**Advancements in Wastewater Treatment: Understanding Microbial Communities and Their Functions** ππ§**Introduction** π¬ The efficiency o...
Published on by Hossein Ataei Far, Deputy Manager of the Research, Technology Development, and Industry Relations Center at NWWEC
**Introduction** π¬
The efficiency of biological wastewater treatment systems is heavily influenced by the intricate interactions and structures of microbial communities. Although substantial laboratory research has been conducted on microbial consortia, a gap remains in understanding how microbial structure correlates with operational parameters in full-scale wastewater treatment plants (WWTPs). This review explores various types of microbial consortia in WWTPs, the role of extracellular polymeric substances (EPS) in microbial structure, and insights from advanced molecular techniques like high-throughput sequencing. It also addresses issues such as sludge bulking, microbial composition related to antibiotic and micropollutant removal, and how microbial activity impacts overall system efficiency.
**Types of Microbial Communities** π¦
**Extracellular Polymeric Substances (EPS)** π§«
- **EPS Production**: EPS are crucial for forming spatial structures within microbial communities. They are produced through cell lysis, secretion, and absorption and are primarily composed of proteins and polysaccharides.
- **Function of EPS**: EPS create a protective diffusion barrier around cells, shielding them from toxic compounds and facilitating microbial interactions, thereby influencing biomass structure and stability.
**Activated Sludge** π§
- **Formation**: Activated sludge consists of microbial flocs that form through physico-chemical adhesion and colony development. The size, shape, and stability of these flocs are influenced by filamentous bacteria and environmental stress.
- **Stability Issues**: Environmental stress can cause floc fragmentation and increase suspended solids in the effluent.
**Biofilm** π’
- **Structure**: Biofilm is a multi-layered microbial structure adhered to solid supports, characterized by channels and pores that facilitate nutrient and gene transfer.
- **Composition Differences**: Biofilm-derived EPS contains similar amounts of proteins and polysaccharides, whereas activated sludge EPS is predominantly protein-rich.
**Aerobic Granules** π
- **Technology**: Aerobic granules form through microbial self-immobilization, offering benefits such as improved settling and higher microorganism concentration.
- **Granule Formation**: The formation process is influenced by hydrodynamic shear, microbial competition, and specific metabolic activities. Granule size and structure are affected by organic load and nutrient diffusion.
**Microbial Composition in WWTPs** π¬
**Molecular Techniques** π
- **High-Throughput Sequencing**: This technique provides detailed insights into microbial diversity and community structure, surpassing traditional methods in resolution.
- **Community Dynamics**: Microbial community dynamics are influenced by both deterministic factors (e.g., competition, niche variables) and stochastic factors (e.g., random colonization, environmental fluctuations).
**Bacterial Diversity** πΏ
- **General Trends**: Proteobacteria, particularly Betaproteobacteria, dominate municipal WWTPs. Other prevalent phyla include Bacteroidetes, Acidobacteria, and Chloroflexi.
- **Filamentous Bacteria**: These have low diversity but can cause sludge bulking, with key species such as *Microthrix parvicella* often linked to bulking issues.
**Microbial Groups** π§¬
- **Nitrifiers**: This group includes *Nitrosomonas* sp. (ammonia-oxidizing) and *Nitrospira* sp. (nitrite-oxidizing). Their abundance and activity are affected by temperature and system type.
- **Denitrifiers**: Diverse groups facilitate denitrification, with community composition varying based on operational parameters and system design.
- **Anammox Bacteria**: Crucial for nitrogen removal in certain WWTP configurations, their community structure is influenced by operating conditions.
**Microorganisms in Nutrient Removal** βοΈ
- **Phosphorus Removal**: Polyphosphate-accumulating organisms (PAOs), such as *Accumulibacter* sp. and *Tetrasphaera* sp., play a key role. The balance between PAOs and glycogen-accumulating organisms (GAOs) affects phosphorus removal efficiency.
- **Nitrogen Removal**: Ammonia-oxidizing bacteria (AOB) and autotrophic ammonia-oxidizing archaea (AOA) are essential. Their balance and activity are influenced by influent concentrations and system design.
**Microorganisms in Micropollutant Removal** β»οΈ
- **Antibiotics and ARB**: WWTPs can be sources of antibiotic-resistant bacteria (ARB). Process design affects ARB abundance and distribution, and effective disinfection strategies are critical for controlling ARB spread.
- **Micropollutant Degradation**: Specific bacteria and enzymes are involved in degrading micropollutants like bisphenol A (BPA) and polycyclic aromatic hydrocarbons (PAHs). Long sludge retention times (SRTs) and certain bacterial strains enhance removal efficiency.
**Assessment of Microbial Activity** π
- **Metagenomics and Metatranscriptomics**: These methods assess microbial activity by analyzing gene expression and metabolic functions, offering insights into community dynamics and process efficiency.
**Reference:**
Cydzik-Kwiatkowska, A., & ZieliΕska, M. (2016). Bacterial communities in full-scale wastewater treatment systems. *World Journal of Microbiology and Biotechnology*, 32, 1-8.
**Figure 1**: A floc of bacteria at 400X magnification removing phosphorus from medium in the lab. All bacteria were stained green, with *Candidatus Accumulibacter Phosphatis* (phosphorus-accumulating) stained blue. Courtesy of Connor Skennerton. Source: Wikimedia Commons. This figure is shown in the American Society for Microbiology.