Operation problems in activated sludge systems from Uruguay ¿Which bacteria are responsible?

Abstract

In Uruguay there are two types of Activated Sludge (AS) system when considering the wastewater and management of the systems. First, the urban wastewater of several cities are treated by diverse AS systems. These AS systems are managed by a public company (OSE: Obras Sanitarias del Estado). Second, industrial wastewaters are treated by the industries and therefore, AS system are also managed by private companies. So, there is high diversity of AS plants in Uruguay. However, scares information on operation problems such as filamentous bulking or foaming is available. Moreover, the diversity of filamentous bacteria in these systems has not been thoroughly studied in Uruguay. In this work we performed a national survey to obtain systematic information on the AS plants of Uruguay and determine if they have operation problems related to filamentous bulking or foaming. We also studied the diversity of the microbial communities by amplicon sequencing of the 16SrRNA gene to identified which bacteria might be related to these events. The urban wastewater plants have different designs and operation conditions according to the wastewater flow rates, region and age of the plant. Regarding industrial wastewater AS systems we gathered information treating diverse wastewaters from the production of malt, beverages, jam, dairy products, cellulose, paper, oil, wine, chemical products, meat, fish, poultry as well as solid waste treatment plants. Some of the plants have severe foaming of bulking problems other only sporadic events and some have never had any problems. We have the complete analysis for four plants (urban WW: PA, ET and SC; and one winery WW) and are processing the rest of the samples. The winery plant had a strong dominance of Trichococcus (34%), the samples from plants PA and ET had high abundance of Ca. Microthrix, both known to cause bulking problems. On the other hand, in SC plant, Dietzia was detected in high abundance, which has been described as responsible for foaming in AS. In samples from SC and PA, we detected a bacteria belonging to Chloroflexota (Caldilinaceae and Ca. Sarcinithrix), known to have filamentous morphology and some species have been related to bulking episodes.