Characteristics Of Activated Sludge Research Articles

Phosphorus recovery from calcium phosphate enriched activated sludge

This study explores the potential of activated sludge from wastewater treatment plants (WWTP) as an alternative source of phosphorus, vital for fertilisers and other products, compared to large-scale phosphorus mining. The research focuses on analysing optimal conditions and the impact of activated sludge characteristics on phosphorus release from calcium phosphate compounds, particularly hydroxyapatite (HAP). Using batch reactor experiments with varying pH and contact time, the results reveal that lower pH values, particularly pH 4, result in higher phosphorus release. The study also finds that calcium, the predominant metal content in activated sludge, plays a vital role in bonding with phosphates and forming new compounds, effectively reducing phosphorus concentration in the solution. Moreover, the VSS/TSS value in the activated sludge has no significant effect on phosphorus release, but interventions occur at high VSS/TSS values. The reaction rate coefficient is calculated at 0.00033/min at pH 4. Overall, this research emphasises the potential of phosphorus recovery from calcium phosphate enriched activated sludge and underscores the importance of optimising pH and considering activated sludge characteristics for efficient phosphorus release.

Application of CaO2-enhanced peroxone process to adjust waste activated sludge characteristics for dewaterability amelioration: Molecular transformation of dissolved organic matters and realized mechanism of deep-dewatering

Sludge dewaterability is commonly poor due to the hydrophilic biopolymeric substances. The highly efficient oxidation process is of great significance for extracellular biopolymers disintegration and bound water discharge. This work investigated the novel CaO2-enhanced peroxone (CaO2/O3) process to adjust sludge characteristics for dewaterability enhancement and focused on the molecular composition and transformation of dissolved organic matters (DOM). CaO2/O3 (60/40 mg/gTS (total solid)) treatment showed more powerful sludge solubilization of 57.8% and cell death proportion of 46.1% over single CaO2 or O3 treatment. Hydrophilic extracellular polymeric substances, especially protein-like substances, were substantially degraded, and their conformation turned to be more hydrophobic, and carbohydrate-like, aminosugars-like, and lignins-like substances increased in CaO2/O3 process. Meanwhile, CaO2/O3 handling resulted in more decomposition of CHO-containing compounds than N-containing or S-containing compounds. Subsequently, 60 mg/gTS PFS (polyferric sulfate) reflocculation exerted a strengthened role in eliminating proteins & lipids-like, lignins-like, and unsaturated hydrocarbons-like substances, and especially S-containing compounds, which compensated for the unsatisfactory removal effects of these substances in the CaO2/O3 oxidation process. Therefore, the CaO2/O3-PFS treated sludge with less hydrated DOM easily harvested deep-dewatering in pressure filtration. Furthermore, it was noteworthy that the presence of CaO2 created an alkaline environment and served as the source of sustained-release H2O2, which accelerated O3 decomposition and greatly improved •OH generation. These findings provided molecular insight into a novel sludge conditioning approach for ideal dewaterability based on the CaO2-enhanced peroxone process in sludge treatment.

Integral analysis of hydrodynamic cavitation effects on waste activated sludge characteristics, potentially toxic metals, microorganisms and identification of microplastics

Wastewater treatment plants, the last barrier between ever-increasing human activities and the environment, produce huge amounts, of unwanted semi-solid by-product - waste activated sludge. Anaerobic digestion can be used to reduce the amount of sludge. However, the process needs extensive modernisation and refinement to realize its full potential. This can be achieved by using efficient pre-treatment processes that result in high sludge disintegration and solubilization. To this end, we investigated the efficiency of a novel pinned disc rotational generator of hydrodynamic cavitation. The results of physical and chemical evaluation showed a reduction in mean particle size up to 88%, an increase in specific surface area up to 300% and an increase in soluble COD, NH4-N, NO3-N, PO4-P up to 155.8, 126.3, 250 and 29.7%, respectively. Microscopic images confirmed flocs disruption and damage to yeast cells and Epistilys species due to mechanical effects of cavitation such as microjets and shear forces. The observed cell ruptures and cracks were sufficient for the release of small soluble biologically relevant dissolved organic molecules into the bulk liquid, but not for the release of microbial DNA. Cavitation treatment also decreased total Pb concentrations by 70%, which was attributed to the reactions triggered by the chemical effects of cavitation. Additionally, the study confirmed the presence of microplastic particles and fibers of polyethylene, polyethylene terephthalate, polypropylene, and nylon 6 in the waste activated sludge.

Integral analysis of hydrodynamic cavitation effects on waste activated sludge characteristics, potentially toxic metals, microorganisms and identification of microplastics

Integral analysis of hydrodynamic cavitation effects on waste activated sludge characteristics, potentially toxic metals, microorganisms and identification of microplastics

Investigation of activated sludge characteristics and their influence on simultaneous sludge minimization and nitrogen removal from an advanced biological treatment for tannery wastewater

The role of extracellular polymeric substances (EPS) in the minimization of the excess sludge yield underlying hybrid activated sludge treatment (as MANODOX system) for tannery wastewater was experimentally elucidated. The operational strategies designed for the MANODOX system configuration and a parallel-run conventional aerobic activated sludge (p-CAS) treatment were tested throughout the study period of 320 days. In comparison with the p-CAS system, MANODOX experimentation received prominently lowered sludge yield (averaged around 0.36 gVSS/gCOD). The experimental observation further affirmed that the sludge generation found influenced by the variation in the sludge characteristics like protein to polysaccharides ratio (ranged around 0.62–0.73), food to microorganism ratio (0.41 ± 0.04), dissolved oxygen (2.23 ± 0.30 mg/L) and bioflocculation ability (71.8–73.8%). Here, MANODOX implementation exhibited three times lowered EPS accumulation and around 70% less sludge generation compared with the p-CAS system. However, the ascertained was positively attributed to the purposeful nourishment of cell-lysis in the MANODOX system. Importantly, the strict maintenance of desired sludge retention time of 23–26 days imposed a profound effect on the aforementioned floc characteristics and EPS degradation. Furthermore, the Fourier transform infrared spectroscopy and specific ultra-violet absorbance analysis reveals, the facultative microbiota had a prominent influence on organic functional groups that presumed to be originated from the disintegration of EPS in the sludge. The corroborated has further been supported by thermogravimetric analysis and batch anaerobic and aerobic digestion test of the volatile sludge pool performed at end of the mainstream operation.

Effects of 5-hydroxymethylfurfural on removal performance and microbial community structure of aerobic activated sludge treating digested swine wastewater

5-Hydroxymethylfurfural (HMF) is a high value-added chemical, the starting material for the production of a large number of platform chemicals, and an inhibitor of anaerobic digestion. The selection of microorganisms that can metabolize HMF or have high tolerance to HMF is rapidly arousing scientific interest. For selecting suitable microorganisms from aerobic sludge and exploring the effects of HMF on aerobic digestion, the removal capability, activated sludge characteristics, and microbial community structure of activated sludge treating digested swine wastewater in the presence of HMF were studied. Results showed that HMF deteriorated the removal performance of activated sludge. Removal rates of chemical oxygen demand (COD), total phosphorus (TP) and ammonium (NH4+-N) were reduced from 95.7%, 84.6% and 80.0% to 46.5%, 77.6% and 21.0%, respectively. Besides, HMF also increased EPS content which reduced the settleability and dewatering capacity of activated sludge. Moreover, HMF inhibited dehydrogenase (DHA) activity in activated sludge and increased superoxide dismutase (SOD) activity. Meanwhile, the functions of microorganisms had changed, extracellular structure increased, carbohydrates and lipids transport and metabolism decreased, and energy production and conversion were inhibited. Microbial community analysis illustrated HMF adversely affects Enterobacteriaceae and streptococcaceae, while Bacillaceae, Rhodocyclaceae and Nitrospira better tolerate HMF.

Treatment of printing and dyeing wastewater in biological contact oxidation reactors comprising basalt fibers and combination fillers as bio-carriers: Elucidation of bacterial communities and underlying mechanisms

This study investigates the nitrogen removal and sludge reduction efficiency of biological contact oxidation reactors in the presence of two bio-carriers namely basalt fibers (R-BF) and combination fillers (R-CF). The results were also compared with a conventional anoxic-oxic reactor (R-A/O). The reactors were operated at pilot-scale (550 L) and pollutant removal mechanisms were studied based on physicochemical parameters, bio-carrier surface morphology, microbial community structures, and activated sludge characteristics. It was found that chemical oxygen demand (COD) removals for R-BF, R-CF, and R-A/O were comparable in all reactor types, whereas R-A/O performed better in terms of ammonium-nitrogen (NH4+-N) and total nitrogen (TN) removal followed by R-BF and R-CF. The sludge reduction in R-BF was 40.4% higher than that in R-CF and 61.9% higher than that in R-A/O. This observation was further correlated with the abundance of protozoa (Vorticella and Epistylis) and metazoan (Aeolosoma hemprichi) communities, diverse and rich bacterial communities, stronger dehydrogenase activity, and low specific oxygen uptake rate in R-BF. The results of 16S amplicon sequencing suggested that microbiological conditions in R-BF were more favorable for heterotrophic nitrification and aerobic denitrification, sulfur cycle, hydrolysis and fermentation compared to R-CF. In R-A/O, however, sulfur oxidizing and reducing bacteria were completely absent which also indicated its poor efficiency for sulfur removal. This study concludes that R-BF was a better choice towards sludge reduction whereas conventional R-A/O could be a favorable approach for TN removal.

Effect of solid-liquid separation on food waste fermentation products as external carbon source for denitrification

Food waste fermentation products could be one of cost-effective organic products to replace marketable carbon source for denitrification, whereas the effects of simple separation on food waste fermentation products and its denitrification performance are limited. In this study, the effect of gauze separation on production of food waste fermentation products, denitrification performance, effluent characteristics and activated sludge characteristics were investigated. The total chemical oxygen demand of separated and unseparated fermentation products were 48.0 ± 7.7 g/L and 105.0 ± 11.6 g/L, respectively, and 32% of organic matters in fermentation liquid was in the form of small particles. Lactate and polysaccharide were the dominant organic components in two products. The total nitrogen removal efficiencies with sodium acetate, unseparated fermentation slurry or separated fermentation liquid were 94.8 ± 3.4%, 72.7 ± 7.4% and 88.6 ± 8.1%, respectively. Protein and specific ultraviolet absorbance (SUVA254) in the denitrification reactor with separated fermentation liquid was about 2–4 times lower than unseparated fermentation slurry. Furthermore, Proteobacteria, which is related to denitrification, obviously increased in the denitrification reactor with separated fermentation liquid as carbon source. Therefore, gauze separation can be used to separate food waste fermentation products, and obtain reliable alternative carbon source.

Effects of sulfate on activated sludge characteristics and membrane fouling in membrane bioreactor treating penicillin wastewater

Treating penicillin wastewater is receiving more and more attention, because penicillin has strong anti-oxidant, anti-degradation and strong inhibitory effect on microbial growth. Membrane bioreactor (MBR) with stable and superior performance, has been used in the treatment of pharmaceutical wastewater. In this paper, effects of sulfate on activated sludge and membrane fouling in MBR treating penicillin wastewater were investigated. The results showed MBR could guarantee excellent effluent in the chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) removal. However, sulfate reduced the biodegradability of wastewater due to the changes in microbial species and the inhibition of microbial metabolic activity. Difference in the transmembrane pressure (TMP) indicated that sulfate made membrane fouling more serious. Colloids which exacerbated the clogging of the membrane pores and the formation of a dense cake layer, were the major contributor to membrane fouling.

The Self-Forming Dynamic Membrane BioReactor (SFD MBR) as a suitable technology for agro-industrial wastewater treatment

Two bench-scale Self-Forming Dynamic Membrane BioReactors (SFD MBR), equipped with 50 μm nylon meshes were set up and operated under aerobic conditions in order to treat canning and winery wastewaters. The results showed different behaviors of the two systems, confirming the strong dependence of SFD MBR performance on the type of biomass and, in turn, on the type of stream being treated. Both plants achieved good results in terms of effluent quality, demonstrating the suitability of the proposed technology. Median values of effluent turbidity were 2.7 and 15.4 NTU (Nephelometric Turbidity Units) in the reactors fed with canning wastewater and winery wastewater, respectively. The removal of organic matter (as COD, Chemical Oxygen Demand) was consistently above 90 %, although the retention of suspended solids was variable and somewhat dependent on operating conditions and feed composition. The activated sludge characteristics were observed to affect filtration performance and in particular the capillary suction time (CST) was a possible indicator of efficiency, with a threshold value of 11 s above which filtration performance decreased. This parameter is proposed as an early warning tool for changes in the filtration performance of an SFD MBR, both for effluent quality and cleaning requirements.

Performance and microbial communities of different biofilm membrane bioreactors with pre-anoxic tanks treating mariculture wastewater

The performance of pollutant removals, activated sludge characteristics, and microbial communities of two biofilm membrane bioreactors coupled with pre-anoxic tanks (BF-AO-MBRs) (one using fiber bundle bio-carriers (FB-MBR) and the other using suspended bio-carriers (MB-MBR)) were compared at the salinity between zero and 60 g/L. At all salinities, three bioreactors showed good COD average removal efficiencies (>94.1%), and FB-MBR showed the best TN removal efficiency (90.4% at 30 g/L salinity). Moreover, FB-MBR had the faster process start-up time and better salt shock resistance. At high salinities (30–60 g/L), more extracellular polymeric substances were produced by the BF-AO-MBRs to avoid the penetration of salt and protect the bacterial community. Because of the different attachment patterns of biofilms, the microbial community structure in the FB-MBR exposed to 30 g/L salinity had higher nitrite-oxidizing/ammonia-oxidizing bacteria ratio (6.44) with more abundance of denitrifiers, which contribute to higher TN removal efficiency and lower nitrite accumulation.

Using high frequency and low-intensity ultrasound to enhance activated sludge characteristics

In this study, high-frequency ultrasound wave (1.8 MHz) at low intensity was applied to improve activated sludge settleability at high MLSS concentration. The effect of irradiation intensity, sonication mode, MLSS concentration and sample volume on the physical characteristics of sludge in a pilot scale settling column were investigated for optimizing the conditions. The obtained results showed that high-frequency ultrasound decreased the height of sludge (44%) and effluent turbidity (82.2%) and increased sludge settling velocity about 3 times at high biomass concentration. Irradiation intensity of 0.4 w/cm2 and sonication mode with interval times of 10 s showed the best results on the performance of the system at MLSS concentration of 8000 mg/L with a sample volume of 3 L.

Effect of Deionization on Activated Sludge Characteristics: A Case Study of Activated Sludge Culture with Tap Water and Distilled Water

Activated sludge dewaterability and settleability properties are of prime importance in sludge treatment and disposal. Herein, we have experimentally examined the effect of deionization on activated sludge characteristics taking a case study of activated sludge inoculated in tap water and distilled water. The quality of the effluent, both distilled water and tap water were analyzed to determine the characteristics of activated sludge. Results indicated the increasing of the sludge volume index from 51.67 ml/g to 146.9 ml/g leading to the sludge bulking for sludge inoculated in distilled water. The Capillary Suction Time (CST) of sludge cultivated in distilled water varied from 23.1 to 38.4 s, which suggests poor dewaterability. These are due to the growth of some filamentous bacteria in distilled water system. These have further confirmed by light microscope images that showed a significant difference between the sludge systems cultivated in tap water and those grown in distilled water. The present work indeed advances our understanding of activated sludge treatment and would serve as a handy reference for researchers or scholars who want to deal with sewage water treatment.

The Effects of Ultrasonic Disintegration as a Function of Waste Activated Sludge Characteristics and Technical Conditions of Conducting the Process-Comprehensive Analysis.

A comprehensive analysis of the effects obtained in the process of ultrasonic disintegration (UD) of waste activated sludge (WAS), was conducted. Sludge samples were collected periodically from Central Wastewater Treatment Plant (WWTP) in Gliwice (Poland) and disintegrated in the two ultrasonic devices of different construction and technical parameters, i.e., WK-2010 (A) and ultrasonic washer (B). The experiments were performed under a constant energy supply per sludge volume EV = 160 kWh·m−3. The direct and technological effects, i.e., after UD and anaerobic digestion (AD) were investigated, respectively. Statistical analysis showed that characteristics and parameters of the WAS, which affects the magnitude of the direct effects create the following sequence: TS (total solids), VS (volatile solids), ΔT (temperature increase) > EPS (extracellular polymeric substances) > SCOD (soluble chemical oxygen demand) > CST (capillary suction time) > NTOT (total nitrogen), PTOT (total phosphorus) > pH. Whereas, in the case of technological effects, the above sequence was as follows: TS, VS > CST > NTOT, PTOT > pH. Ultrasonic disintegration of WAS prior to AD increased total biogas production (from 13.0% to 19.7%) and reduced the content of TS (from 4.1% to 8.2%) and VS (5.8% to 9.5%) in comparison to the control sample. This confirms the usefulness of ultrasonic disintegration as an effective method of sludge digestion intensification. The obtained results showed that changes in the characteristics of WAS have a significant impact on the magnitude of the effects of ultrasonic disintegration, especially TS, VS, ΔT, EPS, SCOD and CST. Concluding, it can be inferred that the most promising conditions for ultrasonic pretreatment conducted under constant energy supply per sludge volume, are: low power, long sonication time, large surface area of the emitter, and high increase of sludge temperature while conducting the process.

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.

Effect of salinity on removal performance and activated sludge characteristics in sequencing batch reactors

The removal performance, activated sludge characteristics and microbial community in sequencing batch reactors (SBRs) were studied at salinity ranging from 0 to 20 g/L. Results showed that salinity deteriorated the removal performance. Removal rate of ammonium (NH4+-N), total phosphorus (TP) and chemical oxygen demand (COD) were gradually dropped from 95.34%, 93.58% and 94.88% (0 g/L) to 62.98%, 55.64% and 55.78% (20 g/L), respectively. The removals of NH4+-N and TP were mainly influenced during aerobic phase. Besides, salinity increased the extracellular polymeric substances (EPS) content of activated sludge, decreased the content of protein (PN) and loosely bound extracellular polymeric substances (LB-EPS) which led to better settleability of activated sludge. Moreover, salinity inhibited the dehydrogenase activity (DHA) of activated sludge. Sequence analysis illustrated Zoogloea and Thioclava were predominant at 0 and 20 g/L salinity, respectively. The difference of microbial community under high salinity was likely caused by the variation of richness.

Metagenomic and metabolomic analysis reveals the effects of chemical phosphorus recovery on biological nutrient removal system

Side-stream phosphorus recovery coupled with biological nutrient removal can achieve the dual goals of resource recycling and meeting effluent discharge standards in wastewater treatment processes. However, suboptimal side-stream ratios (SSRs) for phosphorus recovery exert a negative effect on the performance of the combined process. The aim of this study was to reveal the comprehensive effect of chemical phosphorus recovery on the biological nutrient removal process using combined bio-omics (metagenomics and metabolomics) analysis. The optimal SSR was 0.3, at which point the effluent concentrations of COD, TN, NH4+-N and TP were approximately 32.56, 11.35, 3.71 and 0.23mg/L, respectively. Initially increasing the SSR favored resource recovery; however, SSRs>0.3 disrupted the phosphorus balance of the system and inhibited the metabolic activity of microorganisms related to the phosphorus removal process. Variations of activated sludge characteristics at different SRR indicated that the polysaccharide were more important than protein in resisting the toxicity of the imported Ca2+ on microorganisms. Relevant changes in the microbial community, functional potential, key enzymes and intracellular metabolites were illustrated in the bio-omics analysis, which revealed the influencing mechanism of chemical phosphorus recovery on activated sludge system at the micro level. The results of this study provide a novel perspective on the interactions between resource recovery and pollutant removal in a combined process using a bio-omics approach.

The effect of the feeding pattern of complex industrial wastewater on activated sludge characteristics and the chemical and ecotoxicological effluent quality.

Research has demonstrated that the feeding pattern of synthetic wastewater plays an important role in sludge characteristics during biological wastewater treatment. Although considerable research has been devoted to synthetic wastewater, less attention has been paid to industrial wastewater. In this research, three different feeding strategies were applied during the treatment of tank truck cleaning (TTC) water. This industry produces highly variable wastewaters that are often loaded with hazardous chemicals, which makes them challenging to treat with activated sludge (AS). In this study, it is shown that the feeding pattern has a significant influence on the settling characteristics. Pulse feeding resulted in AS with a sludge volume index (SVI) of 68±15mLgMLSS-1. Slowly and continuously fed AS had to contend with unstable SVI values that fluctuated between 100 and 600mLgMLSS-1. These fluctuations were clearly caused by the feeding solution. The obtained settling characteristics are being supported by the microscopic analysis, which revealed a clear floc structure for the pulse fed AS. Ecotoxicological effluent assessment with bacteria, Crustacea and algae identified algae as the most sensitive organism for all effluents from all different reactors. Variable algae growth inhibitions were measured between the different reactors. The chemical and ecotoxicological effluent quality was comparable between the reactors.

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.

Effects of sludge retention times on nutrient removal and nitrous oxide emission in biological nutrient removal processes.

Sludge retention time (SRT) is an important factor affecting not only the performance of the nutrient removal and sludge characteristics, but also the production of secondary pollutants such as nitrous oxide (N2O) in biological nutrient removal (BNR) processes. Four laboratory-scale sequencing batch reactors (SBRs), namely, SBR5, SBR10, SBR20 and SBR40 with the SRT of 5 d, 10 d, 20 d and 40 d, respectively, were operated to examine effects of SRT on nutrient removal, activated sludge characteristics and N2O emissions. The removal of chemical oxygen demand or total phosphorus was similar under SRTs of 5–40 d, SRT mainly affected the nitrogen removal and the optimal SRT for BNR was 20 d. The molecular weight distribution of the effluent organic matters was in the range of 500–3,000 Da under SRTs of 5–40 d. The lowest concentration of the effluent soluble microbial products concentration was obtained at the SRT of 5 d. Nitrifier growth was limited at a short SRT and nitrite existed in the effluent of SBR5. With increasing SRTs, mixed liquor suspended solids concentration increased while the excess sludge production was reduced due to the high endogenous decay rate at high SRTs. Endogenous decay coefficients were 0.020 d−1, 0.036 d−1, 0.037 d−1 and 0.039 d−1 under SRTs of 5–40 d, respectively. In BNR, the N2O emission occurred mainly during the aerobic phase and its emission ratio decreased with increasing SRTs. The ratio between the N2O-N emission and the removed ammonium nitrogen in the aerobic phase was 5%, 3%, 1.8% and 0.8% at the SRT of 5 d, 10 d, 20 d and 40 d, respectively. With low concentrations of dissolved oxygen and high concentrations of oxidized nitrogen, the N2O emission was significantly accelerated due to heterotrophic denitrification activities.