CASE STUDY:
Food Processing Plant
NIBBLER SUCCEEDS AT CLAREMONT
NORTH CAROLINA BAKERY
Background
Pierre Foods (formerly WSMP Bakery Systems) owns and operates a bakery in Claremont, North Carolina. Wastewater from the bakery is discharged into the city of Claremont’s municipal sewage treatment plant. Averaging 4,000 gallons per day, Pierre Foods accounts for just over 1% of the city’s total sewage flow. However, considering the very high waste strength generated by the bakery, Pierre Foods contributed over 19% of the total organic waste load (lbs/day BOD5) requiring treatment.
With a single industrial source tying up such a large percentage of the treatment plant’s capacity, the City of Claremont was being severely limited in its ability to grow. Bakery waste in such large concentrations also created major operating problems at the treatment plant. Normal process waste is very acidic – with a pH of about 3.5. Sugars and flour utilized in the baking process will drop pH like a rock. It’s not a sweet smell.
During wash down cleaning periods just after plant shut down, wastewater will become very basic - with a pH approaching 11.0. Such a high pH is caused by cleaning chemicals used in the wash down cleaning process. These chemicals also will kill the microbial population needed to break down waste in the treatment plant. All of this becomes a treatment plant operators worst nightmare.
In 1995, the City of Claremont initiated a surcharge program whereby sewer rates were to be based not just on the gallons per day discharged, but also on the waste strength contributed. Surcharges included specific rates for the pounds of BOD5 (Biochemical Oxygen Demand 5 Day), TSS (Total Suspended Solids) and FOG (Fats, Oils and Grease) discharged when it exceeds normal residential waste strength levels. Pierre Foods wastewater had a BOD5 of nearly 3,000 mg/L. The residential BOD5 discharge standard is 200 mg/L.
A solution was needed. Pierre Foods could not afford to pay the surcharge and the city could not afford to treat the bakery waste without a large surcharge.
The Nibbler Solution
Pierre Foods initiated a search for pre-treatment alternatives. Conventional technologies proved to be expensive to install, complex and costly to operate – requiring a full time operator. Pierre Foods is in the bakery business, not the sewage treatment business. The search continued for a waste treatment process that was simple and economical to install and operate.
During their search, Pierre Foods became aware of the Nibbler high strength wastewater treatment system. The Nibbler has proven very effective at treating wastewater high in BOD5 and even high in Fats, Oils and Grease. Nibblers have successfully treated high strength waste from restaurants, supermarkets, entire shopping centers, egg processing plants and meat processing plants. Rather than requiring an operator on site on a daily basis, only monthly or quarterly maintenance and monitoring is all that is required. In addition, NCS provides a performance warranty for the life of the system that Nibbler systems will meet or exceed design discharge standards (e.g., BOD5 < 200 mg/L). Pierre Foods elected to install a Nibbler system.
Pierre Foods Nibbler System Description
Wastewater flows can vary significantly throughout the day and over a production cycle. It is not unusual for a bakery that averages 4,000 gal/day (gpd) to see peak daily flows of 8,000 gallons or more.
Since building a treatment plant capable of treating 8,000 gal/day is clearly a lot more expensive than for 4,000 gal/day, NCS designs all Nibbler systems with flow equalization/surge tanks. 10,000 gallons of surge tank capacity was installed at Pierre Foods.
The Nibbler system may then be time dosed every 30 minutes – about 83 gallons each dose. Fluctuations in bakery flows are absorbed in the surge tank while the Nibbler system receives a constant flow. In addition to saving money, time dosing also improves treatment.
Four 10,000 gallon tanks contain 120 Nibbler pods capable of treating 97.6 lbs/day BOD5 - equivalent to 4,000 gal/day at 2,925 mg/L BOD5. Each Nibbler pod will treat 0.81 lbs/day BOD5. With 83 gallon doses into 40,000 gallons of tank capacity, shock loading from fluctuations in pH and other waste characteristics are easily absorbed. The pH exiting the Nibbler is nearly neutral or 7.0.
One 10,000 gallon clarifier tank follows the Nibbler and from there treated wastewater flows to a lift station for discharge to the Claremont municipal sewer.
Plant start-up began in October 1995.
Results
For the past 5 years, the Nibbler system has consistently met design discharge limits. This is according to Jim Templeton, Vice President for Real Estate with WSMP at the time and the decision maker responsible for installing the Nibbler at Claremont