A Novel Alkaline Biosolids Product as Alternative Landfill Cover
By:David Leffler, City of Toledo, Solid Waste Division, Toledo, OH
Cindy Drill, N-Viro International Corporation, Toledo, OH
James D. O'Neil, N-Viro International Corporation, Toledo, OH
Ervin L. Faulmann, Ph.D., BioCheck Laboratories, Toledo, OH
The City of Toledo has been using an alkaline stabilization process to treat their municipal biosolids for over 10 years. The resultant product (N-Viro Soil) is sold as an agricultural soil amendment and topsoil component. In 1998, a demonstration project utilizing N-Viro Soil (NVS) as alternative daily landfill cover material (ADC) was carried out. The physical characteristics of the product were acceptable as a daily landfill cover, but ammonia emissions were a problem for the operators. Limiting ammonia emissions would make the product more acceptable from an odor-generating standpoint when used as an ADC and have additional advantages by retaining the nutrient benefits of the ammonia in the product when used as a traditional soil amendment.
Previous research done for N-Viro International has shown that chipped pine boughs are effective in reducing the ammonia emissions from the alkaline stabilized biosolids products in a number of formats. In view of this, a demonstration project to test the ability of chipped Christmas trees to limit ammonia emissions from the alkaline-treated biosolids and utilize this pine-alkaline product as an alternative landfill cover was initiated. This processing yielded a daily landfill cover product that was very workable from a physical viewpoint without the previous problem of ammonia emissions. The demonstration project was divided into two stages, the first in February of 1999 and the second in April 1999. In both demonstrations, the operators noted no objectionable ammonia odor, and the workability of the product was acceptable. The City of Toledo and N-Viro International were both satisfied with the results of the demonstration and will continue to use the "pine-alkaline" material in the future.
HISTORY
Since December of 1989, the City of Toledo has been using an alkaline stabilization process known as Advanced Alkaline Sludge Stabilization with Accelerated Drying, or N-Viro process, to stabilize their biosolids. The resultant N-Viro Soil product is distributed as an agricultural soil amendment, topsoil component, and for landscaping needs.
All USEPA approved alkaline stabilization processes raise the pH of biosolids to greater than 12 for varying periods of time. Such conditions favor the release of ammonia during processing, storage, handling, and final use of the product. This is especially true for alkaline treated, anaerobically digested biosolids, the wastewater digestion method used by the City of Toledo. If these emissions could somehow be limited, the final product would be more acceptable from an odor standpoint and, the nutrient content of the product would be increased.
The Toledo product is registered as a fertilizer with the Ohio Department of Agriculture. Therefore, it would be beneficial to be able to increase the nitrogen content of the end product. The City of Toledo's Hoffman Road landfill tried the traditional alkaline stabilized product as alternative daily cover in a 1997 demonstration. According to the 3/31/97 report1 to the Northwest District Office of the Ohio EPA, Division of Solid and Hazardous Waste Management, the product was effective in providing litter control on the working face and had handling characteristics similar to their existing cover material.
One problem noted was that ammonia emissions from the stockpile and during handling were problematic for on-site operators. They were not problematic off-site. Because of this and other non-related issues, it was decided not to go forward with the request for use as ADC until the ammonia problem could be solved.
PROBLEM
It is generally known that pine oil is useful in masking or eliminating ammonia odors from animal litter. The use of pine oil on its own to control ammonia emissions in a large-scale biosolids processing facility is impractical and cost prohibitive. An economical method that could mimic the pine oil effect for limiting gaseous ammonia from alkaline-stabilized biosolids, would be very useful.
Other waste disposal problems encountered by municipalities and private industry include dealing with greenwaste such as grass clippings, leaves and discarded Christmas trees. Another large body of greenwaste is generated by the lumber and paper industries, particularly with respect to needles of coniferous (evergreen) trees. Often, this type of "waste" is dumped in compost heaps or placed in a landfill. In particular, the City of Toledo normally collects approximately 30,000 Christmas trees each season. The vast majority of these trees had been placed in the municipal landfill. The ability to recycle this "waste" material to enhance other processes or products would be beneficial.
METHODOLOGY AND DISCUSSION
While looking for a way to decease the pH of fresh N-Viro Soil it was discovered that the addition of pine needles to the alkaline stabilized biosolids product, while not significantly affecting pH, did decrease ammonia emissions. With that in mind, it was determined that using the City's Christmas trees could help manage ammonia emissions in the biosolids product and at the same time provide a beneficial use for the City's annual Christmas tree disposal problem. A small-scale bench test was conducted to determine the best method for controlling ammonia emissions from the alkaline-treated biosolids product. Two scenarios were tried: blending chipped spruce with the product, and arranging chipped pine as a filter positioned above the product. Each of these methods prevented a large amount of ammonia that would otherwise have been released from the alkaline-treated biosolids product to the atmosphere.
Table 1 lists the two methods of ammonia control used in the bench test conducted by BioCheck Labs for NVIC and compares emissions over time of the treated and untreated N-Viro soil product from the Toledo Bayview facility. Chipped spruce boughs mixed with two month old product achieved about a 55% reduction in ammonia emissions relative to the control sample. When a larger amount of chipped spruce was used an even greater reduction (98% at 21 hrs) was achieved. This reduction in detectable ammonia did not appear to have been due to any change in the pH level of the biosolids material since the addition of the chipped spruce did not substantially effect the pH of the samples. When the chipped spruce was utilized as a filter, a 69% reduction was seen after just one hour (see Table 2). Other evergreen species such as pine and balsam were also tried and yielded similar results2
Effects of Ground Spruce and Pine Boughs on NVS Ammonica Emissions
Effects of Ground Spruce Overlay on NVS Ammonia Emissions
Many advantages can be realized if treatment of the ammonia emissions can occur utilizing this simple and cost effective recycling method for evergreen trees. These advantages include: low processing cost and time, elimination of large-scale capital expense for air-scrubbing equipment, retention of valuable nitrogen in the final alkaline stabilized biosolids product, and removal of ammonia from the air without the use of dangerous hazardous chemicals. Another important advantage includes the beneficial reuse of a greenwaste that would normally take up precious landfill space.
From these results, it was decided that a full-scale test was in order and that the "mixing" method would be used. The final mixed product would then be taken to the Hoffman Road Landfill and demonstrated as an ADC material.
FULL-SCALE DEMONSTRATION
In December of 1998, the city of Toledo made a formal request (pursuant to OAC 3745-27-19(F)) to the NWOEPA, Division of Solid and Infectious Waste, to conduct two, five-day demonstrations. Due to a limit on the number of trees available, and the on-site space available for chipping, it was decided to test the suitability of NVS with 10% pine mulch for use as an alternative daily cover at the city's Hoffman Road landfill. That request was granted in January of 19993 and the first stage was begun in February.
Christmas trees that had been collected after the holidays by city crews were delivered to the biosolids stabilization facility at the Bayview WWTP. The trees were then chipped at the biosolids stabilization facility. Each tree had to be handled individually due to the trash and metal hangers that came in with some of the trees. Chip sizes ranged from ¼ in. to 2 in. yielding a course mixture of tree bark, stems and needles. After chipping, a windrow of two-month-old N-Viro Soil (same age as used in the bench test) was laid down. The chipped trees were then placed over the windrow with a bucket loader product at a rate of 10% (10 yards of chipped pine to 100 yards of NVS), forming a blanket over the pile. The chipped pine was then blended into the stabilized biosolids using a Scarab windrow turner.
The first shipment of NVS was delivered to the landfill on Feb. 9, 1999. Each truck was weighed at the scale house prior to entering the landfill and unloaded near the working face. About 100 tons of material was delivered each day (200 tons total) for the daily cover operation utilizing their normal equipment. The NVS/pine mix was applied in layers, with a minimum of 6 in. of thickness. The NVS/pine mix was allowed to remain in place for seven days to test its durability as an alternative daily cover. On the seventh day this area was stripped, and the working face continued to be developed.
The NVS/pine mix that was stripped from this area was then reapplied, followed by 6 in. of conventional soil cover.4 The operators reported that the mix spread evenly, was easy to work with, and displayed similar working characteristics as traditional cover during both days of the demonstration. The most important item noted by the operators was the lack of ammonia odor in this product as compared to the material used in a demonstration the previous year. The pine chips not only reduced the ammonia odor but also made the material easier to spread due to its more "mulch-like" nature. This demonstrated that even coarsely chipped Christmas trees could provide a material that was less objectionable with regard to ammonia emissions and positively effect product "workability."
The second half of the demonstration took place in April 1999. Due to constraints on the use of the chipper, all the Christmas trees were chipped in February. Therefore, a pile was reserved for mixing with the alkaline stabilized biosolids product for the April demo. On March 19, ammonia emissions were measured before the mulch was added and again after the chipped pine was laid over the NVS windrow. The pine mulch was then mixed into the pile and emissions were once again measured.
The final mix was then shipped to the landfill on April 21 and utilized in the same manner over a two-day period as in February. The operators reported the workability of the product as well as ammonia odor to be the same in April as it was in February. The Ohio EPA was also concerned about potential leachate problems the product might cause. The landfill was able to report that no leachate or leachate-related problems were experienced at any time during or after application of the NVS/pine mix was applied to the working face in either February or April.
DISCUSSION/CONCLUSIONS
Christmas trees disposed of after the holidays are an annual problem for the Hoffman Road landfill and take up precious space that could be used for materials that are not recycled. Two-month-old Toledo NVS made from anaerobically digested sludge cake still has a high ammonia content. Previously, it had to be aged and aerated for about three to six months before a decrease in ammonia emissions was observed. Bench scale tests conducted for NVIC by BioCheck Labs indicated that the "mixing" method (directly mixing greenwaste or pine mulch into the NVS), was effective in reducing (not masking) ammonia emissions emitted by the anaerobically digested, alkaline-stabilized biosolids in a much shorter time. Therefore, it was decided that the material designated for use at the landfill for the ADC demonstration would be the "mixed" material made with chipped Christmas trees.
Data from the mixed product indicated that ammonia emissions decreased by 78% at three days and 96% at 30 days once the pine mulch was mixed into the NVS product. Also, landfill operators reported a marked reduction in ammonia odor in both phases of the demonstration project when compared with a similar demonstration done with traditional NVS in 1997. The operators liked the physical characteristics of the NVS/pine mix and noted that the added pine mulch made the product easier to spread. The time of year that the Hoffman Rd. landfill would prefer to utilize NVS/pine blend (January through April) is a slow distribution time for the Toledo N-Viro facility. The ability to ship product during this time would greatly improve product management and decrease storage of the biosolids product at the facility. Because of this, both the City of Toledo Solid Waste Division and N-Viro International recommended to the OEPA that they grant final approval for the use of this NVS mix as an alternative daily cover.5
FINAL NOTES
Approval of the NVS/pine mix for use as ADC at the City of Toledo's Hoffman Road landfill was granted in October 1999 by the NWOEPA, Division of Solid and Infectious Waste. The product was approved for use from January through April. Full-scale use of the approved product at the landfill will begin in January of 2000. A public relations campaign will be launched to inform the public about this recycling opportunity and encourage citizens to recycle their Christmas trees after the holidays. The City looks forward to saving space in the landfill by reusing the trees in the alternative daily cover mix and to using a product without adverse characteristics such as nuisance ammonia emissions. NVIC will enjoy the benefit of reducing storage needs in the winter by being able to ship this product to the landfill on a regular basis.
The above text was provided by N-Viro International Corporation and was edited by Kate Goff.
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