With IWA’s Leading Edge Technologies Conference taking place in Reno, Nevada, early next year, The Source spoke with conference president Professor Bruce Rittmann.
The innovation agenda around sewage and wastewater treatment spans opportunities that are ready for implementation and those where considerably more research and development is needed. The programme at the next IWA Leading Edge Technologies (LET) conference will reflect this, as highlighted by some of the topical themes mentioned by IWA Fellow and Conference President Dr Bruce Rittmann, professor and director of the Biodesign Swette Center for Environmental Biotechnology at Arizona State University.
The resource recovery route
Rittmann points to resource recovery from sewage and wastewater as an area where technology is broadly ready to deliver a shift in practice.
“High-strength organic wastewaters have a lot of value,” he says. “Energy, nutrients, the water itself are always present. We would like to be able to capture the value out of them, instead of making wastewater treatment a very big burden in terms of energy and money consumption.”
This creates a switch from wastewater as something to be disposed of to viewing it as a source of resources – something, Rittmann says, is a big theme in his research, as well as a feature of the conference programme.
The opportunity is greatest in high-strength wastes, such as in the dairy and food industries. “That is where the benefits are really magnified,” Rittmann says, but it also applies to treatment of domestic wastewater because of developments in anaerobic membrane bioreactors, for example. The core of the opportunity is a move from aerobic to anaerobic treatment, says Rittmann. This reduces cost in terms of energy use and greenhouse gas production, allowing conversion of the organic content into methane, in particular.
“PFAS are called ‘forever chemicals’ because they don’t break down. They have become a hot topic in recent years”
The result is “something with tangible social benefit and tangible economic benefit to whoever is operating the facility”, says Rittmann. “We have done economic analysis looking at standard domestic wastewater treatment, and we can make it a money-producing venture by capturing the value in the energy, the nutrients, and the water.
“This is a huge change in how we view treatment, and it has tremendous benefits to society – environmentally and economically.”
Of the technology required, Rittmann says “for the most part, it is more on the mature side than on the emerging side”. Anaerobic treatment has been in use for a long time. “What is emerging now – and it is also pretty well-developed – is the treatment of relatively low-strength organic wastes, including domestic sewage.”
In terms of where technical improvements are needed, Rittmann mentions the ability to capture all methane generated, given that some still stays dissolved in the effluent. Another area is improving biomass retention inside the reactor. Both areas are well advanced, however, putting the timescale for remaining research at just a few years.
Widespread implementation would bring changes for utilities. Anaerobic treatment systems avoid the electricity costs associated with aeration, says Rittmann, who adds: “That is an obvious huge benefit.” Processes typically require a smaller footprint than aerobic systems. “This is very valuable, whether you are using an existing site or going to a new site.”
Utilities will be able to make use of the energy generation potential. Surplus energy can be connected to wider society by feeding electricity into the power grid or by exporting the energy as methane gas. Both options, but particularly the latter, depend on factors beyond the utility for scale-up to be achieved. “It is partly technical, and partly legal and regulatory – who is allowed to do what,” says Rittmann. A similar point applies to the opportunities to use other resources, such as recovered ammonium and phosphate by the fertiliser industry.
“There needs to be a market for the outputs as you produce them,” adds Rittmann. “That is, in my opinion, the biggest challenge right now to doing this on a widespread basis – we haven’t developed the markets for the outputs in most cases, except electricity.”
Longer time horizons
Rittmann highlights two other areas that will feature in the LET programme, but that require work over a longer time horizon to meet the practical needs of the sector. One is per- and polyfluoroalkyl substances (PFAS) – currently subject to a great deal of attention in the US in particular – while the other is antibiotic resistance genes (ARGs) and the wider issue of antimicrobial resistance.
Rittmann says PFAS are an environmental legacy from uses such as firefighting. They are found at low concentrations, but bioaccumulate. “It is a doubly huge challenge because these fluorinated compounds are basically recalcitrant under normal conditions in the environment,” he adds. “These are called the ‘forever chemicals’ because they don’t break down naturally. PFAS have become a hot topic in the past four or five years.”
To address these substances at treatment plants will require new technology, probably integrated as an additional treatment step. In his research, Rittmann has been looking at using catalytic reduction to start defluorination, after which microorganisms can biodegrade the PFAS.
Regarding ARGs, Rittmann notes the growing global concerns, which will need a response in other areas – such as medicine and animal farming – but questions arise around the role of wastewater treatment plants. “We need to pay attention to what the fate is of ARGs in our wastewater treatment facilities,” says Rittmann. “Are we amplifying them by the way we operate our facilities, or the opposite? If we are amplifying them, what can we do to the processes to reduce ARGs?
“Using biofilm processes can help minimise the release of bacteria containing antibiotic resistance genes. Maybe you can’t prevent ARGs from existing in the process, but if you don’t let any of the microorganisms out, perhaps you are not creating a problem.”
The technology contribution
What happens at the treatment plant is part of a wider picture, both in terms of addressing underlying issues or capitalising on opportunities.
“We have a lot of challenges in front of us,” says Rittmann. “LET deals with the science and technology advancements that will be needed to deal with problems that are pressing today or just emerging. We need to have advanced technologies; it is not the whole solution – social and economic factors play important roles, too – but without technology we will never get anywhere.”
The 17th IWA Leading Edge Conference on Water and Wastewater Technologies, 21-26 February 2021, Reno, Nevada, USA, iwa-let.org