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Many wastewater treatment plants in the USA, which were originally designed as secondary treatment systems with no or partial nitrification requirements, are facing increased flows, loads, and more stringent ammonia discharge limits. Plant expansion is often not cost-effective due to either high construction costs or lack of land. Under these circumstances, integrated fixed-film activated sludge (IFAS) systems using both suspended growth and biofilms that grow attached to a fixed plastic structured sheet media are found to be a viable solution for solving the challenges. Multiple plants have been retrofitted with such IFAS systems in the past few years. The system has proven to be efficient and reliable in achieving not only consistent nitrification, but also enhanced bio-chemical oxygen demand removal and sludge settling characteristics. This paper presents long-term practical experiences with the IFAS system design, operation and maintenance, and performance for three full-scale plants with distinct processes; that is, a trickling filter/solids contact process, a conventional plug flow activated sludge process and an extended aeration process.

In order to evaluate the efficacy of using reduced sulfur species in lieu of conventional substrates, a sequencing batch reactor (SBR) was used to develop an autotrophic denitrifying culture which in turn was used to seed a static granular bed reactor (SGBR) for continuous flow treatment. Both bioreactors were able to quickly acclimate to the anoxic environment and achieve stable autotrophic denitrification within several weeks of being placed in operation. The seed for the SBR was obtained from operating basins at the Cedar Rapids plant. MiSeq analysis showed the presence of the autotrophic denitrifier Thiobacillus in the seed from the sulfur oxidation basin; however, Shinella and Sulfurovum became the dominant autotrophic denitrifiers in the SBR. Both the SBR and SGBR achieved excellent nitrate removal (i.e., >95%) with stoichiometric amounts of thiosulfate added to the synthetic influent. The results of this feasibility study suggest that anaerobic granules from the UASB at the plant serve as good seed biomass for autotrophic denitrification when augmented by sulfur oxidation basin and sulfide scrubber biomass, and that reduced sulfur species at the plant (or augmented with an external sulfur source) can serve as electron donors for nearly complete denitrification. • Practitioner points• Autotrophic denitrification of industrial wastewater was investigated to evaluate reduced sulfur species as electron donor for nitrogen removal. • An autotrophic denitrifying culture was cultivated in an SBR, and continuous autotrophic denitrification was accomplished in an SGBR. • No increase in head loss was observed in the SGBR, and it was able to operate without the need for backwashing in more than 200 days of operation. • Reduced sulfur was demonstrated to be a sufficient electron donor for nearly complete denitrification. • MiSeq analysis resolved primary species responsible for autotrophic denitrification in this study.

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