Sludge Deflocculation Research Articles

Synergetic effect of biochar and intermittent electricity stimulation on mitigating the adverse effects of tannic acid on anaerobic granular sludge in wastewater

Tannic acid (TA), a common industrial contaminant in sectors such as papermaking and leather production, affects the anaerobic treatment of wastewater by forming complexes with proteins in sludge granules, thereby inhibiting microbial efficiency and promoting sludge deflocculation. Although techniques such as intermittent electricity can promote microbial growth, they do not effectively resolve sludge deflocculation. Additionally, although biochar (BC) enhances the abundance of microbes, it does not significantly improve microbial activity or treatment performance. This study aimed to alleviate the adverse effects of TA on anaerobic granular sludge (AnGS) by synergistically applying intermittent electrical stimulation and BC. Co-treatment with 1 h-on/off intermittent electricity and 3 g/L BC notably reduced granular sludge deflocculation. Consequently, the chemical oxygen demand (COD) removal efficiency in wastewater reached 91.73 %, with a maximum methane production per cycle of 230.59 mL/g COD, 16.95 % higher than that of the control reactor (197.17 mL/g COD). This improvement was attributed to the synergistic action of intermittent electricity and BC, which enriched the functional microorganisms and stimulated their activity, thereby facilitating direct interspecies electron transfer. Additionally, enhancing the polysaccharide and protein levels in extracellular polymeric substances improved the stability of granular sludge, ultimately mitigating the adverse effects of TA on AnGS.

Effect of thermal-calcium peroxide mediated exopolymer release on disperser pre-treatment for efficient anaerobic digestion

The present study aimed to improve the hydrolysis potential of paper mill sludge through a two-phase disintegration process. In Particular, attention was focused on removal of extracellular polymeric substance (EPS) i.e. deflocculation of sludge in order to improve the efficiency of subsequent disperser disintegration. During deflocculation, carbohydrate, protein and deoxyribonucleic acids (DNA) were used as assessment parameters. During disintegration, soluble chemical oxygen demand (SCOD) and suspended solids (SS) reduction were used as assessment index to evaluate the efficiency of disintegration. A greater EPS removal was attained while deflocculating the sludge at calcium peroxide dosage of 0.05 g/g suspended solids (SS) and at a temperature of 70 °C. When comparing the disintegrated samples, a clear variation was noted in deflocculated and disintegrated sludge (19.2%) than the disintegrated sludge alone (13.5%). This clearly shows the need for deflocculation prior to disintegration. Likewise, a higher biomethane production of 0.214 L/g COD was achieved in deflocculated and disintegrated sludge than the pretreated sludge alone. Deflocculation reduces sludge management cost from 170 USD (Disperser alone (D alone disintegration)) to 51 USD (Thermal calcium peroxide mediated-Disperser (TCaO2-D disintegration), indicating the efficiency of the proposed disintegration.

Nutrients Enrichment and Process Repercussions in Hybrid Microfiltration Osmotic Membrane Bioreactor: A Guideline for Forward Osmosis Development Based on Lab-Scale Experience

The effects of reverse salt diffusion through a forward osmosis membrane were studied in a microfiltration osmotic membrane bioreactor. The reactor was used to treat and simultaneously concentrate nutrients from wastewater. The system was operated at different draw solution concentrations, leading to varying salinity conditions. A relatively low, yet stable forward osmosis flux was observed regardless of increasing draw solution conductivities from 10 to 50 mS cm−1. A substantial increase in sludge conductivity from 5.7 to 19.8 mS cm−1 was observed during the operation. Batch transmembrane pressure-step experiments showed a decline in sludge filtration properties with increasing salinity buildup in sludge due to increasing deflocculation and associated release of protein and carbohydrate fractions of extracellular polymeric substances. Mathematical simulations showed that accumulation of total dissolved solids could mainly be attributed to reverse flux of salts from the draw solution rather than by the enrichment of incoming nutrients when forward osmosis membrane’s salt permeability was high and water permeability low. Ideally, salt permeability below 0.010 L m−2 h−1 and effective water permeability above 0.13 L m−2 h−1 bar−1 are crucial to ensure enhanced nutrient enrichment and reduce sludge osmotic pressure, microbial inactivation, sludge deflocculation and membrane fouling.

TiO2 - chitosan thin film induced solar photocatalytic deflocculation of sludge for profitable bacterial pretreatment and biofuel production

The proposed research intended to acquire the perception of proficient biomethane generation enhanced by TiO2 embedded chitosan thin film (TCTF) mediated enzyme secreting bacterial pretreatment of sludge. Impregnates 0.05 g/g SS TiO2 dosage on chitosan solid matrix effectively disperse sludge flocs and induces deflocculation of 99.35%. This TCTF enhances the enzyme secreting bacterial disintegration by increasing the hydrolytic activity. A higher solubilisation of 16% achieved in TCTF mediated bacterial disintegration while related to enzyme secreting bacterial disintegration alone. The high specific growth rate of 0.2 h−1 for enzyme secreting bacterial growth rate is attained at 42 h. Deflocculation and enzyme secreting bacterial pretreatment has a major impact on methane potential assay. The sludge sample TCTF mediated bacterial disintegration yields 140.40 mL/g COD higher methane than the other samples. The energetic and cost analysis of the proposed work confirms the feasibility of this sludge management process having profitable net cost of 89.92 USD/Ton of sludge.

Immobilized ZnO nano film impelled bacterial disintegration of dairy sludge to enrich anaerobic digestion for profitable bioenergy production: Energetic and economic analysis

Proper treatment and disposal of sludge is a substantial task around the biosphere. To address this issue, sludge deflocculation using photocatalyst was opted to enhance bacterial disintegration which in turn accelerate sludge digestion anaerobically. During this investigation, Direct current (DC) sputtering together with annealing process was used to immobilize Zinc oxide (ZnO). This immobilized ZnO removes the extracellular components at 15 min. The deflocculation mediated bacterial pretreatment induced 22.9% of soluble organics solubilization which auguments the biodegradability to 0.195 g COD/g COD during anaerobic digestion. The quantity of methane generated by deflocculated sludge was 39.2% higher than sludge with bacterial disintegration only with maximum methane yield of 437.14 mL/g COD. Hence, the outcome of the proposed work confirmed that the method is scalable with a net profit of 27 USD with the maximum methane generation of 413.1 kWh. Additionally, this method reduced 57% of dry sludge (solid).

Sodium azide inhibition of microbial activities and impact on sludge floc destabilization.

Absence of sludge deflocculation under prolonged (24h or longer) conditions with dissolved oxygen (DO) less than 0.5mgL⁻1 was recently reported. The reduced aerobic microbial activity, was speculated, had been compensated by the activity of other bacterial (i.e. facultative) communities. To assess such a compensation mechanism and to better evaluate impact of overall microbial activity on the flocculation process, SBR sludge samples were inhibited by using sodium azide under various DO conditions. Sludge deflocculated only in the presence of sodium azide, regardless of DO conditions. This was linked to sodium azide's inhibitory effects on the microbes as indicated by the reduced ammonium and DOC removals. Extracellular potassium level in the mixed liquor of azide spiked samples also indicated simultaneous cell lysis. Fluorescence excitation emission matrix (FEEM) analysis of the extracted bound EPS and fluorescence quenching based interaction studies indicated sodium azide had interacted with the EPS components, and especially with the bound EPS proteins. The impact of such interactions on reduced floc stability needs consideration. This study confirmed the importance of overall microbial activity in the biological flocculation process and the role of bacterial communities, other than the aerobes, in mitigating deflocculation under low DO conditions.

Effect of biomass features on oxygen transfer in conventional activated sludge and membrane bioreactor systems

Abstract The aim of the present study was to compare the oxygen transfer efficiency in a conventional activated sludge and a membrane bioreactor system. The oxygen transfer was evaluated by means of the oxygen transfer coefficient and α-factor calculation, under different total suspended solids concentration, extracellular polymeric substances, sludge apparent viscosity and size of the flocs. The oxygen transfer coefficient and α-factor showed an exponential decreasing trend with total suspended solid, with a stronger oxygen transfer coefficient dependence in the conventional activated sludge compared to the membrane bioreactor. It was noted that the oxygen transfer coefficient in the conventional activated sludge become comparable to that in membrane bioreactor when the total suspended solid concentration in the conventional activated sludge was higher than 5 g L−1. Operating under high carbon to nitrogen ratio, the oxygen transfer coefficient increased in both conventional activated sludge and membrane bioreactor because of sludge deflocculation and it was noticed a weaker dependence of the oxygen transfer coefficient with total suspended solid. The results indicated that the most important parameters on the oxygen transfer efficiency were in order: the total suspended solid concentration, flocs size, sludge apparent viscosity and extracellular polymeric substances content. Based on the influence of the main biomass features affecting the oxygen transfer coefficient and considering the typical operating conditions in both systems, those of membrane bioreactor appeared to be more favorable to oxygen transfer efficiency. The paper provides a useful insight about some peculiarities of oxygen transfer in a conventional activated sludge and a membrane reactor system, highlighting new and useful information in the light of a more sustainable management of these systems.

Effect of deflocculation on photo induced thin layer titanium dioxide disintegration of dairy waste activated sludge for cost and energy efficient methane production

In the present study, the deflocculated sludge was disintegrated through thin layer immobilized titanium dioxide (TiO2) as photocatalyst under solar irradiation. The deflocculation of sludge was carried out by 0.05g/g SS of sodium citrate aiming to facilitate more surface area for subsequent TiO2 mediated disintegration. The proposed mode of disintegration was investigated by varying TiO2 dosage, pH and time. The maximum COD solubilization of 18.4% was obtained in the optimum 0.4g/L of TiO2 dosage with 5.5 pH and exposure time of 40min. Anaerobic assay of disintegrated samples confirms the role of deflocculation as methane yield was found to be higher in deflocculated (235.6mL/gVS) than the flocculated sludge (146.8mL/gVS). Moreover, the proposed method (Net cost for control – Net cost for deflocculation) saves sludge management cost of about $132 with 53.8% of suspended solids (SS) reduction.

Effects of titanium dioxide mediated dairy waste activated sludge deflocculation on the efficiency of bacterial disintegration and cost of sludge management

This investigation explores the influence of titanium dioxide (TiO2) in deflocculating (removal of extracellular polymeric substance – EPS) the sludge and subsequent biomass disintegration by bacterial pretreatment. The EPS removed at an optimized TiO2 dosage of 0.03g/g of SS of TiO2 and a solar radiation exposure time of 15min to enhance the subsequent bacterial disintegration. The outcomes of the bacterial pretreatment reveal SS reduction and COD solubilization for the deflocculated (EPS removed and bacterially pretreated) sludge was observed to be 22.8% and 22.9% which was comparatively greater than flocculated (raw sludge inoculated with bacteria) and control (raw) sludge. The higher methane production potential of about 0.43(gCOD/gVSS) was obtained in deflocculated sludge than the flocculated (0.20gCOD/gVSS) and control (0.073gCOD/gVSS). Economic assessment of this study provides a net profit of about 131.9USD/Ton in deflocculated sludge.

Effect of sonically induced deflocculation on the efficiency of ozone mediated partial sludge disintegration for improved production of biogas

In this study, ultrasonication was used for sludge deflocculation, followed by cell disintegration using ozone. The effect of this phase separated sono-ozone pretreatment is evaluated based on extra polymeric substances release, deoxyribonucleic acid (DNA) in the medium, solubilization of intra cellular components and suspended solids (SS) reduction. Ultrasonically induced deflocculation was optimized at an energy dosage of 76.4(log1.88)kJ/kgTS. During cell disintegration (ozone dosage 0.0011mgO3/mgSS), chemical oxygen demand solubilization (COD) and SS reduction of sonic mediated ozone pretreated sludge were 25.4% and 17.8% comparatively higher than ozone pretreated sludge, respectively. Further, biogas production potential of control (raw), flocculated (ozone pretreated), and deflocculated (sonic mediated ozone pretreated) sludges were observed to be 0.202, 0.535 and 0.637L/(gVS), respectively. Thus, the phase separated pretreatment at lower ultrasonic specific energy and low dose ozone proved to enhance the anaerobic biodegradability efficiently.

Pollutant removal and membrane fouling in an anaerobic submerged membrane bioreactor for real sewage treatment.

Real sewage was continuously treated by a laboratory-scale anaerobic submerged membrane bioreactor (AnSMBR) for over 160 days. Results showed that around 90% of chemical oxygen demand, and 99% of turbidity and total suspended solids in the sewage could be removed by the AnSMBR system. Membrane flux sustained at 11 L/(m(2) h) was realized with biogas sparging. Small flocs from sludge deflocculation in the early operational period caused a high membrane fouling rate, and the high specific filtration resistance of the cake layer appeared mostly attributable to the osmotic pressure effect. The performance results were also compared with those in the literature for upflow anaerobic sludge blanket reactors and aerobic membrane bioreactors for sewage treatment, demonstrating that AnSMBR could provide a desirable alternative for sewage treatment.

Microscopic Image Analysis versus Sludge Volume Index to Monitor Activated Sludge Bioflocculation: A Case Study

The influent ratio of Mono- over Polyvalent cations (M/P ratio) influences activated sludge bioflocculation. A more thorough insight through means of conventional macroscopic parameters, Sludge Volume Index (SVI), and Effluent Suspended Solids (ESS), and microscopic image analysis was pursued in this work. Therefore, a long term experiment was conducted during which activated sludge was exposed twice to a transition in influent M/P ratio from 1.5 to 15. Two distinct observations were made. The first transition indicates the existence of a loosely attached layer evidenced by the temporary release of small sludge particles as observed by image analysis. This release was followed by a decrease in the amount of small sludge particles and increase in floc size indicating good bioflocculated sludge. The second transition results in a massive release of small particles leading to complete sludge deflocculation. (De)flocculation was monitored by both SVI and microscopic image analysis, whereas during the first transition the change in bioflocculation condition could only cleary be monitored by means of microscopic image analysis. Based on this study, microscopic image analysis proves to be a powerful monitoring tool to assess the bioflocculation condition of the activated sludge, whereas SVI is unable to accurately monitor its bioflocculation condition.

Dynamics of the microfauna community in a full-scale municipal wastewater treatment plant experiencing sludge bulking

We investigated the dynamics of the microfauna community in activated sludge, with special reference to sludge bulking, in two parallel municipal wastewater treatment systems in Beijing, China over a period of 14 months. Annual cyclic changes in microfauna community structures occurred in both systems. RELATE analysis based on Spearman's Rank correlation indicated that microfauna community structures were highly correlated with the sludge volume index (SVI) (p<0.001), which indicates sludge settleability. Nutrient conditions of raw sewage (p<0.01) and hydraulic retention time (HRT) (p<0.05) were also related to microfauna community structures. Abundances of the species Epistylis plicatilis and Vorticella striata increased significantly with an increase in SVI (p<0.001) and decrease in water temperature (p<0.001), suggesting that sludge bulking may have created favorable conditions for the two species, even under unfavorable temperature conditions. Sludge de-flocculation primarily due to the excessive growth of Microthrix parvicella-like filaments could be an important driving force for the microfauna community changes. The release of flocculated non-filamentous bacteria may represent a suitable food source for these species. The two species may be considered as potential bioindicators for sludge bulking.

Biological treatment of saline wastewaters in an aerobic sequencing batch reactor

The influence of different chloride salts (sodium, potassium, calcium, and magnesium) on wastewater biological treatment performance was investigated. Long term assays were performed (30 d) operating aerobic sequencing batch reactors (SBR) with a 24‐h cycle (23 h of reaction and 1 h of sedimentation and draining). Salt content varied from 0% to 6% m/v in different assays, using synthetic wastewater with an average COD of 2000 mg/L. When salt was not added to the SBR influent chemical oxygen demand (COD) removal averaged 95%. For the higher salt concentration tested (6% m/v), average COD removals for NaCl, KCl, MgCl2, and CaCl2 were, respectively, 81%, 92%, 83%, and 87%. Some deleterious effects caused by salt concentration were: reduction of protozoa population and diversity and sludge deflocculation, which caused a rise on the SBR effluent turbidity. © 2011 American Institute of Chemical Engineers Environ Prog, 32: 198‐205, 2013

Particle counting as a tool to predict filterability in membrane bioreactors activated sludge?

Activated sludge quality is one of the major factors influencing flux decline in membrane bioreactors (MBRS). Sludge filterability is a recognized parameter to characterize the physical properties of activated sludge. Decrease in filterability is linked to a higher number of submicron particles. In our present research we studied whether particle counting techniques can be used to indicate deflocculation of the sludge suspended fraction to submicron particles, causing the aforementioned filterability decrease. A total number of 105 activated sludge samples were collected in four full scale municipal MBRS. Samples were tested for filterability and particle counting in the range 2-100 microm. In 88% of the membrane tank samples the filterability varied between good and poor, characterized by the deltaR20, being 0 < deltaR20 < 1. Filterability varied following the season of the year, stability of the MBR operation and recirculation ratio. The membrane tank filterability can be improved by applying low recirculation ratio between MBR tanks. The applied particle counting methodology generated reproducible and reliable results in the range 10-100 microm. Results show that differences in filterability cannot be explained by variations in particle size distribution in the range 10-100 microm. However, measurable deflocculation might be masked by the large numbers of particles present. Therefore, we cannot exclude the suspended particles as a possible source of submicron particles that are subsequently responsible for MBR sludge filterability deterioration.

Effect of membrane bioreactor configurations on sludge structure and microbial activity

The aim of this paper was to determine the effect of two different membrane bioreactor (MBR) configurations (external/immersed) on sludge structure and microbial activity. Sludge structure was deduced from rheological measurements. The high shear stress induced by the recirculation pump in the external MBR was shown to result in decreasing viscosity due to activated sludge (AS) deflocculation. Besides, soluble microbial products (SMP) release was higher in the external MBR (5 mgCOD gMLVSS(-1)) than in the immersed configuration (2 mgCOD gMLVSS(-1)). Microbial activity was followed from respirometry tests by focusing on the distinction between heterotrophs and autotrophs. An easier autotrophic microbe development was then observed in the immersed MBR compared to the external one. However, the external MBR was shown to allow better heterotrophic microbe development.

Treatment of kraft evaporator condensate using a thermophilic submerged anaerobic membrane bioreactor

The feasibility of using a thermophilic submerged anaerobic membrane bioreactor (SAnMBR) for kraft evaporator condensate treatment was studied at 55+/-1 degrees C over 6.5 months. Under tested organic loading rate of 1-7 kg COD/m(3) day, a soluble COD removal efficiency of 85-97% was obtained. The methane production rate was 0.35+/-0.1 L methane/g COD and the produced biogas was of excellent fuel quality with 80-90% methane. A higher membrane fouling rate was related to the presence of a larger portion of fine colloidal particles (1-10 mum). The thermophilic SAnMBR was sensitive to the presence of toxic compounds in feed and unexpected pH probe failure (leading to a higher pH). Feed toxic shock caused sludge deflocculation and thus deteriorated membrane performance. Operating the reactor as a conventional anaerobic reactor to waste some of the fine flocs in treated effluent during the start-up process was an effective strategy to reduce membrane fouling. The experimental results from this study indicate that treatment of kraft evaporator condensate is feasible in terms of COD removal and biogas production using thermophilic SAnMBRs but pre-treatment may be needed to remove toxic sulfur compounds and membrane fouling caused by the large portion of fine particles may be a challenge.

Long-term operation of submerged membrane bioreactor (MBR) for the treatment of synthetic wastewater containing styrene as volatile organic compound (VOC): Effect of hydraulic retention time (HRT)

In this study, the membrane bioreactor (MBR) was utilized to remove styrene from a synthetic wastewater having a chemical oxygen demand (COD) and styrene concentration of 1500 mg/L and 50 mg/L, respectively. At two hydraulic retention times (HRTs) of 24 h and 18 h, the MBR was operated for a period in excess of 100 days. The HRT effects were studied and it was found out that the removal efficiency of COD and styrene for both HRTs was consistently higher than 99%. Unlike conventional activated sludge processes (CASPs), no styrene was detected in the exhaust air, which meant that biodegradation was the major styrene removal mechanism at both HRTs. The transmembrane pressure (TMP) profile during the operation of the MBR showed a fairly low and constant TMP up to day 70, after which, the TMP showed a dramatic rise, as a result of the occurrence of severe membrane fouling. It was thought that an increase in styrene loading rate, when HRT was reduced to 18 h, resulted in the release of extracellular polymeric substance (EPS) from the bacterial cells, which in turn was responsible for the rise in soluble microbial product (SMP) and sludge deflocculation. The severe fouling observed during operation of MBR at HRT of 18 h was attributed to the rise in SMP concentrations and decrease in mean floc size and increase in the proportion of small particles in the activated sludge.

The impact of deflocculation–reflocculation on fouling in membrane bioreactors

Membrane bioreactors (MBRs) have proven to be a valuable alternative for conventional activated sludge plants. Membrane fouling remains, however, a significant drawback. Stable operation of a membrane bioreactor requires a good sludge condition. In this paper it is evidenced that bioflocculation is a crucial factor within that context. By changing the ratio of monovalent over polyvalent cations ([M/P]) in the influent, a deflocculation–reflocculation event was induced during which the impact of bioflocculation on fouling in membrane bioreactors could be studied. In a first phase, a high [M/P] influent was fed to the MBR which resulted in severe sludge deflocculation and worsened filtration characteristics. A low [M/P] influent was subsequently fed to the MBR. Within 3 weeks, the activated sludge reflocculated and filtration characteristics improved significantly. Monitoring of bioflocculation in MBRs is thus of extreme importance to start possible remediation as quickly as possible. Fragment surface proved to be a valuable parameter in that respect. In contrast, no clear relation between EPS and filtration characteristics could be found. This work substantiates the hypothesis that a well functioning dynamic secondary membrane, built up by robust activated sludge flocs, can prevent severe (irreversible) fouling in MBRs.

The Effect of Short-Term Dissolved Oxygen Transients on Activated Sludge

Abstract The effect of short-term dissolved oxygen (DO) disturbances on municipal activated sludge was studied, in a batch system, with respect to changes in supernatant turbidity, suspended solid (SS) concentrations, proteins, polysaccharides, and cations in the extracellular polymeric substances (EPS). Results showed that turbidity increased by 20 times when the DO concentration decreased below 0.5 mg/L, and supernatant SS concentrations increased by 1 to 2 times with DO reduction, implying the presence of more unsettled particles in the supernatant. Concomitantly, soluble proteins increased from less than 1 mg/L to up to 30 mg/L, and bound proteins decreased by more than 15% under DO limitation. Further enzymatic tests confirmed that, compared with polysaccharides, proteins were more involved in preventing sludge deflocculation. The DO stress also caused significant changes in the bulk concentrations of K+ and Ca2+; K+ increased by 40% and Ca2+ decreased by 30%. When the DO concentration was restored after 6 hours, reversible changes were observed in supernatant turbidity and SS, and concentrations of EPS proteins and cations, indicating a possible physiological response of microorganisms to a short-term low DO disturbance.