Long-term dynamics of the bacterial community in a Swedish full-scale wastewater treatment plant

Matrix-associated microbial communities in a nitrogen-removing on-site wastewater treatment system are largely structured by niche processes

On-site wastewater treatment systems (OWTSs) can be designed to promote microbial communities with naturally occurring metabolic functions desirable to wastewater treatment. Among such OWTSs are nitrogen-removing biofilters (NRBs), comprising a sand layer overlying a sand-lignocellulose (sand-lc) layer and intended to promote sequential nitrification and denitrification. The design of NRBs is based on the hypothesis that niche processes like environmental selection strongly structure the microbial communities, which predicts that immigrating wastewater communities and matrix-associated communities will be distinct and that the matrix communities in the two layers will be distinct. We characterized NRB microbial communities by 16S ribosomal RNA amplicon sequencing. Selection of the matrix-associated communities was indicated by clear differences from the immigrating community. For matrix-associated communities, alpha and beta diversity differed between the matrix layers, as did the relative abundances of many functional groups and genera. Functional groups with strict metabolisms were nearly exclusively detected in either the sand (ammonia and nitrite oxidizers) or sand-lc layer (methanogens), consistent with the niche hypothesis. Contrary to expectations, denitrifiers as a functional group were not present at greater relative abundance in the sand-lc than sand matrix because of a portfolio effect: some denitrifying genera were more abundant in the sand layer, whereas others were more abundant in the sand-lc layer. This study reveals niche processes acting at different levels of community organization for different biogeochemical functions, a crucial consideration in designing effective and reliable OWTSs to mitigate nitrogen pollution.

Performance and microbial community dynamics relationship within a step-feed anoxic/oxic/anoxic/oxic process (SF-A/O/A/O) for coking wastewater treatment

A step-feed anoxic/oxic/anoxic/oxic (SF-A/O/A/O) was developed and successfully applied to full-scale coking wastewater treatment. The performance and microbial community were evaluated and systematically compared with the anoxic/oxic/oxic (A/O/O) process. SF-A/OA/O process exhibited efficient removal of COD, NH₄⁺-N, TN, phenols, and cyanide with corresponding average effluent concentrations of 317.9, 1.8, 46.2, 1.1, and 0.2 mg·L^-1, respectively. In particular, the TN removal efficiency of A/O/O process was only 7.8%, with an effluent concentration of 300.6 mg·L^-1. Furthermore, polycyclic aromatic hydrocarbons with high molecular weight were the dominant compounds in raw coking wastewater, which were degraded to a greater extent in SF-A/OA/O. The abundance in Thiobacillus, SM1A02, and Thauera could be the main reason why SF-A/O/A/O was superior to A/O/O in treating TN. The microbial community structure of SF-A/O/A/O was similar among stages in system (P ≥ 0.05, Welch's t-test) and was less affected by environmental factors, which may have been one of the important factors in the system's strong stability.

Multivariate analysis of activated sludge community in full-scale wastewater treatment plants

We investigated changes in protozoa and metazoa community in relation to process parameters in activated sludge from four wastewater treatment plants (WWTPs) throughout the period of 1 year. Principal component analysis (PCA) showed that activated sludge from investigated treatment plants had different dominating species representatives and community composition mainly depends on individual features of the treatment plants. Redundancy analysis (RDA) showed that the temperature in bioreactors was the most relevant factor explaining changes in the microorganism community, whereas reduction rate of chemical oxygen demand (COD), biological oxygen demand (BOD₅), suspended solids (SS), and total nitrogen (TN) did not sufficiently explain the variation in protozoa and metazoan community composition. The results indicate that in stable working WWTP it is difficult to find a pronounced link between activated sludge species composition, process parameters, and plant configuration. Applied multivariate analysis can be a valuable tool for the exploration of the relations between community composition and WWTP process parameters.

Low-Temperature Adapted Nitrifying Microbial Communities of Finnish Wastewater Treatment Systems

In this study, the microbial community of nitrifying activated sludge adapted to Finnish climate conditions was studied to clarify the microbial populations involved in low-temperature nitrification. Microbial community analysis of five full-scale wastewater treatment plants (WWTPs) showed several differences compared to WWTPs from other countries with a similar climate. In particular, very low abundance of ammonium oxidizing bacteria (AOBs) (altogether ˂ 0.25% of total community) as well as typical NOBs (˂0.35%) and a high abundance of orders Cytophagales and Micrococcales was observed in all Finnish WWTPs. To shed light on the importance of autotrophic and heterotrophic nitrifying processes, laboratory studies of activated sludge were carried out with a presence of and a lack of organic carbon in wastewater at 10 ± 1 °C. Two different sludge retention times (SRTs) were compared to determine the effect of this operational parameter on low-temperature nitrogen removal. The important role of previously reported Candidatus Nitrotogaarctica for nitrite oxidizing in cold climate conditions was confirmed in both full-scale and laboratory scale results. Additionally, potential participation of Dokdonella sp. and Flexibacter sp. in nitrogen removal at low-temperatures is proposed. Operation at SRT of 100 days demonstrated more stable and efficient nitrogen removal after a sharp temperature decrease compared to 14 days SRT.

Density-Based Separation of Microbial Functional Groups in Activated Sludge

Mechanistic understanding of how activated sludge (AS) solids density influences wastewater treatment processing is limited. Because microbial groups often generate and store intracellular inclusions during certain metabolic processes, it is hypothesized that some microorganisms, like polyphosphate-accumulating organisms (PAOs), would have higher biomass densities. The present study developed a density-based separation approach and applied it to suspended growth AS in two full-scale domestic water resource recovery facilities (WRRFs). Incorporating quantitative real-time PCR (qPCR) and fluorescence in situ hybridization (FISH) analyses, the research demonstrated the effectiveness of density-based separation in enriching key microbial functional groups, including ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and PAOs, by up to 90-fold in target biomass fractions. It was observed that WRRF process functionalities have significant influence on density-based enrichment, such that maximum enrichments were achieved in the sludge fraction denser than 1.036 g/cm³ for the enhanced biological phosphorus removal (EBPR) facility and in the sludge fraction lighter than 1.030 g/cm³ for the non-EBPR facility. Our results provide important information on the relationship between biomass density and enrichment of microbial functional groups in AS, contributing to future designs of enhanced biological treatment processes for improved AS settleability and performance.