Activated sludge recycle rate. 1 General Approach 41 3.
Activated sludge recycle rate MCRT is an industry standard formula. Ancient Origins (2018). The aeration conditions are achieved by the use of diffused or mechanical aeration. Lockett, added the concept of recycling sludge and patented the process. 5 - 8. 1 mgd x 8. There are a number of different ways to control the waste sludge rates. Collected activated sludge was concentrated to achieve a hydration of 93-94%, then immobilized and used in technological tests. Waste Activated Sludge (WAS) Pumping Rate. The algorithms included: constant waste flow rate; constant proportion of the mass; proportional-integral-derivative (PID) control of the dynamic sludge age (DSA); PID control of mass inventory; and feedforward ratio control based on Sludge Wasting System (Waste Activated Sludge (WAS)): This can be accomplished by controlling the rate of activated sludge returned to the aeration basin for additional treatment. In high rate, or low MCRT systems, the RAS flow is traditionally 25-50% of the Aeration can be "conventional rate" based on mechanical aeration, or "extended rate" based on diffused aeration. 2) Another is sludge wasting through waste sludge. Respirogram is an efficient and powerful tool for estimating the status of activated sludge systems as well as the optimization of the whole system performance (Li et al. T. Assume that the temperature is 20 °C and the The Activated Sludge Process - Part II Instructor Guide – Answer Key . Typical primary sludge concentration will tend in the low end of the range listed with co-thickening of waste activated sludge. , 2018a, 2018b). Other plants keep track of Recycling the settled sludge at a rate proportional to influent flow therefore is an effective control. Activated sludge, 5) A sludge recycling system for returning to the beginning of the process. where, Y: Maximum yield coefficient (microbial mass synthesized/mass of substrate utilized) k. [9], compounds with a K d < 500 L/kg are eliminated by less than 10% through sorption onto activated sludge at an average specific sludge production of 200 g m − 3. The activated sludge was collected from a semi-technical scale Sequencing Batch Reactor treating municipal waste water. 2 Wastewater Plants Used for Site Testing 42 3. A conventional excess sludge treatment chain consists This paper reviews available tools and techniques required to optimize activated sludge secondary clarifier performance and capacity. 25*Average Daily Influent Flow Rate. Sent to solids handling (digesters). Chamber pot being emptied out a window. In the reactor, an activated sludge concentration of X (kg/m 3) is maintained in suspension. E. 1 Field Reactor Feed Sources, Reactor Preparation and Flow Rates 46 The Activated Sludge Process . 1 General Approach 41 3. We'll dive into Waste Activated Sludge (WAS): The portion of settled secondary sludge that is removed from the system. 25 m 3 /sec. In addition, as solids are recycled around a treatment plant, the particle size continues to reduce, increasing surface area, slowing the rate at which the small particles will settle. W. is reported for the first time The operation of an activated sludge plant is typically presented by a flow diagram as shown in Fig. Paul, MN. 15% – 100% *F/M = food to microorganism ratio . Waste Activated Sludge (WAS) is the excess quantity of microbes, in mg/L, that must be removed from the process to keep the biological system in balance. 6) The MCRT of an activated sludge process can be calculated by dividing the pounds of suspended solids or MLSS in the activated sludge process by the pounds of suspended solids leaving the activated sludge process (Equation I. In the Activated Sludge Process for waste water treatment, microorganisms are used to speed Waste Activated Sludge Mixed Liquor Recirculation Secondary Clarifier Anoxic Aerobic Return Activated Sludge Primary Settling 3Q – 4Q Q Q BOD loading rate of 240,000 mg/1000 liters per day (15 lb. TKN ox = total mass of oxidizable TKN (nitrates) produced in the aerobic reactor, g/day. You can control the WAS rate by various means. 066 g Cl 2 /g MLSS and a retention time of 20hr followed by the recycling of sludge to the Overflow Rate, m3/m2@d OR = Q/A Avg Peak Peak 41 60-120* 49 Weir Loading, m3/m@d WL = Q/L < 1 mgd > 1 mgd < 1 mgd > 1 mgd 250 375 250 375 * for tanks not receiving waste activated sludge, use 49 m3/m2@d for primary clarifiers receiving WAS Activated Sludge Operational Considerations An operator of an activated sludge plant is concerned with Recycling the settled sludge at a rate proportional to influent flow therefore is an effective control. BOD 5 concentration of settled wastewater is 250 mg/L. The liquid phase volumetric mass transfer coefficient (k L a) affects the investment cost (aerator capacity) along with the operational cost Waste Activated Sludge (WAS) Receiving Water Primary Sludge Plant Influent Internal Effluent Recycle 18 Aeration: Adding O 2 & Mixing 19 Loading Rate Sludge age (days) Volumetric Loading (lb BOD/1000 ft3) F/M ( lb/. , 2019c, 2020b). The MLSS, WAS concentration, and RAS recycle rate measurements are routinely used to adjust the WAS withdrawal rate and to maintain consistent steady-state activated sludge system performance. The tank must be large enough to allow sufficient contact time (retention time) between • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time • Be able to calculate the required air/oxygen blower requirements and alkalinity • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time • Be able to use an Excel spreadsheet for making activated sludge design and • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time • Be able to use an Excel spreadsheet for making activated sludge Excess organic load can be remedied by reducing the waste-activated sludge rate by an amount less than 10 percent per day, to return to proper loading parameters and increase the returned activated sludge rates. Aerobic SRT for Nitrification 0 2 4 6 8 10 12 14 16 18 20 22 4 6 8 10 12 14161820 22 24 These include: temperature, return sludge rates, amount of oxygen available, amount of organic matter available, pH, sludge waste rates, and aeration time and toxicity, if any, present in wastewater. 1 General 7. 3. 11IAWQ General Model for Biological Nutrient Removal in Activated Sludge Systems 35 2. W is the waste activated sludge flow rate in units of MGD . 1. About a 30 percent level of settled solids in the clarifier should be established and maintained. Rules of Thumb: Maintain pH in the range 6. between 0 and 40 °C (32 and 104 °F), the rate of biological reactions increase with temperature. Of the numerous factors affecting the capacity and performance of the activated sludge process, the operator can control the return activated sludge (RAS) flow rate to a greater degree than any This is usually the case for waste activated sludge (WAS) which demands a relatively low solids loading rate (SLR) of 20−30 kg dry solids per m 2 tank area per day (kgDS/(m 2 d)) if treated by gravity thickening, compared to almost five times this rate for DAF. • The paper they published in 1914, first used the term “Activated Sludge”. Most surface aerated matter occur. Q. The volume (V) of the aeration tank is known, the MLSS and RAS (Xr) concentrations are measured biokinetic characteristics, and it is considered one of the most important information sources in activated sludge process modelling. An extended-aeration system includes capabilities for aeration & mixing, settling, return of activated sludge and solids removal, this last in the form of a biomass known as waste-activated sludge. In this case the bioreactor mass balance method generates a return sludge flow rate 5. 0 for optimum – Recycle Rates – Sludge Settleability Process Control Methods • Controlling MCRT: – Data Collection – MCRT Calculation Methods – Seasonal Adjustment It has been figured out that sludge from this plant makes up 3% of the influent flow rate. 1. 6/24/2020 15 Min. 5 Organism Growth Rate: Slow Download scientific diagram | Effect of recycle ratio on removal efficiency from publication: Heterogeneous Modeling, Identification and Simulation of Activated Sludge Processes | Problem Several algorithms for the control of the waste flow rate of the activated sludge process were compared by computer simulation. Solids loading rate criteria assume sludge recycle is 100% of the average design flow and the design mixed liquor suspended solids (MLSS) concentration. The solids concentration of the underflow sludge (blowdown) f rom the secondary clarifier affects: · The operational control of the activated sludge process in terms of sludge recycle rate, which in turn Waste Activated Sludge (WAS) Pumping Rate. The wastewater with a substrate concentration of S 0 (kg/m 3) and an activated sludge concentration of X 0 is fed to a reactor at a flow rate of Q 0 (m 3 /day). Activated-sludge solids are separated in a secondary settling tank 85 -95 Complete-mix Process is an application of the flow regime of a continuous-flow stirred tank reactor. 6). May plants operate efficiently by keeping their mixed liquor suspended solids (MLSS Excess sludge is called "surplus activated sludge" or "waste activated sludge" and is removed from the treatment process to keep "food to biomass" (F/M) ratio in balance (where biomass refers to the activated sludge). #BOD = pounds of Biochemical Oxygen Demand (BOD) . 9/d with a concomitant variation in effluent soluble bod Example #5: For the 3. Parameter # 1. Waste activated sludge (WAS) is the amount of microbes that must be removed from the process to keep the biological system in balance. 0 - S) - k. 55101 clarifier underflow rate, the waste sludge flow rate and aeration tank volume in service. The method is most simple in that no sludge concentration determination is required. In one simula tion described, the authors noted that diurnal variations in influent bod resulted in a varia tion in instantaneous loading rate from ap proximately 0. This course includes content developed by the Pennsylvania Department of Environmental Protection Solids Recycle Rate**. The activated sludge process uses microorganisms and oxygen to biologically treat wastewater. 1 MGD • Waste activated sludge suspended solids (WASSS) = 8,000 mg/L . SECONDARY CLARIFIER •For example, for a 1 MGD plant, a 40% RAS rate would be 0. Q w X r = YQ (S O CONVENTIONAL ACTIVATED SLUDGE • Suspended growth type • Unique –the name activated sludge was originated in referring to the return sludge (biomass), since these masses of microorganisms were observed to be very “active”in removing soluble organic matter from solution. As sludge experiences anoxic and then oxic conditions in Activated Sludge 7. 066 g Cl 2 /g MLSS and a retention time of 20hr followed by the recycling of sludge to the Overflow Rate, m3/m2@d OR = Q/A Avg Peak Peak 41 60-120* 49 Weir Loading, m3/m@d WL = Q/L < 1 mgd > 1 mgd < 1 mgd > 1 mgd 250 375 250 375 * for tanks not receiving waste activated sludge, use 49 m3/m2@d for primary clarifiers receiving WAS Activated Sludge Operational Considerations An operator of an activated sludge plant is concerned with The internal recirculation rate can vary from 100 to 350% of the raw water flow rate depending on the target denitrification performance. An activated sludge process re Because activated sludge is characterized by high water of which the effect on the removal of UV 254 and dissolved organic carbon is similar to the activated carbon. The volume (V) of the aeration tank is known, the MLSS and return activated sludge (RAS) (Xr mixed reactor. 2 General features of a plug flow activated sludge system. 5-3. Typically, the return rate is set as a constant percentage of total plant flow. 3 Field Test Reactor Description 44 3. 5 0. Relatively high rates of protozoan removal during activated sludge treatment may be due to The waste activated sludge flow is ignored to simplify things a bit: for now we assume that there is no biomass growth, just for the sake of this design methodology. Currently, high-rate activated sludge (HRAS) process is gaining importance as a good option to reduce the energy demand of wastewater treatment and to Metric Mathematics for Operators 7 The Metric System The metric system is used in all of the industrialized countries of the world except the United States. 25*Q or Return Activated Sludge = 1. Since the discovery of the activated sludge process in the beginning of the 20th century it has been recognised that the rate at which activated sludge consumes oxygen, the respiration rate, is an important per day and the pounds of activated sludge or secondary effluent solids discharged per day (Equation I. Diffusers are provided at the tank bottom, and mechanical aerators are provided at the surface of Figure 19. 5 1-2 (up to 8) 1-2. 1 Conventional Activated Sludge Process . The paper also discusses the benefits and Recycle Flow affects hydraulics influent/underflow solids flux hydraulic loading and a low return activated sludge flow rate with the basin scraper . 34 + 8,000 mg/l x 0. A proper balance must be maintained between the amount of organic matter, microorganisms (activated sludge), and dissolved oxygen to obtain desired level of In general, sorption to activated sewage sludge is of minor importance for many pharmaceuticals, as shown by their relative low sorption constants (K d). AS treatment operating at high sludge retention time (SRT) enhances cryptic growth, low food to microorganism ratios (F/M), high recycle activated sludge (RAS) rate and low waste activated sludge (WAS) that is the controlling parameter for regulating the SRT (Grady et Operation of Activated Sludge Nitrification Maximum Nitrifier Specific Growth Rate (mg/mg-d) Temperature Impacts on Nitrification Activated Sludge Nitrification Waste Sludge 27 28. The recycle stream is known as return activated sludge (RAS), while the fraction of sludge that is This document provides information about the activated sludge process for wastewater treatment. **Note: Sludge age The loading rate of aeration tank is based on the following four parameters: 1. • MLVSS represents biomass present in activated sludge and is 70-80% of MLSS. 7). Waste activated sludge (WAS) calculations in your plant may be based on data similar to the following: /WAS concentration is 5,950 mg/L, find the WAS pumping rate in gallons per minute (GPM) if the pump operates 17 minutes out of each hour to maintain a sludge age of 15 days. design, we should know the recycle flow rate. (I. R) was set equal to influent flow rate Activated sludge bulking caused by filamentous bacteria Eikelboom type 021N and Thiothrix spp. Denitrification effectiveness depends on the recycling rate; the anoxic contact time and, WAS is the waste activated sludge concentration, which is typically the same value as the RAS concentration . These case studies show how sludge production rates vary based on population size, treatment processes, and influent characteristics. The recycle ratio, the waste sludge ratio and the oxygen recycle and the waste sludge flow rate impact both the investment and the operational costs. Excess sludge produced each day (waste activated sludge) must be processed in a further treatment chain together with the sludge from the primary treatment facilities. Other plants keep track of Improves BNR Activated Sludge Performance Stephen Greenwood, P. MCRT and F/M are inversely related. Many plants operate efficiently by keepting their MLSS concentration within a certain range. [Note: Rectangles refer to the is a critical part of any activated sludge system control strategy. 1 to 0. The objective of SRT control is to manage the mass balance shown in Figure 2 through adjustment of the waste activated sludge (WAS) flow rate (Qw). The big unknown to solve this equation is the sludge concentration of the recycle flow, Xr. day) Medium 5 - 15 20 - 40 0. It eliminates the need for costly TSS sampling at various points in the process, along with its The objective of SRT control is to manage the mass balance shown in Figure 2 through adjustment of the waste activated sludge (WAS) flow rate (Qw). The calculation is straightforward: the inventory of biomass is divided into the rate of sludge wasting. SBAC’s removal rate of UV 254 and dissolved organic carbon could Recycling of sludge activity should take into account the cost of recycling and repreparation of sludge the activated sludge mixed liquor. 0 can significantly inhibit nitrification. Math Solutions to solve WAS pumping rate in GPM include Sludge Wasting System (Waste Activated Sludge (WAS)): While the microbes are in the aeration tank they reproduce very quickly, becoming overpopulated (increasing MLVSS Complete nitrification of ammonia is normal in the low-rate activated sludge process with a BOD removal rate of 75-985%. Busch (11) stated that before the reaction rate could be obtained . Volumetric BOD Loading or Volumetric Organic Loading 3. • Sludge wasting rate (WAS flow) = 0. 3 will produce an actual substrate concentration (S) of about 192 mg/L; however, an R of 1. Hydraulic Retention Time (HRT): Hydraulic retention The activated sludge operational parameters calculated by the Excel formulas in the spreadsheet are: recycle activated sludge flow rate, Qr; waste activated sludge flow rate, Qw, and aeration tank food to microorganism ratio, F:M. Part III . The reaction rate or the substrate removal rate, was . The effluent soluble BOD 5 is 6. • Wastewater is fed continuously into an aerated tank, as inert particles and organic matter in the activated sludge process. Loading Rate: The organic matter loading rate applied The Activated Sludge (AS) process is currently the most widely used biological wastewater treatment process in the world. 0 MGD RAS Flow = 0. Hydraulic Retention Time (HRT) 2. Sludge wasting, is the single most important parameter affecting the performance of activated sludge systems. The consequences of incorrect flow should be avoided. Waste activated sludge mass rate is approximated by the aeration tank volume (V) and the target SRT. Under steady state operation the mass of waste activated sludge is given by. 34 Estimation of RAS (Activated Sludge Return): A part of the remaining sludge is sent back to the treatment unit, called return activated sludge. Waste Activated Sludge (WAS) Rate. XV . S = YQ(S. 5 5000-10000 Fig. The chlorination of excess sludge at a chlorine dose of 0. The parameters in the diagram and a few others that will be used for the upcoming activated sludge calculations are summarized in the list activated sludge process must also cope with massive fluctuations in flow rates, and "PLUG-FLOW" Activated Sludge Plants Effluent Waste Sludge Effluent Waste Sludge High Rate plants 1. Food to Micro-Organism Ratio (F/M Ratio) 4. 1 Applicability 7. pH below 6. Revised October 2014. (Some it is supt only, some it is senses, some extremely mathematical). 5 mg/l x 5 MGD x 8. To control return-sludge flow, monitor and evaluate performance resulting from return-sludge flow-rate changes. Increase in the mass of MLVSS is 1,646 kg/day. Davyhulme Sewage Works, Manchester, UK, first full-scale activated sludge plant. 3) And the third is sludge recirculation, either through return activated sludge and/or internal mixed liquor recycle for nutrient removal. )(8. 34 3. continuous activated sludge reactor at a loading condition estimated waste activated sludge rate, (m. 2 - 0. The volumetric waste activated sludge rate (W) is governed by the SRT and the ratio of the MLSS concentration and the For activated sludge, it is necessary to recycle most of the settled solids and return settled biomass back to the biological reactors to maintain a desired mixed liquor suspended solids (MLSS) concentration. High-rate aeration activated sludge is characterized by high F/M ratio, low sludge age, Sludge recycling rate (Q. . from a batch test the mixed culture should be acclimated in a . Reactor Configurations As well as classifying the Recycling is necessary for activated sludge process. Each organization determines it differently. The MCRT ACTIVATED SLUDGE (BOD) load on aeration tank, (lbs BOD/1,000 ft3/day) = BOD,lbs/day (VolumeofAerationTank ,ft3)/1000 (SVI) Sludge Volume (Sludge, Gal. Microorganisms consume organic matter in the wastewater to grow, reproducing and removing pollutants through metabolic processes. 2. MCRT = 3,000 mg/l x 4 MG x 8. Mean Cell It aerates activated sludge to dissolve oxygen and makes organic matter (BOD) available to bacteria. 3 /d). d. Organic matter and food adhere toactivated sludge. TABLE 5-1 FINAL CLARIFIER DESIGN PARAMETERS **For rectangular-shaped clarifiers following activated sludge treatment, the recommended SWD shall be no less than 12 feet at the shallow end Changes in return-sludge flow-rate affect return-sludge and mixed-liquor concentration in the aeration tank. Polymer dosing at 2−5 g polymer per kg DS (g/kgDS) increases the SLR value further through • Separate quiescent settling basins with recycle of settled activated sludge typically at 25% of influent flow rate • Microbial growth rate control of activated sludge process • Continuous culture of microorganisms and Monod kinetics • Rate KEYWORDS: Activated sludge, return sludge flow rate, feast/famine, microbiology, bioreactor, sludge settleability, specific oxygen uptake rate, respiration rate, state-point a return sludge recycle ratio (R) of 0. 5 mechanisms The Activated Sludge Process • In1914, British researchers Edward Ardern and W. 5 MGD activated sludge plant in Example #1, with an aeration tank volume of 170,275 ft3, calculate a) the required recycle activated sludge flow rate (using the simplified equation), b) the waste activated sludge flow rate, and c) the aeration tank F:M ratio, based on the following: primary effluent BOD = 175 mg/L, primary effluent TSS = 200 mg/L, waste/recycle 2. The calculation is straightforward: the inventory of biomass divided into the rate of sludge wasting. The Average Daily Influent Flow Rate is the total The units for HRT will be whatever the time units are for the flow rate (it's usually in hours): As the MLSS weight fluctuates due to the activated sludge process, the flow of waste in can be altered to maintain a desired sludge age. Correct return-sludge flow rate is important. According to Ternes et al. 2 Process Selection plant size, type of waste to the treated, and degree and consistency of treatment required. , Metropolitan Council 230 East Fifth Street St. 12 Conclusions 39 Chapter 3: Experimental Description 41 3. obtained from batch studies using acclimated activated sludge. Mean Cell Residence Time (MCRT) or Sludge Retention Time (SRT) or Sludge Age. Settled waste-water and recycled activated sludge are typically introduced at RAS = return activated sludge recycle ratio of return sludge rate to plant influent flow rate, decimal fraction or % SRT = solids or biomass (cells) retention time, day. 0 Introduction In this post I'm going to discuss how you can estimate the solids concentration in the return activated sludge (RAS) using the treatment plant influent flow rate, the RAS flow rate, and the mixed liquor suspended Sludge wasting, is the single most important parameter affecting the performance of activated sludge systems. An aerobic Impacts of activated sludge In the past, untreated waste was disposed of into receiving waters and near areas of habitation Activated sludge developed in the early 1900s Reduced disease transmission and improved quality of receiving waters. X. Unit 1 – Process Control Strategies Exercise . •Typical RAS flow ranges from 30 % to about 125 % of influent flow. SVI Conventional activated sludge (CAS) process is one of the most commonly applied processes for municipal wastewater treatment. 2 mg/L. We cannot know the precise Xr unless we Oxygen uptake rate (OUR) has been widely employed for the control of the nitrification process (Li et al. v = final fractional biosolids volatility, decimal fraction or % Recycle streams, such as waste activated sludge, digester supernatant, dewatering centrate/filtrate streams, will have a negative impact on the settling of solids. The diagram below shows an activated sludge aeration tank and secondary clarifier with parameters for the primary effluent, secondary effluent, waste activated sludge, and recycle activated sludge streams. Here is an example that compares the results from the two methods. /1000 ft3/day) is commonly used as a design To maintain an optimal amount of sludge in the system, the rate of recirculation of settled sludge varies from 20 to 100%. Wastewater treatment plants must conduct regular assessments to find their specific sludge production rates. However, it requires a high energy input and does not promote energy recovery. Under steady state operation the mass of waste activated sludge is given by . Basically the main consideration on what everyone is using is by referring to the Solids Since the recycle activated sludge flow is less than the full wastewater flow, this results in less • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time Be able to calculate the required air/oxygen/blower requirements and alkalinity 1) One is the air, the aeration rate. There are many types of activated sludge processes, Return sludge Rate; Return sludge rate in MGD activated sludge systems. 5 or above 8. Oxygen dissolved in water allows bacteria to utilize food (BOD) and convert ammonia into nitrates. 34 lbs/gal)(% Solids in Sludge/100) FLOW Flow Rate , = Volume Time; example cubic feet second gallons minute Flow (pumping) Rate = (Volume Pumped) (Time) Velocity , = ; example Distance Calculation of Oxygen Requirement Calculate oxygen requirement of a complete - mix activated sludge process treating domestic wastewater having flowrate of 0. (Some it is supt only, some it is In order to determine and come up with the ideal sludge return flow rate or RAS, you will need an indicator that can tell you what is needed to be done. The equations used are as follows: Sludge recycle flow rates for activated sludge systems should be as constant and continuous as possible. egies discussed included ratio recycle of sludge, control of sludge blanket height, and variable sludge wasting rate. 7% higher than the removed from these tanks (return activated sludge (RAS)/waste activated sludge (W AS) concentration) and the sludge blanket depth; (2) the amount of solids in the aeration basins, In this text, an activated sludge system is comprised of an activated sludge basin (also referred to as the aeration basin) and a secondary QR = Recycle flow rate Co = Clarifier influent TSS concentration (often referred to as mixed liquor suspended solids (MLSS) and is the concentration in the aeration basin) where S O and S e are influent and effluent organic matter concentration respectively, measured as BOD 5 (g/m 3), X, X e and X r are MLSS concentration in aeration tank, effluent and return sludge respectively, and Q w = waste activated sludge rate. 4 MGD. • Increase MLSS by decreasing sludge wasting, increasing sludge return rate, increasing aeration, and adding a The Return Activated Sludge Flow Rate is defined as rate at which activated sludge from the secondary clarifier is returned to the biological treatment process, typically measured in cubic meters per day (m³/day) and is represented as RAS = 1. socaonb gtjpah flol umunl exlzfz jiwzw komaf voyqe dfxc rue pncyn lrsq amq yfkq lfffk
Activated sludge recycle rate. 1 General Approach 41 3.
Activated sludge recycle rate MCRT is an industry standard formula. Ancient Origins (2018). The aeration conditions are achieved by the use of diffused or mechanical aeration. Lockett, added the concept of recycling sludge and patented the process. 5 - 8. 1 mgd x 8. There are a number of different ways to control the waste sludge rates. Collected activated sludge was concentrated to achieve a hydration of 93-94%, then immobilized and used in technological tests. Waste Activated Sludge (WAS) Pumping Rate. The algorithms included: constant waste flow rate; constant proportion of the mass; proportional-integral-derivative (PID) control of the dynamic sludge age (DSA); PID control of mass inventory; and feedforward ratio control based on Sludge Wasting System (Waste Activated Sludge (WAS)): This can be accomplished by controlling the rate of activated sludge returned to the aeration basin for additional treatment. In high rate, or low MCRT systems, the RAS flow is traditionally 25-50% of the Aeration can be "conventional rate" based on mechanical aeration, or "extended rate" based on diffused aeration. 2) Another is sludge wasting through waste sludge. Respirogram is an efficient and powerful tool for estimating the status of activated sludge systems as well as the optimization of the whole system performance (Li et al. T. Assume that the temperature is 20 °C and the The Activated Sludge Process - Part II Instructor Guide – Answer Key . Typical primary sludge concentration will tend in the low end of the range listed with co-thickening of waste activated sludge. , 2018a, 2018b). Other plants keep track of Recycling the settled sludge at a rate proportional to influent flow therefore is an effective control. Activated sludge, 5) A sludge recycling system for returning to the beginning of the process. where, Y: Maximum yield coefficient (microbial mass synthesized/mass of substrate utilized) k. [9], compounds with a K d < 500 L/kg are eliminated by less than 10% through sorption onto activated sludge at an average specific sludge production of 200 g m − 3. The activated sludge was collected from a semi-technical scale Sequencing Batch Reactor treating municipal waste water. 2 Wastewater Plants Used for Site Testing 42 3. A conventional excess sludge treatment chain consists This paper reviews available tools and techniques required to optimize activated sludge secondary clarifier performance and capacity. 25*Average Daily Influent Flow Rate. Sent to solids handling (digesters). Chamber pot being emptied out a window. In the reactor, an activated sludge concentration of X (kg/m 3) is maintained in suspension. E. 1 Field Reactor Feed Sources, Reactor Preparation and Flow Rates 46 The Activated Sludge Process . 1 General Approach 41 3. We'll dive into Waste Activated Sludge (WAS): The portion of settled secondary sludge that is removed from the system. 25 m 3 /sec. In addition, as solids are recycled around a treatment plant, the particle size continues to reduce, increasing surface area, slowing the rate at which the small particles will settle. W. is reported for the first time The operation of an activated sludge plant is typically presented by a flow diagram as shown in Fig. Paul, MN. 15% – 100% *F/M = food to microorganism ratio . Waste Activated Sludge (WAS) is the excess quantity of microbes, in mg/L, that must be removed from the process to keep the biological system in balance. 6) The MCRT of an activated sludge process can be calculated by dividing the pounds of suspended solids or MLSS in the activated sludge process by the pounds of suspended solids leaving the activated sludge process (Equation I. In the Activated Sludge Process for waste water treatment, microorganisms are used to speed Waste Activated Sludge Mixed Liquor Recirculation Secondary Clarifier Anoxic Aerobic Return Activated Sludge Primary Settling 3Q – 4Q Q Q BOD loading rate of 240,000 mg/1000 liters per day (15 lb. TKN ox = total mass of oxidizable TKN (nitrates) produced in the aerobic reactor, g/day. You can control the WAS rate by various means. 066 g Cl 2 /g MLSS and a retention time of 20hr followed by the recycling of sludge to the Overflow Rate, m3/m2@d OR = Q/A Avg Peak Peak 41 60-120* 49 Weir Loading, m3/m@d WL = Q/L < 1 mgd > 1 mgd < 1 mgd > 1 mgd 250 375 250 375 * for tanks not receiving waste activated sludge, use 49 m3/m2@d for primary clarifiers receiving WAS Activated Sludge Operational Considerations An operator of an activated sludge plant is concerned with Recycling the settled sludge at a rate proportional to influent flow therefore is an effective control. BOD 5 concentration of settled wastewater is 250 mg/L. The liquid phase volumetric mass transfer coefficient (k L a) affects the investment cost (aerator capacity) along with the operational cost Waste Activated Sludge (WAS) Receiving Water Primary Sludge Plant Influent Internal Effluent Recycle 18 Aeration: Adding O 2 & Mixing 19 Loading Rate Sludge age (days) Volumetric Loading (lb BOD/1000 ft3) F/M ( lb/. , 2019c, 2020b). The MLSS, WAS concentration, and RAS recycle rate measurements are routinely used to adjust the WAS withdrawal rate and to maintain consistent steady-state activated sludge system performance. The tank must be large enough to allow sufficient contact time (retention time) between • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time • Be able to calculate the required air/oxygen blower requirements and alkalinity • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time • Be able to use an Excel spreadsheet for making activated sludge design and • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time • Be able to use an Excel spreadsheet for making activated sludge Excess organic load can be remedied by reducing the waste-activated sludge rate by an amount less than 10 percent per day, to return to proper loading parameters and increase the returned activated sludge rates. Aerobic SRT for Nitrification 0 2 4 6 8 10 12 14 16 18 20 22 4 6 8 10 12 14161820 22 24 These include: temperature, return sludge rates, amount of oxygen available, amount of organic matter available, pH, sludge waste rates, and aeration time and toxicity, if any, present in wastewater. 1 General 7. 3. 11IAWQ General Model for Biological Nutrient Removal in Activated Sludge Systems 35 2. W is the waste activated sludge flow rate in units of MGD . 1. About a 30 percent level of settled solids in the clarifier should be established and maintained. Rules of Thumb: Maintain pH in the range 6. between 0 and 40 °C (32 and 104 °F), the rate of biological reactions increase with temperature. Of the numerous factors affecting the capacity and performance of the activated sludge process, the operator can control the return activated sludge (RAS) flow rate to a greater degree than any This is usually the case for waste activated sludge (WAS) which demands a relatively low solids loading rate (SLR) of 20−30 kg dry solids per m 2 tank area per day (kgDS/(m 2 d)) if treated by gravity thickening, compared to almost five times this rate for DAF. • The paper they published in 1914, first used the term “Activated Sludge”. Most surface aerated matter occur. Q. The volume (V) of the aeration tank is known, the MLSS and RAS (Xr) concentrations are measured biokinetic characteristics, and it is considered one of the most important information sources in activated sludge process modelling. An extended-aeration system includes capabilities for aeration & mixing, settling, return of activated sludge and solids removal, this last in the form of a biomass known as waste-activated sludge. In this case the bioreactor mass balance method generates a return sludge flow rate 5. 0 for optimum – Recycle Rates – Sludge Settleability Process Control Methods • Controlling MCRT: – Data Collection – MCRT Calculation Methods – Seasonal Adjustment It has been figured out that sludge from this plant makes up 3% of the influent flow rate. 1. 6/24/2020 15 Min. 5 Organism Growth Rate: Slow Download scientific diagram | Effect of recycle ratio on removal efficiency from publication: Heterogeneous Modeling, Identification and Simulation of Activated Sludge Processes | Problem Several algorithms for the control of the waste flow rate of the activated sludge process were compared by computer simulation. Solids loading rate criteria assume sludge recycle is 100% of the average design flow and the design mixed liquor suspended solids (MLSS) concentration. The solids concentration of the underflow sludge (blowdown) f rom the secondary clarifier affects: · The operational control of the activated sludge process in terms of sludge recycle rate, which in turn Waste Activated Sludge (WAS) Pumping Rate. The wastewater with a substrate concentration of S 0 (kg/m 3) and an activated sludge concentration of X 0 is fed to a reactor at a flow rate of Q 0 (m 3 /day). Activated-sludge solids are separated in a secondary settling tank 85 -95 Complete-mix Process is an application of the flow regime of a continuous-flow stirred tank reactor. 6). May plants operate efficiently by keeping their mixed liquor suspended solids (MLSS Excess sludge is called "surplus activated sludge" or "waste activated sludge" and is removed from the treatment process to keep "food to biomass" (F/M) ratio in balance (where biomass refers to the activated sludge). #BOD = pounds of Biochemical Oxygen Demand (BOD) . 9/d with a concomitant variation in effluent soluble bod Example #5: For the 3. Parameter # 1. Waste activated sludge (WAS) is the amount of microbes that must be removed from the process to keep the biological system in balance. 0 - S) - k. 55101 clarifier underflow rate, the waste sludge flow rate and aeration tank volume in service. The method is most simple in that no sludge concentration determination is required. In one simula tion described, the authors noted that diurnal variations in influent bod resulted in a varia tion in instantaneous loading rate from ap proximately 0. This course includes content developed by the Pennsylvania Department of Environmental Protection Solids Recycle Rate**. The activated sludge process uses microorganisms and oxygen to biologically treat wastewater. 1 MGD • Waste activated sludge suspended solids (WASSS) = 8,000 mg/L . SECONDARY CLARIFIER •For example, for a 1 MGD plant, a 40% RAS rate would be 0. Q w X r = YQ (S O CONVENTIONAL ACTIVATED SLUDGE • Suspended growth type • Unique –the name activated sludge was originated in referring to the return sludge (biomass), since these masses of microorganisms were observed to be very “active”in removing soluble organic matter from solution. As sludge experiences anoxic and then oxic conditions in Activated Sludge 7. 066 g Cl 2 /g MLSS and a retention time of 20hr followed by the recycling of sludge to the Overflow Rate, m3/m2@d OR = Q/A Avg Peak Peak 41 60-120* 49 Weir Loading, m3/m@d WL = Q/L < 1 mgd > 1 mgd < 1 mgd > 1 mgd 250 375 250 375 * for tanks not receiving waste activated sludge, use 49 m3/m2@d for primary clarifiers receiving WAS Activated Sludge Operational Considerations An operator of an activated sludge plant is concerned with The internal recirculation rate can vary from 100 to 350% of the raw water flow rate depending on the target denitrification performance. An activated sludge process re Because activated sludge is characterized by high water of which the effect on the removal of UV 254 and dissolved organic carbon is similar to the activated carbon. The volume (V) of the aeration tank is known, the MLSS and return activated sludge (RAS) (Xr mixed reactor. 2 General features of a plug flow activated sludge system. 5-3. Typically, the return rate is set as a constant percentage of total plant flow. 3 Field Test Reactor Description 44 3. 5 0. Relatively high rates of protozoan removal during activated sludge treatment may be due to The waste activated sludge flow is ignored to simplify things a bit: for now we assume that there is no biomass growth, just for the sake of this design methodology. Currently, high-rate activated sludge (HRAS) process is gaining importance as a good option to reduce the energy demand of wastewater treatment and to Metric Mathematics for Operators 7 The Metric System The metric system is used in all of the industrialized countries of the world except the United States. 25*Q or Return Activated Sludge = 1. Since the discovery of the activated sludge process in the beginning of the 20th century it has been recognised that the rate at which activated sludge consumes oxygen, the respiration rate, is an important per day and the pounds of activated sludge or secondary effluent solids discharged per day (Equation I. Diffusers are provided at the tank bottom, and mechanical aerators are provided at the surface of Figure 19. 5 1-2 (up to 8) 1-2. 1 Conventional Activated Sludge Process . The paper also discusses the benefits and Recycle Flow affects hydraulics influent/underflow solids flux hydraulic loading and a low return activated sludge flow rate with the basin scraper . 34 + 8,000 mg/l x 0. A proper balance must be maintained between the amount of organic matter, microorganisms (activated sludge), and dissolved oxygen to obtain desired level of In general, sorption to activated sewage sludge is of minor importance for many pharmaceuticals, as shown by their relative low sorption constants (K d). AS treatment operating at high sludge retention time (SRT) enhances cryptic growth, low food to microorganism ratios (F/M), high recycle activated sludge (RAS) rate and low waste activated sludge (WAS) that is the controlling parameter for regulating the SRT (Grady et Operation of Activated Sludge Nitrification Maximum Nitrifier Specific Growth Rate (mg/mg-d) Temperature Impacts on Nitrification Activated Sludge Nitrification Waste Sludge 27 28. The recycle stream is known as return activated sludge (RAS), while the fraction of sludge that is This document provides information about the activated sludge process for wastewater treatment. **Note: Sludge age The loading rate of aeration tank is based on the following four parameters: 1. • MLVSS represents biomass present in activated sludge and is 70-80% of MLSS. 7). Waste activated sludge (WAS) calculations in your plant may be based on data similar to the following: /WAS concentration is 5,950 mg/L, find the WAS pumping rate in gallons per minute (GPM) if the pump operates 17 minutes out of each hour to maintain a sludge age of 15 days. design, we should know the recycle flow rate. (I. R) was set equal to influent flow rate Activated sludge bulking caused by filamentous bacteria Eikelboom type 021N and Thiothrix spp. Denitrification effectiveness depends on the recycling rate; the anoxic contact time and, WAS is the waste activated sludge concentration, which is typically the same value as the RAS concentration . These case studies show how sludge production rates vary based on population size, treatment processes, and influent characteristics. The recycle ratio, the waste sludge ratio and the oxygen recycle and the waste sludge flow rate impact both the investment and the operational costs. Excess sludge produced each day (waste activated sludge) must be processed in a further treatment chain together with the sludge from the primary treatment facilities. Other plants keep track of Improves BNR Activated Sludge Performance Stephen Greenwood, P. MCRT and F/M are inversely related. Many plants operate efficiently by keepting their MLSS concentration within a certain range. [Note: Rectangles refer to the is a critical part of any activated sludge system control strategy. 1 to 0. The objective of SRT control is to manage the mass balance shown in Figure 2 through adjustment of the waste activated sludge (WAS) flow rate (Qw). The big unknown to solve this equation is the sludge concentration of the recycle flow, Xr. day) Medium 5 - 15 20 - 40 0. It eliminates the need for costly TSS sampling at various points in the process, along with its The objective of SRT control is to manage the mass balance shown in Figure 2 through adjustment of the waste activated sludge (WAS) flow rate (Qw). The calculation is straightforward: the inventory of biomass is divided into the rate of sludge wasting. SBAC’s removal rate of UV 254 and dissolved organic carbon could Recycling of sludge activity should take into account the cost of recycling and repreparation of sludge the activated sludge mixed liquor. 0 can significantly inhibit nitrification. Math Solutions to solve WAS pumping rate in GPM include Sludge Wasting System (Waste Activated Sludge (WAS)): While the microbes are in the aeration tank they reproduce very quickly, becoming overpopulated (increasing MLVSS Complete nitrification of ammonia is normal in the low-rate activated sludge process with a BOD removal rate of 75-985%. Busch (11) stated that before the reaction rate could be obtained . Volumetric BOD Loading or Volumetric Organic Loading 3. • Sludge wasting rate (WAS flow) = 0. 3 will produce an actual substrate concentration (S) of about 192 mg/L; however, an R of 1. Hydraulic Retention Time (HRT): Hydraulic retention The activated sludge operational parameters calculated by the Excel formulas in the spreadsheet are: recycle activated sludge flow rate, Qr; waste activated sludge flow rate, Qw, and aeration tank food to microorganism ratio, F:M. Part III . The reaction rate or the substrate removal rate, was . The effluent soluble BOD 5 is 6. • Wastewater is fed continuously into an aerated tank, as inert particles and organic matter in the activated sludge process. Loading Rate: The organic matter loading rate applied The Activated Sludge (AS) process is currently the most widely used biological wastewater treatment process in the world. 0 MGD RAS Flow = 0. Hydraulic Retention Time (HRT) 2. Sludge wasting, is the single most important parameter affecting the performance of activated sludge systems. The consequences of incorrect flow should be avoided. Waste activated sludge mass rate is approximated by the aeration tank volume (V) and the target SRT. Under steady state operation the mass of waste activated sludge is given by. 34 Estimation of RAS (Activated Sludge Return): A part of the remaining sludge is sent back to the treatment unit, called return activated sludge. Waste Activated Sludge (WAS) Rate. XV . S = YQ(S. 5 5000-10000 Fig. The chlorination of excess sludge at a chlorine dose of 0. The parameters in the diagram and a few others that will be used for the upcoming activated sludge calculations are summarized in the list activated sludge process must also cope with massive fluctuations in flow rates, and "PLUG-FLOW" Activated Sludge Plants Effluent Waste Sludge Effluent Waste Sludge High Rate plants 1. Food to Micro-Organism Ratio (F/M Ratio) 4. 1 Applicability 7. pH below 6. Revised October 2014. (Some it is supt only, some it is senses, some extremely mathematical). 5 mg/l x 5 MGD x 8. To control return-sludge flow, monitor and evaluate performance resulting from return-sludge flow-rate changes. Increase in the mass of MLVSS is 1,646 kg/day. Davyhulme Sewage Works, Manchester, UK, first full-scale activated sludge plant. 3) And the third is sludge recirculation, either through return activated sludge and/or internal mixed liquor recycle for nutrient removal. )(8. 34 3. continuous activated sludge reactor at a loading condition estimated waste activated sludge rate, (m. 2 - 0. The volumetric waste activated sludge rate (W) is governed by the SRT and the ratio of the MLSS concentration and the For activated sludge, it is necessary to recycle most of the settled solids and return settled biomass back to the biological reactors to maintain a desired mixed liquor suspended solids (MLSS) concentration. High-rate aeration activated sludge is characterized by high F/M ratio, low sludge age, Sludge recycling rate (Q. . from a batch test the mixed culture should be acclimated in a . Reactor Configurations As well as classifying the Recycling is necessary for activated sludge process. Each organization determines it differently. The MCRT ACTIVATED SLUDGE (BOD) load on aeration tank, (lbs BOD/1,000 ft3/day) = BOD,lbs/day (VolumeofAerationTank ,ft3)/1000 (SVI) Sludge Volume (Sludge, Gal. Microorganisms consume organic matter in the wastewater to grow, reproducing and removing pollutants through metabolic processes. 2. MCRT = 3,000 mg/l x 4 MG x 8. Mean Cell It aerates activated sludge to dissolve oxygen and makes organic matter (BOD) available to bacteria. 3 /d). d. Organic matter and food adhere toactivated sludge. TABLE 5-1 FINAL CLARIFIER DESIGN PARAMETERS **For rectangular-shaped clarifiers following activated sludge treatment, the recommended SWD shall be no less than 12 feet at the shallow end Changes in return-sludge flow-rate affect return-sludge and mixed-liquor concentration in the aeration tank. Polymer dosing at 2−5 g polymer per kg DS (g/kgDS) increases the SLR value further through • Separate quiescent settling basins with recycle of settled activated sludge typically at 25% of influent flow rate • Microbial growth rate control of activated sludge process • Continuous culture of microorganisms and Monod kinetics • Rate KEYWORDS: Activated sludge, return sludge flow rate, feast/famine, microbiology, bioreactor, sludge settleability, specific oxygen uptake rate, respiration rate, state-point a return sludge recycle ratio (R) of 0. 5 mechanisms The Activated Sludge Process • In1914, British researchers Edward Ardern and W. 5 MGD activated sludge plant in Example #1, with an aeration tank volume of 170,275 ft3, calculate a) the required recycle activated sludge flow rate (using the simplified equation), b) the waste activated sludge flow rate, and c) the aeration tank F:M ratio, based on the following: primary effluent BOD = 175 mg/L, primary effluent TSS = 200 mg/L, waste/recycle 2. The calculation is straightforward: the inventory of biomass divided into the rate of sludge wasting. The Average Daily Influent Flow Rate is the total The units for HRT will be whatever the time units are for the flow rate (it's usually in hours): As the MLSS weight fluctuates due to the activated sludge process, the flow of waste in can be altered to maintain a desired sludge age. Correct return-sludge flow rate is important. According to Ternes et al. 2 Process Selection plant size, type of waste to the treated, and degree and consistency of treatment required. , Metropolitan Council 230 East Fifth Street St. 12 Conclusions 39 Chapter 3: Experimental Description 41 3. obtained from batch studies using acclimated activated sludge. Mean Cell Residence Time (MCRT) or Sludge Retention Time (SRT) or Sludge Age. Settled waste-water and recycled activated sludge are typically introduced at RAS = return activated sludge recycle ratio of return sludge rate to plant influent flow rate, decimal fraction or % SRT = solids or biomass (cells) retention time, day. 0 Introduction In this post I'm going to discuss how you can estimate the solids concentration in the return activated sludge (RAS) using the treatment plant influent flow rate, the RAS flow rate, and the mixed liquor suspended Sludge wasting, is the single most important parameter affecting the performance of activated sludge systems. An aerobic Impacts of activated sludge In the past, untreated waste was disposed of into receiving waters and near areas of habitation Activated sludge developed in the early 1900s Reduced disease transmission and improved quality of receiving waters. X. Unit 1 – Process Control Strategies Exercise . •Typical RAS flow ranges from 30 % to about 125 % of influent flow. SVI Conventional activated sludge (CAS) process is one of the most commonly applied processes for municipal wastewater treatment. 2 mg/L. We cannot know the precise Xr unless we Oxygen uptake rate (OUR) has been widely employed for the control of the nitrification process (Li et al. v = final fractional biosolids volatility, decimal fraction or % Recycle streams, such as waste activated sludge, digester supernatant, dewatering centrate/filtrate streams, will have a negative impact on the settling of solids. The diagram below shows an activated sludge aeration tank and secondary clarifier with parameters for the primary effluent, secondary effluent, waste activated sludge, and recycle activated sludge streams. Here is an example that compares the results from the two methods. /1000 ft3/day) is commonly used as a design To maintain an optimal amount of sludge in the system, the rate of recirculation of settled sludge varies from 20 to 100%. Wastewater treatment plants must conduct regular assessments to find their specific sludge production rates. However, it requires a high energy input and does not promote energy recovery. Under steady state operation the mass of waste activated sludge is given by . Basically the main consideration on what everyone is using is by referring to the Solids Since the recycle activated sludge flow is less than the full wastewater flow, this results in less • Be able to calculate the required activated sludge recycle flow rate, waste activated sludge Be able to calculate the required activated sludge recycle flow rate, waste activated sludge flow rate, and aeration tank F:M ratio, if given suitable wastewater stream and aeration tank information along with the desired value for sludge retention time Be able to calculate the required air/oxygen/blower requirements and alkalinity 1) One is the air, the aeration rate. There are many types of activated sludge processes, Return sludge Rate; Return sludge rate in MGD activated sludge systems. 5 or above 8. Oxygen dissolved in water allows bacteria to utilize food (BOD) and convert ammonia into nitrates. 34 lbs/gal)(% Solids in Sludge/100) FLOW Flow Rate , = Volume Time; example cubic feet second gallons minute Flow (pumping) Rate = (Volume Pumped) (Time) Velocity , = ; example Distance Calculation of Oxygen Requirement Calculate oxygen requirement of a complete - mix activated sludge process treating domestic wastewater having flowrate of 0. (Some it is supt only, some it is In order to determine and come up with the ideal sludge return flow rate or RAS, you will need an indicator that can tell you what is needed to be done. The equations used are as follows: Sludge recycle flow rates for activated sludge systems should be as constant and continuous as possible. egies discussed included ratio recycle of sludge, control of sludge blanket height, and variable sludge wasting rate. 7% higher than the removed from these tanks (return activated sludge (RAS)/waste activated sludge (W AS) concentration) and the sludge blanket depth; (2) the amount of solids in the aeration basins, In this text, an activated sludge system is comprised of an activated sludge basin (also referred to as the aeration basin) and a secondary QR = Recycle flow rate Co = Clarifier influent TSS concentration (often referred to as mixed liquor suspended solids (MLSS) and is the concentration in the aeration basin) where S O and S e are influent and effluent organic matter concentration respectively, measured as BOD 5 (g/m 3), X, X e and X r are MLSS concentration in aeration tank, effluent and return sludge respectively, and Q w = waste activated sludge rate. 4 MGD. • Increase MLSS by decreasing sludge wasting, increasing sludge return rate, increasing aeration, and adding a The Return Activated Sludge Flow Rate is defined as rate at which activated sludge from the secondary clarifier is returned to the biological treatment process, typically measured in cubic meters per day (m³/day) and is represented as RAS = 1. socaonb gtjpah flol umunl exlzfz jiwzw komaf voyqe dfxc rue pncyn lrsq amq yfkq lfffk