Small biochar addition enhanced anammox granular sludge system for practical wastewater treatment: Performance and microbial community

Deciphering the anammox microbial community succession with humic acid exposure to optimize large anammox granules for robust nitrogen removal

The robustness of the anaerobic ammonia oxidation (anammox) process in treating wastewater with high concentrations of humic acids (HAs), including landfill leachate and sludge anaerobic digestion liquid, has been paid great attention. This study revealed that the anammox sludge granule size of 1.0-2.0 mm could be robust under the HA exposure with high concentrations. The total nitrogen removal efficiency (NRE) was 96.2% at the HA concentration of 20-100 mg/L, while the NRE was 88.5% at the HA concentration of 500 mg/L, with reduced by 7.7%. The increased extracellular polymeric substances (EPS) content which was stimulated by the HA exposure favored the formation of large granules (1.0-2.0 mm) by enveloping medium and micro granules (0.2-1.0 mm). The abundance of anammox bacteria Candidatus Brocadia was found to be higher (14.2%) in large anammox granules sized 1.0-2.0 mm, suggesting a potentially high anammox activity. However, the abundance of denitrifiers Denitratisoma increased by 4.3% in ultra-large anammox granules sized >2.0 mm, which could be attributed to the high EPS content for heterotrophic denitrifiers metabolism as organic matter. The feedback mechanism of the anammox community for maintaining the ecological function under the HA exposure resulted in a closely related microbial community, with positive and negative correlations in the ecological network increased by 64.3%. This study revealed that the HA exposure of the anammox system resulted in the anammox granules of 1.0-2.0 mm size being the dominant granules with robust nitrogen removal, providing significant guidance for the optimization of anammox granules for an efficient treatment of HA-containing wastewater in anammox applications.

Study on the mechanism of enhanced anaerobic ammonia oxidation performance by extracellular electron acceptor biochar

ABSTRACTAnaerobic ammonia oxidation process has the advantages of energy and cost reduction, therefore, it has been considered as one of the main alternatives to conventional biological denitrification process in recent years. Biochar has been applied in the anammox process for nitrogen removal efficiency. But, due to its extracellular electron transfer capacity and abundance of redox-specific functional groups, which served as extracellular electron acceptor to anaerobically oxidize NH4+ is still controversy. In this study, the anaerobic ammonia oxidation was investigated when biochar was used as electron acceptor in the wastewater. According to the optimal process variables determined in the batch tests, when the influent NH4+-N concentration in the anaerobic ammonia oxidation reaction was 30-50 mg/L and the biochar dosing was at 10 g/L, it showed some promotion in the long-term experiments. The anaerobic ammonia oxidation process with biochar as the electron acceptor reached more than 60% NH4+-N removal efficiency in the system, and the ΔNO3--N/ΔNH4+-N ratio reached 0.19 which tended to the theoretical value. After 20 days, the voltage in the system keeps fluctuating about 4 mV, indicated that the functional bacteria using biochar as the electron acceptor gradually dominated the system. In addition, the abundance of norank_f__norank_o__SBR1031 in the Chloroflexi phylum has increased significantly at 29.92%, while the abundance of the major genus Candidatus_Kuenenia in AnAOB has decreased slightly at 11.47%.

Mechanism of self-supporting montmorillonite composite material for bio-enhanced degradation of chlorotetracycline: Electron transfer and microbial response

The efficient degradation of antibiotics holds significant implications for mitigating environmental pollution. This study synthesized a montmorillonite chitosan composite material (MMT-CS) using the gel template method. Subsequently, a bio-enhanced reactor was constructed to facilitate the degradation of chlorotetracycline (CTC). The addition of MMT-CS composite material enables the degradation of different concentrations of CTC. MMT-CS, a conductive carrier, effectively promotes microbial adhesion and boosts the metabolic activity of functional microorganisms. Additionally, it facilitates the maintenance of microbial activity under CTC pressure by promoting the secretion of extracellular polymeric substances, increasing critical enzyme activity, and enhancing the electron transfer capacity within the system. In this MMT-CS bio-enhanced process, Paracoccus (11.4%) and Bacillus (3.9%) are utilized as essential bacteria genes. The results of metabolic pathways prediction indicated significant enhancements in membrane-transport, nucleotide-metabolism, replication-repair, and lipid-metabolism. Thus, the developed self-supporting MMT-CS bio-enhanced process ensured the stability of the system during the removal of antibiotics.

Promotion of anaerobic biodegradation of azo dye RR2 by different biowaste-derived biochars: Characteristics and mechanism study by machine learning

The addition of biochar resulted in a 31.5 % to 44.6 % increase in decolorization efficiency and favorable decolorization stability. Biochar promoted extracellular polymeric substances (EPS) secretion, especially humic-like and fulvic-like substances. Additionally, biochar enhanced the electron transfer capacity of anaerobic sludge and facilitated surface attachment of microbial cells. 16S rRNA gene sequencing analysis indicated that biochar reduced microbial species diversity, enriching fermentative bacteria such as Trichococcus. Finally, a machine learning model was employed to establish a predictive model for biochar characteristics and decolorization efficiency. Biochar electrical conductivity, H/C ratio, and O/C ratio had the most significant impact on RR2 anaerobic decolorization efficiency. According to the results, the possible mechanism of RR2 anaerobic decolorization enhanced by different types of biochar was proposed.

Dynamic pulse approach to enhancing mainstream Anammox process stability: Integrating sidestream support and tackling nitrite-oxidizing bacteria challenges

Nitrite-oxidizing bacteria (NOB) seriously threaten the partial nitritation and Anammox (PN/A) process, hindering its mainstream application. Herein, a one-stage PN/A reactor was continuously operated for 245 days under nitrogen loading rate lifted from 0.4 g N/L/d to 0.6 g N/L/d and 0.8 g N/L/d with the nitrogen removal efficiency of 71 %, 64 %, and 41 %, respectively. Furthermore, the NOB species over time was identified as Nitrospira_sp._OLB3, exhibiting an increase of the relative abundance from 0.9 % to 4.3 %. The hydroxyapatite (HAP) granules gradually lost their microbiological function of Anammox bacteria then aged, leading to NOB dominance. Therefore, one "pulse therapy" was introduced and combined with "continuous enhancement" of Anammox sludge supported by sidestream to competitively limit the NOB dynamics. The treatment's effect persisted for around two months. The strategy that returning at least 50 % of the impaired HAP granular sludge to the sidestream for recultivation could fulfill the bottlenecks of mainstream PN/A.

Biological carbon promotes the recovery of anammox granular sludge after starvation

This article adopts the strategy of adding biochar and increasing HRT to accelerate the performance and particle morphology recovery of anaerobic ammonia oxidation granular sludge stored at room temperature for 68 days. The results showed that biochar accelerated the death of heterotrophic bacteria, shortened the cell lysis and lag period of the recovery process by 4 days, and it only took 28 days for the nitrogen removal performance of the reactor to recover to the original level, and 56 days for re-granulation. Biochar promoted the secretion of EPS (56.96 mg gVSS^-1), and the sludge volume and nitrogen removal performance of the bioreactor remain stable. Biochar also accelerated the growth of Anammox bacteria. The abundance of Anammox bacteria in the biochar reactor reached 38.76% on the 28th day. The high abundance of functional bacteria and the optimized community structure of biochar made system (Candidatus_Kuenenia: 38.30%) more risk-resistant than control reactor.

Iron-loaded sludge biochar alleviates the inhibitory effect of tetracycline on anammox bacteria: Performance and mechanism

The anaerobic ammonia oxidation (anammox) process is sensitive to environmental pollutants, such as antibiotics. In this study, the harmful effect of tetracycline (TC) on the performance of an anammox reactor and the mitigation of TC inhibition by iron-loaded sludge biochar (Fe-BC) were studied by analyzing extracellular polymeric substances (EPS), microbial community structure and functional genes. The total inorganic nitrogen (TIN) removal rate of the TC reactor was reduced by 5.86% compared to that of the control group, while that of the TC + Fe-BC reactor improved by 10.19% compared to that of the TC reactor. Adding Fe-BC increased the activity of anammox sludge by promoting the secretion of EPS (including protein, humic acids and c-Cyts). The results of the enzymolysis experiment showed that protein can improve the activity of anammox sludge, while the ability of polysaccharide to improve the activity of anammox was related to the treated enzymes. In addition, Fe-BC alleviated the inhibitory effect of TC by mediating the anammox electron transfer process. Furthermore, Fe-BC increased the absolute abundance of hdh and hzsB by 2.77 and 1.18 times compared to the TC reactor and improved the relative abundance of Candidatus Brocadia in the absence of TC. The addition of Fe-BC is an effective way to alleviate the inhibitory effect of TC on the anammox process.

Exploring the mechanism of Self-Consistent balance between microbiota and high efficiency in wastewater treatment

Sewage treatment mediated by microbial organisms is a promising green trend. However, the complex balance between microbiota stability and highly efficient wastewater treatment requires investigation. This study successfully improved the effectiveness of sewage treatment by resetting the microbial community structure in the activated sludge. Truepera, Methylophaga, unclassified_Fodinicurvataceae, and unclassified_Actinomanarales were the dominant genera, while salinity and NH₃-N content were identified as the key environmental factors governing the microbial structure. By optimizing the microflora structure driven by environmental factors, the key minor genera were activated and coordinated with the aforementioned genera, thereby promoting wastewater treatment. Finally, the chemical oxygen demand, NH₃-N, and total phosphorus removal rates were improved to 86.8 ± 1.9%, 82.4 ± 4.1%, and 94.8 ± 3.8%, respectively. It provides a new insight to improve the wastewater treatment through setting microbiota by environmental factor driven.

Effects of biochar on anaerobic treatment systems: Some perspectives

Many anaerobic activities involve carbon, nitrogen, iron, and sulfur cycles. As a well-developed porous material with abundant functional groups, pyrolytic biochar has been widely researched in efforts to promote microbial activities. However, the lack of consensus on the biochar mechanism has limited its practical application. This review summarizes the effects of different pyrolysis temperatures, particle sizes, and dosages of biochar on microbial activities and community in Fe(III) reduction, anaerobic digestion, nitrogen removal, and sulfate reduction systems. It was found that biochar could promote anaerobic activities by stimulating electron transfer, alleviating toxicity, and providing suitable habitats for microbes. However, it inhibits microbial activities by releasing heavy metal ions or persistent free radicals and adsorbing signaling molecules. Finding a balance between the promotion and inhibition of biochar is therefore essential. This review provides valuable perspectives on how to achieve efficient and stable use of biochar in anaerobic systems.