A survey of filamentous organisms at the Deer Island treatment plant

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

The use of pure oxygen for aeration in aerobic wastewater treatment: A review of its potential and limitations

In aerobic wastewater treatment, aeration is the most critical element of the treatment system. It supplies microorganisms with the required dissolved oxygen, maintains solids in suspension and, in membrane bioreactors, it controls fouling. However, conventional activated sludge is limited to the treatment of low strength wastewaters, as higher loadings require both higher biomass and higher dissolved oxygen concentrations. By replacing air with pure oxygen, oxygen transfer rates increase at lower flowrates. In this work, the potential and limitations of pure oxygen aeration are reviewed. The effect of the system's operational parameters and the mixed liquor characteristics on oxygen transfer, and vice versa, are determined. Pure oxygen treats higher loadings without compromising effluent quality. Fine bubbles are more efficient in oxygen transfer due to their increased contact area. However, pure oxygen is not always essential, so it is recommended to be restricted to applications where air is not adequate.

Use of an aerobic selector to overcome filamentous bulking in an activated sludge wastewater treatment plant

An urban wastewater treatment plant (WWTP) with two different parallel lines of treatment and located in the north of Portugal was studied during four months, following recurrent episodes of filamentous bulking caused by Sphaerotilus natans and eventual occurrences of Nocardioforms and Type 1863. An aerobic selector was introduced in both lines in the beginning of the studied period, suppressed in one of the lines during six weeks, and then put into operation again until the end of the study. A total of 14 filamentous bacteria morphotypes were identified. The results showed that the presence of an aerobic biological selector in continuous operation prevented the overgrowth of the filamentous Type 1863, of Nocardioforms and, in particular, of S. natans. Simultaneously, it allowed lowering the oxygen levels in the aeration tanks without negative consequences in the overall performance of the WWTP, namely bulking occurrence. Dissolved oxygen (DO) in the aeration tank varied initially between 2 and 3 mg/L, but the introduction of the selector enabled to lower it to 1-1.5 mg/L in the aeration tank and around 0.5 mg/L in the selector. A significant energy save was allowed, even considering the aeration of the selector. The results are more relevant if one considers the fact that the main cause of the bulking problems in this WWTP was the overgrowth of S. natans, a filamentous bacterium known to be stimulated by low DO levels.