Zero Waste: A Look at the Future of Reverse Osmosis
With millions of gallons of water wasted daily by reverse
osmosis systems in the United States alone, it is no surprise that ZeroWaste technology
is coming to the forefront of the point-of-use (POU) industry. Watts Industries
of North Andover, Mass., is offering its ZRO-4 under counter system intended to
target the independent water dealer market.
Even the best home reverse osmosis systems use four gallons
of water for every one gallon produced. This typically is obtainable only if an
Aqua-Tech permeate pump is used. Most systems waste as much as 20 gallons just
to produce one gallon of product water.
The new technology called "ZeroWaste" eliminates
this problem by returning the concentrate water from the reverse osmosis system
back to the home's plumbing, resulting in 100 percent efficiency. There are
several versions of zero waste available through various vendors but when
shopping around, keep in mind that many of these systems will not meet plumbing
codes. (The only known code-compliant process is the Watts Industries patented
technology.) The system allows for a "legal" cross connection between
the hot and cold water supplies, subsequently reintroducing the concentrate
into the hot water side.
Here is How It Works
The typical POU system (Figure 1) is a five-stage unit
utilizing three stages of pretreatment (one sediment and two carbon filtration)
then a TFC membrane and subsequent permeate and concentrate waters being routed
to both the tank and traditional drain connections.
The ZeroWaste system (Figure 2) takes the water outlet of
the sediment and carbon filters and routes it through a solenoid valve and pump
before going to the membrane inlet. This provides filtered water to the
solenoid and pump, which will keep foreign material from damaging them. Carbon
block filters are preferred because they release fewer carbon fines, but GAC
filters can be used if flushed with water prior to connecting them to the pump.
(Carbon fines will damage the pump and solenoid.) In some systems the filter
configuration allows for water to be routed through the solenoid valve and
pumped from the water outlet of the sediment filter and then to the water inlet
of the carbon filter(s).
A pressure switch will be used to stop the system by opening
the circuit to the solenoid valve and pump. When the pressure in the reverse
osmosis storage tank reaches a predetermined pressure indicating the tank is
full, the pressure switch will open, stopping the system from producing more
reverse osmosis water.
The concentrate water is routed through a flow restrictor as
before, except the flow restrictor size is larger to allow for the back
pressure of the hot water line. The flow restrictor rated size is from 500ml/m
to 600ml/m. The larger flow restrictor will allow the pump to circulate water
at approximately a 4 to 1 ratio of concentrate to permeate.
The actual flow ratio is the same as a standard reverse
osmosis system with no back pressure from the tank.
International Association of Plumbing and Mechanical
Officials (IAPMO) requires the water from the outlet of the flow restrictor be
routed through two check valves before flowing to the hot water supply line.
These check valves ensure the hot water will never reach the membrane on the
reverse osmosis system due to a surge or back pressure in the hot water system.
All of the concentrate water from the reverse osmosis system
will be routed to the hot water supply via a fitting on the angle stop valve
under the sink. This valve is similar to the one on the cold water angle stop
used to provide water to the system. The difference now is the concentrate
water will be flowing into the house water system at the hot water angle stop
valve and out of the water system at the cold water angle stop valve. This
patented process allows for the traditional wash or concentrate water to be
reused in the hot water side of the home.
None of the water is wasted to the drain by the reverse
osmosis system. Instead it is filtered and then diluted in the hot water system
of the house for other uses such as dishwashers, showers, hand washing, etc.
Keep in mind that this concentrate has been filtered by sediment and carbon
filtration and the only reintroduction is in the form of dissolved solids
primarily consisting of calcium carbonates and sodium.
With the long and many times short-term outlook on water
supplies appearing bleak, it is no surprise that zero waste reverse osmosis systems
are here to stay. The efficiency of traditional reverse osmosis systems rated
in the 10 percent to 20 percent range. With the new technology, the rating is
100 percent. As consumers become more aware of water costs and shortages zero
waste technology will become a standard configuration.