Facilitated UASB granule formation using organic–inorganic hybrid polymers

Abstract

Maintaining high concentrations of microorganisms is crucial for the anaerobic treatment of organics. The granulation of sludge is a good method but it takes more than 6 months to form sludge granules spontaneously. In this study, a large amount of granular sludge was prepared within 5 min by adding organic–inorganic hybrid polymers to the sewage digester sludge. The size of the granular sludge ranged from 1 to 5 mm and its falling velocity was higher than that of the granular sludge from the actual wastewater treatment facility. Since the granule was stable throughout the operation of a UASB, the removal efficiency was as high as 90% at high organic loading rate up to 18 kg-COD/m³ day.

Introduction

Over 1000 high-speed anaerobic reactors containing granular sludge are operated over the world, particularly in developed countries such as Europe and USA.

When sewage digester sludge is used as a seed in the reactor, however, it is difficult to operate elaborately during start-up and the period lasts as long as 4–6 months. Although well-adapted sludge should be used in anaerobic treatment of toxic materials, during the early operation period the foreign sludge is usually inoculated into the reactor. The process of inoculating foreign sludge is known to be expensive.

In an effort to shorten the start-up period, Lettinga et al. suggested that a small amount of granular sludge should be used as seed [1]. To facilitate granulation of sludge, charcoal power, ferrous or calcium compounds have been added to sludge as the core of granulation. However, it also takes over 6 months to form granular sludge, furthermore, these compounds should be added at intervals [2]. Polymer coagulants were also tried but the resulting shape of the granule formed was far from ordinary and its density was lower. The coagulants also caused inhibition of the sludge [3].

In this study, a novel method to make granular sludge in a very short time was employed. Special polymers were added to the sewage digester sludge to make compact-granular sludge. The sludge can be easily obtained in great quantity and can be granulated economically. The anaerobic reactor containing this granular sludge treated high organics-loaded wastewater stably.