Aeration Basin Research Articles

Application of biological indices and a mathematical model for the detection of metal coagulant overload in a laboratory scale activated sludge reactor with phosphate simultaneous precipitation

Phosphorous simultaneous precipitation by coagulants reduces the volatile solids percentage which can be deleterious to the biological process. In this work a mathematical model was developed and biological indices were applied to control Fe(III)-dosed activated sludge systems. A molar ratio Fe:P = 1.9–2.3:1 on the aeration basin of a laboratory-scale activated sludge reactor caused a progressive enrichment of the sludge with inorganic solids deteriorating the system performance. Crawling and attached ciliates were the most sensitive organism groups to these changes. The proposed mathematical model estimated: (i) the threshold concentration of fixed suspended solids, above which the reactor performance deteriorates, and (ii) the decay of the most sensitive organism groups with time. The Shannon–Wiener and sludge biotic indices predicted the decrease of the reactor performance by coagulant overload. The simultaneous application of the mathematical simulation and the biological indices guarantees a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).

Influence of temperature on process performance of activated sludge in coking wastewater treatment plant

Coking wastewater contains toxic compounds such as ammonia, phenolics, cyanides, thiocyanate, and thiosulfate. In normal situation, these compounds can be 100% decomposed by activated sludge in the wastewater treatment plant. However, a new factor, high water temperature, caused by the covering of the basins, has been found to reduce the removal rate of the pollutants, especially the thiocyanate. Several remediation measures were applied to improve the biological process performance. A series of batch and continuous-flow biodegradation tests have demonstrated that the relatively low temperature ranging from 20 to 37°C attained perfect removal efficiency (∼100%) of SCN− from the coke plant wastewater. When the temperature is increased to 38, 39°C, the SCN− removal rate decreased to 30 ∼ 50% after 48 hours of temperature shift. Moreover, when the temperature is increased to 40 to 45°C, SCN− biodegradation is significantly decayed one day after the temperature shock, and the SCN− removal efficiency dropped gradually to 0%, with microbial deterioration during day 1 to day 4. Meanwhile, the COD removal has also decreased from 85% down to 45% at 45°C. Both laboratory verifications confirmed that 40°C should be the critical water temperature for the SCN− degrading microbe to function well in the activated sludge process. In order to stabilize the pollutant removing ability of the procedure, the water temperature of aeration basin is set to operate under 37°C. Four modifications were practiced on site to decrease the temperature of activated sludge. Only the last alternative measure worked well with the opened hand hole, 50% of total cover area, to discharge the water vapor and gas emission from the head space of aeration basin. The water temperature has dropped from 41 to 36°C in the early summer of June with ambient temperature of 37°C, suggesting that partially uncovering the basin does help maintain the water temperature. Finally, we suggest some measures that can be applied to establish a standard process on site in order to ensure that the aeration basin temperature stays under 37°C and that our biotreatment system can maintain its function in the future.

Application of a combined biological and chemical system for the treatment of phosphorus-containing wastewater from the food industry

Coagulants can be dosed at different points during the wastewater treatment process to achieve phosphorous removal. Addition of metal coagulants on the aeration basin (simultaneous precipitation) involves lowest cost; however, inert solids reduce the volatile solids percentage which can be deleterious to the biological process. The general objective of the present study was to analyze the feasibility of P removal in a wastewater model system of the dairy industry using simultaneous precipitation in a laboratory-scale activated sludge reactor by addition of ferric chloride. Results showed that the addition of a high dose Fe:P (molar ratio)= 1.9-2.3:1 on the aeration basin of the reactor caused a progressive enrichment of the sludge with inorganic solids. This phenomenon, which involved a gradual deterioration of the environmental quality of the biological system, led finally to a strong decline of the reactor performance. The organisms associated to flocs (crawling ciliates and attached ciliates) were the more sensitive to these changes. A mathematical model allowed the estimation of the concentration of total fixed suspended solids as well as the decrease in the abundance of these organism groups as a function of time of Fe(III) application, considering the influent flow rate, the influent Fe concentration, and the waste flow rate of the sludge. The Shannon-Wiener diversity index and the sludge biotic index (SBI) can early predict the decreasing of the system performance due to metal salts overload. The simultaneous application of the proposed mathematical model and the biological indices guarantee a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).

Investigating the mechanism of sludge reduction in activated sludge with an anaerobic side-stream reactor

To investigate the mechanism of sludge reduction in activated sludge (AS) with an anaerobic side-stream reactor (ASSR), four AS systems with different digestion schemes were operated in the laboratory. The four systems are: a) AS+ASSR; b) AS+aerobic digester; c) AS+anaerobic digester; and d) AS with no solids wastage. The average sludge yield of AS+ASSR from two phases was 0.14 mgVSS/mgCOD, which is 22-54% less than that from the three other systems. The accounting of biomass in AS+ASSR system revealed that 50% of sludge is degraded in ASSR while the other half is degraded in the aeration basin. Furthermore, both whole sludge and centrate from ASSR led to a significant oxygen uptake in AS, indicating the importance of aerobic biodegradation in AS+ASSR system. The extracellular polymeric substances (EPS) data showed that base-extractable EPS was much smaller for AS with ASSR than with no wastage. In contrast, cation exchange resin-EPS was similar for both systems. These results indicate that degradation of base-extractable EPS accounts for the lower sludge yield in AS+ASSR, and based on the literature this organic pool is believed to be aluminium and/or iron-bound EPS. The microbial profile data suggests that recirculation in AS+ASSR selects some unique microorganisms. Further research is warranted to study their role in sludge reduction.

Development of an on-site Fe<SUP align=right>0</SUP> system for treatment of copper- and zinc-contaminated roof runoff

The objective of the present work was to develop an on-site Fe 0 system for treatment of metal-contaminated roof runoff. Breakthrough experiments were performed under laboratory flow-through conditions using runoffs that have varying water quality parameters. Phase analyses and the chemical-equilibrium model were employed for describing the removal mechanisms. The study demonstrated that the breakthroughs of copper and zinc were either accelerated or hindered under different water characteristics. In most cases, the Fe 0 treatment columns can hardly cope with efficient removal of contaminants and maintenance of adequate hydraulic conductivity. To enhance performance of the system, various carbonatic materials were tested and combined into the iron system. Following the assessment, the most promising configuration consisted of a column containing spiral shaped Fe 0 , followed by an aeration basin and a fixed bed of pumice/dolomite filter was installed on-site for treatment of copper and zinc roof runoff.

The Effect of Aeration Basin Reactor Configuration on Anaerobic Digestion and Sludge Properties

The Effect of Aeration Basin Reactor Configuration on Anaerobic Digestion and Sludge Properties

Performance of mechanical aerator in wastewater treatment with special reference to oxidation ditch: a critical review

Mechanical aerators used in wastewater treatment are the largest energy consumers in biological reactors. Well-known researchers have been working on the oxygen transfer by mechanical aerators in oxidation ditch process and they have successfully enhanced the efficiency of aeration system with considering the factors affecting oxygen transfer such as speed of rotors and geometry of aeration basin. In this paper, attempts are made to review the performance of aeration system in wastewater treatment with special reference to oxidation ditch, reported by various workers globally and to conclude for the best and effective performance.

Municipal Wastewater Treatment Automated Oxygenation and Mixing of Aeration Basins – Saving up to 60% on Energy

Municipal Wastewater Treatment Automated Oxygenation and Mixing of Aeration Basins – Saving up to 60% on Energy

Research Article: The Effect of Ferric Chloride Addition for Phosphorus Removal on Ultraviolet Radiation Disinfection of Wastewater

In light of the potential need for disinfection and nutrient removal at the Metropolitan Water Reclamation District of Greater Chicago's water reclamation plants (WRPs), the inhibitory effects of ferric chloride (FeCl3) on ultraviolet (UV) radiation disinfection was examined. Results of a 2007 preliminary study indicated that a 2-log reduction in fecal coliform (FC) concentrations for each WRP secondary effluent was achieved with a UV dose of 10 mJ/cm2 except for the John E. Egan (Egan) WRP, where FeCl3 addition in the aeration basin for phosphorus removal was being employed. A subsequent study examined the effect of Egan unfiltered (secondary) and filtered (final) effluent on UV disinfection in 2008 during FeCl3 application and 2009 upon cessation of FeCl3 application: FeCl3 addition and filtration had little effect on UV transmittance (UVT). However, with FeCl3 addition, secondary and final effluent had higher total iron and lower total phosphorus relative to the respective secondary and final effluent without FeCl3 addition. Final effluent with and without FeCl3 addition showed lower total suspended solids concentrations relative to secondary effluent. Collimated beam test results indicated that a higher UV dose was needed to achieve the desired log reductions with FeCl3 addition and secondary effluent. Therefore, filtration of the effluent may be required if FeCl3 addition for nutrient removal is used at WRPs that employ UV disinfection.

Synthetic musk emissions from wastewater aeration basins

Wastewater aeration basins at publicly owned treatment works (POTWs) can be emission sources for gaseous or aerosolized sewage material. In the present study, particle and gas phase emissions of synthetic musks from covered and uncovered aeration basins were measured. Galaxolide (HHCB), tonalide (AHTN), and celestolide (ADBI) were the most abundant, ranging from 6704 to 344,306 ng m−3, 45–3816 ng m−3, and 2–148 ng m−3 in the gas phase with particle phase concentrations 3 orders of magnitude lower. The musk species were not significantly removed from the exhaust air by an odor control system, yielding substantial daily emission fluxes (∼200 g d−1 for HHCB) into the atmosphere. However, simple dispersion modeling showed that the treatment plants are unlikely to be a major contributor to ambient air concentrations of these species. Emission of synthetic musk species during wastewater treatment is a substantial fate process; more than 14% of the influent HHCB is emitted to the atmosphere in a POTW as opposed to the <1% predicted by an octanol–water partition coefficient and fugacity-based US EPA fate model. The substantial atmospheric emission of these compounds is most likely due to active stripping that occurs in the aeration basins by bubbling air through the sludge.

Economic evaluation of alternative wastewater treatment plant options for pulp and paper industry

Excessive water consumption in pulp and paper industry results in high amount of wastewater. Pollutant characteristics of the wastewater vary depending on the processes used in production and the quality of paper produced. However, in general, high organic material and suspended solid contents are considered as major pollutants of pulp and paper industry effluents. The major pollutant characteristics of pulp and paper industry effluents in Turkey were surveyed and means of major pollutant concentrations, which were grouped in three different pollution grades (low, moderate and high strength effluents), and flow rates within 3000 to 10,000 m 3/day range with 1000 m 3/day steps were used as design parameters. Ninety-six treatment plants were designed using twelve flow schemes which were combinations of physical treatment, chemical treatment, aerobic and anaerobic biological processes. Detailed comparative cost analysis which includes investment, operation, maintenance and rehabilitation costs was prepared to determine optimum treatment processes for each pollution grade. The most economic and technically optimal treatment processes were found as extended aeration activated sludge process for low strength effluents, extended aeration activated sludge process or UASB followed by an aeration basin for medium strength effluents, and UASB followed by an aeration basin or UASB followed by the conventional activated sludge process for high strength effluents.

A ferricyanide-mediated activated sludge bioassay for fast determination of the biochemical oxygen demand of wastewaters

Activated sludge was successfully incorporated as the biocatalyst in the fast, ferricyanide-mediated biochemical oxygen demand (FM-BOD) bioassay. Sludge preparation procedures were optimized for three potential biocatalysts; aeration basin mixed liquor, aerobic digester sludge and return activated sludge. Following a 24h starving period, the return activated sludge and mixed liquor sludges reported the highest oxidative degradation of a standard glucose/glutamic acid (GGA) mixture and the return activated sludge also recorded the lowest endogenous FM-respiration rate. Dynamic working ranges up to 170 mg BOD(5)L(-1) for OECD standard solutions and 300mg BOD(5)L(-1) for GGA were obtained. This is a considerable improvement upon the BOD(5) standard assay and most other rapid BOD techniques. Time-series ferricyanide-mediated oxidation of the OECD(170) standard approached that of the GGA(198) standard after 3-6h. This is noteworthy given the OECD standard is formulated as a synthetic sewage analogue. A highly significant correlation with the BOD(5) standard method (n=35, p<0.001, R=0.952) was observed for a wide diversity of real wastewater samples. The mean degradation efficiency was indistinguishable from that observed for the BOD(5) assay. These results demonstrate that the activated sludge FM-BOD assay may be used for simple, same-day BOD analysis of wastewaters.

Monitoring of bacterial communities during low temperature thermal treatment of activated sludge combining DNA phylochip and respirometry techniques

Sludge reduction is one of the major challenges in biological wastewater treatment. One approach is to increase the sludge degradation yield together with the biodegradation kinetics. Among the various sludge pretreatment strategies proposed, thermal pretreatment at around 65 °C was described as promising. The enhancement in the biodegradation activity due to the selection of thermophilic hydrolytic bacteria was proposed, but further experiments are needed to demonstrate the specific role of these bacteria. In this study, concentrated activated sludge grown at 20 °C was subjected to thermal treatment at 65 °C for different periods. The originality of the work relied on a polyphasic approach based on the correlation between kinetics (chemical oxygen demand, COD; mixed liquor suspended solids, MLSS), bacterial activity (respirometry) and bacterial community structure (phylochip monitoring) in order to characterize the mechanisms involved in the thermal reduction of sludge. The bacterial activity in the aeration basin decreased to a very low level when recycling sludge was treated at 65 °C from 13 to 60 h, but then, started to increase after 60 h. In parallel to these fluctuations in activity, a drastic shift occurred in the bacterial community structure with the selection of thermophilic bacteria (mainly related to genera Paenibacillus and Bacillus), which are known for their specific hydrolases.

Wastewater: Odour control in an open aeration basin

A District created to promote public health decided to scrub off-gas odours from its Vallejo wastewater treatment plant. The two open aeration basins were targeted as part of the odour control upgrade. A retractable geomembrane cover was selected for the basins, which combines a gas-tight barrier with low life cost benefits.

The Role of Dispersed Nocardioform Filaments in Activated Sludge Foaming

Activated sludge foaming caused by filamentous microorganisms is a major wastewater treatment plant operating problem. This paper presents the results of an investigation of the role of dispersed nocardioforms in activated sludge foaming. Dispersed nocardioforms had a greater propensity for foaming than floc-bound nocardioforms. The mode of effluent withdrawal from an aeration basin plays a major role in determining the relative proportion of dispersed and floc-bound nocardioforms in the activated sludge. Reactors with "trapping" features (sub-surface mixed liquor withdrawal) had significantly higher dispersed nocardioform populations than reactors with "non-trapping" features (surface mixed liquor withdrawal). High dispersed nocardioform filament concentrations were correlated with a high propensity for foaming. Cationic polymer and polyaluminum chloride reduced foaming by flocculating dispersed nocardioforms, thereby converting them to floc-bound nocardioforms. Low non-ionic surfactant concentrations changed the relative proportions of dispersed and floc-bound nocardioforms by deflocculating floc-bound filaments and converting them to the dispersed growth form. This could act as a trigger for initiating the rapid-onset nocardioform foaming events observed at activated sludge plants.

The Effect of Iron Concentration and Aeration Basin Configuration on Susceptibility to Sonication Pretreatment and Subsequent Anaerobic Digestion

The Effect of Iron Concentration and Aeration Basin Configuration on Susceptibility to Sonication Pretreatment and Subsequent Anaerobic Digestion Author(s)Philip TeagueMeng WangChul ParkSourceProceedings of the Water Environment FederationSubjectSession 58: Anaerobic DigestionDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:13L.3985;1-DOI10.2175/193864710798181638Volume / Issue2010 / 13Content sourceWEFTECFirst / last page(s)3985 - 3986Copyright2010Word count19

Effect of Using Effective Microorganisms EM-1 on the Performance of Extended Aeration Activated Sludge in Treating Domestic Wastewater

This research concerning with the effect of using the effective microorganisms on the efficiency of extended Aeration Activated Sludge Units which consist from many strain of Bacteria, Fungi and Actinomycetes in addition to board spectrum of nutrient and elements which important to growth, The use of this product is practically applied by using two bench scale laboratory units where they are operated to treat the wastewater after completing and preparing the activated sludge units to work under the same conditions of temperature and detention time (DT).&#x0D; One bench scale is fed with wastewater and the other is operated by using a mixture of EM-1 along with the wastewater. It is noticed that the use of EM-1 with wastewater has reduced the smell resulting from disintegration in the aeration basin. Further, the color of sludge in the unit where EM-1 is added is light brown which means more activity and vitality. Besides, the concentration of mixed liquor volatile suspended solids (MLVSS) is increased by using EM-1 by 30% due to the increase of nutrients and a reduction in the sludge volume index (SVI) which is an important factor in the performance of the secondary settling basins which means a reduction in bulking of sludge, which is considered one of the most notable operating problem in activated sludge units. As a result bulking of sludge reduced by25% when EM-1 is used. Thus, EM-1 has participated in solving three important operating problems suffered by operators of these treatment units easily and without using complicated technologies or appliances. Further, EM-1 improves the removal efficiency of the units about 6-8% due to the reduction in chemical oxygen demand in the treated wastewater leaving the unit by 32%.

Effect of Using Effective Microorganisms EM-1 on the Performance of Extended Aeration Activated Sludge in Treating Domestic Wastewater

This research concerning with the effect of using the effective microorganisms on the efficiency of extended Aeration Activated Sludge Units which consist from many strain of Bacteria, Fungi and Actinomycetes in addition to board spectrum of nutrient and elements which important to growth, The use of this product is practically applied by using two bench scale laboratory units where they are operated to treat the wastewater after completing and preparing the activated sludge units to work under the same conditions of temperature and detention time (DT). 54 One bench scale is fed with wastewater and the other is operated by using a mixture of EM-1 along with the wastewater. It is noticed that the use of EM-1 with wastewater has reduced the smell resulting from disintegration in the aeration basin. Further, the color of sludge in the unit where EM-1 is added is light brown which means more activity and vitality. Besides, the concentration of mixed liquor volatile suspended solids (MLVSS) is increased by using EM-1 by 30% due to the increase of nutrients and a reduction in the sludge volume index (SVI) which is an important factor in the performance of the secondary settling basins which means a reduction in bulking of sludge, which is considered one of the most notable operating problem in activated sludge units. As a result bulking of sludge reduced by25% when EM-1 is used. Thus, EM-1 has participated in solving three important operating problems suffered by operators of these treatment units easily and without using complicated technologies or appliances. Further, EM-1 improves the removal efficiency of the units about 6-8% due to the reduction in chemical oxygen demand in the treated wastewater leaving the unit by 32%.

Potential Impact on Activated Sludge Treatment from the Implementation of Cellulosic Ethanol Production at a Pulp and Paper Mill

The potential impacts of additional flow and organic loads resulting from the production of cellulosic ethanol on an existing integrated newsprint mill were simulated in this paper. It was found that depending on the ethanol production rate and the existing spare capacity for additional biochemical oxygen demand (BOD), treatment plant modifications may be required. In terms of operating costs, it was found that nutrients use could increase by 50% to 150%, while aeration flow could increase by 5% to 140% depending on the desired level of dissolved oxygen in the aeration basin. Significant increases in polymer use for mixed sludge dewatering could result due to additional biosolids production. Additional capital costs for air blowers could also be necessary unless the mill has existing spare capacity. It was also found that ethanol recovery efficiency and production rate had little impact on BOD removal up to a certain ethanol production level, and that the impact on operating costs decreased with increasing recovery.

Including the effects of filamentous bulking sludge during the simulation of wastewater treatment plants using a risk assessment model

The main objective of this paper is to demonstrate how including the occurrence of filamentous bulking sludge in a secondary clarifier model will affect the predicted process performance during the simulation of WWTPs. The IWA Benchmark Simulation Model No. 2 (BSM2) is hereby used as a simulation case study. Practically, the proposed approach includes a risk assessment model based on a knowledge-based decision tree to detect favourable conditions for the development of filamentous bulking sludge. Once such conditions are detected, the settling characteristics of the secondary clarifier model are automatically changed during the simulation by modifying the settling model parameters to mimic the effect of growth of filamentous bacteria. The simulation results demonstrate that including effects of filamentous bulking in the secondary clarifier model results in a more realistic plant performance. Particularly, during the periods when the conditions for the development of filamentous bulking sludge are favourable – leading to poor activated sludge compaction, low return and waste TSS concentrations and difficulties in maintaining the biomass in the aeration basins – a subsequent reduction in overall pollution removal efficiency is observed. Also, a scenario analysis is conducted to examine i) the influence of sludge retention time (SRT), the external recirculation flow rate ( Q r) and the air flow rate in the bioreactor (modelled as k La) as factors promoting bulking sludge, and ii) the effect on the model predictions when the settling properties are changed due to a possible proliferation of filamentous microorganisms. Finally, the potentially adverse effects of certain operational procedures are highlighted, since such effects are normally not considered by state-of-the-art models that do not include microbiology-related solids separation problems.