Improved performances and reduced energy consumption at an industrial wastewater treatment plant in response to a strategy of filamentous bulking control

Lab-scale research aiming to develop aerobic granular sludge in Sequential Batch Reactors (SBR) led to the design of new protocols for the control of filamentous bulking based solely on reactor feeding strategies. In industrial scale applications, the implementation of these protocols yielded excellent phosphorous removal and resulted in energy savings. Molecular techniques (quantitative PCR and high-throughput sequencing) proved crucial to understanding and controlling the process. This optimization study fits into today's environmental policies as encouraged by the European Union's Water Framework Directive (2000/60/EC). CONTEXT: FROM APPLIED RESEARCH TO PLANT IMPLEMENTATION In wastewater treatment, the activated sludge aerobic digestion process is widely used, both in industrial and domestic treatment plants. Using this process, bacteria develop in the form of slightly flocculated aggregates or flocs. Even after more than 100 years, activated sludge remains the benchmark technology for wastewater treatment. The advent of molecular tools like fluorescence in situ hybridization (FISH), quantitative PCR (qPCR) or high-throughput sequencing, make it now possible to understand microbiomes and from there, to intensify the process by developing complex granular microbial architectures, characterized by very high settling velocities (> 10 m/h). This topic constitutes one of the research topics developed by CEBEDEAU since 2010 in collaboration with UCL. From the first laboratory tests, it quickly appeared that the granular structures and the filaments were in close competition as they fed on the same substrates (certain volatile fatty acids). Major work on reactor operating conditions allowed controlling the filament population while creating dense microbial architectures. INDUSTRIAL APPLICATIONS AND RESULTS Based on this research, in October 2015 we started to apply a specific protocol for managing the cycles and phases of the SBR wastewater treatment plant at the dairy industry Luxlait. The aim was to specifically fight filaments while avoiding the use of even the slightest quantity of reagent. Over a year and a half later, the results are excellent, Thiothrix filaments are under control and no losses of suspended solids were observed in the overflow, despite sporadic peaks in organic loading. The biomass structured into dense aggregates, phosphorous was eliminated without co-precipitation reactive products and energy demand for aeration was reduced by 30.2%. 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. Microscopy analysis confirmed the transition between a bulking sludge towards a granular-like sludge . STATE OF RESEARCH AND PROSPECTS Alongside this topic on filamentous control, the relationship between the density of the biomass and the removal performances were also investigated, especially as part of the GRASS® (Granulated Activated Sludge System) project conducted in partnership with exelio, a company active in water treatment. This project aims to develop a compact biological wastewater treatment unit using Granulated Activated Sludge.