Microbial Control and Wastewater Treatment Study Notes

Learning Objectives

• Understand terminology of bacterial control levels and types.
• Understand methods for killing bacteria using physical and non-antibiotic compounds.
• Learn about the disk diffusion test and its application.
• Comprehend principles of wastewater treatment.
• Identify which microbes are easier or harder to kill.

Wastewater Treatment

• Feces: Composed of approximately 80% bacteria.
• Sanitation: Process of removing harmful microbes making water drinkable (potable).
• Waste Treatment Process:
• Remove, isolate, sediment, and purify waste.
• Involves protozoan ecosystems that consume bacteria, enhancing the waste treatment process.
• Example: Chlorine treatment kills most microbes but leaves behind chemicals such as pharmaceuticals.

Treatment Phases

1. Primary Treatment: Screening and sedimentation of sewage.

• Sewage is screened, skimmed, and ground.
• Solid matter settles out in primary sedimentation tanks.

1. Secondary Treatment (Biological Oxidation):

• Primary effluent aerated to allow microorganisms to oxidize organic materials.
• Uses trickling filters or activated sludge systems.

1. Disinfection and Release:

• Effluent is disinfected (e.g., chlorination) before being released into the environment.

1. Sludge Digestion:

• Remaining sludge undergoes anaerobic digestion, producing methane.
• Dried sludge is disposed of or utilized in agriculture.

Methods for Killing Bacteria

• Oxidation/Reduction: Causes mutations in DNA and alters enzyme activity.
• Membrane Disruption: Leads to loss of proton motive force and integrity.
• Protein Folding Disruption: Alteration in folding due to temperature/chemical changes leads to dysfunction.

Key Terms

• Sepsis: Microbial contamination.
• Asepsis: Absence of significant contamination.
• Sanitization: Lowering microbial counts on utensils.
• Biocide/Germicide: Kills microbes.
• Bacteriostasis: Inhibiting microbes without killing them.
• Sterilization: Complete removal of all microbial life.
• Disinfection: Removal of pathogens.
• Antisepsis: Removal of pathogens from living tissue.

Physical Control of Microbes

• Dry Heat: Kills bacteria via oxidation; used in sterilization of lab equipment.
• Moist Heat: Denatures proteins by breaking hydrogen bonds; example - boiling eggs.
• Autoclaving: Utilizes steam under pressure (121°C for 30 min) for sterilization; common in hospitals/labs.
• Pasteurization: Low temperature exposure kills pathogenic bacteria while preserving proteins (e.g., milk).
• Filtration: Mechanical removal, effective against small microbes (use in lab settings and air filtration).
• Desiccation: Removal of water inhibits growth but does not necessarily kill all microbes.
• Radiation: Uses ionizing (gamma rays, X-rays) and non-ionizing (UV light) to kill or damage microorganisms.

Chemical Control of Microbes

• Disk Diffusion Test: A method to test the effectiveness of an antimicrobial compound on bacteria using a filter disk.
• Surfactants: Soap/detergents; low antimicrobial activity, effective mechanical removal.
• Chemical Preservatives: Organic acids, sulfur dioxide, sodium nitrates/nitrites in foods prevent spoilage.
• Alcohols: Denature proteins; effective but not sporicidal.
• Halogens: Chlorine and iodine inhibit protein synthesis and are used as disinfectants.
• Heavy Metals: Silver, copper, and mercury interfere with protein function but can be toxic.
• Aldehydes: Formaldehyde is a strong disinfectant and preservative.
• Chemical Sterilization: Done using ethylene oxide or vaporous hydrogen peroxide in closed environments.

Resistance of Microbes

• Most Resistant: Prions, endospores, mycobacteria.
• Least Resistant: Gram-positive bacteria, viruses with lipid envelopes.

Effective Use of Antimicrobials

• Different agents show varied effectiveness across bacterial genera; choose appropriate agent based on the microbial target.