Steering a 165-acre botanical garden through the perils of a statewide drought and record-high temperatures that, not too long ago, scorched thousands of plant species has Descanso Gardens thinking critically about water use in the years ahead.

So, when the site’s largest septic system began failing in 2017, officials looked for more than a mere fix and landed on a compact sewage treatment plant that would turn sewage into reclaimed water suitable for irrigation.

The membrane bioreactor (MBR) being installed this week will combine biological wastewater treatment with ultrafine membrane filtration. Capable of processing up to 40,000 gallons per day, the system should be up and running by January.

“When our sewer system started to fail, we really saw it as an opportunity to do something better,” said Descanso Executive Director Juliann Rooke. “The new MBR will take water that was not being used and put it right back into the gardens.”

When operational, the system will help drip irrigate a 1.5-acre front entrance garden along Descanso Drive being replanted after triple-digit heat last year killed several prominent redwoods.

“They just couldn’t handle the heat,” said Descanso horticulturalist David Bare. “They were never going to be able to recover from that. We got to the point where we thought they were a fire hazard.”

The trees were removed last month, their lumber given to other gardens and school groups that use recycled redwood. New oaks and other native species will be planted in their place.

Bare’s team plans to experiment with “hügelkultur,” a practice where dead and decaying wood is placed into raised beds to create nutrient-rich soil for new plantings. The hope is the redesigned space will better reflect the horticulture seen inside the gardens.

“This landscape didn’t really seem like a Descanso landscape,” Bare said. “What we want to do is put in a garden that’s definitely more representational of what’s inside.”

The front entrance should use about 17,000 gallons of reclaimed water per day for irrigation, far below the new system’s total capacity.

Rooke and Bare said the treatment plant can carry the load of other septic systems on site as they fall into disrepair and allow for the irrigation of new green spaces being drawn into Descanso’s upcoming master plan.

“When Manchester Boddy founded his ranch [which later became Descanso Gardens] in the 1930s, he secured water rights in Hall Beckley Canyon, about 3 miles away. We’ve had concerns over that water source and the pipes that bring the water to us,” Rooke said. “[Now] up to 40,000 gallons of water that were currently not usable will be treated and used to water the front drive and, eventually, parking lot gardens.”

Bare praised the new addition for not only answering Descanso’s septic needs but solving several other issues at the La Cañada facility.

“This is a problem we’ve turned into an asset,” he said.