DESIGN, CONSTRUCTION, INSTALLATION, AND OPERATION OF A COMPACT BIO-OXIDATION SYSTEM TO MANAGE ODORS AT THE CITY OF WILSONVILLE WWTP

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1 DESIGN, CONSTRUCTION, INSTALLATION, AND OPERATION OF A COMPACT BIO-OXIDATION SYSTEM TO MANAGE ODORS AT THE CITY OF WILSONVILLE WWTP Jim Boswell*, Paul John*, Karl Mundorff*, and Baron Adams* Bob Deithorn**, Leo Zappa**, Mike Stone*** *Bio Reaction Industries 9675 S.W. Tualatin-Sherwood Rd. Tualatin, OR **Calgon Carbon Corporation ***City of Wilsonville ABSTRACT The 5 mgd Wilsonville WWTP was experiencing odor complaints from the adjacent residential neighborhood. An existing in-ground, bark and wood-chip biofilter was not performing well. In December 2004, the City of Wilsonville contacted BioReaction Industries (BRI) requesting the design of a bio-oxidation system with guaranteed performance criteria. The project required an understanding of the nature of the odor problem and quick implementation of a solution to reduce odors under the agreed-upon performance criteria. The design necessitated a small footprint due to site limitations, and rapid construction and installation to address the recurring odor problems. An induced draft, multi-stage system consisting of a 12 d x 24 h biotrickling filter followed by a 12 d x 24 h biomatrix tower was the solution, providing greater than 99% reduction of H 2 S and reduce organo-sulfur compounds to below the odor threshold in the 8,000 cfm process airstream. Construction and installation was rapid and the bio-oxidation system has been in continuous operation since start-up in early June 2005 with no malfunctions and no increases in back pressure or other operational issues. Data collected on system performance demonstrated that the engineered biofilter is achieving all performance criteria. KEYWORDS Odor control, biofilter, H 2 S, WWTP, organo-sulfur compounds. INTRODUCTION In December 2004, the City of Wilsonville contacted BioReaction Industries (BRI) and asked if they could design a bio-oxidation system that would treat the odors emanating from the WWTP (located in the Willamette River flood plain and adjacent to a residential area); and provide the City this equipment under a guaranteed performance criteria. Wilsonville had some experience with BRI s odor control equipment in a pilot demonstration several years earlier that was very successful in eliminating the odors from a grit box. The Wilsonville WWTP had fully-enclosed and ducted odor containment and collection system in place, but the two year old existing inground biofilter odor abatement system was not able to accomplish the task of 99% odor 4499

2 removal. The problems were excessive back pressure, channeling and added maintenance (bed tilling and replacement) in the existing forced-draft system. BRI was successful in providing Wilsonville the odor control system they needed without extensive maintenance and without replacing the bed annually, if not more often, and at a cost-effective price. GOALS AND OBJECTIVES The primary goal of this project was to understand the nature of the odor problem and quickly implement a solution to reduce odors under agreed-upon performance criteria. Two additional requirements were: 1 -design of a system with a small footprint due to site limitations, and 2 - rapid construction and installation to address potential odor problems during the upcoming summer season. IDENTIFYING THE PROBLEM During the summer months, with warmer temperatures and winds from the south, the 5 mgd Wilsonville WWTP experienced odor complaints from the residential neighborhood located approximately feet above its north property boundary. A forced draft in-ground biofilter system was installed in 2003 and was very successful initially. However, after approximately 12 months severe backpressure problems developed (compaction), and repeated attempts to till the bio-bed only resulted in short-term fixes with secondary short-circuiting and finally, compaction again, which severely limited the airflow. After several months of working on the problem the existing bed was removed and a new bed installed with a different mix of materials, designed to provide longer bed life without compaction. This new bed lasted a relatively short time, developing the same problems encountered in that first bed. At this point, the City determined that an alternative odor control system was necessary. At that time BRI was contacted for evaluation of the system and potential design of a complete odor control system. A characterization of the emissions air stream was initiated so that the bio-oxidation unit could be appropriately designed for the type and concentration of odor emissions, as well as the air flow (volume) that it would receive. This project was required to be a turn-key installation, from design and construction to installation - including connecting to the existing duct work - followed by commissioning. Tedlar bag samples were collected and analyzed for H 2 S and reduced sulfur compounds. These data were compared with data that had been previously collected and analyzed. It was determined that the primary odor causing compounds were H 2 S (up to 10 ppm) and several additional organic sulfur compounds at less than 500 ppb. Ammonia was present in the emissions stream at relatively high levels (up to 180ppm) which could have an effect on the optimal operation of the system and had to be addressed in the design and operation of the system so that it could be removed from the airstream. SOLUTION AND RESULTS After reviewing the data with the City Engineer, a design was requested to achieve a greater than 99% reduction in H 2 S, and reduce other organic sulfur compounds (methylmercaptans, dimethyl sulfide, and dimethyl disulfide) to below the odor threshold in a WWTP process airstream of up to 8,000 cfm. BioReaction designed an induced draft, multi-stage system consisting of a 12 d x 4500

3 24 h biotrickling filter (BTF) followed by a 12 d x 24 h biomatrix tower (Figure 1). The biotrickling filter is designed to increase residence time, humidify the airstream, and provide additional area for microbial digestion. It consists of two separate chambers; each with plastic, cross-flow media, continuously sprayed from above with 100 gpm of recirculated water creating a cascading labyrinth for the emissions air stream to pass through. The BTF has a 1,280 gallon sump with those waters loaded with microbes (in excess of 8 million cfu s/ml), not unlike an extended aeration treatment system. The cross-flow media develops a biofilm on all of the surfaces, providing a very large surface area for air-water interface. Both of these areas of microbial activity provide initial biodegradation of hydrophilic compounds (hydrogen sulfide and ammonia) and the initial contact with, and some biodegradation of the hydrophobic compounds (organo-sulfur compounds), while the overall goal of 100% water saturation of the air stream is achieved for its movement into the biomatrix chamber. Saturation of the airstream is very important for overall moisture maintenance in the biomatrix chamber, and a periodic bed watering regime is maintained. Figure 1 Wilsonville Oregon WWTP Bio-oxidation Unit The biomatrix tower is composed of two beds of BioAIRSphere biomatrix for completion of the bio-oxidation process. This compost media is approximately 1 inch in diameter and comprised of a plastic sphere packed with specifically ground and composted mulch. The biomatrix media is guaranteed for four years to be free of compaction, channeling, and degradation (Figure 2). Media installation was easily accomplished by simply lifting super sacks into the cavity, opening them and depositing the BioAIRSpheres in the cells. The balled media 4501

4 is strong and can be blown into existing, man-way-only, accessible units for easy retrofits/fills, providing even distribution with rapid placement. Figure 2 BioAIRSphere Media With approval of the final design, manufacturing and installation of the FRP vessels with appropriate flanges and interconnecting FRP ductwork was completed on schedule by June 1, The City also purchased a full service maintenance contract from BRI that includes routine maintenance and system optimization, as well as scheduled sampling (including weekly GasTec tube tests and GCMS analysis of Tedlar bag samples collected every six weeks) and performance evaluations. Initial data collected after 48 hours of operation revealed 97+% reduction in H 2 S concentrations and essentially no odor from the stack. As the system developed more extensive microbial biomass over the next several days of operation, removal efficiency increased to the desired 99+% removal efficiency. Subsequent air samples collected from the inlet to and the exhaust stack of the bio-oxidation unit during the initial 12 months of operation have revealed excellent removal of the odor compounds as indicated by the data presented in Figure 3. During March of 06 there was a marked increase in organo- and reduced sulfur compounds in the air emissions to the bio-oxidation system (Table 1). 4502

5 Figure 3 Bio-oxidation Treatment of Sulfur Compounds at Wilsonville WWTP PPM /15/2005 6/22/2005 6/29/2005 7/6/2005 7/13/2005 7/20/2005 7/27/2005 8/3/2005 8/10/2005 8/17/2005 8/24/2005 8/31/2005 9/7/2005 9/14/2005 9/21/2005 9/28/ /5/ /12/ /19/ /26/ /2/2005 Inlet H2S Reduced Sulfur Compounds Inlet Outlet H2S Reduced Sulfur Compounds Outlet Date 4503

6 Table 1 Organo-sulfur Compounds in the Bio-oxidation System Inlet and Outlet Airstreams Date Compound 11/05 12/05 03/06 05/06 In Out In Out In Out In Out Hydrogen Sulfide Carbonyl Sulfide Methyl Mercaptan Dimethyl Sulfide Dimethyl Disulfide 1.3 N.D. 1.8 N.D. 4.0 N.D. 22 N.D N.D. N.D. N.D. N.D n. s N.D n. s N.D N.D n. s N.D. N. D. = Non-detect n. s. = No Sample Because of the elevated concentrations of these compounds, for which the bio-oxidation system was not designed, odors were emanating from the exhaust stack and several complaints were registered by the residential neighbors. To provide effective control of these compounds at the levels encountered would have required a bio-oxidation system almost 3 times as large (and costly). Very low concentrations of these compounds had been encountered in the pre-design emissions evaluation (that was used for the design) and were observed for the first 7 to 8 months of operation. Careful evaluation of the circumstances at the WWTP under which these concentrations occurred revealed problems with the blower systems on the digesters. Overnight power outages, although very brief had apparently shut the blowers down and the automatic restart system had failed for several hours. During these periods of anaerobiosis the organo- and reduced sulfur compounds were formed and the concentrations at which they were emitted were too great for the bio-oxidation system to handle. Subsequent maintenance on the electronics of the re-start system and some changes in the wastewater process implemented by the municipality has eliminated the problem and no more high concentrations of these compounds have been observed (Figure 4). 4504

7 Figure 4 Bio-oxidation of Sulfur Compounds and Ammonia at Wilsonville WWTP, Concentration () H2S Inlet H2S Outlet NH3 Inlet NH3 Outlet /5/2006 1/12/2006 1/19/2006 1/26/2006 2/2/2006 2/9/2006 2/16/2006 2/23/2006 3/2/2006 3/9/2006 3/16/2006 3/23/2006 3/30/2006 4/6/2006 4/13/2006 4/20/2006 4/27/2006 5/4/2006 5/11/2006 5/18/2006 The rather high levels of ammonia in the inlet gas stream beginning in April, and continuing, are not a problem for the bio-oxidation system as virtually all is removed and used by the microbial biomass in the BTF and the biomatrix chambers. Based on the data from 2005 these high ammonia levels are found throughout the year, and are part of the normal WWTP operational conditions. Periodic blower malfunctions in February, March and into April created conditions conducive to formation of additional H 2 S and organo-sulfur compounds, with very low ammonia evolution into the bio-oxidation system. CONCLUSION The bio-oxidation system has been in continuous operation since start-up in early June 2005 with no malfunctions and no increases in back pressure or other operational issues. Data collected on system performance shows that the system is achieving all performance criteria required by the City. The elevated concentrations of organo-and reduced sulfur compounds could not be effectively treated because of the size and retention time of the unit as it was based on the design criteria that were used for sizing, and that data had no elevated levels of these constituents. The WWTP operational situations that created these elevated concentrations were determined, evaluated and appropriate corrective maintenance was taken to assure that the conditions would not recur. Date 4505

8 ADDED BENEFITS Along with achieving the goal of odor reduction and the minimization of complaints, the City of Wilsonville and WWTP operators are pleased with additional benefits afforded by the Bio Reaction bio-oxidation system. This new bio-oxidation system solution occupies only onefifth of the space required by the original in-ground biofilter system, which allows for the anticipated WWTP expansion in the near future. The system operating conditions of airflow, temperature, and humidity are easily controlled. Because the media is guaranteed for four years and has a large compost component that provides macro- and micronutrients, there should be no need for nutrient additions. The ammonia that enters the system is absorbed in the sump water and is utilized by the microbes with no ammonia emissions from the exhaust stack. Finally, system installation was neat, clean and quick, with the unit operating quietly with little or no hands-on maintenance or control. 4506