News splash! Wastewater treatment surges toward being energy neutral

anaerobic-water-treament-works image www.h2o-water.com

There’s a buzz at the point where wastewater and energy meet—and the buzz phrase is “energy neutrality”. Hear it this week at the Ozwater conference, on any day at the University of Queensland Advanced Water Management Centre, in the offices of Melbourne Water and Yarra Valley Water… in Australian cities and country areas.

As populations increase, our demand for water is growing; as the flow of water in and water out stretches Australia’s environmental capacity, regulations are necessarily being tightened, requiring more intensive water processing; and all the time the electricity meter at the wastewater plant is ticking over, and over the top. Figures from UNESCO in 2015 estimate that electricity accounts for 40% of all operational costs in wastewater treatment.

As the price of electricity climbs and the need to reduce carbon emissions grows, Australia’s more than 700 community sewage treatment plants have begun seriously paddling towards energy neutrality—a state of operations in which they produce as much energy as they use.

And yes, our wastewater utilities, do have a paddle in this endeavour—an oarsome set of options—in the form of rapidly developing technologies that will both reduce electricity requirements and capture the energy generated through breaking down biosolids.

In fact, watch this space as new technologies transform water-treatment utilities from energy consumers to energy producers.

If energy neutrality is the buzz phrase of the moment, the core concept in turning the wastewater tide towards productivity is to view treatment plants not as waste-disposal facilities, but as resource-recovery plants, says Jeff Peeters, senior product manager at GE Water & Process Technologies. Based in Canada, Peeters is widely considered a thought leader in the field of water processing, and has turned a masters of engineering toward commercialising innovative water-treatment systems.

In a recent guest column, The future of energy-neutral wastewater treatment is here, for Water Online, he writes: “We all need water and energy, and we all need to take part in the efforts to secure them for generations to come. Water reuse, policies and partnerships, and emerging disruptive technology solutions are vital to the cause.”

One strategy used by wastewater facilities to achieve neutrality in their energy consumption is to produce energy onsite by harnessing renewables such as wind, solar and hydro power. But the real disruptor here is increasingly efficient technology for capturing and using energy generated by the very breakdown of biosolids (sewage sludge) and biowastes (household and commercial food wastes, fats, oils and grease) that treatment plants are contracted to carry out.

Advanced anaerobic digestion processes, such as that developed by GE’s Monsal, maximise biogas yields from waste and/or wastewater solids, delivering more energy than previous digestion systems, which were often deemed uneconomical. Peeters explains anaerobic digestion, in simple terms, as using “bacteria in the absence of oxygen to break down organic matter to create biogas. The biogas can then be combusted or oxidised and used for heating or with a gas engine to produce electricity and heat. It can also be compressed and used as fuel for vehicles or sold for use in a natural-gas grid.

“Consider this,” he continues: “A city of 500,000 people produces roughly 75,000 tons of household and commercial food waste and more than 14,000 tons of sewage sludge. By treating that waste with advanced anaerobic digestion, the value of the methane byproduct used in one of GE’s Jenbacher gas engines would produce about 5MWe of electricity alone—enough to power 10,000 homes.”

Smart city! One of the key themes of this month’s Ozwater conference has been Liveable and sustainable cities of the future, with speakers from Flinders University, Beca (engineering and project management), Sydney Water and Veolia (water, energy and waste management) posing recent findings and solutions to the wastewater-energy equation.

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New technologies can transform treatment plants from energy customers to energy producers.  

The infrastructure and logistical change required to swing a small city to processing combined biowaste and sewage sludge does require some capital outlay. But GE also has a focus on low-hanging-fruit approaches that can help utilities burdened with older infrastructure simultaneously switch down their power usage and switch up processing to meet increased demand.

In partnership with the Metro Water Reclamation District of Greater Chicago, Peeters is leading a GE team in carrying out large-scale testing of ZeeLung, GE’s latest water-treatment membrane technology.

Chicago’s Metro Water operates the Terrence J. O’Brien Water Reclamation Plant, one of the largest sewage-treatment plants in the US, which processes almost a billion litres of sewage each day. Says plant manager Sanjay Patel, “It takes a lot of energy to do what we do. My electric bill is about US$5 million a year. So anything we can do to cut back on that bill would not only help us, but also help the citizens who pay the taxes.”

ZeeLung membrane-aerated biofilm reactor (MABR) technology uses a quarter of the energy required by fine-bubble aeration, which is widely used to provide oxygen in activated sludge processing. ZeeLung improves on the process by transferring atmospheric air down the lumen of hollow fibre membranes; oxygen is then diffused through the membrane walls to a biofilm that grows on their outer surface. Microorganisms in the biofilm break down, or metabolise, the organic compounds in the sewage. Says Peeters, “ZeeLung addresses the largest energy consumer in wastewater-treatment plants: the aeration process, which is responsible for approximately 60% of energy used.”

In an interview with Treatment Plant Operator magazine last month, Peeters explained, “Until now, the game in aeration has been how to make smaller and smaller bubbles, because that increases the surface area of air in contact with the liquid. That has limitations in transfer efficiency, as typically 60% to 70% of the oxygen that goes into the basin comes out at the surface and isn’t used. With ZeeLung MABR, we use a membrane to diffuse oxygen directly into a biofilm.”

Unlike GE’s ZeeWeed membrane filtration systems, which famously protect Australia’s Great Barrier Reef from dirty-water outfalls, ZeeLung does not filter the water. Although it looks identical to ZeeWeed, its bundles of membrane fibres, deployed in cassettes and installed in the aeration tank are made of material “that has an affinity for diffusing oxygen”, says Peeters—“it’s a gas-transfer membrane”.

Importantly, ZeeLung cassettes can be installed in new plants or retrofitted to existing aeration tanks. In this way, it can upgrade space-constrained facilities to meet new regulatory requirements or expand their capacity without increasing their footprint.

For Sanjay Patel at the Terrence J. O’Brien plant, “The promise is that it would cut back on our aeration energy by about 40%. That’s a lot of money to gain!” And it will take the Chicago plant one large step closer to energy neutrality.

Enabling great leaps in energy reduction for utilities is at the heart of GE’s Energy Neutral water portfolio, which also includes LEAPprimary. This advanced primary wastewater treatment system combines separation, thickening and dewatering of primary solids in a compact unit that reduces the energy used in conventional biological treatment by 25%.

For wastewater-processing facilities, “energy efficiency has not historically been at the top of the list of priorities,” writes Peeters in Water Online. But, “Energy conservation, on-site generation and renewable energy are becoming increasingly important to wastewater utilities as energy policy, energy economics and actions to mitigate climate change converge with the need to meet higher standards of wastewater treatment… Emerging disruptive innovations in technology combined with operational best practices are bringing into focus the opportunity to achieve energy-neutral wastewater treatment.”

www.energy-options.info

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Henry Sapiecha

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