What you flush down the toilet or send down the drain becomes Mark Houghton’s problem.

Houghton, Manteca’s public works director, oversees the city’s wastewater treatment plant that is currently undergoing a $20.1 million rehabilitation to prevent structural failing as well as make it possible to convert sewer methane gas and food waste into compressed biogas to fuel the city’s fleet of nearly two dozen solid waste collection trucks.

“In time, things wear out,” Houghton said last week as he walked above various tanks where air is infused into wastewater as part of a step to treat wastewater.

The $20.1 million endeavor is the most expensive Manteca municipal project in 15 years. When completed it will help keep a lid on long-range costs as well as make sure Manteca meets or exceeds standards for air quality, wastewater treatment, and solid waste disposal.

 Western Water Contractors — the firm awarded the project — will finish the renovations and upgrades next year.

One of the two new 65-foot diameter anaerobic digesters is already in place. If you keep track of the dome roof atop the digester during the course of a day you will notice that it moves. The dome is attached to tracks along the walls that allow it to move up and down over a 5-foot range. It is designed to allow for the storage of methane gas that will start in about mid-2019 being used to produce compressed biogas.

For now, the methane gas is being burned off atop a pipe “chimney” that produces a noticeable flame.

The need to burn off methane gas will virtually disappear when the food waste to fuel program is 100 percent up and running.

Senior engineer Bret Swain noted that when the city started dealing with the need to address what essentially are wear and tear issues at the treatment plant that serves 81,450 residents plus a large chunk of Lathrop’s 26,000 residents, it was also faced with a state mandate to stop burying food waste.

Department personnel, in comparing notes, quickly realized the needed renovation of the wastewater treatment facilities could easily be done in a manner that would allow the production of compressed biogas.

Houghton noted by capitalizing on the synergy of the two needs Manteca is able to parlay the $20.1 million being invested currently into upgrades to produce long-term cost savings for both solid waste and wastewater ratepayers.

At the same time the Manteca plant will continue to meet standards that allow it to release treated water to the San Joaquin River that exceed requirements as well as significantly reduce methane gas that is being targeted by the San Joaquin Valley Air Quality Control District. The food waste to fuel portion will divert food waste from landfills as well as allow city solid waste vehicles that most currently run on diesel to burn the clean compressed biogas.

The project also involved the rehabilitation of the two older digesters. It not only provides backup given coupled with the new two digesters it doubles the number of digesters, but it will allow for an expansion of the treatment plant for up to 12 million gallons per day at some point down the road.

Once the current $20.1 million project is completed, the plant will be able to process nearly 9.8 million gallons of wastewater a day. Currently it averages right around 7 million gallons.

Work now underway also  involves the construction of a new digester control building, installation of a new compliant flare system, installation of new compliant boilers, installation of new gas handling and treatment equipment plus other associated improvements to support the treatment of waste solids, production of biogas, and the continued smooth operation of the wastewater treatment plant.

When the work is done, wastewater will be cleaned to the point it is one process short of being drinkable as it has been for more than 17 years. It will assure that the treated wastewater that Manteca in the coming years while recycle to irrigate municipal parks continues to be significantly cleaner that the water in the San Joaquin River where it is released.

The plant was last upgraded and expanded in 1998 at a cost of more than $61 million.

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 are 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.

Treatment plant

blends into background

The treatment plant has effectively blended into the background thanks to the upgrades made previously that provide water that is almost 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 development is occurring around the plant and nearby including the $180 million Great Wolf Resort that is being built on 30 acres that once were part of the wastewater treatment plant site.

The city plans to develop right up to the plant. Milo Candini Drive will be extended north to Yosemite Avenue where the city envisions smaller business parks developing.

Making sure that there is no chance for smell issues to develop was a decision by the City Council years ago to put in a second centrifuge 

The only smell issues that arise occasionally have to do with the land disposal of water used to wash bell peppers — green, red, and yellow — that Eckert’s Cold Storage processes for pizza firms. That water is piped to the city property where it is applied to land the city leases to a farmer to grow silage to feed dairy cattle.

The centrifuge effectively gets the water out much quicker from the sludge without relying on Mother Nature.

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

The use of expensive chemicals — specifically chlorine — was greatly reduced when previous work was conducted 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 $1.6 million year.

Manteca is working to reduce that bill with the goal of making the plant almost self-sufficient in terms of electricity by employing solar panels. Manteca is currently soliciting bids for a solar farm that would nearly wipeout the wastewater treatment plant’s need to buy electricity from PG&E. The treatment plant is the largest consumer of electricity in Manteca.

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To contact Dennis Wyatt, email dwyatt@mantecabulletin.com