Tecnologia De Digestión Anaerobia

ANAEROBIC DIGESTION TECHNOLOGY FOR INDUSTRIAL WASTEWATER TREATMENT


Medhat M. A. Saleh * and Usama F. Mahmood **

* Prof. of Sanitary Engineering, El Azhar Univ., Egypt
** Assistant Prof. of Sanitary Engineering, El Azhar Univ., Egypt
E-mail: msaleh@brainy1.ie-eg.com



Abstract

Anaerobic digestion is the most suitableoption for the treatment of high strength organic effluents. The presence of biodegradable components in the effluents coupled with the advantages of anaerobic process over other treatment methods makes it an attractive option. This paper reviews the suitability and the status of development of anaerobic reactors for the digestion of selected organic effluents from sugar and distillery, pulpand paper, slaughterhouse and dairy units. In addition, modifications in the existing reactor designs for improving the efficiency of digestion has also been suggested.


Keywords : Anaerobic digestion; Reactors; Effluents; Sugar; Distillery; Pulp and paper; Slaughterhouse; Dairy



1. Introduction

There is a growing interest in alternate energy sources as a result of increased demandfor energy coupled with a rise in the cost of available fuels. Rapid industrialization has resulted in the generation of a large quantity of effluents with high organic contents, which if treated suitably, can result in a perpetual source of energy. In spite of the fact that there is a negative environmental impact associated with industrialization, the effect can be minimized and energycan be tapped by means of anaerobic digestion of the wastewater. In recent years, considerable attention has been paid towards the development of reactors for anaerobic treatment of wastes leading to the conversion of organic molecules into biogas. These reactors, known as second generation reactors or high rate digesters, can handle wastes at a
high organic loading rate of 24 kgCOD/m3 dayand high upflow velocity of 2-3 m/h at a low hydraulic retention time [1]. However, the treatment efficiencies of these
reactors are sensitive to parameters like wastewater composition, especially the
concentration of various ions [2,3] and presence of toxic compounds such as phenol [4]. The temperature and pH are also known to affect the performance of the reactor by affecting the degreeof acidification of the effluent and the product formation [5].

An improvement in the efficiency of anaerobic digestion can be brought about by either suitably modifying the existing digester design or by incorporating appropriate


advanced operating techniques. Thus, a plug flow reactor or USSB reactor is found to be superior to the conventional processes due to low concentrations of VFAin the effluent, a high degree of sludge retention and stable reactor performance [6]. Another common problem encountered in the industrial anaerobic plants is biomass washout. This can be addressed, for instance, by the use of membranes coupled with the anaerobic digester for biomass retention [7]. This paper reviews the development of various reactors for the treatment of highstrength wastewaters from selected industries viz distillery, pulp and paper, dairy and slaughterhouse. The emphasis is on identifying the critical factors affecting performance so that the reactor efficiency can be improved by maintaining optimal operating conditions.



2. High rate anaerobic reactors

All modern high rate biomethanation processes are based on the concept of retaining highviable biomass by some mode of bacterial sludge immobilization. These are achieved by one of the following methods [8].
* Formation of highly settleable sludge aggregates combined with gas separation and sludge settling, e.g. upflow anaerobic sludge blanket reactor and anaerobic baffled reactor.
* Bacterial attachment to high density particulate carrier materials, e.g. fluidized bed reactors...