Understanding the mechanism of polybrominated diphenyl ethers reducing the anaerobic co-digestion efficiency of excess sludge and kitchen waste

Innovative overview of the occurrence, aging characteristics, and ecological toxicity of microplastics in environmental media

Microplastics (MPs), pollutants detected at high frequency in the environment, can be served as carriers of many kinds of pollutants and have typical characteristics of environmental persistence and bioaccumulation. The potential risks of MPs ecological environment and health have been widely concerned by scholars and engineering practitioners. Previous reviews mostly focused on the pollution characteristics and ecological toxicity of MPs, but there were few reviews on MPs analysis methods, aging mechanisms and removal strategies. To address this issue, this review first summarizes the contamination characteristics of MPs in different environmental media, and then focuses on analyzing the detection methods and analyzing the aging mechanisms of MPs, which include physical aging and chemical aging. Further, the ecotoxicity of MPs to different organisms and the associated enhanced removal strategies are outlined. Finally, some unresolved research questions related to MPs are prospected. This review focuses on the ageing and ecotoxic behaviour of MPs and provides some theoretical references for the potential environmental risks of MPs and their deep control.

Coupling between 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) debromination and methanogenesis in anaerobic soil microcosms

Polybrominated diphenyl ethers (PBDEs) are persistent pollutants that may undergo microbial-mediated debromination in anoxic environments, where diverse anaerobic microbes such as methanogenic archaea co-exist. However, current understanding of the relations between PBDE pollution and methanogenic process is far from complete. To address this knowledge gap, a series of anaerobic soil microcosms were established. BDE-47 (2, 2', 4, 4'-tetrabromodiphenyl ether) was selected as a model pollutant, and electron donors were supplied to stimulate the activity of anaerobes. Debromination and methane production were monitored during the 12 weeks incubation, while obligate organohalide-respiring bacteria (OHRBs), methanogenic, and the total bacterial communities were examined at week 7 and 12. The results demonstrated slow debromination of BDE-47 in all microcosms, with considerable growth of Dehalococcoides and Dehalogenimonas over the incubation observed in most BDE-47 spiked treatments. In addition, the accumulation of intermediate metabolites positively correlated with the abundance of Dehalogenimonas at week 7, suggesting potential role of these OHRBs in debromination. Methanosarcinaceae were identified as the primary methanogenic archaea, and their abundance were correlated with the production of debrominated metabolites at week 7. Furthermore, it was observed for the first time that BDE-47 considerably enhanced methane production and increased the abundance of mcrA genes, highlighting the potential effects of PBDE pollution on climate change. This might be related to the inhibition of reductive N- and S-transforming microbes, as revealed by the quantitative microbial element cycling (QMEC) analysis. Overall, our findings shed light on the intricate interactions between PBDE and methanogenic processes, and contribute to a better understanding of the environmental fate and ecological implication of PBDE under anaerobic settings.

A comprehensive review on the preparation of biochar from digestate sources and its application in environmental pollution remediation

The preparation of biochar from digestate is one of the effective ways to achieve the safe disposal and resource utilization of digestate. Nevertheless, up to now, a comprehensive review encompassing the factors influencing anaerobic digestate-derived biochar production and its applications is scarce in the literature. Therefore, to fill this gap, the present work first outlined the research hotspots of digestate in the last decade using bibliometric statistical analysis with the help of VOSviewer. Then, the characteristics of the different sources of digestate were summarized. Furthermore, the influencing factors of biochar preparation from digestate and the modification methods of digestate-derived biochar and associated mechanisms were analyzed. Notably, a comprehensive synthesis of anaerobic digestate-derived biochar applications is provided, encompassing enhanced anaerobic digestion, heavy metal remediation, aerobic composting, antibiotic/antibiotic resistance gene removal, and phosphorus recovery from digestate liquor. The economic and environmental impacts of digestate-derived biochar were also analyzed. Finally, the development prospect and challenges of using biochar from digestate to combat environmental pollution are foreseen. The aim is to not only address digestate management challenges at the source but also offer a novel path for the resourceful utilization of digestate.

Assessing emerging and priority micropollutants in sewage sludge: environmental insights and analytical approaches

The application of sewage sludge (SS) in agriculture, as an alternative to manufactured fertilizers, is current practice worldwide. However, as wastewater is collected from households, industries, and hospitals, the resulting sludge could contaminate land with creeping levels of pharmaceuticals, pesticides, heavy metals, polycyclic aromatic hydrocarbons, and microplastics, among others. Thus, the sustainable management of SS requires the development of selective methods for the identification and quantification of pollutants, preventing ecological and/or health risks. This study presents a thorough evaluation of emerging and priority micropollutants in SS, through the lens of environmental insights, by developing and implementing an integrated analytical approach. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction method, coupled with gas chromatography and liquid chromatography, was optimized for the determination of 42 organic compounds. These include organophosphorus pesticides, organochlorine pesticides, pyrethroid pesticides, organophosphate ester flame retardants, polybrominated diphenyl ethers, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. The optimization of the dispersive-solid phase for clean-up, combined with the optimization of chromatographic parameters, ensured improved sensitivity. Method validation included assessments for recovery, reproducibility, limit of detection (LOD), and limit of quantification (LOQ). Recoveries ranged from 59.5 to 117%, while LODs ranged from 0.00700 to 0.271 µg g-1. Application of the method to seven SS samples from Portuguese wastewater treatment plants revealed the presence of sixteen compounds, including persistent organic pollutants. The quantification of α-endosulfan, an organochlorine pesticide, was consistently observed in all samples, with concentrations ranging from 0.110 to 0.571 µg g-1. Furthermore, the study encompasses the analysis of agronomic parameters, as well as the mineral and metal content in SS samples. The study demonstrates that the levels of heavy metals comply with legal limits. By conducting a comprehensive investigation into the presence of micropollutants in SS, this study contributes to a deeper understanding of the environmental and sustainable implications associated with SS management.

Metagenomic approach reveals the mechanism of calcium oxide improving kitchen waste dry anaerobic digestion

In light of the characteristics of excessive acidification and low biogas yield during kitchen waste (KW) dry digestion, the impact of the calcium oxide (CaO) on KW mesophilic dry digestion was investigated, and the enhanced mechanism was revealed through metagenomic approach. The results showed that CaO increased the biogas production, when the CaO dosage was 0.07 g/g (based on total solid), the biogas production reached 656.84 mL/g suspended solids (VS), approximately 8.38 times of that in the control. CaO promoted the leaching and hydrolysis of key organic matter in KW. CaO effectively promoted the conversion of volatile fatty acid (VFA) and mitigated over-acidification. Macrogenome analysis revealed that CaO increased the microbial diversity in KW dry digestion and upregulated the abundance of genes related to amino acid and carbohydrates metabolism. This study provides an effective strategy with potential economic benefits to improve the bioconversion efficiency of organic matter in KW.

Microbial metabolism and health risk assessment of kitchen waste odor VOCs

Kitchen waste (KW) generates odors comprising complex volatile organic compounds (VOCs). We used gas chromatography-mass spectrometry to analyze VOCs, and 16S gene sequencing was used to analyze the microbial community composition and microbial metabolic mechanism. The results showed that the major odor-causing VOCs were hydrogen sulfide, methanethiol, methyl sulfide, dimethyl disulfide, and ethyl acetate. As the temperature increased, the VOCs and microbial community composition became more complex, and the microbial community related to VOC production included Leuconostoc, Pediococcus, Acetobacter, and Weissella. Based on PICRUSt2 analysis, the possibility of typical VOC interconversion by microbial metabolism was low. It was more likely that precursor substances were catalyzed by enzymes to generate the corresponding VOCs. Attention should be given to trichloromethane and 1,2-dichloroethane, which may cause adverse health effects through long-term inhalation. The study results provide guidance for controlling VOCs from KW.

Enhanced methane production from the anaerobic co-digestion of food waste plus fruit and vegetable waste

Food waste (FW) and fruit, vegetable waste (FVW) are important components of municipal solid waste, yet the performance and related mechanisms of anaerobic co-digestion of FW and FVW for methane production have been rarely investigated. In order to get a deeper understanding of the mechanisms involved, the mesophilic FW and FVW anaerobic co-digestion in different proportions was investigated. The experimental results showed that when the ratio of FW and FVW was 1/1 (in terms of volatile suspended solid), the maximum biomethane yield of 269.9 mL/g TCOD from the codigested substrate is significantly higher than that in FW or FVW anaerobic digestion alone. FW and FVW co-digestion promoted the dissolution and biotransformation of organic matter. When the recommended mixing ratio was applied, the maximum concentration of dissolved chemical oxygen demand (COD) was high as 11971 mg/L. FW and FVW co-digestion reduced the accumulation of volatile fatty acids (VFA) in the digestive system, thus reducing its negative impact on the methanogenesis process. FW and FVW co-digestion process synergistically enhanced microbial activity. The analysis of microbial population structure showed that when FW and FVW were co-digested at the recommended ratio, the relative abundance of Proteiniphilum increased to 26.5%, and the relative abundances of Methanosaeta and Candidatus Methanofastidiosum were also significantly increased. The results of this work provide a certain amount of theoretical basis and technical support for the co-digestion of FW and FVW.

Impact of emerging pollutant florfenicol on enhanced biological phosphorus removal process: Focus on reactor performance and related mechanisms

Florfenicol (FF), an emerging pollutant antibiotic that is difficult to biodegrade, inevitably enters sewage treatment facilities with high level. To date, however, the performance and related mechanism of FF on enhanced biological phosphorus removal (EBPR) have not been reported. In order to fill this gap, this work investigated the potential impacts of FF on EBPR and revealed the relevant mechanisms. The effect of FF on EBPR was dose-dependent, that was, low dose had no effect on EBPR, while high FF concentration inhibited EBPR. Mechanism investigation showed that FF had no effect on anaerobic phosphate release, but reduced oxic phosphorus uptake. Three-dimensional Excitation-emission Matrix fluorescence spectroscopy and X-ray photoelectron spectroscopy analysis showed that FF affected the structure and components of activated sludge extracellular polymers (EPS). High content of FF stimulated sludge to secrete more EPS. High level of FF reduced the relative abundance of microorganisms responsible for biological phosphorus removal. Microbiological community structure analysis indicated 2.0 mg FF/L increased the relative abundance of Candidatus_Competibacter and Terrimonas from 9.22 % and 12.49 % to 19.00 % and 16.28 %, respectively, but significantly reduced the relative abundance of Chinophagaceae from 11.32 % to 0.38 %, compared with the blank.

In-situ sulfite treatment enhanced the production of short-chain fatty acids from waste activated sludge in the side-stream anaerobic fermentation

Sulfite-based technology could enhance methane production from anaerobic sludge digestion. However, its potential for in-situ direct sludge treatment without anaerobic sludge addition in the side-stream remains unclear. This study investigated the feasibility of using in-situ sulfite treating sludge for short-chain fatty acids (SCFAs) production via anaerobic fermentation of waste activated sludge (WAS) as a side-stream treatment. In-situ sulfite direct sludge treatment enhanced SCFAs and acetic acid production by 2.03 and 4.89 times at 500 mg S/L compared to the control. With in-situ sulfite treatment, WAS hydrolysis and acidification were enhanced while methanogenesis was spontaneously hindered. The in-situ sulfite treatment inactivated pathogens and improved the sludge dewatering properties. The relative abundances of SCFAs-production microbial were stimulated, facilitating the sludge bioconversion. The produced SCFAs from in-situ sulfite side-stream treatment could be applied as an "internal carbon source" to enhance biological nutrient removal to improve economic and environmental value from sludge treatment.

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.

Enhancing anaerobic co-digestion of primary settled-nightsoil sludge and food waste for phosphorus extraction and biogas production: effect of operating parameters and determining phosphorus transformation

The study aimed to comprehensively determine P extraction efficiency and co-digestion of food waste (FW) and primary settled-nightsoil sludge (PSNS) process performance influenced by different hydraulic retention times (4, 7, 10, and 15 days) and mixture ratios of FW:PSNS in substrates (100:0, 75:25, 50:50, 25:75, and 0:100). P-transformation was evaluated to identify P fractionation in both supernatant and sludge accumulated in reactors. The results showed that anaerobic co-digestion was inhibited by the accumulation of undigested feedstock due to higher %PSNS found in AD4 (25FW:75PSNS) and AD5 (100PSNS). A more stable process was found in AD2 (75FW:25PSNS) under hydraulic retention time (HRT) 15 days in which COD removal efficiency and P release were 97.2 and 80.2%, respectively. This recommended condition allowed a high organic loading rate (OLR) at 12 gVS/L/day resulting in the highest biogas yield of 0.93 L/L/day. Distribution of P data demonstrated that most of P in feedstock was deposited and accumulated in sediment up to 97.8%. Poor biodegradability resulting from using shortened HRT led to high increased P-solid content in effluent. In addition, available P in effluents and accumulated P-solids in sediment obtained from the AcoD process has the potential to serve as sources for P recovery.

Promoting the overall energy profit through using the liquid hydrolysate during microwave hydrothermal pretreatment of wheat straw as co-substrate for anaerobic digestion

Liquid hydrolysate (LH) derived from the microwave hydrothermal pretreatment (MHP) of wheat straw (WS) was anaerobically digested together with the solid residual to promote the overall energy profit. Different MHP temperatures (90, 120, 150, 180 °C) and retention times (10, 20, 40 min) were investigated. Increased MHP intensity generated plenty of VFAs (mainly acetate) and phenols in the LH, implying the double-side effect of LH on AD. The highest methane production of 227.92 mL CH₄·gVS^-1 Raw was obtained with MHP at 120 °C for 10 min, 21.53 % higher than the control. While, MHP at 180 °C for 40 min exhibited 29.02 % lower methane production (113.13 mL CH₄·gVS^-1 Raw) and 115.86 % longer lag phase (3.13 days) than the control. Butyrate fermentation endowed the treatment groups of 180 °C with resilience from the overload and inhibition. Methanosarcina was largely enriched by the abundant acetate in LH on the early stage of anaerobic digestion (AD), especially when with high MHP intensity. Increased abundance of Methanosaeta and Methanobacterium played a crucial role in maintaining methane production at the middle and later stage. The high number of species and evenness in methanogens community were beneficial for the startup of batch AD. Although negative net energy was obtained, the lower ratio of energy input and output compared with the most researches using the solid residual after MHP as the sole substrate for AD demonstrated the contribution of LH to the overall energy profit.

Volatile fatty acids changed the microbial community during feammox in coastal saline-alkaline paddy soil

In order to indicate the effect of volatile fatty acids (VFAs) on the characteristics of feammox and dissimilatory iron reducing bacteria (DIRB) in paddy soils, different VFAs were selected with paddy soils for anaerobic cultivation. Five treatments were set up, respectively, only adding N and both adding N and C (formate + NH₄⁺ (Fo-N), acetate + NH₄⁺ (Ac-N), propionate + NH₄⁺ (Pr-N), and butyrate + NH₄⁺ (Bu-N)) treatments. The concentration of Fe(II), Fe(III), NH₄⁺, and VFAs was assessed within 45 d, and the bacterial community was determined after cultivation. The oxidation rates of NH₄⁺ were the highest in N treatment, while it was the lowest in Fo-N treatment. Under the four C treatments, the consumption of NH₄⁺ and Fe(III) was the fastest in Pr-N treatment, which was consumed by 31.2% and 76.3%, respectively. Different VFAs selected for distinct DIRB. Compared with N treatment, Ac-N and Bu-N treatment increased the relative abundance of DIRB, such as Geobacter and Clostridia, which increased the consumption of VFAs during incubation. Overall, VFAs, especially formate, could promote Fe(III) reduction and compete with the feammox process for the electron acceptors to decrease the feammox reaction, and prohibited soil NH₄⁺ loss. Therefore, VFAs, which was released from organic fertilizer, could reduce NH₄⁺ loss in feammox process of saline-alkaline paddy soils.

New insights into mechanism of emerging pollutant polybrominated diphenyl ether inhibiting sludge dark fermentation

Polybrominated diphenyl ethers (PBDEs), derived from electronics, furniture, etc., are detected with high level in excess sludge (ES). In this work, the influence of PBDEs on ES dark fermentation (ESDF) hydrogen production and the related key mechanisms were explored. The result shows PBDEs exposure reduced hydrogen production, and hydrogen accumulation decreased from 17.6 mL/g in blank to 12.3 mL/g with 12.0 mg/Kg PBDEs. PBDEs induced the reactive oxygen species production, which directly led to cell inactivation and reduced hydrogen production. Furthermore, PBDEs decreased ES disintegration, hydrolysis, acidification and homoacetogenic processes and inhibited the activities of enzymes related to hydrogen production. PBDEs also affected the diversity and richness of microbial communities in dark fermentation systems, especially high doses of PBDEs reduced the relative abundance of microorganisms associated with hydrogen production. In conclusion, PBDEs reduce hydrogen generation from ES.

Alkaline fermentation of refinery waste activated sludge mediated by refinery spent caustic for volatile fatty acids production

Volatile fatty acids (VFA), produced from waste activated sludge (WAS), provide unique opportunities for resource recovery in wastewater treatment plants. This study investigates the potential of refinery spent caustic (RSC) on VFA production during refinery WAS (RWAS) alkaline fermentation. The highest VFA yield was 196.3 mg/g-VS at a sludge retention time of 6 days. Amplicon sequencing revealed the enrichment of Soehngenia (20.21%), Bacilli (11.86%), and Brassicibacter (4.17%), which was associated with improved activities of protease (626%) and α-glucosidase (715%). Function prediction analysis confirmed that acetyl-CoA production and fatty acid biosynthesis were enhanced, while fatty acid degradation was inhibited. Accordingly, hydrolysis, acidogenesis, and acetogenesis were improved by 6.87%, 10.67%, and 28.50%, respectively; whereas methanogenesis was inhibited by 28.87%. The sulfate and free ammonia in RSC likely contributed to increased acetic acid production. This study showcases that RWAS alkaline fermentation mediated by RSC for VFA production is the practicable approach.

Alkyl polyglycosides enhanced the dark fermentation of excess sludge and plant waste to produce hydrogen: performance and mechanism

Alkyl polyglycosides (APG), a biodegradable biosurfactant, have been widely used in environmental pollution control. However, the application of APG to enhance anaerobic dark fermentation of excess sludge (ES) and plant waste (PW) to improve hydrogen production has not been reported so far. In order to fill this gap, the effect of APG on hydrogen production from ES and PW was studied in mesophilic (30 °C) environment. The results showed that APG increased the yield of hydrogen, and the recommended dose was 0.15 g/g (calculated as volatile suspended solids), accompanied by 18.7 mL/g. The contribution of APG self-degradation to hydrogen can be ignored. Mechanism investigation revealed that APG promoted the dissolution, hydrolysis, and acidification of complex organic matter, and when the content of APG was 0.15 g/g, the concentration of dissolved chemical oxygen demand (COD) was as high as 3151 mg/L; however, the dissolved concentration of COD in the blank group was only 1548 mg/L. In addition, APG improved the output of volatile fatty acids (VFA). APG promoted the proportion of acetate and butyrate in VFA, which was conducive to hydrogen production. As for the process of methanogenesis, APG reduced the consumption of hydrogen and accumulates hydrogen. This work provides an alternative strategy for the recycling of organic waste and the enhanced generation of hydrogen.