RESULTS OF TRIALS OF CHEMICALS, ENZYMES AND BIOLOGICAL AGENTS FOR REDUCING ODORANT INTENSITY OF BIOSOLIDS

William E. Toffey, Philadelphia Water Department Matthew Higgins, Bucknell University

1101 Market Street, Suite 5 Philadelphia, PA 19107

ABSTRACT One goal of Philadelphia’s biosolids program is to produce neither nuisance odors at its processing plant nor in the communities to which biosolids is delivered, through improving its biosolids product quality. In this commitment, Philadelphia joins many other utilities. While a major thrust of the biosolids profession is on equipment innovation and process modification, one fruitful avenue for investigation, due to relatively low capital requirements and quick implementation timeframe, is use of enzymes, chemicals and microbial blends as additives within the biosolids “value chain.” Toward that end, the Philadelphia Water Department’s biosolids and wastewater operators conducted trials of such amendments at its wastewater and biosolids facilities. Three products were added directly to conventional anaerobic digesters; three products were dosed into the liquid sludge just prior to centrifuge dewatering; two products were applied to biosolids cake prior to subsequent land application; one ash products was mixed into cake at the application site just prior to land spreading; and, a second ash was shown in bench top experiment to also be effective. Product performance was measured objectively by tracking the concentration of odorant emissions (i.e., methyl mercaptan and dimethyl sulfide) from field-gathered samples over time. Several effective products include: coal cogeneration ash used at the application site; a humate product spread on the cake before placement in storage; and, application of a nutrient supplement to the digester and holding tank in advance of dewatering. Recent reports, not yet verified by field application, have suggested that alum, used as a partial replacement for polymer into the centrifuge during dewatering, produces a low-odor cake. Reductions of odorant concentrations of 50 percent to more than 90 percent were observed during these trials for several products, but others showed no improvement in odor characteristics in the biosolids. This research highlights the value of objectively evaluating odor control products as part of a comprehensive effort to eliminate odor nuisances in the biosolids value chain. The research also underscores the limited understanding of the physical, biological and chemical processes at work with CEBA products. The research also suggests that application of biotechnology to wastewater treatment might open up new opportunities for achieving new treatment objectives, such as reduction of organic pollutants and optimized energy capture.

KEYWORDS Biosolids, anaerobic digestion, odorants, enzymes, additives, microbial blends, nutrients

INTRODUCTION The Philadelphia Water Department (PWD) is commitment to reducing risks of odor nuisances from its biosolids processing and utilization programs. One expression of this commitment is in its participation in a series of odor studies sponsored by the Water Environment Research Foundation (WERF). Phase I and Phase II of the project Identifying and Controlling Odor in the Municipal Wastewater Environment led first to the acknowledgement that a basic understanding of the connection between plant process and biosolids odors had not developed and second to a study of plant parameters related to odor characteristics of biosolids. PWD’s Southwest Water Pollution Control Plant and its adjoining Biosolids Recycling Center were one of eleven facilities studied in depth. To this effort was added corollary projects sponsored by PWD and other individual wastewater agencies, notably D.C. Water and Sewer Authority, and research projects funded by the Mid Atlantic Biosolids Association, of which PWD is a contributing agency. The recent research focus has developed several fundamental new understandings of odor emissions from anaerobically digested, dewatered biosolids. The principal odorant is volatile organic reduced sulfide compounds, notably the two odorants methyl mercaptan and dimethyl sulfide, that are formed from the decomposition of soluble methionine released during centrifugation (Adams, 2003). Centrifuges, particularly the new generation of high solids machine, tend to cause the shearing of microbial cells that constitute a predominant fraction of organic material (Higgins, 2002). Centrifuges also damage naturally occurring populations of methanogenic organisms that would otherwise breakdown odorants into odorless methane (Higgins, 2005a). Some operational aspects previously thought to influence odorant intensities were not clearly connected by this research. For instance, relationship between sludge retention time in digesters and the extent of volatile solids destruction were not shown, in the relatively narrow range of the study, related to potential odorant intensities (Adams, 2003). Research sponsored by WERF is underway, but not yet complete, to explore the benefit in lower odor potential of a number of other processing changes controls. These include: pre-processing of waste activated sludge (e.g., ultrasound; high temperature and pressures; high energy homogenization) in advance of digestion; increased sludge retention (say, beyond 25 days); reduced speed or torque differential in high-solids centrifuges; and adding metallic ions. Some of this work is associated with the “Phase III” of the WERF odor project (Novak, 2005). The WERF project has been modified to include nonstructural approaches (WERF, 2005a). Vendors of Chemical, Enzymatic or Biological Agents (CEBA) have been invited to submit their products as part of Water Environment Research Federation (WERF) Project 03-CTS-9T, Biosolids Processing Modifications for Cake Odor Reduction (WERF, 2005b). A protocol has been developed to compare these products in the treatment plant. This involves either adding the product to the digester or applying the product as part of the dewatering process. The study reported here is preliminary to this national study, and several of the products used here will be examined again under

the WERF protocol. The method of odor characterization, however, is essentially identical. The animal production industry has pursued research with similar CEBA additives. Studies have been undertaken to control odors in poultry houses, in swine pits, and cow barns using microbial blends (Lavoie (undated); Lorimore 1998). Other studies have documented that correcting micronutrient deficiencies can improve digestion (Murray, 1981; Kong, 1994; Ivanov, 2002; Jarrell, 1987; Gonzalez-Gil, 1999, Paulo, 2003). The overall results have not been encouraging (Powers, 1999). When objective measurements are applied to the effectiveness of CEBA, the measured reductions in odorant and gas emissions are smaller than vendor claims, and costs of products may not justify the modest odor reductions (National Pork Board; Heber, 2002; Ni 2005; Zhu, 2003). Researchers discuss the lack of information on the mechanisms of actions by which the CEBA products claim effectiveness (Johnston, 2002). Even when use of CEBA products shows a moderate effect on reducing such emissions as ammonia and hydrogen sulfide, researchers and vendors typically have not directed further experimentation toward improved effectiveness (McCrory, 2002). The study reported here differs from the variety of trials with additives to manure in several respects. First, it examines a different class of odorants; most manure studies look at ammonia and hydrogen sulfide, while this study examines volatile organic sulfide compounds (Karakashev, 2005). Second, this study is limited to a specific type of odorous organic material – an anaerobically digested, centrifuge dewatered biosolids – in which organic wastes are not highly putrescible and in which volatile fatty acids are not dominant. Third, the CEBA products treating animal wastes usually reside in lagoons or pits in which a complex variety of conditions – aerobic, anoxic and anaerobic – may exist in a single facility and vary over time and space (Schur, 2005; Schneegurt, 2005). By contrast, anaerobic digestion at municipal wastewater plants has steady, well-monitored operating conditions. This paper reports on a number of proprietary CEBA products that were subject to trial use by PWD for the purpose of enhancing anaerobic digestion and reducing the odor intensity of digested cake. In these trials, the companies supplied the product at no charge to the city, and helped design and install a delivery system. Background information on the functionality of the products was solicited from the vendors. Product literature was typically not specific about mechanisms of action. Chemicals were claimed to supplied missing nutrients or compounds; other products were said to reduce toxic conditions, and encouraged improved performance of natural processes. Enzymes and catalysts speeded up natural processes. Biological agents introduced organisms that overcame competition with background organisms. With this study, Philadelphia attempted to demonstrate performance claims by objectively monitoring operations and sponsoring testing with protocols that related to odor mitigation performance. The mechanisms of action were, however, not studied. This study used an objective, quantifiable and reproducible method of comparing products and displaying results. To accomplish this, Philadelphia contracted with Dr.

Matthew Higgins at Bucknell University to use the protocol developed for the WERF Phase 3 Biosolids Odor Study. Higgins employed a method developed by Dietmar Glindemann that characterizes odorant concentrations in the head-space above biosolids samples held in glass jars for up to 40 days (Murthy 2002a and 2002b; Higgins, 2002). The profile of sulfurous gas emissions in the headspace has been shown to correlate well with the biosolids’ potential to yield offensive odors. The effectiveness of biosolids additives and process can be compared against both untreated biosolids and between different products. The validity of the approach used by Higgins for characterizing biosolids cake odors has been presented in other publications. First, a clear relationship has been established between headspace concentrations of reduced organic sulfide and human estimations of odor intensity reported in olfactometry studies, and thereby predicts odor nuisance potential (Higgins, 2003). Second, the headspace concentrations of biosolids samples held during the sampling period in glass jars correlate strongly to concentrations of biosolids cake samples grabbed from field storage piles in a sequence of days subsequent to centrifugation (Higgins, 2005c). Third, the process objectively quantifies the effects of CEBA treatments against control samples, and readily accommodates a dose response tests for optimizing CEBA use (Higgins, 2003 and 2005b).

RESULTS

CEBA Selection

Twelve CEBA products were used in this trial work, either in bench top or field scale testing. . These products are shown in Table 1. Three companies contacted by PWD with CEBA products offered commercially for odor control in animal manure or composting operations elected not to be part of this study. Most of these products have some basis for their claim for effectiveness at odor control in wastewater processes, but most of the information supplied by vendors is anecdotal in nature (Battersby, 1998; Neozymes, 2005; Prinčič, 1998; Schink, 1997; Schur, 2005). Table 1: Additives Participating in PWD Odor Mitigation Experiments Company or Product Name Product Type Experiment Type Eco-Cure Enzyme Bench top & Field Trial EnviroVizion/Virotec Chemical Bench top Organica Biotech Microbial Blend Bench top & Field Trial Enzymatic Odor Solutions Enzyme Bench top NRP/ HydroPress - BioKat Nutrient 2 Field Trials Waste Management and Processors, Inc. Chemical - ash Bench top & Field Trial ArchaeaSolutions Microbial Blend Field Trial Bio-Organic Catalyst Chemical Field Trial Nanoscale Zero Valent Iron/ Lehigh U. Chemical Bench top

HMA/ Guardian CSC Chemical Field Trial EcoTechnology Chemical - ash Bench top Eaglebrook Chemical Field Trial

Characterization of Odorant Emissions

Samples of biosolids treated with CEBA products either at the point just prior to or just following centrifugation are evaluated for odorant production using the Glindemann method. This method yields large matrices of gas concentration measurements. The two critical points of comparison between treated and control samples are: the peak concentration of total volatile organic sulfide compounds (primarily the simple summation of concentrations of methyl mercaptan and dimethyl sulfide), and the graph of total volatile organic sulfide concentrations plotted over time, from which an estimate of mass odorant production may be estimated on a comparative scale. Figure 1 (from Higgins, 2005c) is representative of the odor profile of PWD biosolids cake. Many dozen similar graphs have been produced from PWD biosolids, probably the most highly studied biosolids for odorant emissions

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Points of Dosage

PWD applied the products at different points in the biosolids treatment and use “value chain.” PWD was guided by instructions of the vendors, and usually under their supervision. One point of use has been a direct feed to digesters. Other points include: to

a mixing chamber of digester effluent; to the sludge feed line to the centrifuges; to the cake discharge belt after centrifugation; and, to the cake just prior to land spreading. The CEBA products are shown in Table 2 with their dosage points. Table 2: Dosage Points for Products Used in Field Trials Company or Product Name Dosage Points for Field Trials Eco-Cure Cake Spray Organica Biotech Digester Additive Enzymatic Odor Solutions Cake Spray Natural Resource Protection/ HydroPress Digester & Holding Tank Additive Waste Management and Processors, Inc. Cake Incorporation ArchaeaSolutions Digester Additive Bio-Organic Catalyst Centrifuge Additive Nanoscale Zero Valent Iron Centrifuge Additive Material Matters, Inc. Cake Additive HMA/ Guardian CSC Cake Spray EcoTechnology Cake Additive Eaglebrook Centrifuge Additive

Digester Additives

Three products were introduced to three different conventional mesophilic digesters at PWD’s Southwest plant. Each digester is approximately 2 million gallons in capacity and is maintained at 95 degrees F, and has a sludge retention time calculated at approximately 19 days. The point of introduction of the additives was to the recirculation line, the pump for which recirculates the entire content of the digester once daily. Each firm was responsible for installing a tank and feed delivery system for their product, and for establishing and maintaining dosage rates. Operators at the plant provided electrical and water utilities. Operators also sampled the digesters daily for the purpose of laboratory characterization of the operating performance of the digesters. Operators also inspected the apparatus daily to ensure proper operation, and would notify the vendor of any apparent failure, such as leaks or inoperable pumps. The vendors established the length of the trials. Table 3 gives the name of the company, the type of additive, and the length of the trial. Table 3: Additives to Digester Testing Improvement in Performance and Reduced Odors Company Name Nature of Product Dosage Rate Length of Trial NRP’s BioKat Nutrient Supplement 10 parts per

million daily 65 days

Organic BioTech Blend of anaerobic bacteria

Not known 45 days

Archaea Solutions Blend of Not known 90 days

methanogens of archaea domain

Holding Tank Additive

Researchers have hypothesized that short-term resting of digested biosolids in tanks prior to dewatering may mitigate potential odor releases. A corollary hypothesis is that aeration of liquid digested biosolids prior to dewatering may also reduce potential odorant releases. Therefore, by extension, the treatment of liquid biosolids in a holding tank may be reasonably tested with additives that support biological stabilization. NRP’s BioKat, a nutrient supplement, was added to a holding tank at PWD’s Southwest plant for a four week period in November 2004. During this period, a dose of 5 to 10 gallons per day was added by the company to a digester, the feed to which is approximately 100,000 gallons daily (2,200 pounds of volatile solids feed) of combined primary and waste activate sludges. Weekly samples of dewatered cake were taken at PWD’s BRC on Mondays, following a weekend of storage. The odorant emissions were measured using the Glindemann protocol on the treated samples, and compared to samples taken both prior to treatment and a week after treatment, to serve as a control.

Centrifuge Additives

A third point of dosage for CEBA products is the feed line to the centrifuges. This point of addition allows for thorough mixing and for reaction time prior to dewatering. Three products have been added at this dosage point. These are ferric chloride (provided by Eaglebrook), an organic catalyst (Bio-Organic Catalyst), and alum (planned for winter 2006). Both treated and control samples of cake may be taken because identical feed and polymer are added to comparable centrifuge machines at the same time. Cake samples are analyzed using the Glindemann protocol for characterizing odorant emissions from the samples over a period of several weeks.

Cake Spray

A fourth point of dosage is application of a liquid product to the biosolids cake after it is discharged to the belt and prior to temporary field storage or shipment to application sites. Two products have been trialed in this fashion, the EnvoGuard HMA (humate-derived material) and the Eco-Cure enzyme product. These products are drawn by pumps delivering to fine mist nozzles 5 to 30 gallons per hour to the belt on which biosolids is carried at a rate of 30 to 40 tons per hour. The spray set up was designed and operated by the vendor, at rates set up the vendor. Treated samples were taken by PWD personnel; control samples were taken at times when the CEBA product was not being sprayed. Whereas PWD engages in aerated static pile composting to achieve a Class A, homeowner-grade biosolids product, and whereas odors from composting are frequently carried off-site from the PWD facility, this point of dosage enabled treatment of the

biosolids-woodchip blend used for composting. Thereby, products were tested to demonstrate efficacy in controlling compost odor control. Samples of treated and control, both cake and compost mix, were tested for odorant potential, again using the Glindemann method.

Cake Incorporation

Ash has been shown by others to control odors from biosolids when blended in with cake. Two products were trialed by PWD. One ash, provided by the Gilberton Coal Company (an affiliate of PWD’s reclamation contractor, WMPI) is created by co-generation of waste coal culm in a facility fired at a temperature appropriate for creating a high carbon, low calcium carbonate equivalent ash. This ash was distinguished in a report prepared by Higgins on a bench top testing of alternative control products potentially suited for use in controlling odors at the mine reclamation site. The results are given in the table below for two alternative coal ashes. The performance of the ashes was compared to two other early candidates for odor mitigation, potassium permanganate and an enzyme control agent typically recommended for suppressing odors at landfill operations. On the strength of this study, the Gilberton coal ash was employed in full scale field operations. Table 4: Characterization of Ash and Chemicals on Cake with Glindemann Method and Olfactometry

Sample

Butanol Intensity Number

Butanol Equivalent

Concentration (ppm)

Hedonic Tone

Methyl Mercaptan

(ppmv)

Dimethyl Sulfide (ppmv)

Dimethyl Disulfide (ppmv)

Control Cake Sample 9.34 3164.5 -6.7 387 60.11 38.25 Schylkill Energy Recovery Ash 9.24 2952.6 -6.4 90.16 35.17 17.53 Potassium Permanganate 9.85 4506.4 -6.4 483 20.71 32.17 Enzymatic Odor Solutions 11.19 11408 -7.8 157 53.61 34.23 Gilberton Cogeneration Fly Ash 8.67 1988.9 -5.4 0 9.16 0

A second ash was subsequently trialed for odor control to cake. It is a byproduct of an experimental thermal processing technology operated at PWD’s BRC by EcoTechnology, of Sacramento, CA, also a neutral, high carbon content ash. The EcoTechnology ash was demonstrated at the BRC, by adding a pneumatic feed system to the existing paddle mixers used for compost blending. Samples of the cake and ash blend are analyzed using the Glindemann method of odorant emission characterization.

Table 5 : Use of EcoTechnology Ash to Control Odors in Cake After Dewatering Control Treated

No Ash Added

(1.0 gram Ash to 10 grams of Cake)

Days After Cake

Production

Methyl Mercaptan

(ppmv)

Dimethyl Sulfide (ppmv)

Dimethyl Disulfide (ppmv)

Methyl Mercaptan

(ppmv)

Dimethyl Sulfide (ppmv)

Dimethyl Disulfide (ppmv)

1 6.1 71.8 2.8 0.0 23.5 0.4 2 58.2 152.9 19.0 1.2 56.5 4.3 3 205.4 199.0 18.0 4.0 62.7 2.5 4 252.4 262.3 0.4 8.4 67.6 3.2 5 148.1 317.0 1.0 9.9 74.2 3.2 6 46.5 233.9 0.8 6.2 24.7 0.5 7 1.0 0.0 0.0 1.1 0.0 0.4 8 0.0 0.0 0.0 0.6 0.0 0.0

Methods for Assessing Performance of Additives in Digesters

Digester Performance Parameters

For products added to the digester, data was collected for parameters that are used for digester process monitoring. These are: alkalinity, volatile acids, pH, total solids, and volatile solids. During the trial period, the treated digester and a control digester were sampled daily, Monday through Friday, for these parameters. The sampling protocol was not changed from standard plant procedures during this period, to avoid sampling bias compared to historical records of digester performance. The hypothesis being tested by measuring these parameters is that the treated digesters would show lower volatile acids, indicating more complete conversion of fatty acids to methane, and would have lower volatile solids, indicating more complete conversion of organic matter to gases. The digesters did not have operable gas meters for direct measurement of gas production.

Microbiological Parameters

For samples of the liquid digester effluent were taken of treated and control, and PWD microbiology lab analyzed them for fecal coliform and E. coli using standard EPA methods. These were organisms selected to test the hypothesis that digester additives that promoted anaerobic cultures for digestion would be competitive with the organisms indicating fecal contamination, yielding lower concentrations in the effluent of treated digesters.

Inorganic Parameters

Three additional parameters were examined to characterize the digested biosolids with and without treatment. These are: total sulfides, ammonia and COD. These were selected based on a hypothesis that treatments to increase digestion would increase ammonia and sulfide concentrations and decrease COD in the liquid digestate

Dewaterability Parameters

The dewaterability of treated and control samples of digester effluent were compared by measuring the rate of free drainage in samples to which a fixed concentration of polymer was added. The hypothesis for testing this parameter is that increased digestion would reduce intracellular bio-polymers, thereby reducing dewaterability.

Odor Parameters

Samples of effluent of treated and control digesters were evaluated for potential odorant intensity using a protocol developed by Higgins as part of the WERF Phase III study to simulate in liquid biosolids samples the shear effects of high solids centrifuges that would occur during dewatering. This involves a laboratory based flocculation with polymer followed by application of shear force in a commercial food blender. The product of this sample preparation is then analyzed using the analysis of headspace concentrations of odorants over a period of two to six weeks.

Measurements of Additive Performance on Digesters and Dewatering

Results of Digester Performance

Standard parameters for digester performance did not seem to be influenced by use of the additives. No difference among treated and control digesters were discerned for any of the five parameters (total solids, pH, volatile acids, alkalinity, volatile solids) used for operational monitoring, nor the three additional parameters (chemical oxygen demand, total sulfides, and ammonia). Tables 6 and 7 compare control and treated samples for these conventional parameters for both products.

Table 6: Comparison of Digester Parameters of Organica BioTech Additives to Digesters

Parameter

Control Digester (Mean

and S.D.) Treatment with

Organica Biotech pH 1 units 7.44+/-0.05 7.34+/-0.05 Total Solids 1 in % 2.53 +/- 0.64 2.17+/-0.36 Volatile Solids 1 in % 51.3 +/-1.9 51.5+/-1.6 Alkalinity mg/Liter 3,050 2,934 Volatile Acids mg/Liter 147 115 Total Sulfides mg/Liter 173 216 Chemical Oxygen Demand mg/Liter 19,800 21,700 Ammonia mg/Liter 810 870 1. Average of 5 grabs for treated and control digester 2. Single analysis of a composite sample

Table 7: Comparison of Digester Parameters of BioKat Additives to Digesters

Parameter

Control Digester (Mean

and S.D.) Treatment with

NRP BioKat pH 1 units 7.38+/-0.04 7.28+/-0.08 Total Solids 1 in % 2.29 +/- 0.14 2.45+/-0.10 Volatile Solids 1 in % 54.2 +/-2.4 54.3+/-0.9 Alkalinity mg/Liter 3,080 3,030 Volatile Acids mg/Liter 131 211 Total Sulfides mg/Liter 182 194 Chemical Oxygen Demand mg/Liter 1750 18500 Ammonia mg/Liter 750 797 1. Average of 5 grabs for treated and control digester 2. Single analysis of a composite sample

The grab samples of digester effluent showed no clear difference in measurement of fecal coliform or E coli (see Table 8).

Table 8: Microbiological Effects of Digester Additives Fecal Coliform E.coli Digester No. Treatment

FC /100 mL (CFU/g)

E.coli/100 mL (CFU/g)

#7 Control 360,000 200,000 300,000 170,000

#9 Organica BioTech 430,000 220,000 360,000 180,000

#11 BioKat NRP 250,000 130,000 180,000 90,000 Membrane filter technique was used and calculated bacterial counts per 100 mL . Solids analysis on the liquid sample provided a calculation per gram of total solids (dry weight).

Dewatering Performance Results

The efficiency of dewatering was assessed by a consultant to PWD, Wayne Laraway, of PolyPro. In a comparison of digesters each with one additive, against a control digester, one additive exhibited properties of free drainage markedly better than the control digester and better than the second additive. Table 9 [to be supplied] gives these results. The liquid digested biosolids drawn from the digester to which BioKat nutrient supplement had been applied showed substantially faster free drainage than the digested biosolids drawn from the control digester and from the digester to which the bacterial blend had been added. This was an unexpected benefit of the use of this CEBA.

Measurements of Odorant Emissions from Products

Odorant Evaluation of Digester Additives

Three digester additives have been subject to trial use in digester at PWD’s Southwest Water Pollution Control Plant. As of December 2005, two have completed the trial use, and characterization of the comparative odorant intensity of treated and control biosolids were completed using the Glindemann protocol by Higgins at Bucknell University. One product, the microbial blend of anaerobic organisms provided by Organica Biotech, showed no effect on the profile of odorant emissions from cake produced by treated and control digesters. This data is shown in Table 10. Table 10: Total Volatile Organic Sulfide Compounds In Simulated Centrifugation of Control Digester and Digester Treated with Organic Biotech Microbial Blend

Storage Time (days)

Control Digester, TVOSC (ppmv)

Organica Biotech Treated Digesters, TVOSC (ppmv)

2 155 151 3 104 89 4 61 53 5 27 12

6 0 0 7 0 0

A second product, a nutrient blend provided by Natural Resource Products (NRP), a proprietary nutrient product called BioKat, showed both a substantially lower profile of odor emissions of biosolids from treated digesters, and a peak TVOSC of about one-half the control sample. Table 11: Comparison of BioKat Treated Digester to Control in Odor Through Measurement of Total Volatile Organic Sulfide Compounds

Storage Time (days)

Control Digester, TVOSC (ppmv)

BioKat Treated Digester, TVOSC (ppmv)

1 73 49 2 213 87 3 166 105 4 140 97 5 0 0

A third product, a blend of methanogens provided by ArchaeaSolutions, has not had it trial use at the SW plant completed at the time of this paper’s preparation.

Odorant Evaluation of Holding Tank Additives

One product was used as an additive to the holding tank for a period up to four days prior to centrifugation. The biosolids that had resided in the holding tank was subsequently centrifuged, and samples of the cake were analyzed for odorant emission using the Glindemann method. The profile of odorants was compared to biosolids that later was centrifuged, but without the addition of the product. Table 12: Comparing Odor Profile of Total Volatile Organic Sulfide Compounds When BioKat was Added to Holding Tank Ahead of Centrifuges

Storage Time of

Cake (days)

Prior To Treatment with BioKat, TVOSC (ppmv)

During Two Weeks Of Addition of BioKat, TVOSC (ppmv)

1 36 81 2 293 494 3 1,224 578 4 1,659 557 5 1,894 508 6 1,917 394

Table 12 shows the profile of odorant emissions from cake produced before, during and after the application of the nutrient additive. This product is NRP’s BioKat formulation. This shows a reduction of 70% in the peak concentration of TVOSCs.

Odorant Evaluation of Centrifuge Additives

A metallic salt and an organic catalyst were trialed as additives, and alum was planned as a third additive for early 2006. Table 13 [to be supplied] shows the results of the trial of the ferric chloride salt on the peak odor intensity. Ferric chloride was shown to reduce odor intensity. The effective dosage is a 10 percent addition on a dry weight basis, and is considered above the dosage that is economically practicable; lower dosages were not particularly effective. Table 14 shows the results of the organic catalyst when added ahead of the digester and, additionally, sprayed on the cake. At the dosage employed in this trial, the odor quality of the cake was not notably affected by use of the catalyst. Table 14. Summary of Peak Volatile Organic Sulfide Compounds (VOSC) for Treatment with Bio-Organic Catalyst (BOC)

Sample

Peak MT

(ppmv)

Peak DMS

(ppmv)

Peak TVOSC (ppmv)

% Reduction in TVOSC

Control 823 446 1178 - BOC Added to Centrifuge

616 314 899 24%

Control Plus Surface Application of BOC

1295 265 1501

BOC Added to Centrifuge & Surface Treated

1356 364 1678 none

Odorant Evaluation of Cake Additives

Ashes have been the most successful of additives for odorant control. Both the Gilberton Coal ash and the EcoTechnology ash have achieved better than 90 percent reduction of peak TVSOC concentrations. Graph 2 shows the comparison of peak Total Volatile Organic Sulfide Compounds (TVSOC) of the cake to which Gilberton ash was added at different dosages compared to an unamended biosolids cake. The reduction of peak TVOSC was 80% at the lower dosage. Subsequent to this test, PWD contractor WMPI has used the Gilberton ash as a regular component of its land application procedures, using up to 200 tons of cake per acre. No odor violations have been issued to WMPI in its application program when the

ash was used to help control malodors from the operation. In bench top trials with similar high-carbon ash of coal combustion, but with mostly neutral pH, a similar level of odor control has been achieved; this has been shown at PWD with an ash supplied by VFL/Headwaters from a Conectiv electrical generating facility near Wilmington, Delaware.

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Table 15 is a tabulation showing the TVSOC of a sample of cake to which the EcoTechnology ash was added, compared to a sample of untreated cake. The reduction of peak odorant is about 70%. Table 15: Use of EcoTechnology Ash to Control Odors in Cake After Dewatering Control Treated

No Ash Added

(1.0 gram Ash to 10 grams of Cake)

Days After Cake

Production

Methyl Mercaptan

(ppmv)

Dimethyl Sulfide (ppmv)

Dimethyl Disulfide (ppmv)

Methyl Mercaptan

(ppmv)

Dimethyl Sulfide (ppmv)

Dimethyl Disulfide (ppmv)

1 6.1 71.8 2.8 0.0 23.5 0.4 2 58.2 152.9 19.0 1.2 56.5 4.3 3 205.4 199.0 18.0 4.0 62.7 2.5 4 252.4 262.3 0.4 8.4 67.6 3.2 5 148.1 317.0 1.0 9.9 74.2 3.2 6 46.5 233.9 0.8 6.2 24.7 0.5 7 1.0 0.0 0.0 1.1 0.0 0.4 8 0.0 0.0 0.0 0.6 0.0 0.0

Two liquid products were added to cake on the discharge belt. Table 16 is a profile of a product provide by EnvoGuard, which is a humate product. A profile of odorant emissions from cake samples sprayed with the Eco-Cure enzyme, together with a control cake sample, showed a similar, though not as marked reduction. While both products seemed to provide some response, the humate product performed the better Table 16: Comparison of Total Volatile Organic Sulfide Compounds With Use of a Humate Product from EnvoGuard

Days After Cake

Production Control Cake Sample

TVOSC (ppmv) HMA Treated Cake

TVOSC (ppmv) 1 197 169 2 316 197 3 450 201 4 447 185 5 377 131 6 154 55 7 4 14

These same two products were used to test whether the additive would alter the odor intensity of a cake/woodchip blend used in static pile composting. Again, both products seemed to yield some results, and the stronger performer is the humate product. The results for EcoCure are shown in Graph 3.

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Compost MixTreated withEcoCure (TVOSCin ppmv)

DISCUSSION Three products have so far showed positive results for odor control in field scale applications. These are: 1) co-generation coal ash, supplied by Waste Management and Processors, Inc., Pottsville, PA; 2) a nutrient product, Bio-Kat, supplied for addition to digesters by Natural Resource Protection of Fort Lauderdale, FL, ; and 3) a humate product, named HMA, supplied by EnvoGuard for application to cake. In bench top experiments, the Eco-Cure product and Organica Biotech bacterial blend showed some effectiveness, but scale-up has not been accomplished successfully. Alum has been shown in pilot scale trials to both serve as a cost-effective replacement for polymer while also significantly reducing odor potential. But alum has not been employed in a full-scale odor control trial involving centrifuges, as of this writing. Several trials are incomplete: Archaea Solutions’ methanogen blend applied to the digester, and alternative application of the Bio-Organic Catalyst. The experiments have confirmed that additives to biosolids processes and products can cause a meaningful reduction of odorant emissions. That is, the peak odor concentrations of TVOSC in a closed container can be reduced by more than 50 percent at practicable dosage rates, and in some cases peak concentrations can be reduced 90 percent. These experiments suggest that follow-up work with the product vendor and wastewater

agencies are warranted in order to demonstrate consistent performance and efficacy, and to optimize prescriptions for product use with specific biosolids. The cost effectiveness of these approaches has not been fully evaluated. For the ash and metal salt additives, the effect of the additive is to add mass to the biosolids, which is a negative factor for cost effectiveness. For other products, the purchase of these additives would become a new cost item for regular operations, so that the benefit for odor control needs to be verified to justify increased costs. Managers will need to make the difficult case for comparing easily-measured operational costs along side the difficult-to-quantify benefits of lower risks of community objection and compliance problems. Another difficult cost-benefit consideration is the comparison of product costs against equipment improvement that might result in similar benefits. For example, equipment for hydrolyzing waste activated sludge ahead of digestion is increasingly being considered for optimizing digester performance. Several of the tested additives might show enhancements comparable to such equipment. In that event, the operational costs would be compared to amortization of capital equipment purchases. The culture of wastewater agencies might be expected to favor equipment improvements to CEBA product purchases, so a persuasive cost-benefit analysis is important for vendors. It should be noted that PWD was not able to directly measure increased gas production during digestion, nor did it show increased VS destruction, so the effect of the CEBA products is not directly comparable to pre-processing equipment. The possibility of combining products at different steps of the biosolids “value chain” is also an unexplored possibility. For example, addition of the BioKat nutrient supplement to the wastewater system, followed by addition of a high-carbon ash after centrifugation might provide a compounding of odorant mitigation. Also, these product trials did not model longer term storage of biosolids, say one to four months, for the effect on odorant intensities. Multiple dosing points and multiple products might be required to deal with a full range of use and disposal programs. These products have been trialed in a biosolids treatment process that has run steadily during the short time of this testing period. Unexamined in this experimentation is whether one or more product might benefit other portions of the treatment system over time. A number of the additives have the possibility of being returned, via the return flow of centrate from the centrifuges, to the headworks of the plant, and thereby influence wastewater treatment at primary or secondary stages, either positively or negatively. Also, given the variable nature of plant processes over different seasons and under different flow regimes, these additives might alter customary seasonal variations in plant performance. So, in the full-scale use of additives, a careful monitoring of all plant performance measurements is particularly warranted. One other potential side benefit of additives is that they might moderate the swings in performance of solids handling processes that may arise seasonally or over varying flow regimes. The development and use of biosolids additives are in the infancy of wastewater and biosolids management. The apparent success shown in this study might be sufficient

motivation for companies and agencies to sponsor further research into mechanisms of action and optimization of control, such that effectiveness can be improved while holding down costs. Also, the variety of wastewater processes across the country is so great that products that work in one environment may not be effective elsewhere, and new experience and technology will need to be applied to allow vendors to more wisely specify products for effective application. Only in that way might the “snake oil” reputation that has preceded the salesperson be overcome. The study above lays out an approach to objectively quantifying the performance of additives that should be a model for field application everywhere new products are trialed. The savvy wastewater manager has little patience with unsupported claims of performance, even when anecdotal testimonials sound convincing. WERF has initiated a CEBA study that is a rigorous comparison of product performance, and this study should only be a start for future product trials. Companies offering CEBA products to the wastewater profession should come to expect participation in trials yielding objective performance data, and should be willing to have results published. In the farther future, successful demonstration of CEBA products for mitigating biosolids odors raises even larger future possibilities for wastewater managers. Treatment trains in wastewater facilities could be tailored to accomplish more than standard effluent criteria, just as the goal of this present study was enlarged to embrace mitigation of biosolids odors. The biological decomposition of endocrine disrupting and pharmaceutical compounds, the inactivation of parasitic cysts, the maximum capture of energy value from organics -- these are examples of treatment goals that might be “front-stage” in the future, each of which might employ non-capital-intensive “biotechnology” within the wastewater treatment system (Kleerebezem, 1999). The wastewater profession might find itself joining the food and pharmaceutical industries in a new world of advanced biotechnologies. Something may have come from those stinky biosolids after all.

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