Performance Of Activated Sludge Research Articles

Protozoans as indicators of sequential batch processes for phenol treatment; an autoecological approach

The objective of this study was the investigation of the potential use of protistan species as quality indicators of the activated sludge performance in sequential batch processes receiving toxic compounds. Two laboratory scale sequential batch reactors (SBR) were used, a conventional one and a system with plastic biofilm carriers (SBBR), treating wastewater containing phenol at concentrations ranging from 1 up to 40mg/L. Physicochemical analyses of the samples included the determination of MLSS, effluent suspended solids, BOD5, nitrogen–ammonia, nitrogen–nitrate and phenol. The activated sludge protistan community was identified and enumerated in each reactor. Statistical analyses included Canonical Correspondence Analysis and Indicator Species Analysis of the collected experimental data. Canonical Correspondence Analysis showed inversely proportional relationships between the protozoa and the physicochemical parameters of the effluent as well as protozoan species competition. Indicator species analysis revealed the presence and the prevalence of different species under various phenol influent concentrations.No indicator species were observed for the period of operation under 5mg/L influent phenol in both reactors, while no indicator species were observed for 20mg/L influent phenol in the SBR reactor. Carchesium and Epistylis sp. showed the higher values for 1mg/L phenol in the SBR, while Holophrya sp. showed lower indicator values for the same period in the SBBR. Although several species showed a good correlation to the treatment efficiency of the reactors, Blepharisma sp., could be used as the primary indicator species in both reactors for the operation period under 40mg/L phenol, as deduced by statistical analysis.

Biodegradation of perchloroethylene and chlorophenol co-contamination and toxic effect on activated sludge performance

This study investigated the effects of PCE and 2-CP co-contamination on growth of microbial community in terms of enzymatic activity and microbial diversity in activated sludge. Results showed that the activities of three key enzymes (dehydrogenase, phosphatase and urease) decreased significantly when PCE (in the range of 5–150mg/L) was mixed with 2-CP (in the range of 25–150mg/L). Especially, activity of dehydrogenase decreased by more than 93% as the concentration of PCE and 2-CP both reached 150mg/L. PCR–DGGE revealed that short-term exposure with PCE and 2-CP did not lead to shift in the microbial community structure, while clone library demonstrated a significant change in the microbial diversity after long-term exposure. As the population of Alphaproteobacteria and Gamaproteobacteria decreased, with Actinobacteria eventually disappeared, species including Firmicutes, Bacteroidetes and Synergistetes became dominating groups. This study demonstrated that co-contamination with PCE and 2-CP affected the performance of activated sludge in a significant way.

Effect of trace amounts of polyacrylamide (PAM) on long-term performance of activated sludge

This study aims at evaluating the impacts of PAM addition on activated sludge performance. Four lab-scale sequencing batch reactors (SBRs), each with a working volume of 3 L, were investigated with different PAM concentrations. Experiments were conducted with varying organic loading rate and the sludge volume index (SVI), particle size, zeta potential, specific oxygen uptake rate (SOUR), mixed liquor suspended solids (MLSS), COD and ammonium removal efficiency were monitored over a 105-day period. The results showed that all of the PAM addition not only improved the removal efficiencies of COD and ammonium, but also exhibited some advantages on sludge performance. It was found that the sludge performance of settling property, flocculation and microbial activity increased with increasing concentration of PAM. However, high level of PAM (1 mg/L) led to the formation of large amounts of loose-structure flocs, which eliminated dissolved oxygen transfer and caused the sludge disintegration, resulting in bad settleability and lower microbial activity. In this way, when the dosage of PAM was 0.1 mg/L, the sludge had the best settling property and activity.

Effects of floc aluminum on activated sludge characteristics and removal of 17-α-ethinylestradiol in wastewater systems

The effects of floc aluminum (Al) on activated sludge performance and 17-α-ethinylestradiol (EE2) removal were studied using bench-scale activated sludge systems. The results showed that higher Al-fed activated sludge led to better settling, dewatering, and effluent quality with better EE2 removal. EE2 concentrations in the effluent revealed correlations with effluent suspended solids and large particulate/colloidal effluent biopolymer (protein + polysaccharide). Furthermore, a significant correlation existed between effluent proteins and EE2 for all size fractions, indicating that hydrophobic proteinaceous colloids provide binding sites for EE2 and washout together into the effluent. These results suggest that aluminum plays a crucial role in bioflocculation of activated sludge and the efficacy of flocculation influences the removal of endocrine disrupting compounds (EDCs) from wastewater treatment systems.

Aerobic vs. Anaerobic-Aerobic Biotreatment: Paper Mill Wastewater

The operation of existing activated sludge treatment plants at paper mills in the world is often characterized by disturbances, caused by bad biosolids settling, sludge bulking, and reduction of biomass activity. This paper presents a comparison between the results obtained in a case study based on a full-scale activated sludge treatment (AST) system working as the only biotreatment and the AST working with anaerobic pretreatment by upflow anaerobic sludge blanket (UASB). The study was performed at paper mills in Hedera, Israel. The data was collected during 8 years. The anaerobic/aerobic system (2002–2004) provided steady operation performance, while the AST system without anaerobic pretreatment (1997–2001) produced effluent characterized by oscillatory values. The results indicate much lower levels of total suspended solids in the anaerobic/aerobic treatment system effluent, 5–10 mg/L, compared to 50–85 mg/L in the AST system only. Similar improvement was observed in terms of the organic matter removal: 220–250 mg/L vs. 80–120 mg/L as CODt, and 20–40 mg/L vs. 4–7 mg/L as BODt with low corresponding fluctuations. After the operation of the anaerobic pretreatment, the sludge age increased from 8–10 days to 30–40 days and the activated sludge performance substantially improved: the sludge volume index decreased from 200 to 80 mL/g with significant reduction of the excess sludge amount. The data collected during the operation monitoring clearly indicates that the anaerobic process followed by AST considerably reduced electrical and chemicals consumption in the biological treatment plant and provided low operational cost.

Enhancement of activated sludge performance on ammonium removal by clinoptilolite

This study evaluated the influence of clinoptilolite on the performance of activated sludge system shocked by high concentration of ammonium. The ammonium and chemical oxygen demand (COD) removal from the experimental reactor containing clinoptilolite and from the clinoptilolite-free control reactor was determined. The ammonium and COD removal was approximately 8 and 20% higher in the experimental reactor than in the control reactor, respectively. The removal increased with an increase in clinoptilolite concentration over the tested range up to 50 mg L−1. The presence of clinoptilolite resulted in the sludge flocs being more compacted with smoother surfaces and edges. Molecular biological analysis revealed that clinoptilolite increased the DNA diversity, richness, and evenness of sludge microbes. The enhanced-performance activated sludge previously treated with clinoptilolite was less influenced by the shock of ammonium than non-treated sludge in terms of the ammonium and COD removal. These results suggest that clinoptilolite enhanced the performance of activated sludge system in the removal of ammonium and COD. Amendment of activated sludge with natural zeolites may thus improve the efficiency of wastewater treatment.

Case Study II: Application of the Divalent Cation Bridging Theory to Improve Biofloc Properties and Industrial Activated Sludge System Performance—Using Alternatives to Sodium‐Based Chemicals

The objective of this study was to investigate the application of the divalent cation bridging theory (DCBT) as a tool in the chemical selection process at an activated sludge plant to improve settling, dewatering, and effluent quality. According to the DCBT, to achieve improvements, the goal of chemical selection should be to reduce the ratio of monovalent-to-divalent (M/D) cations. A study was conducted to determine the effect of using magnesium hydroxide [Mg(OH)2] as an alternative to sodium hydroxide (NaOH) at a full-scale industrial wastewater treatment plant. Floc properties and treatment plant performance were measured for approximately one year during two periods of NaOH addition and Mg(OH)2 addition. A cost analysis of plant operation during NaOH and Mg(OH)2 use was also performed. During NaOH addition, the M/D ratio was 48, while, during Mg(OH)2 addition, this ratio was reduced to an average of approximately 0.1. During the Mg(OH)2 addition period, the sludge volume index, effluent total suspended solids, and effluent chemical oxygen demand were reduced by approximately 63, 31, and 50%, respectively, compared to the NaOH addition period. The alum and polymer dose used for clarification was reduced by approximately 50 and 60%, respectively, during Mg(OH)2 addition. The dewatering properties of the activated sludge improved dewatering as measured by decreased capillary suction time and specific resistance to filtration (SRF), along with an increase in cake solids from the SRF test. This corresponded to a reduction in the volume of solids thickened by centrifuges at the treatment plant, which reduced the disposal costs of solids. Considering the costs for chemicals and solids disposal, the annual cost of using Mg(OH)2 was approximately 30,000 dollars to 115,000 dollars less than using NaOH, depending on the pricing of NaOH. The results of this study confirm that the DCBT is a useful tool for assessing chemical-addition strategies and their potential effect on activated sludge performance.

The Impact of Residual Coagulant on Downstream Treatment Processes

A series of jar tests were undertaken to optimise for suspended solids (SS) and phosphorus removal from raw wastewater. The residual metal concentration in the settled wastewater from the jar test experiments and the residual concentration from the optimum doses plus two higher doses were selected for investigation. The identified levels of residual metal were fed into a four lane activated sludge pilot plant to investigate the impact of metal concentration on (i) activated sludge performance and (ii) sludge production and characteristics. Optimum pre-precipitation studies showed residual ion concentrations of 1.68 and 3.46 mg l−1 for Fe(III) and Al(III) respectively. At these levels %P removal increased by approximately 25 and 60 % respectively. NH3 removal decreased by approximately 20 and 34% in the activated sludge treatment process. Chemically dosed biomass had a significantly lower oxygen uptake rate than the control which was accompanied by a reduction in VSS; 10% for Fe(III) and 17% for Al(III). Changes in sludge characteristics were also observed. Chemical sludge had a greater settleability but a lower dewaterability than biological sludge. Sludge floc morphology was characterised which showed chemical flocs to be consistently smaller and visually denser than biological sludge flocs. The work presented in this paper considers the impact of residual iron and aluminium coagulants on downstream treatment processes.

Effects of electrolyte and curing on freeze/thaw treatment of sludge

This work experimentally examined the role of electrolyte and curing on freeze/thawed sludge dewaterability. We herein, for the first time, demonstrate that the presence of sludge particles have diminished the formation of salt/water eutectic, which is against the results in previous literature. The eutectic temperature of the electrolyte thereby had no effect on the sludge filterability and settleability. Furthermore, curing has profound effects on activated sludge performance, whose effect, however, is negligible for clay slurry. The mass transfer processes interpret the experimental results. Curing time alone is not a fundamental measure for the curing process.

Combined effects of Ni(II) and Cr(VI) on activated sludge

The combined effects of Ni(II) and Cr(VI) on activated sludge kinetics were studied in this paper. The metals were added to a synthetic medium with a chemical oxygen demand (COD) of 1300 mg 1 −1 to give various combinations of Ni(II) and Cr(VI). Activated sludge performance, in terms of COD removal, was not adversely affected in an acclimatized culture by the metal combinations, compared with the single metals. The combination effects of Ni(II) and Cr(VI) on biokinetic constants, i.e. the maximum specific growth rate, μ m , was found to be stimulatory in general. The same effect was observed on the half-saturation substrate concentration, K s . Effects were therefore classified as synergistic with respect to these constants.

Improvement of activated sludge performance by the addition of Nutriflok 50 S

By means of rigorously controlled lab-scale activated sludge systems operated in parallel, the effect of the addition of a nutritive supplement on the overall performance of these systems was verified. Nutriflok 50 S is a commercially available product, containing nutrients and flocculating agents. In a first series of tests by means of SCAS (semi-continuous activated sludge) reactors, fed with synthetic wastewater, the positive effect of the supplement (dosed at 5% of the chemical oxygen demand (COD) load) on the sludge volume index (SVI) (39% improvement) and the residual COD (40% improvement) was demonstrated. In a second series, an industrial wastewater was used in a benchscale set-up according to the OECD procedure. The overall efficiency and sludge sedimentation characteristics were compared for two parallel activated sludge systems continuously fed with pharmaceutical wastewater. In the control no additive was given; the other reactor received on a daily basis a dose of Nutriflok 50 S corresponding to 10% of the COD load. The performance of the Nutriflok 50 S supplemented reactor was found to be statistically better in terms of sedimentation characteristics, nitrification and COD removal than the control. Especially when operated under winter conditions (10°C) and at higher sludge loading rates (Bx = 0.26 kg COD/kg VSS.d) the COD removal efficiency was about 35% higher in the treated reactor. Moreover, nitrification could be maintained in the supplemented reactor at low temperatures, whilst it became minimal under those conditions in the control reactor. Also in the second series of tests, sludge sedimentation characteristics improved with Nutriflok 50 S. The SVI was 40% lower for the Nutriflok 50 S amended sludge and the recycled sludge was 27% more concentrated. When operated at higher temperatures (20–26°C) the amended sludge was less sensitive to denitrification linked flotation in the settler. Microscopic examination of the sludge revealed a more diverse microbial community and the presence of higher trophic organisms in the supplemented reactor. These results indicate a potential for considerable improvement, not only of the overall conversion efficiency, but also of the sludge management characteristics when Nutriflok 50 S is dosed to the activated sludge.

Biomembrane wastewater treatment by activated sludge method

The paper compares the biomembrane and classical activated sludge methods of wastewater treatment and presents the influence of ultrafiltration on the activated sludge condition. It specifies the difference of enzymatic activity of activated sludge in both systems. In effect of both activated sludge performance and separation properties of the ultrafiltration membrane, the effluent from the biomembrane system is less loaded.

Small Activated Sludge Performance and Viability Characteristics under Intermittent and Reduced Flows

Small activated sludge systems operate in transient states under intermittent and variable flows. Simulations for such a treatment plant in a summer house site operating on a seasonal basis is investigated for system performance and viability using the five component inert soluble substrate generation model. The results have revealed that the viability drops to zero within the first month after the cessation of the feed for intermittently loaded systems that are fed during the summer months, while it never reaches that value for systems operating all year round with reduced flows off season. Restartup is compulsory for the intermittent loadings while the system adapts itself in a stepwise manner for the year round operation. Other factors being comparable, conventional operation with shorter sludge ages may be preferable since viability of the sludge is higher and the effluent COD is comparable.

Activated Sludge Treatment of Phenoxy Herbicides and Chlorophenols

A laboratory scale activated sludge treatment system was developed for the treatment of phenoxy herbicide chemicals and the associated chlorophenols in a toxic landfill leachate. A novel sludge recycle system was employed to ensure high specific activity of the return sludge. The activated sludge treatment resulted in 99.5% removal of phenoxies and chlorophenols and 84% TOC reduction for 10% influent leachate concentrations. The corresponding toxicity reduction was 76%. An increase in influent concentration resulted in a decline in activated sludge performance.

Bio-agglutination for improving activated sludge performance

An attempt was made to improve the treatment efficiency of an activated sludge system by operating it in a combination of high-growth and low-growth conditions for maximum biooxidation and bioflocculation, respectively. The experiment was conducted in batch and continuous reactors and simulation was carried out to evaluate the system proposed on the basis of the results obtained. The observed yield coefficient and specific substrate utilization rate were affected by the mean cell residence time (MCRT). Mixing intensity had a marginal effect on the sludge volume index (SVI) and supernatant chemical oxygen demand (COD). Bioflocculation was more affected by sludge characteristics than by mixing intensity. The simulation results indicate that the proposed system could produce the same amount of sludge as conventional processes but with improved treatment efficiency.

Discussion of “ Hydraulic Regime and Activated Sludge Performance ” by Robert M. Sykes (April, 1982)

Discussion of “ <i>Hydraulic Regime and Activated Sludge Performance</i> ” by Robert M. Sykes (April, 1982)

Closure to “ Hydraulic Regime and Activated Sludge Performance ” by Robert M. Sykes (April, 1982)

Closure to “ <i>Hydraulic Regime and Activated Sludge Performance</i> ” by Robert M. Sykes (April, 1982)

Hydraulic Regime and Activated Sludge Performance

The standard bio-kinetic theory used to describe the activated sludge process predicts that the soluble organic matter (SOM) concentration in the effluent of plug flow aeration tanks will be less than the SOM concentration in the effluent of completely mixed aeration tanks, if both contain the same total biomass and are operated at the same solids' retention time (SRT). Large-scale field studies indicate that this prediction is false. An alternate model of the process is presented that identifies the effluent SOM as a product synthesized and excreted by the microbes of the activated sludge. This model predicts that all aeration tanks treating a given wastewater will produce the same effluent SOM concentration if they contain the same total biomass and are operated at the same SRT. The alternate model also predicts that the effluent SOM concentration will be proportional to the influent organic matter concentration, that the apparent microbial decay rate will vary as different nutrients are considered, and that plots of the specific uptake rate vs. the effluent SOM concentration will show a positive SOM intercept. All these predictions are supported by experiment.