Optimisation of the removal capacity of UASB systems for varying hydraulic and organic loading rates
09 / 2000 - 06 / 2004
The purpose of this work is to contest the prejudice on the use of anaerobic process (mainly UASB reactors) for treating municipal wastewater. The reasons of the companies responsible for the wastewater treatment to be against the anaerobic processes are focused in three main points: (1) anaerobic reactors spread unpleasant odour; (2) anaerobic reactors are unstable; and (3) the UASB reactors cannot cope with high load rate variations. The first argument is easy to solve by rightly disposing the gases. Though there is not enough experimental information to confirm or to rebut the second and third points, i.e. that the reactor UASB would be unstable and very sensitive to variations of the sewage flow or concentration. For this reason the present research seeks specifically to point out this aspect. [Aim:] General Objective: To study the limits or instability of the UASB reactors, treating sewage, under different organic and hydraulic loading rates, and under shock loads. [Specific Objectives:] To describe the effects of the steady-state operation using different parameters such as Organic Loading Rate, influent concentration, and Hydraulic Retention Time, on the UASB performance. To evaluate the effect of organic load variations (both duration and intensity) on important process variables such as: 1) COD and solids removal efficiency; 2) operational stability and 3) sludge properties (concentrations, activity, stability, and expansion during the high superficial load rate). To propose optimised design or operational parameters for UASB reactors treating sewage with high variation in the flow rate and concentration.