No abstract

Flavor profile analysis proves to be a reliable method of evaluating odors in water, especially when performed by well‐trained panelists using familiar descriptors. The odors of 15 organic compounds were evaluated by the flavor profile analysis (FPA) method. The FPA data were well described by the Weber‐Fechner law, as indicated by the R2 values (0.6–0.99). Odor threshold concentrations were obtained and ranged from <0.01 μg/L (geosmin, 2‐methylisoborneol, and 2t,6c‐nonadienal) to 60 μg/L (phenethyl alcohol). Changes in qualitative descriptors were observed among structurally related compounds and with changes in compound concentration; thus, exposing FPA panelists to a variety of compounds, each at several concentrations, will aid in familiarizing the panelists with the diverse odor descriptors that can be encountered.

The influence of several environmental factors (e.g., light intensity, temperature, nitrogen, and phosphorus) on population density and odor-compound production of two chrysophytes, Synura petersenii and Dinobryon cylindricum; and two cyanobacteria, Anabaena laxa and Phormidium calcicola was investigated. The odors associated with each alga were evaluated by flavor profile analysis (FPA) at several intervals during their initial culturing in defined media. Algal cell and media extracts were analyzed individually by capillary gas chromatography-mass spectrometry (GC-MS). Both cyanobacteria produced geosmin (“earthy” and “corn” odors); however, the P. calcicola also produced relatively large amounts of MIB (“musty-earthy” odors). Both chrysophyte cultures contained 2t,4c,7c-decatrienal (“fishy” odor); and in addition, 2t,6c-nonadienal (“cucumber” odor) was isolated from the S. petersenii. Young cultures of Anabaena laxa (e.g., &lt;20 days) retained most of the geosmin produced. Throughout its population growth, more than 80 percent of the MIB and geosmin produced by P. calcicola was detected in the media rather than in the cells. Synura petersenii,produced more 2t,4c,7c-decatrienal than 2t,6c-nonadienal and retained nearly 90 percent of both compounds throughout the algal population growth. Dinobryon cylindricum produced 2t,4c,7c-decatrienal, and, like the S. petersenii, retained most of the compound. Greater production of the compounds by the two chrysophytes was apparently associated with log-phase growth rather than specific environmental conditions; extended log-phase growth (and prolonged production of compounds) was observed in the S. petersenii culture during the low-temperature treatment.

The six algal metabolites, at concentrations of 20-225 μg/l, were oxidized with potassium permanganate, chlorine, or chlorine dioxide at doses of 0.25-3 mg/l. Flavor profile analysis (FPA) was used to determine the odors of the solutions before and after oxidation. Linoleic and palmitic acids, which are odorless compounds, were oxidized to odorous products by all three oxidants. The odor intensity of β-cyclocitral (grape, sweet tobacco) and phenethyl alcohol (rose, floral) was only slightly decreased by any of the oxidants. Oxidation by permanganate or chlorine either eliminated or greatly reduced the odors associated with linolenic acid (watermelon) and 2t,6c-nonadienal (cucumber); chlorine dioxide was ineffective at reducing the cucumber odor of 2t,6c-nonadienal. Oxidation, at doses typically applied for drinking water treatment, can result in the destruction of certain algae-related odors but in the formation of other odors.

Anaerobic lagoons and liquid manure storage basins are widely used for the treatment and storage of livestock and poultry manure. Although relatively inexpensive to construct, these devices have been widely criticized based upon their odor and ammonia release. A floating, permeable, composite cover manufactured from recycled polyethylene chips topped with a geotextile layer containing zeolite particles was evaluated under both laboratory and field conditions. Under laboratory conditions, the cover was found essentially to eliminate odor release and to reduce ammonia emissions by approximately 80%. When installed on a 0.4 ha swine manure lagoon in eastern North Carolina, the cover survived severe storms and allowed even intense rainfall to pass through without causing cover inundation. Under these field conditions, the cover was found to reduce ammonia emissions approximately 80%. Odor emissions measured twice during one month of the study were consistently low in concentration and near neutral relative to quality, as determined by an analysis by a trained odor panel. Microbiological examination of the cover after four months of use showed an active population of aerobic bacteria and protozoa; analysis showed that nitrifying, sulfide oxidizing, and methanotrophic bacteria were likely trophic components of the microbial populations observed. The surface of the cover became covered with an algal population within two weeks of installation. This and other vegetative growth had no discernable impact on the performance of the cover.