Activated Sludge Aeration Tank Research Articles

Efficiency of the work of almond shells as biological carriers in activated sludge aeration tanks

Based on the interest in environmentally friendly materials for wastewater treatment, this research is aimed at evaluating the efficiency of almond shells work as biological carriers in activated sludge aeration tanks, known as the integrated fixed-film activated sludge treatment, a hybrid tank with attached growth and suspended growth is obtained. Almond shells were placed at 7% of the size of the aeration tank throughout the experiment period for about 4 months with a number of indicators such as hydraulic retention time and mixed liquor suspended solids. Two sets of experiments were performed, the first group with a constant hydraulic retention time ( HRT= 4 hours), and mixed liquor suspended solids was changed (500-1000-2000-3000 mg/ L), with the best removal efficiency at MLSS = 2000 mg/ l, by 91.3% and 92.1% for COD and SS respectively. The optimal MLSS concentration was adopted for the second group of experiments where HRT was increased to 5 and 6 hours. As a result, the best chain was found to be MLSS = 2000 mg/ l and HRT = 5 hours, with a removal efficiency of 93.4% and 93.9% for COD and SS respectively. As a result, the rate of return activated sludge was reduced from 100% to 60% and the rate of inflow into the aeration tank was increased due to the reduction HRT from 6 hours to 5 hours compared to conventional activated sludge treatment.

Biological Oxidation of Air-Borne Volatile Organic Compounds by Pilot Sieve-Plate Absorption Tower

Abstract An activated sludge aeration tank and a sieve-plate column with six sieve plates were utilized to remove gas-borne volatile organic compounds (VOCs) in air streams. The tank was used for t...

Effects of Small-Size Suspended Solids on the Emission of Escherichia coli from the Aeration Process of Wastewater Treatment

ABSTRACTThe concentrations of bioaerosols near pretreatment facilities are often higher than those near activated-sludge aeration tanks in wastewater treatment plants (WWTP). The reason for this difference is not yet clear and the differences between the characteristics of suspended solids (SS) in these two processes might play a critical role. In this study, a lab-scale wastewater treatment system was tested with Escherichia coli (E. coli) in order to investigate the effects of the type and concentration of SS on the concentration and size distribution of emitted bioaerosols. Two types of SS, activated sludge from a hospital WWTP and kaolin clay, were selected to represent floc-type mixed-liquor SS (MLSS) and non-floc-type SS, respectively. An Andersen six-stage sampler was used to analyze the size distribution of the airborne E. coli aerosols. When the tested aeration rate was as low as 0.5 L min–1, it was found that the presence of bioaerosols slightly decreased in air/water ratio (AWR, CFU m–3 air/CFU 100 mL–1 water) when the SS increased from 500 to 2000 mg L–1 for both floc and non-floc SS. However when the aeration rates went up to 5–15 L min–1, the pattern of AWR vs. SS curve was different with an increase trend for non-floc SS and a decrease trend for floc SS, with an exception of increase trend for floc SS as the MLSS increased from 0 to 500 mg L–1. The major sizes of emitted bioaerosols ranged from 0.65 to 1.1 µm. A peak was observed at an aerodynamic diameter greater than 7 µm when the aeration rate was 15 L min–1. In conclusion, floc-type activated sludge can inhibit the emission of E. coli from an aeration tank. In contrast, the non-floc-type small-size kaolin clay can enhance the emission of E. coli from the pretreatment process.

Co-treatment of acid mine drainage with municipal wastewater: performance evaluation

Co-treatment of acid mine drainage (AMD) with municipal wastewater (MWW) using the activated sludge process is a novel treatment technology offering potential savings over alternative systems in materials, proprietary chemicals and energy inputs. The impacts of AMD on laboratory-scale activated sludge units (plug-flow and sequencing batch reactors) treating synthetic MWW were investigated. Synthetic AMD containing Al, Cu, Fe, Mn, Pb, Zn and SO4 at a range of concentrations and pH values was formulated to simulate three possible co-treatment processes, i.e., (1) adding raw AMD to the activated sludge aeration tank, (2) pre-treating AMD prior to adding to the aeration tank by mixing with digested sludge and (3) pre-treating AMD by mixing with screened MWW. Continuous AMD loading to the activated sludge reactors during co-treatment did not cause a significant decrease in chemical oxygen demand (COD), 5-day biochemical oxygen demand, or total organic carbon removal; average COD removal rates ranged from 87-93%. Enhanced phosphate removal was observed in reactors loaded with Fe- and Al-rich AMD, with final effluent TP concentrations<2 mg/L. Removal rates for dissolved Al, Cu, Fe and Pb were 52-84%, 47-61%, 74-86% and 100%, respectively, in both systems. Manganese and Zn removal were strongly linked to acidity; removal from net-acidic AMD was <10% for both metals, whereas removal from circum-neutral AMD averaged 93-95% for Mn and 58-90% for Zn. Pre-mixing with screened MWW was the best process option in terms of AMD neutralization and metal removal. However, significant MWW alkalinity was consumed, suggesting an alkali supplement may be necessary.

The effect of the sludge recycle ratio in an activated sludge system for the treatment of Amol's industrial park wastewater

An activated sludge aeration tank and a sedimentation basin were used to treat Amol's industrial park effluents originating from all industrial units. A continuous system was implemented and the kinetic parameters were measured. The parameters such as rate constant, substrate utilization rate constant, yield and decay coefficient were 2.12 d-1, 232.4 mg l-1, 0.33 g/g of substrate and 0.096 d-1, respectively. The hydraulic retention times (HRT) were in the range of 9 to 27 h. The sludge recycle ratios in the range from 0.3 to 1 were considered. The COD removal, SVI and DO were determined and the optimal values were obtained. It was observed that at HRT of 16 h and the sludge recycle ratio of 0.85, the COD removal and SVI were 95 and 85 %, respectively. The sludge recycle ratio greater than 0.85 had no significant effect on the COD removal.

Dimethyl Sulfoxide (DMSO) Waste Residues and Municipal Waste Water Odor by Dimethyl Sulfide (DMS): the North-East WPCP Plant of Philadelphia

This study shows for the first time that overlooked mg/L concentrations of industrial dimethyl sulfoxide (DMSO) waste residues in sewage can cause "rotten cabbage" odor problems bydimethyl sulfide (DMS) in conventional municipal wastewater treatment. In laboratory studies, incubation of activated sludge with 1-10 mg/L DMSO in bottles produced dimethyl sulfide (DMS) at concentrations that exceeded the odor threshold by approximately 4 orders of magnitude in the headspace gas. Aeration at a rate of 6 m3 air/m3 sludge resulted in emission of the DMS into the exhaust air in a manner analogous to that of an activated sludge aeration tank. A field study atthe NEWPCP sewage treatment plant in Philadelphia found DMSO levels intermittently peaking as high as 2400 mg/L in sewage near an industrial discharger. After 3 h, the DMSO concentration in the influent to the aeration tank rose from a baseline level of less than 0.01 mg/L to a level of 5.6 mg/L and the DMS concentration in the mixed liquor rose from less than 0.01 to 0.2 mg/L. Finding this link between the intermittent occurrence of DMSO residues in influent of the treatment plant and the odorant DMS in the aeration tank was the keyto understanding and eliminating the intermittent "canned corn" or "rotten cabbage" odor emissions from the aeration tank that had randomly plagued this plant and its city neighborhood for two decades. Sewage authorities should consider having wastewater samples analyzed for DMSO and DMS to check for this possible odor problem and to determine whether DMSO emission thresholds should be established to limit odor generation at sewage treatment plants.

Bio-Oxidation of Airborne Volatile Organic Compounds in an Activated Sludge Aeration Tank

An activated sludge aeration tank (40 × 40 × 300 cm, width × length × height) with a set of 2-mm orifice air spargers was used to treat gas-borne volatile organic compounds (VOCs; toluene, p-xylene, and dichloromethane) in air streams. The effects of liquid depth (Z), aeration intensity (G/A), the overall mass-transfer rate of oxygen in clean water (K L a O2 ), the Henry’s law constant of the tested VOC (H), and the influent gaseous VOC concentration (C 0) on the efficiency of removal of VOCs were examined and compared with a literature-cited model. Results show that the measured VOC removal efficiencies and those predicted by the model were comparable at a G/A of 3.75–11.25 m3/m2·hr and C 0 of ∼1000–6000 mg/m3. Experimental data also indicated that the designed gas treatment reactor with K L a O2 = 5–15 hr−1 could achieve >85% removal of VOCs with H = 0.24–0.25 at an aerated liquid depth of 1 m and >95% removal of dichloromethane with H = 0.13 at a 1-m liquid depth.

HYDRAULIC CHARACTERISTICS OF ACTIVATED SLUDGE AERATION TANKS

HYDRAULIC CHARACTERISTICS OF ACTIVATED SLUDGE AERATION TANKSHydraulic characteristics of activated sludge aeration tanks with different geometry and aeration systems were measured using slug dye tracer tests. The results suggest that multiple pass fine bubble aeration systems have a much greater plug flow characteristic than would have been predicted by previous research, based on tank geometry alone. Test results from single pass aeration tanks showed...Author(s)R. W. SamstagB. NarayananJ. HagstromT. G. BridgesA. BahlSourceProceedings of the Water Environment FederationSubjectSession 33: Municipal Wastewater Treatment Processes: Design OptimizationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2005ISSN1938-6478SICI1938-6478(20050101)2005:13L.2712;1-DOI10.2175/193864705783865253Volume / Issue2005 / 13Content sourceWEFTECFirst / last page(s)2712 - 2727Copyright2005Word count192

Determination of some rheological parameters for the characterization of activated sludge

The rheological characterization of activated sludge originating from different aeration tanks and from a lab-scale plant was carried out using rotation tests. Two rheological parameters were used: limit viscosity ( μ ∞) and reduced hysteresis area (rHa). μ ∞ was strongly influenced by the total suspended solids (TSS) content of sludge and an exponential relation was found between TSS and the rheological parameter μ ∞. Significant differences in sludge viscosity were found for sludge of different origins, but all of 10 g/l TSS content, indicating ability of viscosity to show different sludge qualities. Marked changes in activated sludge microorganisms communities were shown to have an influence on rheological parameters. During aerobic digestion of sludge, variations in μ ∞ were noticed, indicating change of sludge quality. An over-growth of filamentous bacteria species was shown to induce a particular rheological behavior which could be characterized by rHa. This parameter was proposed as an index of filamentous bacteria proliferation in activated sludge aeration tanks.

Treatment of slaughterhouse wastewater using an activated sludge/contact aeration process

This study combines a two-phase biological treatment system of activated sludge/contact aeration process by adding biological contact filters into the rear sector of the activated sludge aeration tank of the slaughterhouse wastewater treatment plant. This system keeps the advantages of complete mixing of substrates and microorganisms and flexible operation of the activated sludge process, and increased biological phase, less sludge, process stability and good settleability of sludge of the contact aeration process. This system could avoid the defects of sludge bulking, increased sludge production and difficult operation of the activated sludge process, and system clogging and rigid operation of the contact aeration process. Because suspended microorganisms are flowing into the contact aeration system, which then degrade or suspend within the biological contact filters after being adsorbed by the fixed biological film, on which partial bio-solids will act as seeding microorganisms. Suspended microorganisms and the dropped biological film will settled in the secondary settling tank, then reflux into the activated sludge aeration tank. The partial dropped biological film will decompose in the activated sludge aeration tank to achieve the function of decreasing sludge. Large specific gravity and good settling ability of biofilm sludge will provide better effluent quality. It has been proven through a practical experiment at a slaughterhouse wastewater treatment plant in Taiwan, that the activated sludge process effluent COD value of 150-200 mg/L and SS value of 80-100 mg/L were decreased to around 40 mg/L and 22 mg/L, respectively, after changing its system to the two-phase biological treatment system of activated sludge/contact aeration process.

Novel Nitrogen Removal Process Using Attached Activated Sludge.

In a conventional activated sludge aeration tank, organic nitrogen was almost completely converted to ammonium but very little was converted to oxidized forms of nitrogen (nitrite and nitrate) . Nitrification and denitrification in the aerated unit process, though, was achieved by using three submerged cells with porous sides consisting of nonwoven materials for retention of biomass. When synthetic wastewater with nitrogen only in organic form was fed directly into a cell (as opposed to the surrounding aeration tank), T-N decreased from 42 to 30 mg/l and TOC levels, from 110 to 10 mg/l. Because virtually all activated sludge was attached to cell walls, there was essentially no excess sludge wastage over 100 days of operation. Denitrification efficiency using the novel apparatus was shown to be effected by TOC and alkalinity in the influent wastewater as well as dissolved oxygen levels and the method of influent feed. When wastewater was fed simultaneously into two cells, versus only one, the T-N removal efficiency improved from 34% to 45%. Effluent T-N was shown to decrease with a decrease in DO in the aeration tank and careful control of TOC and alkalinity levels in the wastewater feed allowed for nitrogen removal efficiencies as high as 75%.

The Application of ORP in Activated Sludge Wastewater Treatment Processes

This study researched, at full and pilot scale, the potential for using ORP to control the operation of activated sludge aeration tanks. Results indicate that ORP values can clearly show the COD removal occurring along the length of an aeration tank; ORP values increased dramatically as organic matter was removed. Based on the experimental data obtained on site during more than a half year of study, the ORP and COD in the aeration tank effluent followed a good linear relationship. Because ORP control is much easier and quicker than using COD measurements, the ΔORP of the influent and effluent and the ORP values of the effluent could be used to in situ indicate the pollutant removal efficiency and the effluent quality, respectively. ORP changes occurring under different COD and DO concentrations were also examined using a pilot column. The pilot column data confirmed the results from the aeration tanks. The ORP values of the mixed liquor increased during biodegradation of the organic matter, and then level...

Modelling of Oxygen Transfer Rate in Diffused-Air Aeration Tanks

The oxygen transfer rate, which is the most energy demanding unit process, is an essential factor in the operation of an activated sludge plant. Energy conservation effort has been directed at designing high efficiency and optimal air diffusers for use in activated sludge aeration tanks. This paper proposes a model for oxygen transfer rate in diffused air systems. The model parameters were found by means of nonlinear regression analysis, using plant data given in the literature. The proposed model may be useful for the preliminary design of diffused air aeration tanks.

Upgrading of Secondary Clarifiers by Inclined Plate Settlers

Secondary sedimentation is one of the most commonly used unit operations in wastewater treatment plants. It is customarily designed to achieve solids separation from biologically treated effluent through clarification of biological solids and thickening of sludge. As treatment plants receive increasingly high wastewater flow, conventional sedimentation tanks suffer from overloading problems which result in poor performance. Inclined plate settlers, a form of tube settlers, may have good potential in upgrading sedimentation tanks. This study was conducted to examine the possibility of applying inclined plate settlers in secondary sedimentation in order to upgrade conventional rectangular sedimentation tanks and improve their performance. Experiments were carried out at Al-Awir sewage treatment plant in Dubai using a pilot-scale inclined plate settler which received a mixed liquor stream from the high-rate activated sludge aeration tank. The results showed that inclined plate settlers perform slightly better than conventional type settlers during normal operation of plants, but during peak flows the inclined plate settlers showed much better performance than conventional settlers. The inclined plate settlers are less affected by overloading in comparison to conventional settlers. The solids removal efficiency increased as the hydraulic residence time was increased or as the surface loading rate was decreased. Application of these plates will not cause any interruption of daily operation of treatment plants and could be achieved at minimal cost when compared with other methods such as addition of chemicals, application of deep tanks, … etc. The study revealed that SS is a better parameter than TS, BOD, COD to evaluate the performance of sedimentation tanks. A statistical model was formulated to describe tank performance and design parameters were obtained based on the experimental results.

Upgrading of secondary clarifiers by inclined plate settlers

Secondary sedimentation is one of the most commonly used unit operations in wastewater treatment plants. It is customarily designed to achieve solids separation from biologically treated effluent through clarification of biological solids and thickening of sludge. As treatment plants receive increasingly high wastewater flow, conventional sedimentation tanks suffer from overloading problems which result in poor performance. Inclined plate settlers, a form of tube settlers, may have good potential in upgrading sedimentation tanks. This study was conducted to examine the possibility of applying inclined plate settlers in secondary sedimentation in order to upgrade conventional rectangular sedimentation tanks and improve their performance. Experiments were carried out at Al-Awir sewage treatment plant in Dubai using a pilot-scale inclined plate settler which received a mixed liquor stream from the high-rate activated sludge aeration tank. The results showed that inclined plate settlers perform slightly better than conventional type settlers during normal operation of plants, but during peak flows the inclined plate settlers showed much better performance than conventional settlers. The inclined plate settlers are less affected by overloading in comparison to conventional settlers. The solids removal efficiency increased as the hydraulic residence time was increased or as the surface loading rate was decreased. Application of these plates will not cause any interruption of daily operation of treatment plants and could be achieved at minimal cost when compared with other methods such as addition of chemicals, application of deep tanks, … etc. The study revealed that SS is a better parameter than TS, BOD, COD to evaluate the performance of sedimentation tanks. A statistical model was formulated to describe tank performance and design parameters were obtained based on the experimental results.

Activated sludge foaming: what causes hydrophobicity and can it be manipulated to control foaming?

Activated sludge aeration tanks frequently suffer from the formation of a stable foam on their surfaces, a problem which results in increased operating costs and reduces performance. Current control strategies are often unsuccessful, mainly because of a lack of understanding of the microbes involved, and often employ expensive and environmentally undesirable procedures, such as the addition of chemicals. Here we have attempted to better understand the mechanism(s) involved in foam formation. We have investigated the possible relationship between the mycolic acid content in a Rhodococcus rhodochrous strain isolated from foam, its cell surface hydrophobicity (CSH) and ability to form stable foam. Results show that mycolic acid composition is not the only contributor to CSH, nor is the CSH the only factor responsible for foam formation and stabilisation. Other possible explanations for mechanisms of foaming and ways to control it are addressed.

Activated sludge foaming: What causes hydrophobicity and can it be manipulated to control foaming?

Activated sludge aeration tanks frequently suffer from the formation of a stable foam on their surfaces, a problem which results in increased operating costs and reduces performance. Current control strategies are often unsuccessful, mainly because of a lack of understanding of the microbes involved, and often employ expensive and environmentally undesirable procedures, such as the addition of chemicals. Here we have attempted to better understand the mechanism(s) involved in foam formation. We have investigated the possible relationship between the mycolic acid content in a Rhodococcus rhodochrous strain isolated from foam, its cell surface hydrophobicity (CSH) and ability to form stable foam. Results show that mycolic acid composition is not the only contributor to CSH, nor is the CSH the only factor responsible for foam formation and stabilisation. Other possible explanations for mechanisms of foaming and ways to control it are addressed.

Application of air backflushing technique in membrane bioreactor

The optimum air backflushing and filtration cycle was investigated for a 0.1 μm hollow fiber membrane module immersed in an activated sludge aeration tank. It was found that 15 minutes filtration and 15 minutes air backflushing gave the best result both in terms of flux stability and net cumulative permeate volume. Although this cyclic operation could not completely remove the clogging, this process improved the flux by up to 371% compared to the continuous operation. During the long term runs, three different hydraulic retention times (HRT) of 12, 6 and 3 hours, corresponding to 0.16, 0.32 and 0.64 m3/m2.d of permeate flux respectively, were investigated. Stable operation was obtained at the HRT of 12 hours. Decrease in HRT led to rapid formation of a compact cake layer on the membrane surface thus increasing the transmembrane pressure. It was also noted that filtration pressure increases with increase in bioreactor MLSS concentration. With operation time, the MLVSS/MLSS value decreased without significant effect on the process performance, indicating that inorganic mass constantly accumulated in the bioreactor. All the experimental runs produced more than 90% removal of COD, and TKN. In terms of physical, chemical, biological and bacteriological parameters, the membrane bioreactor effluent was superior to the conventional activated sludge process.

Effects of Air Diffuser Arrangement on Hydrodynamics and Oxygen Transfer in Activated Sludge Aeration Tanks

Effects of air diffuser arrangement as well as tank geometry on the spiral liquid circulation rate, i.e., the liquid ascending velocity in the bubbling zone, and on the gas-liquid oxygen transfer performance were investigated based on a theoretical analysis of the data obtained in commercial-scale activated sludge aeration tanks. It is ascertained that the total floor coverage arrangement of air diffusers on the bottom of the tanks is effective in hindering the spiral liquid circulation and in enhancing the gas-liquid oxygen transfer.

Effect of biosorption on the damping of influent fluctuation in activated sludge aeration tanks

To describe the organic removal performance in an activated sludge process, the effect of biological adsorption (biosorption, hereinafter) of both soluble and particulate organic substances (SOS and POS, respectively, hereinafter) on the rate of organic removal must be taken into account. This study quantitatively investigated the biosorption of organic pollutants in the domestic wastewater by the activated sludge. The capability of biosorption and the rate of bio-oxidation of organic pollutants were formulated based on the experimental results as functions of both COD concentration and temperature. The biosorption capacity of activated sludge was proportional to COD concentration in the mixed liquor originated from the influent. The kinetic expressions were combined with the equation of longitudinal liquid mixing to set up the mathematical model to predict the effluent COD, and thus to clarify the effect of biosorption on the damping of influent fluctuations of both COD concentration and the inflow rate. The model was also successfully applied to assessing the effectiveness of MLSS control strategies in equalizing the effluent water quality.