Properties Of Activated Sludge Research Articles

The spread of different resistance genes fractions in nitrification system under chronic exposure to varying alkyl chain length benzalkyl dimethylammonium compounds

Benzalkyl dimethylammonium compounds (BACs) are generally applied as surfactants and disinfectants. In this study, the nitrification systems were exposed to different alkyl chain lengths (C12-C16) and different levels of BACs (0-5 mg/L), respectively, totally 120 days and to explore the chronic effect of BACs on resistance genes (RGs). RGs were classified into four fractions based on activated sludge properties. Ammonia oxidation performance were not significantly affected by BACs, whereas BACs increased the absolute abundance of most intracellular RGs in sludge (si-RGs). Under the exposure of BACs, extracellular RGs in water (we-RGs) showed a decrease trend and si-RGs tended to be converted to we-RGs. Tightly bound-Tyrosine side chain was significantly correlated with most we-RGs, and we-intI1 might contribute to the propagation of RGs. Therefore, the risk of transmission of different fractions of RGs in the nitrification system under the stress of BACs should be taken seriously.

Evaluation of activated sludge properties’ changes in industrial-wastewater pre-treatment: role of residual aluminum hydrolyzed species with different polymerization degree

Evaluation of activated sludge properties’ changes in industrial-wastewater pre-treatment: role of residual aluminum hydrolyzed species with different polymerization degree

The effects of varying Zn2+ on the activated sludge properties and its distribution patterns

Metallurgy, electroplating and pharmaceutical industries generate a large amount of wastewater containing Zn2+, which influences the activated sludge properties. The present work investigated the effects of Zn2+ on sludge properties and its distribution patterns and chemical forms under a Zn2+ concentration range of 0–20 mg/L. When the influent Zn2+ concentration was 1 mg/L, parameters indicating sludge properties such as Zeta potential (−14.80 mV), contact angle (78.93°), particle size (54.43 μm) and re-flocculation (FA, 30%) reached the optimal states. Zn2+ was adsorbed by the functional groups of extracellular polymeric substances (EPS) and low EPS promoted the sludge flocculation. The lower pH affected the EPS functional groups, which in turn affected the adsorption of Zn2+. The FeMn oxidation state Zn (2.66–6.86 mg/gVSS) predominated in the sludge and decreased as sludge flocculation increased. The results provided evidence to make full use of low concentration of Zn2+ to ensure wastewater treatment performance.

An evaluation of the effects of nanoplastics on the removal of activated-sludge nutrients and production of short chain fatty acid

Nanoplastics in the environment and their effect on the ecosystem has aroused wide concern. This study investigated the effect of polystyrene nanoplastics on activated sludge properties, including nutrient removal, dewaterability, and short chain fatty acid (SCFA) production potential. The results indicated that the nanoplastics inhibited the ammonia oxidation rate and nitrate generation rate during nitrification. The denitrification rate was also inhibited in the presence of nanoplastics, while the percentage of total inorganic nitrogen removed was not affected. The phosphorus absorption rates during the aerobic stage were 75.52 %, 76.19 %, 60.69 %, 71.58 %, and 49.48 % for nanoplastics concentrations of 0, 10, 50, 100, and 1,000 μg/L. The phosphorus release was inhibited in the reactors where nanoplastics were added during denitrification. These results indicate that bacteria, including nitrifiers, denitrifiers, and phosphorus-accumulating bacteria are affected by the nanoplastics. This probably attributed to the nanosize of the polystyrene effect on bacterial cells or overproduction of reactive oxygen species that caused dysfunction of microbial metabolism. SCFA production was inhibited by adding nanoplastics, particularly at a concentration of 10 μg/L, suggesting that the hydrolysis and acidification processes were affected by the nanosized polystyrene. The dewaterability of the activated sludge was improved after adding nanoplastics, this probably attributed to the aggregation of polystyrene and its function as a sludge skeleton builder. The results of this study reveal that nanoplastics have a negative effect on activated sludge properties, which should be considered for practical applications.

Influence of road salt thawing peaks on the inflow composition and activated sludge properties in municipal wastewater treatment.

Operational data over 2 years from three large Austrian wastewater treatment plants (WWTPs) with design capacities of 4 million, 950,000 and 110,000 population equivalent (PE) were examined. Salt peaks, due to thawing road salt were detected and quantified by electrical conductivity, temperature and chloride measurement in the inflow of the WWTPs. Daily NaCl inflow loads up to 1,147 t/d and PE-specific loads of 0.26-0.5 kg NaCl/(PE · y) were found. To mimic the plants' behaviour in a controlled environment, NaCl was dosed into the inflow of a laboratory-scale activated sludge plant. The influence of salt peaks on important activated sludge parameters such as sludge volume index, settling velocity and floc size were investigated. Influent and effluent were sampled extensively to calculate removal rates. Respiration measurements were performed to quantify activated sludge activity. Particle size distributions of the activated sludge floc sizes were measured using laser diffraction particle sizing and showed a decrease of the floc size by approximately two-thirds. The floc structure was examined and documented using light microscopy. At salt concentrations below 1 g/L, increased respiration was found for autotrophic biomass, and between 1 and 3 g NaCl/L respiration was inhibited by up to 30%.

Robust removal of phenolic compounds from coal pyrolysis wastewater using anoxic carbon-based fluidized bed reactor

Coal industry provided various carbon derived products, but it also caused serious environmental pollution by phenolic wastewater emission. By in-situ applications of coal-derived carriers, carbon-based fluidized bed reactors established a sustainable system that realized byproducts recycling and waste elimination, contributing to cleaner production of coal industry. Benefitted from adsorption capacity, powdered activated carbon/lignite activated coke-based fluidized bed reactors significantly promoted start-up and recovery efficiency with higher phenolic degradation rate than activated sludge reactor (avg. 90% vs 70%) when total phenols ranged at 250–350 mg/L, whereas iron-carbon (Fe–C)-based reactor showed the highest stability (70 ± 5%) under supreme phenolic impact (450 mg/L). Combined with adsorption capacity and activated sludge properties, resilient adsorption benefited lignite activated coke-based reactor with toxicity alleviating while intensified sludge flocs equipped Fe–C-based reactor with superior resistance. Moreover, Brachymonas genus provided microbial basis for robust performance of carbon-based systems in methylphenolic degradation. Higher abundance of functional genes for demethylation and cleavage of aromatic ring contributed to superior methylphenolic degradation for fluidized bed reactors in contrast to activated sludge reactor, while up-regulated oxidative stress evidenced superior oxidative resistance of Fe–C-based reactor. In summary, carbon-based fluidized bed reactors provided a cost-efficient and sustainable way for coal pyrolysis wastewater treatment.

Short-term effect of shock ammonium nitrogen load on activated sludge properties.

The activated sludge process suffers from rapid load changes of ammonium (NH4), which may result in process failure during wastewater treatment. In this study, the response of activated sludge properties in terms of microfauna composition and sludge volume index (SVI5 and SVI30) on short-term increase of NH4 concentration (from 55 mg/l to 105 mg/l) was evaluated in batch scale reactors over 72 h. The results show that the first-step nitrification (NH4 transformation to nitrite (NO2)) was inhibited after 24 h, whereas the second-step nitrification (NO2 transformation to nitrate (NO3)) was not significantly affected. Sludge volume indices (sedimentation ability characteristics) SVI5 and SVI30 in the reactor with NH4-N shock concentration increased, whereas microfauna diversity decreased (Shannon-Weaver index decreased from 2.12 at 48 h to 1.23 at 72 h) leading to dominance of stalked ciliate Epistylis sp. Notable changes in inorganic carbon concentration (IC) were observed, indicating that rapid decrease of IC concentration leads to nitrification inhibition and challenges the overall process recovery. To conclude, short-term exposure of about two times higher concentration of NH4 caused significant changes in activated sludge properties by inhibiting NH4-oxidizing bacteria, reducing sludge microfauna diversity and deteriorating sludge sedimentation ability.

Unravelling the influences of sewer-dosed iron salts on activated sludge properties with implications on settleability, dewaterability and sludge rheology

Although the beneficial impacts of iron dosing to sewer on activated sludge unit's performance, especially in relation to phosphate removal, have been reported, the extent of impacts on different sludge properties affecting the operation and performance of the activated sludge unit are not fully understood. In this study, we investigated the influences of iron salt dosing to sewer on both settleability and dewaterability of downstream activated sludge unit. We also examined, based on the comparative assessment of different key activated sludge properties, possible underlying factors responsible for the changes in sludge settleability and dewaterability. For this, iron chloride was dosed to a sewer reactor of integrated laboratory sewer-bioreactor system. The activated sludge samples were obtained from two separate reactors, an experimental sequencing batch reactor (SBR-E) downstream of sewer reactor receiving iron dosing and a control SBR (SBR-C) downstream of a sewer reactor without any iron dosing. Iron-conditioned sludge showed improved settleability and dewaterability over the unconditioned activated sludge. Mean differences in settleability and dewaterability between two sludges were 22.5 ± 7.8 mL/g (p < 0.05) and 7.8 ± 1.2% (p < 0.05), respectively. Iron-conditioned sludge showed lower contents of soluble extracellular polymeric substances (EPS) fractions, protein and polysaccharide contents, and monovalent-to-divalent (M+/D++) cations ratio, but higher humification index as compared to the unconditioned sludge. Iron-conditioned sludge exhibited marginal increment in mean particle size (Dv50) and settleable particle size classes (100–400 μm) but reduction in supracolloidal particle size classes (1–100 μm). In terms of sludge rheology, iron-conditioned sludge exhibited relatively lower relative sludge network strength, viscosity, yield stress, elastic/viscous/complex moduli (G′/G′′/G*), and damping factor tan(δ) but increased shear compliance (J) and shear strain (%) with time.The iron-conditioned sludge therefore exhibited relatively weaker deformation resistance and sludge elasticity. Based on the foregoing results, we posit the combined synergistic effect of favourable changes to the key sludge properties, might be responsible for the observed improvement in settleability and dewaterability of iron-conditioned sludge.

Impact of gas injection on physicochemical properties of waste activated sludge: A linear relationship between the change of viscoelastic properties and the change of other physiochemical properties

Aeration process in the waste activated sludge treatment accounts for 75% of total energy consumption of the treatment plant. The main purpose of the aeration process is to enhance the biodegradation of the liquid waste. Gas bubbles, rising through the liquid, improves mixing, reduces inhomogeneities in the treatment tank and enhances biological reactions. Thus aeration intensity and several physicochemical properties of feed such as viscosity, total suspended solids, and surface charge play a significant role in the biological reaction.This paper examines the impact of the gas injection rate on some physicochemical properties of waste activated sludge namely rheological properties, suspended solids, soluble COD (sCOD), surface tension, and zeta potential. The impact of four different gas flow rates on four different concentrations of waste activated sludge properties was analysed.The results showed that in linear viscoelastic regime the viscous and elastic modulus decreases linearly with an increase in gas flow rate. The amount of stress imposed by gas injection also showed a direct relationship with gas velocity. Gas injection also showed a substantial impact on soluble COD, suspended solids, and zeta potential. Additionally, a linear relationship was observed between the percentage change in the above mentioned physical properties and stress imposed by gas injection. These results confirm that gas injection produces additional shear impacting sludge physicochemical properties and therefore changes its rheological behaviour. The extra stress induced by gas injection can be predicted using a simple model based on sludge concentration and gas velocity.

Biofouling control and sludge properties promotion through quorum quenching in membrane bioreactors at two aeration intensities.

A modified method was used for cell entrapped beads (CEBs) preparation and two aeration intensities (low and high aeration intensity) was supplied as factors to investigate the change of quorum quenching performance for membrane biofouling in membrane bioreactor (MBR). Dehydrogenase activity and growth trend of activated sludge were improved at high aeration intensity. Compared with C-MBR (with vacant beads), QQ-MBR (with CEBs) had more stable quorum quenching activity and longer application time at high aeration intensity, in which the proteins and polysaccharides were reduced by 15 and 20%, respectively. The difference of EPS concentration in mixed liquor was attributed to the protein concentration controlled by quorum quenching bacteria, meanwhile sufficient organics was necessary to maintain the process. The better settleability, greater stability and relatively lower hydrophobicity of activated sludge properties was achieved with quorum quenching. The scouring effect of CEBs was promoted at high aeration intensity, further controlling the membrane biofouling.

Mechanism of Action of Activated Sludge Properties in Nitrogen Removal by Endogenous Denitrification Through an Intelligent Aeration-controlled A/O Process

In order to evaluate the mechanism of action of activated sludge properties in nitrogen removal by endogenous denitrification (henceforth EDNR), a new kind of automatic oxygen supply device(AOSD), was applied to the A/O process. The domestication effect of the aeration mode on the activated sludge properties and microbial communities was investigated under the intelligent aeration-controlled A/O process (I-A/O)and the continuous aeration A/O process (C-A/O). The results demonstrated that the effluent NH4+-N and NO2--N components showed obvious accumulation efficiencies and activated sludge generated conspicuous limited bulking in the I-A/O process. Domesticated sludge in the I-A/O process was able to enrich more SCOD to transfer into the polymeric substances as Gly, under a rich exogenous carbon supply state, and stimulated nitrogen removal by endogenous denitrifying under a scarce exogenous carbon supply state. The EDNR rate went up to 0.83 mg·(L·h)-1 in the I-A/O process, which was more than that achieved by the C-A/O process. The microbial communities in the two processes were evaluated by the Illumina HiSeq high-throughput sequencing technology. The results showed that there was no obvious difference in the sludge microbial community diversity between the two processes, but the Candidate division TM7 proliferated in the I-A/O process, and become the abundant taxa to prompt limited filamentous sludge bulking and Gly storage capability enhancement. The oxygen supply mode of AOSD made the activated sludge properties and microbial communities to be screened selectively in the new environment, aerobic heterotrophic bacterial activity to decline, and endogenous denitrifying action to strengthen, which made the I-A/O process implement a kind of dynamic balanced state that limited the DO demand.

Performance and activated sludge characteristics at short solid retention time in a submerged MBR: effects of C/N ratio of wastewater

ABSTRACTThis study investigated the effect of carbon to nitrogen (C/N) ratio of influent wastewater on performance and activated sludge properties at a sludge retention time of 5 d in a submerged membrane bioreactor. The chemical oxygen demand and ammonia–Nitrogen (NH3–N) removal efficiencies were found to be over 96.3% and 86.9% in the sMBRs having different C/N ratios. It was found that total extracellular polymeric substances and total soluble microbial products increased with an increase in C/N ratio. It was also observed that critical flux, relative hydrophobicity and zeta potential values decreased, and capillary suction time, particle size and viscosity of sludge increased as the C/N ratio increased.

The investigation of paper mill industry wastewater treatment and activated sludge properties in a submerged membrane bioreactor.

The paper mill industry produces high amounts of wastewater and, for this reason, stringent discharge limits are applied for sustainable reclamation and reuse of paper mill industry wastewater in many countries. Submerged membrane bioreactor (sMBR) systems can create new opportunities to eliminate dissolved substances present in paper mill wastewater including. In this study, a sMBR was operated for the treatment of paper mill industry wastewater at 35 h of hydraulic retention time (HRT) and 40 d of sludge retention time (SRT). The chemical oxygen demand (COD), NH3-N and total phosphorus (TP) removal efficiencies were found to be 98%, 92.99% and 96.36%. The results demonstrated that sMBR was a suitable treatment for the removal of organic matter and nutrients for treating paper mill wastewater except for the problem of calcium accumulation. During the experimental studies, it was noted that the inorganic fraction of the sludge increased as a result of calcium accumulation in the reactor and increased membrane fouling was observed on the membrane surface due to the calcification problem encountered. The properties of the sludge, such as extracellular polymeric substances (EPS) and soluble microbial products (SMP), relative hydrophobicity, zeta potential and floc size distribution were also monitored. According to the obtained results, the total EPS was found to be 43.93 mg/gMLSS and the average total SMP rejection by the membrane was determined as 66.2%.

Activated sludge properties in a submerged membrane bioreactor: effect of COD/TKN ratio of wastewater

The properties of activated sludge are very important in a membrane bioreactor (MBR) in terms of membrane fouling. The most important parameters affecting the membrane fouling can be listed as mixed liquor suspended solid (MLSS) concentration, soluble microbial products (SMPs), extracellular polymeric substances (EPSs), floc size, aeration and viscosity of both supernatant and activated sludge. The COD/TKN ratio also affects the physical properties of sludge in MBR system. This study aimed to investigate the effect of chemical oxygen demand-to-total Kjeldahl nitrogen (COD/TKN) ratio of feed wastewater treated in an MBR on biological components of activated sludge. The activated sludge characteristics were determined by quantitative analyses such as MLSS, EPS, SMP, floc size distribution, zeta potential, relative hydrophobicity and capillary suction time in a submerged MBR treating simulated wastewater having different COD/TKN ratios (16, 56 and 107). The COD and TKN removal efficiencies were found to be almost equal in the sMBRs having different COD/TKN ratios. However, it was seen that the EPS content and SMP concentration in the supernatant increased with increasing COD/TKN ratio. The results indicated that the COD/TKN ratio of feed should be considered as an effective parameter on activated sludge properties in sMBR systems.

Effect of Worm Predation on Changes in Waste Activated Sludge Properties.

This study explored the effects of worm predation on changes in waste activated sludge properties. Results showed that the rate by which worm predation reduced mixed liquor volatile suspended solids (MLVSS) was approximately 23.7% ± 3.1%. Particle size distribution and extracellular polymeric substance (EPS) analyses indicated that the reduction of fine particles and EPS content in sludge predated by worms mainly increased dewaterability and reduced the ratio of MLVSS/mixed liquor suspended solids. Moreover, both mean particle size and protein/carbohydrate ratio increased. The results of three-dimensional excitation-emission matrix and gel filtration chromatogram analyses demonstrated the varied properties of soluble microbial products and EPS were attributed to the worms' selective predation of low molecular-weight organic matter, which facilitated the hydrolysis of macromolecular organic matter.

Degradation of extracellular polymeric substances (EPS) extracted from activated sludge by low-concentration ozonation.

Reaction mechanisms between ozone and extracellular polymeric substances (EPS) can be the key of understanding the improvements in microbial aggregates properties by low-concentration ozonation. In this study, EPS are extracted from activated sludge and treated continuously by ozone gas at 270 ± 41 ppm. The reaction between ozone and EPS was investigated by observation of EPS component concentrations, functional groups and molecular weight distributions using UV-Vis spectrometry, excitation-emission matrix fluorescence spectroscopy (EEM), high performance size-exclusion chromatography (HPSEC) and gas chromatography-mass spectrometry (GC-MS). In a 12-hour-ozonation experiment, significant ozone consumption was observed in the first 4 h and protein concentration in EPS solution was reduced by 30 ± 12%. However, the polysaccharides concentration only had a slightly decrease at the end of the ozonation process. UV-Vis spectra and EEM spectra results suggest that ozone removed protein and fluorescent matters (SMP and tryptophan-like aromatic protein) rapidly by attacking specific amino acid residues on polypeptide chain. After ozonation, the molecular weight of polysaccharide and protein dropped by 4 orders of magnitude according to HPSEC results. TOC concentration of EPS solution was reduced by 13 ± 2% after ozonation. The loss in TOC could be explained by the observation of volatile organic compounds such as carboxylic acids, aldehydes and ketones in the off-gas detected by GC-MS. The results in this study can provide a better understanding towards the mechanisms of improvements in activated sludge properties by ozonation.

Impact of sonication on activated sludge properties and consequences on PAH partitioning

AbstractSonication is an efficient sludge disintegration technique that can be used for reducing the excess sludge produced in water treatment. The effects of activated sludge sonication on its physicochemical properties and their consequences on the partitioning of hydrophobic polycyclic aromatic hydrocarbons (PAH) are reported. Ultrasound treatment led to an increase in dissolved and colloidal matter in the aqueous phase, with a predominance of proteins compared to the initial supernatant. This transfer of DCM was found to be directly correlated to the energy applied, and resulted in proportional transfer of PAHs from the particulate phase to the aqueous fraction. The PAH aqueous fraction, initially ranging from 0.012 g/g (pyrene) to 0.19 g/g (naphthalene), reached between 0.25–0.37 g/g when a specific energy of 40 000 kJ/kgTS0 was applied. For the raw sludge, the logarithm of the equilibrium constant varied between 3.0–4.3, depending on the hydrophobicity of the molecule, but when sonication was applied, the affinity for particles decreased significantly, resulting in a narrow distribution (log KG = 2.8–3.0 after 40 000 kJ/kgTS0 was applied). PAH partition is governed by molecule hydrophobicity (log Kow) for raw sludge and by sonication intensity for sonicated sludge.

Impact of suspended solids on the activated sludge non-newtonian behaviour and on oxygen transfer in a bubble column

This paper presents the experimental study and analysis performed in order to better understand the link between activated sludge properties, rheological behaviour and oxygen transfer. The experimental set-up consists of a bubble column of 0.3m3 continuously fed with activated sludge and a capillary rheometer, installed in two different wastewater treatment plants: a conventional activated sludge plant and a membrane bioreactor. In the bubble column, equipped with a fine bubble diffuser, the overall gas hold-up (ϵG) and volumetric oxygen transfer coefficients (kLa) were measured. A fraction of the column outflow was sent to the capillary rheometer where the activated sludge rheological behaviour was investigated. Several properties of the studied activated sludge were characterised (MLSS, MLVSS, soluble COD, surfactants, surface tension, soluble cations) and their impact on rheology and oxygen transfer was examined.The experimental data showed that the parameters K and n, from the Ostwald-de Waele rheological model, were strongly related to the suspended solids concentration (in terms of MLSS or MVLSS). An increase in kLa was observed as the superficial gas velocity (UG) was increased. Compared to clean water, the kLa coefficient was lower in activated sludge and still reduced with an increase of the MLSS concentration. This reduction could be partially attributed to a lower gas holdup (εG) associated with an increase in the sludge apparent viscosity (μapp) leading to a reduction of the specific interfacial area (a). Subsequently, an estimation of the mean shear rate exerted by the bubble swarm in the column allowed to evaluate the sludge apparent viscosity (μapp) of the mixed liquor at a given superficial gas velocity and MLSS concentration. Finally an empirical correlation linking kLa to the superficial gas velocity (UG) and the sludge apparent viscosity was obtained for both types of sludge. The good agreement between the experimental and the fitted data suggests that kLa can be estimated from the superficial gas velocity and the rheological behaviour.

Effects of ZnO nanoparticles on wastewater treatment and their removal behavior in a membrane bioreactor

Long-term effects of ZnO nanoparticles on the system performance of an MBR were investigated together with their removal behavior in the system. Continuous operation over 242days showed that ZnO NPs at both 1.0 and 10.0mg/L caused moderate deterioration in the removal of COD, nitrogen and phosphorus. Denitrification was affected upon the exposure but recovered subsequently. Although no significant acute effect on ammonia-oxidization was observed, permanent inhibition occurred after long-term exposure. Nitrite-oxidization was not affected even with 10.0mg/L ZnO NPs. Significant changes were observed in activated sludge properties which resulted in severe membrane fouling. Although ZnO NPs caused changes in the bacteria community structure, the diversity however remain unchanged. ZnO NPs was removed effectively in the MBR (>98%) with biosorption being a major removal mechanism. Membrane filtration also played an important role (20% of the total removal) especially at high ZnO NPs concentrations (around 10.0mg/L).

Impact of inflow conditions on activated sludge filterability and membrane bioreactor (MBR) operational performance

Operation and performance of membrane bioreactors (MBRs) for wastewater treatment is influenced by changes in activated sludge properties. Therefore, understanding of the factors influencing sludge filterability is of major importance for efficient operation of MBR installations. This paper assesses the impact of the influent characteristics on activated sludge filterability and treatment performance of full-scale MBRs. The full-scale MBRs were closely monitored both in summer and winter. The measurement campaign, consisting of activated sludge filterability tests and physicochemical analyses, is supplemented with operational performance data evaluation of the various full-scale plants. Based on these data, it is shown that an undesired and refractory composition of incoming wastewater, hydraulic and/or organic load shocks, as well as abrupt temperature changes of the influent, lead to operational problems and affect sludge filterability.