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Most people think as little as possible about the wastewater that is produced daily from their showers, bathtubs, sinks, dishwashers and toilets. But with the right techniques, it can become a valuable resource.

On average, every Americans uses for purposes that include flushing toilets, showering and doing laundry. This figure can easily double if outdoor uses, such as watering lawns and filling swimming pools, are also included.

Most of the used water will eventually become wastewater that must be . And that treatment uses a lot of energy. According to the U.S. Environmental Protection Agency, water and wastewater facilities account for .

My research focuses on . This process is difficult because wastewater contains many different types of contaminants. But researchers in our fields are exploring many creative ways to make valuable products from them.

Energy from organic materials

Diehard wastewater engineers understand the value of wastewater, which they view as an asset rather than a waste. That's why some of them call it "used water" instead, and refer to what most people call wastewater treatment plants as water resource recovery facilities.

In fact, wastewater can contain . One simple and mature technique for recovering part of this energy is , a natural process in which microorganisms feed on grease and other organic materials in wastewater and produce biogas, just as yeast can eat up barley and spit out beer. Biogas contains , which can be used as a renewable fuel for boilers, furnaces and heating systems or to turn turbines and generate electricity.

More advanced techniques, such as , take sewage sludge – the solids removed from wastewater during treatment – and convert it into biobased fuels that can be used to replace gasoline and diesel fuel. This process is currently at the .

In additional to sewage sludge, many researchers – including me – are very interested in microalgae. Microalgae are , and some of them can grow in wastewater. My colleagues and I have designed hydrothermal systems to . They are still being tested in the lab, but we hope to scale them up in the near future.

Mining nutrients from wastewater

Wastewater also contains nutrients like nitrogen and phosphorus, which are essential elements that plants need to grow. In current wastewater treatment processes, we use energy to , which comes , into nitrogen gas. However, industries then use large quantities of natural gas to convert nitrogen gas back into ammonia, predominantly for producing fertilizer, through the .

Clearly, it would be much more efficient to directly extract the ammonia from wastewater without converting it. One way is to use urine-diverting toilets, which already are , to separate urine from other sources of wastewater. Then the collected urine could be used as fertilizer after sanitizing it to remove pathogens.

Sanitized urine also contains other nutrients like phosphorus and potassium. The , a Vermont-based nonprofit supported by federal agencies and foundations, is researching ways to turn human urine into fertilizer. The institute is testing harvested urine on real crops, and has found that .

Alternatively, we can recover these nutrients as , or magnesium ammonium phosphate, a mineral that contains magnesium, nitrogen and phosphorus. Struvite can naturally form during wastewater treatment processes, but tends to deposit in tanks and pipes and will damage the equipment if left unattended. By controlling the formation of struvite, it can be recovered in separate reactors.

Researchers have tested recovered struvite on crops in laboratories and achieved yields . The technique is still maturing, but companies are developing .

More possibilities

Want more valuable stuff? Wastewater is literally a gold mine. It contains metals . These metals are often toxic to aquatic life, so they need to be removed. But conventional removal technologies .

Researchers are developing new ways to remove and reuse these metals, including membrane systems that can and biosystems that . These techniques are at a very early stage and it is not clear yet whether they will make economic sense, but they have the potential to make wastewater more valuable.

In addition, wastewater is generally warmer than natural water supplies, especially in the winter, so it can serve as a heat source. This technique is and is not limited to commercial scale. You can install at home to lower your energy bill.

To me, this is just a beginning. With proper techniques, "wastewater" can offer us much more – and I very much look forward to the day when there is no "wastewater," just "used water."

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