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About the Authors

Mahmood Alimahmoodi is a Ph.D. student in the Department of Building, Civil, and Environmental Engineering at Concordia University. Catherine N. Mulligan is an associate professor and research chair in environmental engineering in the Department of Building, Civil, and Environmental Engineering at Concordia University. Please address correspondence to: Catherine N. Mulligan, Department of Building, Civil, and Environmental Engineering, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec, Canada H3G 2W1; phone: 514-848-2424 ext. 7925; fax: 514-848-7965; e-mail: mulligan@civil.concordia.ca.

Mahmood Alimahmoodi and Catherine N. Mulligan

Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Quebec, Canada

RELATED ARTICLE: IMPLICATIONS

C[O.sub.2] is the major contributor to the greenhouse gas effect and global warming. In this study a new approach was developed to convert C[O.sub.2] to C[H.sub.4], which in addition to reducing its emission provides C[H.sub.4] as a clean source of energy. Air and energy management sections would benefit from the application of this method and in the long term, it could have a major impact on reduction of atmospheric levels of this greenhouse gas. Table 1. Composition of the inorganic materials used in the experiments.

Purity Amount Component (%) (g/L) Sodium chloride 99.7 0.6 Potassium phosphate 100 0.44 Magnesium chloride 99.8 0.2 Calcium chloride 98.6 0.2 Ammonium chloride 99.5 1.2 Trace mineral solution - 10 mL Table 2. Composition of the trace minerals used in the experiments.

Purity Amount Minerals (%) (g/L) Manganese (II) sulfate hydrate 98.0 0.1 Cobalt chloride 97.0 0.013 Calcium chloride 98.6 0.076 Copper chloride 99.0 0.02 Zinc chloride 97-100.5 0.1 Sodium chloride 99.7 1.0 Nickel (II) chloride hexahydrate 99.9 0.12 Iron (III) chloride hexahydrate 100.0 1.34 Table 3. COD values and concentration of the basic components used (g/L) in the three systems for each run of the reactor (indicated by 1-4).

System 1 System 2 Parameter/Substance 1 2 3 4 1 2 3 4 COD 2.7 2.8 5.2 8.3 3.2 3.4 5.8 8.2 Sodium acetate 1.5 1.5 2.5 4.0 1.5 1.5 2.5 4.0 Acetic acid 0.7 0.7 1.3 2.0 0.25 0.25 0.5 0.7 Propionic acid - - - - 0.25 0.25 0.5 0.7 Butyric acid - - - - 0.25 0.25 0.5 0.7 Peptone 0.4 0.4 0.75 1.0 0.4 0.4 0.75 1.0 Yeast extract 0.8 0.8 1.5 2.0 0.8 0.8 1.5 2.0

System 3 Parameter/Substance 1 2 3 4 COD 3.5 3.6 6.1 8.3 Sodium acetate 1.5 1.5 2.5 4.0 Acetic acid - - - - Propionic acid 0.5 0.5 0.75 1.1 Butyric acid 0.5 0.5 0.75 1.1 Peptone 0.4 0.4 0.75 1.0 Yeast extract 0.8 0.8 1.5 2.0 Table 4. Comparison of specific methanogenic activity (SMA) for several studies and this work. SMA L(C[H.sub.4])/ gVSS x d Test Conditions Reference 0.2-0.4 Respirometer at 35 [degrees]C, James et al. (24)

acetic acid 0.42-0.5 Individual and mixed VFAs (a), Soto et al. (25)

37 [degrees]C 0.072 (max) SMA test reactors, acetic acid, Ince et al. (26)

35 [degrees]C 0.44 (max) SMA test, acetate, 31 [degrees]C Gonzalez et al. (27) 0.40 (max) Batch tests, acetic acid, and This study

mixed VFAs (a), 35 [degrees]C Notes: (a) VFAs included acetic, propionic, and butyric acids Table 5. Anaerobic degradation reactions of VFAs. (28)

[DELTA] [G.sup.0] Reaction (kJ/mole C[H.sub.4]) Methanogenic reaction of acetate:

Acetat[e.sup.-] + [H.sub.2]O [right arrow] -31.0

HC[O.sub.3.sup.-] + C[H.sub.4] Syntrophic (net) reactions with [H.sub.2] use by

methanogens:

4 Propionat[e.sup.-] + 3[H.sub.2]O [right arrow] -34.0

4Acetate[.sup.-] + HC[O.sub.3.sup.-] +

[H.sup.+] + 3C[H.sub.4]

2 Butyrat[e.sup.-] + HC[O.sub.3.sup.-] + -39.4

[H.sub.2]O [right arrow] 4Acetate[.sup.-] +