Minimizing extracellular DNA improves the precision of microbial community dynamic analysis in response to thermal hydrolysis

A new perspective on the simultaneous removal of nitrogen, tetracycline, and phosphorus by moving bed biofilm reactor under co-metabolic substances

With the burgeoning growth of aquaculture industry, high concentration of NH4+-N, phosphorus and tetracycline are the prevalent pollutants in aquaculture wastewater posing a significant health risk to aquatic organisms. Therefore, an effective method for treating aquaculture wastewater should be urgently explored. Simultaneous removal of NH4+-N, phosphorus, tetracycline, and chemical oxygen demand (COD) in aquaculture wastewater was developed by moving bed biofilm reactor (MBBR) under co-metabolic substances. The result showed that co-metabolism substances had different effects on MBBR performance, and 79.4 % of tetracycline, 68.2 % of NH4+-N, 61.3 % of total nitrogen, 88.3 % of COD, and 38.1 % of total phosphorus (TP) were synchronously removed with sodium acetate as a co-metabolic carbon source. Protein (PN), polysaccharide (PS), and electron transfer system activity were used to evaluate the MBBR performances, suggesting that PN/PS ratio was 1.48, 0.91, 1.07, 3.58, and 0.79 at phases I-V. Additionally, a mode of tetracycline degradation and TP removal was explored, and the cell apoptosis was evaluated by flow cytometry. The result suggested that 74 %, 83 %, and 83 % of tetracycline were degraded by extracellular extracts, intracellular extracts, and cell debris, and there was no difference between extracts and non-enzyme in TP removal. The ratio of viable and dead cells from biofilm reached 33.3 % and 7.68 % with sodium acetate as a co-metabolic carbon source. Furthermore, Proteobacteria and Bacteroidetes in biofilm were identified as the dominant phyla for tetracycline and nutrients removal. This study provides a new strategy for tetracycline and nutrients removal from aquaculture wastewater through co-metabolism.

Proteinase K impact on anaerobic co-digestion of modified biodegradable plastic and food waste: Step-by-step analysis with microorganism

This study was designed to explore the key impact of Proteinase K (PK) on every step of anaerobic co-digestion. The results of step-by-step experiments indicated that PK promoted the hydrolysis of biodegradable plastic by initiating self-hydrolysis reactions, directly promoting the hydrolysis step of anaerobic co-digestion. Subsequently, PK indirectly promoted the acidogenesis and acetogenesis steps by impacting the proliferation of acid-producing bacteria. Besides, it could also hydrolyze PLA. Thus, the lactic acid content peaked at 255.7 mg/L on the 5th day, representing an increase of 35.9 % compared to the condition without PK. Finally, PK indirectly promoted the methanogenesis step through its impact on the composition of methanogenic bacteria. This led to more food waste being digested into methane, 41.5 % compared to the condition without PK. This work served as an essential foundation for advancing the application of PK modified BP as a replacement for traditional plastics.

Effects of ammonia nitrogen and organic carbon availability on microbial community structure and ecological interactions in a full-scale partial nitritation and anammox (PN/A) system

Nutrient availability significantly impacts microbial biosynthesis, cell growth, and cell cycle progression. In this study, a full-scale plug-flow partial nitritation/anammox (PN/A) system was used to investigate variations in the microbial community structure in both immobilized carriers and flocs, as well as a gradual decrease in nutrient availability from upstream to downstream. We found that reduced ammonia nitrogen (from 150.4 to 30.6 mg/L) and organic carbon (from 415.7 to 342.8 mg/L) availability significantly lowered microbial diversity and altered microbial communities in biofilms other than flocs from upstream to downstream. The abundance of all anammox bacteria increased by 1.97 times, from 3.25 × 1010 to 6.40 × 1010 copies per gram of wet sludge, in the biofilm core microbiome. Furthermore, from upstream to downstream, taxa with lower ribosomal RNA operon copy numbers were consistently enriched in both biofilm and floc communities, indicating that slow-growing microorganisms are more likely to be enriched in low-nutrient environments. Rare taxa with a relative abundance of less than 0.1% exhibited unique metabolic functions, including amino acid, carbohydrate, cofactor, and vitamin metabolisms, which was inferred by PICRUST2 and persisted across the nutrient gradient in both the biofilm and floc communities. Despite their low abundance, they may play important roles in mediating the stability and function of the PN/A system. Overall, the results demonstrate the impact of a naturally formed ammonia nitrogen and organic carbon gradient in a full-scale plug-flow PN/A installation on nutrient availability and its effects on microbial diversity, community composition, and microbial interactions, which expands our fundamental understanding of this energy-efficient and promising biotechnology for treating high-strength ammonium wastewater.

Effects of incineration leachate on anaerobic digestion of excess sludge and the related mechanisms

Anaerobic digestion (AD) refers to a reliable channel for energy recovery from organics. However, the digestion efficiency of excess sludge (ES) has been unsatisfactory since there are defects relating to ES hydrolysis. Therefore, this study explored a method to improve the anaerobic digestion of ES, which could simultaneously treat ES and incineration leachate, and revealed the potential mechanism of AD process. As the investigation was conducted on the influences exerted by incineration leachate on the four phases (i.e., solubilization, methanogenesis, acidogenesis and hydrolysis) of ES anaerobic digestion, and the effect mechanism. According to obtained results, adding appropriate amounts of incineration leachate could facilitate the steps of solubilization, hydrolysis, acidogenesis and methanogenesis of ES. The hydrolysis and acidogenesis efficiency in the leachate added digesters were 5.7%-17.1% and 13%-45% higher than that of the control digester, respectively. Meanwhile, cumulative methane yields (CMY) were 27-86 mL/gVS higher than that in the control digester. Besides, the sludge floc stability was reduced by the leachate with the decrease in the median particle size (MPS) and apparent activation energy (AAE) of the sludge. According to microbial community and diversity analysis, adding incineration leachate increased the relative abundance of hydrolytic-acidification bacteria in the digesters and the relative abundance of Methanosaeta and Methanosarcina. Thus, the digestive performance exhibited by the leachate participated system was improved. These mentioned findings may provide an approach for treating ES and incineration leachate in practical engineering.

Implications for mitigation of antibiotic resistance: Differential response of intracellular and extracellular antibiotic resistance genes to sludge fermentation coupled with thermal hydrolysis

Thermal hydrolysis pretreatment (THP) can effectively remove the antibiotic resistance genes (ARGs) from sewage sludge, but the rebounding effects in the subsequent anaerobic fermentation are often observed. The purpose of this study was to elucidate the distribution and fate of intracellular and extracellular ARGs (iARGs and eARGs) in the sludge acidogenic fermentation process coupled with THP. Our results revealed that THP significantly reduced the absolute abundance of total ARGs in raw sludge but increased eARGs by 0.3-1.4 log units under practical conditions (140 °C for 30 min). There is no significant difference in the removal of total ARGs between the two acidogenic fermenters receiving raw and hydrolyzed sludge, with iARGs prevailing in the produced biosolids. The succession of bacterial community and the co-occurrence relationships among ARG type, mobile genetic elements and bacterial taxa were observed, suggesting a phylogenetic basis for the iARGs patterns in fermented sludge. However, eARGs were susceptible to biodegradation with a half-life of 2.34 h and they contributed limitedly to the ARGs propagation through transformation. These findings suggest an emphasis on the mitigation of iARGs during the acidogenic fermentation of sludge, which would be achieved by lowering the richness and physicochemical destruction of potential hosts.

Aged landfill leachate enhances anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) is considered as a sustainable pathway to recover energy from organic wastes, but the digestive efficiency for waste activated sludge (WAS) is not as expected due to the limitations in WAS hydrolysis. This study proposes an effective strategy to simultaneously treat WAS and landfill leachate, aiming to promote WAS hydrolysis and enhance organics converting to methane. The effects of landfill leachate on the four stages (i.e., solubilization, hydrolysis, acidogenesis, and methanogenesis) of AD of WAS, as well as the effect mechanisms were investigated. Results showed that adding appropriate amounts of landfill leachate could promote the steps of solubilization, hydrolysis and acidogenesis of WAS, but had no-effect on methanogenesis. The hydrolysis and acidogenesis efficiency in the leachate added digesters were 2.0%-8.4% and 35.2%-72.7% higher than the control digester. Mechanism studies indicated that humic acid (HA) contained in the leachate was conducive to the processes of both hydrolysis and acidogenesis, but detrimental to the methanogenesis. Effects of heavy metals (HMs) on AD of WAS was also dose-dependent. Digestive performance was inhibited by excessive HMs but promoted by moderate dosages. Humic acid and metal ions tend to interact to form complexes, and thus relieve their each inhibition effects. It is also found that the stability of sludge flocs was reduced by the leachate through reducing both apparent activation energy (AAE) and median particle size (MPS) of the sludge. Microbial community and diversity results revealed that the relative abundance of microbes responsible for hydrolysis and acidogenesis increased when landfill leachate was present. This research provides a more technically and economically feasible approach to co-treating and co-utilizing WAS and landfill leachate.

Microbial analysis and enrichment of anaerobic phenol and p-cresol degrading consortia with addition of AQDS

Quinones and humus are ubiquitous in the biosphere and play an important role in the anaerobic biodegradation and biotransformation of organic acids, poisonous compounds as well as inorganic compounds. The impact of humic model compound, anthraquinone-2, 6-disulfonate (AQDS) on anaerobic phenol and p-cresol degradation were studied. Four methanogenic AQDS-free phenol and p-cresol enrichments and two phenol-AQDS enrichments were obtained using two sludges with potential biodegradability of phenol and cresol isomers as inoculum. 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that syntrophic aromatic compound degrading bacterium Syntrophorhabdus aromaticivorans was dominant in four AQDS-free enrichments, whereas phenol degrading Cryptanaerobacter phenolicus was dominant in two phenol-AQDS enrichments. Neither co-culture of S. aromaticivorans with Methanospirillum hungatei nor two phenol-AQDS enrichments could metabolize phenol using AQDS as the terminal electron acceptor. Further degradation experiments suggested that C. phenolicus related microbes in two phenol-AQDS enrichments were responsible for the conversion of phenol to benzoate, and benzoate was further degraded by benzoate degraders of Syntrophus aciditrophicus or Sporotomaculum syntrophicum to acetate.

The effects of C/N (10-25) on the relationship of substrates, metabolites, and microorganisms in "inhibited steady-state" of anaerobic digestion

The carbon/nitrogen ratio (C/N) is a key parameter that affects the performance of anaerobic digestion (AD). Recent AD research has focused on optimizing the C/N of feedstock. The so-called "inhibited steady-state" refers to a special state of ammonia inhibition of AD that often occurs at low-C/N (below 25) when degradable nitrogen-rich substrates, such as livestock manure, are used as feedstock. However, the mechanism behind the "inhibited steady-state" is still unknown. In the current study, co-digestion and recirculation were used to create a C/N gradient in the influent to explore the relationship between substrates, metabolites, and microorganisms in the "inhibited steady-state." Data were collected at the macro, microbial, and genetic levels. Three CSTRs were successfully made run into the "inhibited steady-state" using influent C/Ns of 10-12. Digestion performance levels of R10-R12 were low and stable, transitioning from an aceticlastic methane-producing pathway to a hydrogenotrophic pathway as the C/N gradually decreased. As the abundance of the hydrogenophilic methanogens increased, the abundance of syntrophic acetate-oxidizing bacteria (SAOB) also increased. The succession between populations of Methanosaeta and Methanosarcina may be used as a microbiological indicator of ammonia inhibition. Under high-C/Ns, cooperation among bacteria was high, while under low-C/Ns, competition among bacteria was high. These results clarify the processes underlying the "inhibited steady-state," which is a condition often faced in actual large-scale biogas facilities that use degradable nitrogen-rich substrates. Moreover, practical guidelines for evaluating ammonia inhibition are provided, and strategies to alleviate ammonia suppression are developed.