A Mississippi plant copes with high flows from two poultry plants with a new SCADA system and automated control over dissolved oxygen.
When most flow comes from just two industrial sources, a wastewater treatment plant has to be ready to respond to changes in operations. That is easier in Morton, Miss., since a plant update in summer of 2012.
Two poultry processing plants account for about 85 percent of the average 2.5 mgd flow at the Morton Wastewater Treatment Plant. When the plants operate at peak output, however, their flows often push the treatment plant up to or beyond its 3.15 mgd design capacity. “If not for the poultry processing plants, we would have hardly any flow at all,” says Rickey Parker, plant manager. “They run from Sunday night to Friday night.” When they shut down for the weekend, flows quickly drop to 0.5 mgd.
New automation technology, including a new SCADA system, dissolved oxygen probes and DO controls, has made life easier on Morton’s four operators. “Somebody used to have to come in Friday or Saturday morning after the processing plants shut down and reset the blowers,” Parker says. “And then we’d have to come back several hours before they started up Sunday night and reset the blowers again.
“Changing flows from a half-million mgd to more than 3 million, treatment would slow down dramatically for the first couple days of the week. The system gets behind, and it takes a while for it to catch up. It was kind of a guessing game. We always had to have the blowers running more than was necessary.”
Time for renewal
While treatment in its two sequencing batch reactors (SBRs) was effective, the 1991-era plant needed to improve its energy efficiency and replace aging equipment. The staff called longtime engineering consultants WGK of Clinton, Miss., to develop an improvement plan. The changes that went online in the summer of 2012 also provided an opportunity for expansion to make room for additional growth in the community of 3,500, about 200 miles north of New Orleans.
Over the years, the plant’s analog programmable logic controller (PLC) had become outdated. The manufacturer eventually told Parker that parts would no longer be available because the system was so old. “If something happened, we’d have to run the plant manually until we could change over to a new PLC,” says Parker. “Other pieces of equipment were also wearing out.”
Aqua-Aerobic Systems provided a new SCADA system, since the company had provided the original SBR equipment. All three 150 hp blower motors were also replaced with U.S. Motors high-efficiency models of the same size (Nidec Motor Corporation).
The key to the plan was adding Hach LDO DO sensors and sc200 analyzers; the plant had no DO monitoring equipment previously. “We had to set the blowers at a level we knew would maintain a DO level no matter what the loading was,” says Parker. “We were wasting a lot of power. That’s where we get most of our energy savings — by controlling the amount of air we put into the aeration tanks.”
Other improvements included:
- Replacing a worn-out mechanical screen with an Aqua Guard bar screen (Parkson Corporation)
- Adding a Philadelphia Mixing Solutions model 3801-S headworks mixer (motor, shaft and support bearings)
- Adding a Wallace & Tiernan Series 32-050 lime feed system (Evoqua Water Technologies)
- Replacing all 1,000 diffuser sleeves
After the first year of operation, Parker found the plant’s annual electricity use had dropped by 12.5 percent (21,500 kWh). That equates to about $1,100 a month off the plant’s electric bill, compared to a monthly debt payment of $2,000 for the improvements The total projects cost of $400,000 was reduced by a 20 percent loan forgiveness for green infrastructure programs through the state Department of Health.
“I’m real pleased with the upgrade,” says Parker. So was the Mississippi Municipal League: The project earned an excellence award from the group for the city and WGK.
Parker credits the processing plants for running pretreatment programs that make sure their flows don’t challenge the plant’s treatment capabilities. “Our BOD coming in is about 200 mg/L” he says. “Solids are less than 100 mg/L, ammonia is 25 to 30, TKN is about 35, and oil and grease is less than 5 mg/L.”
Despite the high volume, the plant never had a problem providing proper treatment to meet its effluent permit levels, even before the improvements. “BOD removal is normally around 98 percent,” says Parker. “TSS is somewhere around 88 to 96 percent, and pretty much 99 percent on ammonia. The plant has run well ever since we put it in. The improvements make it a lot more efficient.”