Traditionally, wastewater treatment has focused on removing toxic waste from the water so it could be safely discharged into the environment. Little thought was given to the actual composition of the waste, most of which ends up being discarded.
These days, however, as treatment facilities are faced with higher energy costs and more stringent regulations surrounding emissions and disposal, the industry is spluttering into a new era where the constituents of the wastewater are being looked at as valuable resources that can be repurposed or converted into clean energy sources.
Every day, the more than 15,000 treatment plants across the US have to treat billions of gallons of wastewater. According to calculations by the environmental biotechnologist Willy Verstraete, every 1000 gallons of wastewater contains the equivalent of $1.88 worth of fertilisers, organic matter, energy-producing gases and more. The industry is slowly starting to realise that failing to reclaim these resources is akin to throwing hundreds of millions of dollars into the ocean. As a result, teams of scientists and innovative startups have begun developing cost- and energy-efficient technologies to capture these resources instead of dumping them.
A team of scientists at Stanford University, led by Craig Criddle, Brian Cantwell and Yaniv Scherson, has developed a system that literally applies the principles of rocket science to treating nitrogen in wastewater to make the process more sustainable. Wastewater contains large amounts of nitrogen in the form of ammonia, partly because of the agricultural processes that rely heavily on ammonia-based fertilisers and partly because ammonia is released when organic waste matter in water breaks down.
When this waste nitrogen gets into water bodies, it over-fertilises the water causing an algal bloom that sucks out the oxygen and kills all marine life in the area, creating what are known as dead zones. Many wastewater facilities simply do not have the capability to treat the ammonia in a cost or energy efficient way so the nitrogen resource doesn’t only get lost but also becomes a damaging pollutant.
In a conventional treatment process, ammonia is converted back into nitrogen gas, a non-harmful gas which can be safely released into the atmosphere. The conversion process is expensive, however, and energy prohibitive. What the Stanford team do, instead, is to use a less energy-intensive process to convert the ammonia into nitrous oxide (N2O), a powerful substance that is typically used to turbo-boost cars or fire rockets. Normally, N2O is discouraged from forming because it is a harmful greenhouse gas, but when it is burned along with methane, it becomes an energy source that can be used to power the treatment facility. According to Scherson, there is a double energy-saving benefit.
“Our process reduces energy input in nitrogen treatment and then the energy from nitrous oxide can potentially be used to power the plant making it energy neutral or even energy positive.”
Metals are another major contaminant in wastewater. Every year more metal is being used by the electronics industry, in transportation and in construction. This means that more rare and precious metals are being mined from the earth and more metal contaminants are ending up in our water, rendering it hazardous. Hazardous wastewater is much more expensive and difficult to treat. Industries that generate a lot of it often prefer to accept fines or move to areas where there are less stringent regulations rather than treat it.
A Colorado startup called Tusaar has developed a new cost-effective, technology that uses environmentally friendly compounds targeting over 40 different metals. The technology is currently being used by the University of Colorado to treat hazardous wastewater generated by their 400 laboratories. Previously, the University had to have hazardous water treated, at considerable cost, by an external vendor. By utilising Tusaar’s technology, most of the wastewater is rendered safe and can be treated quite easily by the city along with regular household waste. According to Guatam Khanna, Tusaar’s chief executive, the technology was originally designed to remove contaminating metals from the waste stream, but it is now being adapted to recover valuable metals also.
There have been some interesting developments in the food and beverage industry also to prevent fats, oils or grease (FOG) ending up in wastewater. A California startup called FogBusters has licensed technology originally invented in the UK that uses a liquid separator to remove nearly 100% of the FOG in wastewater effluent without the use of chemicals.
Separating the FOG from wastewater before it enters the drains prevents them from clogging obviously, but it also helps industries comply with ever stricter FOG regulations, cut down on their wastewater treatment costs and enables them to sell their oily waste for use as animal fodder or as feedstock for biofuel
Traditionally, only more refined waste oil has been converted into a fuel source, but another innovative startup, BlackGold Biofuels has developed a technology that can take the worst kind of sewer grease from highly degraded water and convert it into a low-carbon biofuel. Both BlackGold and Fogbusters were recognised as leaders in the field by Imagine H2O, a non-profit dedicated to solving water problems.