Characterization of odors from limed biosolids treated with nitrate and anthraquinone

Complaints from the public due to odor emissions are one of the biggest problems associated with any biosolids land application program. Chemical additives to reduce or mask odors are one option for producers; however, many chemicals are too expensive or are too unstable to use safely. This project provides a preliminary evaluation of nitrate or nitrate + anthraquinone as additives in controlling odors from limed biosolids. Over a twenty-four day period, odors were measured in the headspace over several treatment levels using two different chemical analysis tools along with olfactometric evaluation of odor intensity and hedonic tone. On six days during the sample period, hydrogen sulfide was measured using a Jerome 631X, a sensor that also responds to other reduce sulfur gases. Other specific sulfides, amines, and mercaptans were also determined using solid phase microextraction with gas chromatography-mass spectrometry. A simple sniff test approach was used with six panelists on five days during the project. The chemical analysis results revealed that the addition of nitrate and especially nitrate + anthraquinone was effective in reducing concentrations of hydrogen sulfide and methylmercaptan when compared to untreated limed biosolids. However, the olfactometric results did not reveal any significant differences between treatments. The panelists also found that all treatments exhibited a fishy or ammonical character, indicative of amines, or ammonia. More advance olfactometric analysis utilizing dilution techniques might have been able to distinguish between treatments, but it is likely that amines were the dominant odorant released from all treatments. This preliminary project suggests that chemical addition of nitrate or nitrate + anthraquinone would be most effective in controlling odors from unlimed biosolids such as anaerobically digested materials.