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The Nebraska Department of Environmental Quality cited Big Ox Energy in South Sioux City in April for failing to control emissions. Big Ox has had repeated problems with the venting of hydrogen sulfide gas and with solid-waste spills.

DAKOTA CITY, Neb. — The owner of a biogas plant in northeast Nebraska said in replies to several lawsuits that two other companies are responsible for toxic odors that fouled a neighborhood.

The Sioux City Journal reported that Denmark, Wisconsin-based Big Ox Energy filed the replies in July in Dakota County District Court to more than a dozen lawsuits filed against the company. The neighbors who filed the lawsuits said odors and gases backed up into their homes, caused health problems and forced them to leave.

Big Ox denied the lawsuits’ allegations and said in its replies that the blame for the odor lies with CHS Inc., a soybean processor that released acidic wastewater into South Sioux City’s sewer system, and Olsson, an Omaha-based engineering firm that Big Ox says recommended wastewater from the plant be routed through a sewer main that ran through residential areas.

Big Ox also said the residents’ plumbing systems did not comply with city codes because they were not equipped with features to prevent odors and gases from entering their homes.

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A CHS spokeswoman has declined to comment on the pending litigation. Olsson representatives and an attorney for the neighborhood residents didn’t immediately return calls Wednesday from the Associated Press.

The plant separates solids from industry wastewater and processes them through anaerobic digesters to create methane that is sold and then injected into a nearby natural gas pipeline.

The remaining wastewater has been piped through South Sioux City’s sewer system to Sioux City, Iowa’s regional wastewater treatment plant on the other side of the Missouri River.

The plant was closed in April for repairs. Big Ox’s Kevin Bradley said Wednesday that the repairs haven’t been completed and that the plant can’t be reopened until Nebraska renews the plant’s two environmental permits. A hearing on that matter is scheduled for Sept. 29.

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