In previous posts we have talked about reuse of wastewater for drinking purposes including the feelings of Americans towards the use of wastewater for their water supply. In reality, many American’s already use wastewater as their drinking water source. If your drinking water plant is down stream of another cities wastewater plant, you are in effect drinking their wastewater. This does not include the impact of farm run off and run off from animal waste. The standards for treating water downstream of the wastewater plant is not nearly as high as for direct reuse, but that is what is happening ecluding teh dilution effect.
One aspect of the issue of water reuse that we have not covered is the anlytical aspects for evaluating water quality in these situations. Obviously, utilities must be aware of the different contaminants present in the water and have clearly defined public health goals before deploying technologies to treat the water. Some of the contaminants associated with pharmaceutical or personal care producsts are in extrmely low concnetrations, e.g. nano gram per liter quantities. So, sophisticated analytical techniques are required to measure these contaminants before and after treatment. Additional analytical techniques are required for measuring the advanced oxidants that are sometimes applied in these applications.
In terms of treatment, the complexity of the chemistry of water contaminants at different stages of the water cycle results in no single technology being able to remove all the contaminants. Thus, a multiple barrier system is needed to ensure their reduction and removal. This is the same approach promoted by the US EPA to balance treatment of difficult to remove micro organisms while minimizing disinfection by products.
Advanced oxidation technologies effectively remove many pharmaceutical and personal care products and disinfect the water. Ultraviolet (UV) light can be effective in destroying some contaminants, such as N-nitrosodimethylamine, as well as killing a most micro organisms. Reverse osmosis can remove most contaminants, but creates a concentrated waste stream that contains the contaminants. Ozone, another strong oxidant, can also be used before or after water enters the reverse-osmosis membranes to remove contaminants.
Water reuse treatment often includes the use of UV or oxidation and membrane-based technologies as part of a multibarrier treatment scheme. Alternative schemes such as ozone and granular activated carbon filters are being explored to disinfect the water and remove contaminants, residual odours, discolouration and by-products created by other treatment processes.
Water reuse is slowly becoming a reality in the US out of necessity due to decling water source quality and increasingly stringent regulations. Ozone and advanced oxidation have an important role to play in this regard along with other advanced water treatment technlogies.