Biogas production from municipal wastewater sludge

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Edition 5 of the Metcalf and Eddy (M&E) "Wastewater Engineering - treatment and resource recovery" state on page 1521 that with regard to biogas production "Typical values vary from 0.75 to 1.12 m3/kg volatile solids destroyed." but does not state state pressure and temperature at which these volumes apply.

Can someone please confirm if this is at standard temperature and pressure (0 C, and 1 atm), or what pressure and temperature should be assumed for this biogas production rate?

Thank you!

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5 Answers

  1. I am interested in Bioelectrochemical systems producing methane/ hydrogen gases/fuels/renewable energy from wastewater sludge+urban wastes as feedstock. I am retired from university and still in need of a simplified lab PhD. I need assistance in kind, be it online or lab training to start with. I wish therefore,  introduce our TRUST’s brief statement thus: Interwaste R&D (EA) Trust is a nonprofit registered in Kenya, and focused in Africa and also UNEP  accredited and CTCN Network Member etc. Please see www.interwaste-ea.co.ke for more information. As principal catalyst partner, we are looking for strategic and specialized partners, investors, and technical assistance for implementation services of our initiatives in Africa, through value addition and use of advanced technologies currently available. Our concerns are environmental challenges caused by urban solid wastes, wastewater, WASH, agriculture/irrigation, DEFORESTATION and chemical and hazardous wastes sectors in Africa. and look forward to a planet pollution free. We target waste to energy schemes, urban waste, wastewater engineering, land filling engineering, landfill gas, dump sites rehabilitation; with development of mechanism for reduction of GHG Emissions in developing countries; anaerobic digestion and Bioelectrochemical systems, education, research & development and training  young men and women in these sectors in Africa. We need support from countries, companies and experts with environmental success stories, and other infrastructure development projects (including real estate)  as  committed relevant Organizations. We can also partner,working together in Africa. Can't we? Thank you.

     

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    Founder and Managing Trustee

    Interwaste R&D (EA) Trust

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  2. AD design, the effect of temp is considered and if required, heat exchangers are provided. The focus is given to achieve more VS destruction in AD with proper mixing, THP and other processes. 

    1 Comment

  3. Interesting question, Andre.

    Before addressing the question, it's important to see that many different countries/regions/industries use different bases for "standard" or "normal" conditions.  Typically the pressure is 1 atm (101.325 kPa), but the reference temperature often changes.  Perhaps the most common terms are:

    Normal: Nm3 (0 degC; 101.325 kPa).

    Standard: Sm3  (20C; 101.325 kPa).

    As far as the numbers go, if you are digesting a typical mix of PS and WAS - see diagram below - the rule of thumb would say to expect about 1 m3 of digester gas per kgVSS destroyed.  That would be at field conditions, and that would mostly be digesters at about 36 C.  Perhaps the range from M&E comes from digesters over a range of temperatures, and also WAS from longer SRT systems will produce less gas.

    Another rule of thumb may be to look at the decrease in COD across the digester, and expect about 0.37 m3 of methane per kgCOD removed.

    If I take a BioWin Cabinet file - EBPR + Anaerobic Digester - here are the numbers:

    Delta VSS = 1295 kgVSS/d

    Delta COD = 2056 kgCOD/d

    Gas produced from digester at 36C = 1,238 m3/d with 0.644 methane fraction.  So methane production at 36C = 0.644 x 1,238 = 797 m3/d.

    Gas/VSS reduced = 0.96 m3/kgVSS

    Methane/COD reduced = 0.39 m3/d

    These are for 36C.  Converting to the "Normal" of o C would reduce these by a factor of 273 / (273+36) = 0.884.

    Good luck and good wishes,

    Peter Dold.

     

    1 Comment

    1. Hi Peter,

      Thank you very much for your time taken for this very thorough reply, finally sorting out this issue which has bugged me for a while. It makes sense that the biogas volume would be at field conditions. The elevation and atmospheric pressure remain an issue though, but I guess the range of values could cover elevation/pressure as well. I suppose one could assume sea level and then adjust for higher elevations if required. M&E also refer to the methane formula based on BOD which is very specific in terms of temperature and pressure, but unfortunately BOD and COD information in and out of AD's is seldomly reported in SA.  One could convert from VS to BOD or COD but this all adds to the variability of the answer.

      Thanks again for your reply, much appreciated.

      Best wishes, Andre

  4. It is at standard temperature and pressure. Actual gas yield depends on thr nature of the VSS destroyed.