Vibratory Screener Solves Water-Recycling Problem
The water recycling process is an integral part of many growing operations due to water's rising cost and increasing scarcity in many parts of the world. In many cases, an important feature of the recycling system is that it does an efficient job of cleaning up the water to avoid contamination problems.
Catoctin Mountain Growers, Detour, Md., a wholesale grower that recycles up to 500,000 gals. per day, had a contamination problem. Catoctin grows 600,000-700,000 chrysanthemum and 200,000 poinsettia plants annually plus a variety of bedding plants that the company sells to big box stores, such as Wal-Mart and Sam's Club. The company grows this huge quantity of plants in a 9-acre greenhouse and 3 acres of outdoor space.
Chrysanthemums and poinsettias are grown in pots on a concrete floor, which is divided into 54 bays, each of 4,500 or 9,000 sq.ft. The plants are watered by flooding the bays sequentially to a depth of about 4 inches for a total of approximately 10,000 gals. in a smaller bay. Water is pumped continuously from storage to the floor then back to storage at a rate of 1,000 gals. per minute. At the 10,000-gal. main storage tank, the water is filtered to remove leaves, peat moss and other debris before being recycled.
The company was using a cascading filter (a sloped screen) to remove this material, but it did not work well, said Robert VanWingerden, Catoctin's owner. "It was a pretty fine screen, but it let debris fall into the tank and this became a source of disease that caused problems with the flowers."
VanWingerden had the filter replaced by an electrically driven circular vibratory screener that solved the problem. The Flo-Thru Vibroscreen separator, made by Kason Corp., uses a 72-inch-diameter vibrating screen to remove debris before the water goes into the tank. "It does a good job — the water is clean," said VanWingerden.
Catoctin's Water Usage
For about eight hours a day, Catoctin cycles water from storage, through the greenhouse and back through the vibratory screener. The company does not discharge water to the sewer and supplies water from a well or a pond to make up what is used by the plants. Make-up water accounts for about 10 percent of the volume.
Catoctin has enough storage to fill two bays and part of a third at one time, so the usual situation is that the first bay in the sequence is being drained while the second is full and the third is being filled. Valves control the flow in and out of each bay. Water is retained in a bay for a few minutes then is drained to one of two 2,000-gal. sump tanks.
From there, the water is pumped up to the Flo-Thru Vibroscreen separator mounted atop the main storage tank, which is about 10-ft. tall. Water recycled through the tank is retained in two 30,000-gal. tanks, for a total storage capacity of 70,000 gals.
The volume of water recycled ranges from zero up to 500,000 gals. per day, and an individual bay may be flooded once a day or only once every few days. "It all depends on the type of crop, the size of the flowers and the ambient temperature," VanWingerden said. The entire operation is computer controlled.
Catoctin's separator has a single screen deck of 145-mesh tensile bolting cloth (TBC), with a 16-mesh TBC backing screen for reinforcement. The stainless-steel screen is supported on a stainless-steel frame that has radial arms for structural strength. The machine is powered by two unbalanced-weight gyratory motors (0.75 horsepower each), mounted opposite each other on the unit's exterior wall. Wastewater is fed onto the middle of the screen and the vibratory motion imparted by the motors causes oversized particles to migrate to the periphery, where they are removed through a discharge spout. Water falls directly through the screen and through a funnel into the main tank.
The side-mounted motors differentiate the Flo-Thru machine from Kason's standard Vibro-screen separators, which have a ç single gyratory motor mounted under the screening chamber. The Flo-Thru design has a bottom outlet that can be located directly below the inlet, allowing a much higher flow rate. This was important for Catoctin's needs, said Kason representative Christopher Dugan of Separator Technology Co., who installed the machine.
Another feature of the separator is it has a much lower profile since the motors are side mounted. This was important because of the limited space between the top of the tank and the ceiling. The separator, which is only 47 inches tall, fits into the restricted space with little room to spare.
Easy To Clean, Maintain
Prior to installing the machine, VanWingerden considered a textile cloth filter in which water is pumped over a section of cloth that is pulled from a large spool. Periodically, a clean length of cloth is pulled off the roll. VanWingerden opted for the Flo-Thru machine with a stainless steel screen because, "I liked how it took the debris off and you don't have to keep putting in new cloth."
On the other hand, silt left on the Kason machine's screen at the end of the day dries overnight and slowly builds up over time, he said. "Material would not build up if we operated 24 hours a day, but the screen is relatively easy to remove, so we take it out about once a month to flush it with water.