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10-hour trip from smelly to fresh

$61.3M project upgrades sewer treatment process for Manteca

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10-hour trip from smelly to fresh

Manteca wastewater treatment plant operator Benjamin Abulencia looks over one of the sedimentary clarifiers.

HIME ROMERO/The Bulletin


POSTED July 19, 2009 2:39 a.m.
Anglers know where the best water is to catch fish.

It is usually the cleanest water on the river.

It explains why you can often find fisherman huddled around the outlet that sends treated wastewater from Manteca back into the San Joaquin River.

Returning water that is cleaner that what can be found in the San Joaquin River is the end process of a journey that takes about 10 hours once you flush your toilet.

On the way it will pass through the wastewater treatment plant just north of the Big League Dreams sports complex where the state-of-the-art cleansing process using bacteria and ultraviolet light that is part of a $61.3 million expansion, upgrade and retrofit that started construction in December of 2003.

Most don’t give a second thought to what happens to the water and its contents after flipping the handle, draining the sink or tub, turning on the washing machine or dishwasher or taking a shower. That’s not the case, though, for Plant Operator III Benjamin Abulencia and other municipal employees whose job is to keep Manteca sewers flowing and making sure the treated effluent meets stringent state quality standards so it doesn’t harm fish, fowl or human that may use the river.

They oversee a simple process employing high tech with built in redundancy and back-up for environmental protection to treat an average of 9.87 million gallons of wastewater a day. If it doesn’t create a lot of fanfare, that’s exactly the way Manteca Public Works Director Mark Houghton likes it.

The treatment plant has effectively blended into the background thanks to the upgrades that ends up providing water that is essentially clean enough to drink. The covering of various initial treatment tanks has also made the plant so unobtrusive that the 300,000 plus visitors to the Big League Dreams sports complex can’t smell a thing even though they are downwind. The process has been upgraded to such a point that the firm building a small business park adjacent to the plant site has no reservations about the location.

“The city plans to develop right up to the plant,” Houghton said as he pointed out where Milo Candini Drive will be extended north to Yosemite Avenue. It is along this stretch of future road that San Joaquin County is currently negotiating with the city for a South County satellite office.

Making sure that there is no chance for smell issues to develop in the event of a failure was a decision by the City Council to put in a second centrifuge in the current expansion now getting underway that will also provide a larger maintenance shop as well as locker rooms. The centrifuge will not only help when the plant is operating at maximum capacity at the city grows but it will effectively eliminate one old school portion of the process – the spreading of sludge on large, flat concrete bins to reduce water weight.

City works to reduce future plant costs
This is essential to keep costs down as the city pays by the ton to landfill the sludge. Drying it takes a long time to get the moisture out and runs the risk of more smells. The centrifuge effectively gets the water out much quicker without relying on Mother Nature.

It isn’t the only cost saving part of the process.

The use of expensive chemicals – specifically chlorine - has been greatly reduced by installing state-of-the-art ultraviolet light channels to kill off disease causing organisms. There are 16 modular banks of UV lights that contain 2,240 separate UV light tubes.

The process is much more effective as there is a 100 percent kill rate of bacteria that causes diseases. The trade-off, though, is higher power costs that push the energy tab for running the plant past $1.2 million year.

Manteca is working to reduce that bill with the goal of making the plant self-sufficient in terms of electricity by employing solar panels and a cogeneration unit to generate power by burning methane gas.

City staff is also working on plans to divert treated wastewater from being returned to the river to instead help irrigate everything from landscaping to parks. It would cut costs in two ways – by helping reduce No.1 use of expensive treated drinking water to irrigate landscaping and to avoid possible future state-mandated upgrades in treating water returned to the river including more extensive removal of salts.

Manteca currently uses agricultural wash water sent to the treatment plant site via a purple pipe from Eckert’s Cold Storage on Moffat Boulevard. There are some 240 acres of corn used as silage for dairy cattle that is irrigated with the Eckert’s water.

In addition, the city is working with the Central Valley Regional Water Quality Control Board to have contractors fill water trucks at purple pipe hydrants near the entrance of the treatment plant off Yosemite Avenue. That way when dust control is needed during construction, it can come from recycled water and not from fire hydrants on the streets. That could save enough water during construction season to serve up to 30 households a day.

Manteca’s plant operators also will “store” effluent to allow as much of it to be treated a possible during off-peak hours for electricity use. In doing so, they have managed to cut Manteca’s power bills.

Houghton noted treatment costs could be reduced substantially if the city was simply treating human waste and not items sent down the drain such as household cleaning chemicals and stuff ground up by garbage disposals.

“That really adds to the cost but I don’t think you are going to get anyone to do away with garbage disposals,” Houghton said.

 The $61.3 million project that has been under construction for almost six years is a combination retrofit of worn out components, upgrades for new state-mandated treatment processes, and expansion. Existing ratepayers are on the hook for the upgrading of existing components and their share of retrofitting the process while growth fees are paying for the rest.

Houghton noted work has already started on the next expansion due to the long lead time needed for the state’s approval process.

The plant underwent a mid-construction redesign in a bid to reduce future expansion costs. The key components have been oversized and laid out in such a manner that the next expansion – that growth will pay for 100 percent – will take less time to go through the environmental process and less time to build.

How treatment process works
Raw wastewater flows initially through a bar screen that removes large rags, paper and plastic. The stuff removed is trucked to a landfill.

From there it goes to an aerated grit chamber that removes heavier inorganics, sand and such. The grit goes to the landfill as well.

The third step takes the wastewater to primary sedimentation tanks that remove settable floating organics. The primary sludge and grease is sent to anaerobic digesters.

Next comes the aeration basins that have an activated sludge process using bacteria to convert the remaining dissolved organics to settable mater.

From there it goes to the secondary sedimentation tanks that settle and removes activated sludge where some bacteria are returned to aeration basins for more work.

Next are the tertiary filter tanks. They remove the remaining suspended solids particles. The last step is the ultraviolet disinfection channels that disinfect wastewater using UV light by killing disease causing organisms.

From there the treated wastewater goes to the San Joaquin River or to purple pipes for construction purposes.

The anaerobic digester takes 30 days to break down and stabilize organic solids that were removed in the primary sedimentation tanks. Methane gas is produced as a byproduct.

That methane gas currently is flared off. The water is separated from stabilized solids in a centrifuge. The water goes to a bar screen and the stabilized solids are buried in a landfill.
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