WASTEWATER
Which type of filter is used to reduce the organic loading on downstream biological processes?
A. Tertiary filter
B. Vacuum filter
C. Traveling bridge rapid sand filter
D. Roughing filter
Answer: D. A roughing filter may be used where very high organic strength waste must be biologically treated. The roughing filter is essentially a high-rate trickling filter placed ahead of other biological treatment processes, such as rotating biological contactors, other trickling filters, or activated sludge processes. The roughing filter is placed in the flow pattern just after the primary clarifiers but before the downstream biological processes. Roughing filters could see organic loading rates up to or exceeding 300 pounds of BOD per day per 1,000 cubic feet of media. A standard-rate trickling filter would likely see only up to 25 pounds of BOD per day per 1,000 cubic feet of media.
DRINKING WATER
What is a disadvantage of ion exchange softening?
A. The amount of land space needed to build the plant
B. The complexity of the operation and amount of training needed
C. Disposal of the spent brine and rinse water
D. Excessive operation and maintenance costs
Answer: C. Ion exchange softening is a relatively straightforward process of water softening and capable of reducing the finished water hardness to zero. The process consists of service, backwash, brine and rinse stages. A disadvantage of the process is figuring out what to do with the spent brine and rinse water. These are considered industrial strength wastes since the amount of total dissolved salts, conductivity and pH can be very high.
Discharge of these wastes into a sanitary sewer is common, especially if the utility owns both the drinking water and wastewater treatment plants. However, the wastewater plant operator must be made aware of the discharges since they may affect the biological processes. Slug loads of water with high pH, conductivity and saline can harm the bacteria used for secondary treatment, so it is imperative that these wastes be controlled. The ion exchange plant may have to apply for an industrial waste discharge permit from the receiving utility to accept the spent brine, backwash and rinse waters.
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.
