Residue Management

RESIDUE MANAGEMENT

Water treatment plants produce a wide variety of waste products as well as safe and gaseous forms depending on the source of raw water and the type of treatment processes, commonly, coagulation/filtration, precipitative softening plant, membrane separation, ion exchange, granular activated carbon. The differences between the unit processes of the five plant types listed above characterize the type of residuals generated at a given facility. In the current regulatory climate, a complete management program for a water treatment facility should include the development of a cost-effective plan to remove and dispose of residuals.

The following steps need to be considered when developing a comprehensive water treatment residuals management plan:

• Characterize form, quantity, and quality of the residuals;

• Determine appropriate regulatory requirements;

• Select appropriate residuals processing/ treatment technologies; and

• Develop a residuals management strategy that meets both the economic and noneconomic goals established for a water treatment facility.

What are the residuals categories?

Water treatment plant residuals form when suspended solids in the raw water react with chemicals (e.g., coagulants) added in the treatment processes and associated process control chemicals (e.g., lime). Some potable water treatment processes generate residuals that are relatively easy to process and dispose. For example, leaves, limbs, logs, plastic bottles, and other large floating debris separated from water during the initial screening process can be disposed of at conventional solid waste landfills. However, most other treatment processes produce more complex residual waste streams that may require advanced processing and disposal methods to protect human health and the environment.

• The four major types of residuals produced from water treatment processes are:

• Sludges (i.e., water that contains suspended solids from the source water and the reaction products of chemicals added in the treatment process). Pre sedimentation, coagulation, filter backwashing operations, lime softening, iron 1800 and manganese removal, and slow sand and diatomaceous earth filtration all produce sludge.

• Concentrate (brines) from ion exchange regeneration and salt water conversion, membrane reject water and spent backwash, and activated alumina waste regenerate.

• Ione exchange resins, spent granular activated carbon (GAC), and spent filter media (including sand, coal, or diatomaceous earth from filtration plants).

• Air emissions (off-gases from air stripping, odor control units, or ozone destruction).