The management of a 1.2-million gal per day (mgd) wastewater treatment plant (WWTP) in Star, Idaho, recently reported the successful installation of a solids separation and removal system that protects the membranes in its new, state-of-the-art membrane bioreactor (MBR) addition.
At the same time, immediate maintenance benefits have been gained through the elimination of aerator plugging in three lagoons.
Installed in November 2005, the Monster Separation System (MSS) from JWC Environmental, which also integrates a Bandscreen Monster with a Screenings Washer Monster (SWM), provides for initial screening of solids, plus processing of remaining solids by grinding, washing, dewatering and compacting.
"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 grit or other material that could damage them," said Hank Day, maintenance and operations foreman for Star Sewer and Water District. "We also wanted to filter out as much total solids as we could to keep the new MBR plant running at optimum capacity. Meanwhile, we've already gotten a big benefit with the aerators in
our lagoons not plugging up anymore. We had been pulling all nine of them for a day, 10 times a year, for cleaning. We haven't had to do that at all since we installed the Monster Separation System."
Lagoons filled to capacity
The WWTP now serves about 2,000 residential customers and another 25 commercial operations. The new MBR plant, featuring state-of-the-art Kubota technology, opened in January 2005 as the means for handling a dramatic, continuing increase in the customer base. The district's lagoons were already filled to capacity.
At the WWTP's headworks, a manual bar screen removes rags and other large debris. The flow then moves through a separator, which deposits to a 3-yard dumpster.
The remaining wastewater stream then enters the MSS, with 2-mm perforated ultra-high molecular weight plastic panels Bandscreen Monster for removal of solids such as trash and plastics, integrated with an SWM, which grinds, washes, dewaters and compacts the solids and discharges them into the grit dumpster.
The effluent from the MSS proceeds through a flowmeter to a splitter box, which sends 20% of the stream to the three 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, 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 12 cassettes for each train. Flow in the east and west trains is now about 0.3 mgd each. Allowance has been made for future expansion of the MBR capacity via more membranes in each train, and additional trains.
The MBR discharges to a chlorine contact basin for final disinfection before the effluent is discharged. Overall, the 1.2-mgd peak flow WWTP is presently operating at about 0.8 mgd.
"They're building 20 new subdivisions in our area as we speak," Day said. "To upgrade, we did everything at the very best we could afford and still be easy to operate."