Chunli Wan

Microbial communities of aerobic granules: Granulation mechanisms

Aerobic granulation is an advanced biological wastewater treatment technology. This study for the first time identified the microbial communities of sliced samples of mature granules by polymerase chain reaction (PCR) amplification and denaturing gradient gel electrophoresis (DGGE) technique and those of whole growing granules by high-throughput sequencing technique. The sliced sample study revealed that mature granules have a spherical core with anaerobic Rhodocyclaceae covered by an outer spherical shell with both aerobic and anaerobic strains. The growing granule study showed that the flocculated flocs were first transited to young granules with increased abundances of Flavobacteriaceae, Xanthomonadaceae, Rhodobacteraceae and Microbacteriaceae, then the abundances of anaerobic strains were increased owing to the formation of anaerobic core. Since the present granules were cultivated from flocculated flocs, the microbial community data suggested that granules were formed via a deterministic rather than via a random aggregation-disintegration mechanism.

Disintegration of aerobic granules: Role of second messenger cyclic di-GMP

Loss of structural stability of aerobic granular process is the challenge for its field applications to treat wastewaters. The second messenger, cyclic diguanylate (c-di-GMP), is widely used by bacteria to regulate the synthesis of exopolysaccharide. This study for the first time confirmed the correlation between concentration of intracellular c-di-GMP and the granular stability under sequencing batch reactor (MBR) mode. In the presence of manganese ions (Mn(2+)), the concentrations of intracellular c-di-GMP and of extracellular polysaccharides and proteins in granules were declined. Clone library study revealed that the polysaccharide producers. Acinetobacter sp., Thauera sp., Bdellovibrio sp. and Paracoccus sp. were lost after Mn(2+) addition. The findings reported herein confirmed that the c-di-GMP is a key chemical factor epistatic to quorum sensing to determine granular stability. Stimulation of synthesis of intracellular c-di-GMP presents a potential way to enhance long-term stability of aerobic granules.

Partial nitrification using aerobic granules in continuous-flow reactor: Rapid startup

This study applied a novel strategy to rapid startup of partial nitrification in continuous-flow reactor using aerobic granules. Mature aerobic granules were first cultivated in a sequencing batch reactor at high chemical oxygen demand in 16 days. The strains including the Pseudoxanthomonas mexicana strain were enriched in cultivated granules to enhance their structural stability. Then the cultivated granules were incubated in a continuous-flow reactor with influent chemical oxygen deamnad being stepped decreased from 1,500 ± 100 (0-19 days) to 750 ± 50 (20-30 days), and then to 350 ± 50 mg l(-1) (31-50 days); while in the final stage 350 mg l(-1) bicarbonate was also supplied. Using this strategy the ammonia-oxidizing bacterium, Nitrosomonas europaea, was enriched in the incubated granules to achieve partial nitrification efficiency of 85-90% since 36 days and onwards. The partial nitrification granules were successfully harvested after 52 days, a period much shorter than those reported in literature.

Calcium precipitate induced aerobic granulation.

Aerobic granulation is a novel biotechnology for wastewater treatment. This study refined existing aerobic granulation mechanisms as a sequencing process including formation of calcium precipitate under alkaline pH to form inorganic cores, followed by bacterial attachment and growth on these cores to form the exopolysaccharide matrix. Mature granules comprised an inner core and a matrix layer and a rim layer with enriched microbial strains. The inorganic core was a mix of different crystals of calcium and phosphates. Functional strains including Sphingomonas sp., Paracoccus sp. Sinorhizobium americanum strain and Flavobacterium sp. attached onto the cores. These functional strains promote c-di-GMP production and the expression by Psl and Alg genes for exopolysaccharide production to enhance formation of mature granules.

Mechanism of enhanced Sb(V) removal from aqueous solution using chemically modified aerobic granules.

Sb(V) removal using Fe-modified aerobic granules was investigated. Increasing the biomass dosage improved the Sb(V) removal rate, but lowered the adsorption quantity; the optimal biomass concentration was 20 g/L (wet basis). Adsorption equilibrium was obtained at 2h at 175 rpm; the adsorption quantity was 36.6 mg/g. NaCl and other salts inhibited Sb(V) adsorption on Fe-modified granules, and the mechanism possibly lied more with the anions. The adsorption isotherms were evaluated using the Langmuir, Freundlich, and Temkin models. The Langmuir model best described the adsorption process, and gave a maximum monolayer adsorption quantity of 125 mg/g. The ΔH value for adsorption was 16.1 kJ/mol, indicating endothermicity, and the negative ΔG values at various temperatures suggested spontaneous adsorption. Outer-sphere and inner-sphere complexations were involved in Sb(V) adsorption.

Partial nitrification of wastewaters with high NaCl concentrations by aerobic granules in continuous-flow reactor.

Wastewaters with high salinity are yielded that need sufficient treatment. This study applied aerobic granules to conduct partial nitrification reactions for wastewaters with high NaCl concentrations in a continuous-flow reactor. The present granules revealed partial nitrification performances at nitrite accumulation rate >95% and chemical oxygen demand (COD) removal at >85% at salt concentration up to 50 g l(-1). High salinity led to compact and tough granules. The granules applied electrogenic ion pump and sodium-calcium exchanger to reduce intracellular Na(+) concentration; generated amino acids as osmoprotectants to resist the high osmotic pressure; produced excess extracellular polysaccharides and proteins with secretion of c-di-GMP; revised microbial community with halophilic strains. The present continuous-flow aerobic granule reactor (CFAGR) is a promising process to convert ammonium in highly saline wastewaters to nitrite, which can be applied with a subsequent Anammox process for efficient nitrogen removal.

Accelerated aerobic granulation using alternating feed loadings: Alginate-like exopolysaccharides

Alginate-like exopolysaccharides (ALE) likely contribute markedly to strength of aerobic granules. This study cultivated aerobic granules from propionate wastewaters using strategies with different organic loading rates (OLRs) (4.4-17.4 kg/m(3)-d). When the OLR increased suddenly, the constituent cells (Pseudomonas, Clostridium, Thauera and Arthrobacter) were stimulated to secret extracellular cyclic diguanylate (c-di-GMP) and produced excess ALE, which formed a large quantity of sticky materials that served as the precursor of aerobic granules. Formation of excess ALE was the prerequisite for accelerated granulation. Conversely, this study observed no enrichment of poly guluronic acid blocks in ALE during granulation.

Effect of initial pH on mesophilic hydrolysis and acidification of swine manure

Effects of initial pH (3-12) on mesophilic hydrolysis and acidification reactions of swine manure was studied. The initial pH changed the microbial community in the suspension so as to affect hydrolysis and acidification reactions on swine manure. At pH 10-12 the Clostridium alkalicellum and/or Corynebacterium humireducens were enriched and the soluble chemical oxygen demand (SCOD), total volatile fatty acids (VFAs), proteins and carbohydrates from manure were increased in quantities. In particular, at pH 10 the VFA concentration peaked at 13,600 mg-COD/L, with acetate and propionate accounting for 71.8% of the total VFAs. Acidic environment facilitates release of ammonium from manure. The Butyricimonas sp. was found existing at initial pH 5 which led to accumulated quantities of butyrate. Initial pH adjustment was revealed to be an effective way to manipulate rates and end products of hydrolysis and acidification of swine manure.

Continuous volatile fatty acid production from waste activated sludge hydrolyzed at pH 12.

This study adopted rapid alkaline treatment at pH 12 to hydrolyze 66% of total chemical oxygen demands. Then the hydrolyzed liquor was fermented in a continuous-flow stirred reactor to produce volatile fatty acids (VFAs) at 8-h hydraulic retention time and at 35 °C. The maximum VFA productivity reached 365 mg VFAs g(-1) volatile suspended solids in a 45-d operation, with most produced VFAs being acetate and propionate, principally produced by protein degradation. The Bacteroidia, ε-proteobacteria and the Clostridia were identified to be the classes correlating with the fermentation processes. The fermented liquor was applied to denitrifying phosphorus removal process as alternative carbon source after excess phosphorus and nitrogen being recycled via struvite precipitation. Fermented liquors from alkaline hydrolysis-acid fermentation on waste activated sludge are a potential renewable resource for applications that need organic carbons.

Aerobic granulation of aggregating consortium X9 isolated from aerobic granules and role of cyclic di-GMP

This study monitored the granulation process of an aggregating functional consortium X9 that was consisted of Pseudomonas putida X-1, Acinetobacter sp. X-2, Alcaligenes sp. X-3 and Comamonas testosteroni X-4 in shaken reactors. The growth curve of X9 was fit using logistic model as follows y=1.49/(1+21.3*exp(-0.33x)), the maximum specific cell growth rate for X9 was 0.33 h(-1). Initially X9 consumed polysaccharides (PS) and secreted proteins (PN) to trigger granulation. Then X9 grew in biomass and formed numerous micro-granules, driven by increasing hydrophobicity of cell membranes and of accumulated extracellular polymeric substances (EPS). In later stage the intracellular cyclic diguanylate (c-di-GMP) was at high levels for inhibiting bacteria swarming motility, thereby promotion formation of large aerobic granules. The findings reported herein advise the way to accelerate granule formation and to stabilize operation in aerobic granular reactors.