Response of microbial interactions in activated sludge to chlortetracycline

Unraveling the effects and mechanisms of microplastics on anaerobic fermentation: Exploring microbial communities and metabolic pathways

To investigate the effects of microplastics (MPs) on hydrolysis, acidification and microbial characteristics during waste activated sludge (WAS) anaerobic fermentation process, five different kinds of MPs were added into the WAS fermentation system and results indicated that, compared to the control group, the addition of polyvinyl chloride (PVC)-MPs exhibited the least inhibition on volatile fatty acids (VFAs), reducing them by 13.49 %. Conversely, polyethylene (PE)-MPs resulted in the greatest inhibition, with a reduction of 29.57 %. MPs, while accelerated the dissolution of WAS that evidenced by an increase of lactate dehydrogenase (LDH) release, concurrently inhibited the activities of relevant hydrolytic enzymes (α-Glucosidase, protease). For microbial mechanisms, MPs addition affected the proliferation of key microorganisms (norank_f_Bacteroidetes_vadinHA17, Ottowia, and Propioniclava) and reduced the abundance of genes associated with hydrolysis and acidification (pfkb, gpmI, ilvE, and aces). Additionally, MPs decreased the levels of key hydrolytic and acidogenic enzymes to inhibit hydrolysis and acidification processes. This research provides a basis for understanding and unveils impact mechanisms of the impact of MPs on sludge anaerobic fermentation.

Insights into the response mechanisms of activated sludge system under long-term dexamethasone stress

Dexamethasone (DEX) is a hormone drug that is often detected in wastewater treatment plants, but its impact on activated sludge systems is unknown. This study explored the long-term effects of DEX on nutrient removal, microbial activities, microbial assembly, and microbial interactions in the activated sludge system. During the 90-day DEX exposure experiment, both chemical oxygen demand and total nitrogen removal efficiencies were initially inhibited and then recovered. Microbial activities, i.e., specific oxygen uptake rate and denitrification, did not differ significantly from that of the control reactor (p > 0.05), possibly due to the secretion of extracellular polymers that act as a protective barrier against excess reactive oxygen species induced by DEX. This barrier protects cell membrane integrity and ensures stable treatment performance. Analysis of microbial assembly identified the drift of stochastic processes (from 92.7 % to 51.8 %) and homogeneous selection of deterministic processes (from 1.6 % to 38.7 %) as the main driving forces of microbial community structure succession under long-term DEX stress. Although long-term exposure to 1000 μg/L DEX did not significantly increase the abundance levels of functional bacteria (Nitrosomonas and 996-1) and key genes (AmoCAB and Hao), the ammonia oxidation capacity of the activated sludge system was enhanced. Analysis of microbial interactions indicated that streamlining of functional subnetworks and increased cooperation were the primary reasons. This is the first study to explore the long-term effects of DEX on activated sludge and provide insights into microbial interaction and assembly. Moreover, the findings of this study broaden our knowledge and lay an experimental foundation for reducing risks associated with hormone drugs.

Modified basalt fibers boost performance of constructed wetlands: Comparison between surface coating and chemical grafting

Modified basalt fiber (MBF) is a potential material that has been applied in wastewater treatment fields. In this study, superior performances of MBFs by calcium (Ca-MBF) and polyethyleneimine modification (PEI-MBF) were compared in constructed wetlands (CWs). Via chemical grafting, higher biofilm contents were observed on the surface of PEI-MBF, compared to Ca-MBF. Moreover, MBF increased key enzyme activities particularly in lower substrate layer, contributing to positive responses of microbial community in CWs. For instance, PEI-MBF boosted microbial richness and diversity and improved the abundances of denitrifying functional bacteria and biomarkers like Thauera, Vulcanibacillus, and Maritimimonas, probably promoting nitrate removal compared with Ca-MBF group. By contrast, Ca-MBF enriched more functional genera involved in nutrients removal, with the highest removal of ammonium (43.9 %), total nitrogen (66.2 %), and total phosphorus (37.1 %). Overall, this work provided new findings on improved performance of CWs with MBF.

Pressure of different level PFOS on aerobic granule sludge: Insights on performance, AGS structure, community succession, and microbial interaction responses

Perfluorooctane sulfonic acid (PFOS) has received much attention due to its potential environmental risks. However, the response of aerobic granular sludge (AGS) to PFOS exposure, particularly the microbial interactions, remains unclear. In this study, we investigated the particle structure of AGS, pollutant removal performance, community succession, and microbial interaction in the AGS system under different PFOS concentrations (0.1 and 1 mg/L). The mass balance showed that PFOS was mainly removed by adsorption with a removal rate of >85 %. PFOS caused some particles to break up and decreased the average particle size from 3.37 mm to 2.64 mm. It also significantly decreased the total nitrogen and total phosphorus removal rates, which was consistent with the deterioration of microbial activity, such as denitrification rate (25 % inhibition), phosphorus uptake rate (73.19 % inhibition), and phosphorus release rate (73.33 % inhibition). PFOS promoted the secretion of extracellular polymer (EPS) in AGS, especially proteins, leading to poor particle hydrophobicity. The network analysis illustrated that PFOS slowed down the information transfer between microorganisms, and increased the competition between them, which may be responsible for the deterioration of the system performance. Connections related to rare species accounted for >75 % of the network, suggesting that rare species have an indispensable role in community information exchange. In addition, rare species acted as seed banks for microorganisms, and under PFOS stress, they transformed into keystone species, which could contribute to system stabilization. This study provides new insights into the effects of PFOS on microbial interactions in AGS systems and the roles of rare species in the AGS microbial community.

Effect of C/N on the microbial interactions of aerobic granular sludge system

The main focus of this study was to evaluate the operational stability and changes in microbial interactions of aerobic granular sludge (AGS) systems at reduced C/N (16, 8 and 4). The results showed that the removal efficiency of total nitrogen and total phosphorus decreased from 95.99 ± 0.93% and 84.44 ± 0.67% to 48.46 ± 1.92% and 50.93 ± 2.67%, respectively, when C/N was reduced from 16 to 4. The granule settling performance and stability also deteriorated. Molecular ecological network analysis showed that the reduction of the C/N ratio made the overall network as well as the subnetworks of the Proteobacteria and Bacteroidota more complex and tightly connected. Similarly, the subnetworks of two dominant genera (Thiothrix and Defluviicoccus) became more complex as the C/N decreased. Meanwhile, the decreased C/N ratio might promote competition among microbes in these overall networks and subnetworks. In conclusion, reduced C/N added complexity and tightness to microbial linkages within the AGS system, while increased competition between species might have contributed to the deterioration in pollutant removal performance. This study adds a new dimension to our understanding of the effects of C/N on the microbial community of AGS using a molecular ecological network approach.

Biodegradation mechanism of chlortetracycline by a novel fungal Aspergillus sp. LS-1

Chlortetracycline (CTC), a widely used typical tetracycline antibiotic, has raised increasing concerns due to its potential health and environmental risks. Biodegradation is considered an effective method to reduce CTC in environment. In this study, a strain Aspergillus sp. LS-1, which can efficiently degrade CTC, was isolated from CTC-rich activated sludge. Under optimal conditions, the maximum removal efficiency of CTC could reach 95.41%. Temperature was the most significant factor affecting the degradation efficiency of LS-1. The 19 products were identified in the CTC degradation by strain LS-1, and three degradation pathways were proposed. All the degradation pathways for CTC exhibited ring-cleaving, which may accelerate the mineralization of CTC. To gain more comprehensive insights into this strain, we obtained the genome of LS-1, which had high GC content (50.1%) and completeness (99.3%). The gene annotation revealed that LS-1 contains some vital enzymes and resistance genes that may carry functional genes involved in the CTC degradation. In addition, other antibiotic resistance genes were found in the genome of LS-1, indicating that LS-1 has the potential to degrade other antibiotics. This study provides a more theoretical basis for the investigation of CTC degradation by fungi and new insights into the biodegradation of CTC.

Aerobic granular sludge formation and stability in enhanced biological phosphorus removal system under antibiotics pressure: Performance, granulation mechanism, and microbial successions

Wastewater containing antibiotics can pose a significant threat to biological wastewater treatment processes. This study investigated the establishment and stable operation of enhanced biological phosphorus removal (EBPR) by aerobic granular sludge (AGS) under mixed stress conditions induced by tetracycline (TC), sulfamethoxazole (SMX), ofloxacin (OFL), and roxithromycin (ROX). The results show that the AGS system was efficient in removing TP (98.0%), COD (96.1%), and NH₄⁺-N (99.6%). The average removal efficiencies of the four antibiotics were 79.17% (TC), 70.86% (SMX), 25.73% (OFL), and 88.93% (ROX), respectively. The microorganisms in the AGS system secreted more polysaccharides, which contributed to the reactor's tolerance to antibiotics and facilitated granulation by enhancing the production of protein, particularly loosely bound protein. Illumina MiSeq sequencing revealed that putative phosphate accumulating organisms (PAOs)-related genera (Pseudomonas and Flavobacterium) were enormously beneficial to the mature AGS for TP removal. Based on the analysis of extracellular polymeric substances, extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and microbial community, a three-stage granulation mechanism was proposed including adaption to the stress environment, formation of early aggregates and maturation of PAOs enriched microbial granules. Overall, the study demonstrated the stability of EBPR-AGS under mixed antibiotics pressure, providing insight into the granulation mechanism and the potential use of AGS for wastewater treatment containing antibiotics.

Biological reduction and hydrodechlorination of chlorinated nitroaromatic antibiotic chloramphenicol under H2-transfer membrane biofilm reactor

Chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a persistent pollutant that is widely present in environments. A H₂ transfer membrane biofilm reactor (H₂-MBfR) and short-term batch tests were setup to investigate the co-removal of CAP and NO₃^-. Results showed that the presence of CAP (<10 mg L^-1) has no effect on the denitrification process while 100% removal efficiency of CAP can be obtained when nitrate was absent. Nitroaromatic reduction and completely dechlorination were successfully realized when CAP was removed. The CAP transformation product p-aminobenzoic acid (PABA) was detected and batch tests revealed that the hydroxy carboxylation was far faster than nitroaromatic reduction when p-nitrobenzyl alcohol (PNBOH) was conversed to p-aminobenzoic acid (PABA). The path way of CAP degradation was proposed based on the intermediate's analysis. Microbial community analysis indicated that Pleomorphomonadaceae accounts for the dechlorination of CAP.