Anammox biofilter with denitrification sludge as seed in treating low nitrogen strength wastewater

New insights on destruction mechanisms of waste activated sludge during simultaneous thickening and digestion process via forward osmosis membrane

This study delved into the efficacy of sludge digestion and the mechanisms involved in sludge destruction during the implementation of forward osmosis process for sludge thickening and digestion (FO-MSTD). Utilizing a lab-scale FO membrane reactor for the thickening and digestion of waste activated sludge (WAS), the investigation explored the effects of sludge thickening and digestion in FO-MSTD processes using draw solutions of varying concentrations. The findings underscored the significance of hydraulic retention time (HRT) as a pivotal parameter influencing the swift thickening or profound digestion of sludge. Consequently, tailoring the HRT to specific processing objectives emerged as a key strategy for achieving desired treatment outcomes. In the investigation, the use of a 1 M NaCl draw solution in the FO-MSTD process showcased enhanced thickening and digestion capabilities. This specific setup raised the concentration of mixed liquor suspended solids (MLSS) to over 30 g/L and achieved a 42.7% digestion efficiency of mixed liquor volatile suspended solids (MLVSS) within an operational timeframe of 18 days. Furthermore, the research unveiled distinct stages in the sludge digestion process of the FO-MSTD system, characterized by fully aerobic digestion and aerobic-local anaerobic co-existing digestion. In the fully aerobic digestion stage, the sludge digestion rate exhibited a steady increase, leading to the breakdown of sludge floc structures and the release of a substantial amount of nutrients into the sludge supernatant. The predominant microorganisms during this stage were typical functional microorganisms found in wastewater treatment systems. Transitioning into the aerobic-local anaerobic co-existing digestion stage, both MLSS concentration and MLVSS digestion efficiency continued to rise, accompanied by a decreasing dissolved oxygen (DO) concentration. More organic matter was released into the supernatant, and sludge microbial flocs tended to reaggregate. The localized anaerobic environment within the FO-MSTD reactor fostered an increase in the relative abundance of bacteria with nitrogen and phosphorus removal functions, thereby positively impacting the mitigation of total nitrogen (TN) and total phosphorus (TP) concentrations in the sludge supernatant. The results of this research enhance comprehension of the advanced FO-MSTD technology in the treatment of WAS.

Enhanced nitrogen removal performance of nitrogen-rich saline wastewater by marine anammox bacteria: Based on different influent loading strengths

In an anaerobic sequential batch reactor (SBR), marine anammox bacteria (MAB) were able to enhance microbial activity in nitrogen-rich saline wastewater and it was significantly affected by influent substrate composition and loading strength. This study therefore enhanced nitrogen removal efficiency by adjusting the influent nitrogen loading strength of MAB-inoculated anaerobic SBRs and assessed the correlation with the bacterial community. The results displayed that the system obtained optimal nitrogen removal efficiency (TN = 83.52%, NH4-N = 90.14%, and NO2-N = 83.57%) as the strength of influent nitrogen loading was increased to 201.35 mg L-1 for NH4-N and 266.42 mg L-1 for NO2-N. Moreover, the increase in the strength of influent nitrogen loading also enhanced the anammox 16S rRNA abundance (4.09 × 108 copies g-1) and ladderanes content (22.49 ng g-1dw). Analysis of 15N isotope further illustrated that all systems were dominated by anammox (average ra = 95.22%). In conclusion, these findings provide scientific guidance for the management of eutrophic seawater and contribute to the realization of industrial applications for the treatment of nitrogen-rich saline wastewater.

Quantitative effect of adding percentages of anammox granules on the start-up process and microbial community analysis

The anaerobic ammonium oxidation (anammox) process is challenging due to its long start-up duration and high demand for mature anammox seed sludge. However, adding a small amount of anammox sludge to the inoculum can be a reasonable solution. This study investigated the effect of adding percentage of anammox granules (0, 1, 2, 4, and 8%) in the seed sludge on the anammox start-up process. The anammox process was achieved in all five reactors after 55, 6, 5, 3 and 0 days. Increasing the adding percentage effectively shortened the duration of lag phase and cell lysis, but had little effect on the final nitrogen removal performance, except for 4% adding percentage. Families of Brocadiaceae, Burkholderiaceae, Ignavibacteriaceae, SJA-28, and Rhodocyclaceae were dominant, with a core microbiota of eight operational taxonomic unites (OTUs), and Candidatus Brocadia fulgida became the dominant anammox species. Seven synergistic members with anammox bacteria were identified by correlation network analysis. Major potential functional groups involved in C and N cycle were also observed by FAPROTAX. Together with the qPCR and sequencing results, it was suggested that more than 2% of adding percentages would result in a short lag phase, rapid growth rate in elevation stage, high final performances, and anammox bacteria abundance comparable to that in the anammox seed sludge. This crucial finding indicated the feasibility of economical and rapid start-up of the anammox process with a minimum amount of anammox seed sludge.