An advanced wastewater treatment plant is designed and built to remove BOD, TSS, total nitrogen and total phosphorus to very low levels before discharging effluent to a river. The unit processes are arranged in the following order: primary clarification, anaerobic zone, pre-anoxic zone, aerobic zone, post-anoxic zone, re-aeration zone, final clarifiers, filtration, disinfection. What process is described here?

A. Modified Ludzack-Ettinger, or MLE, process

B. Wuhrmann process

C. Kraus process

D. Bardenpho process

Answer: D. The other processes used as distractors (incorrect choices) are modifications of the activated sludge or nutrient-removal processes, only the Bardenpho uses the processes listed in the order shown. Keep in mind that we are really only discussing biological nutrient removal in this question: Some Bardenpho facilities do not have primary clarifiers or filters.

The placement of the anaerobic, anoxic and aerobic basins and the internal recycle streams give the Bardenpho process its characteristics. Many other processes use these types of basins but in a different order, or by varying the number of basins. Processes similar to Bardenpho are Johannesburg, Virginia Initiative, and University of Cape Town, to name a few.


What role does adding a dosage of 2 to 5 mg/L of sodium hexametaphosphate, or SHMP, play in reverse osmosis water treatment?

A. SHMP inhibits the precipitation of calcium sulfate on the membrane.

B. SHMP will reduce the amount of dissolved hydrogen sulfide gas that must be degasified.

C. SHMP will eliminate the need for degasification after membrane treatment.

D. SHMP will eliminate the need to provide corrosion prevention in the distribution system.

Answer: A. The source water to a reverse osmosis water treatment plant can contain dissolved calcium carbonate and calcium sulfate. These can cause significant scaling on the membrane if not controlled. Reducing the pH with an acid helps keep the calcium carbonate from becoming a problem by keeping the alkalinity in the more soluble bicarbonate form. The calcium sulfate, however, can continue to precipitate (form scale) over a wider pH range. The SHMP inhibits both calcium carbonate and calcium sulfate from becoming crystallized and forming the scale on the membrane surface.

About the author

Ron Trygar, a certified environmental trainer, is the senior training specialist for water and wastewater programs at the University of Florida TREEO Center. He has worked in the wastewater industry for more than 30 years and holds Class A wastewater treatment operator and Class B drinking water operator licenses in Florida.  


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