Passage VII
Some soil bacteria can remove sulfate (SO42-) from acid mine drainage (AMD, polluted water drainage from mining areas). The bacteria use the soils organic carbon for energy and remove SO42- by reducing it to sulfide (S2-) Oxygen-poor conditions are required for the reduction process. Researchers studied other organic materials containing bacteria populations to see if those mixtures could also reduce SO42- in AMD.
Study 1
Four organic materials that contained bacteria populations were selected for testing: straw, hay, leaf compost, and manure. The materials, either individually or in mixtures of 2 of the materials, were packed to a depth of 50 cm in 10 cm diameter glass columns (see Figure 1). Duplicates of each column were prepared. The moist and dry densities and the carbon content (in kg/m3) of each column's contents were measured. The results are shown in Table 1.
Study 2
An aqueous solution with a concentration of 100 ppm SO42- (simulated AMD) and a pH of 6.5 was put through each column at a flow rate of 80 mL/day. On Day 50, the S2- concentration in the water in each column was measured at various depths. The results are shown in Figure 2. Table 2 shows the average S2- concentration in a column's water on Days 50, 100, and 150.
35. According to the results of Study 1 for the material packed in the columns, how do the carbon contents of equal volumes of straw and of leaf compost compare? Leaf compost has a carbon content that is approximately:
Your Answer is
Correct Answer is D
Explanation
Looking at table 1, the carbon content of straw is 31, and that of leaf compost is 94, about three times that of straw