Influence of temperature on the performance of anaerobic treatment systems of municipal wastewater

Silvânia Lucas Dos Santos,Sílvia Raphaele Morais Chaves,Adrianus Van Haandel

doi:10.4314/wsa.v44i2.07

Silvânia Lucas Dos Santos, Sílvia Raphaele Morais Chaves + Show 1 more

Open Access

https://doi.org/10.4314/wsa.v44i2.07

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Journal: Water SA	Publication Date: Apr 25, 2018
Citations: 6	License type: cc-by

Affiliation: Universidade Federal de Campina Grande

Abstract

Anaerobic sewage treatment systems, especially upflow anaerobic sludge blanket (UASB) reactors, have found wide application over the past decades, particularly in regions with a warm climate. A low sewage temperature is generally considered as a factor contributing to poor performance, characterized by an increase of the COD fractions in the effluent and the generated sludge, and decreasing the fraction that is transformed into methane. An experimental investigation was carried out at pilot scale to establish the values of the three COD fractions for different values of temperature and the applied organic load. The sludge age of the anaerobic treatment, together with temperature, was identified as the main operational variable that affects the efficiency of anaerobic treatment. An empirical expression was derived for the values of the three factions as a function of these two variables. From the results of the experimental investigation it was apparent that there is no point in applying a sludge age of more than 100 d, when the reactor is near its best performance. An expression was derived to establish the hydraulic retention time for maximum digestion efficiency as a function of temperature, concentration and composition of organic material and sludge mass. It was established that the main limit to the sludge hold-up in UASB reactors treating sewage is not the sludge settleability, but rather the break-up of flocs leading to loss of small, poorly-settling particles.

Highlights

In anaerobic digestion organic material in wastewaters is transformed into biogas due to four sequential processes (Gujer and Zehnder, 1983): (i) hydrolysis, the solubilisation of particulate organic material or macromolecules generating soluble materials like sugars, amino acids and lipids; (ii) the fermentation of the soluble material to secondary metabolites of smaller molecular weight; (iii) the fermentation of these metabolites to acetate and hydrogen, the substrates of the fourth process; and (iv) methane production, accompanied by variable production of carbon dioxide and other gases
If anaerobic treatment is to be applied, these wastewaters must be digested at the temperature at which they are generated, which is lower than the optimal value
The aim of this paper is to develop a relationship between the anaerobic digestion efficiency and the two most important operational variables: temperature and sludge age

Summary

Introduction

In anaerobic digestion organic material in wastewaters is transformed into biogas due to four sequential processes (Gujer and Zehnder, 1983): (i) hydrolysis, the solubilisation of particulate organic material or macromolecules generating soluble materials like sugars, amino acids and lipids; (ii) the fermentation of the soluble material to secondary metabolites of smaller molecular weight (volatile acids, alcohols etc.); (iii) the fermentation of these metabolites to acetate and hydrogen, the substrates of the fourth process; and (iv) methane production, accompanied by variable production of carbon dioxide and other gases. The transformation rates increase with rising temperature until a maximum is reached at about 35–37°C, the optimal temperature (Luostarinen et al, 2007). In concentrated wastewaters or solid wastes, the produced methane can be used to increase the temperature to the optimal value, even at low environmental temperatures. If anaerobic treatment is to be applied, these wastewaters must be digested at the temperature at which they are generated, which is lower than the optimal value

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