Supplementary Methods

Cumulative effect of various parameters on power density of MFC

After performing the experiments as per Taguchi’s experimental design, plots for power density were plotted for MFCs with different combinations of inlet pH, S/V ratio, anode distance and inlet COD concentration (Supplementary Fig 1). A main effect is a direct effect on parameters on response and dependent variables. It is plotted by considering mean of response at each level of parameters. Maximum deviation of power density with respect to the means was obtained with S/V ratio followed by the anode distance, inlet pH and finally the inlet COD. Thus, it is observed that S/V ratio is ranked 1 (Table III) suggesting that among the different parameters studied, it is the most crucial parameter for power generation in MFC.

ANOVA

ANOVA is a statistical tool which helps to reduce the error variance and quantifies the dominance of control factor. This analysis aids in justifying the effects of input changes on the responses in experiment. It was found that P value from ANOVA was significant for inlet pH, S/V ratio and anode distance (P<0.05) depicting the importance of these parameters for designing MFCs.

Verification of Taguchi‘s method

After conducting the nine experiments (as per the orthogonal array, Table I), a Taguchi prediction analysis was performed to validate the optimized combination of process parameters (Supplementary Fig. 2). To verify the accuracy of the predicted value of power density, experiments were conducted and a comparison of experimental values was made with the predicted values. The predicted values were in accordance with the experimental values.

Supplementary Table 1. Basal media composition

Sr. No. / Components / Quantity per litre
(mg)
1 / CH3COONa / 3843
2 / NaHCO3 / 2500
3 / NH4Cl / 1000
4 / Yeast extract / 500
5 / CaCl2.2H2O / 80
6 / Thioglycollic acid / 100
7 / MgCl2.6H2O / 200
8 / Trace metals- Feso4.7H2O / 60
9 / Niso4.6H2O / 3.156
10 / Mnso4.H2O / 3.156
11 / Znso4.7H2O / 0.636
12 / Boric Acid (H3BO3) / 0.636
13 / Cocl2.6H2O / 0.3156
14 / CuSo4.5H2O / 0.027
15 / (NH4)6MO7O24.4H2O / 0.3156
16 / Vitamins-Biotin / 0.02
17 / Folic acid / 0.02
18 / Vitamin B6 (pyridoxine) / 0.1
19 / Vitamin B1 (thiamine) / 0.05
20 / Vitamin B2 (riboflavin) / 0.05
21 / Nicotinic acid (niacin) / 0.05
22 / Pantothenic acid / 0.05
23 / Crystalline vitamin B12 (cyanocobalamin) / 0.001
24 / p-aminobenzoic acid / 0.05
25 / lipoic acid (thioctic). / 0.05

Supplementary Table 2. Acetate-based synthetic wastewater media composition

Sr. No. / Components / Quantity per litre
(mg)
1 / CH3COONa / 3843
2 / NaHCO3 / 4500
3 / NH4Cl / 954
4 / K2HPO4 / 81
5 / KH2PO4 / 27
6 / CaCl2.2H2O / 750
7 / MgSO4.7H2O / 192
8 / Trace metals- FeSO4.7H2O / 60
9 / NiSO4.6H2O / 3.156
10 / MnSO4.H2O / 3.156
11 / ZnSO4.7H2O / 0.636
12 / Boric Acid (H3BO3) / 0.636
13 / CoCl2.6H2O / 0.3156
14 / CuSO4.5H2O / 0.027
15 / (NH4)6MO7O24.4H2O / 0.3156

Supplementary Table 3 ANOVA Table for the anodic parameters. The P value below 0.5 indicates the significance of the parameters under study

Source / DF / Seq SS / Adj SS / Adj MS / F / P
pH / 2 / 0.078006 / 0.078006 / 0.039003 / 19.47 / 0.049
S/V ratio / 2 / 0.704956 / 0.704956 / 0.352478 / 175.99 / 0.006
Anode distance / 2 / 0.156956 / 0.156956 / 0.078478 / 39.18 / 0.025
Residual Error / 2 / 0.004006 / 0.004006 / 0.002003
Total / 8 / 0.943922

Supplementary Fig. 1. Factor effect plot of pH, S/V ratio, anode distance and inlet COD concentration vs. power density of MFC. It could be observed that the S/V ratio had the most significant effect on power density as compared to pH, anode distance and inlet COD.

Supplementary Fig. 2. Taguchi prediction analysis for the maximization of power density using optimized process parameters. It was observed that the experimental values corroborated well with the predicted values (Mean) obtained with the Taguchi model.