Fast start-up of anammox process: Effects of extracellular polymeric substances addition on performance, granule properties, and bacterial community structure

Comparation on the responses and resilience of single-Anammox system and synergistic partial-denitrification/anammox system to long-term nutrient starvation: Performance and metagenomic insights

Starvation disturbance was a common problem in biological sewage treatment processes. However, understanding about the responses and resilience of different active anammox biomass in autotrophic and heterotrophic systems to long-term nutrient starvation remains limited. This study compared responses and potential recovery mechanisms of autotrophic single-Anammox and heterotrophic synergistic partial-denitrification/anammox (PD/anammox) systems to prolonged starvation (31-40 days). After starvation, total inorganic nitrogen (TIN) removal efficiency of single-Anammox and synergistic PD/anammox systems decreased to 62.16 % and 78.52 %, respectively, of their original level. After the nutrient resupply, the performance of both systems gradually recovered to a similar-to-pre-starvation level at the rate of 1.26 %/day and 1.89 %/day, respectively. Compared with single-Anammox system, complex synergistic relationship of microorganisms and effective quorum sensing (QS) regulation strategies might mitigate the negative influences were caused by starvation and ensure the performance quickly return of synergistic PD/anammox system. This study would contribute to promote the application of Anammox technology.

Recovery effects of the long-term cryopreserved Anammox sludge by adjusting the sludge amount

Anammox process was one of the most promising nitrogen removal technologies. This study investigated the recovery performance of Anammox sludge after 83 days of cryopreservation in two reactors (R1 and R2). Reactor R1 utilized Anammox sludge pretreated with low-substrate simulated wastewater prior to long-term cryopreservation, and successful recovery was achieved by discharging sludge under ammonia nitrogen concentrations of 100 mg/L. The total nitrogen removal efficiency (TNRE) reached 70.0% on day 48. Reactor R2 used Anammox sludge pretreated with high-substrate simulated wastewater before cryopreservation. At an ammonia nitrogen concentration of 100 mg/L, the TNRE reached 87.0% on day 18. After increasing the ammonia nitrogen concentration to 300 mg/L and discharging sludge, the TNRE reached 84.6% on day 38. When the ammonia nitrogen concentration was elevated to 500 mg/L, system performance deteriorated. Recovery was unsatisfactory when the ammonia nitrogen concentration was reduced back to 300 mg/L. Finally, adding Anammox sludge restored the TNRE to 85.6% after 35 days of operation. The results suggest that adding Anammox sludge is essential for nitrogen removal recovery in reactors under high ammonia nitrogen concentration inhibition, while sludge discharge is crucial when free ammonia (FA) is present. This study provides a simple and effective strategy for recovering the activity of Anammox sludge after long-term cryopreservation.

Synergistic effects of ozonation pretreatment and trace phosphate on water quality health risk and microbial stability in simulated drinking water distribution systems

The proliferation and chlorine resistance of pathogenic bacteria in drinking water distribution systems (DWDSs) pose a serious threat to human health. In this study, the synergistic effects of ozonation pretreatment and trace phosphate on water quality health risk and microbial stability were investigated in the small-scale DWDSs simulated by biofilms annular reactors with cast iron coupons. The results indicated that ozonation of drinking water containing trace phosphate was equivalent to increasing microbial carbon and phosphorus sources, further leading to the rapid proliferation of opportunistic pathogens (OPs) in subsequent DWDSs. Under the influent condition of ozonation pretreatment and 0.6 mg/L phosphate, the gene copy numbers of living Legionella spp., Mycobacterium spp., and Acanthamoeba spp. reached up to 1.50 × 104, 1.21 × 104, and 2.29 × 104 gene copies/mL, respectively. The extracellular polymeric substances from suspended biofilms in DWDSs exhibited higher content, molecular weight, and flocculating efficiency, contributing to the improvement of microbial chlorine resistance. Meanwhile, more Fe3O4 appeared in the corrosion products, which enhanced the extracellular electron transfer via cytochrome c and weakened the electrostatic repulsion between corrosion products and microbes in DWDSs. Finally, more active OP growth and microbial metabolic activity occurred in DWDSs. This study revealed that ozonation pretreatment and trace phosphate, as a green technology and an inconspicuous nutrient, respectively, can trigger significant microbial health risks in subsequent DWDSs. Therefore, the phosphate in drinking water should be more strictly restricted when ozonation technology is used in waterworks, especially without a biofiltration treatment process.

Start-up of Anammox-HAP in IC reactors: Revelation of sludge characteristics and microbial community structure

The scarcity of seed sludge poses a significant barrier to the advancement of anaerobic ammonia oxidation (anammox) process. In this investigation, two alternative sludge (anaerobic granular sludge (AGS) and activated flocculent sludge (AFS)) were employed to start up the anammox process in internal circulation (IC) reactors with the hydroxyapatite (HAP) strategy. Both reactors achieved rapid start-up on days 83 and 53, respectively. Subsequently, a nitrogen removal rate (NRR) of 1.34 gN/L/d was attained at a nitrogen loading rate (NLR) of 1.39 gN/L/d on days 107 and 81 correspondingly. The analysis of granular properties revealed that the anammox granular sludge (AMXGS) transformed from AGS exhibited superior granular size distribution and settling performance. Furthermore, the assessment of microbial community structure demonstrated that inoculating AFS was capable of enriching anammox bacteria (AnAOB) in a shorter time. Last but most importantly, this study provides a comprehensive analysis of the distinct granulation routes of AGS and AFS. AGS predominantly underwent a "broken-adsorption-granulation" process, whereas AFS exhibited not only a typical "adsorption-granulation" process but also a "biofilm growth-granulation" cycle process. The findings of this study offer a novel approach for quickly initiating anammox process when inoculating alternative sludge.

Response of anammox to organics with different degradation characteristics and exposure time: Performance, sludge characteristics and bacterial community

The effects of typical organic compounds including easily degradable organic matters sodium acetate, yeast and methanol, and refractory organic matter (ROM) humic acid on anaerobic ammonium oxidation (anammox) systems in short-term and medium-term exposure time were studied. During short-term experiments, nitrogen removal activity (NRA) was inhibited at sodium acetate level of 150 mg L-1 total organic carbon (TOC) and methanol level of 30-150 mg L-1 TOC, but humic acid and yeast (≤150 mg L-1 TOC) enhanced nitrogen removal in anammox systems. The greatest NRA of 30.10 mg TN g-1 VSS h-1 was recorded at yeast level of 90 mg L-1 TOC. In medium-term experiments, organics significantly inhibited the nitrogen removal ability. As a ROM, humic acid enhanced sludge aggregation and biological diversity, but decreased the bioactivity and extracellular polymeric substances levels. Due to the endogenous denitrification, the relative abundance of anammox bacteria (AnAOB) was decreased. Candidatus Kuenenia is still dominant in sludge with methanol and humid acid, but AnAOB are not dominant due to the addition of sodium acetate and yeast. This research would be beneficial for the full-scale application of the anammox process in treating real wastewater with organics and ammonia.

Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by Fe(Ⅲ)

The rapid enrichment of anammox bacteria and its fragile resistance to adverse environment are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation, nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III) (R5). These enhanced pathways were crucial to energy generation, nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Ca. Brocadia and facilitating their resistance to adverse environments. Microbial community analysis showed that the proportion of Ca. Brocadia in R5 also increased to 64.42 %. Hence, R5 could adapt rapidly to the increased nitrogen loading rate and increase the nitrogen removal rate by 108 % compared to the system without Fe(III) addition. However, the addition of 10 and 20 mg/L Fe(III) showed inhibitory effects on the growth and activity of anammox bacteria, which exhibited the lower relative abundance of Ca. Brocadia and unstable or even collapsed nitrogen removal performance. This study not only clarified the concentration range of Fe(III) that promoted and inhibited the enrichment of anammox bacteria, but also deepened our understanding of the functional and metabolic mechanisms underlying enhanced enrichment of anammox bacteria by Fe(III), providing a potential strategy to hasten the start-up of anammox from conventional activated sludge.

Synergistic effects of trace sulfadiazine and corrosion scales on disinfection by-product formation in bulk water of cast iron pipe

The effects of trace sulfadiazine (SDZ) and cast-iron corrosion scales on the disinfection by-product (DBP) formation in drinking water distribution systems (DWDSs) were investigated. The results show that under the synergistic effect of trace SDZ (10 μg/L) and magnetite (Fe3O4), higher DBP concentration occurred in the bulk water with the transmission and distribution of the drinking water. Microbial metabolism-related substances, one of the important DBP precursors, increased under the SDZ/Fe3O4 condition. It was found that Fe3O4 induced a faster microbial extracellular electron transport (EET) pathway, resulting in a higher microbial regrowth activity. On the other hand, the rate of chlorine consumption was quite high, and the enhanced microbial EET based on Fe3O4 eliminated the need for microorganisms to secrete excessive extracellular polymeric substances (EPS). More importantly, EPS could be continuously secreted due to the higher microbial activity. Finally, high reactivity between EPS and chlorine disinfectant resulted in the continuous formation of DBPs, higher chlorine consumption, and lower EPS content. Therefore, more attention should be paid to the trace antibiotics polluted water sources and cast-iron corrosion scale composition in the future. This study reveals the synergistic effects of trace antibiotics and corrosion scales on the DBP formation in DWDSs, which has important theoretical significance for the DBP control of tap water.

Characteristics variations of size-fractionated anammox granules and identification of the potential effects on these evolutions

Anaerobic ammonium oxidation (anammox) granulation which contributed to system stabilization and performance improvement has great potential in the field of wastewater nitrogen removal. The researchers fractionated anammox granules into small-size (0.5-0.9 mm), medium-size (1.8-2.2 mm), and large-size (2.8-3.5 mm) categories to examine their properties and mechanisms. Various analyses, including high-throughput sequencing, determination of inorganic elements and extracellular polymeric substances (EPS), and microbial function prediction, were conducted to characterize these granules and understand their impact. The results revealed distinct characteristics among the different-sized granules. Medium-size granules exhibited the highest sphericity, EPS content, and anammox abundance. In contrast, large-size granules had the highest specific surface area, heme c content, specific anammox activity, biodiversity, and abundance of filamentous bacteria. Furthermore, the precipitates within the granules were identified as CaCO3 and MgCO3, with the highest inorganic element content found in the large-size granules. Microbial community and function annotation also varied with granule size. Based on systematic analysis, the researchers concluded that cell growth, chemical precipitation, EPS secretion, and interspecies interaction all played a role in granulation. Small-size granules were primarily formed through cell growth and biofilm formation. As granule size increased, EPS secretion and chemical precipitation became more influential in the granulation process. In the large-size granules, chemical precipitation and interspecies interaction, including synergistic effects with nitrifying, denitrifying, and filamentous bacteria, as well as metabolic cross-feeding, played significant roles in aggregation. This interplay ultimately contributed to higher anammox activity in the large-size granules. By fully understanding the mechanisms involved in granulation, this study provides valuable insights for the acclimation of anammox granules with optimal sizes under different operational conditions.