Granules In Wastewater Treatment Research Articles

REVIEW OF AEROBIC GRANULAR SLUDGE TECHNOLOGY AND APPLICATION IN WASTEWATER TREATMENT

This paper focuses on introducing an overview of aerobic granular sludge technology, granulation, removal efficiency and application of aerobic granules in wastewater treatment. Aerobic granular sludge has a bacterial layered structure including anaerobic, anoxic and aerobic bacteria in order from inside to outside layer, so it is capable of simultaneous chemical oxygen demand, nitrogen and phosphorus removal. Granular sludge also has capacity to remove persistent organic substances and adsorb heavy metals. As a result, aerobic granular sludge technology can be effectively applied for municipal and industrial wastewater treatment. Many wastewater treatment plants applying aerobic granular sludge technology have been deployed, most commonly in Europe and especially in the Netherlands, which is the first place to apply this technology in practical wastewater treatment with Nereda® trademark. However, aerobic granular sludge is stable on batch reactors and takes months to form stable granular sludge. Therefore, it is necessary to have further researches on the granulation mechanism and affective factors to shorten the time of aerobic granular sludge formation as well as maintain the long-term stability of the granular sludge and develop continuous reactors to maintain the stability of the aerobic granular sludge to meet the requirement of wastewater treatment plants in practice.

Treatment of slaughterhouse wastewater in an upflow anaerobic sludge blanket reactor: Sludge characteristics

Aims: Present study was done by using upflow anaerobic sludge blanket (UASB) reactor to investigate the effect of influent chemical oxygen demand (COD) and organic load rate on the formation of anaerobic granules in wastewater treatment. Martials and Methods: Upflow anaerobic sludge blanket reactor with working volume 30 L was studied using actual slaughterhouse wastewater at a hydraulic retention time of 1.24 d and at temperatures in the range of 35°C ± 0.5°C for 320 days. The inoculum was extracted from the anaerobic digester of municipal sewage treatment plant, and the UASB reactor was filled with 8 L of sludge. Results: The results indicated that under the optimal conditions, about 94.6% of COD could be effectively removed from slaughterhouse wastewater with the UASB. The highest and lowest COD removal efficiency was 40.5 and 94.6% corresponding to influent COD of 1266.8 and 1222.2 mg/L, respectively. The fluctuation of solution pH in UASB operation was in the range of 6.68-8.03. The average of solution pH was 7.46 ± 0.36. The solution pH was gradually improved with UASB operation. Different granule sizes coexisted in the UASB reactor, but granules with the size of 1-3 mm were predominant. The maximum observed size of anaerobic granule was 7 mm. Conclusion: Application of slaughterhouse wastewater as feed wastewater demonstrated that the slaughterhouse wastewater to be more effective in promoting the formation of anaerobic granules and granule size in UASB reactor.

Aerobic Granules: Microbial Landscape and Architecture, Stages, and Practical Implications

For the successful application of aerobic granules in wastewater treatment, granules containing an appropriate microbial assembly able to remove contaminants should be retained and propagated within the reactor. To manipulate and/or optimize this process, a good understanding of the formation and dynamic architecture of the granules is desirable. Models of granules often assume a spherical shape with an outer layer and an inner core, but limited information is available regarding the extent of deviations from such assumptions. We report on new imaging approaches to gain detailed insights into the structural characteristics of aerobic granules. Our approach stained all components of the granule to obtain a high quality contrast in the images; hence limitations due to thresholding in the image analysis were overcome. A three-dimensional reconstruction of the granular structure was obtained that revealed the mesoscopic impression of the cavernlike interior of the structure, showing channels and dead-end paths in detail. In "old" granules, large cavities allowed for the irrigation and growth of dense microbial colonies along the path of the channels. Hence, in some areas, paradoxically higher biomass content was observed in the inner part of the granule compared to the outer part. Microbial clusters "rooting" from the interior of the mature granule structure indicate that granules mainly grow via biomass outgrowth and not by aggregation of small particles. We identify and discuss phenomena contributing to the life cycle of aerobic granules. With our approach, volumetric tetrahedral grids are generated that may be used to validate complex models of granule formation.

The Short-term Effects of Temperature and Free Ammonia on Ammonium Oxidization in Granular and Floccular Nitrifying System

The short-term effects of temperature and free ammonia (FA) on ammonium oxidization were investigated in this study by operating several batch tests with two different partial nitrification aggregates, formed as either granules or flocs. The results showed that the rate of ammonium oxidation in both cultures increased significantly as temperature increased from 10 to 30 °C. The specific ammonium oxidation rate with the granules was 2–3 times higher than that with flocs at the same temperature. Nitrification at various FA concentrations and temperatures combination exhibited obvious inhibition in ammonium oxidation rate when FA was 90 mg·L−1 and temperature dropped to 10 °C in the two systems. However, the increase in substrate oxidation rate of ammonia at 30 °C was observed. The results suggested that higher reaction temperature was helpful to reduce the toxicity of FA. Granules appeared to be more tolerant to FA attributed to the much fraction of ammonia oxidizing bacteria (AOB) and higher resistance to the transfer of ammonia into the bacterial aggregates, whereas in the floc system, the bacteria distributed throughout the entire aggregate. These results may contribute to the applicability of the nitrifying granules in wastewater treatment operated at high ammonium concentration.

Purification and Conformational Analysis of a Key Exopolysaccharide Component of Mixed Culture Aerobic Sludge Granules

The application of aerobic sludge granules in wastewater treatment could increase the intensity of wastewater treatment processes because of their greater density and size relative to conventional sludge flocs. It has been suggested that granules are distinguished from flocs by gel forming exopolysaccharides. In this study, evidence is presented linking a specific exopolysaccharide component with granule extracellular polymeric substance (EPS) gelation. Granular EPS comprised three components: high-molecular-weight (MW) exopolysaccharide, medium-MW proteins and glycosides, and low-MW proteins and glycosides. The high-MW fraction was separated by fractional precipitation and preparatory-scale gel permeation chromatography (GPC). The MW profile of this fraction appears to be exclusively attributable to high-MW polysaccharide. The exopolysaccharide exists as a gel at normal wastewater treatment operating pH (i.e., 6.0-8.5), whereas the low/medium-MW material does not. Conformational analysis by atomic force microscopy (AFM) of the dried material showed that the polysaccharide forms pearl-necklace-like, intramolecularly condensed structures when dissolved in Milli-Q water and partially relaxed helical aggregates when in alkali solution. Consequently, the gel-forming property of EPS in the aerobic sludge granules tested is probably associated with high-MW polysaccharide components.

Granular inorgano-organo pillared clays (GIOCs): Preparation by wet granulation, characterization and application to the removal of a Basic dye (BY28) from aqueous solutions

The aim of the study was to prepare resistant and spherical inorgano-organo pillared clays (GIOCs) granules for wastewater treatment using a new and simple method named high-shear wet granulation. To optimize the preparation method, the effects of the main process parameters, such as binder concentration, liquid to solid ratio and impeller speed on granule properties (size distribution, friability and disintegration tests) were investigated. Experimental results showed that the granulation of inorgano-organo pillared clays (PIOCs) with industrial Silicone is significantly influenced by the binder concentration, the liquid to solid ratio ( H %) and the impeller speed ( N). A modification of these parameters can greatly alter the characteristics of the granules. The impact of wet granulation on the kinetics and adsorption capacities of GIOCs was estimated using Basic Yellow 28 as model pollutant. Kinetic studies reveals that BY 28 adsorbed faster on PIOCs ( k 1 = 7.40 × 10 −2 min −1) than on granular forms. Results best fitted the pseudo-first-order kinetic model. It was also found that the adsorption kinetic is directly related to the surface diffusion of prepared GIOCs. The adsorption equilibrium data were analyzed by the Langmuir and Freundlich models using non-linear regression. The best fit to the data was obtained with the Langmuir isotherm. The highest adsorption capacities ( Q max = 514 mg/g; pH 6) for GIOCs were obtained for the finest forms (300–400 μm).

Toxicity effect of phenol on aerobic granules

Aerobic granular sludge cultivated in a pilot‐scale sequencing batch reactor, through mechanical separation using metal sieves, was categorized into five size categories of 0.09 (flocs), 0.35, 0.82, 1.65 and 2.54 mm in mean diameter. Granule microbial activity of each size category and the activity of the sludge flocs were determined after exposure to phenol (0–3000 mg L−1) at various exposure times of 4, 12, and 24 hours. The microbial activity reduction follows a linear relationship with the increase in phenol concentration for both granules and sludge flocs. The C50 value, i.e. the phenol concentration causing 50% inhibition of the microbial activity, decreased significantly with the exposure time, but it increased with granule size. The C50 increased by 18% from 1273 mg L−1 for sludge flocs to 1497 mg L−1 for granules of size 2.54 mm at an exposure time of 24 hours. The results indicated that the granular structure could protect the microbial cells from phenol toxicity. The application of aerobic granules in wastewater treatment could provide an improved ability to tolerate toxic chemical shock, particularly at longer exposure times.

Formation and characterisation of fungal and bacterial granules under different feeding alkalinity and pH conditions

Laboratory experiments were carried out using two identical bioreactors to investigate the effect of feeding alkalinity and pH on the formation of aerobic sludge granules in wastewater treatment. Both bioreactors, of 2.4 L each in working volume and seeded with activated sludge, were operated as sequencing batch reactors (SBR) and fed at the same rate with a glucose-based synthetic wastewater. The first SBR, with a low alkalinity of 28.7 mg CaCO 3/L in the influent, had a pH of about 3.0 in the reactor and achieved rapid formation of fungi-dominating granules in 1 week. The second SBR, with a high alkalinity of 301 mg CaCO 3/L from the addition of 440 mg NaHCO 3/L to the influent, maintained a reactor pH of around 8.1 and had a slower formation of bacteria-dominating granules, taking about 4 weeks. After granulation, both reactors performed well in organic degradation and sludge–liquid separation. However, according to examinations carried out using scanning electronic microscopy (SEM) and confocal laser scanning microscopy (CLSM), the mature fungal granules with a mean size of 7.0 mm had a loosely packed fluffy structure. Both fungi and extracellular polymeric substances (EPS) were distributed uniformly throughout the granules. The bacterial granules were smaller, with a mean size of 4.8 mm and a compact structure. EPS were distributed throughout and bacteria were mainly situated in the outer layer of the mature granules. Granulation of fungal sludge could be completed more rapidly than bacterial granulation. However, fungal granules were apparently weaker in structure and subject to more breakage and erosion than bacterial granules in aeration turbulence. The results suggest that by controlling the feeding alkalinity and reactor pH, a strategy of species selection can be developed for aerobic sludge granulation at different rates with different microbial communities and structural features.

Formation of Aerobic Granules with Domestic Sewage

The use of aerobic granules in wastewater treatment can reduce the land area that is needed for the treatment of sewage. Until now granulation has been mainly studied using artificial wastewater. Studying the possibility of forming aerobic granules on domestic sewage in a sequencing batch reactor was a logical step in the scaling-up process and development of this technology. Therefore, aerobic granulation was studied using presettled sewage as influent. After 20 days of operation at high chemical oxygen demand (COD) loading heterogeneous aerobic granular structures were observed, with a sludge volume index after 10 min settling of 38 mL g−1 and an average diameter of 1.1 mm . Applying a high COD load was found to be a critical factor for the formation of aerobic granules on this type of influent. Therefore short cycle times and concentrated wastewater are preferred to form granules in a sequencing batch reactor when low strength wastewater is used. The nutrient removal was not optimized in this study.