Tech 110: Pretreatment Technologies

1. Tech 110:Pretreatment Technologies Between the tank and the soil

2. Overview of Pretreatment Adapted from The University Curriculum for Decentralized Wastewater Management Prepared by: John R. Buchanan, Univ. of TN; Robert W. Seabloom, Univ. of WA; Dave Lenning, Alternatives Northwest Edited by: David Lindbo and Nancy Deal, NCSU

3. NDWRCDP DisclaimerThis work was supported by the National Decentralized Water Resources Capacity Development Project (NDWRCDP) with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (EPA No. CR827881-01-0) with Washington University in St. Louis. These materials have not been reviewed by the U.S. Environmental Protection Agency. These materials have been reviewed by representatives of the NDWRCDP. The contents of these materials do not necessarily reflect the views and policies of the NDWRCDP, Washington University, or the U.S. Environmental Protection Agency, nor does the mention of trade names or commercial products constitute their endorsement or recommendation for use.

4. CIDWT/University Disclaimer These materials are the collective effort of individuals from academic, regulatory, and private sectors of the onsite/decentralized wastewater industry. These materials have been peer-reviewed and represent the current state of knowledge/science in this field. They were developed through a series of writing and review meetings with the goal of formulating a consensus on the materials presented. These materials do not necessarily reflect the views and policies of University of Arkansas, and/or the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT). The mention of trade names or commercial products does not constitute an endorsement or recommendation for use from these individuals or entities, nor does it constitute criticism for similar ones not mentioned.

5. CIDWT/University Disclaimer These materials are the collective effort of individuals from academic, regulatory, and private sectors of the onsite/decentralized wastewater industry. These materials have been peer-reviewed and represent the current state of knowledge/science in this field. They were developed through a series of writing and review meetings with the goal of formulating a consensus on the materials presented. These materials do not necessarily reflect the views and policies of North Carolina State University, and/or the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT). The mention of trade names or commercial products does not constitute an endorsement or recommendation for use from these individuals or entities, nor does it constitute criticism for similar ones not mentioned.

6. Why Pretreat? “Pretreat” wastewater so downstream component(s) can function more reliably for longer terms

7. Pretreatment Options • Traditionally, have been categorized as: • Primary – solids removal • Secondary –organics and BOD removal • Tertiary – generally, nutrient removal • Microbes typically used to assist • Aerobic • Anaerobic • Facultative • Aerobic and anaerobic processes are compatible

8. Primary treatment • Septic tanks • Grease traps • Grease interceptors

9. Primary treatment: Septic tanks • Functions • Separate solids from liquid • Anaerobic decomposition • Attenuate surges • Ventilation

10. Primary treatment: Septic tanks • Most common unit for OWTS • Used alone or with other pretreatment units • Simple and generally inexpensive ($100s) • 30-50% reduction BOD5, 60-80% reduction TSS

11. Primary treatment: Grease traps • Function • Remove grease and oils • Used where greases/oils expected (usually commercial sites like restaurants) • Does not normally receive blackwater

12. Primary treatment: grease separators • Typically, proprietary products • High maintenance products • Historically, not good performance because of poor maintenance

13. Advanced pretreatment • Secondary treatment • TSS and BOD removal • Microbes typically used to assist • Aerobic • Anaerobic • Facultative

14. Secondary treatment • Use aerobic microorganisms to provide secondary treatment to domestic wastewater • Focuses on removal of biodegradable organics and suspended solids • Convert soluble particulates to insoluble ones so we can remove them • usually accomplished with biological reactors • Biodegradable organics must be removed to minimize impact on subsequent processes

15. Aerobic reactions • If enough dissolved O2 is in the effluent then the effluent is Aerobic • O2 > 1.0 ppm • Bacteria break down waste constituents under these conditions

16. CO2 H2O Respiration O2

17. Nitrification NO2 NH3 H2O O2 NO2 NO3 O2

18. Providing Dissolved Oxygen (DO) • Advanced treatment systems are designed to provide lots of DO • high-rate carbon removal and ammonification • occupies a small-footprint • requires energy to maximize oxygen transfer • biological reactor

19. BOD • Often used as a measure of wastewater strength • a high BOD suggests that the organic compounds are easily biodegradable • indicates the mass of dissolved oxygen that could be removed by aerobic microbes as they metabolize • Secondary treatment devices reduce the oxygen demand of a wastewater

20. Advanced pretreatment • Tertiary treatment • Generally, nutrient removal • Disinfection

21. Anoxic/anerobic reactions • If all O2 is low effluent becomes anoxic/anaerobic • O2 < 0.5 ppm

22. Denitrification CO2 NO3 N2 gas

23. It’s all about the bugs (Microbes)

24. Optimizing a natural process • Bioreactors are built to maximize the production of beneficial end-products • alcohols (beer, wine) • insulin • other medications • And • Renovate wastewater

25. The good bugs • Convert colloidal and dissolved carbonaceous organic matter into various gases and into cell tissue • gases evolve (CO2, N2, and others) • new cells can settle – thus carbon is removed • Break other nutrients out of organic compounds • nitrogenous compounds • phosphorus species

26. The bad bugs • Pathogens • Use disinfection to inactivate these • Generally UV, Chlorine

27. The soil… • Is a bioreactor too!

28. Shallow system = Aerobic treatment Well Aerobic soil needed for treatment Groundwater

29. Deep system = Less aerobic to anaerobic system Well Low O2 results in less aerobic soil therefore treatment Groundwater

30. Advanced treatment • Lessens the burden placed on the soil • Allows use of less-than-optimum sites • Increased risk requires attention to O&M

31. Wastewater Treatment • Examples of Aerobic Bioreactors used for Secondary Treatment • activated sludge plants • rotating biological contactors • packed-bed media filters • Highly-engineered systems that utilize microbial metabolism to convert organic compounds into cells and carbon dioxide

32. Environmental Effects • Microbes need more than organic carbon, dissolved oxygen and water • need steady supply of food to maintain stable microbial population • pH needs to be monitored • low alkalinity can cause large changes in pH • Be careful with biocides • acid drain cleaner • antibiotics

33. Environmental effects: Temperature • Overall, as temperature rises, microbial activity increases (but not too hot) • Microbes can be grouped by temperature preference • Psychrophilic microorganisms • optimum temperature 12° to 18° C • Mesophilic microorganisms • optimum temperature 25° to 40° C • Thermophilic microorganisms • optimum temperature 55° to 65° C

34. Summary • Aerobic Treatment of Wastewater • takes advantage of a natural process • process can be easily engineered into a biological reactor for high-rate wastewater treatment • removes the oxygen demand from wastewater before being discharged back into the hydrologic cycle • Carbon is transformed into cell mass and into carbon dioxide

35. Questions?

36. N Cycle in Septic Systems Mineralization Immobilization Nitrification and Sorption Denitrification ?