Beneficial Use of Dairy Wastes in POTWs
Publicly Owned Treatment Works (POTWs) are increasingly facing more restrictive effluent nutrient limits as Total Maximum Daily Loads (TMDLs) are being applied to receiving waters that are impaired due to the presence of excessive nutrients. This is causing an increasing number of POTWs to upgrade to provide total nitrogen control (denitrification and nitrification) and total phosphorus control. The cost of iron addition and subsequent excess sludge handling and disposal are causing more POTWs to upgrade to biological phosphorus removal. The readily biodegradable chemical oxygen demand (CODrb) naturally present in domestic sewage is inadequate for the denitrification and total phosphorus removal needs of these facilities. Historically, these facilities have added methanol as their additional source of CODrb. The cost of methanol had increased 380 percent through the 5 year period ending in January 2007. Additionally, the safety and security risks of handling methanol have posed concerns. These concerns have caused many of these facilities to turn to 56 percent by weight acetic acid as the current low cost source of CODrb. The cost of this material has increased by 35 percent during this same 5-year period. In either case, the cost of this type of supplemental CODrb is only expected to increase for POTWs making the operating costs of denitrification and biological phosphorus removal only increase with time while continuing to be influenced by market conditions. In addition, POTWs are facing rising energy costs (greater than 26 percent increase over the last 5 years). This has caused an increasing number of POTWs to implement energy recovery with anaerobic digestion facilities. This practice will only expand as energy costs continue to increase. Within 200 miles of nearly all POTWs, there are fluid milk plants that supply our nation's steady demand. These plants dispose of a small quantity of benign wastes generated from return products and off-spec products (approximately 0.5 percent of production). This concentrated waste has historically been transported at the industry's expense and utilized as animal feed or applied to agricultural lands. As more and more livestock operations consolidate and the distances to suitable agricultural lands increase, the disposal costs will continue to increase. These concentrated wastes offer a source of CODrb. There is a "win-win" solution for POTWs and the dairy industry with a combined savings projected at $15 million per year. One needs a low cost source of CODrb; the other provides this source and needs a low cost disposal option. This paper presents greater details of this synergy and concludes with case histories of those who have benefited from implementing this solution.
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Document Type: Research Article
Publication date: 2007-10-01
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