Pollutants In Sludge Research Articles

Identification and determination of emerging pollutants in sewage sludge driven by UPLC-QTOF-MS data mining.

Sludge from sewage treatment plants (STPs) is recognized as a sink of moderate to high lipophilic compounds resistant to biodegradation. Herein, we investigate the presence of emerging pollutants in sewage sludge combining the information provided by mass spectrometry detection, following ultra-performance liquid chromatography (UPLC), with the use of an accurate spectral database of pesticides and pharmaceuticals. In a first step, the performance of matrix solid-phase dispersion, as sample preparation technique, and two non-target data acquisition strategies (data dependent, DDA, and data independent analysis modes, DIA), used in combination with a UPLC quadrupole time-of-flight system, are assessed using a selection of deuterated compounds added either to freeze-dried sludge samples, or to sludge extracts. Possibilities and limitations of both modes are discussed. Following the DDA approach, a group of 68 micropollutants was identified in sludge from different STPs. Some of them are reported in this compartment for the first time. Finally, semi-quantitative concentration data are reported for a group of 37 pollutants in samples obtained from 16 STPs. Out of them, 10 pharmaceuticals, showing detection frequencies and median sludge residues above 50% and 100ngg-1, respectively; are highlighted as pollutants to be monitored in sludge in order to understand their behaviour during the wastewater treatment.

Study on enhanced bioremediation effect of oil-bearing dredging sediment

To solve the problem of difficult treatment of oil-bearing dredging sediment, the effects of three methods of microbial remediation, phytoremediation and combined bioremediation on the treatment of oily river dredging sediments were compared and studied, and the influence factors of microbial remediation were explored through static bacteria-fling tests. The results showed that the combined remediation method was better than the single biological method in treating bottom mud. The oil content of the treated sediment was 1.21g/kg, and the removal rate was 95.31%; the organic matter of the treated sediment was 72.30g/kg, and the degradation rate was 37.33. %, which can meet the requirements in the “Control Standards of Pollutants in Sludge for Agricultural Use (GB4284–2018)” and can be used for agricultural purposes.

Pollution level and risk assessment of heavy metals in sewage sludge from eight wastewater treatment plants in Wuhu City, China

Aim of study: To investigate the content, contamination levels and potential sources of five heavy metals (Hg, Pb, Cd, Cr, As) in sewage sludge from eight wastewater treatment plants (W1 to W8).Area of study: Wuhu, located in southeastern Anhui Province, southeastern China.Material and methods: The sewage sludge pollution assessment employed the single-factor pollution index, Nemerow’s synthetic pollution index, monomial potential ecological risk coefficient and potential ecological risk index. The potential sources among the five heavy metals were determined using the Pearson’s correlation analysis and principal component analysis (PCA).Main results: The mean concentrations of the heavy metals were 0.27 mg/kg (Hg), 70.78 mg/kg (Pb), 3.48 mg/kg (Cd), 143.65 mg/kg (Cr) and 22.17 mg/kg (As). W1, W5 and W6 sewage sludge samples showed the highest levels of heavy metal contamination, and cadmium had the highest contamination level in the study area. Pearson’s correlation analysis and PCA revealed that Pb and Cd mainly derived from traffic emissions and the manufacturing industry and that As and Cr originated from agricultural discharges.Research highlights: The pollution of cadmium in Wuhu should be controlled preferentially. The heavy metal pollution of W1, W5 and W6 sewage treatment plants is relatively high, they should be key prevention targets.

Fluorimetric Analysis of the Impact of Coal Sludge Pollution on Phytoplankton

The results of biomonitoring of the Olkhovaya River (Donetsk oblast) are presented. The impact of mine sludge waste on the state of surface water was shown. The assessment of physical and chemical parameters made it possible to characterize the water in the Olkhovaya River as dirty and polluted with a large number of suspended coal particles, whose content significantly exceeded the maximum permissible standards. The decrease in the content of chlorophyll in water samples taken below the sludge drains into the riverbed was determined by the fluorimetric method. The results of analysis of chlorophyll fluorescence induction curves are presented. It was found that contamination by sludge drains leads to disruption of primary photosynthetic reactions in phytoplankton cells.

Toxic Rational Analysis of Oily Sludge and Its Treatment Residues

In view of the present situation of oily sludge pollution, the different treatment methods for oily sludge in different uses were briefly described. The composition and structure of oily sludge are affected by sludge type, source, pyrolysis conditions and subsequent treatment conditions, which lead to different treatment methods and treatment effects. At present, there is no unified standard for the treatment of oily sludge at home and abroad, which brings difficulties to the unified management of oily sludge treatment. Through the toxicity analysis of oily sludge and its residues, it is helpful to judge the harmfulness of oily sludge and its treatment residues, according to the harmfulness of oily sludge, effectively choose different follow-up treatment methods, it is beneficial to establish the scientific standard of oily sludge treatment. In this paper, the present post-treatment indexes of petroleum hydrocarbon content, heavy metal ion content, water content, Polycyclic aromatic hydrocarbon content and sulfur content in oily sludge are summarized.

Toxicological Effects of Petroleum Refinery Sludge on the Terrestial Environment Using Bacteria and Earthworm as Bio Indicators

Aim: The aim of the study is to assess the sublethal (chronic) Ecotoxicological effects ofpetroleum refinery sludge pollution on the biota of the terrestrial environment using the effects on bacteria nitrogen transformation activity and growth rate of the soil fauna, Earthworm (Aporrectodea longa) as bioindicators.
 Place and Duration of Study: Department of Environmental Management and Toxicology, Federal University of Petroleum Resources, Effurun, between 2017 and 2018.
 Methodology: The OECD TG 216 (2000) test method was used to determine the chronic effects (% inhibition and EC50) of the petroleum sludge on the nitrogen transformation activity of Nitrobacter sp. in the soil, while the methods of Sandoval et al. [13] and OECD, 207 was used for the chronic effects of the sludge on the growth rate of the earthworms. Bioconcentration factor (BCF) of the sludge in the earthworms was also determined. Both tests were conducted for 28 days. Results from the test with multiple concentrations were analyzed using a regression model (ANOVA). EC5O was also determined using the Probit analytical software. Analyses weredone using ASTM methods.
 Results: Analysis of the Nigerian petroleum refinery sludge used for this research indicated that the sludge wasacidic with a pH value of 5.91and had a high TPH content of 340,000 mg/kg made mainly of between 10-40 carbon unit compounds. There was a progressive increase in the percentage (%) inhibition of the nitrogen transformation activitiesof the bacteria, from 18.0% (3125 mg/kg) to 79.30% (5000mg/kg) with increase in concentration and time. The effective concentration that decreased 50% (EC50) of the nitrogen transformation activity was 13761.059 mg/kg. The growth rate of the test earthworms decreased from 9.19x103 g/day (375 mg/kg) to 3.55x103 g/day (3000 mg/kg) for the test period. The BCF decreased from 5.168 (375 mg/kg) to 1.22 (3000 mg/kg) in the earthworms, while the EC50for the earthworms was 825.02mg/kg as the concentration of the sludge increased with time.
 Conclusion: The sludge inhibited the nitrogen transformation activity of Nitrobacter sp. because it exceeded the 25% inhibition limit for chemicals with the potential to cause chronic effects on soil microbial activities as specified in OECD TG 216. Similarly, the sludge reduced the growth rate of the earthworm progressively as the sludge concentration increased in relation to the control. Bioaccumulation factor also increased with increasing sludge concentration and time.

Wood-Based Panel Industry Wastewater Meets Microbial Fuel Cell Technology.

Although the wood-based panel industry is not considered to be a water-consuming sector, it generates ca. 600 M m3 of wastewater every year on a global scale. The wastewater is usually highly polluted and environmentally toxic even after dilution. Common wastewater treatment techniques require high-energy input or addition of various chemicals to the treated wastewater, which cause secondary pollution and production of toxic sludge. Microbial fuel cells (MFCs) have become an attractive technology, allowing for zero-energy treatment of various types of wastewater with simultaneous production of electric current. Recent investigations have shown that MFCs can also be utilized for sustainable treatment and energy production from the wastewater generated by the wood-based panel industry. This article contains a critical summary of the investigations in this field as well as a discussion of the research needed and perspectives for the future.

EXPERIENCE IN THE STUDY OF THE DURATION OF THE INFLUENCE OF OIL POLLUTION ON THE CHARACTERISTIC OF BIOELECTRIC RESISTANCE OF BIRCH (BETULA PENDULA ROTH)

The study of bioelectric resistance (impedance) of woody plants by electrometric method under the influence of adverse factors, including oil sludge, is one of the adequate methodological approaches to assessing the state of forest biogeocenoses. The aim of the study is to study the peculiarities of the influ-ence of oil sludge pollution of soils on the duration of changes in the bioelectric resistance of the precam-bial tissue complex of birch trunks. The object of the study is the trees of the hanging birch (Betula pendu-la Roth.) growing in the basin of buffer ponds of JSC «Gazpromneft - ONPZ» (Omsk). The research area is the Central forest-steppe of the South of Western Siberia. The results of the studies were processed by standard methods of variational statistics, correla-tion, regression and variance one-factor analysis using the package Statistica 10. Comparisons of experience variants were carried out according to student and Fisher criteria. The dependence of elec-trical resistance of birch trunk PCT (precompiling complex tissues) on the level of oil sludge pollution of soils was studied. A recommendation for rapid assessment of the condition of birch trees in the con-ditions of oil sludge pollution by electrometric meth-od was developed. According to the results of our long-term studies, it can be noted that the duration of a significant negative impact of oil sludge on the electrical resistance precompiling complex tissues of birch trees in the forest-steppe zone of Western Sibe-ria is manifested within six years, and in the seventh year these differences are not reliable and already in the ninth year-these differences disappear (τfact > τ0.5). The results obtained can be used in screening studies of forest biogeocenoses and in the planning and or-ganization of bioreculture activities on the territory of sanitary protection zones of oil refineries and in areas of oil production and oil transportation.

+Efficient dewatering and heavy-metal removal in municipal sewage using oxidants

Municipal sewage sludge (MSS) is widely used in agriculture. In this study, three oxidants (Fenton’s reagent, K2S2O8, and CaO2) were used to simultaneously dehydrate MSS and remove heavy metals, and the heavy metals in the supernatant were separated via the addition of CaO. The respective removal rates of Pb, Zn, Cu, and Cd were 56.8%, 84.9%, 88.3%, and 92.3% using Fenton’s reagent; 66.9%, 86.1%, 88.9%, and 82.8% using K2S2O8; and 53.0%, 58.3%, 64.8% and 2.1% using CaO2. Thus, Fenton’s reagent and K2S2O8 were preferable for heavy metal removal, especially for Cd. The treated sludge was safe for agricultural use based on the standards for pollutants in sludge for agricultural use (GB4284-84). The oxidants also exhibited good dewatering performance for MSS and caused the extracellular polymeric substance (EPS) of MSS to decompose quickly. The water content of the sludge was reduced from 99.08% to 76.1% (Fenton’s reagent), 74.7% (K2S2O8), and 66.5% (CaO2). Hence, the treated sludge was easy to transport and could be safely used in agricultural production. After oxidant treatment, CaO was added to the supernatant, allowing the metals in the supernatant to be separated. This method can reduce Wc and heavy metal content of sludge at low cost.

Extraction of nonylphenol, pyrene and phenanthrene from sewage sludge and composted biosolids by cyclodextrins and rhamnolipids.

Sewage sludge generated by Waste Water Treatment Plants (WWTPs) are frequently used as organic amendments in agriculture, but they contain pollutants such as Potentially Toxic Elements (PTEs) and organic contaminants which contaminate the agricultural soils. The study presented here is part of a larger study based on the application of environmentally friendly chemical and biological techniques to decrease the content of organic pollutants in sewage sludge before agricultural application. The aim of this study was to evaluate the performance of biodegradable extractants, such as some cyclodextrins (CDs), β-cyclodextrin (BCD), hydroxypropyl-β-cyclodextrin (HPBCD) and randomly methylated-β-cyclodextrin (RAMEB), and a biosurfactant (rhamnolipid, RL) on the removal and availability of pyrene (PYR), phenanthrene (PHE) and nonylphenol (NP) from several biosolids samples in order to improve their subsequent biodegradation. The influence of pollutants retention time on biosolids was studied, as well as the effect of each extractant on PTEs solubilization. Results obtained were pollutant and extractant-dependent. BCD extracted similar amounts of pollutants compared to water, whereas HPBCD and RAMEB actually increased the availability of the three pollutants in most of the samples and aging times. RL seems to be the best election for Polycyclic Aromatic Hydrocarbons (PAHs) extraction from biosolids, with percentages of extraction multiplied by more than 80 and 40 times for PHE and PYR, respectively, relative to water extraction. The extraction enhancement was the highest for NP, the most hydrophobic pollutant, reaching more than 500-fold higher with HPBCD and RAMEB. PTEs extractability was not affected by the different CDs used, but RL caused an increment in their soluble content what could endanger a subsequent biodegradation of the organic pollutants.

Cultivation of aerobic granular sludge in a microbial fuel cell

Aerobic granular sludge(AGS) is a special biofilm formed by the self-aggregation of sludge material. In this study, AGS was cultivated in the biocathode of a continuous flow microbial fuel cell (MFC). During the formation of AGS, changes in sludge concentration, extracellular polymers (EPS), pollutants removal and power generation were examined. The results showed that, MLVSS kept above 5 g/L, the PS, PN and PN/PS of TB-EPS showed a gradually increasing trend, the removal efficiency of COD and ammonia nitrogen was 94.46% and 93.03%, respectively. A maximum voltage output of 350 mV was achieved.

Analysis of Biogenic Secondary Pollution Materials from Sludge in Surface Waters.

Many countries of the world, including Lithuania, are making an effort to reduce surface water pollution. State monitoring data show that almost 80% of the lakes in Lithuania have an increased amount of sludge. One of the reasons for this increase in sludge is an excessive amount of biogenic material in the water. It is known that even after the source of pollution is removed, the condition of the lake water does not improve; rather, the condition of the lake water worsens due to the secondary pollution of sludge in the water. A study was conducted to determine the impact of secondary sludge pollution on water. For this study, 5 sludge samples were taken from different lakes in Lithuania. Fresh water was poured on the sludge samples, the concentrations of Nt, NO2-N, NO3-N, NH4-N, PO4-P, Pt, the pH and the changes in the electric conductivity (C) were measured in the water within 28 h. Research has shown that the thickness of the sludge layer influences the total amounts of nitrogen, phosphorus, and organic matter present in the sludge. As the thickness of the sludge layer increases in a lake, the total concentrations of nitrogen, total phosphorus and organic matter increase. Studies have also shown that the concentrations of all biogenic substances in water increase, with the exception of total phosphorus. This finding shows that organic phosphorus is "locked" in sludge, and no secondary pollution occurs from this source. Moreover, the electrical conductivity values of the water influence the release of biogenic substances from sludge in the water.

The Preparation of Biochar Particles from Sludge and Corncobs and Its Pb2+ Adsorption Properties.

In the present study, biochar particles (BPs) produced by the co-pyrolysis of sewage sludge and corncobs at temperatures of 300, 500, and 700°C were characterized. The Pb2+ adsorption properties and the heavy metal leaching toxicity rates of the BPs were investigated. It was found that the adsorption kinetics of the Pb2+ can be accurately described by a pseudo-second-order model, and the equilibrium adsorption data were well represented by both the Langmuir and the Freundilich Equations. The toxicity characteristic leaching procedure (TCLP) results indicated that the leaching concentrations of all the heavy metals were below the set limit of China's national standard (Identification Standard for Hazardous Waste Extraction Toxicity Identification, China National Standard, GB 5085.3-2007). The results of this study can successfully provide scientific support for future corncob treatment and sludge pollution control.

Pre-magnetized Fe0 as heterogeneous electro-Fenton catalyst for the degradation of p-nitrophenol at neutral pH

Pre-magnetized Fe0 (Pre-Fe0) was for the first time applied as heterogeneous catalyst to enhance the oxidation efficiency of electro-Fenton (EF) for the degradation of p-nitrophenol (PNP). The parameters including current, initial pH and pre-Fe0 dosage of Pre-Fe0/EF process were optimized and compared with other two processes (conventional Fe0/EF and electro-oxidation) to confirm its advantage. The rate constants of PNP removal were 1.40–3.82 folds of those by Fe0/EF process under various experimental conditions. The application of pre-Fe0 as catalyst could extend the working pH range from 3.0 to neutral conditions for PNP removal and reduce the Fe0 dosage from 2 to 0.5 mM corresponding to Fe0/EF, avoiding the second pollution of iron sludge. The superiority of Pre-Fe0/EF process was also verified to improve the degradation and mineralization of other phenols and antibiotics. Furthermore, a possible pathway of PNP degradation was revealed by the identification of intermediates and organic acids, and the possible mechanism of pre-Fe0 efficiently enhanced the EF efficiency was proposed. This work demonstrated that such a novel heterogeneous EF process using pre-Fe0 catalyst was clean and promising for the degradation of refractory organic pollutants.

Diversity and phylogenetic composition of bacterial communities and their association with anthropogenic pollutants in sewage sludge

Despite wastewater treatment, sewage sludge is often contaminated with multiple pollutants. Their impact on the phylogenetic composition and diversity of prokaryotic communities in sludge samples remains largely unknown. In this study, we analyzed the phylogenetic structure of bacterial communities and diversity in sludge from six waste water treatment plants (WWTPs) and linked this information with the pollutants identified in these samples: eight potentially toxic metals (PTMs) and four groups of organic pollutants [polychlorinated biphenyls (PCBs), polyromantic hydrocarbons (PAHs), brominated flame retardants (BFRs) and organochlorine pesticides (OCPs)].Alpha diversity measures and the distribution of dominant phyla varied among the samples, with the community from the thermophilic anaerobic digestion (TAD)-stabilized sample from Prague being the least rich and the least diverse and containing on average 36% of 16S rRNA gene sequence reads of the thermotolerant genus Coprothermobacter of the class Clostridia (phylum Firmicutes). Using weighted UniFrac distance-based redundancy analysis (dbRDA), we found that a collection of 5 PTMs: Cr, Cu, Ni, Pb, Zn, and a pair of BFRs: hexabromocyclododecane (HBCD) and tribromodiphenyl ethers (triBDEs) were significantly associated with the bacterial community structure in mesophilic anaerobic digestion (MAD)-stabilized samples, whereas PCBs were observed to be marginally significant. Altogether, 85% of the variance in bacterial community structure could be ascribed to these pollutants. The data presented here contribute to a greater understanding of the ecological effects of combined pollution on the composition and diversity of bacterial communities, hence have the potential to aid in predicting ecosystem functions and/or disruptions associated with pollution.

16S rRNA Gene and Transcript Profiling: an Application on Full-scale Anaerobic Reactors of Wastewater Sludges

Sludge anaerobic digestion is a wastewater treatment plant crucial point for the impact mitigation on environment. Such process reduces the disposable sludge volume and pollution potential, generating biogas. Despite its crucial role, sludge digestion microbiology is not clearly understood. In this work, the characterization of the microbiota into digesters fed by primary and secondary sludges was performed. Two sampling sessions were conducted and more than 120 samples were extracted and analyzed by PCR-DGGE. Cluster analysis on DGGE profiles suggested the presence of diverse communities associated with different sludge characteristics (ANOVA, p < 0.01) and Shannon’s diversity index showed higher evenness into the secondary one. Moreover, the comparison of community structure based on DNA and bacterial rRNA genes highlighted the presence of unexpressed bacterial genome, leading to a potential functionality overestimation using a DNA-based approach (Shannon index mean − 16%, t test, p < 0.05). This approach has proven to be suitable for a first useful assessment of microbial community dynamics during the anaerobic digestion process.

Occurrence of Arbuscular Mycorrhizal Fungi in Hemp (Cannabis sativa) Plants and Soil Fertilized with Sewage Sludge and Phosphogypsum

ABSTRACT The colonization of soil and roots by arbuscular mycorrhizal fungi and the formation of spores under the influence of fertilization with phosphogypsum and sewage sludge were examined. Identification of arbuscular mycorrhizal fungi was carried out in soil and in roots of outdoor experimental hemp plantation. Assessment of the colonization was carried out by molecular and microscopic methods. The material for the isolation of DNA consisted of soil samples taken from mycorrhizal soil and hemp roots of cv. Białobrzeskie, cv. Tygra, and cv. Beniko. In nested PCR reactions part of the small subunit (SSU) region, the region of the internal transcribed spacer (ITS) and part of large subunit (LSU) rDNA region were amplified. As a result of the cloning and sequencing of the DNA, it was found that the greatest similarity of the obtained sequences present in the samples of roots and soil was to the following species: Diversispora sp., Funneliformis sp., Glomus sp., Funneliformis mosseae, Glomus caledonium, Funneliformis geosporum, Glomus occultum. The colonization by the fungi was estimated and found to differ depending on the hemp cultivar and doses of fertilizers. Cultivar Tygra showed no negative impact on biomass production by intensive mycorrhization, proved its high tolerance to phosphogypsum and sewage sludge pollution, and responded positively regarding biomass production.

Efficient Copper Removal from an Aqueous Anvironment using a Novel and Hybrid Nanoadsorbent Based on Derived-Polyethyleneimine Linked to Silica Magnetic Nanocomposites.

Due to the extreme rise of sludge pollution with heavy metals (e.g. copper), the options for its disposal or treatment are decreasing. On the contrary, properly heavy metal-cleaned sludge can be used as an alternative sustainable energy and agriculture source. The aim of this study was to develop a novel nanoadsorbent, based on irreversibly linked amino-rich polymer onto previously silica-coated magnetic nanoparticles (MNPs) that can be applied efficiently for metal removal. MNPs were coated uniformly by 3 nm thick silica layer (core-shell structure), and were additionally modified with systematic covalent attachment of derived branched polyethyleneimine (bPEI). The formed structure of synthesized MNPs composite was confirmed with several analytical techniques. Importantly, nanoadsorbents exhibit high density of chelating amino groups and large magnetic force for easier separation. The importance of introduced bPEI, effect of pH, initial heavy metal concentration onto copper uptake efficiency and, further, nanoadsorbent regeneration, were studied and explained in detail. The adsorption isotherm was well fitted with Langmuir model, and the maximum adsorption capacity was shown to be 143 mg·g−1 for Cu2+. The reusability and superior properties of silica-coated MNPs functionalized with derived-bPEI for copper adsorption underlie its potential for the removal application from heavy metals contaminated sludge

Fate and Ecological Risk Assessment of Nutrients and Metals in Sewage Sludge from Ten Wastewater Treatment Plants in Wuxi City, China.

The concentrations of nutrients (total nitrogen, total phosphorus and organic matter) and metals (Cu, Pb, Zn, Ni, Cd, Cr, As and Hg) in sewage sludge samples were determined to evaluate the level of contamination. Sewage sludge samples were collected from ten wastewater treatment plants from 2016 to 2018 in Wuxi city, China. All the studied sewage sludge samples displayed high fertility properties due to their richness. Total concentrations of metals in the sewage sludge samples were within the regulation of the Chinese legislation. The levels of the eight metals temporally varied. Sewage sludge pollution assessment was undertaken using pollution index, geo-accumulation index, potential ecological risk index and aggregative toxicity index. Multivariate statistical analysis indicated that Pb, Cr, As and Hg may have similar transport behavior and derive from anthropogenic sources. Ecological risk assessment revealed that Hg contamination is the major concern for human health, since the treated sewage sludge is used for agricultural purposes.

Calcium peroxide promotes hydrogen production from dark fermentation of waste activated sludge

Calcium peroxide (CaO2), one of versatile and harmless inorganic peroxy compounds, has been recently used as a highly effective oxidant to degrade pollutants in sludge and a method to achieve sludge resource utilization. However, its impact on hydrogen production has never been studied before. This investigation therefore aims to fill this knowledge gap. Results indicated that with CaO2 increased from 0.05 to 0.25 g/g VSS (volatile suspended solids), the maximum hydrogen yield increased from 0.77 to 10.55 mL/g VSS. The mechanism studies revealed that CaO2 accelerated the breakage and death of sludge cells. Excitation emission matrix (EEM) analyses further indicated that CaO2 increased the biodegradability of the released substances, which could provide more biodegradable organics for the following reactions. Although CaO2 caused inhibitions to some extents to all the tested microbes, its inhibition to hydrogen consumers was much severer than that to hydrolytic microbes and hydrogen producers. The enzyme analyses also demonstrated that the suppression of calcium peroxide to the activities of enzymes related to hydrogen consumption process was much severer than that to the activities of the activities of enzymes related to hydrogen production process. Further investigations exhibited that alkali, O2− and OH radicals, were the major intermediate products of CaO2 decomposition. All of them were verified to contribute the increased hydrogen production, and their contributions were in the order of alkali > O2− > OH. This is the first work demonstrating that CaO2 can enhance hydrogen production from WAS. The findings reported in our paper not only expand the application field of CaO2 but also deepen the understanding of the CaO2-involved sludge fermentation process.