Recycling Treated Municipal Wastewater for Industrial Water Use

TM3: Recycled Wastewater System Components and Costs
Recycling Treated Municipal Wastewater for Industrial Water Use
discharge limits, notably for phosphorus. The WWTP can incorporate a unit process
that optimizes chemical addition for phosphorus removal and achieves some other
dissolved solids removal. While lime softening is what is needed for hardness
removal; metal salts, the chemical of choice for phosphorus removal, can achieve
some reduction in dissolved solids. In addition it provides a polishing step to ensure
that phosphorus concentrations in the reclaimed supply are consistently below 1
mg/L.
The facilities for chemical addition through sedimentation can be package or
proprietary systems or designed systems, typically with in-ground tanks. The
proprietary systems are typically more compact and well suited for a reduced
footprint. Two process systems commonly used for coagulation, flocculation and
sedimentation are the Kruger Actiflo and Infilco Densadeg. For larger flows, it is
likely that specifically designed facilities would be used. The sedimentation process
would be followed by a filtration process, as described in Section 3.2.3.
3.2.3 Residual Suspended and Colloidal Solids Removal (Filtration)
The removal of suspended solids from WWTP secondary effluent is a physical
process typically performed by one of the following technologies: depth filtration,
surface filtration, membrane filtration, and dissolved air flotation (DAF). Membrane
filtration is also used for colloidal solids removal.
Depth Filtration
Depth filtration is used in water reuse applications for a variety of purposes
including: additional removal of particles for more effective disinfection; as part of the
process train following lime softening or chemical precipitation of phosphorus; and as
a pretreatment step for additional treatment processes such as membrane filtration,
carbon adsorption or advanced oxidation.
Depth filtration has a long history of use in the treatment of potable water. The same
principles and design features are used in the treatment of wastewater effluent.
Particulate material is removed by passing the water through a filter bed of granular
or compressible filter media. There are a variety of depth filters used for reclaimed
water applications (Metcalf & Eddy, 2007; as adapted from Tchobanoglous et al, 2003)
and include:
Conventional downflow – consists of a single, dual or multimedia filter material
(sand and anthracite are most common)
Deep-bed downflow – a deeper bed filter than conventional downflow filters;
allows for extended run lengths
Pressure filters – operate as conventional gravity filters, but in a closed vessel
under pressurized conditions achieved by pumping; achieve longer filter runs and
are typically used for smaller systems
Proprietary Filters
o Deep-bed upflow continuous backwash
o Pulsed-bed
o Traveling bridge
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