Influence of seasonality, wastewater treatment plant process, geographical location and environmental parameters on bacterial community selection in activated sludge wastewater treatment plants treating municipal sewage in South Africa

Proactive monitoring of changes in the microbial community structure in wastewater treatment bioreactors using phospholipid fatty acid analysis

Diverse microbial community structures (MCS) in wastewater treatment plants (WWTPs) are vital for effectively removing nutrients and chemicals from wastewater. However, the regular monitoring of MCS in WWTP bioreactors remains unattractive owing to the skill and cost required for deploying modern microbial molecular techniques in the routine assessment of engineered systems. In contrast, low-resolution methods for assessing broad changes in the MCS, such as phospholipid fatty acid (PLFA) analysis, have been used effectively in soil studies for decades. Despite using PLFA analysis in soil remediation studies to capture the long-term effects of environmental changes on MCS, its application in WWTPs, where the microbial mass is dynamic and operational conditions are more fluid, remains limited. In this study, microbial communities in a controlled pilot plant and 12 full-scale activated sludge plants (ASPs) were surveyed over a two-year period using PLFA analysis. This study revealed that changes in the MCS in wastewater bioreactors could be detected using PLFA analysis. The MCS comprised 59 % Gram-negative and 9 % Gram-positive bacteria, 31 % fungi, and 1 % actinomycetes. The abundances of Gram-negative bacteria and fungi were strongly inversely correlated, with an R2 = 0.93, while the fatty acids cy17:0 and 16:1ω7c positively correlated (R2 = 0.869). Variations in temperature, solid retention time, and WWTP configuration significantly influenced the MCS in activated sludge reactors. This study showed that WWTP bioreactors can be routinely monitored using PLFA analysis, and changes in the bioreactor profile that may indicate imminent bioreactor failure can be identified.

Pilot scale on-site demonstration and seasonality assessment of nitrogen recovery and water reclamation from pig's slurry liquid fraction

Livestock slurry has gathered significant interest as a secondary raw material for fertilisers industry due to its content on macronutrients -nitrogen, phosphorous, and potassium- and organic carbon. In this study, the performance of an on-site pilot plant composed by microfiltration, membrane-assisted stripping, and reverse osmosis for selective recovery of nitrogen as fertiliser and water reclamation was demonstrated for 2 years in a pig farm, referenced to 8 batches for seasonal assessment. Microfiltration mitigated the seasonal variation in the composition of pig slurry leading to stable process efficiency in the following steps. Membrane-assisted stripping resulted in the recovery of up to 56% of nitrogen as high-purity ammonium sulphate, and up to 42% of reclaimed water as reverse osmosis permeate. The proposed train of technologies reported proper performance and robustness during the whole demonstration period as it resulted in the production of reclaimed water and ammonium sulphate with no significant quality variations. The energy cost for both products obtained in this study was found in the average of the previous works reviewed with 12.49 kWh kg-1 NH3 produced, and 0.37 kWh m-3 of reclaimed water. The environmental assessment showed that nitrogen losses could be reduced by up to 90 kg N ha-1 d-1 by replacing manure spreading with precise fertilisation techniques, enabled by the selective recovery of nitrogen from SLF. Finally, the financial study showed that the scaling up of the proposed train of technologies would result in benefits for farms with more than 1600 pig heads.

Comparative analyses on nitrogen removal microbes and functional genes within anaerobic-anoxic-oxic and deoxidation ditch sewage-treating processes in Wuhan and Xi'an cities, China

Introduction

Anaerobic-anoxic-oxic (A2/O) and deoxidation ditch (DOD) processes are being increasingly preferred owing to their effectiveness in treating various wastes in wastewater treatment plants (WWTPs). Considering seasonal variations is crucial in optimizing treatment processes, ensuring compliance with regulations, and maintaining the overall efficiency and effectiveness of WWTPs. This study aimed to determine the influence of seasonality on nitrogen removing microbes and functional genes within A2/O and DOD processes in the humid Wuhan and semi-arid Xi'an cities, China.

Methods

The physicochemical parameters of water quality were determined, and molecular and bioinformatic analyses of the bacterial community and nitrogen metabolism functional genes in the two different treatment processes of two WWTPs were performed over four seasons.

Results and discussion

Our analyses revealed a significant difference in all physicochemical parameters across all experimental groups (p < 0.05). At the genus level, the abundance of Dokdonella, one unidentified genus of Nitrospiraceae, Terrimonas, and one unidentified genus of Chloroflexi was the highest in all groups. Generally, warmer seasons exhibited higher biodiversity indices. The A2/O system exhibited higher values in terms of most nitrogen metabolism functional genes than those of the DOD sewage treatment system. In both WWTPs, the abundance of most genes in spring and summer were higher than that of autumn and winter seasons. Taken together, changes in temperature, caused by seasonal changes, may contribute to changes in abundance of nitrogen metabolic functional genes.

Lessons learned from a one-year study of Legionella spp. cultivation from activated sludge samples

Risk assessment and management of Legionella spp. contamination in activated sludge in wastewater treatment plants is carried out using the culture method. Underestimation of Legionella spp. is frequently reported in the literature, but a comprehensive long-term study of the performance of the method under comparable conditions is still lacking. The aim of this study is to evaluate the recovery rate and limit of detection of the culture method for Legionella spp. from activated sludge samples collected during the different seasons of the year. Activated sludge samples spiked with Legionella pneumophila subsp. pneumophila strain Philadelphia-1 (mean concentration 5.2 ± 0.35 logCFU/mL) were analysed monthly for one year using the culture method. Three different sample pre-treatments were compared, namely filtration, acid treatment and thermal treatment, and the recovery rate and limit of detection were assessed for each. The recovery rate of the culture method for Legionella spp. depended on the type of sample pre-treatment and the season of activated sludge sampling, while the limit of detection depended only on the sample pre-treatment. The best performance of the culture method, defined as the combination of the highest recovery rate and lowest limit of detection, was obtained for the filtered acid pre-treated samples (recovery rate: 89 ± 4 %; limit of detection: 1.3 logCFU/mL in 83 % of the samples). The lowest limit of detection was observed for the filtered thermally pre-treated samples (1.0 logCFU/mL in 93 % of the samples). Simultaneously, both thermally pre-treated samples showed up to a third lower recovery rates than the other pre-treatments in winter, while untreated and acid pre-treated samples showed consistently high recovery rates (>80%, logCFU/mL). The recovery rates of the unfiltered and filtered thermally pre-treated samples showed significant weak to strong positive correlations with the organic and phosphorus load in the influent as well as with the water and atmospheric temperatures, indicating that the recovery rate depends on the seasonal variation of the wastewater composition. This study presents new insights into the detection and quantification of Legionella spp. in activated sludge samples and considers seasonal dependencies in analytical results.

Global diversity of airborne pathogenic bacteria and fungi from wastewater treatment plants

Wastewater treatment plants (WWTPs) have been recognized as one of the major potential sources of the spread of airborne pathogenic microorganisms under the global pandemic of COVID-19. The differences in research regions, wastewater treatment processes, environmental conditions, and other aspects in the existing case studies have caused some confusion in the understanding of bioaerosol pollution characteristics. In this study, we integrated and analyzed data from field sampling and performed a systematic literature search to determine the abundance of airborne microorganisms in 13 countries and 37 cities across four continents (Asia, Europe, North America, and Africa). We analyzed the concentrations of bioaerosols, the core composition, global diversity, determinants, and potential risks of airborne pathogen communities in WWTPs. Our findings showed that the culturable bioaerosol concentrations of global WWTPs are 102-105 CFU/m3. Three core bacterial pathogens, namely Bacillus, Acinetobacter, and Pseudomonas, as well as two core fungal pathogens, Cladosporium and Aspergillus, were identified in the air across global WWTPs. WWTPs have unique core pathogenic communities and distinct continental divergence. The sources of airborne microorganisms (wastewater) and environmental variables (relative humidity and air contaminants) have impacts on the distribution of airborne pathogens. Potential health risks are associated with the core airborne pathogens in WWTPs. Our study showed the specificity, multifactorial influences, and potential pathogenicity of airborne pathogenic communities in WWTPs. Our findings can improve the understanding of the global diversity and biogeography of airborne pathogens in WWTPs, guiding risk assessment and control strategies for such pathogens. Furthermore, they provide a theoretical basis for safeguarding the health of WWTP workers and ensuring regional ecological security.

Fine-Tuning of DADA2 Parameters for Multiregional Metabarcoding Analysis of 16S rRNA Genes from Activated Sludge and Comparison of Taxonomy Classification Power and Taxonomy Databases

Taxonomic classification using metabarcoding is a commonly used method in microbiological studies of environmental samples and during monitoring of biotechnological processes. However, it is difficult to compare results from different laboratories, due to the variety of bioinformatics tools that have been developed and used for data analysis. This problem is compounded by different choices regarding which variable region of the 16S rRNA gene and which database is used for taxonomic identification. Therefore, this study employed the DADA2 algorithm to optimize the preprocessing of raw data obtained from the sequencing of activated sludge samples, using simultaneous analysis of three frequently used regions of 16S rRNA (V1-V3, V3-V4, V4-V5). Additionally, the study evaluated which variable region and which of the frequently used microbial databases for taxonomic classification (Greengenes2, Silva, RefSeq) more accurately classify OTUs into taxa. Adjusting the values of selected parameters of the DADA2 algorithm, we obtained the highest possible numbers of OTUs for each region. Regarding biodiversity within regions, the V3-V4 region had the highest Simpson and Shannon indexes, and the Chao1 index was similar to that of the V1-V3 region. Beta-biodiversity analysis revealed statistically significant differences between regions. When comparing databases for each of the regions studied, the highest numbers of taxonomic groups were obtained using the SILVA database. These results suggest that standardization of metabarcoding of short amplicons may be possible.

Profiling pathogenic protozoan and their functional pathways in wastewater using 18S rRNA and shotgun metagenomics

Despite extensive research, little is known about the composition of eukaryotic protists in environmental samples. This is due to low parasite concentrations, the complexity of parasite diversity, and a lack of suitable reference databases and standardized protocols. To bridge this knowledge gap, this study used 18S rRNA short amplicon and shotgun metagenomic sequencing approaches to profile protozoan microbial communities as well as their functional pathways in treated and untreated wastewater samples collected from different regions of South Africa. Results demonstrated that protozoan diversity (Shannon index P-value = 0.03) and taxonomic composition (PERMANOVA, P-value = 0.02) was mainly driven by the type of wastewater samples (treated & untreated) and geographic location. However, these WWTPs were also found to contain a core community of protozoan parasites. The untreated wastewater samples revealed a predominant presence of free-living, parasitic, and potentially pathogenic protists typically found in humans and animals, ranging from Alveolata (27 %) phylum (Apicomplexa and Ciliophora) to Excavata (3.88 %) (Discoba and Parasalia) and Amoebozoa (2.84 %) (Entamoeba and Acanthamoeba). Shotgun metagenomics analyses in a subset of the untreated wastewater samples confirmed the presence of public health-importance protozoa, including Cryptosporidium species (3.48 %), Entamoeba hystolitica (6.58 %), Blastocystis hominis (2.91 %), Naegleria gruberi (2.37 %), Toxoplasma gondii (1.98 %), Cyclospora cayetanensis (1.30 %), and Giardia intestinalis (0.31 %). Virulent gene families linked to pathogenic protozoa, such as serine/threonine protein phosphatase and mucin-desulfating sulfatase were identified. Additionally, enriched pathways included thiamine diphosphate biosynthesis III, heme biosynthesis, Methylerythritol 4-Phosphate Pathway, methyl erythritol phosphate (MEP), and pentose phosphate pathways. These findings suggest that protozoan pathogens may possess metabolic and growth potential within WWTPs, posing a severe risk of transmission to humans and animals if inadequately disinfected before release. This study provides a baseline for the future investigation of diverse protozoal communities in wastewater, which are of public health importance.

Ammonium oxidizing bacterial populations in South African activated sludge wastewater treatment plants

This is the first study that describes ammonium oxidizing bacterial populations and correlations of these populations with a range of criteria in activated sludge wastewater treatment plants in South Africa. In this study, not only the influent but also the activated sludge chemistry was comprehensively characterized. Multivariate statistical analyses were used to determine the relative significances of the geographical location (factor: site), wastewater treatment plant process (factor: configuration), seasonality (factor: season), and environmental parameters on the ammonium oxidizing bacterial genera in six municipal activated sludge wastewater treatments plants from two sites (the cities of Cape Town and Ekurhuleni). The geographical location (site) was significant for selection of the ammonium oxidizing genera (Global ANOSIM R value = 0.538, p = 0.001). It was established that the inter-site differences were not climatic in origin, nor related to the composition of the influent, but were rather driven by the activated sludge chemistry. It was found using BEST analysis that the activated sludge ammonia, activated sludge total phosphate, and activated sludge total chemical oxygen demand were the most significant (p < 0.001) drivers for ammonium oxidizing bacterial selection (ANOSIM Global R value 0.419) and were significantly higher in the activated sludge from the City of Cape Town wastewater treatment plants. Nitrosospira was the most abundant ammonium oxidizing bacterial genus, with notably higher relative and estimated actual abundances in the City of Cape Town wastewater treatment plants than the City of Ekurhuleni wastewater treatment plants. The strong selection of Nitrosospira in the City of Cape Town wastewater treatment plants with higher nutrient concentrations strongly suggests that high concentrations of activated sludge ammonia, activated sludge total phosphate, and activated sludge total chemical oxygen demand are key selective drivers for this genus. PRACTITIONER POINTS: First comprehensive study describing ammonium oxidizing bacterial populations in Southern African domestic activated sludge wastewater treatment plants. The geographical location (site) was significant for selection of different ammonium oxidizing genera (Global ANOSIM R value = 0.538, p = 0.001). Inter-site differences driven by the activated sludge chemistry, not climate or influent wastewater composition. Selection of Nitrosospira driven by high concentrations of activated sludge ammonia, total phosphate and total chemical oxygen demand.