Benzalkonium chloride effect over activated sluge

As a representative of the most common type of WWTPs in Costa Rica, we selected a small size residential plant located in the city of Mora, San José (9.920687, -84.243345). From the selected plant we collected a sample of the activated sludge (4 L) from an aeration tank (4 meters deep). The sample was then transferred to a sterile amber glass container, kept at a temperature of 4 ºC, and immediately transported to the laboratory. Once in the laboratory, the sample was divided into three portions. The first portion (T1 samples) was frozen immediately and used as a baseline. The second portion (T2 samples) was homogenized, distributed in 3 aliquots of 500 mL (A, B and C) and enriched with 10 mg BAC/L. Later, the three containers enriched were incubated with aeration at a temperature of 20 ºC for 96 hours. The third portion (T3) was used as a control of the process, where it followed the same protocol as B samples except that it did not have enrichment with BAC.