Sample Sample Sludge should not be wasted directly to an anaerobic digester because it has excess water. What should be done instead?(a) Add polymers(b) pump to thickeners or primary clarifiers(c) Add lime(d) Pump excess water to headworksWhen the content of CO2 in digester gas increases to above 30 to 40 percent, the digester is:(a) Operating very well(b) Improving its gas production(c) Operating normally(d) Not functioning properlyThe effective heat value per cubic foot of digester gas is:(a) 3,000 to 5,000 Btu's (b) 500 to 800 Btu's(c) 5,000 to 8,000 Btu's(d) 2 to 4 Btu's