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March 23, 2011

Achieving Zero Liquid Discharge Status

By converting one of its ethanol plants to a zero-discharge facility, one renewable-fuels manufacturer is saving 100 million gal/yr of water

Rick Vondra, Patriot; and Charlie Kroeger, US Water Services

Water-supply issues are emerging as a national concern with certain sectors coming under increasing scrutiny. This is certainly the case with the ethanol industry. State discharge regulations dictate that plant designs incorporate technological solutions to minimize water use. These designs give operators increased flexibility in terms of enabling the reuse of water streams internally, with the goal to discharge no water to the environment. When this can be accomplished, the plant operates as a zero liquid discharge (ZLD) facility.

Efforts to operate as a ZLD facility bring additional challenges to an ethanol production plant, because process water quality must be compatible with the biological processes that are at work during critical fermentation stages, and will affect co-product quality, as well. As a result, the complexity and risks associated with failing to properly integrate the water system design with the underlying ethanol process can become painfully manifest. The wrong decisions can be disastrous and costly, leading to operational difficulties, unscheduled downtime and even complete process shutdown.

US Water Service (USWS) has participated in the design of a number of ZLD plant designs in order to allow plant operators to meet key water-quality requirements that are required for ethanol production. While USWS had historically designed traditional water systems in a number of industry sectors, the company embarked on its first ZLD facility for an ethanol plant in California. That facility began operations in 2006 after a year and a half of careful design and construction. This was the first operational ethanol plant in the U.S. to incorporate ZLD concepts that were mandated by California regulations.


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