Effect of anaerobic phases length on denitrifying dephosphatation biocenosis – a case study of IFAS-MBSBBR

Gnida et al. BMC Microbiology (2020) 20:222 https://doi.org/10.1186/s12866-020-01896-3 RESEARCH ARTICLE Open Access Effect of anaerobic phases length on denitrifying dephosphatation biocenosis – a case study of IFAS-MBSBBR Anna Gnida1* , Monika Żubrowska-Sudoł2, Katarzyna Sytek-Szmeichel2, Jolanta Podedworna2, Joanna Surmacz-Górska1 and Dorota Marciocha1 Abstract Background: The study aimed to evaluate the influence of the duration times of anaerobic phases on the bacterial biocenosis characterisation while denitrifying dephosphatation in the Integrated Fixed-Film Activated Sludge – Moving-Bed Sequencing Batch Biofilm Reactor (IFAS-MBSBBR). The experiment was conducted in a laboratory model. The study consisted of four series, which differed in terms of the ratio of the anaerobic phases. duration concerning the overall reaction time in the cycle. The anaerobic phases covered from 18 to 30% of the whole cycle duration. During the reactor performance that took 9 months, the influent and effluent were monitored by analysis of COD, TKN, NH4-N, NO2-N, NO3-N, TP, PO4-P, pH, alkalinity and the phosphorus uptake batch tests. Characterisation of the activated sludge and the biofilm biocenosis was based on fluorescent in situ hybridisation (identification of PAO and GAO) and the denaturing gradient gel electrophoresis patterns. Results: The organic compounds removal was high (more than 95.7%) independently of cycle configuration. The best efficiency for nitrogen (91.1%) and phosphorus (98.8%) removal was achieved for the 30% share of the anaerobic phases in the reaction time. Denitrifying PAO (DPAO) covered more than 90% of PAO in the biofilm and usually around 70% of PAO in the activated sludge. A substantial part of the polyphosphate accumulating organisms (PAO) community were Actinobacteria. The denitrifying dephosphatation activity was performed mainly by Accumulibacter phosphatis. Conclusions: High nutrient removal efficiencies may be obtained in IFAS-MBSBBR using the denitrifying dephosphatation process. It was found that the length of anaerobic phases influenced denitrification and the biological phosphorus removal. The extension of the anaerobic phases duration time in the reaction time caused an increase in the percentage share of denitrifying PAO (DPAO) in PAO. The biocenosis of the biofilm and the activated sludge reveal different species patterns and domination of the EBPR community. Keywords: Denitrifying dephosphatation, Polyphosphate accumulating organisms, Moving bed reactor, Activated sludge, Biofilm, Wastewater treatment * Correspondence: 1 Department of Environmental Biotechnology, Faculty of Energy and Environmental Engineering, Silesian University of Technology, 2A Akademicka St., 44-100 Gliwice, Poland Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Gnida et al. BMC Microbiology (2020) 20:222 Background Efficient removal of nutrient compounds such as carbon, nitrogen, and phosphorus from different types of wastewater is still one of the priority issues concerning the environment and its protection. Many wastewater treatment plants (WWTPs) suffer from a too low load of organic compounds in wastewater concerning the requirements associated with the removal of nitrogen and phosphorus [1]. The problem is usually solved by a dosage of an external carbon source or by performing chemical dephosphatation, which increases the operating costs of the plant. The alternative seems to be the use of denitrifying dephosphatation, which is based on the obtainment of a specific group of organisms capable of accumulating orthophosphates in anoxic conditions with a simultaneous reduction of nitrates to nitrogen gas. The discovery of a bacterial group capable of binding the excess of phosphates under anoxic conditions and at the same time reducing nitrate or nitrite to nitrogen gas (DPAO, denitrifying polyphosphate accumulating organisms) resulted in acknowledging the possibility of using this phenomenon (denitrifying dephosphatation) to a synergistic removal of nitrogen and phosphorus from wastewater with significantly lower demand for organic carbon. Denitrifying dephosphatation has been attracting the attention of researchers for more than two decades now. It shows important advantages apart from simultaneous dephosphatation and denitrification. These are a lower demand for organic carbon, reduction of aeration (lower oxygen demand), and decline in the biomass growth [2, 3]. Although the process allows reducing wastewater treatment costs, it is not ideal and easy to apply. Denitrifying dephosphatation shows a lower denitrification efficiency in comparison with traditional solutions for the N and P removal. Moreover, the demand for N:P of 7 is rarely encountered in municipal wastewater [3]. Thus, ensuring optimal conditions and the enrichment of DPAO can be difficult. Due to the mentioned advantages and disadvantages of the process, it is necessary to search for such working conditions of the bioreactor in which the performance of denitrifying dephosphatation represents the highest possible share in the total efficiency of nitrogen and phosphorus removal represented by all processes. The factors that promote growth and stimulate the activity of DPAO in activated sludge and favour the denitrifying orthophosphate consumption have a significant influence on the efficiency increase in denitrifying dephosphatation. Enrichment of DPAOs requires conditions inhibiting the growth of other bacteria that can compete with them. DPAOs proliferate particularly easily in a continually repeating sequence of alternating anoxic and anaerobic conditions, while in anaerobic conditions sufficient quantities of a readily biodegradable organic substrate Page 2 of 12 (e.g. acetates) must be available [4, 5]. The load of the substrate should provide an adequate efficiency of the orthophosphates release (...truncated)