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ENVR 430-1 Microbial Control Measures by Wastewater Processes

ENVR 430-1 Microbial Control Measures by Wastewater Processes. Suggested Reading: Brock Chapter 28- Wastewater Treatment, Water Purification, and Waterborne Microbial Diseases pp. 934-942 (posted as .PDF file on website). Wastewater Impacts to Natural Receiving Waters.

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ENVR 430-1 Microbial Control Measures by Wastewater Processes

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  1. ENVR 430-1Microbial Control Measures by Wastewater Processes Suggested Reading: Brock Chapter 28- Wastewater Treatment, Water Purification, and Waterborne Microbial Diseases pp. 934-942 (posted as .PDF file on website)

  2. Wastewater Impacts to Natural Receiving Waters

  3. Wastewater Impacts to Natural Receiving Waters • Treated wastewater is often discharged to nearby natural waters • Biological oxygen demand (BOD) • Chemicals (nitrogen, phosphorus) • Synthetic Chemicals • Antibiotics • Microbial Pathogens • Metals

  4. Water Distribution System Water Treatment Plant Water Source Wastewater Collection Wastewater Treatment Plant Discharge to Receiving Water Water Use Water Use Cycle

  5. Pathogen Concentrations in Raw Sewage • Influenced by many factors: • Types and prevalence of enteric infections in the population • Geographic, seasonal, and climate factors • Water use patterns • Pathogen concentrations in raw sewage • Enteric Viruses and Protozoan Cysts: ~ 104/L • Enteric Bacteria: ~105/Liter

  6. Conventional Sewage Treatment

  7. Microbial Reductions in Wastewater Treatment • Treatment processes are designed for reduction of solids and organics • Targets are total suspended solids and BOD, not pathogens • Pathogens are removed by processes that reduce organic matter • Typical overall pathogen reductions ~90‑99%.

  8. Primary Treatment or Primary Sedimentation • Settle solids for 2‑3 hours in a static, unmixed tank or basin. • ~75-90% of particles and 50-75% of organics settle out as “primary sludge” • enteric microbe levels in primary sludge are ~10X higher than in raw sewage • Little removal of enteric microbes: typically ~50%

  9. Trickling Filter and Aeration Basin for Wastewater Treatment

  10. Secondary or Biological Treatment • aerobic biological treatment • activated sludge or trickling filtration • Settle out the biological solids produced (secondary sludge) • ~90-99% enteric microbe/pathogen reductions from the liquid phase • enteric microbe retention by the biologically active solids • Biodegradation of enteric microbes • proteolytic enzymes and other degradative enzymes/chemical • Predation by treatment microbes/plankton (amoeba, ciliates, rotifers, etc.)

  11. Waste Solids (Sludge) Treatment • Treatment of the settled solids from 1o and 2o sewage treatment • Biological “digestion” to biologically stabilize the sludge solids • Anaerobic digestion (anaerobic biodegradation) • Aerobic digestion (aerobic biodegradation) • Mesophilic digestion: ambient temp. to ~40oC; 3-6 weeks • Thermophilic digestion: 40-60oC; 2-3 weeks • Produce digested (biologically stabilized) sludge solids for further treatment and/or disposal • Waste liquids from sludge treatment are recycled through the sewage treatment plant • Waste gases from sludge treatment are released or burned if from anaerobic digestion: methane, hydrogen, etc.

  12. Processes to Further Reduce Pathogens (PFRP)Class A Sludge • Class A sludge: • <1 virus per 4 grams dried sludge solids • <1 viable helminth ovum per 4 grams dried sludge solids • <3 Salmonella per 4 grams of dried sludge solids • <1,000 fecal coliforms per gram dry sludge solids • Class A sludge or “biosolids” can be disposed by a variety of options • marketed and distributed as soil conditioner for use on non-edible plants)

  13. Processes for producing Class A sludge • thermal (high temperature) processes (incl. thermophilic digestion); hold sludge at 50oC or more for specified times • lime (alkaline) stabilization; raise pH 12 for 2 or more hours • composting: additional aerobic treatment at elevated temperature

  14. Land Application of Treated Wastewater: Alternative Disposal Option

  15. Facultative Oxidation (Waste Stabilization) Pond

  16. On-site Septic Tank-Soil Absorption System

  17. Modular Wastewater Treatment Systems electrochemical metals removal process, pH adjustment, coagulation, clarification, multi-media filtration, air stripping, activated carbon adsorption, final pH adjustment, sludge dewatering

  18. Wastewater Reuse • Wastewater is sometimes reused for beneficial, non-potable purposes in arid and other water-short regions • Often use advanced or additional treatment processes, sometimes referred to as “reclamation” • Biological treatment in “polishing” ponds and constructed wetlands • Physical-chemical treatment processes as used for drinking water: • Coagulation-flocculation and sedimentation • Filtration: granular medium filters; membrane filters • Granular Activated Carbon • Disinfection

  19. Disinfection • Disinfection is any process to destroy or prevent the growth of microbes • Many disinfection processes are intended to inactivate microbes by physical, chemical or biological processes • Inactivation is achieved by altering or destroying essential structures or functions within the microbe • Inactivation processes include denaturation of proteins, nucleic acids, and lipids

  20. When Wastewater Disinfection is Recommended or Required • Discharge to surface waters: • near water supply intakes • used for primary contact recreation • used for shellfish harvesting • used for irrigation of crops and greenspace • other direct and indirect reuse and reclamation purposes • Discharge to groundwaters: • used as a water supply source • used for irrigation of crops and greenspace • other direct and indirect reuse and reclamation purposes

  21. Disinfection of Wastewater • Intended to reduce microbes in 1o or 2o treated effluent • Typically chlorination • Alternatives: UV radiation, ozone, and chlorine dioxide • Good enteric bacterial reductions: typically, 99.99+% • Meet fecal coliform limits for effluent discharge • Less effective for viruses and parasites: typically, 90% reduction • Toxicity of chlorine and its by‑products to aquatic life now limits wastewater chlorination • Dechlorination • Alternative less toxic chemical disinfectants • Alternative treatment processes to reduce enteric microbes • granular medium filtration or membrane filtration

  22. Estimated Pathogen Reductions by Sewage Treatment Processes: An Example

  23. Calculating Microbial Reductions by Treatment Processes: Log10 vs. Percent • Microbial reductions are computed to normalize the raw data on treatment efficacy of different systems or at different sites • Reductions provide a uniform way to compare different treatment processes or systems Examples:

  24. Disinfection Kinetics • Disinfection is a kinetic process • increased inactivation with increased exposure or contact time • Chick's Law: disinfection is a first‑order reaction. (Nt/No = e-kT) • Assumptions of Chick’s Law • all organisms are identical • death (inactivation) results from a first-order or “single-hit” or exponential reaction • Seldom true in practice

  25. Disinfection Activity and the CT Concept • Disinfection activity can be expressed as the product of disinfection concentration (C) and contact time (T) • Assumes first order kinetics (Chick’s Law) • disinfectant concentration and contact time have the same “weight” or contribution in disinfection activity and in contributing to CT • Example: If CT = 100 mg/l-minutes, then • If C = 10 mg/l, T must = 10 min. for CT = 100 mg/l-min. • If C = 1 mg/l, then T must = 100 min. for CT = 100 mg/l-min. • If C = 50 mg/l, then T must = 2 min. for CT = 100 mg/l-min.

  26. Disinfection Activity and the CT Concept • So, any combination of C and T giving a product of 100 is acceptable because C and T are interchangeable • The CT concept fails if disinfection kinetics do not follow Chick’s Law (are not first-order or exponential)

  27. Common Disinfectants in Water and Wastewater Treatment • Free Chlorine • Monochloramine • Ozone • Chlorine Dioxide • UV Light • Low pressure mercury lamp (monochromatic) • Medium pressure mercury lamp (polychromatic) • Pulsed broadband radiation

  28. First Order Multihit Log Survivors Retardant Contact Time DISINFECTION AND MICROBIAL INACTIVATION KINETICS • Declining rate or “Shoulder” Curve Kinetics: • decline in disinfectant concentration over time; • multi-hit kinetics; • aggregation • Retardant Kinetics: • persistent fraction; • mixed populations; • different susceptibilities of microbes to inactivation; • aggregation Nt/N0

  29. Properties of an Ideal Disinfectant • Broad spectrum: active against all microbes • Fast acting: produces rapid inactivation • Effective in the presence of organic matter, suspended solids and other matrix or sample constituents • Nontoxic; soluble; non-flammable; non-explosive • Compatible with various materials/surfaces • Stable or persistent for the intended exposure period • Provides a residual (sometimes this is undesirable) • Easy to generate and apply • Economical

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