•Capsaicin was completely degraded in anaerobic co-digestion of FW and WAS•Methane can be produced during the degradation of capsaicin•Capsaicin inhibited methane production from anaerobic ...co-digestion of FW and WAS•The presence of capsaicin restrained acetotrophic methanogenesis•Capsaicin promoted the population of complex organic degradation microbes
Anaerobic co-digestion is an attractive option to treat food waste and waste activated sludge, which is increasingly applied in real-world situations. As an active component in Capsicum species being substantially present in food waste in many areas, capsaicin has been recently demonstrated to inhibit the anaerobic co-digestion. However, the interaction between capsaicin and anaerobic co-digestion are still poorly understood. This work therefore aims to deeply understand the fate and impact of capsaicin in the anaerobic co-digestion. Experiment results showed that capsaicin was completely degraded in anaerobic co-digestion by hydroxylation, O-demethylation, dehydrogenation and doubly oxidization, respectively. Although methane was proven to be produced from capsaicin degradation, the increase in capsaicin concentration resulted in decrease in methane yield from the anaerobic co-digestion. With an increase of capsaicin from 2 ± 0.7 to 68 ± 4 mg/g volatile solids (VS), the maximal methane yield decreased from 274.6 ± 9.7 to 188.9 ± 8.4 mL/g VS. The mechanic investigations demonstrated that the presence of capsaicin induced apoptosis, probably by either altering key kinases or decreasing the intracellular NAD+/NADH ratio, which led to significant inhibitions to hydrolysis, acidogenesis, and methanogenesis, especially acetotrophic methanogenesis. Illumina Miseq sequencing analysis exhibited that capsaicin promoted the populations of complex organic degradation microbes such as Escherichia-Shigella and Fonticella but decreased the numbers of anaerobes relevant to hydrolysis, acidogenesis, and methanogenesis such as Bacteroide and Methanobacterium.
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Wastewater treatment plants (WWTPs) are deemed reservoirs of antibiotic resistance genes (ARGs). Bacterial phylogeny can shape the resistome in activated sludge. However, the co-occurrence and ...interaction of ARGs abundance and bacterial communities in different WWTPs located at continental scales are still not comprehensively understood. Here, we applied quantitative PCR and Miseq sequence approaches to unveil the changing profiles of ARGs (sul1, sul2, tetW, tetQ, tetX), intI1 gene, and bacterial communities in 18 geographically distributed WWTPs. The results showed that the average relative abundance of sul1and sul2 genes were 2.08 × 10−1 and 1.32 × 10−1 copies/16S rRNA copies, respectively. The abundance of tetW gene was positively correlated with the Shannon diversity index (H′), while both studied sul genes had significant positive relationship with the intI1gene. The highest average relative abundances of sul1, sul2, tetX, and intI1 genes were found in south region and oxidation ditch system. Network analysis found that 16 bacterial genera co-occurred with tetW gene. Co-occurrence patterns were revealed distinct community interactions between aerobic/anoxic/aerobic and oxidation ditch systems. The redundancy analysis model plot of the bacterial community composition clearly demonstrated that the sludge samples were significant differences among those from the different geographical areas, and the shifts in bacterial community composition were correlated with ARGs. Together, these findings from the present study will highlight the potential risks of ARGs and bacterial populations carrying these ARGs, and enable the development of suitable technique to control the dissemination of ARGs from WWTPs into aquatic environments.
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•ROX can enhance VFA recovery from waste activated sludge.•ROX promoted the disruption of extracellular polymeric substances.•ROX inhibited hydrolysis and methanogenesis ...processes.•ROX is harmful to CH4 production in anaerobic fermentation.
The removal of antibiotics and resistance genes in wastewater treatment plants has attracted widespread attention, but the potential role of residual antibiotics in the disposal of waste activated sludge (WAS) has not been clearly understood. In this study, the effect of roxithromycin (ROX) on volatile fatty acid (VFA) recovery from WAS anaerobic fermentation was investigated. The experimental results showed that ROX made a positive contribution to the production of VFAs. With the increase of ROX dosages from 0 to 100 mg/kg TSS, the maximum accumulation of VFAs increased from 295 to 610 mg COD/L. Mechanism studies revealed that ROX promoted the solubilization of WAS by facilitating the disruption of extracellular polymeric substances. In addition, ROX enhanced the activity of acetate kinase and inhibited the activities of α-glucosidase and coenzyme F420, and showed a stronger inhibitory effect on methane production than the hydrolysis process, thus resulting in an increase in VFA accumulation. These findings provide a new insight for the role of antibiotics in anaerobic fermentation of WAS.
Antibiotic resistance genes (ARGs) and microplastics (MPs) are recognized as emerging contaminants and threats to global human health. Despite both of them being significantly detected in their ...“hotspots”, i.e., waste activated sludge (WAS), rare studies on how MPs affect ARGs and antibiotic-resistant bacteria (ARB) in anaerobic sludge digestion are available. Herein, the fate of ARGs and ARB after exposure to MPs of three dosages (10, 30, and 80 particles/g-TS), three polymer types (LDPE, PET, and PS), and three branching extents (LDPE, LLDPE, and HDPE) in anaerobic sludge digestion was investigated. Metagenomic results indicated that all variants of MPs resulted in an increase of the relative abundance of ARGs in the digester compared to the control. The abundance of ARGs demonstrated a dosage-dependent relationship within the range from 10 to 80 particles/g-TS, resulting in an increase from 4.5 to 27.9% compared to the control. Branching structure and polymer type influence ARG level in the sludge digester as well. Mechanism studies revealed that LDPE selectively enriched potential ARB and ARGs in the surface biofilm, possibly creating a favorable environment for ARB proliferation and ARG exchange. Furthermore, vertical transfer of ARGs was facilitated by LDPE through increasing bacterial cell proliferation accompanied by the enhancement of relevant functional genes. The elevated abundance of mobile genetic elements (MGEs) and ARGs-carrying plasmids also demonstrated that MGE-mediated horizontal transfer was promoted by LDPE at 80 particles/g-TS. This effect was compounded by increased oxidative stress, cell membrane permeability, and cell cohesion, collectively facilitating horizontal ARG transfer. Consequently, both vertical and horizontal transfer of ARGs could be concurrently promoted by LDPE an in anaerobic sludge digester.
Slaughterhouse plants, especially meat and poultry products (MPPs), generate significant quantities of wastewater during the slaughtering process and the cleaning of machinery. The handling and final ...disposal of wastewater from the slaughterhouse is a public and environmental health issue due to its pollution potential. The monitoring of three full-scale buffalo meat-based abattoir effluent treatment plants (ETPs) to remove organic matter and nutrients was conducted at three separate sites in India. Rotary and static screens, an equalization tank, a dissolved air flotation (DAF) system, aeration tanks, and clarifiers were the component unit operations/processes of the wastewater treatment systems. All the treatment plants were operating at an average flow rate of 254 m
3
/d Meem Agro (designed capacity 500 m
3
/d); 427 m
3
/d Al Noor (designed capacity 500 m
3
/d), and 353 m
3
/d International Agro Foods (IAF) plant (designed capacity 750 m
3
/d) for the treatment of slaughterhouse wastewater. The Al Noor and Meem Agro’s ETP consisted of a DAF unit working at the surface-loading rates of 5.7 and 1.48 m3/m
2
h, respectively, applied during the analysis to the DAF system, resulting in 46.5 and 56.8% efficiencies of O&G and SS removal. The ETP of Al Noor and Meem Agro and IAF was loaded at an organic loading rate of 276 kg COD/day, 746 kg COD/day, and 629 kg COD/day, respectively. Performance of ETPs showed that the efficiency of total COD, total BOD, and TSS removal was 97, 98, and 99%; 94, 94, and 93%, and 95, 98, and 99% for Al Noor, Meem Agro, and IAF plants, respectively. The treatment plants’ efficiencies in all three plants for the removal of organic matter surpassed the effluent discharge level (as per Indian standards). Still, it is concluded that the ETPs need to be upgraded by incorporating the advanced wastewater treatment methods for the removal of nutrient concentration from treated effluents.
To understand how to optimize performance of a partially nitrifying plant, the dynamics of
Nitrospira and
Nitrobacter abundance were studied over a 1 year period using quantitative polymerase chain ...reaction (qPCR) and their relative contributions to nitrite oxidation assessed including the affects of temperature and dissolved oxygen (DO). Correlation coefficients linking shifts in the community composition of nitrite-oxidizing bacteria (NOB) to operational or environmental variables indicated
Nitrospira was significantly and negatively correlated to nitrite concentrations (
r = −0.45,
P < 0.01) and DO (
r = −0.46,
P < 0.01), while temperature showed a strong positive correlation (
r = 0.59,
P < 0.0001). However, the
Nitrobacter portion of the total NOB populations showed a positive correlations with DO (
r = 0.38,
P < 0.01) and hydraulic retention time (HRT) (
r = 0.33,
P < 0.05), as well as being negatively correlated with temperature (
r = −0.49,
P < 0.001) suggesting specific niche adaptations within the NOB community.
Nitrospira was dominant being better adapted to the low DO and shorter sludge retention times (SRT) of this plant, while
Nitrobacter increased in abundance during the winter months, when temperatures were lower and DO concentrations higher. Principal component analysis (PCA) results supported these findings by the close proximity of
Nitrospira and temperature biplots of PC1 and PC2 as well as grouping
Nitrobacter, NO
2
−-N, HRT, and DO in the loadings together. The clustering of samples from specific dates also exhibited a strong seasonality.
A system using a two-phase anaerobic configuration (mesophilic/thermophilic) was tested by feeding waste activated sludge (WAS). The first acidogenic stage presented a hydraulic retention time (HRT) ...of 3 days, while the second methanogenic stage had an HRT of 10 days. Both raw and ultrasonically pretreated WAS samples were utilized for the experiment. Previous Fluorescence in Situ Hybridization (FISH) observations, revealed that in the thermophilic phase, the acetoclastic methanogenesis was likely replaced by a nonacetoclastic pathway, namely, syntrophic acetate oxidation (SAO). A modified version of Anaerobic Digestion Model n°1 (ADM1), accounting for the SAO pathway, was implemented and calibrated. The proposed model addressed the relationship between the hydrogen concentration and Gibbs free energy and showed the thermodynamic feasibility of the SAO pathway, while simultaneously highlighting the role played by hydrogenotrophic methanogens in maintaining a sufficiently low hydrogen partial pressure so that the SAO was energetically feasible. The estimated energy loss was estimated to be approximately 20% due to the switch of the microbial pathway from acetoclastic methanogenesis to SAO.
•A two-staged (meso/thermophilic) configuration for WAS digestion is proposed.•Acetoclastic archaea were absent in the thermophilic stage at TAN = 1.4 g L−1.•Syntrophic Acetate Oxidation (SAO) was modeled with a modified ADM1 version.•The model was used to detect the feeding strategy capable to stabilize the process.•The energetic loss due to SAO corresponded to 20% of the acetoclastic pathway.
This paper consists on a global environmental analysis of a waste water treatment (Conventional Activate Sludge System, CAS, designed for 13,200 population equivalent) and some possible additional ...tertiary treatments allowing water reuse to that purified waters (UF and immersed and external Membrane Biological Reactors, MBR). The environmental assessment of these water treatment technologies has been realized by means of the Life Cycle Assessment (LCA) technique, in order to establish with a broad perspective and in a rigorous and objective way the technology that provokes the lowest environmental load. The software SimaPro 5.1, developed by Dutch PRé Consultants, has been used as the LCA analysis tool, and three different evaluation methods—CML 2 baseline 2000, Eco-Points 97 and Eco-Indicator 99—have been applied. The results show that tertiary treatment does not increase significantly the environmental loads but provide new uses for that purified water, thus justifying the intensive use of water reuse techniques in water scarce areas.
The activated sludge (AS) process is a type of suspended growth biological wastewater treatment that is used for treating both municipal sewage and a variety of industrial wastewaters. Economical ...modeling and cost estimation of activated sludge processes are crucial for designing, construction, and forecasting future economical requirements of wastewater treatment plants (WWTPs). In this study, three configurations containing conventional activated sludge (CAS), extended aeration activated sludge (EAAS), and sequencing batch reactor (SBR) processes for a wastewater treatment plant in Tehran city were proposed and the total project construction, operation labor, maintenance, material, chemical, energy and amortization costs of these WWTPs were calculated and compared. Besides, effect of mixed liquor suspended solid (MLSS) amounts on costs of WWTPs was investigated. Results demonstrated that increase of MLSS decreases the total project construction, material and amortization costs of WWTPs containing EAAS and CAS. In addition, increase of this value increases the total operation, maintenance and energy costs, but does not affect chemical cost of WWTPs containing EAAS and CAS.
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