problems such as material loss and greenhouse gas emission in the process of treatment. In this study, biochar and magnesium chloride were used to explore the synergistic effect of enhancing sludge biodrying and reducing greenhouse gas emissions. The highest temperature of biodrying was raised to 68.2 °C within 3 days, extending the longest high-temperature period to 5 days, which reduced the water content to 28.8 % in the single addition of biochar treatment. The complex addition increased the NH4+-N content of materials by 57.49 % and decreased the NO3--N content of materials by 40.62 %. The use of additives significantly reduced the emissions of CO2, CH4, and N2O compared to the no-addition treatment. The increase in dominant Actinomycetes and Chloroflexibacter was the main reason for the reduction in gas emissions.

Enhanced disintegration mechanism of surplus activated sludge to improve dewatering by thermally activated persulfate oxidation under mild temperature

The dewatering treatment is an essential process for the treatment and disposal of surplus activated sludge (SAS), and improving sludge dewatering performance is still a challenge and has become a research hotspot in recent years. The oxidation and disintegration of bacterial cells and extracellular polymeric substances (EPS) by active radicals produced by advanced oxidation processes (AOPs) were extremely promising to achieve deep sludge dewatering. This paper systematically studied the efficiency and mechanism of thermally activated persulfate (TAP) oxidation technology to the improvement of SAS dewatering performance. The results showed that the relative filterability (CST0/CST) was increased 2.52 times with 2.0 mmol/g VSS potassium peroxydisulfate (PDS) at 80 °C in 90 min. Under this condition, the Zeta potential of SAS significantly decreased from - 14.8 to - 1.44 mV, while the average particle size (dp50) decreased from 52.981 to 48.259 μm. Thermal treatment disrupted the sludge structure to release large amounts of EPS including polysaccharides and protein. Meanwhile, the results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the TAP treatment could expedite the disintegration of sludge, facilitating the decrease of total EPS content and conversion of tightly bound EPS (TB-EPS) to loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). The mechanism of TAP process to improve SAS dewatering performance was revealed, which could contribute to breaking the bottleneck of sludge depth dewatering and provide a theoretical and technical basis for its practical application.

Enhancing acidogenic fermentation of waste activated sludge via urea hydrogen peroxide pretreatment: Performance and mechanisms

Improving the anaerobic treatment performance of waste activated sludge (WAS) to achieve resource recovery is an indispensable requirement to reduce carbon emissions, minimize and stabilize biosolids. In this study, a novel strategy by using urea hydrogen peroxide (UHP) to enhance SCFAs production through accelerating WAS disintegration, degrading recalcitrant substances and alleviating competitive suppression of methanogens. The SCFAs production and acetate proportion rose from 436.9 mg COD/L and 31.3% to 3102.6 mg COD/L and 54.1%, respectively, when UHP grew from 0 to 80 mg/g TSS. Mechanism investigation revealed that OH, O2 and urea were the major contributors to accelerate WAS disintegration with the sequence of OH> O2 > urea. Function microbes related to acidification and genes associated with acetate production ([EC:2.3.1.8] and [EC:2.7.2.1]) were upregulated while genes encoding propionic acid production ([EC:6.4.1.3] and [EC:6.2.1.1]) were downregulated. These results raised the application prospects of UHP in WAS resource utilization.

Activation of calcium peroxide by nitrogen and sulfur co-doped metal-free lignin biochar for enhancing the removal of emerging organic contaminants from waste activated sludge

The accumulation of emerging organic contaminants (EOCs) in waste activated sludge (WAS) is a global concern. In this study, a multi-heteroatom nitrogen and sulfur was successfully embedded into lignin-based biochar (N-S-LGBC) and used it to activate calcium peroxide (CP) for the degradation of 4-nonylphenol (4-NP) in WAS. N-S-LGBC/CP was effective in degrading 85 % of 4-NP within 12 h through the activation of CP owing to hydroxyl radicals and singlet oxygen species generated from the synergism among pyrrolic-N, thiophenic-S, and lattice oxygen, i.e., active sites responsible for 4-NP degradation. These results highlight substrate biodegradability for subsequent bioprocesses that improves WAS treatment in EOC degradation by the N-S-LGBC/CP-mediated process. There was abundance of distinct Aggregatilinea genus within the phylum Chloroflexi during N-S-LGBC/CP treatment, indicating high 4-NP pretreatment efficiency in WAS. This work provides a new understanding of N-S-co-doped carbocatalysts in green and sustainable hydroxyl radical-driven carbon advanced oxidation (HR-CAOP) platforms for WAS remediation.

Sodium alginate/sinter gel spheres immobilized lysozyme producing strain SJ25 enhanced sludge reduction: Optimization and mechanism

In order to promote sludge hydrolysis and improve the efficiency of aerobic digestion, the sodium alginate immobilized gel spheres pellet B (SIP B) were prepared using sodium alginate (SA) and sinter as carrier to immobilize lysozyme producing strain SJ25. The optimal conditions for SIP B to promote sludge hydrolysis were 5.6 mg SS^-1 dosage and pH of 9.0. Under the optimal condition compared with the control group, the reduction efficiency of suspended solids (SS) in 24 h was increased by 26.89 %, the release of soluble chemical oxygen demand (SCOD) was increased by 517.79 mg L^-1, polysaccharide (PS) and protein (PN) concentrations were increased by 186.69 and 368.68 mg L^-1, respectively. SIP B enhanced the degradation efficiency of sludge by promote the release of lysozyme, prolonging the action time of the enzyme, enhancing the metabolism and membrane transport of xenobiotics, carbohydrate and amino.

Degradation of high-strength acrylic acid wastewater with anaerobic granulation technology: A mini-review

The anaerobic granulation technology has been successfully applied full-scale for treating high-strength recalcitrant acrylic acid wastewater. This mini-review highlighted the recalcitrance of acrylic acid and its biological degradation pathways. And then, the full-scale practices using anaerobic granulation technology for acrylic wastewater treatment were outlined. The granules are proposed to provide barriers for high-concentration acrylic acid to the embedded anaerobic microbes, maintaining its high degradation rate without apparent substrate inhibition. Based on this proposal, the prospects of applying anaerobic granulation technology to handle a wide range of high-strength recalcitrant wastewaters, to improve the current process performances, and to recover renewable resources were delineated. The anaerobic granulation for high-strength recalcitrant wastewater treatment is an emergent technology that can assist in fulfilling the appeals of the circular bioeconomy of modern society.

Enhanced biohydrogen generation through calcium peroxide engendered efficient ultrasonic disintegration of waste activated sludge in low temperature environment

Waste activated sludge is a renewable source for biohydrogen production, whereas the presence of complex biopolymers limits the hydrolysis step during this process, and thus pretreatment is required to disintegrate the sludge biomass. In this study, the feasibility of utilizing waste activated sludge to produce biohydrogen by improving the solubilization by means of thermo CaO₂ engendered sonication disintegration (TCP-US) was studied. The optimized condition for extracellular polymeric substance (EPS) dissociation was obtained at the CaO₂ dosage of 0.05 g/g SS at 70 °C. The maximum disintegration after EPS removal was achieved at the sonic specific energy input of 1612.8 kJ/kg TS with the maximum solubilization and SS reduction of 23.7% and 18.14%, respectively, which was higher than the US alone pretreatment. Thus, this solubilization yields higher biohydrogen production of 114.3 mLH₂/gCOD in TCP-US sample.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Molecular transformation of dissolved organic matter and formation pathway of humic substances in dredged sludge under aerobic composting

Using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) and molecular reaction network analysis, this study investigated molecular transformation of dissolved organic matter (DOM) and formation pathway of humic substances (HS) in dredged sludge during aerobic composting. The results showed that macromolecular N-containing compounds in dredged sludge are abundantly transformed into unsaturated and aromatic oxygenated compounds, exhibiting physicochemical properties similar to those of humus. Especially, N-containing compounds with one nitrogen atom are susceptible to oxidative deamination. Furthermore, assemblages of reactive fragments (e.g., -C7H8O2, -C10H12O2, -C2H2O2, and -C4H6O2) were identified as potential precursors to HS formed by the following reactions: starting with protein deamination and desulfurization, lignin delignification cascaded, finally decarbonylation occurred. This work provides novel insight for optimizing the process of stabilization and humification of dredged sludge.

Performance and bacterial community dynamics of lignin-based biochar-coupled calcium peroxide pretreatment of waste-activated sludge for the removal of 4-nonylphenol

Waste activated sludge contaminated with high levels of 4-nonylphenol (4-NP) is a major environmental concern. We have synthesized lignin-based biochar (LGBC) for use as a carbocatalyst in calcium peroxide (CP)-mediated sewage sludge pretreatment. Treatment of sewage sludge with 3.1 × 10^-4 M of CP and 3.0 g L^-1 of LGBC removed 76% of 4-NP in 12 h, which were 3.8 and 2.4 times higher than that with the LGBC and CP alone, respectively. There was synergy between reactive oxygen species (HO•, O₂^•-, and ¹O₂) and graphitic frameworks of LGBC. Pretreatment using the LGBC/CP system enhanced the release of biodegradable organic xenobiotics from the sludge. LGBC/CP enriched Proteobacteria and Thermostilla bacterial consortium (Planctomycetes) in the sludge and promoted 4-NP biodegradation. This work provides new insights into the chemical and biological mechanisms by which LGBC promotes 4-NP biodegradation in waste activated sludge via hydroxyl radical-driven carbon advanced oxidation pretreatment.