Diederik Rousseau Tineke Hooijmans. Anaerobic wastewater treatment

Transcription

1 Diederik Rousseau Tineke Hooijmans Anaerobic wastewater treatment

2 Anaerobic degradation Organic pollution -----> CH 4 + CO 2 ( biogas ) + biomass No oxygen, different anaerobic organisms

3 Application of anaerobic treatment Sludge stabilization at sludge digester wwtp Treat dilute to concentrated liquid organic wastewaters (distillery, brewery, food industry, paper manufacturing, petrochemical) Treat municipal wastewater in tropical countries

4 Anaerobic organic matter degradation Source: N. Mahmoud, Institute for Water Studies (IWS), Birzeit University

5 Anaerobic reactor systems treating wastewater

6 Advantages (wwtreatment) Production of energy-rich methane No energy demand for aeration No removal of nitrogen and phosphorus (this is an advantage if effluent is to be reused in agriculture) High organic loading rates can be applied Suitable for high-strength wastewater (high BOD) Low production of excess sludge; the digestate is highly stabilized and can easily be dewatered

7 Limitations treating domestic sewage Not effective in removing nutrients Only partially effective in removing pathogens Difficulties in removing finely dispersed solids Low activity at temperatures < C At low temperatures the hydrolysis rate of particulate matter becomes the rate limiting step

8 Low rate/ high rate anaerobic systems Low rate: Anaerobic digester Anaerobic pond High rate Able to separate hydraulic retention time (HRT) from solids retention time (SRT): higher volumetric loading rates can be applied, and enhanced removal efficiencies can be achieved.

9 Application of high rate reactors so far Mainly treating industrial wwater Majority based on the UASB design concept developed by Prof. Lettinga COD removal efficiency 85-90% In case of domestic wwtp: T> 15 o C, HRT = 4-8 hours, Organic loading rate = 1-2 kg COD m -3. day -1, COD removal 65-80%

10 Upflow anaerobic sludge blanket Source:Anaerobic Granular Sludge Bed Technology Pages, Jim Field

11 UASB History Anaerobic sludge bed Pellets: 0.5 to 2 mm diameter developed by Prof. Lettinga and colleagues in the late 1970's at the Wageningen University (The Netherlands); First pilot plant was installed at a beet sugar refinery in The Netherlands Anaerobic sludge granules from a UASB reactor treating effluent from a recycle paper mill (The Netherlands). The background is millimeter paper indicating the size of the granules. Red arrows point to gas vents in the granules, where biogas is released Source:Anaerobic Granular Sludge Bed Technology Pages,

12 Basic idea of UASB concept Flocculent or granular sludge: good settling characteristics The required good contact is achieved by: Even feed distribution at the bottom of the reactor Agitation brought about by the natural biogas production High upward velocity Gas Solids Separator installed at the top of the reactor

13 Gas Liquid Solids Separator (GLSS) Device Separation of the biogas To enable the sludge to slide back into the digester compartment To prevent the wash out of floating granular sludge

14 Feed Inlet System The feed inlet distribution system is a crucial part of the reactor It is important to accomplish optimal contact between sludge and waste water: To prevent channeling of the waste water through the sludge bed, To avoid the formation of dead corners in the reactor The danger of channeling will be bigger at low gas production rates (less than 1 m 3 /m 3 day)

15 Options for treatment of raw or settled municipalwastewater at temperature < 15 o C in high-rate anaerobic systems One-step UASB reactor long HRT is needed hours COD removal = % Two-step system: UASB + EGSB (expanded granular sludge bed) AF (anaerobic filter) + UASB First step:- HRT = 3-4 hours Second step:- HRT = 4-8 hours COD removal = %

16 Post treatment of the anaerobically treated municipal wastewater Removal of pathogens, Removal of the nutrients (depending on the effluent standards) The most applied systems for the post treatment: Pond, Duckweed, Wetland Tricking filter Rotating biological contactor Aerated lagoon, Activated sludge process