DECATUR — The new wastewater treatment plant, which has been up and running since June, uses state-ofthe-art equipment and new technology to turn raw sewage into clean creek water.
The technical name for Decatur’s new wastewater treatment plant is a Fluidyne Sequencing Batch Reactor System, and some of the equipment used in it is the first of its kind in Arkansas. The final price tag on the plant will be around $7.7 million plus engineering costs.
Turning sewage into clean water is all about “bug farming,” according to city utilities director James Boston. The treatment plant depends on bacteria to break down the waste, so it’s a priority to keep the bugs happy.
Sewage begins its journey through the new plant at the chemical building. Pumps with very precise controls feed sodium hydroxide into the raw sewage to adjust the pH level and alkalinity so the bacteria can thrive, Boston explained.
After the pH level is adjusted, the sewage goes through a filter that uses an auger with a screen and brush to pull out trash like paper, plastics and rocks. Then the water passes through an ultrasonic flow meter that automatically records the gallons per minute on the computer in the office on the other side of the plant. The meter averages 15,000 gallons per minute on weekdays, Boston said.
At the end of the flow meter, the water streams into the hydrogrit system, which looks like a giant whirlpool. The water swirls and tumbles around, pulling grit - even as small as two millimeters - to the bottom.
“We don’t want grit in that new plant. This is a really nice set-up. It keeps the grit out of the pumps and wires and protects the equipment,” Boston said.
After the sewage leaves the hydrogrit system, it heads down the hill and across the valley to the huge concrete structure where the “bug-farming” process begins.
Actually the new plant is much more compact than the old one. While the old plant had several treatment ponds sprawling across the valley, the new plant fits in the footprint of just one of the old ponds.
As water enters the new plant, it separates into three independent systems of tanks that each act like their own treatment plant. All three of the systems can be in use, or only one or two can be used, at one time. If the plant needs added capacity in the future, it will be easy to expand by adding another line of tanks, Boston said.
The disadvantage is that the system requires three times the hands-on management.
Phosphorus is the hardest nutrient to control, Boston said. The wastewater plant actually doesn’t have enough food - in the form of waste - for the bacteria to effectively keep the phosphorus in compliance without some extra help.
Employees add sugar water and vinegar - or acetic acid - to give the bugs more food.
The water goes into a covered tank first where anaerobic bacteria - those which don’t like oxygen - begin to break down the waste. The tank is covered, both to keep the air out and the smell in.
The water then goes into a series of two 20-foot-deeptanks with anoxic - or oxygen loving - bacteria. The water is cycled from one tank to the next and then back again over and over to keep it stirred up, otherwise the bacteria would settle out in the bottom and not come into contact with the nutrients it needs to break down, Boston explained. Alum is also added to the batches to remove the excess phosphorus.
Each batch contains 152,000 gallons of water and takes six to seven hours to process between the two tanks. It takes 33 minutes to empty a tank and 18 minutes to refill it, Boston said. When the cycle is complete, the mixing stops and the bugs settle to the bottom. The clean water is pulled off the top and joins water from the other two treatment systems in a large holding pit. If a batch of water doesn’t pass tests, then it is pumped back up the hill into a holding pond to go through the whole process again.
“We have a lot of control over where the water goes,” Boston said.
Each line of tanks makes an average of three to five batches of wastewater a day, he explained.
The plant has a touchscreen control panel thatsends the water on to the final filter. The more water in the tank, the faster water is pumped through, but as the water in the tank gets lower, it’s pumped at a slower and slower rate so there will be a constant supply of water running through the filter and ultraviolet-light sanitizer.
If the water drops down below one foot deep, the UV system automatically turns off so it won’t overheat, Boston said.
“There are safety features all the way around so we don’t send water that hasn’t been disinfected back into the creek,” he said.
The UV light sanitizer is the first of its kind in Arkansas, Boston said. The only other one in the state is in Hot Springs. In the past, chlorine was used to sanitize the water, followed by another chemical to remove the chlorine.
There are other UV sanitizers in the state, but they are extremely large and spread the lights over a large area of shallow water, requiring a lot of concrete work. Decatur’s UV sanitizer does all the work in the space of a few feet. It has eight 4,500-watt bulbs. Maintenance is very easy and bulbs only have to be changed once a year, Boston said. It even has little wipers that go across inside to keep it clean.
The UV sanitized water tests almost perfect, he said.
Once the water is sanitized, it passes through a flow meter - a device that adds oxygen back into the water - and its ready to go back into the creek.
All of the water used in the plant for things like washing down and watering the grass is finished wastewater - no city water is used.
Decatur’s new wastewater treatment plant also boasts a new sludge press. There are only one or two other similar presses in Arkansas, and Decatur has the largest press the company makes.
Sludge is a by-product of the treatment process, and the press removes all the liquid from it so it can be disposed of in a landfill. So far, the plant’s sludge tank hasn’t been filled, but the press will soon be put to work.
Boston said he is still working with chemists and engineers to find a better way to remove phosphorus from the wastewater. The plant is still using quite a bit of alum to help remove the phosphorus.
“Hopefully in six months from now, these little problems will be history,” he said.
The new plant is capable of treating more than 3 million gallons of wastewater a day.
“We have some room for growth. I think it’s going to serve us for years to come,” Boston said.
News, Pages 1 on 10/28/2009