WASTEWATER

By Rick Lallish

When using membrane bioreactors, what is typically required for upstream screening?

A. Stringent pretreatment standards for all industrial users

B. Primary clarification followed by UV pretreatment

C. 1 to 3 mm fine screens for larger particles and debris

D. Pre-aeration in the grit chamber followed by primary clarification

Answer: C. Membrane bioreactors are becoming more common. Due to their fragile and somewhat stringent membrane technologies, fine screens with 1 to 3 mm openings are typically used upstream. It is important to remove as much debris and solids as possible, as those items may clog the membrane pores, which may be as small as 0.01 µm. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals III: Advanced Treatment, Chapter 6.

DRINKING WATER

By Drew Hoelscher

What chemical is used for haloacetic acid sample preservation?

A. Sodium sulfite

B. Sodium thiosulfate

C. Ascorbic acid

D. Ammonium chloride

Answer: D. Halogenated disinfection byproducts are the result of hypochlorous acid (or hypochlorite) reacting with naturally occurring organic matter in water. Disinfection byproduct compliance samples are collected from the distribution system and analyzed by a certified laboratory within 14 days. The samples are preserved so that the analytical results reflect the concentrations at the time of sample collection. Preservation of HAA samples is best done with ammonium chloride because it is less likely to cause HAA degradation. The ammonium chloride reacts with the free chlorine and creates a chloramine, which helps prevent bacterial degradation.

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.