Inhibition Of Methane Production Research Articles

Residual ciprofloxacin in chicken manure inhibits methane production in an anaerobic digestion system

Anaerobic digestion (AD) is commonly used to dispose of laying hen manure. However, veterinary antibiotic residues present in chicken manure may affect the AD process. Here, the effects of three types of veterinary antibiotics commonly used in laying hen breeding on AD were explored. Manures containing antibiotics at two different concentrations were continuously added during AD for 5 days: amoxicillin (HAMX: 145.06 mg/kg, LAMX: 57.88 mg/kg), doxycycline (HDOC: 183.61 mg/kg, LDOC: 98.00 mg/kg), and ciprofloxacin (HCIP: 96.34 mg/kg, LCIP: 40.43 mg/kg). Compared with a control with no veterinary antibiotics, the amoxicillin and doxycycline groups presented no significant effects on biogas production, methane production, VFA concentration, acetic acid concentration or the pH of the AD system (P > 0.05). However, compared with the control, the ciprofloxacin groups presented significantly inhibited biogas and methane production during AD (P < 0.05), and the HCIP and LCIP groups presented significantly decreased biogas (47.82% and 45.37%, respectively) and methane (58.24% and 52.55%, respectively) production (P < 0.05). Moreover, the VFA and acetic acid concentrations of the ciprofloxacin groups were significantly higher than those of control during the entire AD period (P < 0.05), and the pH value at the withdrawal stage was significantly lower than that of the control group (P < 0.01), with no significant difference between the HCIP and LCIP groups (P > 0.05). Our results suggest that ciprofloxacin causes VFA and acetic acid accumulation in AD systems, thereby reducing the pH of the systems and inhibiting methanogen growth, ultimately reducing methane production in the AD systems. These findings contribute to a deeper understanding of the impact of ciprofloxacin on methane production in AD systems and offer some considerations for the application of AD systems.

Enhancement of the anaerobic biodegradation efficiency of azo dye by anthraquinone-loaded biochar biofilm: factors affecting biofilm formation and the enhancement mechanism

Carbon-based materials that serve as microbial carriers, and the role of surface-formed biofilms in anaerobic digestion, merit further investigation. This study explored the role and mechanism behind the biodegradation enhancement of biofilms formed onto anthraquinone-loaded biochar (AQS-BC) surfaces through the anaerobic decolorization process of azo dye Reactive Red 2, and optimized the conditions for AQS-BC biofilm formation. The results indicated that the AQS-BC biofilm system exhibited high treatment efficiency and stability in RR2 anaerobic decolorization. RR2 led to the accumulation of volatile fatty acids (VFAs) and inhibition of methane production, while the presence of AQS increased methane production. The effects of sludge concentration, contact time, carbon source concentration, and RR2 concentration on biofilm maturity were also analyzed. Combining biochemical characteristics, electrochemical properties, surface structure, and microbial community analysis, a mechanism for the anaerobic decolorization of RR2 via AQS-BC as a microbial carrier was proposed. This study provides insights into the roles of biofilms in the anaerobic wastewater treatment processes.Graphical

Enhancing Biogas Production Through the Co-Digestion of Fish Waste (FW) and Water Hyacinth (WH) Using Cow Dung as an Inoculum: Effect of FW/WH Ratio

The current investigation explores biogas production from water hyacinth (WH) and fish waste (FW) with cow dung (CD) as an inoculum source in two scenarios. In the first scenario, the optimization of mono-digestion was performed where the effect of WH/FW (substrates) with CD (inoculum) in varied ratios of 1:1, 1:2, 2:1, and 3:1 was observed to enhance the biogas production. In the second scenario, the optimization of co-digestion using both FW and WH as substrates in different ratios (1:1, 1:2, and 2:1) with a fixed amount of inoculum was studied. The experiments were conducted in 500 mL digesters in duplicate under mesophilic conditions. Under mono-digestion conditions for FW, the digester operating with FW/CD in a 1:2 ratio demonstrated the highest biogas yield of 970 ± 14.1 mL/g VS, containing 610 CH4 mL/g VS, while in WH, the WH/CD ratio of 1:1 exhibited the highest biogas yield of 925 ± 49.4 mL/g VS, with a methane content of 440 CH4 mL/g VS. The co-digestion of the WH/FW ratio (1:1) showcased the highest biogas production of 1655 ± 91.92 mL/g VS, accompanied by 890 ± 70.7 CH4 mL/g VS. This was followed by the 1:2 and 2:1 ratio, yielding 1400 ± 56.5 and 1140 ± 169.7 mL/g VS. of biogas and 775 and 585 CH4 mL/g VS, respectively. The CD and WH mixture at a 1:1 ratio demonstrated the most significant decrease in chemical oxygen demand (COD), reaching 91.68%. COD reductions over 80% in all combinations were observed in all instances. Anaerobic digestion (AD) simulations were validated using the Gompertz model, with high correlation coefficient values (R-squared) above 0.99 for all of the studied ratios, depicting a significant correlation between experimental data and model predictions. The propionic to acetic acid ratio did not cross the threshold level, indicating no inhibition of methane production. ANOVA analysis of biogas production between the co-digestion and mono-digestion of substrates showed non-significant results (p &gt; 0.310 and p &gt; 0.824, respectively), while overall digestion was significant (p &lt; 0.024), indicating efficiency variations among substrates. Paired sample t-tests revealed substantial differences between co-digestion ratios, which were also significant.

Deciphering the Impact of Lignin on Anaerobic Digestion: Focus on Inhibition Mechanisms and Methods for Alleviating Inhibition.

China has abundant lignocellulosic biomass resources. These resources are converted into biogas by anaerobic digestion (AD), which not only realizes the comprehensive utilization of waste resources but also obtains abundant biomass energy. However, the low biodegradability of lignocellulosic biomass caused by the complex structure has seriously hindered its utilization by enzymes and microorganisms, resulting in low biogas production and limited development of biogas engineering. The purpose of this work is to analyze the mechanism of lignin inhibiting AD and summarize the main methods for alleviating inhibition. Based on this, this review examines the factors influencing lignin's inhibition of methane production during AD from two key perspectives: (1) discussing lignin's biodegradability challenges, with a focus on its structure, functional groups, and the impact of lignin content in lignocellulosic biomass on its methanogenic potential, and (2) analyzing lignin's impact on each stage of AD. In addition, we provide insights into future research directions in this field.

Electric stimulation mitigated the mixed microplastic inhibition to anaerobic digestion during wastewater treatment

The presence of mixed microplastics (MPs) in anaerobic wastewater treatment processes has been shown to impede fermentation performance by suppressing microbial activity. Microbial electrosynthesis (MES), with its extensive potential, offers a promising solution for refractory substances management and methane recovery, achieved through the enhancement of microbial metabolism and interspecies electron transfer. This study, therefore, delves into the functional impacts and the microbial response to MES in the remediation of wastewater contaminated with mixed-MPs. Results indicated that mixed-MPs could inhibit methane production (−52.38%) and substance removal (−26.59%), and MES could effectively mitigate this inhibitory effect (−22.86%, −19.01%). Concurrently, MES also boosts enzymatic activities pivotal for electron transfer, such as cytochrome c and nicotinamide adenine dinucleotide (NADH), as well as those linked to energy metabolism like adenosine triphosphate (ATP). Furthermore, MES bolsters microbial resistance to mixed-MPs, as evidenced by an increase in extracellular polymeric substances (EPS), albeit with a minor rise in reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release. Correspondingly, electric stimulation promoted the enrichment of functional microorganisms associated with fermentation, acetate production, electrogenesis, and methanogenesis, and stimulated elevated expression levels of genes related to methane metabolism. Notably, the Methanothrix-mediated acetoclastic pathway emerges as the predominant methanogenic route, succeeded by the Methanobacterium-driven hydrogenotrophic pathway. Lastly, the study underscores the supportive role of applied voltage and carriers in energy metabolism and substance transport, which are associated with methanogenesis. Overall, MES demonstrates efficacy in mitigating the biotoxicity induced by mixed-MPs exposure and in enhancing anaerobic wastewater treatment and methane recovery.

Evolution mechanism of microbial community structure and metabolic activity in aquatic nutrient-poor sedimentary environments driven by 17β-estradiol pollution.

17β-Estradiol (E2) is a novel micro-pollutant that is widely distributed in aquatic sediments and has a universal toxicological effect on aquatic organisms. However, its ecological impact on aquatic microorganisms is not yet clear. In this study, we designed a simulation system for oligotrophic water deposition in the laboratory, analyzed the impact of different concentrations of E2 pollution on the carbon metabolism activity (carbon gas emission rate) of water microorganisms. Based on high-throughput sequencing results, we revealed the impact of E2 pollution on the community structure succession and metabolic function of bacteria, archaea, and methanogens in the simulated system, explored the impact mechanism of E2 pollution on microbial carbon metabolism in water bodies. Our results suggested that E2 significantly impacts the bacterial and archaeal community rather than the methanogen community, thereby indirectly inhibiting methane production. The achievements will bridge the theoretical gap between estrogen metabolism and carbon metabolism in sedimentary environments and contribute to enriching the ecological toxicology theory of steroid estrogen.

A novel strategy combining hydrogenotrophic methanogens' bioaugmentation and biochar biostimulation for simultaneous polycyclic aromatic hydrocarbon biodegradation and bioenergy recovery.

A novel strategy combining bioaugmentation using methanogenic archaea and biostimulation using biochar was proposed for the first time to obtain simultaneous improvement of mixed PAHs' anaerobic biodegradation and bioenergy production. The results showed that the addition of PHAs immediately resulted in inhibition in methane production and accumulation of VFA, indicating that PHAs are more toxic to methanogens than the acetogenic bacteria. The coupling of biochar with hydrogenotrophic methanogen alleviated the inhibitory effects of PAHs, allowing the anaerobic fermentation system to recover its methane production capability rapidly. Compared to the Fe3+ + bioaugmentation group, the biochar + bioaugmentation group exhibited a 7.5% higher restored cumulative methane production. This coupling strategy ultimately facilitated the degradation of most PAHs, achieving a removal rate of over 90%. Moreover, the coupled biochar and bioaugmentation induced significant changes in the archaeal community structure. Direct interspecies electron guilds (i.e., Streptococcus and Methanosarcina) were enriched in the presence of biochar and bioaugmentation, responsible for prominent PAH removal and methane recovery. This study demonstrated the feasibility of simultaneous PAH biodegradation and bioenergy production using electron acceptor and enriched microorganisms.

The Bifidobacterium-dominated fecal microbiome in dairy calves shapes the characteristic growth phenotype of host

The dominant bacteria in the hindgut of calves play an important role in their growth and health, which could even lead to lifelong consequences. However, the identification of core probiotics in the hindgut and its mechanism regulating host growth remain unclear. Here, a total of 1045 fecal samples were analyzed by 16S rRNA gene sequencing from the 408 Holstein dairy calves at the age of 0, 14, 28, 42, 56, and 70 days to characterize the dynamic changes of core taxa. Moreover, the mechanisms of nutrient metabolism of calf growth regulated by core bacteria were investigated using multi-omics analyses. Finally, fecal microbiota transplantation (FMT) in mice were conducted to illustrate the potential beneficial effects of core bacteria. Four calf enterotypes were identified and enterotypes dominated by Bifidobacterium and Oscillospiraceae_UCG-005 were representative. The frequency of enterotype conversion shifted from variable to stable. The close relationship observed between phenotype and enterotype, revealing a potential pro-growth effect of Bifidobacterium, might be implemented by promoting the use of carbohydrate, activating the synthesis of volatile fatty acids, amino acids and vitamin B6, and inhibiting methane production in the hindgut. The FMT results indicated the beneficial effect of Bifidobacterium on host growth and hindgut development. These results support the notion that the Bifidobacterium-dominated fecal microbiome would be an important driving force for promoting the host growth in the early life. Our findings provide new insights into the potential probiotic mining and application strategies to promote the growth of young animals or improve their growth retardation.

Impact of aging of primary and secondary polystyrene nanoplastics on the transmission of antibiotic resistance genes in anaerobic digestion

Sewage sludge is a significant reservoir of nano/microplastics (NPs/MPs) and antibiotic resistance genes (ARGs). Research has revealed that NPs/MPs may exert an inhibitory effect on anaerobic digestion (AD) of sludge. Moreover, NPs/MPs can influence microbial community diversity and composition, potentially increasing ARGs dissemination. The morphological changes to NPs/MPs surface due to aging contribute to modifying hydrophobic properties. To date, there is limited comprehension regarding how various surface properties of NPs influence ARGs dissemination during AD. This study investigated the impact of primary aged/non-aged and secondary aged/non-aged polystyrene nanoplastics (PSNPs) on ARGs and mobile genetic elements (MGEs) propagation during AD. The findings indicated that the UV-aging process resulted in surface oxidation and distinct morphological characteristics in both primary and secondary PSNPs, while the surface oxidation effect was more pronounced in the secondary aged PSNPs. High concentrations (150 μg/L) of primary and secondary PSNPs inhibited methane production, with secondary PSNPs causing greater inhibition by 16 to 20 % compared to control. In contrast, low concentration (25 μg/L) had negligible or slightly positive effects on methane production. PSNPs at 150 μg/L reduced total VFA concentration, indicating an inhibitory effect on the fermentation step in the AD process. Primary and secondary PSNPs exhibited changes in EPS characteristics. ARGs abundance was enriched in reactors amended with PSNPs, with the highest abundance of 8.54 × 105 copies/g sludge observed in the secondary aged PSNPs (150 μg/L) reactor. Reactors exposed to aged PSNPs exhibited a relatively higher abundance of ARGs compared to reactors exposed to non-aged PSNPs. Exposure to PSNPs increased the microbial community diversity within the digesters and triggered the enrichment of Comamonadaceae and Syntrophaceae, belonging to Proteobacteria phylum. On the other hand, archaeal communities tended to shift towards hydrogenotrophic methanogens in PSNPs reactors. The correlation analysis showed that Comamonadaceae were positively correlated with the majority of ARGs and intl1. A positive correlation was observed between MGEs and most ARGs, suggesting that the increased proliferation of ARGs under PSNPs exposure may be linked to the abundance of MGEs, which in turn promotes the growth of hosts carrying ARGs. These findings suggest that aged and non-aged NPs could substantially impact the spread of ARGs and MGEs, which also led to notable alterations in the composition of the microbial community. Overall, this study provides valuable insights into the multifaceted impacts of PSNPs with various characteristics on AD processes, microbial communities, and ARGs proliferation, highlighting the urgent need for comprehensive assessments of NPs pollutants in the environment.

Effect of Pretreatment of Anaerobic Acid Fermentation Sludge from Mixed Swine Wastewater and Food Waste Leachate on Biohydrogen Generation

Objectives:This study aims to investigate the effects of heat shock and 2-bromoethanesulfonate (2-BES) injection on hydrogen production and methanogens inhibition in anaerobic acid fermenter sludge and methane fermenter sludge using mixed swine wastewater and food waste leachate as substrates. Additionally, the analysis of biogas, fermentation products such as volatile fatty acids (VFAs) and alcohols, and microbial community changes were conducted to derive efficient pretreatment conditions for anaerobic hydrogen generation.Methods:Sludge samples were collected from two-phase anaerobic digesters treating swine wastewater and food waste leachate. Heat shock (90°C, 15 min) and 2-BES injection (1, 5, 10, 50, and 100 mmol/L) pretreatments were applied to the each sludge, along with control reactor without pretreatment before anaerobic digestion. Batch experiments were conducted at 30°C to assess biogas, organic compounds (COD, VS, VFAs, and alcohols), and microbial community composition.Results and Discussion:In methanogenic sludge, hydrogen gas was not produced under all conditions, but heat shock method inhibited methane production more effectively than 2-BES injection method. As the concentration of 2-BES increased, methane production decreased. Conversely, hydrogen was produced from the all acid fermentation sludges, mainly attributed to the butyric acid production by dominant Clostridium spp., but the pattern of biogas production varied over time. In the experimental group injected with 2-BES, even at a low concentration of 1 mmol/L, methane gas did not produce due to the inhibition of methanogens. However, in the control group, produced hydrogen was entirely converted to methane by hydrogenotrophic methanogens such as Methanobrevibacter and Methanosphaera. The heat shock group showed delayed hydrogen production due to prolonged lag phase of hydrogen-producing bacteria, with hydrogenotrophic methanogen metabolism starting after 12 days. Heat shock and 2-BES injection reduced bacterial diversity in the acid fermentation process compared to the initial stage.Conclusion:For efficient anaerobic hydrogen production from swine wastewater and food waste leachate, 2-BES injection into the acid fermentation sludge was found to be a preferable method over heat shock, considering hydrogen production efficiency and sustained methanogen inhibition. Further research is needed to find more economical and efficient pretreatment methods and operational strategies considering subsequent methane production processes for practical application in the field.

Regulatory mechanisms of biochar alleviating ammonia inhibition to methanogenesis during long-term operation of anaerobic membrane bioreactor treating swine wastewater

Anaerobic Membrane Bioreactor (AnMBR) is regarded as an advanced technology for the anaerobic digestion (AD) of swine wastewater. However, the high ammonia level in swine wastewater is a crucial issue to inhibit methane production. This study aimed to establish a biochar-assisted AnMBR (BC) to mitigate ammonia inhibition during AD of swine wastewater. As the gradual ammonia loading rate (ALR) increased from 3.0 g/L to 6.0 g/L, BC maintained methane yields ranging from 74.9 % to 48.1 %, which were 9.1 % to 33.3 % higher than those of a regular AnMBR (CT). Moreover, the COD removal efficiency steadily surpassed 80 %. Although the increase in ALR had negative effects on both BC and CT, the presence of biochar enhanced the methanogenic activity of bulk sludge, specifically accelerating processes involved in syntrophic acetate oxidation and CO2-reducing methanogenesis under high ALR conditions. Integrated characterizations using PARAFAC-based EPS analysis, INT-ETS, and WO3 probe-based extracellular electron transfer (EET) activities indicated that biochar stimulated the secretion of humic-like and aromatic protein-like compounds in the TB-EPS, which likely established a redox-active matrix with biochar between VFA oxidation bacteria and CO2-reducing methanogens to facilitate EET. This potentially made the syntrophic VFA oxidation with favorably thermodynamic kinetics under high ammonia stress. Furthermore, the analysis of microbial community coupling prediction of functional genes associated with methanogenic pathways revealed that as ALR increased, the presence of biochar re-shaped the microbial communities by enriching electro-active Syntrophomonas and Methanosarcina/Methanospirillum, which mainly triggering EET-based syntrophic methanogenesis by accelerating the intracellular enzymatic transformation from Formylmethanofuran to 5,10-Methylenetetrahydromethanopterin process. We expect the major findings of this study provide new insights to understand the mechanisms of biochar alleviating ammonia inhibition during long-term operation of AnMBR.

Isolation of Bacillus velezensis from Silage and Its Effect on Aerobic Stability and In Vitro Methane Production of Whole-Plant Corn Silage

Once a silo has been opened, the silage inside will face challenges such as aerobic deterioration, rot, and contamination. Biocontrol bacteria, as a kind of biological antiseptic, are highly effective and natural and are gaining increasing attention. This study aimed to screen a strain with anti-microbial activity against silage spoilage microorganisms and examine its effects on the fermentation quality, aerobic stability, in vitro digestion, and methane production of silage. Lactic acid bacteria, pathogenic and rot-causing microorganisms, were used as indicators to screen the strains for putrefactive silage. The bacteriostatic spectrum, growth performance, and tolerance to the silage environment of the strain were tested. A strain named D-2 was screened from rotten whole-plant corn silage and identified as Bacillus velezensis through physiological and biochemical tests as well as 16S rDNA sequencing. This study found that D-2 exhibits antibacterial effects on several microorganisms, including Escherichia coli, Staphylococcus aureus, Salmonella enteritidis, Aspergillus niger, Saccharomyces cerevisiae, Fusarium oxysporum, and Fusarium graminearum. However, it has no adverse effect on Lactobacillus reuteri, Enterococcus faecium, or Lactobacillus casei. D-2 can attain a stable stage within 10 h and withstand temperatures of up to 70 °C. Moreover, this study found that D-2 had a high survival rate of over 97% after 48 h in a lactic acid environment with pH 4. Freshly chopped whole-plant corn was inoculated without or with D-2 and ensiled for 60 days. The results show that D-2 inoculations increase the content of water-soluble carbohydrates, acetic acid, and propionic acid in the silage and decrease the number of yeasts and molds, the NH4+-N/TN ratio, and the pH. We also found that fermenting whole-plant corn with D-2 significantly increased the in vitro digestibility and the propionic acid content, while also significantly inhibiting methane production. After being exposed to air for 10 days, D-2 can still effectively reduce the total number of yeasts and molds, prevent the decrease in lactic acid bacteria, and inhibit the increase in the pH and NH4+-N/TN ratio of silage products. Overall, D-2 is resistant to pathogenic and rot-causing microorganisms, allowing for easy adaptation to silage production conditions. D-2 can effectively improve aerobic stability and reduce losses in the nutritional value of silage, indicating possible applications for the prevention of silage rot and methane production.

Tris (2-chloroethyl) phosphate presence inhibits methane production from anaerobic digestion: Alterations in organic matter transformation, cell physiological status, and microbial community

Organophosphate flame retardants (OPFRs) are widely used in consumer products, leading to their unavoidable release into the environment, especially accumulation in anaerobic environments and posing potential risks. This study focused on Tris(2-chloroethyl) phosphate (TCEP), a representative OPFR, to investigate its effects on carbon transformation and methane production in anaerobic digestion. Increasing TCEP concentrations from control to 16 mg/L resulted in decreased cumulative methane yield (from 235.4 to 196.3 mL/g COD) and maximum daily methane yield (from 40.8 to 16.17 mL/(g COD·d)), along with an extended optimal anaerobic digestion time (from 15 to 20 days). Mechanistic analysis revealed TCEP binding to tyrosine-like proteins in extracellular polymeric substances, causing cell membrane integrity impairment. The TCEP-caused alteration of the physiological status of cells was demonstrated to be a significant contribution to the inhibited bioprocesses including acidogenesis, acetogenesis, and methanogenesis. Illumina Miseq sequencing showed TCEP decreasing the relative abundance of acidogens (58.8 % to 46.0 %) and acetogens (7.1 % to 5.0 %), partly shifting the methanogenesis pathway from acetoclastic to hydrogenotrophic methanogenesis. These findings enhance understanding of TCEP's impact on anaerobic digestion, emphasizing the environmental risk associated with its continued accumulation.

Effect of Biochar on Anaerobic Co-Digestion of Untreated Sewage Sludge with Municipal Organic Waste under Mesophilic Conditions

Anaerobic digestion (AD) is a biological process that occurs in the limited presence of oxygen. This process involves various difficulties during the operation, such as acidification and increased concentration of volatile fatty acids, which can inhibit methane production. Therefore, in this work, the impact of biochar on the co-digestion of untreated sludge and residual biomass under mesophilic conditions was studied. For the production of biochar, the gasification process was used at different temperatures: 759 °C (BL), 798 °C (BM), and 888 °C (BH). This biochar was added in concentrations of 0 g/L, 3.33 g/L, and 6.67 g/L at the beginning of the co-digestion process. The results showed that a concentration of 6.67 g/L with BH biochar increased the PBM by 18% compared to the control sample and reduced the chemical oxygen demand (COD) by 88%. In addition, there was a reduction of volatile fatty acids (VFA) of 42.75%. Furthermore, FTIR analysis demonstrated that biochar has appropriate functional groups for this process. These data suggest a good interaction of biochar with the mixture of sludge and municipal waste, indicating that biochar can improve the anaerobic co-digestion of untreated sludge and municipal waste.

Plasticizers inhibit food waste anaerobic digestion performance by affecting microbial succession and metabolism

The widely existed plastic additives plasticizers in organic wastes possibly pose negative influences on anaerobic digestion (AD) performance, the direct evidence about the effects of plasticizers on AD performance is still lacking. This study evaluated the influencing mechanism of two typical plasticizers bisphenol A (BPA) and dioctyl phthalate on the whole AD process. Results indicated that plasticizers addition inhibited methane production, and the inhibiting effects were reinforced with the increase of concentration. By contrast, 50 mg/L BPA exhibited the strongest inhibition on methane production. Physicochemical analysis showed plasticizers inhibited the metabolism efficiency of soluble polysaccharide and volatile fatty acids. Microbial communities analyses suggested that plasticizers inhibited the direct interspecies electron transfer participators of methanogenic archaea (especially Methanosarcina) and syntrophic bacteria. Furthermore, plasticizers inhibited the methane metabolisms, key coenzymes (CoB, CoM, CoF420 and methanofuran) biosynthesis and the metabolisms of major organic matters. This study shed light on the effects of plasticizers on AD performance and provided new insights for assessing the influences of plasticizers or plastic additives on the disposal of organic wastes.

Comparing the effects of Al-based coagulants in waste activated sludge anaerobic digestion: Methane yield, kinetics and sludge implications

Due to its effectiveness and ease of application, the process of flocculation and coagulation is often used for pollution removal in wastewater treatment. Most of these coagulants precipitate and accumulate in waste activated sludge (WAS), and could negatively affect sludge treatments, as observed for anaerobic digestion. Nowadays, wastewater treatment plants (WWTPs) are widely discussed because of the current paradigm shift from linear to circular economy, and the treatments performed at the facility should be planned to avoid or reduce adverse effects on other processes. The aim of this study was to compare the impact of poly aluminum chloride (PAC) and aluminum sulfate (AS) on WAS anaerobic digestion, by feeding replicate serum reactors with different levels of coagulant (5, 10 and 20 mg Al/g TS). Reactors without the addition of any coagulants represented the control group. Results revealed that Al-based coagulants inhibited methane production, which decreased as the coagulant addition increased. The inhibition was much more severe in AS-conditioned reactors, showing average reductions in methane yield from 14.4 to 31.7%, compared to the control (167.76 ± 1.88 mL CH4/g VS). Analytical analysis, FTIR and SEM investigations revealed that the addition of coagulants affected the initial conditions of the anaerobic reactors, penalizing the solubilization, hydrolysis and acidogenesis phases. Furthermore, the massive formation of H2S in AS-conditioned reactors played a key role in the suppression of methane phase. On the other hand, the use of coagulant can promote the accumulation and recovery of nutrient in WAS, especially in terms of phosphorus. Our findings will expand research knowledge in this field and guide stakeholders in the choice of coagulants at full scale plant. Future research should focus on reducing the effect of coagulants on methane production by modifying or testing new types of flocculants.

Thermal hydrolysis alleviates polyethylene microplastic-induced stress in anaerobic digestion of waste activated sludge

Microplastics are known to negatively affect anaerobic digestion (AD) of waste activated sludge. However, whether thermal hydrolysis (TH) pretreatment alters the impact of microplastics on sludge AD remains unknown. Herein, the effect of TH on the impact of polyethylene (PE) microplastics in sludge AD was investigated. The results showed that the inhibition of methane production by PE at 100 particles/g total solids (TS) was reduced by 31.4% from 12.1% to 8.3% after TH at 170 °C for 30 min. Mechanism analysis indicated TH reduced the potential for reactive oxygen species production induced by PE, resulting in a 29.1 ± 5.5% reduction in cell viability loss. In addition, additive leaching increased as a result of rapid aging of PE microplastics by TH. Acetyl tri-n-butyl citrate (ATBC) release from PE with 10 and 100 particles/g TS increased 11.5-fold and 8.6-fold after TH to 68.2 ± 5.5 μg/L and 124.0 ± 5.1 μg/L, respectively. ATBC at 124.0 μg/L increased methane production by 21.4%. The released ATBC enriched SBR1031 and Euryarchaeota, which facilitate the degradation of proteins and promote methane production. This study reveals the overestimated impact of PE microplastics in sludge AD and provides new insights into the PE microplastics-induced impact in practical sludge treatment and anaerobic biological processes.

The Potential of Ozonation to Reduce Impact of Waste Sludge-Entrapped Microplastics to Biogas Production

ABSTRACT Due to low degradability of plastic materials, high usage, and low cost, microplastics (MPs) is becoming ubiquitous environmental pollutant. Wastewater treatment plants (WWTP) are one of main sources, where most of the MPs from wastewaters ends in waste sludge. Anaerobic digestion is one of most promised techniques of waste sludge management. The aim of this paper was to evaluate the impact of polyethylene terephthalate (PET) and polypropylene (PP) microplastics in the waste sludge with and without ozonation as possible pretreatment, on biogas and methane production with OxiTop® method. In the first set of experiments, PET inhibited (up to 6% at 0.1 g L−1) or promoted (up to 3% at 1 g L−1) methane production but increased cumulative biogas production (up to 38% at 0.5 g L−1). PP inhibited methane production (up to 5% at 0.5 g L−1) but its impact on biogas production was dependent upon concentration of MPs added. In the second set of experiments, pretreatment of non-contaminated waste sludge by ozonation (3.54 gozone h−1) inhibited methane yield. Longer time of ozonation of PP-contaminated waste sludge reduced inhibition of methane yield, while in the case of PET-contaminated waste sludge, it was increased.

Influence of Inoculum Thermal Pretreatment Time on Hydrogen Production in Dark Fermentation

Dark fermentation (DF) of kitchen waste (KW) is a promising technology for the production of renewable biohydrogen. It can be both a method of obtaining clean energy and a sustainable waste management. Despite its potential, this process requires further research to improve efficiency. The aim of the research was to test the effect of thermal pretreatment of the inoculum on H2 and volatile fatty acids (VFAs) production in the DF process. The process was carried out at 37 °C, in batch mode. The digested sludge from the Group Wastewater Treatment Plant in Lodz was used as inoculum. KW from households was used as substrate. The inoculum was pre-treated at 70 °C for 15 and 30 min. Two control reference experiments were also used. The first without the inoculum, and the second without heating the inoculum. The thermal pretreatment inhibited methane production and increased hydrogen production. After the thermal pretreatment, the amount of CO2 produced during the process decreased compared to the bioreactor without inoculum pretreatment. Additionally, the main VFAs in the samples with pretreated inoculum were acetic and butyric acids, which are associated with hydrogen production in the biochemical pathways of the DF process. However, the time of thermal pretreatment had no significant effect on H2 production.

Effects of food to inoculum ratio and ultrasound pre-treatment on biogas production from dissolved air flotation waste from dairy industry

Dissolved air flotation (DAF) waste, a byproduct with high lipid content separated from dairy wastewater, is disposed of by land spreading and causing environmental pollution. To develop a sustainable treatment for DAF waste, this study investigated the effects of food to inoculum (F/I) ratio and ultrasound pre-treatment on the anaerobic digestion of DAF waste. The biochemical methane potential (BMP) of tested DAF waste ranged from 436–566 mL CH4/g VSfed. Increasing the F/I ratio (>1.0) inhibited methane production due to long chain fatty acids (LCFA) accumulation, which high concentrations of oleate inhibited methanogenesis and delayed palmitate degradation. Ultrasound pre-treatment with 30 min pulse (10 s on/ 10 s off) and 15 min continuous operations increased soluble chemical oxygen demand in DAF waste by 82% and 52%, respectively. Moreover, continuous sonication removed 38% of LCFA due to the implosion of cavitation bubbles. The BMP of DAF waste increased by 36% after sonication with F/I ratio 3.0. However, the lag time of methane production was prolonged after sonication due to the fast release of LCFA to the bulk solution. By implementing ultrasound pre-treatment and optimizing the F/I ratio, the energy potential of DAF waste can be harnessed, leading to more sustainable practices in dairy production.