Experimental Study On Enhancing Methane Yield With Hydrogen From Fe~0Corrosion

Energy conversion efficiency of traditional anaerobic digestion is often low, whichlimited the practical application of energy recovery from waste activated sludge. To changethis situation, it is necessary to analyze on microbial metabolic processes involved in theanaerobic digestion, and try to strengthen the energy conversion in the intermediate links.During the anaerobic digestion process, a considerable portion of organic matter is directlystabled to CO₂, while autotrophic methanogens and homoacetogens could use H₂and CO₂assubstrates for its growth. Obviously, if the system exists a sufficient number of H₂, the C oforganic matter can maximize converted into CH₄, then the energy conversion efficiency of thewaste activated sludge will be increased.This research project intends to add waste iron scrape （WIS） into anaerobic sludgedigestion reactor, complementing H₂by the hydrogen from Fe⁰corrosion in the anaerobicenvironment, in order to strengthen the methanogenic process and improve the energy yield ofanaerobic sludge digestion. At the same time, Fe²⁺and Fe（OH）₂from Fe⁰corrosion couldprecipitate and remove high concentrations of phosphorus.4steps of experimental study:1) Microbial use H₂from Fe corrosion and external CO₂as substrates for its growth and methanogenesis;2) Hydrogen from NZVI corrosion influenceon methanogenesis and phosphorus removal of anaerobic sludge digestion;3) Hydrogen fromWIS corrosion strengthen the methane yield and phosphorus removal;4) Expand twopotential difference to accelerate the hydrogen evolution corrosion of WIS.First, NZVI which response lively and rapidly was adopted. The results showed thathydrogen evolution NZVI corrosion was very obvious in water, but byproduct of Fe²⁺andOH-did not significantly exceed the tolerance range of methanogens, and NZVI did not showapparent toxic effects on microorganisms. Microbial used H₂from NZVI corrosion andexternal CO₂as substrates for its methanogenesis and reproduction. H₂which from0.5g,1.0g,3.0g and5.0g NZVI corrosion during4d were used by microorganisms formethanogenesis, and the methane yield were32.8mL,47.5mL,96.9mL and140.4mL.Adding NZVI into the actual anaerobic sludge digestion system （300ml）, foud that0.5gand1.0g NZVI respectively made the CH₄content in the biogas generated by the varioussystems increase by27.5%and37.4%, and eventually lead to the methane productivityimproved42.3%and60.5%. These results suggest that, In the anaerobic sludge digestionreactor, microorganism converted the CO₂from waste activated sludge to CH₄with the H₂from Fe corrosion. Until reaction stable, PO₄^3--P concentration in the sludge supernatant werereduced by99.7%and99.9%. This indicates that Fe²⁺and Fe（OH）₂from Fe corrosion almostprecipitated and removed all the PO₄^3-.Selecting WIS which was cheap as corrosion material to carry out the above experiments,foud that10g,20g and30g WIS respectively made the CH₄content in the biogas generatedby the various systems increase by8.4%,15.5%and20.8%, and eventually lead to the methane productivity improved25.3%,35.9%and44.7%, while PO₄^3--P concentration in thesludge supernatant were reduced by87.4%,99.9%and99.9%. These results show that, WIScan also strengthen the process of methanogenesis. However, the facts of CH₄yield did notimprove with increasing Fe dosage explain that, the corrosion speed of WIS is far less thanNZVI.Against the problem that the speed of hydrogen evolution WIS corrosion is too slow,experimental study attempt to expand two potential difference by adding waste copperscrap（WCS） and activated carbon（AC）, in order to accelerate the hydrogen evolution WIScorrosion. Compared to control group （adding10g WIS）,10g WIS+0.2g WCS and10gWIS+0.2g AC made the CH₄content in the biogas only increase by1.4%and2.4%, andeventually lead to the methane productivity improved3.6%and8.4%. These indicate that theeffect of catalyst accelerate the hydrogen evolution WIS corrosion is not very obvious...