Operation
Remember the line from the commercial about potato chips: “Betcha can’t eat just one”? Who would ever think that one of this country’s oldest and most favorite snack foods would have a waste treatment problem in its manufacturing process? Well, that irresistible chip coming out of the bag is the end result of a manufacturing process that, on one hand, is much more sophisticated today, and on the other hand, produces 75% primary solids waste, plus organic solids, Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) that no longer can simply be dumped down the drain. All of this is a compound problem that significantly affects the manufacturer’s bottom line and his ability to compete in the marketplace.
The John Boyd Company is this country’s oldest independent “chip” manufacturer. Founded in 1868 and located in Lynn Massachusetts, the company prides itself on the quality of the 40,000 pounds of chips it manufactures daily. What they have going through their operation is primarily demand production, as 90% is private label, supplying all of the major supermarket chains in New England. They operate two production shifts a day, utilizing two cookers to produce both standard and ripple chips.
The ideal “chip” potato is a USDA #1 grade potato, about the size of a baseball, or approximately 3 inches in diameter. While most of us probably don’t spend a lot of time thinking about potatoes, everything from environmental conditions, amount of insecticides, fungicides, fertilizers, how planted, when planted, how harvested, when harvested and how they are stored all effect the ultimate quality of the potato. For example, if a potato is harvested too early, the sugar content is higher and the result is a dark chip. When you see a dark chip, it is overwhelmingly the result of high sugar content that caramelizes while being cooked as opposed to being overcooked. Today’s modern cookers, many of which are capable of cooking 3,000 to 4,000 pounds of chips an hour, have heat exchangers that provide uniform heat that eliminates hot spots.
The Boyd Company receives its potatoes in bulk on trailer trucks. Each shipment weighs in at 45,000 to 55,000 pounds. Their suppliers are mostly from the New England states, but they occasionally receive shipments from as far away as North Dakota. It’s interesting to note that after washing and inspection, the ratio of raw material to finished product is about 4:1, or for every 100 potatoes used, the “chip” yield is about 25 or 26 pounds, and of that amount, 40% is oil. So it’s important to have potatoes with high solids content, or specific gravity, in order to get the best yield and the most efficient production from the cookers. According to Mike Schena, Director of Operations at the John Boyd Co., “The lower the solids content, or specific gravity, the more waste I have, and consequently the more potatoes I have to buy to attain my desired end product yield. The quality of my raw potatoes directly affects my bottom line, and our suppliers know and respect that.”
Challenge
Until recently his main concern for waste treatment involved primary treatment via skimming the raw material from the water, grinding it and shipping it to area pig farmers. Now, however, even the pig farmers are less and less a means for disposal as the EPA has begun to scrutinize their operations as a source of ground water contamination. Recently, too, the City of Lynn, Massachusetts, Water and Sewer Commission, introduced new, stringent wastewater certification standards, that has necessitated that the John Boyd Co. install a secondary treatment system. “We looked at a whole list of optional techniques and systems,” said Schena, “starting with chemical/physical techniques. The specifications that we had to meet, however, could not be achieved by the chemical/physical method alone. So with the engineering consultant that we retained, we derived a system that utilized the chemical/physical technique, but then added to that by incorporating a biological treatment system.
“Our BOD was 1,800 parts per million (ppm), TSS was 2,000 ppm and oil and grease was at 120 ppm. The Water and Sewer Commission mandated that we had to achieve a BOD level of 300 ppm, TSS of 300 ppm and 100 ppm of oil and grease or cease operations. Paying an increased surcharge wasn’t even an option. For us, it was put up or shut up. With our new system, however, I’m pleased to report that we have achieved a less than 300 ppm BOD level; an average TSS level of 135 ppm and oil and grease is at 10 ppm.”
Solution
Jones and Beach Engineering, Inc. of Stratham, New Hampshire designed the system developed for the John Boyd Co. It was designed as a pretreatment system, incorporating chemical precipitation, and a trickling filter biological treatment system. The biological system components were purchased from ESSI Environmental of Fort Myers, Florida. The whole installation is capable of reducing organic loading by 93% in order to meet the stringent sewer discharge standards of the Lynn Water and Sewer Commission. According to Mike Schena, the John Boyd Company is probably the first “chip” plant in the country to have this type of system in operation.
To handle and dewater the combination of starch, chemical sludge and waste biological sludge generated by the system, Mike Schena and his consulting engineers looked at virtually every conceivable option, including vacuum presses, belt presses and filter presses. They decided upon a filter press, due not only to operational cost efficiency, but he said, “It was very easy to operate, and it doesn’t require a lot of re-calculation every time you use it.”
The filter press chosen for incorporation into the system is manufactured by Siemens Water Technologies of Holland, Michigan. The unit is a 1200mm J-Press® with 25-35 cubic feet capacity. It is a gasketed, one inch recessed chamber type press with mono-multi-filament, polypropylene filter cloths. This filter press is mounted on a roll-off platform to facilitate easy discharge of the filter cake into rollaway dumpsters. The J-Press is capable of producing up to 50% dry solids cake within a two-hour cycle. Schena adds, “Siemens provided lab testing of our wastewater samples in developing the right chemical combination for producing good flocculation of the suspended solids for effective dewatering. In our case it was a combination of an organic salt and Aluminum Chloride Hydroxide.”
Their system was designed to operate with a pre-coat treatment whereby diatomaceous earth is introduced as a slurry to pre-coat the filter cloth in the press so that it aids in catching fine solids from the wastewater as it is introduced into the press. “Pre-coat materials are expensive,” says Schena, “and since we are constantly looking for ways in which to control, if not cut, costs, we found through experimentation that the starch in the wastewater could be separated out with a separator and then introduced into the filter press as a the pre-coat material. The result was totally acceptable to us.”
Results
The wastewater treatment process consists of collecting the dirty water from the washer/peeler, the slicers and wash tank. The washer/peeler wastewater passes through a hydra sieve, which removes the heavy grit and potato pieces before passing through a series of cyclones that remove the finer solids from the wastewater. Most of the processed water is then reused. The water coming from the slicers and washer is laden with starch. This water is pumped through another hydra sieve and cyclonic cone system that removes the starch. This processed water is also reused. The concentrated starch is pumped to a pre-coat holding tank for use as the pre-coat slurry in the filter press. The balance of the wastewater is pumped into the chemical/physical settling tanks and treated by a coagulant/polymer feed system for the flocculation process and the formation of chemical sludge. The settled sludge is drawn off the bottom of the settling tanks and pumped to the filter press for dewatering. The wastewater from the chemical/physical tanks is pumped to the biological trickling filter tank, where the biological sludge is formed, further reducing BOD and TSS. This water then proceeds to a final clarifying tank before being disposed of to the municipal sewer system in compliance with specifications.
Additional wastewater comes off the cooking system from the wash downs, and contains oil and grease in addition to organic solids. This wastewater passes through two receiver tanks, where the oil is removed. It is then pumped into the chemical/physical tanks to settle out the sludge. From there the wastewater is pumped into the filter press. The biological sludge and any sludge from the final clarifier is pumped directly to the filter press for final dewatering and disposal. The resulting filter cake is released into the dumpsters beneath the press for disposal to the pig farmers, landfills or composters. The effluent water from the filter press is either recycled to the Biological Trickling Filter or to the chemical/physical tanks.
It took the John Boyd Company less than 3 months to install their system. “I’m pleased with the way our secondary wastewater treatment system is operating,” said Schena. “It’s the best way we know of to maintain the continuity of our tradition of producing quality chips. While this secondary wastewater treatment system was a substantial investment for us, both in terms of equipment and manpower, had we not made it, we would not be in business today.”