Diving Into Compost
What to do with sludge? It’s a common question for wastewater treatment facilities, and composting arises as one of the potential answers — one that can generate revenue while also supporting the community and the environment. Here’s an inside look at the process done well.
The University Area Joint Authority (UAJA) is a 9-MGD-rated wastewater treatment facility located in State College, PA, home of Penn State University. Outside the bustling campus, however, UAJA’s service area is largely rural — a natural setting ideal for outdoor enthusiasts and a source of pride to the community. “Citizens here are taught from birth to be environmentalists,” said UAJA’s executive director, Cory Miller. In sharing that environmental sentiment and serving the public, UAJA has taken every measure to ensure that its treatment practices are the most eco-friendly available.
In addition to producing drinking water-quality effluent through its water reuse project, UAJA has a composting facility to reuse the most troublesome of wastewater byproducts — sludge. The Class A-designated compost is sold to the public for $2 for small containers or $5 per cubic yard, providing a rich soil amendment to landscapers, nurseries, and homeowners. At the same time, it offsets the sludge disposal costs typical of conventional treatment facilities.
“This is the most progressive plant in Pennsylvania and half the East Coast,” said John Brosious, deputy director of the Pennsylvania Municipal Authorities Association (PMAA), as he accompanied on a group tour PMAA coordinated as part of its annual conference. “Nobody does this stuff.”
The “stuff” Brosious refers to is what UAJA calls ComposT, the utility’s proprietary mixture of ground hardwood material and clean municipal dewatered sludge. The composting process has been online since 1992, and in 1996 earned UAJA the Pennsylvania Governor’s Award for Environmental Excellence in Innovative Technology. Even more notable, UAJA went on the next year to win the U.S. EPA’s national award for the beneficial use of biosolids from a treatment facility operating at less than 5 MGD (though rated for 9 MGD, current average flow is 4.77 MGD).
The final product — UAJA ComposT — is cured and stored prior to sale.
The early adoption of composting is a testament to how ahead of the curve UAJA operates. Since then, UAJA has continually fined-tuned and expanded the process, which I was fortunate enough to see (and smell) firsthand. The following pictures and descriptions provide insight into the state-of-the-art, award-winning operation.
Step 1: Sludge Dewatering
The first step is sludge dewatering, which involves sludge being pumped from both the primary and secondary clarifiers to the dewatering building. Primary sludge typically comes in at about 5 percent solids, while secondary sludge is usually about 1.5 percent solids.
The primary and secondary sludge is blended together with a chemical polymer and sent through centrifuges, which squeeze out water to create a “sludge cake” of about 23 percent solids. From there, the dewatered sludge moves from the dewatering building to the composting facility.
Step 2: Compost Batch Mixing
The next step is batch mixing, wherein 6,000 lbs. of dewatered sludge is combined with 4,500 lbs. of ground hardwood material and 1,500 lbs. of “recycled” compost. The mix is carefully formulated to achieve the right amount of porosity to allow for proper air circulation during composting.
A large commercial mixer creates a 15-cubic-yard mixed batch, which is then transported with a front-end loader to one of 18 compost bays.
Step 3: Composting
Composting is handled in a huge 71,100 square-foot facility, manned by four full-time workers. The facility also employs three automatic agitator/mixers. The individual bays are 220 feet long, 6 feet wide, 6 feet high, and capable of accepting 6 wet tons of organic materials daily. With each agitator capable of moving 11 feet of material per day, running five days per week, the composting process takes 28 days to complete.
An agitator stands at the ready ahead of the compost bay.
As the materials are mixed and moved down the bays, fresh materials fill the void left behind to keep the bays full. Though it appears on the surface an activity of brute force and heavy machinery, there are temperature sensors within the bay walls monitoring a sensitive process. Proper temperatures must be maintained to promote microbial activity and the breakdown of organic materials. When the mixture gets too hot, the sensors trigger blowers to cool it down. Conversely, composting won’t occur if the mixture is too cold.
After the requisite 28 days in the composting facility, the compost is transferred to a separate, enclosed area for static pile curing. Once cured for 30 days, it is tested for a myriad of parameters including, but not limited to, salmonella, metals, and nutrients. Once the results are received and deemed acceptable, the compost is ready for public sale. In addition to local customers, UAJA has large buyers throughout Pennsylvania, and has even sold to the Congressional Country Club in Bethesda, MD (host of three U.S. Opens and a PGA Championship) and a number of NFL teams.
A Step Outside: Odor Control
Though it is not a stage in the composting process per se, an important aspect of the operating procedure (and community relations) is the biofilter outside the composting facility. Touring the inside, the noxious fumes can bring tears to your eyes, but there is nary an odor just beyond the doors. That’s because the foul air is sent from the facility directly through 4 feet of combined leaf compost and softwood chip media contained in the biofilter.
Rather than releasing odors into the atmosphere, UAJA carries them from the facility into the biofilter seen on the ground at right.
The sum total of the process isn’t a moneymaker for UAJA (which merely strives to break even), but it does earn them something even more valuable: the sincere appreciation of the community. By honoring the call for environmental stewardship, the crew at UAJA has earned complete trust and buy-in from ratepayers and officials, enabling them to continually update plant operations with the latest and most sustainable technologies available. Quite literally, innovation is all in a day’s work for UAJA.