WASTEWATER By Rick Lallish
What is the desired pH level for a properly operating anaerobic digester?
A. 4.0 to 6.6
B. 6.8 to 7.2
C. 7.6 to 9.0
D. Above 10.0
Answer: B. Anaerobic digesters can operate at pH 6.0 to 8.0; the desired range is 6.8 to 7.2. If the pH falls below 6.0 or exceeds 8.0, the methane-forming bacteria will die off, and the digestion process will cease. The methane-forming bacteria are the key component for anaerobic digestion. The pH is controlled by the amounts of volatile acids and the alkalinity.
DRINKING WATER By Drew Hoelscher
What membrane filtration process requires the least amount of operating pressure?
A. Ultrafiltration (UF)
B. Reverse osmosis (RO)
C. Microfiltration
D. Nanofiltration (NF)
Answer: C. Compared to UF, NF and RO, microfiltration has the largest pore size openings and requires less applied pressure for the water to pass through. Microfiltration can remove contaminants 0.1 microns in diameter and greater and is effective in removing sediment, algae, protozoa and some bacteria from contaminated water. It can be applied as a pretreatment for UF, NF and RO membranes or as a post-treatment for granular media filtration.
About the authors
Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.
