Effective aerobic granulation: Role of seed sludge

Community successional patterns and inter-kingdom interactions during granular biofilm development

Aerobic granular sludge is a compact and efficient biofilm process used for wastewater treatment which has received much attention and is currently being implemented worldwide. The microbial associations and their ecological implications occurring during granule development, especially those involving inter-kingdom interactions, are poorly understood. In this work, we monitored the prokaryote and eukaryote community composition and structure during the granulation of activated sludge for 343 days in a sequencing batch reactor (SBR) and investigated the influence of abiotic and biotic factors on the granule development. Sludge granulation was accomplished with low-wash-out dynamics at long settling times, allowing for the microbial communities to adapt to the SBR environmental conditions. The sludge granulation and associated changes in microbial community structure could be divided into three stages: floccular, intermediate, and granular. The eukaryotic and prokaryotic communities showed parallel successional dynamics, with three main sub-communities identified for each kingdom, dominating in each stage of sludge granulation. Although inter-kingdom interactions were shown to affect community succession during the whole experiment, during granule development random factors like the availability of settlement sites or drift acquired increasing importance. The prokaryotic community was more affected by deterministic factors, including reactor conditions, while the eukaryotic community was to a larger extent shaped by biotic interactions (including inter-kingdom interactions) and stochasticity.

Up-flow anaerobic sludge blanket treatment of swine wastewater: Effect of heterologous and homologous inocula on anaerobic digestion performance and the microbial community

The effects of heterogenous (anaerobic sludge from treating distillery sewage, ASDS) and homologous (anaerobic sludge from treating swine wastewater, ASSW) inocula on anaerobic digestion and the microbial community in an up-flow anaerobic sludge blanket treating swine wastewater were compared. The highest chemical oxygen demand removal efficiencies with ASDS (84.8%) and ASSW (83.1%) were obtained with an organic loading rate of 15 kg COD/m3/d. For ASSW compared with ASDS, methane production efficiency was 15.3% higher and excess sludge production was 73.0% lower. The abundance of the cellulose hydrolyzing bacterium Clostridium sensu stricto_1 with ASDS (36.1%) was 1.5 times that with ASSW, while that of Methanosarcina with ASSW (22.9%) was > 100 times that with ASDS. ASDS reduced the content of pathogenic bacteria by 88.0%, while ASSW maintained a low level of pathogenic bacteria. ASSW greatly improved the methane production efficiency of wastewater and is more suitable for treating swine wastewater.

Exploring the effects of organic loading rate and domestic wastewater treatment by algal-bacterial granules under natural daylight conditions

Algal-bacterial granules or phototrophic granules (PGs) comprising phototrophic microorganisms and bacteria are explored in wastewater treatment for achieving both environmental and economic sustainability. This study describes development of PGs and their use in biological treatment of synthetic and real domestic wastewater (sewage) under natural daylight conditions and low organic loading rate (OLR). Development of PGs was sequentially recorded in a photobioreactor operated in photo-sequencing batch reactor (photo-SBR) mode at a low OLR of 1 kgCOD.m^-3 .day^-1 and the developed PGs was evaluated for treating synthetic wastewater and real municipal wastewater with 0.14 kg COD m^-3 .day^-1 . PGs formed in the photo-sequential batch reactor (SBR) were compact and dense and exhibited excellent settling properties. The removal efficiencies were determined to be up to 95%, 93%, 97%, 72%, and 88% for turbidity, COD, TOC, NH₄ ⁺ -N, and NO₂ ^- -N/NO₃ ^- -N, respectively. Additionally, a reduction in total viable bacterial counts and fecal coliform bacteria up to 1.7 × 10³ and 7.8 × 10²  cfu.mL^-1 , respectively, during treatment of real municipal wastewater was achieved. This study demonstrated cultivation of algal-bacterial granules or PGs and their application for treating real municipal wastewater under natural daylight and tropical climate conditions. Further studies are needed on understanding interactions among phototrophic, autotrophic, and heterotrophic microorganisms of complex algal-bacterial consortium for emerging applications in bioremediation and wastewater treatment. PRACTITIONER POINTS: Phototrophic granules (PGs) were cultivated from algal consortium and activated sludge inoculum in photo sequencing batch reactors. Granular photobioreactor was operated at low OLR of 1 kgCOD.m³ .day^-1 for developing well-settling algal-bacterial granules. PGs were stable and showed efficient biological treatment of synthetic wastewater and real sewage. Removals for turbidity, pathogens, and ammonium were at 95%, 3-log, and 72%, respectively, from real sewage.

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.

The mechanisms of granulation of activated sludge in wastewater treatment, its optimization, and impact on effluent quality

Granular activated sludge has gained increasing interest due to its potential in treating wastewater in a compact and efficient way. It is well-established that activated sludge can form granules under certain environmental conditions such as batch-wise operation with feast-famine feeding, high hydrodynamic shear forces, and short settling time which select for dense microbial aggregates. Aerobic granules with stable structure and functionality have been obtained with a range of different wastewaters seeded with different sources of sludge at different operational conditions, but the microbial communities developed differed substantially. In spite of this, granule instability occurs. In this review, the available literature on the mechanisms involved in granulation and how it affects the effluent quality is assessed with special attention given to the microbial interactions involved. To be able to optimize the process further, more knowledge is needed regarding the influence of microbial communities and their metabolism on granule stability and functionality. Studies performed at conditions similar to full-scale such as fluctuation in organic loading rate, hydrodynamic conditions, temperature, incoming particles, and feed water microorganisms need further investigations.

Strengthening aerobic granule by salt precipitation

Structural stability of aerobic granules is generally poor during long-term operation. This study precipitated seven salts inside aerobic granules using supersaturated solutions of (NH4)3PO4, CaCO3, CaSO4, MgCO3, Mg3(PO4)2, Ca3(PO4)2 or SiO2 to enhance their structural stability. All precipitated granules have higher interior strength at ultrasonic field and reveal minimal loss in organic matter degradation capability at 160-d sequential batch reactor tests. The strength enhancement followed: Mg3(PO4)2=CaSO4>SiO2>(NH4)3PO4>MgCO3>CaCO3=Ca3(PO4)2>original. Also, the intra-granular solution environment can be buffered by the precipitate MgCO3 to make the aerobic granules capable of degradation of organic matters at pH 3. Salt precipitation is confirmed a simple and cost-effective modification method to extend the applicability of aerobic granules for wastewater treatments.

Aerobic granulation of protein-rich granules from nitrogen-lean wastewaters

Proteins (PN)-rich granules are stable in structure in long-term reactor operations. This study proposed to cultivate PN-rich granules with PN/polysaccharides (PS) >20 from nitrogen lean wastewater, with ammonia-nitrogen as sole nitrogen source at chemical oxygen demand (COD)/N of 153.8. The yielded granules can sustain their structural stability in sequencing batch reactor mode for sufficient treatment of wastewaters up to 7000mg/L COD and with COD/N<500 and in continuous-flow reactor for successful 216-d treatment of wastewaters up to organic loading rate (OLR) of 39kg/m(3)-d. The produced granules were enriched with Firmicutes and β-proteobacteria as dominating strains. More than 58% of the nitrogen fed in the nitrogen-lean wastewater is converted to the PN in the granules. The replacement of ammonia by nitrate as sole nitrogen source led to granules enriched with γ-proteobacteria which are easily deteriorated at low OLR.

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.

Formation of bacterial aerobic granules: Role of propionate

Propionate presents as one of the major volatile fatty acids in municipal wastewaters, which are not readily degraded as acetate by microorganisms. This study cultivated aerobic granules from column reactors with acetate, acetate/propionate mix (3:1 and 1:3) and propionate as carbon sources and noted that propionate-rich feed would delay granulation, but could generate granules with high structural strength. Propionate feed enriched strains fractionated into the hydrophobic phase, Sphaerotilus sp., Sphingomonadaceae and Thauera sp., in granules and altered hydrophobicity of Thauera sp. and Zoogloea sp. The enriched strains could secret high quantities of cyclic-di-diguanylate to increase production of extracellular polymeric substances (EPS). The hydrophobic cell surface and increased EPS quantity led to integrated propionate-fed granules. Feed with high propionate concentration is proposed as promising way to cultivate strong aerobic granules for practical use.