COD Fractionation of Toluca´s Municipal Wastewaters using the STOWA Protocol

Abstract

Activated Sludge Model N° 1 (ASM1), published in 1987, is widely used today. The creation of a database of typical COD fractionation patterns for municipal wastewaters (WW) in Mexico and in Latin America will facilitate the use of dynamic modeling and simulation of WW treatment plants (WWTP) in the sub-region. This research used the physiochemical
characterization protocol developed by the Netherlands Foundation of Applied Water Research (STOWA) to determine the COD fractionation pattern for wastewater in the city of Toluca. Respirometric tests were also performed to estimate some of the kinetic parameters for the ASM1 and to evaluate the amount of heterotrophic biomass, XH0, initially present in the
wastewater. The growth (μHmax) and decay rates (bH) were 5.7 d-1 and 0.54 d-1 (at 20° C), respectively, while XH0 represented as much as 14% of total COD. The average COD fractions in the pre-settled WW were: 13% inert soluble COD (SI), 23% readily biodegradable substrate (SS), 48% slowly biodegradable substrate (XS) and 16% inert particulate COD (XI). With respect to the SS fraction, large differences were noted between values from the respirometric method (SS-respiro) and those from the physiochemical protocol (SS-phys). The differences between SS-respiro and SS-phys, along with the non-repeatability of the BOD measurements
were the main weaknesses observed when attempting to implement the STOWA protocol at the local level.