טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLew Beni
SubjectKinetics of Domestic Wastewater Anaerobic Degradation at
Different Temperatures
DepartmentDepartment of Agricultural Engineering
Supervisors Professor Emeritus Green Michal
Professor Dosoretz Carlos


Abstract

This research focused on anaerobic degradation kinetics and biodegradability of the different domestic wastewater fractions at low temperatures (20, 15 and 10 °C). The various fractions were classified according to size, where Suspended Solids (SS) were greater than 4.5 mm, Colloidal (Col) was from 0.45 mm to 4.5 mm, and Soluble (Sol) was smaller than 0.45 mm.

The investigation was conducted in short and long term anaerobic batch experiments using domestic wastewater from Neve Sha'anam neighborhood after primary sedimentation (566 mg COD/l).

A decrease in the degradation rate with temperature was observed for all the different domestic wastewater fractions. At each temperature, a similar first order degradation rate constant for the different particulate matter fractions (SS and Col) was observed, 4.64, 2.35 and 1.19 1/d at 20, 15 and 10 °C, respectively, indicating that different size particulate matter were similarly affected by temperature. The Soluble fraction degraded was less affected by temperatures changes and had a higher degradation rate constant at all the temperatures; the maximum specific degradation rate observed was 0.26, 0.16 and 0.13 g COD/g VSS/d at 20, 15 and 10 °C, respectively.

An increase in the particulate non-degradable fraction was observed with the decrease in the temperature, with a higher increase in the Colloidal fraction. In contrast, the Soluble non-degradable fraction was quite similar at all temperatures, indicating that particulate matter is more affected by temperature changes than the Soluble fraction, both on the degradation rate constant and the non-degradable fraction remaining.

In addition, it was observed that the Colloidal fraction was first disintegrated (physical mechanism) to particulate matter with size smaller than 0.45 mm and then went through hydrolysis and biodegradation of the Soluble fraction produced. In contrast, the Suspended Solids were partly degraded directly to Soluble and partly went through disintegration followed by hydrolysis to Soluble fraction. In both cases the degradation kinetics were similar to the original Soluble fraction.

A mathematical model was built based on the experimental results. To confirm the model and to validate the anaerobic kinetics values observed an anaerobic membrane bio-reactor (AnMBR) was operated for six months at 25 °C.

Very similar effluent concentration (65 mg COD/l) and average sludge accumulation (260 mg TSS/l/d) were observed for both model and experimental data. The good fit between the model prediction and the AnMBR experimental data confirms the validity of the kinetic data obtained at the different temperatures studied in batch experiments.