Mengsteab, Ghebrekidan (2013)

Theme

The influence of reduced acid capacity on hydrolysis of activated sludge components in terms of sludge age

Subject

There is a multitude of biochemical and chemical reactions that are of great importance for wastewater treatment. One of the most important processes is nitrification/denitrification in connection with the balance of calcium carbonate/carbonic acid. In this regard, nitrification reduces acid capacity, while denitrification produces acid capacity. Therefore, the pH-value of the system is influenced.

This master thesis entails the operation of 2 reactors at laboratory scale to investigate the influence of acid capacity and pH-value on the organic and non-organic sludge components for two different sludge ages. For this reason nitrification is systematically increased whereas denitrification is restrained by intensified aeration. The connection between a low pH-value, hydrolysis, and sludge characteristics influenced by the sludge age has to be analyzed.

A detailed literature review about the knowledge on nitrification and hydrolysis influenced by reduced pH-values has to be carried out and related to the results of the laboratory experiments.

Abstract

Waste activated sludge, nowadays poses an ever increasing challenge and this led wastewater engineers to put a considerable impetus to explore and develop strategies and technologies for reducing it.

This paper will deal with one strategy - by optimizing the process through continuous aeration in such away intensifying the nitrification and restraining the de-nitrification. For this study, lab experiment was performed using two sequence batch reactors, BR1 andBR2, filled with 24 Kg waste activated sludge. Third batch reactor was also in operation as reference for BR1. First the reactors were filled with 16 Kg concentrated waste activated and later fed 8 Kg fresh wastewater 5 days in a week for the entire experiment. BR1 and BR2 were operated only with nitrification, and has a sludge age of 20 and 10 days respectively, while BR3 was with alternate nitrification and denitrification. A robust nitrification yielded a pH value of 5, 5.4 and acid capacity of 0.1 mmol/L in BR1 and BR2. And this led to the hydrolysis of organic and inorganic components of the sludge. As a result dissolved chemical oxygen demand [DCOD] in was 25.5, 24.8 and 19.38 mg/L respectively. The same trend was attained for the inorganic components. This indicates that higher hydrolysis in BR1 and BR2 than in BR3. BR1 registered higher value compared to BR2 mainly due to higher sludge retention time and slightly lower pH. Final analysis for sludge reduction was made and resulted in 25% reduction.

Supervisors