AWWA ACE63059

In addition to water recycling and reclamation programs, indirect potable reuse ofwastewater has occurred over the past few decades, which will likely increase in the future asupstream wastewater treatment plants (WWTPs) discharge water into rivers or lakes that serve asdownstream drinking water supplies. Indirect potable reuse can be defined as any watershed fora drinking WTP (DWTP) that contains point source discharges of wastewater; septic tanksadjacent to rivers may also alter the quality of the surface water. Drought and competing instreamdemands may result in <10- to >50-percent contribution of treated wastewater towardsthe stream flow. Attention has focused on pharmaceuticals and endocrine disruptors, butWWTPs are also sources of disinfection byproducts (DBPs), if chlorine disinfection ispracticed, and DBP precursors.Biological wastewater treatment takes one of two general forms: suspended growth(biofloc) systems (e.g., activated sludge), and attached growth (biofilm) systems (e.g., tricklingfilter). Depending on operational conditions, both can operate as partial or completenitrifying processes. Increased levels of nitrification decrease the concentrations of ammoniaand organic nitrogen (amino) compounds. Nitrification transforms ammonia and organicnitrogen to nitrate. Suspended growth systems under anoxic conditions can denitrify (convertnitrate primarily to nitrogen gas).Treated wastewater (effluent organic matter [EfOM]) has been shown to be a source ofprecursors for a wide range of DBPs (trihalomethanes [THMs], haloacetic acids [HAAs],haloacetonitriles [HANs], and nitrosamines). The objective of this study was to evaluate thecontribution of treated wastewater to DBP formation in drinking water supplies.The authors conducted a full-scale survey of approximately 20 WWTPs in the U.S. (inthe west, southwest, the mountain region, south central, midwest, and northeast). WWTPs weresampled that used a range of treatment processes (oxidation ditch, aerated lagoon, tricklingfilters, activated sludge, nitrification/denitrification, soil aquifer treatment [SAT], powderedand/or granular activated carbon [PAC, GAC], membrane bioreactor [MBR], reverse osmosis[RO], or various combinations). For most of the study sites, samples were collected at theWWTPs and downstream DWTPs, effluent-impacted rivers or monitoring wells.Some of the WWTPs in this study had sequential and/or parallel treatment processes forwhich separate samples were collected. For example, the secondary treatment process at oneWWTP included trickling filters and solids contactors (no nitrification [NH3-N >10 mg/L]),which were followed by nitrifying trickling filters for ammonia removal. Another WWTP hadtwo parallel treatment processes: one train used activated sludge (no nitrification), whereas theother train used advanced biological treatment (nitrification/denitrification).Samples were collected during a wet/cold season and a dry/warm season in 2004, andonce more in a second year (2005). The two sampling events in year 1 were based on hydrologyand treatment considerations. In the summer, river flow is low, so some streams are moreeffluent-dominated; and, there is more nitrification at the WWTP. In the winter there is moreflow and less nitrification. These two seasons showed the different impacts of hydrology andtreatment. In year 2, many of the utilities were re-sampled in the season that provided especiallyinformative data for that system to ascertain temporal (year-to-year) variations. Includes 9 references, figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2006

Number of Pages:

17

File Size:

1 file , 370 KB