Sewer and water systems contain endless varieties of tanks, vessels, digesters, lift stations and wet wells that require continued maintenance. In many cases, they’re cleaned using hoses, high pressure washing devices and brute human force supplied by workers who often enter tanks to achieve acceptable results.

What is the most important factor that contributes to a cleaning program?

“To us, the most important factor in tank cleaning has nothing to do with cleaning the tank,” says Michael Delaney, vice president of business development with automated tank cleaning equipment manufacturer Gamajet. “It has to do with promoting worker safety by eliminating the use of confined-space entry while cleaning, when that cleaning could easily be handled by an automated system.”

Gamajet was founded about 60 years ago, offering a cleaning system that applied detergent to the insides of ocean-going oil tankers. About 20 years ago, the company diversified to include tank cleaning across a number of industries using a wide range of cleaning systems and nozzles. The company’s approach to cleaning employs rotary impingement tank cleaning machines.

“The system combines pressure and flow to create high-impact jets, which clean when the concentrated stream impacts the enclosure’s interior surface,” says  Delaney. “This impact and the tangential force that radiates from the point of impact blasts contaminants from the surface, scouring the tank interior. The action of the cleaner is a shearing force, which works more like a putty knife in removing material from enclosure walls. The jets rotate in a precise 360-degree pattern to ensure the entire interior is cleaned. It’s like a Spirograph that eventually covers the entire interior surface of the enclosure.”

Engineered tank cleaning

Each cleaning application may be engineered differently, ranging from smaller enclosures to lift stations, sewage tanks and vacuum trucks.

“Beyond the advantage of getting workers out of confined spaces, the goal is to thoroughly clean an enclosure in less time with less labor and fewer resources,” notes Delaney.

Municipal clients first need to assess their goals, whether improved worker safety, reduced labor cost, reduced use of cleaning fluids (largely water), reduced downtime for customers and better system performance. They next need to describe how the enclosure is currently cleaned and the type, size and interior layout of the enclosure.

Cleaning jets need to reach the interior surface of the enclosures from wherever the automatic cleaning device is placed.

“We have to look at the entry points of the enclosure as well,” says Delaney. “One of the engineering challenges is to create a cleaning unit with a small enough gearbox so that it will fit through a tiny access hole and still provide cleaning power. In some cases, where access is very controlled, the client may install a permanent cleaning system inside the enclosure. We’ve seen lift stations becoming much larger, so that sometimes a permanent system using more than one jet is required.”

Identifying the grime

Next, clients need to describe the type of material that needs to be cleaned. While sewage sludge is definitely on the list of prime offenders, Delaney says that coatings of fats, oils and grease represent the most stubborn stain on municipal hit lists.

In most cases, the cleaning fluid used on municipal jobs is ambient temperature water. If the work is located near a fire hydrant or a water plant, the volume of water used for cleaning is usually not an issue for the client. If the water is delivered to the site in a combo truck, then water becomes more of an expense.

“In some cases, clients use graywater or even pond water for cleaning,” says Delaney. “That’s not a problem as long as the water is filtered of particulates that can prematurely wear out system components. Getting a twig stuck in the nozzle is a definite deal breaker.”

The final consideration will be the design of the spray delivery system, including the number of nozzles, the flow rate of the cleaning fluids and the gear ratio of the equipment that will deliver the necessary cleaning power.

“In most cases, wastewater clients provide their own pumps, often the ones mounted on combo trucks or in some cases using a fire truck, and we design the system around that,” says Delaney. “We’re often asked how many pounds of pressure our equipment delivers, because many people assume that’s the most important factor in effective tank cleaning. It’s just one factor, but not even the most important one.”

Cleaning water is typically delivered to the Gamajet cleaning unit at about 100 to 200 psi, enough pressure to get the fluid through the plumbing to the business end of the device.

“Our equipment includes an impeller that actually reduces the rotation speed of the jets, because we don’t want the cleaning fluid stream to break apart,” says Delaney. “We also keep the pressure low to prevent the stream from atomizing into water droplets. What we’re looking for is a compact and solid stream of fluid hitting the walls at top impact, delivering a certain number of gallons per minute. However, we don’t want a stream so violent that it can damage the concrete walls of some enclosures.”

Although effective at cutting through grease and sludge, the cleaning jets can’t cut through human flesh. “The worst it would do if you got in the way is to give you a bruise,” Delaney says.

Gamajets have also been used to apply chemicals designed to neutralize acids to the interiors of concrete enclosures, including brick and concrete manholes.

“It’s like watching Pepto Bismol sprayed on the inside of the enclosure,” says Delaney. “The chemicals help the walls of the brick and concrete wet wells and manholes to stand up to acids like hydrogen sulfide and can prepare a surface for remediation.”

How many nozzles?

Gamajet automatic cleaners typically offer either two- or three-nozzle machines. A two-nozzle machine operating at 100 pounds per square inch and 100 gallons per minute can deliver 50 gpm per nozzle. A three-nozzle machine operating at 100 psi and 100 gpm will offer 33 gpm per nozzle and a lower impact force in a tighter pattern.

“For most municipal applications, the Gamajet is suspended through an opening and lowered into the enclosure,” notes Delaney. “The two-nozzle machine is a much better choice for those applications because it’s self-balancing. The three-nozzle machine tends to be less stable when suspended.”

The client also needs to determine how frequently the tank will be cleaned — monthly, weekly, daily or as needed.

“If the cleaning program proves effective by reducing costs and eliminating labor, it often changes the parameters of the cleaning program,” says Delaney. “They tend to clean earlier and more often before the problem gets out of hand.”

A case in point

Matt Taylor, owner of Gamajet distributor Cleancut LLC of Lafayette, La., has assisted numerous municipal clients in developing automated cleaning programs. In the city of Covington, La., the target was lift station maintenance.

“Previously to clean these, a worker would break up the solids using a long wand on a pressure washer, then vacuum up the chunks using a jet vac,” says Taylor. “A station in this condition would typically take 45 minutes to an hour to clean.”

Taylor says he fitted a Gamajet VIII to the existing hose and pump on a municipal vacuum truck, lowered the machine on the hose into the lift station, and then turned on the truck pump.

“No special tools or stands are needed as it will remain steady hanging from the hose in operation,” he says. “In 11 minutes the solids had been broken down to the point where the pumps were able to push them, in fluid form, down to the waste facility to be treated. Total time was about 15 minutes per station, eliminating worker exposure to the open lift station and reducing the hauling of waste from the stations in the vac trucks.”

Economics of effective cleaning

In many cases, the economic argument for using more effective cleaning methods involves pump efficiency.

“In some lift stations, I’ve seen coatings of fats, oil and grease 2 to 3 feet thick along the walls,” says Delaney. “Since lift station pumps are located down below, the grease is really impeding the liquid flow. Even though the pumps are designed to chop up the material, a steady diet of grease will cut their service life drastically.”

Maintenance of the Gamajet system largely involves operator replacement of worn seals and O-rings.

“In municipal settings, we’re typically seeing the systems run for four years or more without requiring maintenance,” says Delaney. “As long as the water used to clean is filtered of particulate, the jets will go a long time between servicing.”