Operators maintaining the Loganville, GA, SBR wastewater system use an on-line Hach LDO dissolved oxygen probe that eliminates electrodes and membranes — resulting in 'wipe-clean' maintenance and the reliable readings necessary to guide the SBR process.
Click here to enlarge imageThe facility received the award, in part, because it experienced no violations of permitted levels of BOD, TSS, ammonia, total phosphorus, and chlorine residual during 2003. According to Plant Superintendent Chris Yancey, the award also is based on consistent use of standard methods and quality control in the facility laboratory as well as thorough equipment and facility maintenance by technicians and the three staff operators. All QC and maintenance is documented thoroughly.
"We have to show we keep up with maintenance – mostly preventative – whether it's daily, weekly, monthly, or seasonal," he said.
For many WWTPs, operating in reaction mode leaves little time for the preventative effort Yancey described, much less journaling those tasks for the record.
New Technology
The Big Flat Creek Water Quality Control Facility has found success using sequencing batch reactor (SBR) technology, applied for decades as an industrial pre-treatment technology yet just building a fan base among municipalities.
The SBR system is well suited for the Loganville plant, which receives a relatively consistent domestic sewage load. Rated at 2.0 mgd, it includes two 1-mgd basins, each completing sequential phases for idle, static fill, mixed (pumped) fill, aerated fill, reaction, settle with waste to digest, and decant. A complete SBR cycle takes 3 1/2 to 4 hours, and each SBR basin usually runs four cycles a day, together treating an average 700,000 gallons daily.
Since the facility went on line, a continuous-reading dissolved oxygen (DO) sensor in each tank sends real-time readings to the plant programmable logic controller (PLC) for air blower control. This on-line aeration control is particularly vital for the SBR basin, in which sequential biological environments must support different types of microorganisms during different phases of the process. Closely controlled sequential aerobic digestion and nitrification/denitrification phases reduce BOD, convert solids, and remove nutrients for compliant discharge to the receiving Big Flat Creek.
The real-time DO readings also are responsible for blower cutback when the temperature drops or loading decreases due to storm inflow. Such blower control can eliminate large amounts of wasted energy.
"But the DO probe maintenance was unreal," said Dean Shirley, Wastewater Operator III.