What happens after you flush
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“People forget about us down here,” Dan Ramer, chief operator at the Ithaca Area Wastewater Treatment Facility (IAWWTF) said in an interview last week. “But these facilities allow for advanced civilization.”
The IAWWTF, in operation since 1987, treats between 6 and 7 million gallons of sewage per day, coming from the City of Ithaca, the Town of Ithaca and some of the town of Dryden (the part along Rt. 13, before NYSEG). Water processed by the plant gets sent a half mile out into the middle of Cayuga Lake.
The plant is currently undergoing major renovations – the first since the plant was commissioned 27 years ago. The changes and updates, which include improvements to the plant’s digesters, biogas storage and biogas utilization (explained further down) are all geared towards improving the efficiency and sustainability of the plant.
Ramer said it’s about investing money to save money.
“We’re community owned,” Ramer said. “Anybody who owns a home or pays rent in Ithaca owns a part of this plant. And so when I invest your – as a rate-payer – your money, I do it based on two concepts. One: efficiency. Two: reliability.”
“Any dollar we save is an immediate savings to the community,” Ramer said.
Getting water ready for “prime-time”
After the sewage from the three municipalities hits the IAWWTF, it’s pumped up to a higher height. This creates a gravity gradient so that the water can flow downward through the plant. This pumping is one of the plant’s main energy sinks.
“We’ve got 120 horsepower motors running 24/7 to move about 50 million pounds of water per day.”
After the water is pumped to the necessary height it flows through primary, secondary, and tertiary tanks. Primary tanks are just for settling – waste settles out the bottom or froths up to the top, and is collected.
The (still very dirty) water which leaves the primary tank runs in to the secondary tank, where it is further cleaned by what’s called an “activated sludge” process. Basically, to “activate” the sludge, the plant just adds oxygen.
Several large blowers (to be upgraded in renovations) located in a gallery below blow dissolved oxygen up into the secondary treatment tanks. The oxygen in the water boosts the metabolic processes of organisms which are either already present in the sewage, or which fall down into the tanks out of the air.
“They’re natural organisms,” Ramer said. “We just give them an optimal engineered environment.”
Once the organisms have eaten up much of the waste in the secondary treatment phase, the water is sent on to tertiary treatment tanks where more waste settles out. Added iron and polymers speed the settling process.
Then, once water has left tertiary treatment, a bit of bleach is added as a disinfectant.
After disinfection is complete, the water is “ready for prime time,” as Ramer puts it, and is sent out into the lake.
The fruits of our waste
Throughout the process, the “waste” which is taken out of the water is largely repurposed. Organisms which collect at the bottom of the secondary treatment tank are either pumped back to the top of the tank “to do more work,” or are pumped out into thickening tanks.
“With every growing system you’ve got to trim the hedges,” Ramer said, “so we send some of these organisms to thicken in tanks, and then we send them on to the digesters.”
The digesters – two massive round tanks – are where all of the waste and organisms are sent to collect.
Inside the digesters is an anaerobic (de-oxygenated) environment where the sludge festers and breaks down. In the first tank, a massive “scotch yoke” churns the waste. In the other tank, the waste is simply left to settle.
The anaerobic breakdown of waste produces methane gas.
Ramer said that the plant has simply optimized a natural process. In swamps, the slow breakdown of organic matter beneath the water creates bubbles of flammable methane gas. Ramer said that if you stirred up the muck in a swamp and placed a funnel where the gas bubbles up, you’d be able to replicate the process which occurs at the IAWWTF.
“Pop the cork, light it, you’ll get a flare that comes up,” Ramer said. “That’s the same process that happens in our digesters.”
Harnessing Swamp Gas
At the IAWWTF, the gas isn’t just set alight and wasted in the open air. It is harnessed.
The biogas, as Ramer calls it, which is produced in the digesters is sent to high-tech “co-generating” microturbines. These machines, which have been installed as part of the new renovations, harness the energy of the biogas to “cogenerate” electricity and heat. The heat is used to warm the digesters and the energy is used to fuel the plant.
“We’re generating about 30-50% of our own electricity,” Ramer said.
The microturbine machines look more like computer servers than engines. The turbines inside spin at about 95,000 RPMs and they generate 182 Kilowatts of power.
“We will never work on these,” Ramer said. “They are ‘other’ to us.”
The installation of new microturbines, along with other improvements to the plant, have been made possible by a $10 million “performance contract” with Johnson Controls. Johnson Controls has guaranteed that the improvements will pay for themselves in 15-20 years.
Although the IAWWTF does a good job of repurposing most of its waste, there are still materials that it cannot, at this point, put to good use. One crucial challenge for the plant is figuring out what to do with 45,000 wet tons of “biosolids” waste which the plant produces annually.
Although these materials tend to be very nutrient rich (and might thus be safe to compost or use as fertilizer) there is some question about their ecological safety. The biosolids which the plant produces contain what are called “emerging contaminants,” and there is a worry that these contaminants might pollute the environment if they are simply laid down on the soil.
Ramer said that the risks associated with emerging contaminants remain largely unknown.
“Are they dangerous? We don’t know. Are they deadly? We know they’re not deadly,” Ramer said.
“This isn’t Love Canal. This isn’t PCBs. This is endocrine disruptors, pharmaceuticals, flame retardant which comes off of furniture – weird stuff at very low levels.”
Although the state does not task the IAWWTF to look for these materials in their biosolids, Ramer and his staff are doing it anyway. They are working with the United States Geological Survey to develop ways of determining the risks associated with emerging contaminants.
“This is not a national priority,” Ramer said. “But it needs to be.”
Until they know the risks associated with emerging contaminants, the IAWWTF will continue to send truckloads of biosolids – about 5 a week – to a landfill in Geneva.
“The big thing is that this community does not have a landfill. That’s not one of our local options. If we want to solve our problems locally we have to come up with other ways of doing it,” Ramer said.
Trucking biosolids to Geneva costs the plant about $300,000 per year and is a black-eye for the plant’s sustainability goals.
“When you look at that from a greenhouse gas perspective,” Ramer said, “it’s a big negative. It’s not trivial.”
Ramer said that improvements currently being made to the IAWWTF are a big step in the right direction, but that they are continuing look for ways to make the plant more sustainable, ecological and affordable for the community.