PreviouslyOutlineSlide 3Slide 4Slide 5Alternative Biological Treatment of Wastewater: Alternatives for Small and Rural CommunitiesFacultative Oxidation (Waste Stabilization) PondStabilization Ponds or LagoonsStabilization Ponds or Lagoons, contEnteric Microbe/Pathogen Reductions in Stabilization PondsSlide 11Constructed Wetlands and Enteric Microbe ReductionsSeptic Tank-Soil Absorption Systems for On-Site Sewage RxMore on sanitation technologies:Log10 Reduction of Pathogens by Wastewater Rx ProcessesSlide 16Slide 17REMOVAL OF ENTERIC BACTERIA BY SEWAGE TREATMENT PROCESSESEntamoeba histolytica Reduction by Sewage TreatmentMicrobial Reductions by Wastewater TreatmentDisinfection of WastewaterWhen Wastewater Disinfection is Recommended or RequiredWastewater Reuse: reading for ThursdayPreviously •Microbial survival in environmental media–Water, land, air •Small scale sanitation, composting latrines, etc•Conventional wastewater treatment in developed countries–Screening/settling/”activated sludge”/disinfection–Overview of processes, chemical and physicalOutline•But what about developing countries?–In many cases, no wastewater treatment–“Natural attenuation”•What are some practical options for wastewater treatment in poor countries? –(& see handouts)•More about microbes and how they are reduced in wastewaterAlternative Biological Treatment of Wastewater:Alternatives for Small and Rural Communities•Letting nature do its thing•Lagoons, Ponds and Ditches–aerobic, anaerobic and facultative; for smaller communities and farms–enteric microbes are reduced by ~90-99% per pond•multiple ponds in series increases microbe reductions•Constructed Wetlands–aerobic systems containing biologically active, oxidizing microbes and emergent aquatic plants•Lagoons and constructed wetlands are practical and economical sewage treatment alternatives when land is available at reasonable cost (Phnom Penh)Facultative Oxidation (Waste Stabilization) PondStabilization Ponds or Lagoons•Aerobic and Facultative Ponds: •Biologically Rx by complementary activity of algae and bacteria.•Used for raw sewage as well as primary‑ or secondary‑Rx’d. effluent.•Bacteria and other heterotrophs convert organic matter to carbon dioxide, inorganic nutrients, water and microbial biomass. •Algae use CO2 and inorganic nutrients, primarily N and P, in photosynthesis to produce oxygen and algal biomass. •Many different pond designs have been used to treat sewage•Used here in the US in decentralized plants and CAFOsStabilization Ponds or Lagoons, cont•Facultative ponds: upper, aerobic zone and a lower anaerobic zone. •Aerobic heterotrophics and algae proliferate in the upper zone.•Biomass from upper zone settles into the anaerobic, bottom zone.•Bottom solids digested by anaerobic bacteria•Also used with aquaculture systemsEnteric Microbe/Pathogen Reductions in Stabilization Ponds•BOD and enteric microbe/pathogen reductions of 90%, esp. in warm, sunny climates.•Even greater enteric microbe /pathogen reductions by using two or more ponds in series•Better BOD and enteric microbe/pathogen reductions if detention (residence) times are sufficiently long (several weeks to months)•Enteric microbes reduced by 90% in single ponds and by multiples of 90% for ponds in series. •Microbe removal may be quite variable depending upon pond design, operating conditions and climate.–Reduction efficiency lower in colder weather and shorter retention timesConstructed Wetlands and Enteric Microbe Reductions•Surface flow (SF) wetlands reduce enteric microbes by ~90%•Subsurface flow (SSF) wetlands reduce enteric microbes by ~99%•Greater reduction in SSF may be due to greater biological activity in wetland bed media (porous gravel) and longer retention times•Multiple wetlands in series incrementally increase microbial reductions, with 90-99% reduction per wetland cell.Septic Tank-Soil Absorption Systems for On-Site Sewage Rx•Used where there are no sewers and community sewage treatment facilities: ex.: rural homes•Septic tank: solids settle and are digested •Septic tank effluent (STE) is similar to primary sewage effluent•Distribute STE to soil via a sub-surface, porous pipe in a trench•Absorption System: Distribution lines and drainfield•Septic tank effluent flows through perforated pipes located 2-3 feet below the land surface in a trenches filled with gravel, preferably in the unsaturated (vadose) zone.–Effluent discharges from perforated pipes into trench gravel and then into unsaturated soil, where it is biologically treated aerobically.•Enteric microbes are removed and retained by the soilMore on sanitation technologies:•www.wateraid.co.uk•Handouts•For more on small-scale sanitation, check out The Humanure HandbookLog10 Reduction of Pathogens by Wastewater Rx ProcessesLog10 Reduction of Pathogens by Wastewater Rx ProcessesIndicator Microbe Levels in Raw and Treated Municipal Sewage: Sewage Treatment Efficacy110100100010000100000100000010000000100000000110100100010000100000100000010000000100000000F. col. E. coli Ent. C. p. F+ phg.Number/100 mlRawTreated(geom. mean values of 24 biweekly samples)REMOVAL OF ENTERIC BACTERIA BY SEWAGE TREATMENT PROCESSESORGANISM PROCESS % REMOVALFecal indicators Primary sed. 0‑60%E. coli Primary sed. 32-50%Fecal indicators Trickling filt. 20‑80%Fecal indicators Activated sludge 40‑95%Fecal indicators Stab. ponds, 1 mo. >99.9999% @ high temp.Salmonellae Primary sed. 79%, 6‑7 hrs.Salmonellae " 73%, 6‑7 hrs.Entamoeba histolytica Reduction by Sewage TreatmentORGANISM PROCESS % REMOVALE. histolytica Primary Sed. 50%E. histolytica Primary Sed., 2 hr. 64%E. histolytica Primary sed., 1 hr. 27%E. histolytica Primary sed. + Trickl. Filt. 25%E. histolytica Primary sed. + Act. Sludge 83%E. histolytica Oxidation ditch + Sedimentation 91%E. histolytica Stabilization ponds + sedimentation 100%E. histolytica " 100%, 94%, 87%E. histolytica " 100%E. histolytica Aerated lagoon (no settling) 84%Microbial Reductions by Wastewater Treatment% ReductionMicrobe 1o&2oFilt. Disinfect. StoreTotal Rx.Tot. colif. 98 69 99.99 75 99.99999Fec. colif. 99 10 99.998 57 99.999996Coliphage 82 99.98 90 90 99.99997Entero-virus98 84 96 91 99.999Giardia 93 99 78 50 99.9993Crypto-sporidium93 98 61 <10
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