Non-rhizosphere reinforces the contributions of Feammox and anammox to nitrogen loss than rhizosphere in riparian zones.

The emergence of anaerobic ammonium oxidation (anammox) coupled to iron reduction (named Feammox) refreshes the microbial pathways for nitrogen (N) loss. However, the ecological role of Feammox, compared with conventional denitrification and anammox, in microbial N attenuation in ecosystems remains unclear. Here, the specific contribution of Feammox to N loss and the underlying microbiome interactive characteristics in a riparian ecosystem were investigated through 15N isotope tracing and molecular analysis. Feammox was highlighted in the riparian interface soils and maximally contributed 14.2% of N loss. Denitrification remained the dominant contributor to N loss (68.0%-95.3%), followed by anammox (5.7%-19.1%) and Feammox (0-14.2%). The rates of Feammox and anammox significantly decreased in rhizosphere soils (0.15 ± 0.08 µg N g-1 d -1 for Feammox, 0.80 ± 0.39 µg N g-1 d -1 for anammox) compared with those in non-rhizosphere soils; however, the activities of denitrification remarkably increased in the rhizosphere (13.17 ± 3.71 µg N g-1 d -1). In rhizosphere soils, the competition between bioavailable organic matter (e.g., amino acids and carbohydrates) and ammonium for electron acceptor [i.e., Fe(III)] was the vital inducement for restricted Feammox, while the nitrite consumption boosted by heterotrophic denitrifiers was responsible for weakened anammox. The functional gene of autotrophic Acidimicrobiaceae bacterium A6, instead of heterotrophic Geobacteraceae spp., was significantly positively correlated with Feammox activity. Rare iron-reducing bacteria showed higher node degrees in the non-rhizosphere network than in the rhizosphere network. A syntrophic relationship was found between iron-reducing bacteria (e.g., Anaeromyxobacter, Geobacter) and iron-oxidizing bacteria (e.g., Sideroxydans) in the non-rhizosphere network and facilitated the Feammox pathway. This study provides an in-depth exploration of microbial driven N loss in a riparian ecosystem and introduces new insights into riparian management practices toward high-efficient N pollution alleviation.

Insights into microbial interactive mechanism regulating dissimilatory nitrate reduction processes in riparian freshwater aquaculture sediments.

Aquaculture can substantially alter the accumulation and cycling of nutrients in sediments. However, the microbial mechanisms mediating sediment dissimilatory nitrate (NO3-) reduction in freshwater aquaculture ponds are still unclear, which rule the removal and retention of N element. In the present study, three microbial NO3- reduction processes in riparian aquaculture pond sediments (i.e., crab, shrimp and fish ponds) and natural freshwater sediments (i.e., lakes and rivers) were investigated via isotopic tracing and molecular analyses. The potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) significantly increased in the aquaculture ponds compared with the natural freshwaters. Denitrification contributed 90.40-94.22% to the total NO3- reduction (product as N2), followed by 2.49-5.82% of anammox (product as N2) and 2.09-5.18% of DRNA (product as NH4+). The availability of C and N substrates, rather than functional gene abundance, regulated the activities of NO3- reductions and microbiome composition. Microbial mechanism based on network analysis indicated that heterotrophic denitrifiers and DNRA bacteria (e.g., Bacillus, Micromonospora, Mycobacterium and Brachybacterium) determined the community structure and function for N conversions in aquaculture ponds, whereas the such microbial network in natural freshwater sediments was manipulated by autotrophic denitrifiers (e.g., Desulfuromonas, Polaromonas, Solitalea). Collectively, this study provides an in-depth exploration of microbial nitrogen removal in freshwater aquaculture areas and supports management strategies for N pollution caused by reclamation for aquaculture in riparian zones.

Efficient activation of peracetic acid by mixed sludge derived biochar: Critical role of persistent free radicals.

Peracetic acid (PAA)-based advanced oxidation processes (AOPs) were increasingly identified as the alternative scheme in wastewater treatment. Cost-effective and easily available catalyst for activation of PAA was in urgent demand for promoting engineering application process. In this study, a new type of biochar catalyst derived from pyrolysis of mixture of primary sludge (PSD) and secondary sludge (SSD) was prepared and showed effective PAA activation ability. The degradation of p-chlorophenol (4-CP) improved with PAA activation by mixed sludge derived biochar (PS-SDBC) than secondary sludge derived biochar (S-SDBC) and primary sludge derived biochar (P-SDBC), and the highest removal efficiency achieved by PS-SDBC with the PSD/SSD ratio of 5/5 (kobs=0.057 1/(M·min), pH 9). Correlation analysis firstly indicated that persistent free radicals (PFRs) rather than chemical composition and material structure dominated PAA activation and organic radicals (RO•) was proved to be the major reactive species through electron paramagnetic resonance (EPR) detection. The mixture of PSD and SSD caused the synergy of inorganic metals and organic matters through pyrolysis processes, resulting in larger specific surface area (SSA) (110.71 m2/g), more abundant electron-donating groups (e.g., C = O, -OH) and massive defects (ID/IG = 1.519) of PS-SDBC than P-SDBC and S-SDBC, which eventually promoted PFRs formation. A fascinating phenomenon was observed in PS-SDBC/PAA system that the active sites of PFRs could be regenerated by RO• attacking onto PS-SDBC, which contributed to the wide pH applicability and continuous stability of PS-SDBC/PAA system in practical wastewater treatment. This study not only significantly deepened the understanding of the reaction mechanism between PAA and biochar, but also provided a potential PAA-based AOPs for micropollutants removal in wastewater.

Evidence for the occurrence of Feammox coupled with nitrate-dependent Fe(II) oxidation in natural enrichment cultures.

Feammox is a newly discovered process of anaerobic ammonium oxidation driven by Fe(III) reduction. Nitrate-dependent Fe(II) oxidation (NDFO) is the coupling of Fe(II) oxidation and nitrate reduction to produce N2 under anaerobic conditions. It has not been reported whether the coupling of the two reactions exists in natural enrichment. In this study, enrichment culture experiments were carrired out to prove the occurrence of Feammox with NDFO. The results indicated that the nitrogen and iron cycle were formed during natural enrichment cultures, including Fe(III) reduction and NH4+-N was oxidation to NO3--N, NO2--N and N2, Fe(III) and Fe(II) were cyclically formed, and Fe(II) was oxidized with NO3--N reduced to N2. The removal efficiencies of ammonium nitrogen and total nitrogen in the incubation were about 92.9% and 20% respectively. Organic carbon experiments indicate that sodium acetate can promote the initial NO3--N removal and a low concentration of organic carbon limited the NDFO process because iron-oxidizing bacteria are mixotrophic microorganisms. The added 9,10-anthraquinone-2,6-disulfonate (AQDS) in the later stage can promote NDFO to remove nitrate, thereby increasing the TN removal efficiency to 50%. 15N-isotope tracer incubations provided direct evidence for the occurrence of Feammox coupled to NDFO, with rates producing 30N2 of Feammox (0.024-0.0288 mg N·L-1·d-1) and NDFO (0.0465-0.0833 mg N·L-1·d-1) in three groups (Wetland/Wheat soil/Sediment). 16S rRNA sequencing further demonstrated that Pseudomonas, Rhodanobacter, Acinetobacter and Thermomonas were the dominant generas among the enrichment cultures, and these bacteria belonged to FeOB and FeRB, which may further promote Feammox coupled to NDFO in the cultivation system.

Synergistic pretreatment of CaO and freezing/thawing to enhance volatile fatty acids recycling and dewaterability of waste activated sludge via anaerobic fermentation.

To avoid the generally deteriorated dewaterability of sludge in waste activated sludge (WAS) anaerobic acidogenesis, the combination of varied calcium oxide (CaO) dosage (i.e., 0.01-0.07 g/g TS) and freezing/thawing pretreatment (5 F/T cycles) was investigated for concurrently improving the production of volatile fatty acids (VFAs) and dewatering performance of sludge. The highest release of soluble chemical oxygen demand (SCOD) (1836 ± 96 mg/L) and accumulation of VFAs (448.0 mg COD/g VS) were reached through the co-pretreatment of CaO (0.07 g/g TS) and F/T (50 h at -24 °C) (i.e., 0.07 CaO-F/T). Meanwhile, optimal dewaterability of sludge was also achieved in 0.07 CaO-F/T co-pretreated WAS fermentation, which was reflected by large particle size (98.32 µm), low capillary suction time (41.6 s), decreased specific resistance to filtration (SRF, reduced 47.5% against blank) and high zeta potential (-9.59 mV). Co-pretreatment of CaO and F/T reduced the species number of total microbial population, but improved the abundance of acid-producing bacteria. Increased abundance of Bacteroides, Macellibacteroides, Petrimonas, Prevotella, Clostridium, and Megasphaera was positively relevant to the high yields of VFAs. The economic analysis indicated that CaO-F/T was economically acceptable with considerable estimated net profits, which provided a feasible and efficient alternative for further WAS treatment at large scale.

Insights into microbial interaction profiles contributing to volatile fatty acids production via acidogenic fermentation of waste activated sludge assisted by calcium oxide pretreatment.

This first-attempted study illustrated the calcium oxide (CaO) agentia-pretreatment for prompting waste activated sludge (WAS) solubilization and enhancing volatile fatty acids (VFAs) bio-production through acidogenic fermentation. The 15-h CaO pretreatment was capable to produce a soluble chemical oxygen demand (SCOD) yield of ca. 153.17 mg COD/g VS and VFAs generation efficiency of 327.8 mg COD/g VS with adding dosage of 0.07 g/g TS. The relative frequencies corresponded to metabolic functions profiling were promoted obviously by CaO pretreatment and contributed to biosolid decomposition/VFAs production in sludge fermentation. Main genera of Azonexus, Arcobacter, Acinetobacter, Thauera, Petrimonas, Clostrium and Macellibacteroides cooperated synergically toward triggering concurrent VFAs generation/biosolid biodegradation. Finally, the CaO-pretreatment displayed positive merits in terms of sludge biosolid decomposition/recoverable resource harvest as compared with other alkali pretreatments. This study might shed lights on enriching intensification strategy for WAS management toward high-efficiency of recoverable resource harvest with lower cost.

Insights into redox mediators-resource harvest/application with power production from waste activated sludge through freezing/thawing-assisted anaerobic acidogenesis coupling microbial fuel cells.

This first-attempted study demonstrated endogenous redox-mediators harvest/application from waste activated sludge (WAS) through freezing/thawing (F/T) pretreatment-enhanced anaerobic acidogenesis coupled with microbial fuel cells (MFCs). A total of 2.57 kWh electricity was produced from per kg soluble chemical oxygen demand (SCOD) via MFCs just in 2 d with about 90% organics removal, which contained 1.152 kWh/kg COD from F/T liquid together with 1.418 kWh/kg COD from fermentation liquid. The fermentation liquor-MFCs fostered higher anodic biodiversity and more power output as compared with the F/T liquid-MFCs. Essentially, the completely endogenous redox mediators-like substances with relatively high redox activities could be retained after MFC electrogenesis from F/T liquid and played electron shuttle-roles sufficiently in enlarging bio-energy production of MFCs, which seemed to be an effective option for harvesting endogenous redox mediators from sludge. This study might inspire progressive thinking toward aims of high-efficiency of resource recycle/bioenergy production from WAS.

Revealing microbial mechanism associated with volatile fatty acids production in anaerobic acidogenesis of waste activated sludge enhanced by freezing/thawing pretreatment.

This study investigated the association of volatile fatty acid (VFA) production with microbial mechanism in waste activated sludge (WAS) anaerobic acidogenesis enhanced by freezing/thawing (F/T) pretreatment. WAS solubilization was enhanced with 955.4 ± 10.0 mg/L soluble chemical oxygen demand (SCOD) release by a 50-h F/T pretreatment at -24 °C. The highest level of VFAs (4852 ± 156 mg COD/L) was obtained after a 12-day fermentation. Moreover, phyla of Proteobacteria, Bacteroidetes, Firmicutes, and Ignavibacteriae played vital roles in VFA generation, while high genera abundance of Clostridium, Macellibacteroides, Prevotella, and Megasphaera were positively associated with high yields of short-chain (C2-C5) fatty acids. A schematic diagram was drawn to illustrate the microbial mechanism of enhanced VFA generation by F/T pretreatment during WAS fermentation. This study provides an in-depth exploration of promoting bio-resource recycling from WAS with a low-cost approach (specially in high latitudes) and bring about some new thinking on future WAS management.