sary when wastewater is to be reclaimed for potable purposes. Table 1-1 provides a list of advanced treatment processes, arranged by the types of constituents they are designed to remove.

The process used by Water Factory 21 in Orange County, California, to treat wastewater prior to injecting it into selected coastal aquifers to form a seawater intrusion barrier is illustrative (see Figure 1-2 and Box 1-2). The advanced treatment of this water includes additional removal of suspended material by chemical coagulation with lime, alum, or a ferric salt. This process is generally quite effective in removing heavy metals as well as dissolved organic materials (McCarty et al., 1980). Recarbonation by the addition of carbon dioxide then neutralizes the high pH created by the addition of lime. After that, mixed media filtration is used to remove suspended solids. The flow is then split between granular activated carbon, which removes soluble organic materials, and reverse osmosis (RO), which is used for demineralization, so that when blended with the remaining water the mixture will meet total dissolved solids requirements specified for injected water. Reverse osmosis can also remove the majority of the dissolved nonvolatile organic materials and achieve less than 1 mg/liter of dissolved organic carbon in the treated water. According to measures of identifiable contaminants, water treated in this manner is often of better quality than some polluted surface waters now used as

TABLE 1-1 Constituent Removal by Advanced Wastewater Treatment Processes

Principal Removal Function

Description of Process

Type of Wastewater Treateda

Suspended solids removal

Filtration Microstrainers


Ammonia oxidation

Biological nitrification


Nitrogen removal

Biological nitrification/ denitrification


Nitrate removal

Separate-stage biological denitrification

EPT + nitrification

Biological phosphorus removal

Mainstream phosphorus removalb



Sidestream phosphorus removal


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