Simulation of an Oxic-Settling-Anaerobic Pilot Plant Operated under Real Conditions Using the Activated Sludge Model No.2d

Oxic-settling-anaerobic (OSA) process has been introduced into the treatment line of wastewater in order to upgrade activated sludge processes and to reduce the production of excess sludge. The aim of the present study was to simulate the performance of an OSA pilot plant by implementing the Activated Sludge Model No.2d (ASM2d) into a mathematical modelling software (BioWin). The stepwise calibration, performed both by off-line experiments and software dynamic calibration, was carried out in a heuristic way, adjusting the parameters values that showed a major influence to the effluent and internal concentrations. All the reduction factors introduced into ASM2d to simulate the processes occurring in anoxic and anaerobic conditions were lowered in order to reproduce the concentrations of interest. In addition, the values of parameters of the PAOs (polyphosphate accumulating organisms)-related process (namely qPHA and YPO4) were found lower than those usually adopted. In general, theoretical results were in good agreement with the experimental data obtained from plant’s operation, showing an accurate predictive capacity of the model. Good performance was achieved considering the phosphorus removal related process, while some failures were detected in COD and ammonia simulations.

Steady-State Methodology for Activated Sludge Model 1 (ASM1) State Variable Calculation in MBR

The complexity of Activated Sludge Model No. 1 (ASM1) is one of the main obstacles slowing its widespread use, particularly among wastewater treatment plant (WWTP) professionals. In this paper, a simplification procedure based on steady-state mass balances is proposed for the conventional activated sludge process (ASP) configuration, consisting of an aerated bioreactor and a perfect settler (without particular compounds in the outlet). The results do, in fact, show perfect suitability to a membrane bioreactor process (MBR). Both organic carbon and nitrogen removal were investigated. The proposed approach was applied to ASM1, and simple analytical expressions of the state variables were obtained. These analytical expressions were then validated by comparison to simulations given by the original ASM1 (implemented in GPS-X software). A strong match (less than 4% of error overall) was obtained between both results in the steady-state; consequently, these analytical expressions may be useful as tools for quickly estimating the main state variables, feeding the filtration models, or identifying the interaction between operating parameters. Moreover, this enables a sensitivity analysis, covering relevant factors such as kinetics or operating parameters. For instance, the sludge retention time (SRT) effect is lower on XBH and XS at high SRT (˃20 days), while it is more pronounced on XP and XI as their variations with SRT are linear.

KINTANČIOS KONCENTRACIJOS VEIKLIOJO DUMBLO PROCESAI: CHARAKTERISTIKA IR ANALIZĖ

Nuotekų valymo įrenginių veikliojo dumblo darbas gali būti projektuojamas, optimizuojamas ir vertinamas taikant matematinį modeliavimą. Šio darbo tikslas – ištirti ilgalaikius (10 mėn. trukmės) mažojo individualaus NVĮ darbo duomenis, rasti priklau-somybes tarp parametrų ir patikrinti, ar yra galimybė optimizuoti vykstančius nuotekų valymo procesus taikant įprastus ASM (angl. Activated Sludge Model) modelius. Modeliuojant svarbiausi yra trys kinetiniai ir stechiometriniai kalibravimo parametrai: maksimalus heterotrofinis mikroorganizmų augimo greitis, aerobinis endogeninis heterotrofinės biomasės kvėpavimas ir aerobi-nis heterotrofinės biomasės prieaugis. Tarp šių parametrų turi būti dinaminė pusiausvyra, veikliojo dumblo koncentracija įrengi-nyje turi būti pastovi ir optimali. Išanalizavus gautus duomenis paaiškėjo, kad mažo našumo NVĮ-102 aeracinėje kameroje išma-tuota veikliojo dumblo koncentracija nėra pastovusis dydis. Tyrimo metu ši koncentracija kito nuo 3 iki 6,9 g/l. Kintant veikliojo dumblo koncentracijai, kinta jo apkrova organinėmis medžiagomis (g BDS5/g dumblo sausosios medžiagos), tūrinė apkrova, grąžinamojo veikliojo dumblo debitas (m3/d.), grąžinamojo veikliojo dumblo koncentracija, grąžinamojo veikliojo dumblo pro-centinis kiekis, deguonies poreikis. Apibendrinus galima teigti, kad mažojo NVĮ darbui optimizuoti įprasti ASM modeliai nėra pritaikyti.