Waste­water UV sys­tem goes live

The Sentinel-Record - - FRONT PAGE - DAVID SHOW­ERS

Chlo­rine dis­in­fec­tion at the Re­gional Waste­water Treat­ment Plant is no more as of ear­lier this month.

For­merly the fi­nal step in trans­form­ing waste­water into ef­flu­ent that emp­ties into Lake Cather­ine, chem­i­cal dis­in­fec­tion has been sup­planted by ul­tra­vi­o­let lamps at the David­son Drive lo­ca­tion. One of two UV chan­nels that’s part of a $9 mil­lion plant up­grade went on line last week.

They will be used al­ter­nately once both are op­er­a­tional, Hot Springs Util­i­ties Di­rec­tor Monty Led­bet­ter said. Both can be opened on heavy flow days, when as much as 24 mil­lion gal­lons passes through the plant. Led­bet­ter said 11 mil­lion gal­lons are treated on an av­er­age day.

The plant can treat up to 42 mil­lion gal­lons a day. Flow can also be di­verted to the 54 mil­lion-gal­lon equal­iza­tion basin, where it can be held un­til the plant is ready to process it.

Con­spic­u­ous by the emer­ald glow they emit, the sub­merged UV lamps are safer and more en­vi­ron­men­tally friendly than chem­i­cal dis­in­fec­tion, said Ray Ome, who is man­ag­ing the con­struc­tion project for RJN Group, the city’s waste­water sys­tem con­sul­tant.

They elim­i­nate the risk of a chlo­rine gas re­lease and don’t im­part a chem­i­cal residue that can have ad­verse im­pli­ca­tions down­stream, where other util­i­ties use the same re­ceiv­ing wa­ters as their raw-wa­ter source.

“Chlo­rine kills the bac­te­ria,” Ome said. “There’s the po­ten­tial of chlo­rine byprod­uct be­ing left in the re­ceiv­ing wa­ters. With UV, as (flow) passes through, it dis­rupts

the DNA of the bac­te­ria. It’s much bet­ter for the re­ceiv­ing wa­ters.”

Led­bet­ter said meet­ing the re­quire­ments of the city’s Na­tional Pol­lu­tant Dis­charge Elim­i­na­tion Sys­tem per­mit while putting less strain on the en­vi­ron­ment is of par­tic­u­lar con­cern to him. He lives in Malvern. The in­take for its wa­ter util­ity is be­low Rem­mel Dam.

“We have to be good stew­ards, be­cause I live down­stream of this plant,” he said, not­ing that no fe­cal or co­l­iform counts have been de­tected in sam­ples tested at the plant’s lab since the UV sys­tem has been in place. “My drink­ing wa­ter comes from the Oua­chita River.”

The newer South­west Waste­water Treat­ment Plant on Win­kler Road al­ready uses UV lamps, but Larry Mer­ri­man, ma­jor cap­i­tal projects man­ager for the city, said the UV ar­ray at the Re­gional Plant is state of the art.

“The sys­tem now is bet­ter than when we put UV in (at the South­west plant),” he said. “At that time, it was be­lieved the tech­nol­ogy worked best when the bulbs were in a hor­i­zon­tal po­si­tion as wa­ter passes by. These are on a

45-de­gree an­gle, which gives it more con­tact time.”

New head­works and a grit-sep­a­ra­tion cham­ber are also part of the up­grade, in­creas­ing the plant’s ca­pac­ity to cap­ture non-degrad­able solids and smaller par­ti­cles such as sand that can dam­age pumps and other equip­ment far­ther down­stream in the treat­ment process.

The plant im­prove­ments dove­tail with the work the city’s do­ing on the waste­water col­lec­tion sys­tem as part of a $70 mil­lion ef­fort to meet the fed­eral man­date it’s been un­der since

2008. Ac­cord­ing to the Con­sent Ad­min­is­tra­tive Or­der it en­tered into with the state Depart­ment of En­vi­ron­men­tal Qual­ity, which en­forces the Clean Wa­ter Act for the En­vi­ron­men­tal Pro­tec­tion Agency, the city agreed to pay a $105,000 civil penalty in 2011 for 359 wet-weather over­flows from Jan­uary 2004 to May 2008.

The city has said it ex­pects to be re­leased from the CAO soon, per­haps as early as next year. Bonds se­cured by rates paid by the sys­tem’s more than 26,000 waste­water ac­counts are fund­ing the over­haul, which in­cludes the $113,081 con­tract the Hot Springs Board of Di­rec­tors awarded last week to Brown Engi­neers LLC.

The Lit­tle Rock com­pany has been cho­sen as the city’s sole-source provider for projects re­lated to the util­ity depart­ment’s su­per­vi­sory con­trol and data ac­qui­si­tion sys­tem. The con­tract awarded ear­lier this week will con­nect con­trol equip­ment for the plant’s new com­po­nents to the city’s SCADA sys­tem.

Led­bet­ter said stormwa­ter that per­co­lates into the col­lec­tion sys­tem dur­ing sig­nif­i­cant rain events dis­rupts the treat­ment process, flush­ing out micro­organ­isms that con­sume sewage. Re­plac­ing and re­hab­bing waste­water lines will keep more stormwa­ter out of the col­lec­tion sys­tem and lower the vol­ume that ar­rives at the plant.

“We in­ject air to make it aer­o­bic, to where bac­te­ria has food and plenty of oxy­gen,” Led­bet­ter said. “That helps break things down a lot faster. On an av­er­age day, you have plenty of food com­ing in to feed the bac­te­ria.

“When we have big rain events and have to take the plant up to 24 (mil­lion gal­lons a day), there’s not as much food some­times. If that’s a pro­longed pe­riod, we can ac­tu­ally lose a lot of our bac­te­ria that’s ac­tively work­ing for us.”

Sludge, or biosolids, the treat­ment process sep­a­rates from the flow ends up at the city’s com­post fa­cil­ity. Be­fore it gets there, it’s heated in an un­der­ground di­gester that di­vests or­ganic ma­te­rial then squeeze dried through a con­veyor belt press.

The fin­ished prod­uct is trucked the short dis­tance to the com­post fa­cil­ity, where free com­post is avail­able to the pub­lic, in­stead of to a land­fill that would charge the city costly tip­ping fees.

The Sen­tinel-Record/Richard Ras­mussen

LIGHT DIS­IN­FEC­TION: Ul­tra­vi­o­let lamps glow at the city’s Re­gional Waste­water Treat­ment Plant. The lamps, which serve as the fi­nal step in the treat­ment process, re­placed the chlo­rine dis­in­fec­tion sys­tem.

The Sen­tinel-Record/Richard Ras­mussen

PLANT UP­GRADE: Util­i­ties Di­rec­tor Monty Led­bet­ter, left, and Ma­jor Cap­i­tal Projects Man­ager Larry Mer­ri­man dis­cuss im­prove­ments to the waste­water plant as a con­struc­tion crew in­stalls the plant’s new head­works.

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