Managers of a 1.2 mgd (189 m3/h) wastewater treatment plant in Star, Idaho, have reported the successful installation of a solids separation and removal system that protects membranes in its new, state-of-the-art membrane bioreactor (MBR) addition.
The plant has also seen immediate maintenance benefits from the elimination of aerator plugging in its three lagoons.
The new MBR plant features state-of-the-art Kubota technology and serves about 2,000 residential customers and 25 commercial operations. It opened last January as a means for handling a dramatic increase in the customer base. The lagoons were filled to capacity and changes needed to be made.
“We had originally settled on a Bandscreen versus a step screen because it would let in less solids, and then specified a 2 mm size to meet the MBR manufacturer’s warranty,” said Hank Day, maintenance and operations foreman for Star Sewer and Water District.
“We then selected the JWC Monster Separation System as it is easiest to operate and maintain. For example, it didn’t have any bearings down in the waterway, and you could take out sections of the belt (Bandscreen) without taking out all of it, which requires disassembling the whole unit.”
Done right the first time
“The membranes in the new MBR plant are really expensive, and we wanted to be sure to have the best screening ahead of them so we don’t get material that could damage them,” added Day. “We also wanted to filter out as much total solids as we could to keep the new MBR plant running at optimum capacity. This combination solids processing system allowed us to meet both objectives from the outset of the new plant operation.”
Day is also pleased with the fact that the aerators in the lagoons are no longer plugging up. Previously, all nine of the aerators had to pulled for a day, ten times a year for cleaning. This tedious step has not been necessary since the Monster Separation System was installed.
Fine screening, cleaner screenings
At the plant’s headworks, a manual bar screen is used to remove rags and other large matter. The flow then moves through a grit separator, which deposits to a 3 yd. (2.3 m3) dumpster.
The remaining wastewater stream then enters the Monster Separation System (MSS). Here there are 2 mm perforated, ultra-high molecular weight Bandscreens for the removal of solids such as trash and plastics, integrated with a Screenings Washer Monster (SWM), which grinds, washes, dewaters, and compacts the solids and discharges them into the grit dumpster.
The effluent from the MSS proceeds through a flow meter to a splitter box, which sends 20% of the stream to the three 1600 equivalent dwelling unit (edu) lagoons, and 80% into the new MBR plant.
In the new plant, another splitter box sets up two separate treatment chains where anoxic and anaerobic cells see mixtures of raw activated sludge (RAS), raw influent, and mixed liquor from membranes, and provide biomass “bugs” for the MBRs.
The membrane portion currently consists of 200 flat plate membranes per cassette, and twelve cassettes for each train. Flow in the east and west trains is now about 0.3 mgd (47 m3/h) each. Allowance was made for future expansion of the MBR capacity via additional trains, as well as more membranes in each train.
The MBR discharges to a chlorine contact basin for final disinfection before the effluent is released. Overall, the 1.2 mgd (189 m3/h) peak flow plant is presently operating at about 0.8 mgd (126 m3/h).
“They’re building 20 new subdivisions in our area as we speak,” said Day. “To upgrade, we did everything at the very best we could afford and still be easy to operate. The Idaho Department of Environmental Quality lent us money to build it, and they like what they’ve seen so far. The cleanliness of the discharged solids (from the SWM) allow for hauling to a sanitary landfill, which was a compliance criterion that was assured by our engineers, Keller Associates of Meridian, ID.”
“We’re pleased the MBR plant is operating as designed,” said Justin Walker, project engineer for Keller Associates . “The facility is producing great quality water.”
Low odor and landfill acceptance
“We wanted to make sure organics were removed to reduce odor and ensure waste would be accepted at the landfill,” said Randy Zollinger, project manager for Keller Associates. “During our initial start-up we saw our decision to utilize the Screenings Washer Monster was justified, as very little odor was generated from the washed compacted screenings.”