Since California has the toughest environmental regulations in the nation, it is particularly noteworthy that Trimac Transportation Services Inc received in 1998 a certificate of merit from the California Water Environment Association and the Hayward (California) Environmental Achievement Award for industrial wastewater control. The awards honored the environmental protection efforts at Trimac's Hayward terminal and tank cleaning facility.
Vehicles based at the terminal provide dedicated transportation service hauling liquid polymers for multinational chemical company Rohm & Haas. After each delivery of the viscous product, the stainless steel tank trailers have to be thoroughly cleaned. Between 20 and 25 polymer trailers are cleaned every day at the Hayward wash rack.
The process requires high-pressure washing of the tank interiors to make sure that all traces of product residue are removed. City water is used for the cleaning process; approximately 160,000 gallons per month.
The waste stream, containing pieces of the solidified polymer, drains into a holding tank before being pumped to a 48-inch stainless-steel Kason Vibroscreen single-deck, circular screen separator. Prior to installation of the separator, the wastewater stream had been pumped directly into the municipal sewer system.
Since city and state regulations demand constant monitoring of the effluent, and payment to the municipality is based on a complicated formula that measures the percentage of solids as well as the volume of water, Trimac's sewerage charges were extremely high. In addition, environmentalists were concerned about the solid particle count, which averaged 8,000 parts per million gallons or approximately 8% of the effluent.
Terry Gillit, Trimac terminal manager, was determined to cut his sewerage costs and satisfy the environmental concerns at the same time. After a series of meetings with the regional Kason representative, the decision was made to install a vibratory screen separator sized to handle the continuous flow of solids-laden waste being pumped by a Wilden diaphragm pump at flows to 158 gallons per minute.
The Kason separator utilizes multi-plane inertial vibration motion in conjunction with carefully selected screens of various mesh sizes to achieve precision liquid/solids and solids/solids separations. Various screen sizes were tested for this application.
The original stainless steel screen was specified in 32 mesh tensile bolting cloth (TBC). Its 610-micron aperture proved unsatisfactory because too great a percentage of solids were allowed to pass into the sewer system. Experiments were then made with a 72-mesh TBC screen. The solids content was cut appreciably, but not enough to satisfy Gillit. Success was achieved with a 105-mesh screen, with an aperture of 165 microns. Solids content was reduced by 50%, providing a savings of $2,000 to $3,000 per month in sewerage costs.
The 48-inch-diameter Kason separator is designed so that all metal parts in contact with the waste feed are made of type 304 stainless steel. All wetted gaskets are furnished in white neoprene. To reduce the impact of the incoming feed on the screen, the unit was equipped with a special splash cover and a velocity breaker. This modification greatly extends screen life without interfering with the rapid discharge of the oversize particles.
A rubber buffered plough mounted in the spout area of the top frame encourages oversize material to discharge without clogging. For portability, the rugged Kason separator is mounted on a modified base with four heavy-duty lockable casters.
As Gillit proudly points to the state and city awards for meritorious service in behalf of the environment, and the economic benefits to Trimac, he is quick to say that he has no intention of resting on his laurels.
He is now reviewing the possibility of further reducing the solids content by additional screening, and the potential for cutting water usage by recirculating the water used for cleaning and screening prior to sending it into the sewer system. For this to be economically feasible, a balance must be found between anticipated savings in water usage and the higher cost of maintenance should the high-pressure spray nozzles become clogged.
One thing is certain. Trimac is determined to improve cleaning and wastewater treatment efficiency while simultaneously cutting costs and serving the ecological needs of the community.