The Brazos River Authority, part of the Waco (TX) Metropolitan Regional Sewage System, has begun using a new odor control treatment process that features a mineral product which is approximately 60 percent limestone and 40 percent magnesium hydroxide.
Over the years, the 37.8 mgd Brazos plant has tried various odor control schemes with limited success. The main source of odors was the plant's solids handling facility. Along with its normal flow, the plant also treats 3 mgd of concentrated solids.
In late 2000, Wayne Rucker, an independent wastewater treatment consultant, discovered an unlikely source for solving this problem. A small mining company called Applied Chemical Magnesias Corp. (ACM), Fort Collins, CO, which has a mine just outside of Van Horn, TX, has been producing a bi-polar mineral made up of limestone and magnesium hydroxide. The deposit of this unique 60/40 mineral combination is the only known deposit in North America. The company had been selling its product into fire retardant applications and was unaware of the potential for its use as a wastewater treatment additive.
It is no secret that magnesium hydroxide slurry can be used to adjust pH and fight the creation of sulfides. However it has not been widely used due to the costs involved. Manufacturing magnesium hydroxide is an expensive process. Add to that the cost of shipping, with half of the weight being water, and its use becomes prohibitively expensive. ACM's product, MW60-40, is a naturally occurring, dry material that is mined at a significantly reduced cost per ton.
The qualities of MW60-40 as an odor control agent were unknown. At first no one was sure that a product that is dry and only 40 percent magnesium hydroxide would work effectively. However, magnesium hydroxide slurry is 50 percent water, so it appeared to be worth testing. The big question was whether or not the addition of limestone would create problems or be an added benefit.
Apparently the limestone did no harm because the preliminary test results were good. The pH stayed between the range of 6.1 and 6.8 while the measurable sulfides stayed below 10 ppm. An exception and spike occurred on Jan. 23, 2001, when the temporary product delivery system failed. While the system was down, the pH dropped and the sulfides skyrocketed.
"Our results are preliminary, but very encouraging," said Rucker. "I will feel better after we get a few more tests completed."
Scientific tests are all good and fine, but the real test comes down to the people affected on a day to day basis. Bob Shumate, Regional Superintendent supervising the plant, said the odors are being eliminated.
"We think it works," Shumate said. "The H2S odors, rotten egg odor can get pretty prevalent. Once we started feeding the material, it changed the way it smelled. And when we ran out last week, we could tell that the odor immediately began to return. According to our noses it is working pretty good."
The plant has been feeding about a ton of the material daily, using an auger feeder with a vibrating hopper to prevent bridging. The dry powder is mixed with water in a tank then a vacuum induction system feeds the slurry into a junction box where it is mixed with the primary sludge using normal system hydraulics, Shumate said.
Robert McCreless, President of ACM, said testing is continuing elsewhere, but the results have all been the same as those found at the Brazos River Authority.
"We have independent laboratory results, as well as acknowledged results from the neighbors of a dairy in Hudson, Colorado. We know that this product stops the formation of hydrogen sulfide and the offensive sulfide odor."
About the Author:
Drake Johnson is a free-lance writer based in Fort Collins, CO.