By Lex Wahl, Pretreatment Coordinator, Panama City
Many municipalities have adopted a fats, oils and grease programs to protect collection systems and prevent sanitary sewer overflows. You have heard of CORE, right? (FIPA’s model Cooking Oil Recycling Effort.) This program, and others, are very well intentioned. On the surface recycling used cooking oil seems like a win-win program. Recycling keeps a good bit of fats, oil and grease out of wastewater collection systems ensuring that wastewater facilities are protected from products they cannot treat and all is well. Correct? Well, not so fast!!!
The purpose of this article is to address the primary application for which used cooking oil is collected, the production of bio-diesel fuel, and by products there from. Due to the escalating cost of petroleum based fuel biodiesel production has become in vogue both in large production facilities and as well as casual pastime for the backyard, do-it-yourself mechanic. Bio-diesel is a renewable fuel that can be used in place of or in addition to petroleum based diesel fuel.
Bio-diesel manufacturing, in many cases, uses transesterification, which involves the mixing of natural vegetable oils or animal fats with an alcohol in the presence of a catalyst and is heated in a reactor (still) to produce biodiesel, and byproducts like glycerin
According to Biodiesel Magazine the US glycerin market is overflowing. At one time glycerin fetched a price of 20 to 25 cents per pound. Thanks to biodiesel sellers are lucky to get 5 cents per pound for glycerin today.
There are a few other things you should know about glycerin. Although sometimes considered environmentally friendly and non-toxic glycerin has a tremendous biological oxygen demand. BOD concentrations of 4,500—to 35,000 mg/l have been observed. Glycerin acts as a surfactant. Some plant operators have reported poor clarifier performance as a result of the presence of glycerin. Due to the density and viscosity properties of glycerin WWFs may experience interference if enough glycerin finds its way into the collection system.
Operators that have been victimized by glycerin dumping complain of the inability to raise dissolved oxygen (DO) in the reactors during React/Fill cycles of Sequencing Batch Reactors and observe very little increase in DO during the React cycle. Operators also complain of a “white milky substance in the supernatant with some foaming.” White, opaque coatings of film have been observed on the crystalline sleeves protecting Ultra Violet (UV) lamps which can render UV disinfection ineffective. The usual suspect, glycerin. Larger WWFs may never feel the effects of glycerin. Smaller plants like those featured under “Spot Light,” are likely to feel the sting.