The Impact of Microbial Ecology and Chemical Profile on the Enhanced Biological Phosphorus Removal (EBPR) Process: A Case Study of Northern Wastewater Treatment Works, Johannesburg

Abstract

The impact of polyphosphate-accumulating organism (PAO) and glycogen-accumulating organism (GAO) populations as well as of the chemical profile on the performance of Unit-3 (open elutriation tanks) and Unit-5 (covered elutriation tank) of the City of Johannesburg Northern Wastewater Treatment Works was determined. Physicochemical parameters of wastewater samples were measured using standard methods. Bacterial diversity was determined using 16S rRNA gene amplicon pyrosequencing of the variable region V1-3. Results showed soluble COD concentrations from settled sewage for Unit-3 at 192.8 mg COD/L and for Unit-5 at 214.6 mg COD/L, which increased to 301.8 mg COD/L and 411.6 mg COD/L in the overflow from elutriation tanks and decreased to 170.9 mg COD/L and 256.3 mg COD/L at the division boxes, respectively. Both long-chain volatile fatty acids (heptanoic acid, isobutyric acid, 3-methylbutanoic acid, pentanoic acid, 4-methylpentanoic acid, methylheptanoic acid) and short-chain volatile fatty acids (acetic acid, propionic acid, isobutyric acid) were present within concentration ranges of 17.19 mg/L to 54.98 mg/L and 13.64 mg/L to 87.6 mg/L for Unit 3 and 38.61 mg/L to58.85 mg/L and 21.63 mg/L to 92.39 mg/L for Unit 5, respectively. In the secondary settling tanks, the phosphate-removal efficiency in Unit-5 appeared to be slightly higher (0.08 mg P/L) compared to that of Unit-3 (0.11 mg P/L). The average DO concentrations (2.1 mg/L and 2.2 mg/L) as well as the pH values (pH 7 to pH 7.5) were found to be slightly higher in Unit-5 in the aerobic zones. The high presence of PAOs in the bioreactors (Unit-5: Dechloromonas (14.96%), Acinetobacter (6.3%), Zoogloea (4.72%) in the anaerobic zone and Dechloromonas (22.37 %) in the aerobic zone; Unit-3: Dechloromonas (37.25%) in the anaerobic zone and Dechloromonas (23.97%) in the aerobic zone) confirmed the phosphate-removal efficiencies of both units. Negligible GAOs were found in the aerobic zones (Defluviicoccus spp.: 0.33% for Unit-5 and 0.68% for Unit-3) and in the anaerobic zones (Defluviicoccus: 9.8% for Unit-3). The high microbial diversity and a negligible percentage of GAOs in Unit-5 could contribute to its high phosphate-removal efficiency, although results did not indicate statistically significant differences between the unit with a covered elutriation tank (Unit-5) and that with open elutriation tanks (Unit-3).

Comparing Bacterial Diversity in Two Full-Scale Enhanced Biological Phosphate Removal Reactors Using 16S Amplicon Pyrosequencing

“…4). The observed unique phyla have similarly been reported elsewhere in low proportions in activated sludge [5,8,32]. In terms of their abundance in both plants separately, five phyla -Proteobacteria (72.37%), Bacteriodetes, Firmicutes, Actinobacteria, and Chloroflexi -occupied approximately 95.71% of all classified bacteria from the failed EBPR, while in the successful EBPR Proteobacteria, Bacteriodetes, Firmicutes, Actinobacteria, and Planctomycetes were the most abundant with approximately 95.77% of the entire classified bacterial population (Fig.…”

“…In order to enhance the wastewater treatment efficiency in removing phosphate, fermenter has been incorporated in the EBPR systems. The fermenter plays an important role in augmenting the availability of VFA needed by phosphate-accumulating organisms to ensure reliable phosphorus removal [5]. In the present study, fermenting bacterial genera such as Acidovorax (2.36%), Enhydrobacter (1.25%), Aeromonas (3.62%), Tolumonas (1.81%), Prevotella (7.09%), Faecalibacterium (0.56%), Fibrobacter (1.81%), unclassified Comamonadaceae (6.12%), unclassified Moraxellaceae (3.34%), unclassified Prevotellaceae (40.89%), and unclassified Lachnospiraceae (4.73%) were found in higher abundance in the successful EBPR as compared to the failed EBPR (Table S7), and are seen as crucial for VFA production [36][37].…”

“…The integrity and purity of the metagenomic DNA was later assessed on the 0.8% agarose gel and NanoDrop TM spectrophotometer (NanoDrop TM 2000, Thermo Scientific, Japan). The PCR reaction was performed on all the extracted metagenomic DNA samples as well as negative controls using the universal primer 27F and 518R [5]. This primer pair amplifies approximately the 500 bp of 16S rRNA gene sequence targeting variable region V1 to V3 of the 16S rRNA gene.…”

“…It has then been reported that the naturally occurring polyphosphate-accumulating organisms (PAOs) were responsible for phosphorus removal, whereas the presence of glycogen-accumulating organisms (GAOs) in the EBPR process was the main cause of EBPR deterioration as the latter also compete for volatile fatty acid (VFA) as a substrate for energy [5]. However, the advent of molecular tools showed that several pure cultures of PAOs such as Acinetobacter, Microlunatus, Tetrasphaera, and Lampropedia genera were not having great effect in full-scale wastewater treatment plants (WWTPs), and a high diversity of phylogenetic groups involved in the removal of phosphorus were present in EBPR sludge [8].…”

“…Due to their advantages over the conventional methods, biological treatment methods such as enhanced biological phosphorus removal (EBPR) have been widely seen as the most effective and eco-friendly option of the available treatment processes of wastewater [3]. This process requires the presence of diverse microorganisms to remove organic contents and nutrients as well as other toxic materials from domestic and industrial wastewater and to protect receiving water bodies from eutrophication [4][5]. Although the EBPR process is regarded as one of the most successful for the removal of phosphorus from wastewater, the phosphorus removal capacity can also be prone to apparent instability and unreliability, and deterioration is often attributed to detrimental bacteria present in the system [4].…”