Filamentous bulking caused by Thiothrix species is efficiently controlled in full-scale wastewater treatment plants by implementing a sludge densification strategy

Abstract

Filamentous bulking caused by Thiothrix species is responsible for sludge washout and loss of performance in dairy wastewater treatment plants. A long-term study was conducted over 1.5 years to test three different mitigation strategies in a full-scale plant composed of two parallel sequential batch reactors (SBR1 and 2). Strategies based on polyaluminium chloride addition and volatile fatty acids reduction were ineffective to permanently solve the problem. On the contrary, modification of the reactor cycle based on the implementation of a periodic starvation proved efficient to solve the biomass wash-out and drastically reduce the sludge volume index in both reactors. Bacterial diversity analysis using 16S amplicon sequencing and quantitative PCR indicated a reduction of Thiothrix abundance from 51.9 to 1.0% in SBR1 and from 71.8 to 0.6% in SBR2. Simultaneously, the abundance of the glycogen-accumulating bacterium Candidatus Competibacter increased in both reactors. Microscopy analysis confirmed the transition between a bulking sludge towards a granular-like sludge. This study confirms the applicability of a periodic starvation to (1) solve recurring Thiothrix bulking, (2) convert loose aggregates into dense and compact granular-like structures and (3) considerably reduce energy demand for aeration.

Impacts of solids retention time and antibiotic loading in activated sludge systems on secondary effluent water quality and microbial community structure

“…Thauera has been linked to microbial community adaptation to denitrification conditions (Liu et al., ), which is consistent with the nitrogen cycling summarized previously in Supporting information Table , and members of Saprospiraceae F are proficient in degrading complex organic compounds (McIlroy & Nielsen, ), which might explain the greater biotransformation of bulk organic matter observed with longer SRTs (Figure ). For the SRT of 20 days, Nitrospira (a known nitrite oxidizer; Fujitani, Aoi, & Tsuneda, ) emerged within the microbial community, while Thiothrix (a known filamentous bulking microorganism; Henriet, Meunier, Henry, & Mahillon, ) decreased in relative abundance as compared with the 2‐ and 7‐day SRTs.…”

Microbial Ecology of Biofiltration Units Used for the Desulfurization of Biogas

“…(Gammaproteobacteria); Sulfurimonas denitrificans (Epsilonproteobacteria); Thiobacillus denitrificans, Thiobacillus sajanensis and Thiobacillus plumbophilus (Betaproteobacteria). Thiothrix is a filamentous SOB that thrives in wastewaters characterized by high organic loads and elevated concentrations of low molecular weight fatty acids and reduced sulfur compounds, low dissolved oxygen (DO) concentrations and deficit in phosphorus and nitrogen [85]. The overgrowth of Thiothrix is related to activated sludge bulking in WWTPs.…”

The microbial community in filamentous bulking sludge with the ultra-low sludge loading and long sludge retention time in oxidation ditch

“…Similarly, Gordonia (5.1%) was the dominant bacterial genus in WWTPs with low DO, long SRT and low temperature 16 . A long-term study that was conducted to identify the dominant filamentous bacteria in a full-scale WWTP found that Thiothrix (51.9%) was the dominant filamentous bacterial genus with the high COD concentration, low DO and nutrient deficits 30 . However, in this study, the relative abundance of Gordonia (0.14–1.28%) and Thiothrix (0.01–0.06%) were low and were not the dominant filamentous bacterial genera in oxidation ditch bulking sludge.…”

“…The mass propagation of Haliscomenobacter hydrossis caused sludge bulking and resulted in high sludge loading and long SRT 29 , whereas Nocardia induced sludge bulking when the sludge loading was less than 0.5 kg BOD 5 /(kg MLSS·d) 13 . Thiothrix proliferated and caused sludge bulking at high chemical oxygen demand(COD) concentration, low DO and low nutrient 30 . Excessive proliferation of Tetrasphaera and Trichococcus Nostocoida limicola I caused sludge bulking at low temperature 31 .…”