Degrading high-strength phenol using aerobic granular sludge

Aerobic granules were adopted to degrade high-strength phenol wastewater in batch experiments. The acclimated granules effectively degraded phenol at a concentration of up to 5,000 mg l⁻¹ without severe inhibitory effects. The biodegradation of phenol by activated sludge was inhibited at phenol concentrations >3,000 mg l⁻¹. The granules were composed of cells embedded in a compact extracellular matrix. After acid or alkaline pretreatment, the granules continued to degrade phenol at an acceptable rate. The polymerase chain reaction-denaturing gradient gel electrophoresis technique was employed to monitor the microbial communities of the activated sludge and the aerobic granules following their being used to treat high concentrations of phenol in batch tests.     

Heterogeneous diffusion in aerobic granular sludge

Aerobic granular sludge (AGS) technology allows simultaneous nitrogen, phosphorus, and carbon removal in compact wastewater treatment processes. To operate, design, and model AGS reactors, it is essential to properly understand the diffusive transport within the granules. In this study, diffusive mass transfer within full-scale and lab-scale AGS was characterized with nuclear magnetic resonance (NMR) methods. Self-diffusion coefficients of water inside the granules were determined with pulsed-field gradient NMR, while the granule structure was visualized with NMR imaging. A reaction-diffusion granule-scale model was set up to evaluate the impact of heterogeneous diffusion on granule performance. The self-diffusion coefficient of water in AGS was ∼70% of the self-diffusion coefficient of free water. There was no significant difference between self-diffusion in AGS from full-scale treatment plants and from lab-scale reactors. The results of the model showed that diffusional heterogeneity did not lead to a major change of flux into the granule (<1%). This study shows that differences between granular sludges and heterogeneity within granules have little impact on the kinetic properties of AGS. Thus, a relatively simple approach is sufficient to describe mass transport by diffusion into the granules.     

Reactivation characteristics of stored aerobic granular sludge using different operational strategies

Aerobic granules after 6 months storage were employed in identical sequencing batch reactors (SBRs) using synthetic wastewater to investigate the impacts of different operational strategies on granules' reactivation process. The SBRs were operated under three operational strategies for reactivation of (a) different organic loading rate (OLR); (b) different ammonia concentration; and (c) different shear force (a superficial upflow air velocity). The results indicated that granules after long-term storage could be successfully recovered after 7 days of operation, and the excellent granule reactivation performance was closely related to the operational strategies, since inappropriate operational strategies could cause the outgrowth of filamentous bacteria and granule disintegration. Based on comprehensive comparison of reactivation performance under different operational strategies, the optimal operation strategy for granule reactivation was suggested at OLR of 0.8 kg COD/m(3)/day, ammonia concentration of 15-20 mg/L, and a superficial upflow air velocity of 2.6 cm/s. After 7 days operation under the optimal strategy, the dark brown granules (12 months storage) restored their bioactivities to previous state, in terms of COD removal efficiency (97.44%) and specific oxygen uptake rate (40.63 mg O(2)/g SS h(-1)). The results shed light on the future practical application of stored aerobic granules as bioseed for reactor fast start-up.     

Potential cause of aerobic granular sludge breakdown at high organic loading rates

Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. Aerobic granules disintegrate under high organic loading rates (OLR). This study cultivated aerobic granules using acetate as the sole carbon and energy source in three identical sequencing batch reactors operated under OLR of 9–21.3 kg chemical oxygen demand (COD) m⁻³ day⁻¹. The cultivated granules removed 94–96% of fed COD at OLR up to 9–19.5 kg COD m⁻³ day⁻¹, and disintegrated at OLR of 21.3 kg COD m⁻³ day⁻¹. Most tested isolates did not grow in the medium at >3,000 mg COD l⁻¹; additionally, these strains lost capability for auto-aggregation and protein or polysaccharide productivity. This critical COD regime correlates strongly with the OLR range in which granules started disintegrating. Reduced protein quantity secreted by isolates was associated with the noted poor granule integrity under high OLR. This work identified a potential cause of biological nature for aerobic granules breakdown.     

Cascade bioreactor with submerged biofilm for aerobic treatment of Tunisian landfill leachate

A bioreactor cascade with a submerged biofilm is proposed to treat young landfill leachate of jbel chakir landfill site south west from capital Tunis, Tunisia. The prototype was run under different organic loading charges varying from 0.6 to 16.3 kg TOC m⁻³ day⁻¹. Without initial pH adjustment total organic carbon (TOC) removal rate varied between 65% and 97%. The total reduction of COD reached 92% at a hydraulic retention time of 36 h. However, the removal of total kjeldahl nitrogen for loading charges of 0.5 kg N m⁻³ day⁻¹ reached 75%. The adjustment of pH to 7.5 improved nitrogen removal to a rate of 85% for loading charge of 1 kg N m⁻³ day⁻¹. The main bacterial groups responsible for a simultaneous removal of organic carbon and nitrogen belonged to Bacillus, Actinomyces, Pseudomonas and Burkholderia genera. These selected isolates showed a great capacity of degradation at different leachate concentrations of total organic carbon.     

Comparison of biological removal via nitrite with real-time control using aerobic granular sludge and flocculent activated sludge

The process of nitrification–denitrification via nitrite for nitrogen removal under real-time control mode was tested in two laboratory-scale sequencing batch reactors (SBRs) with flocculent activated sludge (R1) and aerobic granular sludge (R2) to compare operational performance and real-time control strategies. The results showed that the average ammonia nitrogen, total inorganic nitrogen (TIN), and chemical oxygen demand (COD) removal during aeration phase were 97.6%, 57.0%, and 90.1% in R2 compared with 98.6%, 48.7%, and 88.1% in R1. The TIN removed in both SBRs was partially due to the presence of simultaneous nitrification–denitrification via nitrite, especially in R2. The specific nitrification and denitrification rates in R2 were 0.0416 mgNH₄⁺–N/gSS-min and 0.1889 mgNO_X⁻–N/gSS-min, which were 1.48 times and 1.35 times that of R1. The higher rates for COD removal, nitrification, and denitrification were achieved in R2 than R1 with similar influent quality. Dissolved oxygen (DO), pH, and oxidization reduction potential, corresponding to nutrient variations, were used as diagnostic parameters to control the organic carbon degradation and nitrification–denitrification via nitrite processes in both SBRs. The online control strategy of granular SBR was similar to that of the SBR with flocculent activated sludge. However, a unique U-type pattern on the DO curve in granular SBR was different from SBR with flocculent activated sludge in aerobic phase.     

Treatment of dairy effluents in an aerobic granular sludge sequencing batch reactor

Aerobic granular sludge can successfully be cultivated in a sequencing batch reactor (SBR) treating dairy wastewater. Attention has to be paid to the fact that suspended solids are always present in the effluent of aerobic granular sludge reactors, making a post-treatment step necessary. Sufficient post-treatment can be achieved through a sedimentation process with a hydraulic retention time of 15–30 min. After complete granulation and the separation of biomass from the effluent, removal efficiencies of 90% COD_total, 80% N_total and 67% P_total can be achieved at a volumetric exchange ratio of 50% and a cycle duration of 8 h. Effluent values stabilize at around 125 mg l^–1 COD_dissolved. The maximum applicable loading rate is nevertheless limited, as the stability of aerobic granules very much depends on the presence of distinct feast and famine conditions and the degradation of real wastewaters shows slower kinetics compared with synthetic wastewaters. As loading rate and volumetric exchange ratio are coupled in an SBR system, the potential of granular sludge for improving process efficiency is also limited.     

Co-digestion of intermediate landfill leachate and sewage sludge as a method of leachate utilization

This study examines the co-digestion of intermediate landfill leachate and sewage sludge from a municipal wastewater treatment plant. Application of leachate as a co-fermentation component increased the concentrations of soluble organic compounds (expressed as total organic carbon), ammonium nitrogen, and alkalinity in the digester influents.The biogas yield obtained from the co-fermentation of a 20:1 sewage sludge: intermediate leachate mixture was 1.30 m³ per kg of removed volatile solids (VS), while that from a 10:1 mixture was 1.24 m³ per kg of removed VS. These values exceeded the biogas yield for the sludge alone by 13% and 8%, respectively. The leachate addition influenced the proportion of methane to a minor extent. Increased methane yields of 16.9% and 6.2% per kg of removed VS were found for the two sewage sluge:intermediate leachate mixtures, respectively.     

Factors influencing the density of aerobic granular sludge

In the present study, the factors influencing density of granular sludge particles were evaluated. Granules consist of microbes, precipitates and of extracellular polymeric substance. The volume fractions of the bacterial layers were experimentally estimated by fluorescent in situ hybridisation staining. The volume fraction occupied by precipitates was determined by computed tomography scanning. PHREEQC was used to estimate potential formation of precipitates to determine a density of the inorganic fraction. Densities of bacteria were investigated by Percoll density centrifugation. The volume fractions were then coupled with the corresponding densities and the total density of a granule was calculated. The sensitivity of the density of the entire granule on the corresponding settling velocity was evaluated by changing the volume fractions of precipitates or bacteria in a settling model. Results from granules originating from a Nereda reactor for simultaneous phosphate COD and nitrogen removal revealed that phosphate-accumulating organisms (PAOs) had a higher density than glycogen-accumulating organisms leading to significantly higher settling velocities for PAO-dominated granules explaining earlier observations of the segregation of the granular sludge bed inside reactors. The model showed that a small increase in the volume fraction of precipitates (1–5 %) strongly increased the granular density and thereby the settling velocity. For nitritation–anammox granular sludge, mainly granular diameter and not density differences are causing a segregation of the biomass in the bed.     

Variable aeration in sequencing batch reactor with aerobic granular sludge

This study investigated the effects of reduced aeration in famine period on the performance of sequencing batch reactor (SBR) with aerobic granular sludge. Aerobic granules were first cultivated in two SBRs (R1 and R2) with acetate as sole carbon source. From operation day 27, aeration rate in R1 was reduced from 1.66 to 0.55 cm s(-1) from 110 min to the end of each cycle and further reduced from 30 min to the end of each cycle from day 63. R2 as a control was operated with a constant aeration rate of 1.66 cm s(-1) in the whole cycle during the entire experimental period. Results showed that changing trends of SVI, concentration, average size and VSS/SS of biomass with time in R1 and R2 were similar although different aeration modes were adopted. At steady state, SVI of aerobic granules and biomass concentration maintained at about 40 ml g(-1) and 6 g l(-1), respectively. Average size of granules was about 750 microm in R1 while 550 microm in R2. This is the first study to demonstrate that aerobic granular sludge could be stable at reduced aeration rate in famine period during more than 3-month operation. Such an operation strategy with reduced aeration rate will lead to a significant reduction of energy consumption, which makes the aerobic granular sludge technology more competitive over conventional activated sludge process. Furthermore, the stability of aerobic granular system with variable aeration further indicates that the difference of physiology and kinetics of aerobic granule in feast and famine periods results in the different requirements of oxygen and shear stress for the stability of granules, which will deepen the understanding of mechanism of aerobic granulation in sequencing batch reactor.     

PPCPs removal by aerobic granular sludge membrane bioreactor

An aerobic granular sludge membrane bioreactor (GMBR) was applied to the treatment of pharmaceutical and personal care products (PPCPs) wastewater. The influence of granular sludge on five antibiotic and antiphlogistic PPCPs wastewater and the removal effect of methyl alcohol and conventional organic matter were investigated while constantly reducing the density of inflow organic matter. The results showed that the sludge granulation process in the system was rapid but unstable, and that the system exhibits a dissolution–reunion dynamic equilibrium. The reactor demonstrated varying removal effects of PPCPs on different objects. The use of a GMBR was more effective for the removal of prednisolone, naproxen, and ibuprofen; the first two drugs were lower the average removal rate of which reached 98.46 and 84.02 %, respectively; whereas the average removal rate of ibuprofen was 63.32 %. By contrast, the GMBR has an insignificant degradation effect on antibiotics such as amoxicillin, indicating that such antibiotic medicine is not easily degraded by microorganisms, which plays different roles in system operation. Because of the different chemical structures and characteristics of drugs that result in various degradation behavior. During the GMBR granulation process, the value of mixed liquor volatility suspended solids (MLVSS) gradually increases from 1.5 to 4.1 g/L during the GMBR granulation process, and the removal rate of COD_Cr reaches up to 87.98 %. After reducing the density of organic matter is reduced, the removal rates of NH₃-N and TP both reach more than 90 %, respectively. Moreover, the proposed technique is considerably effective in the removal of methanol.     

Microbial diversity differences within aerobic granular sludge and activated sludge flocs

In this study, we investigated during 400 days the microbial community variations as observed from 16S DNA gene DGGE banding patterns from an aerobic granular sludge pilot plant as well as the from a full-scale activated sludge treatment plant in Epe, the Netherlands. Both plants obtained the same wastewater and had the same relative hydraulic variations and run stable over time. For the total bacterial population, a similarity analysis was conducted showing that the community composition of both sludge types was very dissimilar. Despite this difference, general bacterial population of both systems had on average comparable species richness, entropy, and evenness, suggesting that different bacteria were sharing the same functionality. Moreover, multi-dimensional scaling analysis revealed that the microbial populations of the flocculent sludge system moved closely around the initial population, whereas the bacterial population in the aerobic granular sludge moved away from its initial population representing a permanent change. In addition, the ammonium-oxidizing community of both sludge systems was studied in detail showing more unevenness than the general bacterial community. Nitrosomonas was the dominant AOB in flocculent sludge, whereas in granular sludge, Nitrosomonas and Nitrosospira were present in equal amounts. A correlation analysis of process data and microbial data from DGGE gels showed that the microbial diversity shift in ammonium-oxidizing bacteria clearly correlated with fluctuations in temperature.     

Achieving high-rate partial nitritation with aerobic granular sludge at low temperatures

Biodegradation - Partial nitritation is necessary for the implementation of the mainstream anammox (anaerobic ammonium oxidation) process in wastewater treatment plants. However, the difficulty in...     

Evolution of bioaggregate strength during aerobic granular sludge formation

This work investigated the modification of aggregate properties during the formation of granular sludge in a sequencing batch airlift reactor (SBAR). The cohesion of biological aggregates was quantified by subjecting sludge samples to two different controlled shear stresses in a stirred reactor. For reference sludge (without granules), flocs broke and reformed easily, indicating that floc size was controlled by the turbulence micro-scale (Kolmogorov scale, here from 17 μm to 62 μm). In contrast, granules showed high strength which enabled them to resist turbulence and their size was no longer imposed by the Kolmogorov micro-scale. Different steps were observed during the granulation process: a first increase of aggregate cohesion associated with a decrease in sludge volume index (SVI), a growth of aggregates with detachment of fragile particles from the surface and, finally, an increase in the sizes of small and large granules to reach a pseudo-stable size distribution. Results suggest that small particles could have formed the seeds for new granules, as they were maintained in the bioreactor. Here, granular sludge was formed in an SBAR with a conventional settling time (30 min), i.e. without particle washout, and with a low superficial air velocity (SAV = 0.6 cm s⁻¹): it is thus demonstrated that high SAV and low settling time are not necessary to produce granules, but probably only accelerate the accumulation of granules. It is shown that the increase of cohesion is the initial phenomenon explaining the granule formation concomitantly with bacterial aggregates densification. It seems important, in the future, to investigate the reasons for this cohesion increase, which is possibly explained either by bacterial bounding interactions or the excretion of extracellular polymeric substances (EPS).     

Mathematical modeling of aerobic granular sludge: A review

Aerobic granulation may play an important role in the field of wastewater treatment due to the advantages of aerobic granules compared to the conventional sludge flocs, such as denser structure, better settleability and ensured solid-effluent separation, higher biomass concentration, and greater ability to withstand shock loadings, which is promising for a full-scale implementation. As an aid for this implementation, mathematical modeling would be an invaluable tool. In this paper, the existing mathematical models available in literature concerning aerobic granule systems are reviewed, including the modeling of the dynamic facets of the aerobic granulation process, the mass transfer and detachment in aerobic granules, the granule-based sequencing batch reactor, the fate of microbial products in granules, and the multi-scale modeling of aerobic granular sludge. An overview of the parameters used in the aerobic granular modeling approaches is also presented. Our growing knowledge on mathematical modeling of aerobic granule might facilitate the engineering and optimization of aerobic granular sludge technology as one of the most promising techniques in the biological wastewater treatment.     

Improved phosphate removal by selective sludge discharge in aerobic granular sludge reactors

Two lab-scale aerobic granular sludge sequencing batch reactors were operated at 20 and 30°C and compared for phosphorus (P) removal efficiency and microbial community composition. P-removal efficiency was higher at 20°C (>90%) than at 30°C (60%) when the sludge retention time (SRT) was controlled at 30 days by removing excess sludge equally throughout the sludge bed. Samples analyzed by fluorescent in situ hybridization (FISH) indicated a segregation of biomass over the sludge bed: in the upper part, Candidatus Competibacter phosphatis (glycogen-accumulating organisms--GAOs) were dominant while in the bottom, Candidatus Accumulibacter phosphatis (polyphosphate-accumulating organisms--PAOs) dominated. In order to favour PAOs over GAOs and hence improve P-removal at 30°C, the SRT was controlled by discharging biomass mainly from the top of the sludge bed (80% of the excess sludge), while bottom granules were removed in minor proportions (20% of the excess sludge). With the selective sludge removal proposed, 100% P-removal efficiency was obtained in the reactor operated at 30°C. In the meantime, the biomass in the 30°C reactor changed in color from brownish-black to white. Big white granules appeared in this system and were completely dominated by PAOs (more than 90% of the microbial population), showing relatively high ash content compared to other granules. In the reactor operated at 20°C, P-removal efficiency remained stable above 90% regardless of the sludge removal procedure for SRT control. The results obtained in this study stress the importance of sludge discharge mainly from the top as well as in minor proportions from the bottom of the sludge bed to control the SRT in order to prevent significant growth of GAOs and remove enough accumulated P from the system, particularly at high temperatures (e.g., 30°C).     

Powdered activated carbon augmented activated sludge process for treatment of semi-aerobic landfill leachate using response surface methodology

This study was conducted to investigate aerobic biodegradation of semi-aerobic leachate with and without powdered activated carbon (PAC) addition. The experiment involved operating two 16L laboratory-scale activated sludge reactors in parallel at room temperature and adjusted to pH 6.5+/-0.5. One of the reactors was supplemented with PAC of 75-150microm size to observe its effect on semi-aerobic leachate biodegradation. Three hydraulic retention times (0.92, 1.57 and 2.22 d) and influent COD concentrations (750, 1800 and 2850mg/L) were applied in a factorial design for this study. The results showed enhanced reactor performance due to PAC addition with higher COD, colour and ammoniacal nitrogen removals. The PAC augmented reactor also had higher concentrations of NO(2)-N and NO(3)-N consequent of greater degree of nitrification.     

Influence of phenol on cultures of acetate-fed aerobic granular sludge

AIMS: This paper attempts to investigate the inhibition of phenol on the acetate utilization in acetate-fed aerobic granular sludge culture. METHODS AND RESULTS: Acetate-fed aerobic granules with a mean diameter of 1.0 mm were predeveloped in a column sequencing aerobic sludge blanket reactor. The present study looked into the utilization kinetics of acetate by acetate-fed aerobic granules in the presence of different phenol concentrations ranging from 0 mg l(-1) to 50 mg l(-1). For this purpose, batch experiments were conducted at 25 degrees C, while the initial biomass and acetate concentrations were in a range of 109-186 mg mixed liquor suspended solids (MLSS) l(-1) and 185-300 mg acetate-chemical oxygen demand (COD) l(-1). Results showed that the utilization of acetate in the presence of phenol was subject to a zero-order reaction kinetics. The relative phenol concentration in terms of the ratio of initial phenol concentration (C(p)) to initial biomass concentration (X(0)) was used to describe the real inhibitory strength of phenol imposed on acetate-fed aerobic granules. When the C(p)/X(0) ratio increased from 0 to 0.19 mg phenol mg(-1) MLSS, the zero-order reaction rate constant of acetate dropped from 1.15 mg l(-1) min(-1) to 0.38 mg l(-1) min(-1), and a similar trend was also observed in specific oxygen utilization rate. As compared to the control test without addition of phenol, the acetate-COD removal efficiency was reduced by nearly 50% at a C(p)/X(0) value of 0.19 mg phenol mg(-1) MLSS. It was found that biodegradation of phenol was negligible in acetate-fed aerobic granular sludge batch culture. CONCLUSIONS: It appears that phenol can seriously repress the utilization of acetate in the acetate-fed aerobic granular sludge batch cultures. A simple zero-order reaction model could adequately describe the utilization of acetate by acetate-fed aerobic granules in the presence of phenol. SIGNIFICANCE AND IMPACT OF THE STUDY: It is expected that this study would lead to a better understanding of the behaviour of acetate-fed aerobic granules in the presence of inhibitory organic compounds.     

好氧颗粒污泥对不同底物组成的响应

在序批式间歇反应器（R1、R2和R3）中,采用乙酸钠（R1）、蔗糖（R2）和苯酚（R3）三种不同基质作为碳源,均成功地培养出了好氧颗粒污泥;考察了不同颗粒污泥的理化性质及其对污染物的转化能力。结果表明,R1中颗粒污泥外观呈黄色,其主要的微生物菌群为细菌;R2中颗粒污泥外观呈黑色,内部含有丝状菌;而R3中颗粒污泥表面被大量丝状菌包裹,颗粒污泥呈淡黄色。在进水COD1000mg／L时R1、R2和R3中颗粒污泥比有机物的利用速率大小顺序为R3〉R1〉R2,而COD的去除率顺序却为R2〉R1〉R3。在进水氨氮40mg／L时,R1、R2和R3中氨氮的去除率分别在91％、96％和80％以上。以不同的底物培养出不同的好氧颗粒污泥可以拓展其在有毒化学物质如酚类化合物和高浓度工业废水生物处理中的应用。     

Treatment of leachate from a solid waste landfill site using a two-stage anaerobic filter

Raw leachate was treated using a two-stage upflow anaerobic filter process. Leachate from a solid waste landfill site, which received both municipal and industrial wastes, contained high organic matter (17-21 g/L COD, 13-14 g/L BOD, and 3.5-4.6 g/L volatile acids), and low metal (Zn and Fe) concentrations. Depending on sampling time, leachate composition and characteristics varied considerably. At an organic loading up to 4 g COD/day(2) media area, the BOD and COD removal percentages were 98 and 91%, respectively. The biofilters were also effective for metal removal. However, the filter effluent contained a high concentration of ammonia. System overloading was characterized by the accumulation of large quantities of volatile acids and by a now ratio of alkalinity/volatile acids, resulting in low COD removal and reduced gas production. Once the first filter was upset, the second stage could only partially respond to the volatile acids accumulated in the effluent of first filter.