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CE 421/521- Environmental Biotechnology

 Evaluation of anaerobic sewage treatment at low temperature

Jaeyoung Park

 ABSTRACT

The possibility of anaerobic treatment of the municipal wastewater under psychrophilic conditions was discussed and evaluated. The activity of anaerobic microorganism and the physical and chemical activity of anaerobic treatment condition were decreased as the temperature dropped. However, the UASB reactors or AF reactors which were mainly applied to the low temperature sewage showed the high treatment efficiency and stabilization above 10^oC. The decreased temperature below 10^oC showed the sharply decreased treatment efficiency and the value of the biokinetic coefficients (k, K_d, μ_m). To accomplish the highest overall sewage treatment efficiency, the staged anaerobic reactor was suggested because it can offer significantly better potentials than single compartment reactors. The AF- UASB system might be more feasible than other systems for the treatment of municipal wastewater at low temperature.

 KEYWORD

anaerobic sewage treatment, low temperature, UASB, AF, staged system

 INTORDUCTION

 Anaerobic treatment is an attractive process for domestic sewage because little energy is needed for the process itself, and moreover, removed organic matter is converted to biogas which can be used for the productions of energy. Although the anaerobic treatment of domestic sewage has been applied at several tropical countries, the process so far is not applied at the countries with low temperatures. This is mainly due to lower removal efficiencies. However, much research was progressed at low temperatures, and the experimental data showed that the anaerobic treatment should not be excluded at low temperatures (Elmitwalli et al., 2001; Lettinga et al., 2001; Bodik et al., 2000; Uemura et al., 2000). Most of the related publications described practical relation of the anaerobic treatment of municipal wastewater by use of the upflow anaerobic sludge blanket (UASB) reactors or the anaerobic filter (AF). Moreover, several two-step reactors that included UASB or AF were demonstrated to optimize the anaerobic treatment at low temperature with low HRT (Elmitwalli et al., 2002; Elmitwalli et al., 1999; Bodik et al., 2000). The objective of this paper is to review the performance of the anaerobic sewage treatment at low temperature and evaluate the each system’s characteristics.

 EFFECT OF LOW TEMPERATURE ON THE ANAEROBIC PROCESS

Anaerobic microorganism

Microorganisms are classified into ‘temperature classes’ on the basis of optimum temperature and the temperature span in which the species are able to grow and metabolize. The overlapping growth temperature ranges in Fig.1 indicate that there is not a clear boundary between these classic group of psychrophilic, mesophilic and thermophilic microorganisms. However, the bacterial growth rates of anaerobic groups are well determined (Lin et al., 1987). The growth rates of psychrophilic methanogens are comparably slower than mesophilic and thermophilic methanogens. Moreover, most reactions in the biodegradation of organic matter require more energy to proceed at low temperature than at a temperature optimum of 37 ^oC (Lettinga et al., 2001).