Application of glucose for improving NH4+-N removal in micro-polluted source water by immobilized heterotrophic nitrifiers at low temperature

Response and recovery of nitrifying moving bed biofilm reactor systems exposed to 1°C with varying levels of ammonia starvation

This study investigated the impact of varying total ammonia nitrogen (TAN) feed levels along with water temperature decreases on the performance of nitrifying moving bed biofilm reactor (MBBR) at 1 °C and its recovery at 3 °C. Five MBBR reactors were operated with different TAN concentrations as water temperature decreased from 20 to 3 °C: reactor R1 at 30 mg N/L, reactor R2 at 20 mg N/L, reactor R3 at 15 mg N/L, reactor R4 at 10 mg N/L and reactor R5 at 0 mg N/L. The corresponding biofilm characteristics were also analyzed to understand further nitrifying MBBR under different TAN feeding scenarios. The findings revealed that the higher TAN levels were before reaching 1 °C, the better nitrification performance and the more biomass grew. However, the highest TAN concentration (30 mg N/L) might negatively affect the nitrification performance, the activity of nitrifiers, and the growth of biofilms at 1 °C because of the toxic effects of un-ionized or free ammonia (FA). It was observed that the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were affected by FA concentrations ranging from 0.2 to 0.7 mg N/L at 1 °C, but they could gradually be adapted to such inhibitory environment, with NOB recovering more quickly and robustly than AOB. The study identified 20 mg N/L (67 % of maximum influent TAN at 1 °C in R2 as the optimal TAN feeding concentration, achieving over 90 % TAN removal and a surface area removal rate (SARR) of 0.78 ± 0.02 g N/m2·d at 1 °C. Meanwhile, R2 also exhibited the highest biofilm mass, with total solids at 13.3 mg/carrier and volatile solids at 11.3 mg/carrier. As TAN was removed, nitrite accumulation was observed at 1 °C, and higher influent TAN concentrations prior to 1 °C appeared to delay the accumulation. When water temperature increased from 1 °C to 3 °C, nitrification performance improved significantly in all reactors without nitrite accumulation, and the higher TAN feeding in the previous stage led to faster recovery. Compared with 20 °C, biofilm became thinner and denser at 1 °C and 3 °C. Furthermore, this study revealed significant shifts in microbial community composition and nitrifier abundances in response to changes in water temperature and influent TAN levels. The dominant nitrifiers were identified as Nitrosomonadaceae (AOB) and Nitrospiraceae (NOB). At 1 °C, the nitrifier abundances were significantly correlated with SARRs, FA, and biofilm density. R2, which exhibited the best nitrification performance, maintained higher nitrifier abundances at 1 °C.

Nano manganese dioxide coupling carbon source preloading granular activated carbon biofilter enhancing biofilm formation and pollutant removal

The formation of stable and mature biofilms affects the efficient and stable removal of ammonium by biological activated carbon (BAC). In this study, the new granular activated carbon (GAC) was preloaded with the carbon source (glucose and sucrose) and nano manganese dioxide (nMnO2) before using. Then tests were performed to determine whether substrate preloading promoted ammonium removal. The ammonium removal treated by nMnO2 coupled with sucrose-loaded BAC reached 49.1 ± 2.5%, which was 1.7 times higher than that by the nonloaded BAC 28.2 ± 1.9%). The biomass on the substrate-loaded BAC reached 5.83 × 106-1.22 × 107 cells/g DW GAC on Day 7, which was 4.6-9.5 times higher than the value of the nonloaded BAC (1.28 × 106 cells/g DW GAC). The amount of extracellular polymer (i.e., protein) on nMnO2 coupled to sucrose-loaded BAC was promoted significantly. Flavobacterium (0.7%-11%), Burkholderiaceae (13%-20%) and Aquabacterium (30%-67%) were the dominant functional bacteria on the substrate-loaded BAC, which were conducive to the nitrification or denitrification process. The results indicated that loading nMnO2 and/or a carbon source accelerated the formation of biofilms on BAC and ammonium removal. Additionally, the ammonium removal treated by nMnO2 coupled with sucrose-loaded BAC was contributed by microbial degradation (56.0 ± 2.5%), biofilm adsorption (38.7 ± 2.1%) and GAC adsorption (5.3 ± 0.3%), suggesting a major role of microbial degradation.

Long-term performance and biofilms of the novel nano manganese dioxide coupling carbon source pre-loaded biological activated carbon filters for drinking water

In order to accelerate the start-up of biological activated carbon (BAC) filters and enhance ammonium (NH4+-N) removal performance, three substrates (sucrose and/or nano manganese dioxide (nMnO2)) pre-loaded BAC filters were set up to investigate the pollutants removals and microbiological characteristics for a long-term operation of 197 days. The average NH4+-N removal performance treated by the sucrose coupled with nMnO2 loaded BAC filter was the highest (71.18 %), which was 3.83 times of that by the control filter (18.58 %). 29 % of NH4+-N treated by the sucrose coupled with nMnO2 loaded BAC removed through the traditional nitrification and denitrification, or simultaneous nitrification and denitrification (SND) pathways according to the calculation of the alkalinity consumption (6.12 mmol/L). There was no leakage of carbon source and Mn, and no accumulation of nitrite from the substrates loaded BAC. The dominant bacteria in the sucrose coupled with nMnO2 loaded BAC were Dechloromona (accounting for 8.02% of the total bacterial) and Acidaminobacter (accounting for 15.16% of total bacterial) on the Day 180, which had the capacity of nitrification or denitrification. NH4+-N and micropollutants removals treated by the combined process of peracetic acid (PAA) pre-oxidation and substrates loaded BAC were significant due to the generation of assimilable organic carbon (AOC) (5.98 ± 1.93 μg-C/mL) by PAA (100 μM)/Fe2+ pre-oxidation and the higher biomass ((4.57 ± 3.07) × 107 cells/g DW BAC) in the sucrose coupled with nMnO2 loaded BAC filter. Therefore, nMnO2 coupling carbon source pre-loading strategy could not only enhance initial colonization, but also promote pollutants removals for long-term operation.

Increase in Cd Tolerance through Seed-Borne Endophytic Fungus Epichloë gansuensis Affected Root Exudates and Rhizosphere Bacterial Community of Achnatherum inebrians

Soil cadmium (Cd) pollution is a serious environmental problem imperiling food safety and human health. The endophyte Epichloë gansuensis can improve the tolerance of Achnatherum inebrians to Cd stress. However, it is still unknown whether and how the endophyte helps host plants build up a specific bacterial community when challenged by CdCl2. In this study, the responses of the structure and function of bacterial community and root exudates of E+ (E. gansuensis infected) and E- (E. gansuensis uninfected) plants to Cd stress were investigated. Analysis of bacterial community structure indicated that the rhizosphere bacterial community predominated over the root endosphere bacterial community in enhancing the resistance of CdCl2 in a host mediated by E. gansuensis. E+ plant strengthened the interspecific cooperation of rhizosphere bacterial species. Moreover, the analysis of root exudates demonstrated E. gansuensis and increased the contents of organic acids and amino acids under Cd stress, and most root exudates were significantly correlated with rhizosphere bacteria. These results suggested that E. gansuensis employed a specific strategy to recruit distinct rhizosphere bacterial species and relevant functions by affecting root exudates to improve the tolerance of the host to Cd stress. This study provides a firm foundation for the potential application of symbionts in improving phytostabilization efficiency.

Challenges in Environmental Science/Engineering and fate and innovative treatment/remediation of emerging pollutants

Solid waste Management: There are two articles in this section. Shi et al. (2021) investigated the unbalanced status and multidimensional influences of municipal solid waste management in Africa. It was identified that economic growth, urbanization and geographical location are the most critical factors influencing the unbalanced statue of MSW management in Africa.

Enhanced biodegradation of chlortetracycline via a microalgae-bacteria consortium

Microbial removal of Chlortetracycline (CTC) at low CTC concentrations (in the order of 10-20 mg/L) has been reported. In this study, a novel microalgae-bacteria consortium was developed for effective CTC biodegradation at higher concentrations (up to 80 mg/L). The microalgae-bacteria consortium is resistant to up to 80 mg/L CTC, while the pure microalgal culture could only tolerate 60 mg/L CTC. CTC removal in the initial 12 h was primarily via biosorption by the microalgae-bacteria consortium and the adsorption capacity increased from 61.71 to 102.53 mg/g biomass in 12 h. Further, CTC biodegradation by the microalgae-bacteria consortium was catalyzed by extracellular enzymes secreted under antibiotic stress. The symbiotic bacterial diversity was analyzed by high throughput sequencing. The aerobic bacteria Porphyrobacter and Devosia were the dominant genera in the consortium. In the presence of CTC, a microbial community shift occurred with Chloroptast, Spingopyxis, and Brevundimonas being the dominant genera.