Proceedings

Sludge Hydrolysis: Comparing performance of biological and thermal advanced digestion full scale facilities

Theodoulou, M.1, Bonkoski, N.1, Harrison D.2 and Keutgen H.2

1GE Water & Process Technologies, Canada, 2 GE Water & Process Technologies, United Kingdom

(free)

Abstract

Advanced digestion technologies facilitate maximizing the efficiency of existing anaerobic digester assets. The incoming sludge is pre-treated and conditioned; enabling increased volatile solids destruction and reduced digester retention times. Feed sludge concentrations can be effectively increased, reducing the downstream digester volume and allowing flow and load increases in the existing assets.

As part of this study, full scale facilities owned and operated by a UK Water Utility will be evaluated, representing two types of advanced digestion technologies, Biological hydrolysis and Thermal Hydrolysis.  Through the evaluation it was found that the Renewable Electricity output efficiency of the plants equipped with these respective technologies was 0.65 – 0.86 MWh/tds for Biological Hydrolysis and   0.55 – 0.63 MWh/tds for Thermal Hydrolysis.  It was also seen that the biogas yield efficiency was highest in the Biological Hydrolysis, however, when digester utilization efficiency (MWh/m3) was considered, although Biological Hydrolysis has an opportunity to have the highest utilization efficiency the gap between Biological Hydrolysis and Thermal Hydrolysis was reduced.  Thermal Hydrolysis benefits from the intensity level of the process, namely in digester solids feed rate.

Keywords

Advanced Anaerobic Digestion; Sludge Hydrolysis; Biological Hydrolysis; Thermal Hydrolysis; Biosolids; Renewable Energy

Introduction

The application of Anaerobic Digestion (AD) in wastewater treatment has been done for many years, with the primary objective to reduce the amount of solids and to stabilize them such that they can be disposed.  In more recent years, the intent of beneficially using biosolids has been adopted, with biosolids regularly destined for land application or composting.  The main byproduct of anaerobic digestion, biogas, which is a methane rich fuel, is also now being viewed as a source of renewable energy that can be leveraged.  Biogas can be converted into renewable electricity and heat when supplied as fuel to a Combined Heat and Power (CHP) system.  The enhancement of the anaerobic digestion process, with focus on the increase of biogas production from sludge is a key to increasing the amount of renewable energy that can be produced with wastewater primary solids and activated sludge being the feed.

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