The wet wells and large diameter pipes can be protected from the biofilm formation and zebra mussels attachment using monochloramine. Monochloramine is more stable than free chlorine residuals, so their disinfection ability to prevent biofilm growth and zebra mussel attachment is long-lasting. However, NDMA is formed as disinfection by-product as a result of chloramination of raw water. NDMA is included in the USEPA Contaminants Candidates List 3. Monochloramine can be formed by adding chlorine and ammonia directly to the water in the large diameter pipes, but this method of the addition will fail to protect the intake structure, wet well, and pumps from zebra mussels and biofilm growth. Alternatively, chlorine and ammonia can be added directly to the wet wells, only if proper mixing is established. In reality, it is very challenging to provide complete mixing in the wet wells resulting in the poor recovery of monochloramine. Hence in this study, the preformed chloramine addition (Monochloramine is formed in the smaller pipes with complete mixing and well-controlled pH) is considered. The lake water samples were brought from Cedar Creek (CC), Richland Chambers (RC), Lake Palestine (LP) and Lake Benbrook (LB). The experiments were conducted for both direct and preformed monochloramine additions. The preformed chloramines (2mM) were prepared at different reaction times (2 minutes (CC, RC), 90 seconds (LB, LP), 80 seconds (RC), 35 seconds (CC, RC), 30 seconds (LB, LP) and 20 seconds (RC)), then added to the 2L pH 8.3 adjusted lake water containing batch reactor to target 3.55 mg/L. Also, different chlorine to ammonia ratios was considered. Monochloramine decay and the NDMA concentrations were measured at 30 minutes (short-term decay) and 48 hours (long-term decay). The NDMA concentrations measured from the preformed additions at 30 minutes and 48 hours were not significantly different from the direct additions. In both the methods, the NDMA concentration at 48 hours was significantly greater than 30 minutes. NDMA concentration in the water significantly increases with the longer contact time with monochloramines.Considering different water qualities, reaction times and the two ratios (4:1 and 5:1); the NDMA concentrations increased from 3.2 ± 2.11 ng/L at 30 minutes to 6.0 ± 3.31 ng/L at 48 hours. Though 87 % percent increase seen in the NDMA concentration it is below the California EPA‘s notification level of 10 ng/L.

Study of N-Nitrosodimethhyleamine (NDMA) formation in the untreated surface water using preformed chloramines

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.