It is said that outlaw Willie Sutton, when asked why he robbed banks, replied, “Because that’s where they keep the money.”

When it comes to recovering resources in clean-water plants, the money — and the energy — appear to be mostly in the solids. Water of course is the essential resource being recovered, and in many applications it has commercial value for reuse. But increasingly it’s the solids side that gets attention from the industry’s innovators.

In particular, facility owners and operators see biogas (digester methane) as an essential resource that can help them on the path toward more energy self-sufficiency, net zero energy or even net positive energy production.

This issue of TPO highlights one technology promoted by Pentair as increasing biogas yield by up to 25 percent over traditional anaerobic digestion (see page 38). Called the Memthane anaerobic membrane bioreactor, it combines an enhanced form of anaerobic digestion with ultrafiltration membrane technology.

Innovations on display

Other advanced treatment processes that emphasize resource recovery were on display at the 2014 WEFTEC conference last fall in New Orleans. Here’s a quick look at a few of them.

The SolidStream process from Cambi, based in Norway, reduces biosolids volume by degrading extracellular polymeric substances (EPS), which bind up water. The EPS material is broken down at high temperature and pressure, combined with pressure-drop disintegration. The heated solids are then centrifuged and further dried, yielding a Class A product at 60 to 75 percent solids. Heat recovery and increased biogas production can exceed the energy demand of the process, according to the manufacturer.

Ostara offers the WASSTRIP process designed to reduce biosolids production by 20 percent, increase cake solids content and reduce total biosolids phosphorus content by 10 percent, while reducing struvite formation in digesters. The process optimizes efficiency in plants with biological phosphorus removal by releasing phosphorus and magnesium before they reach the digesters. The nutrients are diverted from the solids stream and into the thickening liquor and combined with the dewatering liquor so they can be recovered in the company’s Pearl reactor, which yields a marketable fertilizer.

The TurboTec continuous thermal hydrolysis process from Sustec, based in the Netherlands, is designed to enhance biogas production in anaerobic digestion. The continuous process treats biomass at high pressure and temperature, ensuring sterilization of the final Class A biosolids cake. Steam demand for heating is limited by efficient heat recovery with heat exchangers. Biomass hydrolysis produces up to 35 percent more biogas than in conventional digestion, while dewatering yields material at 30 percent dry solids.

Thinking forward

Of course, technologies like these aren’t like Tinkertoys that any facility can deploy on a whim. They do deserve consideration as clean-water plants, one after another, surpass their useful life and come due for significant upgrades. Resource recovery is the direction the industry is heading, and clean renewable energy in the form of biogas gains importance as agencies aim to join in the prevention of global climate change.

Are you on board? Short of a wholesale plant upgrade, what is your facility doing to improve resource recovery and energy production? Share your stories by sending me an email to editor@tpomag.com. I promise to respond, and we’ll report on noteworthy initiatives.