Kraft mills are responsible for the massive discharge of highly
polluted effluents, and new bleaching processes (i.e. Total Chlorine
Free (TCF)) is presented as a feasible option to reduce this
environmental impact. However, increased TCF pulp production is
accompanied by an increase in chelate use. The most commonly used
chelates, ethylenediaminetetraacetic acid (EDTA) and
diethylenetriaminepentaacetic acid (DPTA), are considered to be
relatively persistent substances in water treatment plants, and
consequently environmentally critical compounds. The purpose of this
work is to investigate DPTA behaviour in an anaerobic system. An
Anaerobic Filter (AF) was operated with three different DPTA load rates
(LRDPTA = 0.07 - 0.28 gDPTA/L x d), and the operating strategy was to
maintain the anaerobic system stable during the entire operation
(alkalinity ratio below 0.3). The AF's maximum Chemical Oxygen Demand
(COD) removal was 59%, whereas the Biological Oxygen Demand (BOD5) was
around 95%. However, only 5% of DPTA removal was observed under
anaerobic conditions during the first operating period. Scanning
electronic microscopy indicates that the operating system reduced
microorganism biodiversity