Protecting Distillers Grains from Sulfur Build-up

Excess amounts of sulfur in distillers grains could result in a less desirable product, affecting the company's bottom line and its reputation.
By Tom Slunecka | May 04, 2009
In today's marketplace, maximizing the value of ethanol co products has never been more important, and contaminants in an ethanol plant's distillers grains can impact overall profitability in many ways. Producing a product that is in any way not compatible with industry standards could not only potentially reduce the plant's ability to sell its distillers grains but could also affect the plant's overall reputation. A facility's distillers grains customers must feel confident that the feed source they are purchasing for their livestock is a safe, as well as cost-effective, product.

The amount of sulfur in distillers grains is one of the most important product elements for plants to be aware of. While sulfur at small doses is an essential nutrient, excessive amounts are a concern in all species, especially ruminants. Sulfur at high levels can cause a decrease in the rate of weight gain and at worst may cause Polioencephalomalacia (PEM), commonly known as polio,which can lead to death. Such results could cause major damage to a plant's reputation and reduce the price they command for its distillers grains.

Sulfur is an essential macro-mineral for all livestock species. It is contained in essential amino acids such as methionine and cystine and is also found in the B-vitamins, thiamine and biotin. The 2005 National Research Council guidelines recommend a 0.3 percent total dietary sulfur on a dry matter basis for livestock consuming high concentrate rations, such as feedlot cattle and 0.5 percent total dietary sulfur on a dry matter basis for livestock consuming forage-based rations, such as beef cows. Sulfur can come from the following sources:

›Distillers grains

›Water supply

›Other feed additives

In distillers grains, sulfur build-up occurs due to an additive effect associated with typical processing practices. Corn contains about 0.12 percent sulfur. The addition of other sulfur-containing compounds can quickly elevate the sulfur content of distillers grains. Additionally, yeast will add to the amount of sulfur in the distillers grains. Ethanol producers can improve the marketability of their distillers grains by consciously trying to minimize sulfur additions whenever possible.

The recycling and reuse of water streams within these plants may increase the sulfur concentration by as much as 300 percent, according to James Chapman, Ph.D, dairy technology manager for Prince Agri Products Inc. In addition, several chemicals that are utilized during the typical ethanol production process can contribute to higher sulfur levels in the finished product. Among the chemicals that are major culprits in elevated sulfur concentrations in finished products are:
1. Sulfuric acid
2. Cleaning acids (sulfamic acid or sodium bisulfate)
3. Sodium bisulfite used in ethanol carbon dioxide scrubbers.

Sulfuric Acid
Sulfuric acid is the largest non-naturally occurring contributor to sulfur levels. Sulfuric acid is used for pH adjustment to optimize fermentation and distillation conditions. The generation of chlorine dioxide from sodium chlorite is improved with the addition of sulfuric acid. The industry needs to be wary of adopting antimicrobials that can add more sulfur to DG through the addition of sulfuric acid.

Cleaning Acids
Sulfamic acid, as a cleaning agent, is used to remove mineral scale in heat exchangers. The amounts and frequency of cleanings need to be minimized, within reason, to reduce the contribution of sulfur into the recycle streams while still maintaining a clean system.

Sodium Bisulfite
Sodium bisulfite is utilized to remove acetaldehydes from the carbon dioxide scrubber. Its use can be minimized by making more frequent inspections of scrubber gas emissions to insure that the sodium bisulfite dosage is optimized. Overuse of sodium bisulfite will contribute to sulfur levels and can stress the yeast into producing more glycerol thus reducing ethanol yield.

"High sulfur can be devastating to a livestock producer," says Chapman. "As such, making informed decisions about the production aids used in ethanol production plants, and working closely with live-stock producers to minimize the addition of sulfur in their operation will make significant strides towards reducing the negative outcomes associated with distillers grains. This technical vigilance will ultimately increase the broad acceptance, safety and profitability of our industry as a whole."
Chemical companies are willing to work closely with ethanol plants and their distillers grains customers to assist in reducing sulfur content and its associated negative effects. If a plant manager discovers a problem with the facility's fermentation process, an on-site diagnostic test kit can be used to collect data from areas within the plant where suspected contamination has occurred. A successful resolution to a customer's problem will result in a series of recommendations to alter the operating parameters of the fermentation process.

Tom Slunecka is the vice president of marketing for Phibro Animal Health Corp.'s Ethanol Performance Group. Reach him at or (402) 575-5855.