Cut water costs — membrane filtration may help
December 15, 2009
by Anne Giesecke
Each bakery will discharge between 20,000 and 200,000 gallons of water each day and pay between $200,000 and $500,000 a year. The cost of discharging water includes fresh water, ingredients, sewer use charges and surcharges. If the bakery is required to treat their discharge water, that would add a capital expenditure of as much as $1 million and annual operation costs of about $50,000 a year.
The waste water discharge from a bakery will go to a sewage treatment plant usually called a Publicly Owned Treatment Works (P.O.T.W.). The discharge is best divided into a sanitary discharge line and a production
discharge line. If the two are discharged through the same lines it is a combined sewer system.
The bakery is charged for the amount of water used and then charged for the amount that goes to the P.O.T.W. In many towns the bakery may be the largest contributor to the P.O.T.W. The discharge of water requires a permit.
The people on the bakery floor know how to cut water use. Engineers know how to fix water leaks and sanitation people know how to do dry clean up, but someone needs to remind them to do these things. Water meters may help identify opportunities.
Reuse of water is an important
option in decreasing water use. Many bakeries have pan and tray washers that reuse water or use very little water. However, the equipment should be checked regularly to be sure that the water use meets the specifications of the equipment and that the equipment is turned off when not in use.
Water also is reused in equipment washing areas where the last rinse of clean water is then the second rinse and the second rinse is then the first rinse. The water is used three times. Water that has been used or used, cleaned (but not to drinking water use) and reused is called “gray water.” Gray water is used for cleaning as described above or for other non-potable uses such as watering lawns. For example, for years,
homeowners in drought areas have used washing machine rinse water to water their lawns.
The newest waste water treatment technology to be used by the baking industry is membrane technology. Membrane filtration for waste water treatment is a technology that has been in use for 20 years. Now the scale, efficiency and cost are within the reach of bakers. The footprint may be the size of a flat bed truck or a 30-foot by 30-foot space; the cost in the range of $150,000 to $500,000. The systems use less energy than other treatment systems. The operation and maintenance costs may start at $50,000 a year and be comparable or less than systems currently in use.
A membrane is a very thin semi-porous sheet of natural or synthetic material that forms a barrier that permits the passage only of particulates or molecules up to a certain size or of a special nature, while permitting the passage of a liquid. Membranes are used in micro, nano and ultra filters and in reverse osmosis treatments. Ultra filtration and micro filtration are, in general, most applicable to baking industry flour and oil wastes. Nano filtration may be required for sugars.
Microfiltration membranes are available in many configurations, including ceramic, tubular, hollow fiber, spiral and flat sheet membrane. Pressure differential forces the waste water across the membranes. Membrane systems are cleaned by back-flushing, chemical washes or mechanically.
As with all waste water systems costs are dependent on the amount of water and waste through the system. The less flow and the less waste, the less cost. Traditional ways of cutting water use may be combined with new technology to keep the cost of water under control or reduced.
In addition, once or twice a year the plant manager or engineer should talk with the P.O.T.W. operator. They should ask about the budget, ask about the technology, perhaps ask how to improve systems and reduce costs. Too often in the bakery the cost of water is unknown to the users of the water in production, engineering and sanitation. Plant managers will be well served by better understanding the cost of water to the bakery and sharing that information and reduction targets with the people who are turning the water on and — most especially — off.