Effects of Hydraulic Residence Time and Mixing on Wastewater Treatment in a Membrane Bioreactor

M. Čurlin, M. Matić, M. Matošić, I. Mijatović and Ž. Kurtanjek

Abstract
Effects of hydraulic residence time distribution (HRTD) and degree of mixing on aerobic wastewater treatment in a membrane bioreactor are studied. Experimentally are determined HRTD and the life expectancy functions Λ in a 40 L Zenon (ZW 10) hollow- fiber submerged microfiltration membrane bioreactor at liquid flow rate range of 7.4 – 36 L h–1 and gas flow rate range 1.7 – 5.1 m3 h–1. The HRTD functions are modelled by a series of two parallely connected CSTR corresponding to slow and fast liquid flow. The model approximates the HRTD functions with an average relative error of 5 %. A model for prediction of average liquid residence time based on superficial liquid and gas velocities is developed. From HRT functions are evaluated the life expectancy functions Λ of dissolved biodegradable substrates and oxygen in liquid phase. Parameters from Activated Sludge Model No. 1 (ASM1) for aerobic degradation by heterothropic biomass are applied for computer simulation. Concentration of soluble biodegradable substances in the outlet stream is the measure of effects of HRT and mixing. Applied are the following models: ideal mixing, segregated flow, maximum mixidness, and the CSTR network. With reference to the network model, determined are relative differences of outlet concentration of biodegradable substrate 59 %, 86 % and 32 % corresponding to the flow models relative to the CSTR network model.

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Keywords
HRT, membrane bioreactor, degree of mixing, wastewater treatment