Rheological and fractal hydrodynamics of aerobic granules

Towards zero excess sludge discharge with built-in ozonation for wastewater biological treatment

In this study, a biological treatment process, which used a built-in ozonation bypass to achieve sludge reduction, was built to treat the industrial antifreeze production wastewater (mainly composed of ethylene glycol). The results indicated there is a positive correlation between ozone dosage and sludge reduction. At the laboratory level, the MLSS in the system can be stably controlled at around 3400 mg MLSS L-1 under the dosage of 0.18 g O3 g-1 MLSS. Ozonation can increase the compactness of sludge flocs (fractal dimension increased from 1.89 to 1.92). Ozone destroys microbial cell membranes and alters the structure of sludge flocs through direct oxidation through electrophilic reactions. It leads to the release of intracellular polysaccharides, proteins, and other biological macromolecules in microorganisms, thereby promoting the implicit growth of microbial populations. Some bacteria such as g_Pseudomonas, g_Gemmobacter, etc. have strong ethylene glycol degradation ability and tolerance to ozonation. The removal of ethylene glycol includes the glyoxylate cycle, glycine serine carbon cycle, and the glutamate-cysteine ligase pathway of assimilation. Gene KatG and gpx may be key factors in improving microbial tolerance to ozonation. The comprehensive evaluation from the perspectives of cost and carbon emission shows that choosing ozone cracking-implicit growth in wastewater treatment systems has significant cost advantages and application value.

Simultaneous biodegradation of pyridine, indole, and ammonium along with phenol and thiocyanate by aerobic granular sludge

Aerobic granular sludge potential for concurrent biodegradation of two nitrogenous heterocyclic compounds (NHCs), i.e., pyridine and indole, and ammonia nitrogen along with phenol and thiocyanate was investigated in three sequencing batch reactors (SBRs) (R1, R2, and R3). Pyridine and indole were provided, respectively, in R1 and R2, whereas R3 was operated with a mixture of equimolar concentrations of pyridine and indole. Three concentrations of NHCs (1.0, 2.5, and 5.0 mM) were investigated to observe the impact on aerobic granules. Pyridine did not exhibit any adverse effect on the granular characteristics (volatile suspended solids of 6.00 ± 0.08 g L^-1 and sludge volume index of 37.98 ± 0.84 mL gTSS^-1) up to a concentration of 5.0 mM (402.93 ± 6.29 mg L^-1) (R1) with around 74% and >98% removal for pyridine and other pollutants (phenol, thiocyanate, and ammonia nitrogen), respectively. However, indole had a substantial adverse impact on the granular characteristics and other contaminants removal with a concentration of more than 1.0 mM (120.65 ± 4.84 mg L^-1) (R2). The current research work provides an experimental treatment methodology for the wastewater in which pyridine, indole, ammonium, phenol, and thiocyanate coexist.

Impact of high phenol loading on aerobic granules from two different kinds of industrial sludge along with thiocyanate and ammonium

Two sequencing batch reactors inoculated with two different kinds of industrial sludge; refinery sludge (R1) and brewery sludge (R2), were operated to observe the impact of high phenol loading (5.71 kg COD m^-3 day^-1) along with 100 mg L^-1 of ammonia-nitrogen and thiocyanate on the granular stability and performance. R2 granules were stable and degraded all the pollutants up to an organic loading of 5.71 kg COD m^-3 day^-1 with the large size and high extracellular polymeric substances of 2769.94 ± 62.26 µm and 114.83 ± 1.33 mg gVSS^-1, respectively, whereas R1 granules disintegrated at an organic loading of more than 3.32 kg COD m^-3 day^-1. At higher phenol loading, granular biomass activity was 3.43 and 16.35 mg COD removed mgVSS^-1 day^-1 in R1 and R2, respectively, from the initial sludge activities of 8.01 (refinery sludge) and 6.56 (brewery sludge) mg COD removed mgVSS^-1 day^-1.

Influence of inoculum variation on formation and stability of aerobic granules in oily wastewater treatment

This study provides extensive information about oily wastewater treatment in aerobic granular reactors (AGR) using three different inoculums from sewage, refinery and brewery. Initially, sodium acetate was used for granule formation while AGR with brewery inoculum had maximum granule size (5.44 ± 0.05 mm) and extracellular polymeric substances (EPS: 471.22 ± 2.0 mg/g VSS). But, during emulsified diesel exposure, refinery sludge granules achieved maximum granule size of 3.49 ± 0.01 mm and EPS of 204.85 ± 2.01 mg/g VSS with maximum 67.39 ± 0.15% oil removal efficiency. AGRs achieved 99.9 ± 0.05% chemical oxygen demand (COD) and 91.67 ± 0.14% ammonia nitrogen (NH₄⁺-N) removal efficiencies. Refinery granules remained stable at maximum 310 ± 10 mg/L diesel concentration whereas, the stability thresholds for sewage and brewery granules were 170 ± 15 and 250 ± 10 mg/L, respectively. Brevibacterium paucivorans strain SG001, Micrococcus aloeverae strain SG002 and Staphylococcus hominis strain SG003 were identified as the major pollutant degraders isolated from sewage, refinery and brewery sludge. Micrococcus aloeverae strain SG002 exhibited maximum pollutant removal efficiencies (COD: 99.9 ± 0.01%, NH₄⁺-N: 99.9 ± 0.01%, oil: 61.34 ± 0.85%) among the three species. Re-addition of sodium acetate restored granule structure and stability.

Efficiency, granulation, and bacterial populations related to pollutant removal in an upflow microaerobic sludge reactor treating wastewater with low COD/TN ratio

In this study, a novel upflow microaerobic sludge reactor (UMSR) was constructed to conduct anaerobic digestion of municipal wastewater with low carbon and nitrogen ratio (C/N). Oxygen in the UMSR was supplied by falling water and external recirculation. Excellent nitrogen removal performance was obtained in the UMSR for treating wastewater with low C/N ratio at a temperature of 25 °C and a hydraulic retention time of 24 h. Ammonium and total nitrogen removal efficiencies averaged 92.35% and 90.41%, respectively, and sludge granulation occurred during acclimation. The inferred metabolism of nitrogen removal and ecological positions of functional microbe were integrated into a granule model by scanning electron microscopy. Additionally, the analysis of microbial community indicated that aerobic nitrifying bacteria and heterotrophic bacteria survived on the surface of sludge floc and granules while the anaerobic autotrophic, heterotrophic denitrifying, and anaerobic ammonia oxidation bacteria were present in the inner layer.

Effect of air flow rate on development of aerobic granules, biomass activity and nitrification efficiency for treating phenol, thiocyanate and ammonium

The impact of air flow rate on aerobic granulation was evaluated for treating toxic multiple pollutants; phenol (400 mg L^-1), thiocyanate (100 mg L^-1) and ammonia nitrogen (100 mg L^-1) by using three lab scale sequencing batch reactors (SBRs) (R1, R2 and R3). Larger granules (2938.67 ± 64.91 μm) with higher biomass concentration (volatile solids of 4.17 ± 0.09 g L^-1), higher granule settling velocity (55.56 ± 1.36 m h^-1) and lower sludge volume index (35.25 ± 1.71 mL gTSS^-1) were observed at optimal air flow rate of 2.5 L min^-1 (R2). Confocal laser scanning microscopic images illustrated the extended fluorescence for extracellular polymeric substances in R2. In R2, partial nitrification was achieved. Phenol was completely removed in all the reactors while partial removal of SCN^- and no nitrification were observed with a decrease (1.5 L min^-1) and an increase (3.5 L min^-1) in air flow rates (R1 and R3, respectively). This study provides an experimental contribution to examine the effect of optimal combination of aeration and toxic multiple pollutants, governing characteristics and nitrification efficiency of granules along with SBR performance in an economic way in terms of optimal air supply.

Aerobic granular processes: Current research trends

Aerobic granules are large biological aggregates with compact interiors that can be used in efficient wastewater treatment. This mini-review presents new researches on the development of aerobic granular processes, extended treatments for complicated pollutants, granulation mechanisms and enhancements of granule stability in long-term operation or storage, and the reuse of waste biomass as renewable resources. A discussion on the challenges of, and prospects for, the commercialization of aerobic granular process is provided.