A practical framework using odor survey data to prioritize nuisance odors.

There are three main questions that need to be answered to address nuisance odors at the fenceline of a wastewater treatment plant: What odors are occurring at the fenceline of the plant? What processes within the plant give rise to these odors? What priority should we assign to mitigation of the nuisance odors? The prioritization is based on three factors that make odors a nuisance: strength or intensity of the odor when it is detected; quality or description of the odor; persistence or occurrence of the odor at the fenceline. Since fenceline odors vary according to: wind direction; wind speed; atmospheric stability and obstructions (buildings, trees, roadways), this study conducted odor surveys at the fenceline of a wastewater plant between April and November for 20 surveys. The data were used to develop a practical framework in three steps: summarize fenceline (residential vs non-residential) odor survey data; use odor type category and average odor strength to determine the annoyance factor; use annoyance factor and fenceline occurrence to determine the priority rating for nuisance odors to be mitigated.

Philadelphia obtains useful information from its customers about taste and odour quality.

Customers are sensitive to the flavour of water. Customers evaluate drinking water based on their expectations, on experiences with their usual drinking water and on experiences with alternative waters. The Philadelphia Water Department provides one example of success in developing a better understanding of customer perceptions and attitudes about tap water taste and odour. Philadelphia found that customers do communicate in ways that water utilities can understand. Water utilities can enhance that communication and collect useful data. In addition, water utilities can characterise their tap water flavour, track it for changes and correlate changes to customer complaints.

Minerals in drinking water: impacts on taste and importance to consumer health.

More than 100 years of research has focused on removing acute and chronic health threats to produce safe drinking water, but limited research has focused the consequences of removing minerals that affect drinking water taste and health. This paper covers the human sense of taste, typical variations in drinking water taste, comparisons of global taste standards, the role of water chemistry and future research needs for understanding consumer preference. Results of several consumer tap and bottled water acceptability investigations conducted by the authors are presented.

Study of the effect of DMSO on VOS odour production in a wastewater plant.

Odours caused by volatile organic sulphides (VOS) have a history spanning over 20 years for Philadelphia's Northeast Water Pollution Control Plant (NEWPCP). A "canned corn" type of odour has caused residential complaints. Traditional odour control approaches based on hydrogen sulphide failed. This study confirmed that dimethyl sulphoxide (DMSO) from a chemical facility was the dominant cause of the "canned corn" nuisance odour in the form of dimethyl sulphide (DMS). During a discharge, DMSO concentrations up to 12 mg/L were found in the influent of the NEWPCP. Each DMSO concentration peak induced a DMS peak. DMS concentrations increased from less than 50 microg/L to 6 mg/L with a corresponding decrease in DMSO. Approximately 79% of DMSO from the primary sedimentation influent was passed to the effluent, and to downstream processes, such as the aeration tanks where the DMS was volatilised by the aeration. The DMS partial pressure in ambient air of NEWPCP can be between 0.03 and 0.18 x 10(-3) atm during a DMSO discharge. From the above information, the potential of VOS production is estimated and a practical plan for remediation can be designed.

The value of an odor-quality-wheel classification scheme for wastewater treatment plants.

Each odorant possesses a unique odor signature (i.e. odor character or quality, odor threshold and chemical concentration). This paper develops an initial understanding of how the volatile odorous chemicals and their relative concentrations produced are related to the total odor quality from the process by their odor threshold concentrations and odor signatures.

Rating method for evaluating distribution-system odors compared with a control.

A new sensory method was developed and tested at a full-scale water treatment plant. The method evaluates changes in aesthetic water quality during transit in the distribution system. A paired comparison format is used to determine if the odor of a distribution-system sample is different from that of a control sample. The control sample represents the "ideal" water, such as treated water leaving the plant. The method can rapidly determine whether or not a problem exists in the distribution system, and, if one does exist, it allows for characterization of the problem. Over a three-month period a 4-member odor panel evaluated 118 distribution samples by this new procedure. Among the 118 samples tested, 39 samples yielded a consensus among the analysts as to the odor characteristics of the sample; 35 were rated "not different from the control" (about 90%), and only 4 were rated "different from control" (about 10%). The 79 samples for which no consensus was generated had only slight rating differences between analysts and for odor intensity. No taste-and-odor problems were reported by consumers during the time period for this study and the method indicated that no major odor problems existed in the distribution system.

Development of an odor wheel classification scheme for wastewater.

Overall, in the air pollution control field, odor concentration and intensity as well as hedonic rating have been well studied to the point where some level of standardization is being developed or is already in place. However, there has been no standardization with respect to odor quality characterization. There is now sufficient understanding of the types of odorous compounds that can arise from wastewater treatment processes to develop an odor classification scheme. This article presents the first wastewater odor wheel or classification scheme that should form the foundation for the evolution of odor quality data reporting with links to chemical causes.

Health and aesthetic impacts of copper corrosion on drinking water.

Traditional research has focused on the visible effects of corrosion--failures, leaks, and financial debits--and often overlooked the more hidden health and aesthetic aspects. Clearly, corrosion of copper pipe can lead to levels of copper in the drinking water that exceed health guidelines and cause bitter or metallic tasting water. Because water will continue to be conveyed to consumers worldwide through metal pipes, the water industry has to consider both the effects of water quality on corrosion and the effects of corrosion on water quality. Integrating four key factors--chemical/biological causes, economics, health and aesthetics--is critical for managing the distribution system to produce safe water that consumers will use with confidence. As technological developments improve copper pipes to minimize scaling and corrosion, it is essential to consider the health and aesthetic effects on an equal plane with chemical/biological causes and economics to produce water that is acceptable for public consumption.

Predominant bacterial genera in granular activated carbon water treatment systems.

Granular activated carbon (GAC) beds may be used for removal of dissolved organic matter during the treatment of drinking water. However, they might also change the microbiological quality of the water entering the distribution system either by changing the predominant bacteria or the bacterial density of the treated water. A 3-year pilot plant study of water treatment using GAC beds was conducted at the Baxter Water Treatment Plant in Philadelphia. During the study, bacteria were isolated from the raw water and from the effluents of the GAC treatment units. At the end of the study, bacteria were also isolated from the GAC units and from sand beds operated in parallel with the GAC units. Bacterial genera in the GAC effluents and in the GAC units themselves were similar to those found in the raw water and in the sand beds. Prechlorination and (or) preozonation of the water before GAC treatment had no noticeable effect on the bacterial genera found as compared with GAC unit having no predisinfection. The bacterial genera found in this study were similar to those found in seven other studies of GAC water treatment that used a variety of treatment schemes and a variety of heterotrophic plate count techniques to evaluate bacterial populations. From these several studies it appears that GAC treatment does not change the nature of the bacterial populations associated with drinking water.

Bacterial interference with coliform colony sheen production on membrane filters.

The membrane filter (MF) method for detection and enumeration of coliform bacteria in drinking water requires that the coliforms both grow and produce a green metallic sheen when the filter is incubated on modified Endo medium at 35 degrees C for 22 h. Large numbers of noncoliform bacteria, which are enumerated by the standard plate count (SPC) technique, can interfere with the detection of coliforms on MF. This paper presents quantitative evidence from laboratory experiments on the interference of specific SPC bacteria on coliform colony sheen production on MF. Pseudomonas aeruginosa and Aeromonas hydrophila caused significant reductions in Escherichia coli sheen colony counts when present at 3,000 and 220 per filter, respectively. The Flavobacterium sp. and Bacillus sp. selected for this study from SPC did not interfere with coliform colony sheen production. Excessive crowding of E. coli and Enterobacter cloacae colonies on MF also caused a reduction in the number of colonies that produced sheen. Even when there was no crowding (14 colonies per filter), only a fraction of the E. cloacae colonies produced sheen colonies on modified Endo medium.