Treatment Plant Benefits of Upstream Odor Control Chemical Addition

Orange County Sanitation District (OCSD) operates two wastewater treatment plants treating an average 210 million gallons a day (MGD) and maintains 426 miles of trunk lines within the service area. A program to continuously add chemicals to the collection system was initiated in 2001 with the simultaneous addition of ferrous chloride and hydrogen peroxide (PRISC). Prior to that, sodium hydroxide (caustic) was routinely added in trunk lines to remove slime layers and control odors. Continuous chemical addition at strategic locations reduced hydrogen sulfide (H2S) below 25 ppm continuously, protecting the trunk lines from corrosion caused by excess H2S and reducing odor complaints. In 2005 the upstream odor control program utilized alternative chemical treatment which included ferrous chloride, magnesium hydroxide and calcium nitrate. The upstream chemical treatment has reduced treatment plant odor control chemical use and ferric chloride demand in the digester to control Hydrogen Sulfide (H2S) levels below 40 ppm in the digester gas. In addition to direct chemical savings, primary treatment performance is improved and digester gas increase have been realized.