Treatment of odor by a seashell biofilter at a wastewater treatment plant.

UNLABELLED: Biofilters are becoming an increasingly popular treatment device for odors and other volatiles found at wastewater treatment plants. A seashell media based biofilter was installed in April 2011 at Lake Wildwood Wastewater Treatment Plant located in Penn Valley, California. It was sampled seasonally to examine its ability to treat odorous compounds found in the air above the anaerobic equalization basin at the front end of the plant and to examine the properties of the biofilter and its recirculating water system. The odor profile method sensory panels found mainly sulfide odors (rotten eggs and rotten vegetable) and some fecal odors. This proved to be a useful guidance tool for selecting the required types of chemical sampling. The predominant odorous compounds found were hydrogen sulfide, methyl mercaptan and dimethyl sulfide. These compounds were effectively removed by the biofilter at greater than 99% removal efficiency therein reducing the chemical concentrations to below their odor thresholds. Aldehydes found in the biofilter were below odor thresholds but served as indicators of biological activity. Gas chromatography with mass spectrometry and gas chromatography with sensory detection showed the presence of dimethyl disulfide and dimethyl trisulfide as well, but barely above their respective odor thresholds. The neutrality of the pH of the recirculating water was variable depending on conditions in the biofilter, but a local neutral pH was found in the shells themselves. Other measurements of the recirculating water indicated that the majority of the bio-activity takes place in the first stage of the biofilter. All measurements performed suggest that this seashell biofilter is successful at removing odors found at Lake Wildwood. This study is an initial examination into the mechanism of the removal of odorous compounds in a seashell biofilter. IMPLICATIONS: This paper presents a thorough examination of a seashell media biofilter, a sustainable treatment technology used to remove reduced sulfide compounds. The durable performance of the seashell biofilter ensures that odors will be adequately controlled, preventing odor nuisance to surrounding residences, which is an emerging problem faced by waste management facilities. The odor profile method technique used in this study can be applied in many situations by waste management facilities and regulatory air management organizations for source tracking in relation to prevention and management of odor complaints, respectively.

Comparison of two standard odor intensity evaluation methods for odor problems in air or water.

Government agencies responsible for ensuring healthful water and/or air quality are often faced with resolving public complaints of nuisance odors. Understanding variations in odor intensity may ultimately lead to the establishment and application by such agencies of quantitative limits for effective odorant control. An odor panel was trained in suprathreshold odor intensity evaluation using both the ASTM Method E544 (Butanol Method) and the APHA Method 2170 (Flavor Profile Analysis (FPA) Method). A linear mixed model was fitted to the panel data, taking into account the fixed effects of concentration levels and the random effects of panelists and sessions. The FPA method proved easier to administer and revealed less inter-session variance than the ASTM Method, suggesting its greater utility in applications involving odor panels. For both methods, there was a high standard deviation, relative to the mean. This finding indicates that the intensity scales may be useful for understanding relative odor intensities, but should not be used as a precise measure, or as a basis for establishing regulatory limits.