Presentation on theme: "On Site Sewage Facility Pathogen Removal & Disinfection Alternatives Stephanie L Sturman, R. S., D. R., S. E. Senior Inspector, Watershed Protection Group,"— Presentation transcript:
On Site Sewage Facility Pathogen Removal & Disinfection Alternatives Stephanie L Sturman, R. S., D. R., S. E. Senior Inspector, Watershed Protection Group, Harris County Public Infrastructure Department
What is the purpose of disinfecting wastewater? To destroy, de-activate or reduce to an acceptable level, remaining pathogenic organisms in wastewater to prevent the transmission of infection, illness or disease.
What is a pathogenic organism ? An infectious agent or organism that causes or is capable of causing a disease.
Pathogen Survival Even after proper treatment processes have occurred, pathogens can survive for days in the external environment, and most notably, on plant life, (your fruit & vegetable gardens)!
Pathogen Survival (cont.) Transmission of the pathogen, whether directly or not, is most commonly through ingestion. The following pathogens are known to be transmitted by the fecal to oral route.
Common Pathogenic Bacteria in Wastewater Salmonella – Typhoid Fever (general pain, fever, intestinal bleeding) Foodborne Illness Shigella – Shigellosis (Fever, Diarrhea [usually bloody] & Stomach Cramps.) E. Coli (also, an indicator bacterium) – Only a few strains cause infection – Diarrhea, fever, abdominal cramps
Most Recent Bacterial Outbreak? 1. Listeria on Cantalopes 2. Salmonella on Spinach
Common Pathogenic Viruses in Wastewater Rotovirus (stable in the environment) – Fever, Vomiting, Diarrhea, Dehydration Hepatitus A (highly contagious) – Fatigue, Nausea, Loss of appetite, Jaundice Norwalk Virus – Vomiting, Diarrhea, Low-grade fever (photo courtesy of the EPA)
Common Pathogenic Protozoa in Wastewater Giardia Lambia – Nausea, Bloating, Diarrhea, Anorexia Entamoeba histolytica – Colitis, Dysentery, Diarrhea, Liver abscess Cryptosporidium parvum – Mild to Chronic Diarrhea
So now we know what some of the bugs in our wastewater are, how do we eliminate pathogens in wastewater?
Pathogen removal/ disinfection First: Primary Treatment (settling and entrapment) - Is septic tank large enough to handle the organic load and to trap most pathogens in the sludge or scum layer? -Is it sized to prevent too much “carryover”? - Better effluent = Better Disinfection
Pathogen removal/ disinfection (cont.) Second: Secondary Treatment (Aerobic Treatment Systems, Filter Media Systems) Secondary treatment can remove up to 90% of organics and solids Is the Treatment Unit sized properly? Is it functioning properly?
Pathogen removal/ disinfection (cont.) Third: Disposal or Disinfection & disposal – In subsoil disposal, disinfection occurs in the soil itself – In surface disposal, we need to disinfect the waste water further.
Assuming the system is sized and functioning well, what types of disinfection are available to the On Site Septic System owner? Chlorination Ultraviolet Light Ozone
Chlorination Tablet & Liquid Chlorination The appropriate chlorine for disinfecting wastewater is either Calcium Hypochlorite or Sodium Hypochlorite. When diluted with the wastewater, Hypochlorous Acid is formed, which actually attacks the pathogens. Chlorine disinfects by attacking the pathogens’ cell wall & interior structures, causing oxidation and death. 1.Very common disinfectant/ (disinfectant of choice). 2.Easy to use and monitor/measure 3.More effective on bacteria than on viruses or protozoa 4.May leave a chemical residue in the environment.
Examples of chlorinators
Ultraviolet Light 1.Ultraviolet Light kill pathogens by sending electromagnetic energy from the lamp to the cell’s genetic material, which kills or prevents cell reproduction. 2.More effective at pathogenic virus and protozoa removal than chlorination. 3.No chemical residue in the environment. 4.The intensity of the light is important for proper disinfection (250 nm-270 nm is considered the optimal range)
Ultraviolet Light (cont.) 4.Very important to have a fairly clear effluent so the UV light can penetrate all pathogens passing through. 5.Requires knowledge in installation, regular maintenance, and cleaning. 6.Bulbs need to be changes about once a year.
Examples of UV Devices Not really for Septic systems, but the effect is similar- ZAP !
Ozone Utilizes pure oxygen or pure air and a high voltage electrical discharge to produce Ozone. The Ozone is fed into a contact chamber with the wastewater. Ozone disinfects basically by oxidizing the cell wall, damage to interior cell components, rendering them harmless.
Increases dissolved oxygen in effluent and any receiving streams. More effective than UV & Chlorine against virus, bacteria and protozoa. Any off-gases have to either recycled or destroyed. Ozonation is not as readily available as other technologies, as it fairly complex, expensive and can be dangerous for improperly trained persons working on these systems. Ozone
Conclusion It seems that the disinfection methods that work best are also the most complicated. There is not a single method of disinfection that is 100 % perfect for all systems. The designer, installer, maintenance provider and property owner need to work together to determine the most economic and effective method of disinfection for the On- Site Sewage Facility.