Monthly Archives: April 2014

WWTP-SBR: SEQUENCING BATCH REACTOR – Math Procedure for Small WWTP Designing (New!)

SBRenITA WWTP  SBR – Math procedure 

SBRs are a variation of the activated-sludge process. They differ from activated-sludge plants because they combine all of the treatment steps and processes into a single basin, or tank, whereas conventional facilities rely on multiple basins. According to a 1999 U.S. EPA report, an SBR is no more than an activated-sludge plant that operates in time rather than space.

The operation of an SBR is based on a fill-and-draw principle, which consists of five steps—fill, react, settle, decant, and idle. These steps can be altered for different operational applications. Fill During the fill phase, the basin receives influent wastewater. The influent brings food to the microbes in the activated sludge, creating an environment for biochemical reactions to take place. Mixing and aeration can be varied during the fill phase to create the following three different scenarios:

Static Fill – Under a static-fill scenario, there is no mixing or aeration while the influent wastewater is entering the tank. Static fill is used during the initial start-upphase of a facility, at plants that do not need to nitrify or denitrify, and during lowflow periods to save power. Because the mixers and aerators remain off, this scenario has an energy-savings component. Mixed Fill – Under a mixed-fill scenario, mechanical mixers are active, but the aerators remain off. The mixing action produces a uniform blend of influent wastewater and biomass. Because there is no aeration, an anoxic condition is present, which promotes denitrification. Anaerobic conditions can also be achieved during the mixed-fill phase. Under anaerobic conditions the biomass undergoes a release of phosphorous. This release is reabsorbed by the biomass once aerobic conditions are reestablished. This phosphorous release will not happen with anoxic conditions.

Aerated Fill – Under an aerated-fill scenario, both the aerators and the mechanicalmixing unit are activated. The contents of the basin are aerated to convert the anoxic or anaerobic zone over to an aerobic zone. No adjustments to the aerated-fill cycle are needed to reduce organics and achieve nitrification. However, to achieve denitrification, it is necessary to switch the oxygen off to promote anoxic conditions for denitrification. By switching the oxygen on and off during this phase with the blowers, oxic and anoxic conditions are created, allowing for nitrification and denitrification. Dissolved oxygen (DO) should be monitored during this phase so it does not go over 0.2 mg/L. This ensures that an anoxic condition will occur during the idle phase.

React This phase allows for further reduction or “polishing” of wastewater parameters. During this phase, no wastewater enters the basin and the mechanical mixing and aeration units are on. Because there are no additional volume and organic loadings, the rate of organic removal increases dramatically. Most of the carbonaceous BOD removal occurs in the react phase. Further nitrification occurs by allowing the mixing and aeration to continue—the majority of denitrification takes place in the mixed-fill phase. The phosphorus released during mixed fill, plus some additional phosphorus, is taken up during the react phase.

Settle During this phase, activated sludge is allowed to settle under quiescent conditions—no flow enters the basin and no aeration and mixing takes place. The activated sludge tends to settle as a flocculent mass, forming a distinctive interface with the clear supernatant. The sludge mass is called the sludge blanket. This phase is a critical part of the cycle, because if the solids do not settle rapidly, some sludge can be drawn off during the subsequent decant phase and thereby degrade effluent quality.

Decant During this phase, a decanter is used to remove the clear supernatant effluent. Once the settle phase is complete, a signal is sent to the decanter to initiate the opening of an effluent-discharge valve. There are floating and fixed-arm decanters. Floating decanters maintain the inlet orifice slightly below the water surface to minimize the removal of solids in the effluent removed during the decant phase. Floating decanters offer the operator flexibility to vary fill and draw volumes. Fixed-arm decanters are less expensive and can be designed to allow the operator to lower or raise the level of the decanter. It is optimal that the decanted volume is the same as the volume that enters the basin during the fill phase. It is also important that no surface foam or scum is decanted. The vertical distance from the decanter to the bottom of the tank should be maximized to avoid disturbing the settled biomass.

Idle This step occurs between the decant and the fill phases. The time varies, based on the influent flow rate and the operating strategy. During this phase, a small amount of activated sludge at the bottom of the SBR basin is pumped out—a process called wasting.

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The procedure WWTP-SBR is freely available including Mathematical Model and Technical Specification on the algorithms used in calculation:

  • Software License (. Xls)
  • User Manual (. Pdf) – Technical Specification (. Pdf)
  • 12 months / Technical Assistance

SBR Manual (Guidelines – Operational Suggestions – TroubleShooting) To purchase or for more info:

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WDOxy-Fuzzy: On-Demand Dissolved Oxygen Control for WWTPs Efficiency with Energy Saving (by “AUTOMAZIONE Oggi” – N.370 Marzo 2014)

WDoxy Dissolved Oxygen Control for WWTPs Efficiency with Energy Saving  

(by “AUTOMAZIONE Oggi”  – N.370 Marzo 2014)

WDOxy-Fuzzy is a software procedure aimed at achieve an optimal control of the biological depuration of urban/industrial wastewater by using Fuzzy Logic algorithms based on bio-process behaviors and on on-line data derived from field instrumentation. These refers to the detection of values of ​​Ammonium NH4+ concentration (alternatively: on ORP) and on DO (Dissolved Oxygen) values in oxidation, all that by returning as a real time “output”, the optimal set-point of the process control parameters (DO, flow rate of aeration, recirculation, etc..). In this way, WDOxy-Fuzzy procedure determines the optimal value (as dynamic set-point) of DO concentration, that is able to ensure in every operative phase of depuration process the following points:

  1. autotrophic and heterotrophic bacteria metabolism in the depuration process;
  2. non-proliferation and tigger of Bulking conditions control;
  3. minimization of energy consumption (kWh)

The software is implemented in the typical remote control systems, also directly implemented into dedicated PLC to the Dissolved Oxygen local control loop. Since over two years WDOxy-Fuzzy is used on sewage treatment plants with nutrient removal, on small to medium in size WWTPs and it is operating in continuous or with intermittent aeration.

WDOxy-Fuzzy, designed and developed by ANOVA in Naples (Giovanni Mappa), it is used by more than two years from large international companies operating in the field of analytical instrumentation and process control, having successfully passed the Functional Testing on field already in 2012.

Principles of Operation

The principle of operation of WDOxy-Fuzzy is based on the following bio-process correlations:

1)   Biological Oxygen Request and Dissolved Oxygen set-point: the wastewater aerobic biological treatment is based on the fact that the some pollutants (organics, nutrients, etc.) are the “food” (substrate) for “heterotrophic” and “autotrophic” bacteria which accrue as “biomass”, in a fixed volume (reactor). In order that the biomass can metabolize the pollutant substrate in an aqueous environment, it is necessary that it can “breathe”, or dispose of a sufficient dissolved oxygen concentration (DO)  into treated wastewater. The typical used solution to provide DO in this case is, as known, to adopt systems of insufflations and diffusion of air which, exploiting the principle of the solubility of the gas (Henry’s Law), provides oxygen to the entire biomass contained in the reactor. However, considering that (under std conditions) 1m3 of air contains about 21vol %O2, it follows that it is necessary to provide an air flow rate 4-5 times that required, with respect to pure oxygen O2. In function of the different operating parameters of the process (temperature, atmospheric pressure, substrate concentration, biomass concentration, etc.), the oxygen contained in the air is transformed into DO concentration, after having used the energy required, that is about 0.5 kWh for each Kg/h of O2 required.

2)   Dissolved Oxygen set-point and Bulking: dissolved oxygen concentration DO in the reactor is a parameter of a great importance also for its influence with respect to the phenomenon of Bulking and, consequently, on the sludge sedimentation. This correlation is directly influenced by the organic load F/M (Food to Microorganisms): higher is F/M, higher is the concentration of dissolved oxygen necessary to prevent the Bulking (caused by some filamentous bacteria such as S.Natans, Type 1701 and H.hydrossis)

3)     DO set point and Energy Savings: usually biological treatment process takes place under dynamic conditions where input loads may change considerably in space and time. The dynamics of the DO value of concentration in water, compared to dynamics of bacterial metabolism, is an average ratio of about 5/20, that means a variation of concentration of DO in the water takes place in the order of a few minutes (starting from the activation of air insufflations), while because DO as O2 is completely used by biomass to metabolize the substrate it takes 15-20mins. All this allows to focus on the following points:

  • DO is a physico-chemical parameter whose numerical value (expressed in mg/l) is to mean a greater or lesser ” availability ” of oxygen for the bacterial metabolism. This value, however, is linked in turn to the different dynamics of transfer within the biomass (temperature, oxygen gradient, size of the flakes of mud, etc.). In other words, and simplifying the concept: between being in a situation in which DO assumes high values ​​for short periods of time, compared to the case where the DO values ​​are lower for prolonged times, this latter case is certainly not only desirable but also energetically less costly.
  • values of DO too low in relation to the actual needs of the process, i.e. the F/M ratio between the substrate (pollutant) and biomass concentration, favors the proliferation of Filamentous Bacteria, at the expense of bacteria “Floc-Forming” that are required for the proper functioning of the process (sedimentation-recirculation): that means to face to the serious outcomes both from the operational point of view, that from the standpoint of sanitary;
  • DO high values (>2.5 mg/l) do not provide generally further benefits to the bacterial metabolism, because biologic dynamics of using dissolved oxygen are, as already stated, fixed and slower than DO chemism, in every case. In addition, more seriously, DO high values, besides to be an useless waste of energy, may be symptomatic of some problems related to the proper functioning of the process, i.e. a too low biomass concentration, or an insufficient organic load, or presence of toxic substances which have weakened the vitality of the biomass, etc.. Extending the concept, in a balanced system of “substrate – biomass – oxygenation”, a low value (0.4-0.8 mg/l) of average concentration of dissolved oxygen DO, it may even be a good indicator of functionality and efficiency energy, as it is to mean that the insufflations of air,  produce the DO that is necessary and sufficient for the needs of the process.

 

WDOxy-Fuzzy Advantages

In the technical-scientific literature regarding the biological purification of wastewater, is typically reported the value of set-point DO of about 1-2 mg/l, but it is a “safety value” which guarantees neither the state of health of the process, nor the protection from an energy expenditure.

In general, the advantages of WDOxy-Fuzzy system with dynamic set-point DO, compared to the traditional system (fixed set-point OD ) can be summarized in the following points:

  • immediate response to peaks in the variability of hydraulic loads and pollutant input through a continuous adaptation of the set-point of dissolved oxygen;
  • Increased process stability and purifying efficiency, with particular reference to the nitrification process;
  • an high energy saving about 15-20 %, and simultaneous elimination of the excesses of nitrification, as it is prevented the supply of excess air by obtaining a better efficiency of the transfer of oxygen by the diffusers;
  • greater control of the continuity of the performance of removal, in relation to the limits of effluent quality.

 

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For more info:

WDOxy-Fuzzy: Controllo On-Demand dell’Ossigeno Disciolto per il Miglioramento – Depurativo con Risparmio Energetico

WDoxy Modello WDOxy-Fuzzy

(AUTOMAZIONE Oggi  – N.370 Marzo 2014)

WDOxy-Fuzzy è una procedura software finalizzato al controllo ottimale degli impianti di depurazione biologica di acque reflue civili/industriali e che utilizza algoritmi bio-processistici in Logica Fuzzy e dati on-line derivanti dalla strumentazione in campo. Quest’ultima si riferisce alla rilevazione dei valori di concentrazione dell’Ammonio NH4+ (in alternativa: ORP) e dell’OD in aerazione, restituendo come “output” in tempo reale, i valori ottimali di set-point dei parametri di controllo processo (OD, portata di aerazione, di ricircolo, ecc.).

WDOxy-Fuzzy determina quindi, il valore ottimale (set-point variabile)della concentrazione dell’OD che garantisce in ogni momento del processo depurativo:

  • il metabolismo dei batteri eterotrofi e autotrofi protagonisti del processo depurativo;
  • il controllo delle condizioni di non-innesco e proliferazione del Bulking;
  • la minimizzazione dei consumi energetici (kWh) Il software è implementabile nei tipici Sistemi di Telecontrollo (SCADA), ma anche direttamente nei PLC dedicati al loop di controllo locale dell’Ossigeno Disciolto.

Da oltre due anni WDOxy-Fuzzy viene utilizzato su impianti di depurazione con rimozione nutrienti, di piccole-medie dimensioni, sia funzionanti in continuo, sia con aerazione intermittente. WDOxy-Fuzzy, progettato e sviluppato dalla società ANOVA di Napoli, viene utilizzato da oltre due anni da grandi aziende internazionali del settore strumentazione analitica e controllo di processo, avendo superato con successo già nel 2012 i Test di Funzionalità sul Campo.

Per info: