The US Environmental Protection Agency (USEPA) has recently (December 1998)
promulgated the Stage 1 Disinfectants/Disinfection Byproducts (D/DBP) Rule. When
effective (in 2001 for large systems), this rule, will require utilities to
comply with maximum contaminant levels (MCLs) for trihalomethanes (THMs),
haloacetic acids (HAAs), bromate and chlorite. In order to reduce exposure to
other DBPs, this rule will also require utilities to achieve specified removal of
natural organic matter (NOM) as measured by total organic carbon (TOC). All
surface water utilities with conventional treatment systems (including
sedimentation) are required to implement this treatment technique termed enhanced
coagulation. Enhanced coagulation can be achieved by increasing the coagulant
dose, lowering the pH of coagulation or a combination of the two. Increasing the
coagulant dose typically results in the formation of greater quantities of flocs
which incorporate NOM and remove them through settling and filtration. On the
other hand, lowering the pH of coagulation results in better charge
neutralization which increases the rate of incorporation of NOM into the
settleable and filterable flocs. Although both of these techniques may adequately
remove NOM to satisfy the enhanced coagulation requirement, the latter method
will generate smaller quantities of sludge and is preferable for some utilities.
Utilities which practice enhanced coagulation by lowering the pH of coagulation,
typically uses a mineral acid (e.g., sulfuric acid) for pH reduction. An
alternative to the mineral acid for pH adjustment is the use of carbon dioxide.
Carbon dioxide is commonly used in softening plants to perform recarbonation
after the softening process. It has recently been used as a means for pH
reduction for enhanced coagulation at the City of Chandler, Arizona. This paper
presents various design and operational considerations for a carbon dioxide
system for enhanced coagulation purposes. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 760 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 9 |
| Published : | 01/01/1999 |
