Written by Larry Trojak, June 2018
Central Florida is One “Class A” Place
Much like the State of Florida itself, the Water Conserv II facility, located in Orlando, is all about change. Almost since its inception in 1961, Water Reclamation Facility (WRF) has been undergoing periodic upgrades, process changes and, at times, major overhauls to keep pace. So it should come as no surprise that, when confronted with the need to replace major anaerobic digestion components that were impacting capacity, all options were on the table. And when the Florida Department of Environmental Protection (FDEP) indicated that newer, tougher regulations would be impacting continued production of their Class B biosolids product, a range of alternatives was examined. The end result of those efforts is a new Class A Exceptional Quality (EQ) product created through use of the Bioset Process from Schwing Bioset, Inc. (SBI, Somerset, Wisc.) which effectively creates 120,000 lbs. of field-ready fertilizer product per day.
Use Then Reuse
Originally constructed in 1961 as the 4 mgd McLeod Road Treatment Plant, the Orlando facility was upgraded to 12 mgd in 1972 to deal with the area’s rapidly growing population and then further expanded to 25 mgd. Then, in the early 1980s, a number of factors, including the realization that the plant’s discharge was adversely affecting the health of nearby waterways, prompted the City of Orlando and Orange County to team up and create what is today called the Water Conserv II Distribution Center (DC) in west Orange County, about 20 miles from the Water Conserv II WRF. The DC reuses about 35 mgd of treated wastewater (reclaimed water) in west Orange County for agricultural, residential and commercial uses, as well as rapid infiltration basins (RIBs) to help with aquifer recharge. According to Paul Deuel, assistant division manager for the City of Orlando Water Reclamation Division, the scope of what was planned for the newly revised treatment plant was impressive.
“Much of this was driven by the growth we were seeing in the early 1980s and the projected impact on the aquifer that serves this area,” he said. “In addition, the EPA was mandating that discharge issues at nearby Shingle Creek be resolved. So, the Water Conserv II DC, which combined newly improved processes with the use of reclaimed water for area irrigation, was born. That last point is huge: up until then, very little agriculture involved the use of reclaimed water. The Water Conserv II DC went that route and for a long time was the largest citrus irrigation project in the world to do so.”
The move to make the resource available resulted in a contract which provided early participants access to free reclaimed water for a period of 20 years. For some, according to Deuel, the benefits proved invaluable.
“In the case of the citrus growers, this agreement provided a guaranteed water source, even in times of shortages or drought,” he said. “In addition, it could be used for frost and freeze protection when the lives of the trees themselves were at risk. Once we became established, additional users joined in over the years, including several area golf courses, Valencia Community College, Universal Studios’ theme park (which uses it both for site irrigation and in their cooling towers), the Mall at Millennia, even apartment complexes and single-family homes. It has really proven itself an invaluable resource.”
Time Takes a Toll
As mentioned, Conserv II WRF has been undergoing change of one sort or another since its inception. When major components in the anaerobic digestion area began to show signs of wear — and failing on an increasingly regular basis — the facility team started running the numbers to weigh the cost of shoring up the Class B biosolids operation or going in a new direction entirely.
“We started looking at the costs needed to rehab the anaerobic digesters to achieve [Class B] biosolids,” said Steve Shelnutt, Water Conserv II WRF plant manager. “At about the same time, FDEP advised us that new regulations, specific to the generation of a Class B product, were being implemented. It was obvious that continuing to do Class B was going to be more challenging and more costly. So, we began looking at alternatives available to us.”
Shelnutt said they contracted with engineering firm Black & Veatch and considered a combined heat and power process that still relied on anaerobic digestion but, because it went into the thermophilic range, it would give them the Class A EQ product they desired “However, it also added a nutrient load back to the plant,” he said. “So, they sought to remedy that by recycling the gas it created, treating the side streams, and so on. Unfortunately, the project costs started growing into the $40-60 million capital range — far beyond what we had envisioned.”
Let the Games Begin
As is so often the case in any industry, word that Water Conserv II WRF was seeking alternative processing methods traveled quickly. One of the first to call upon them, according to City project manager Kristi Fries P.E., was Brian Schuette, vice president of Moss Kelly, Inc., SBI’s Florida sales representative.
“Brian came in and, based on equal parts: what the Bioset Process could do for us and its estimated costs, quickly got our attention,” said Fries. “He told us that he could take us into a Class A EQ fertilizer-grade product for about $1.8 million. Compared with the other proposal which seemed to be growing more expensive by the day, this seemed almost too good to be true. At the same time, we were hearing from other manufacturers who pitched their processes, each of which had some good points, but ultimately didn’t give us what we really needed.”
The alternatives examined included upgrading the anaerobic digesters, a process that employed a high-pressure steam pre-treatment, another which used a technique to accelerate the composting process, and others.
“We did an evaluation of capital costs for each, measured it against the proposed end-product, and decided that we would move forward with the Bioset Process,” said Shelnutt. “We also took a ‘field trip’ to two different Florida locations where the process was already in operation and liked what we saw. In fact, our chief operator and I spent a good deal of time talking to the staff discussing the process and hearing how they felt about it. That really helped us make our decision.”
Feeling the Heat
The Bioset Process which Water Conserv II WRF has embraced takes biosolids that have been dewatered to about 15% dry solids and, using Schwing KSP-25 piston pump, routes it to a twin-screw mixer in which quicklime and sulfamic acid are added and blended. This type of mixing ensures a homogeneous product and alleviates issues such as unreacted lime in the final product — and the associated costs associated with it.
“At that point, the Schwing KSP-25 piston pump feeds material into the reactor in which heat from the acid and quicklime raises the pH level, thereby stabilizing the biosolids mixture and creating a product that meets EPA 503.33 requirements,” said Shelnutt.
Because the ammonia that is generated through addition of the lime is entrained with the biosolids inside the reactor, thereby killing the pathogens, the Bioset approach has been approved as a process to further reduce pathogens (PFRP). This approval allows the Bioset process to operate at 55°C (131°F) with a residence time of 40 minutes (versus 70°C (158°F) for 30 minutes) lowering operating costs by approximately 35%.
The stabilized Class A EQ product exits the reactor and is pumped directly to a pair of waiting trailers. Even though it is discharged from the process above 25% dry solids, the new product has very little surface tension until it cools, improving its flow characteristics and making it self-leveling in the trucks. According to Deuel, having SBI involved took care of an important step in the upgraded biosolids process: finding a customer for the end-product.
“We are fortunate in that Schwing Bioset has arrangements worked out with customers here in Florida who are anxious to take the Class A EQ material,” he said. “In this case, it is an organization called the Deseret Ranch which runs a cattle operation on about 295,000 acres (450 square miles) in Central Florida. And while they are happy to take the product in its raw form, Bioset will also accommodate customers who demand a pellet or finer product. Not having to deal with [the disposition of] the biosolids has been a nice bonus for us.”
Weathering the Storm
Schwing Bioset’s sister company, Biosolids Distribution Services (BDS) provided the first six months of hauling and marketing of the Class A EQ material . Utilizing more than 15 years’ experience, BDS was able to add the production from the Water Conserv II WRF to their current operation.
The benefit of having BDS haul Water Conserv II WRF’s Class A EQ product was felt soon after the equipment was installed, as Hurricane Irma struck in September of 2017. Due to the high-water table levels after the hurricane’s passage, virtually all sites available for Class B land application couldn’t be utilized and it wasn’t until three months later, when groundwater levels dropped, that those fields could be accessed again. The plant would likely have incurred substantial additional disposal costs taking Class B material to either landfills or longer-distance application sites that could still receive Class B biosolids. BDS and the city only missed one day of scheduled hauling — the actual day the hurricane struck. Otherwise it was business as usual leading up to and immediately after the storm.
The Need for Feed
Making the switch from a Class B biosolids product to a Class A EQ was not without its challenges. For example, at 371 cu. ft., the reactor installed at the Orlando site is quite large, yet the footprint in which the major components had to be installed was extremely tight. In addition, one of Water Conserv II WRF’s primary stipulations said that that their new process needed to be fully automatic.
David Bass P.E., Water Reclamation Division manager added. “We needed to automate everything. So the programming needed to achieve that was intricate and demanding. But Schwing Bioset, working with our own programmers, was able to make it happen.”
A good example of that automation at work can be found in the system’s lime feed process. At Water Conserv II WRF, should the temperature in the reactor drop, the lime feed will automatically increase; conversely, if the process is found to be running too hot, the lime feed will decrease. The program also monitors the output of the transfer pump and — whether they are running one or two dewatering presses — if the pump starts adding more sludge to the outside hopper it will also speed up the lime.
“This has taken our biosolids process to a whole new level,” says Shelnutt. ”We’ve gone from a situation in which the staff felt they needed to monitor things constantly, to one in which they are totally comfortable letting it operate as designed. Everything is now controlled by the HMI (human machine interface) on the control panel and, despite a few hiccups at the outset, it has proven an outstanding solution for us.”
All About the Change
In its previous Class B biosolids scenario, four belt filter presses discharged the dewatered biosolids onto two belts that led to an incline conveyor, then to a traveling conveyor which deposited it into trucks below. True to Water Conserv II WRF’s spirit of continual improvement, those two belts are in the process of being converted to screw conveyors and rather than converging in the center, will go in opposite directions and dump into a pair of Schwing KSP-25 transfer pumps.
“Those pumps take the biosolids to the Bioset unit outside,” said Shelnutt. “While it would have been great to have the entire biosolids process under one roof, size constraints made that impossible. This plant is on an area that measures less than 40-acres — relatively small for a plant of this size — and any open space we have remaining has already been slated for other use such as new clarifiers, additional aeration, etc. However, this does allow us to keep the Bioset process close to the trailer loading area, which was also important for us.”
Shelnutt added that the system design features a pair of Schwing Bioset bulk storage silos for redundancy in the lime storage area. They will also be keeping the traveling and incline conveyors as a backup, should there be anything that results in a service interruption to the Bioset system. In that case, they can simply send material through the belt presses and haul it to another facility for processing. “It’s an option, albeit an expensive one, but it is better than being completely out of business,” he added.
The biosolids process now in place at Water Conserv II WRF is capable of processing 20 dry tons/day and Deuel said that under normal conditions they would do about half that. “Right now, however, we are pulling material that has been stored from the shutdown of the anaerobic digesters,” he said. So we are doing between three and six trailers a day, depending on hauling and plant variables.”
According to Shelnutt, the relationship between the Water Conserv II WRF team and Schwing Bioset has been a good one, based equally on the product’s proven performance and the company’s quick, consistent response to their needs.
“It seems like such basic business sense, but while far too many companies don’t seem to get it, Schwing Bioset does,” he said. “By way of an example: we had a problem with an acid hopper, determined that we caused the problem, and went back to the manufacturer to order a new one. They wanted more details and were dragging their feet on the replacement. SBI found out about it and interacted with that manufacturer directly to make things right. We felt that was over and above what is expected of an equipment supplier — but it’s solidified our relationship.”
Obviously, given the savings cited and the market for the product, Water Conserv II WRF’s decision to go with the Bioset process was largely based on economic concerns. However, according to David Bass, they were also committed to the idea of having a usable, in-demand product leaving their facility.
“It seems like so many biosolids management facilities are coming and going; people are losing their permits, others are opting to leave the industry, and so on,” he said. “And to a certain extent, I can see that. If we were still generating a Class B product, the increasingly stricter regulations that the FDEP and EPA are now promulgating require a much larger application setback than previous regulations. We wanted to eliminate issues like that, create a viable product, and feel good about our operation. The Bioset Process was definitely the right solution for us at this facility.”