Wastewater Biology

• • The study of wastewater is very important with respect to public health due to the large microbial load they contain.
  • Some of the microorganisms may be harmful as the pathogenic orgnisms causing various water boarne where as some others may be crucial as decomposers of waste.
  • The majority of organisms present in wastewater are microorganisms (1 -10 μm).
• Prokaryotic and Eukaryotic Cells

  • On the basis of presence or absence of a distinct membrane bound nucleus (the region of the cell that contains genetic information). biologists recognize the existence of two fundamentally different types of cells in the microbial world, called prokaryotic and eukaryotic cells.
  • Eukaryotic cells have a true nucleus because their DNA is not enclosed within a nuclear membrane.
  • The nuclear region of a prokaryotic cell is referred to as nucleoid, rather than as a nucleus.
• Major Groups of Microorganisms

  • Archaea - differ from bacteria by the absence of peptidoglycan in their cell wall, the cell wall and cell membrane composition of the archaeabacteria is unique and allows them to survive in hostile conditions.
  • Such archaeabacteria include halophiles (salt- lovers), thermoacidophiles (heat and acid lovers) and methane producing bacteria.
• • Bacteria – they are unicellular organisms
  • Approx. 1.0 x 106/mL in fresh water.
  • Typically, 0.5 – 5 mm long and have many shapes including spheres, rods, vibrio and spiral shaped.
  • Algae – are heterogeneous organisms showing characteristic oxygen evolving type of photosynthesis. They are advantageous in oxidation ponds as they produce oxygen and maintain aerobic conditions.
• • Protozoa – they are non-photosynthetic unicellular organisms exhibiting aeukaryotic cell organization. They lack cell wall, some protozoa may be covered by pellicle outside the cytoplasmic membrane.
  • Fungi - One of the most important organisms bringing about recycling of minerals is fungus. All fungi are eukaryotes, they may be unicellular yeast like forms or the filamentous mycelial forms, composed of thin cottony strands called hyphae.
• • Contamination of food and water by microorganism is an important mode of disease transmission.
  • These microorganisms may come from fecal contamination by either human or animal excrements.
  • Wastewater generally shows presence of pathogenic organisms belonging to bacteria, protozoa, helminthes and viruses.
  • Common pathogenic bacteria found in waste water belong to the enteric group of bacteria.
• Indicator Organisms

  One of the most important criteria to check the contamination of surface water or waste waters is the presence of pathogenic microorganisms for example Vibrio cholerae.
• Enumeration of bacteria can be done either by directly counting the individual cells under a microscope or by indirect methods.
• Common Methods of Cell Enumeration

  • Direct cell counting - In this method a sample of bacterial cell suspension is observed under microscope and cells counted using special counting chambers
  • Viable cell counting by plating - Viable counts are obtained by either spread or pour plate method.
• • Membrane filtration - The water sample is passed through a membrane filter that has pore size smaller than bacteria. The filter retains the bacteria present in the water sample. The filter is then transferred to a solid agar medium, the colonies formed can be counted.
  • Multiple tube fermentation - It is useful when sample bacteria do not grow on solid medium.
  • Fluorescent measurement
  • Turbidimetric measurement
• Culture of Bacteria

  
  

  • The identification of pathogenic organisms particularly when there is a disease outbreak is very essential.
  • Selective media – they comprise chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another bacteria. This facilitates the isolation of bacteria of interest.
• • Differential media – they can distinguish morphologically and biochemically related groups of organisms. They comprise chemical compounds that produce characteristic changes in the appearance of bacterial growth and also in the medium surrounding bacterial colonies.
• Identification of Specific Organisms

  • Bacteria are identified on their morphological and biochemical characteristics based on the Bergy’s manual of Bacterial identification.
  • Of late, a variety of molecular techniques have been developed for the identification of specific bacteria.
  • The most important of these methods include the use of fluorescent antibodies, and nucleic acid probes.
  • These two techniques have gained importance because of their use in biological water treatment processes.
• Total coliform bacteria - bacterial species that are gram negative rods, capable of fermenting lactose with gas production. Growth at 35 + 0.5 degree celsius, form a distinctive colony in 24 to 48 hours eg Escherichia, citrobacter, enterobacter
• Fecal coliform bacteria - those bacterial species capable of producing gas or colonies at relatively higher tempreatures (44.5 + 0.2 degrees celsius)
• E. coli - most common indicator organism used as a representative of coliform bacteria
• Klebsiella - capable of growing at 35 + 0.5 degrees celsius to form gas
• Clostridium perfringens - an anaerobic spore forming rod, which is used as an indicator organism to test water pollution and to check the success of disinfection
• Fecal streptococci - used to check fecal contamination of water aided by MPN method