By Len Maniace
Ecotourism usually conjures visions of rain forests and exotic fauna in Costa Rica and other distant locales. On Saturday I journeyed to Greenpoint, Brooklyn. Well, at least my subway trip produced less climate-changing carbon dioxide than a flight to Central America.
My destination was the site of eight gleaming stainless steel structures known as Digester Eggs, which dominate the Newtown Creek Wastewater Treatment Plant there. On most days, 340 million gallons of sewage are transmuted into clean… well let’s just say, cleaner water.
Sewage – that’s the liquid that comes intermittently from your kitchen sink and toilet. In a city of 8.3 million people, however, those intermittent flushes quickly join up to become swift-moving streams and eventually mighty rivers of sewage.
Where the flush goes
One-third of Manhattan’s sewage travels under the East River, one-fifth of Brooklyn’s sewage flows north, and one-seventh of Queens’ sewage flows south, all into the Newtown Creek Wastewater Treatment Plant, the largest of the city’s 14 such facilities.
“And we are happy to receive it here,” Ali Zainool, the plant’s manager, told the audience at an 11 a.m. tour, the first of three that day. It’s an annual event known as the Valentine’s Day Digester Egg Tour, even though it came eight days early.
One has to admire the confidence of New York Department of Environmental Protection officials for picking a holiday dedicated to romance and risking jokes about perfume on tours at facility where olfactory is not necessarily the sense one wants to focus on. For the record, neither I nor other visitors I spoke to, noticed any unpleasant odors.
Standing in a plant’s visitors center classroom, the hum of giant compressors in the background, Zainool explained the operation: wastewater entering the plant first meets up with giants screens that filter out branches, toilet paper and other debris; then said sewage is digested by hungry bacteria, before it is treated with chlorine, and piped to the East River, a reasonable facsimile of water that’s clean enough to meet federal and state pollution codes.
If only that were the entire story, however. When skies over New York open, raining down on roofs, roads and parking lots, water rushes into the city’s 148,000 catch basins, racing down 7,400 miles of sewer lines toward sewage treatment plants, Zainool explained.
Wastewater treatment plants are built to handle some of this added storm water flow – an extra capacity equal to each plant’s usual flow. Larger rains, however, quickly overwhelm this added capacity. The overload is then shunted from underground sewer mains into the city’s waterways, releasing huge volumes of untreated sewage.
This is New York City biggest challenge when it comes to keeping its surrounding waterways clean. Newer cities and suburbs have solved this problem by building separate wastewater and storm water systems. New York City, however, is now looking for ways to keep much of the storm water out of treatment plants, or at least delaying it’s arrival.
Gray versus green
One method is the construction of huge underground tanks that temporarily hold this mix of rainwater and sewage, a project that comes under the heading of gray infrastructure. The other method is green infrastructure, working with nature to prevent runoff from ever reaching city sewers.
These include green roofs, rain gardens and permeable pavement that allows rain and melting snow to penetrate sidewalks and parking lots into soil. Another tool is beginning to transform the streetscape in parts of the city, bioswales. They are street-side gardens surrounding trees that can divert up to 2,000 gallons of water from curbs into soil. Green infrastructure is an exciting innovation, but it’s a tale for another day.
There’s no missing the Digester Eggs at the Newtown Creek Wastewater Treatment Plant. They are 140 feet tall and connected at the top by enclosed glass walkways which not only enable workers to oversee the operations, but they also provide spectacular 360-degree views of the city.
Standing in a walkway atop one digester egg, deputy plant manager Kevin McCormick explained that engineering, not aesthetics, was behind the eggs’ design. The shape is ideal for mixing the digester’s contents, helping bacteria to break down the sewage. The design is so efficient each Digester Egg needs only one 50-horsepower motor to churn 3 million gallons of sludge, resulting in a significant energy savings, McCormick said.
In an egg and the human gut
The breakdown of sewage by bacteria is a biological process similar to how food is digested in our intestines by bacteria. And as happens in the human process, this one also produces natural gas, or methane. But rather than allowing methane, a powerful greenhouse gas, to escape into the atmosphere, McCormick said the city uses the methane to heat the sludge to 98 degrees, the temperature at which the bacteria are most active, and also to heat water that’s occasionally added to the process, thereby saving energy and money.
The city has even bigger plans for tapping methane at the plant – a composting program that would breakdown food scraps much the way backyard compost piles work. A test project that composts scraps from a New York City elementary school is now underway at the site. If successful, the city would collect scraps from many more school cafeterias and then sell the methane to a local supplier.