Rural Water Assists Arizona Wastewater Plant with Bulked Sludge


TIERRA GRANDE, Ariz. – When the Wastewater Plant in Tierra Grande, Ariz. had bulked sludge interfering with the hydraulics of the system, they contacted the Rural Water Association of Arizona for assistance.

“The sludge had accumulated on the inlet side of the clarifier’s inlet baffled wall,” said Nathan Long, an EPA Wastewater Program Training Specialist with RWAA. “The system was short-circuiting through the open area in the baffled wall into the primary aeration basin.”

Bulking is common in small systems, especially when flow rates get low and the solids begin to settle out.

“This accumulation creates anaerobic layers of sludge that will continue to build up into think biomass unless it is physically removed,” Long explained.

Long probed the bulked sludge and found areas of accumulation as much as 12 feet thick and four feet wide. The first step to returning the wastewater plant to normal operation was to remove these massive layers of accumulated sludge in the baffled zone.

After removing the sludge, the next step would be to make repairs and upgrades to prevent the sludge from accumulating again.

“The baffled zone has an air diffuser that should keep solids in suspension during periods of low flow rate,” Long said. “The installed diffuser is not operating.”

Long also recommended installation of additional air diffusers that can be run continuously or on a preventative maintenance schedule.

“A major item that needs to be functioning correctly is the baffle zone’s scum trough,” Long said.

The scum trough provides a mechanism to return bulked sludge to the treatment process instead of accumulating or short circuiting into the aeration basins. The combined improvements should return the plant to normal operations and directly reduce the amount of solids that are pumped from the facility every year.

“I will be available for future discussions,” Long said. “As well as be there to help with any work needed to accomplish these goals.”