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BACKGROUND Microbial consortia resistant to high ammonia concentrations may facilitate biogas production from high ammonia‐containing wastes and manures during anaerobic digestion. Microbial communities were gradually enriched via sequential batch cultivations (stepwise exposure) at increasing ammonia concentrations up to the extremely high concentration of 9 g total ammonia nitrogen (TAN) L−1. This study examined the adaptation of anaerobic microbial consortia to high ammonia concentrations by the use of a complex substrate based on manure in order to generate tailor‐made inocula for bioaugmentation purposes. RNA analysis was performed to determine the microbial community composition and activity of anaerobic bacteria and methanogens. RESULTS The enrichment series was successful in terms of methane production at ammonia concentrations as high as 5 g TAN L−1 in comparison with the control concentration of 2 g TAN L−1. Methanosarcina was the core active dominant methanogen genus in all enrichment cultures and its relative activity was sharply increased at 3 g and 9 g TAN L−1. Cellulolytic bacteria activity mostly decreased with ammonia increase. Moreover, syntrophic butyrate and long‐chain fatty acid degraders along with hydrogenotrophic methanogens were activated at increased ammonia concentrations. CONCLUSIONS The results of the study demonstrated an efficient method to enrich ammonia‐tolerant microbial consortia for bioaugmentation purposes in biogas reactors with concentrations ≤5 g TAN L−1. RNA analysis revealed high relative abundances of Methanosarcina and hydrogenotrophic methanogens at high concentrations of ammonia. © 2020 Society of Chemical Industry

Wastewater treatment plants have been traditionally developed for the aerobic degradation of effluent organic matter, and are associated with high energy consumption. The adoption of sustainable development targets favors the utilization of every available energy source, and the current work aims at the identification of biomethane potential from non-conventional sources derived from municipal wastewater treatment processes. Byproducts derived from the primary treatment process stage were collected from four sewage treatment plants in Greece with great variation in design capacity and servicing areas with wide human activities, affecting the quality of the influents and the corresponding primary wastes. The samples were characterized for the determination of their solids and fats content, as well as the concentration of leached organic matter and nutrients, and were subjected to anaerobic digestion treatment for the measurement of their biomethane production potential according to standardized procedures. All samples exhibited potential for biogas utilization, with screenings collected from a treatment plant receiving wastewater from an area with combined rural and agro-industrial activities presenting the highest potential. Nevertheless, these samples had a methanogens doubling time of around 1.3 days, while screenings from a high-capacity unit proved to have a methanogens doubling time of less than 1 day. On the other hand, floatings from grit chambers presented the smallest potential for energy utilization. Nevertheless, these wastes can be utilized for energy production, potentially in secondary sludge co-digestion units, converting a treatment plant from an energy demanding to a zero energy or even a power production process.

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