New approaches to recovering resources from wastewater

Researchers around the world are working on new ways to recover resources from wastewater, but processes are often costly. One industry leader wants to change that.

Hong Kong University of Science and Technology’s Dr Guanghao Chen and his team have been creating an array of innovative treatment options, with the aim of making resource recovery more efficient and cost-effective. 

Presenting at Ozwater’20 Online, Chen said that while the international water sector was doing well, there was still work to be done in terms of resource, water and energy recovery.

“More than 50% of wastewater resources generate from our daily life and industrial processes are lost. Right now we are pretty limited in terms of what we can do," he said.

“We can use chemical processes to recover phosphorus and nitrogen, and we can then produce fertiliser. But to me this is quite simple. We can also transform organic matter into biogas, but unfortunately there are a lot of bottlenecks in terms of wide application.”

In an effort to create processes that are cheaper and easier to adopt, Chen has been conducting research into assessing news ways of recovering lost resources for industry use. 

“Sulfated polysaccharides (SP) are nothing new to industry; they have been used as an additive in food and in pharmaceutical materials. But it can be very costly to harvest,” he said. 

“We have discovered that a lot of SP can be recovered and purified to meet industry standards, depending on the grade required.

“Furthermore, production of volatile fatty acids (VFA) from sludge and food waste is nothing new, but it’s expensive. In terms of market, VFA can support the production of bio-plasctics, so the market is quite big. 

"Production has not yet caught up with demand. We have a 4% annual increase in the market. If we can devise an easy way to convert organics from sludge into VFA quickly and cheaply, then the door can be opened.” 

Unique to Hong Kong, the use of seawater to flush toilets has opened up a novel opportunity for phosphorus recovery to create fertilisers. 

“Phosphorus removal is also nothing new, but we still have challenges. Hong Kong has used seawater for toilet flushing for more than 50 years, saving a tremendous amount of freshwater. This means we can withdraw fertilisation from wastewater at a much lower cost,” Chen said.

“We have developed a process called Seawater-based Urine Phosphorus Recovery (SUPR) and have been invited to Barcelona to demonstrate the process. It shows that utilising seawater for flushing allows for much cheaper phosphorus recovery.”

Popularising potable reuse

Next up for Chen is a project focused on reducing or removing chemical dosing from wastewater treatment for potable reuse. Chen said the project will focus on reuse of existing resources to clean and purify wastewater. 

“So far, the conversion of wastewater into drinking water is a big dream. We can do it, but at the moment we have a lot of perception issues. The technology is here, but how can we break the perception barrier?” Chen asked.   

“Something that’s quite new to industry is treating wastewater to potable standards without chemical dosing. We have devised a five-year project looking at a compact, integrated system to help reduce chemical dosing. 

“We aim to be able to guarantee a complete removal of chemical dosing from the treatment process. The concept is called Wastewater to Recovery Factory. The idea is to produce potable water through an innovative separation system, using chemicals that are already present within the wastewater.

“The concept is that we separate the dirty water from clean water first. Then we utilise the internal resources of the wastewater to remove free-radicals. We don’t need to add new chemicals, we re-use everything that’s already present.”

To learn more about Ozwater’20 Online and to register, click here.