Effect of thermal hydrolyzed sludge filtrate as an external carbon source on biological nutrient removal performance of A2/O system

Effects of ozonation sludge reduction on nutrient removal and microbial community diversity of conventional A2/O and reversed A2/O processes

To optimise ozonation sludge reduction in the activated sludge process, it is crucial to monitor nutrient removal and pay particular attention to the influential biological species. This study employed high-throughput sequencing to examine the microbial composition and diversity in the anaerobic-anoxic-oxic (A2/O) process, the A2/O process with ozonation, and the reversed A2/O process with ozonation. The diversity analysis aimed to identify discrepancies and similarities in microbial communities among these groups, thereby elucidating the varying biological efficiencies. Furthermore, the results from Illumina MiSeq sequencing revealed significant diversification in microbial community structures in different processes. Ozonation sludge notably inhibited certain species, including the order Bacteroidales within the class Bacteroidia, as well as the orders Rhizobiales and Rhodospirillales within the class Alphaproteobacteria. Additionally, ozonation sludge exerted a notable impact on specific orders within the class Gammaproteobacteria, including Aeromonadales, Chromatiales, and HOC36. In contrast, it stimulated the proliferation of other microbial groups, such as Lactobacillales, Clostridiales, as well as Burkholderiales and Rhodocyclales. The inhibition and promotion of ozonation sludge in conventional and reversed A2/O processes resulted in various microbial richness and diversity, which rendered the distinctive biochemical activities and wastewater treatment performances. Betaproteobacteria increased significantly, especially in the reversed A2/O process, and Betaproteobacteria played an important role in the nitrogen removal and phosphorus removal process. These findings are useful for guiding the ozonised sludge system to reduce carbon, denitrification, and phosphorus removal to meet the emission standards, and the identification and enhancement of the construction of potential key biological flora for better wastewater treatment and sludge reduction.

The dynamic features and microbial mechanism of nitrogen transformation for hydrothermal aqueous phase as fertilizer in dryland soil

Hydrothermal aqueous phase (HAP) contains abundant organics and nutrients, which have potential to partially replace chemical fertilizers for enhancing plant growth and soil quality. However, the underlying reasons for low available nitrogen (N) and high N loss in dryland soil remain unclear. A cultivation experiment was conducted using HAP or urea to supply 160 mg N kg-1 in dryland soil. The dynamic changes of soil organic matters (SOMs), pH, N forms, and N cycling genes were investigated. Results showed that SOMs from HAP stimulated urease activity and ureC, which enhanced ammonification in turn. The high-molecular-weight SOMs relatively increased during 5-30 d and then biodegraded during 30-90 d, which SUV254 changed from 0.51 to 1.47 to 0.29 L-1 m-1. This affected ureC that changed from 5.58 to 5.34 to 5.75 lg copies g-1. Relative to urea, addition HAP enhanced ON mineralization by 8.40 times during 30-90 d due to higher ureC. It decreased NO3-N by 65.35%-77.32% but increased AOB and AOA by 0.25 and 0.90 lg copies g-1 at 5 d and 90 d, respectively. It little affected nirK and increased nosZ by 0.41 lg copies g-1 at 90 d. It increased N loss by 4.59 times. The soil pH for HAP was higher than that for urea after 11 d. The comprehensive effects of high SOMs and pH, including ammonification enhancement and nitrification activity inhibition, were the primary causes of high N loss. The core idea for developing high-efficiency HAP fertilizer is to moderately inhibit ammonification and promote nitrification.

Applying sludge hydrolysate as a carbon source for biological denitrification after composition optimization via red soil filtration

Sludge hydrolysate, the byproduct generated during sludge hydrothermal treatment (HT), is a potential carbon source for biological denitrification. However, the refractory organic matters and the nutrient substances are unfavorable to the nitrogen removal. In this study, effects of HT conditions on the hydrolysate properties, and the hydrolysate compositions optimization via red soil (RS) filtration were investigated. At HT temperature of 160-220 °C and reaction time of 1-4 h, the highest dissolution rate of organics from sludge to hydrolysate achieved 70.1 %, while the acetic acid dominated volatile fatty acids (VFAs) was no more than 5.0 % of the total organic matter content. The NH4+-N and dissolved organic nitrogen (DON) were the main nitrogen species in hydrolysate. When the hydrolysate was filtered by RS, the high molecular weight organic matters, DON, NH4+ and PO43- were effectively retained by RS, while VFAs and polysaccharide favorable for denitrification were kept in the filtrate. When providing same COD as the carbon source, the filtrate group (Fi-Group) introduced lower concentrations of TN and humic substances but higher content of VFAs. This resulted in TN removal rate (57.0 %) and denitrification efficiency (93.6 %) in Fi-Group higher than those in hydrolysate group (Hy-Group), 39.4 % and 83.7 %, respectively. It is noticeable that both Hy- and Fi- Groups up-regulated most of denitrification functional genes, and increased the richness and diversity of denitrifying bacteria. Also, more denitrifying bacteria genera appeared, and their relative abundance increased significantly from 3.31 % in Control to 21.15 % in Hy- Group and 31.31 % in Fi-Group. This indicates that the filtrate is a more suitable carbon source for denitrification than hydrolysate. Moreover, the pH rose from 4.6 ± 0.14 to 6.5 ± 0.05, and the organic carbon, TN, TP and cation exchange capacity (CEC) of RS increased as well after being filtered, implying that the trapped compounds may have the potential to improve soil quality. This study provides a new insight for hydrolysate application according to its composition characteristics, and helps make the most use of wasted sludge.