For all the economic and social benefits that the wine industry has brought to Ontario’s Niagara peninsula region, this expanding sector has also introduced a major environmental challenge to the way local municipal wastewater treatment plants go about their business. At the end of each summer these facilities see a sudden spike in material generated as the annual grape harvest is processed. Although this effluent is the result of a straightforward and well established organic processes that winemakers have followed for millennia, the sheer chemical oxygen demand (COD) generated by winery wastewater (WWW) can overwhelm and de-stabilize the biomass used to treat wastewater from all sources.
“It isn’t even necessarily that the compounds in there aren’t ultimately biodegradable,” explains Melody Johnson. “But if a truck comes to the plant and puts it into the process, even a small volume of wine waste can send the instantaneous loading through the roof.”
Johnson, who is currently completing her PhD in the Department of Chemical Engineering at Ryerson University, spent some 15 years as a consulting engineer in the wastewater management field. While working with municipal authorities in Niagara she was struck by the unique nature of the problem posed by winery wastewater and decided to explore this area for her PhD thesis.
She and her advisor, Ryerson chemical engineering professor Mehrab Mehrvar, MCIC, co-authored an article about this research for the January issue of the Canadian Journal of Chemical Engineering, which is freely available. Their article launches a new special series for Can. J. Chem. Eng., Established Leaders in Chemical Engineering, celebrating the accomplishments of outstanding chemical engineering researchers like Johnson and Mehrvar.
In addition to outlining the nature of the risk posed by WWW, they examined approaches to reducing its impact so that it could be handled by existing treatment facilities. Made up primarily of sugars, tannin, and fining materials such as the absorbent clay bentonite, this waste stream can cause a dramatic rise in COD loadings to the aerobic reactions necessary for breaking down organic material. In a typical municipal treatment plant’s influent these levels average around 250 mg per litre, whereas in liquid introduced from wineries they can reach 100,000 mg per litre or more.
“The biological process can be stunted through a limitation on how much oxygenation you can provide to the process with the equipment on site,” explains Johnson.
These drastic BOD levels might be significantly reduced by treating WWW in constructed wetlands, which are contained cells covered with vegetation as opposed to the open lagoons typically found in water treatment plants. Even if winery operators are unwilling to allow such installations to take up valuable agricultural land on their property, these or other processes could be added to existing wastewater treatment sites to create a preliminary process before this particular waste enters the rest of the stream.
Johnson and Mehrvar observe that the Niagara region will need much more of this infrastructure if it is to meet the needs of this major industry as well as a growing municipal population.
“Although available data indicate anaerobic co-digestion is able to provide high levels of COD removal (89%) while producing potentially beneficial biogas as a by-product,” they concluded in their paper, “the ability to co-treat WWW in this manner is limited by the available organic loading capacity of the digesters.”