Overview of the high rate anaerobic techniques in wastewater treatment

Abstract

Anaerobic processing is an old technology. Recently, Anaerobic Treatment (AT) has become attractive and be developed due to biogas considered a renewable energy source. According to Lettinga [13], although the growth rate of anaerobic bacteria is low, this weakness has gradually been overcome with modern AT technology. The present AT techniques accept the organic loading rates from tens to over 100kg COD/m³/day with its performance from 70% to 90% [11, 12]. The study [4] shows that when the biochemical oxygen demand (BOD) of the effluent exceeds 1000 mg/l, the cost of the Upflow Anaerobic Sludge Blanket (UASB) is lower than that of activated sludge treatment, both in terms of basic construction and maintenance free. According to [4], there are three groups of anaerobic techniques: (i) the reactors with dispersed microorganisms; (ii) the microorganisms immobilized on carrying material; and (iii) the Expanded Granular Sludge Bed (EGSB) system. The UASB technique invented by Lettinga in the 1970s is classified into the group (iii), and has been applied since 1980 using granular microorganisms with very high density (up to 80-100 g/l). According to [11], the modern AT techniques began at the continuous stired-tank reactor (CSTR), then the anaerobic contact reactor (CR), turning-point with the UASB system, peak with the Expanded Granular Sludge Bed (EGSB) and the Internal Circulation Reactor (IC). Suppose that the CSTR has the relative capacity of 1, then 5 for CR, 25 for UASB, 75 for EGSB and IC. This article summarize the development of anaerobic treatment technology and focuses on the high-rate anaerobic treatment systems as UASB, EGSB, IC.