7.1        Introduction

Achieving a reliable biosolids management program is often one of the most challenging and expensive components of a community’s overall wastewater management program. 

This chapter reviews and compares the biosolids management concepts that survived the initial screening process described in Chapter 3.  The discussion is organized as follows:

·        Introduction

·        Projection of sludge quantities

·        Review of key regulatory definitions and limitations

·        Description of current biosolids management practices

·        Development of Biosolids Management Options

·        Listing of biosolids management options surviving screening

·        Description of each alternative

·        Comparison of the Alternatives Relative to the Evaluation Criteria

7.1.1        Projected Sludge Quantity and Characteristics

During wastewater treatment, several streams of residual materials may be produced, depending on the specific liquid treatment technologies selected for use:

·        Grit and screenings removed during pretreatment

·        Organic sludge produced by initial settling of the wastewater (primary sludge)

·        Biological waste sludge resulting from biological treatment processes to remove nutrients and oxygen-consuming organics (secondary sludge)

·        Chemical sludge produced by the chemical precipitation of phosphorus

Typically, the grit and screenings are dewatered to an acceptable moisture content and sent to a landfill or incinerator for disposal.  The other sludge streams are normally blended and passed through treatment processes to prepare the material for its designated end use – either beneficial reuse or disposal.  This processed material is termed “biosolids.”

In developing the biosolids management alternatives, projections of sludge quantities and characteristics were made.  These projections were based on (1) the projected raw wastewater characteristics presented in Chapter 2 and (2) a representative liquid treatment process shown in Figure 7‑1.

Projected primary, secondary (biological) and chemical sludge production are shown in Table 7‑1 for summer and winter operating conditions associated with average, dry-weather plant flow rates of 5, 10 and 20 mgd.  Both average-day and maximum-month sludge generation rates are shown for each season. 

Table 7‑1.  Projected Sludge Generation Rates

In developing the sludge generation projections, the following assumptions were made:

·        Year-round primary sludge production is based on 1) an average suspended solids removal efficiency of 65 percent across the primary clarifiers, and 2) a volatile fraction of 75 percent.

·        Year-round secondary sludge production is based on 1) an average BOD₅[2] removal of 30 percent across the primary clarifiers, and 2) a volatile fraction of 75 percent.

·        Secondary sludge production during the summer permit season is based on operating the activated sludge system to provide nitrification, partial denitrification, and biological phosphorus removal.

·        Secondary sludge production during the winter permit season is based on operating the activated sludge system to provide nitrification and carbonaceous BOD removal only.

·        Chemical sludge production occurs only during the summer permit season and is based on an alum dose of 20 mg/L and removal of 10 mg/L of suspended solids across the tertiary treatment process.

7.1.2        Summary of Regulations

A summary of state and federal regulations pertaining to biosolids was presented in Chapter 4 of the Basis of Planning Report.  Selected information is presented here to facilitate discussion of alternative biosolids management strategies.

The Washington State standards for biosolids management closely follow those promulgated by U.S. EPA under 40 CFR 503, which are frequently referred to as the “Part 503 Regulations.”  All common disposal practices, including land application, surface disposal, and incineration are covered in the 503 regulations.  Major impacts of the 503 regulations include pathogen reduction requirements, vector attraction reduction[3], and limitations on trace element content.

Pathogen Reduction

The 503 regulations create two categories of biosolids:  Class “A” and Class “B”.  Class “A” biosolids are essentially a pathogen-free product that can be applied to agricultural lands, forest reclamation sites, and household lawns and gardens, depending on the vector attraction reduction option.  Class “B” biosolids meet EPA’s stabilization requirements, but are not considered a pathogen-free product.  Class “B” biosolids require additional vector attraction control, such as disking or injection during application to agricultural land.

To meet Class “B” pathogen reduction measures, sludge must be treated with a “Process to Significantly Reduce Pathogens” (PSRP) (see list in Table 7‑2), or an equivalent process accepted by the State.  Alternatively, a Class “B” designation can be attained by meeting specific limits for the density of fecal coliform.

To meet Class “A” pathogen reduction measures, sludge must be treated with a “Process to Further Reduce Pathogens” (PFRP) (see list in Table 7‑3), or an equivalent process accepted by the State.  Also, the final product must meet specific density limits for fecal coliform and Salmonella bacteria.  Alternatively, a Class “A” designation can be attained by meeting specific limits for enteric viruses and helmith ova in addition to the fecal coliform and Salmonella limits. 

Table 7‑2.  Pathogen Reduction Processes for Class “B” Biosolids

Table 7‑3.  Pathogen Reduction Processes for Class “A” Biosolids

Vector Attraction Reduction

The 503 regulations also require vector attraction reduction of sludge prior to disposal.  Table 7‑4 summarizes methods recognized under the 503 rules.

Table 7‑4.  Vector Attraction Controls

If one of these controls is not met, then the biosolids must be injected beneath the soil surface or incorporated into the soil within six hours of application.

Trace Element Limitations

The 503 regulations establish maximum allowable concentrations for trace elements in the biosolids product and govern the cumulative loading of these elements to the land application site. 

The concentration limits are presented in Table 7‑5.  The first column lists the maximum allowable concentration (ceiling limit) of pollutants in biosolids that are applied to land.  If the pollutant concentration in municipal sewage sludge exceeds any of these limits, the sludge is considered a solid waste material, not biosolids, and may not be applied to land.  The second column identifies a lower “threshold” concentration for pollutants.  If the concentration for all listed pollutants remains below these threshold levels, requirements for record-keeping, reporting and labeling are reduced.

Table 7‑5.  Concentration Limits for Biosolids Applied to Land

1.  Milligrams per kilogram, dry weight basis

Allowable annual and cumulative pollutant loading rates for land application of biosolids are presented in Table 7‑6.

Table 7‑6.  Loading Rate Limits for Biosolids Applied to Land

1.                 Kilograms per hectare, dry weight basis

Exceptional Quality Biosolids

The term Exceptional Quality Biosolids applies to biosolids that meet the Class “A” pathogen reduction requirements, comply with one of the vector attraction controls listed in Table 7‑4 and have trace element concentrations below the “threshold concentrations” listed in Table 7‑5.  Management and reporting requirements for application of Exceptional Quality Biosolids are greatly reduced; however, general loading limitations must be followed.

7.1.3        Existing Solids Treatment and Reuse

Nearly all County wastewater is treated at the Spokane Advanced Wastewater Treatment Plant (SAWTP). Solids are generated by preliminary treatment (screenings and grit), the primary and CSO clarifiers (primary), and the secondary clarifiers (waste activated and chemical sludge[4]).  The operating mode for solids processing is the same during the summer and winter seasons, with the exceptions that 1) chemical sludge is produced only during the summer and 2) additional sludge storage may be required in the winter due to limitations on the City’s ability to haul biosolids. The biosolids produced by the SAWTP meet a Class “B” designation.

Screenings are hauled to the regional Waste-to-Energy Plant where they are incinerated; and grit is hauled to the North Side Landfill. 

The solids handling facilities are undergoing modification.  Currently, primary and chemical sludge are thickened using gravity thickeners and secondary sludge is thickened using dissolved air flotation thickeners (DAFTs).  The two thickened sludge streams are combined and fed to anaerobic digesters for stabilization.  Two of the digesters are operated in series to treat the sludge while a third digester is reserved for seasonal storage when weather conditions prevent hauling biosolids to offsite land application sites.  Digested sludge is dewatered using belt filter presses that produce a cake with a solids content of 18 to 20 percent.  Dewatering is practiced 5 days per week for 6 to 15 hours per day.  To equalize ammonia-nitrogen loadings to the liquid treatment processes, the filtrate from the dewatering operation is stored in a spare gravity thickener and metered back to the main wastewater flow stream.

In 1999, the City approved a phased approach to upgrade the solids processing systems. Key elements of this program include:

·        Co-thickening of primary, chemical and secondary sludge using gravity belt thickeners and discontinuing use of the gravity thickeners and DAFTs.

·        Installation of new belt filter presses and new storage facilities for dewatered biosolids.

·        Incorporation of recuperative thickening of anaerobically digesting solids to increase solids storage capacity.

·        Installation of odor control facilities for the solids processing area.

·        Enhanced facilities for side-stream equalization of dewatering filtrate.

The program is scheduled to be implemented in three phases, with all work completed by 2004.  The first facilities to be installed will be the gravity belt thickeners that are projected to be operational in late 2001.

Dewatered biosolids are beneficially used through land application to agricultural fields in Spokane and Lincoln Counties.  In 1999, 7,515 dry tons of biosolids were applied to 2,603 acres.

7.2        Development of Biosolids Alternatives

7.2.1        Listing of Alternatives Surviving Initial Screening 

A wide range of biosolids management alternatives was identified at the brainstorming workshop (see Chapter 3).  Those surviving the initial screening process are listed below: 

·        B-1.  Class B Treatment and Land Application

·        B-2.  Class A Treatment (Thermal Treatment) and Land Application

·        B-3.  Composting

·        B-4.  Send Sludge to SAWTP

·        B-5.  Privatized Biosolids Management

·        B-6.  Co-Incineration with Solid Waste

7.2.2        Basis for Comparing Alternatives

All of the alternatives address biosolids management systems that could be implemented at a new wastewater treatment plant, either by the County alone or by the City and County together.  For the portion of the County’s wastewater that continues to be sent to the SAWTP, it has been assumed that land application of Class “B” biosolids will be continued.

The following sections describe each of the alternatives by presenting the basic concept, discussing the applicability of the idea to Spokane County, identifying key facility requirements and implementation issues associated with treatment and end use, and reviewing the anticipated results that would be achieved by implementing the concept.

The scale of any new biosolids program will depend on the number and size of new treatment plants that will be constructed (if any).  These options are addressed in Chapter 6.  To simplify economic comparison of the options, facility requirements and costs have been developed based on the following assumptions:

·        The County will continue to send 10 mgd of flow (dry-weather basis) to the SAWTP, where Class “B” biosolids will be produced and land applied.

·        All additional flow (12 mgd in 2025) will be treated at one new treatment plant, where the alternative biosolids management practice will be implemented.

Once a preferred concept has been identified for the number, location and size of treatment plants, facility requirements for biosolids management can be adjusted.

7.2.3        Alternative B-1:  Class B Biosolids and Land Application

Concept

In this alternative, biosolids management at a new treatment plant would essentially match the current practice at the SAWTP.  In this approach, the various sludge streams would be thickened, anaerobically digested using mesophilic reactors, dewatered and applied to agricultural land or used for reclamation of historic mining sites.  Sludge storage would be provided in liquid form at the treatment plant and in dewatered form at the application site.  Figure 7‑2 presents a schematic of the concept.

Applicability to Spokane County

of Spokane personnel, there appears to be ample demand for this product within a reasonable proximity of the Spokane County service area.  Although detailed demand surveys have not been conducted, it appears that agricultural application sites would most likely be located within a 30-mile haul distance (one-way) from a new treatment plant site. To gain sufficient acreage for a long-term biosolids management program, it will probably be necessary to locate some land application sites in neighboring counties.

For mining area reclamation, dewatered biosolids most likely would be applied to hillsides at the Kellogg mine site for slope revegetation.  This facility is located in Idaho, about 50 miles (one way) from Spokane.  The State of Idaho Department of Environmental Quality (IDEQ) and the Environmental Protection Agency (EPA) currently manage the Kellogg mine site.  Based on discussions with IDEQ personnel, individual contracts would be needed to take biosolids for each application area where this material is used for revegetation.  Although the amount of land needing revegetation has not been delineated by IDEQ, it appears that as many as 3,000 acres may be available.  Mine site reclamation may not be able to use all of the biosolids generated by a 12 mgd plant; consequently, this program may serve as a supplement to an agricultural reuse program. 

Implementation

Facility Requirements at the Treatment Plant – Facility requirements are based on the process schematic shown in Figure 7‑2.  These facilities are presented as representative unit processes for production of Class “B” biosolids.  If this concept were eventually selected for implementation, a more detailed evaluation and selection process would be conducted for the individual unit processes.  The number and size of the unit process elements (listed in Table 7‑7) are based on the sludge generation rates associated with a 12-mgd plant flow (average dry weather) and the redundancy criteria outlined in Chapter 3.

The following comments outline key assumptions associated with the facility requirements.

·        Grit and screenings would be disposed of off-site at the landfill and Waste-to-Energy Facility, respectively.

·        A fermenter/gravity thickener would thicken primary sludge.  This facility could run unattended during weekend and nighttime periods and could be used to generate organic substrate to augment the performance of biological phosphorus removal in the liquid treatment system. 

·        Secondary sludge and seasonally-generated chemical sludge would be thickened in a dissolved air floatation thickener, which could run unattended during weekend and nighttime periods.

·        The two thickened sludge streams would be combined for digestion in mesophilic digesters (operated at 95^oF).  Digester sizing is based on a 20-day detention time at maximum-month sludge generation rates.

·        Digested sludge storage would be provided in a mixed tank equipped with biogas safety equipment.  This tank would serve as a “wide spot” between digestion and dewatering, allowing shut down of the dewatering process over the weekend or for prolonged maintenance measures.  The storage tank would also be used when icy roads or other conditions prevented haul of dewatered sludge to the application sites.  For initial evaluation, a detention time of 7 days was used.
 

Table 7‑7. Alternative B-1 Facility Requirements

                        1.         Design criteria based on maximum month loading conditions
 

·        Dewatering would be provided by centrifuge, operating 8 hours per day, 5 days per week.  It is estimated that a cake solids concentration of 25 percent would be produced.

·        Centrate from the dewatering operation would be collected in a storage tank for equalization.  The centrate would then be metered back to the liquid treatment process to equalize the ammonia loading to the process.  This is needed to improve permit compliance and prevent process upset.

·        A small amount of dewatered sludge storage would be provided on-site in the form of “live-bottom” hoppers used to load the haul trucks.  One day of storage would be provided.

·        All solids handling facilities would be covered, with exhaust air routed to odor control systems.

Biogas produced in the digestion process would be recovered for use in heating the digesters.  Excess gas could be used for other purposes such as power generation or building heat, however, no costs have been included for these facilities at this time.

Facility Requirements for Hauling Biosolids – It is assumed that sludge haul to the application sites would be provided by 12 cubic yard trucks.  Based on the biosolids production associated with a 12-mgd plant flow, the estimated number of trips per week is shown in Table 7‑8:

Table 7‑8.  Biosolids Haul Truck Trip Requirements for 12-mgd Plant.

Agriculture Reuse Requirements – For agricultural reuse, dewatered biosolids would be land applied through cooperative arrangements with local farmers.  Typically, a multi-year contract is negotiated between the utility and the farmer for this purpose.  The land application program must be developed subject to approval by the Department of Ecology (DOE).  This program would include locating, investigating, and permitting sites to receive Class “B” biosolids, as well as developing an operational plan and a monitoring/reporting program.  The application sites would need to meet regulatory requirements governing crop growth, harvesting, and public access. 

Biosolids application rates are governed by nutrient and trace element loading rates.  Typically, nitrogen loading is the controlling factor.  Based on the City of Spokane’s experience, an average annual loading rate of 3 dry tons/acre has been assumed.  For a 12-mgd plant, this equates to approximately 1,300 acres.  As a general rule of thumb, it is a good idea to have an additional 50% of your total required acreage as useable land under contract in a given year.  Consequently, a total of 2,000 useable acres should be under contract.

In addition to hauling the dewatered biosolids to the application site, it is assumed that the County would be responsible for loading the material into spreading equipment and applying the biosolids to the land.  The local farmer would be responsible for disking or plowing in the biosolids following application.  Consequently, County-supplied on-site equipment would include a front-end loader and a spreader truck.

Since dewatered biosolids cannot be land-applied year-round, storage for dewatered solids during the winter months must be provided.  Again, it is assumed that this practice would be modeled after the SAWTP operation.  That is, dewatered biosolids would be stored in bermed areas at the land application sites.  This on-site stockpiling occurs after the ground has frozen.  The biosolids are then piled in the bermed area.  Since the biosolids act as an insulator, the ground remains frozen until the solids can be applied to the land in the spring. 

Mining Site Reuse Requirements – For mine site reclamation, the County would likely be responsible for hauling biosolids to the mine site.  IDEQ would be responsible for loading and spreading the biosolids on the hillsides.  Due to the steepness of the application sites, application would only take place during the spring and summer months when revegetation would occur quickly.  However, biosolids may be stored at the mine site during the winter months if sites have been identified for revegetation during the following spring or summer months. 

Estimated Costs – Costs estimates are provided only for the 12-mgd of capacity associated with the new treatment plant.  The 10 mgd of capacity provided at the SAWTP is a common element for all alternatives.  Consequently, these costs were not needed for comparison purposes and were not developed.

Capital Costs.  Capital costs for treatment facilities and equipment needed for sludge haul and application are summarized in Table 7‑9.

Table 7‑9.  Capital Costs for Alternative B-1

Land Costs.  Land costs are associated with the space requirements for the solids handling facilities at the new treatment plant.  For this analysis, it is assumed that the facility would be sited in an urbanized location in the Spokane Valley.  Based on 5 acres and a unit cost of $100,000 per acre, the cost would be $500,000.

O&M Costs.  Operations and maintenance costs for Alternative B-1 are shown in Table 7‑10.  The estimates are based on an average plant flow of 8.5 mgd during the first 20 years of operation (5 mgd initial flow, and 12 mgd in 2025)

Table 7‑10.  Annual O&M Costs for Alternative B-11

    1.     Based on an average plant low of 8.5 mgd.

Agreements with End Users.  In this alternative, it is assumed that the biosolids would be provided at no cost to the end users.  Consequently, neither cost nor revenue would be associated with this transaction.

Present Worth.  A 20-year present worth value for Alternative B-1 is presented in Table 7‑11.

Table 7‑11.  Present Worth for Alternative B-1

Anticipated Result

Implementation of this alternative would produce biosolids that could be reused on agricultural land and mining sites.  Demand for this product by end users seems adequate to ensure a successful, long-term program. This process is well established and relatively easy to operate.  The key risk is whether future regulatory requirements will change in a manner that precludes application of a Class “B” biosolids.

7.2.4        Alternative B-2: Class A Treatment (Thermal Treatment ) and Land Application

Concept

In this alternative, a high-temperature digestion process would be used to produce biosolids that meet Class “A” requirements.  There are several technologies available for achieving this.  The most commonly applied methods are:

·        Pasteurization at 160 ^oF before mesophilic anaerobic digestion (pre-pasteurization)

·        Anaerobic digestion at 130 ^oF (thermophilic anaerobic digestion)

·        Aerobic digestion at 130 ^oF (thermophilic aerobic digestion)

While these technologies involve differing facility requirements and have differing operational characteristics, they all produce end products that have fairly similar characteristics and essentially the same end-use potential.  For simplification, the analysis of this alternative is based on only one of the technologies – pre-pasteurization.  In addition to meeting Class “A” requirements, it has been assumed that the end product will meet other requirements for an Exceptional Quality Biosolids. 

The process schematic for Alternative B-2 is shown in Figure 7‑3.  The end product will be a dewatered biosolids that has similar appearance to the Class “B” sludge currently produced by the City of Spokane, although cake dryness would likely be somewhat higher.  Some Class “A” processes have produced final biosolids with fairly high odor levels, but with proper design and control, it is anticipated that the product resulting from the pre-pasteurization process would be fully acceptable to end users.  This product would be suitable for land application.

Figure 7‑3.  Alternative B-2 – Class “A” Treatment & Land Application

Applicability to Spokane County

The Class “A” biosolids produced may be used for both the agricultural and mine reclamation applications described for Alternative B-1.  It is anticipated that the level of demand for the product would be the similar to, or perhaps higher, than for Class “B” biosolids.  The higher acceptance of the product may result from fewer restrictions on the farmer’s operational practices.  If future regulatory changes should prohibit use of Class “B” biosolids, than the ability to reuse Class “A” biosolids would be a strong driver for considering this alternative.

Exceptional Quality Class “A” biosolids may also be used for urban applications such as parks and golf courses since it has low pathogen levels and meets vector attraction controls

Currently, production of Class “A” biosolids using high temperature processes is not practiced by many communities in Washington State, with no applications in the Spokane region.  This is driven primarily by the ability of the utilities to reuse Class “B” biosolids, which require less cost and less complex technology.

Implementation

Facility Requirements at the Treatment Plant – Treatment facilities would be the same as those described for Alternative B-1 (see Table 7‑7), with the exception that pre-pasteurization vessels would be installed upstream of the digesters.  These units would be sized to provide 30 minutes of detention at maximum-month sludge generation rates.  Along with the pre-pasteurization tanks, additional heating, pumping and mechanical systems would need to be installed.

Facility Requirements for Hauling Biosolids – In some installations, pre-pasteurization has been found to achieve greater destruction of volatile solids than mesophilic anaerobic digestion.  Also, it has been found to increase the cake dryness achieved by biosolids dewatering equipment.  Both of these factors may result in a slight reduction in the volume of biosolids to be hauled to application sites.  In this analysis, a 10 percent reduction in final biosolids volume has been assumed.  The resulting number of truck trips per week is shown in Table 7‑12.

Table 7‑12.  Biosolids Haul Trips

Agriculture Reuse Requirements

Implementation of Class “A” biosolids application would be similar to implementation of Class “B” reuse.  The major differences are (1) reduced monitoring and reporting requirements, (2) fewer restrictions on site access, (3) fewer restrictions on crop harvesting, and (4) reduction of the need to immediately incorporate the biosolids into the soil.  All of these factors make it easier to implement agreements with end users.

It is assumed that the County would be responsible for hauling, loading and spreading dewatered biosolids, as in Alternative B-1.  The farmer would be responsible for disking of plowing the biosolids into the soil following application.  

Mining Site Reuse Requirements – Application of Class “A” biosolids at the Kellogg mine site would be similar to Alternative B-1.  Biosolids would likely be accepted on an individual contract basis for each area to be covered.  The County would be responsible for transfer to the mine site, and IDEQ would be responsible for loading and spreading. 

Urban Reuse Requirements – Urban reuse of Class A biosolids produced by thermal treatment would likely be limited to County-managed applications on parks or golf courses.  Even though regulations permit more widespread use of this material, the nature of the end product (a dewatered, somewhat gelatinous material) does not lend itself to widespread acceptance by small-scale, individual users.

Estimated Costs – As discussed earlier, for comparison purposes, costs estimates are provided only for the 12 mgd of capacity associated with the new treatment plant. 

Capital Costs.  Capital costs for treatment facilities and equipment needed for sludge haul and application are summarized in Table 7‑13.

Table 7‑13.  Capital Costs for Alternative B-2

Land Costs.  Land costs are associated with the space requirements for the solids handling facilities at the new treatment plant.  For this analysis, it is assumed that the facility would be sited in an urbanized location in the Spokane Valley.  Based on 5 acres and a unit cost of $100,000 per acre, the cost would be $500,000.

O&M Costs.  Operations and maintenance costs for Alternative B-2 are shown in Table 7‑14.  The estimates are based on an average plant flow of 8.5 mgd during the first 20 years of operation (5 mgd initial flow, and 12 mgd in 2025).

Table 7‑14.  Annual O&M Costs for Alternative B-2

 1.    Based on an average plant low of 8.5 mgd.

Agreements with End Users.  In this alternative, it is assumed that the biosolids would be provided at no cost to the end users.  Consequently, neither cost nor revenue would be associated with this transaction.

Present Worth.  A 20-year present worth value for Alternative B-2 is presented in Table 7‑15.

Table 7‑15.  Present Worth for Alternative B-2

Anticipated Results

Implementation of this alternative would produce a Class “A” biosolids that could be land applied with few restrictions.  Class “A” biosolids may be more attractive from viewpoint of the both the public and end users due to the reduced pathogen concentration and the fewer restrictions on farming practices, reporting, etc.  Application opportunities would likely be similar to that for Class “B” biosolids – agricultural and mining sites.  Use of the material on urban green spaces would likely be limited to County-controlled applications on parks or golf courses.  The appearance of the end product from this treatment technology does not make it appealing for widespread use in homes or small commercial applications. 

Production of Class “A” sludge using pre-pasteurization would result in higher capital and operating costs, particularly with respect to energy consumption.  Consequently, this alternative should be viewed as attractive from a risk and public relations standpoint, but less attractive economically.  

7.2.5        Alternative B-3:  Composting

Concept

This alternative involves the use of composting to produce a Class “A” biosolids.  The composting process uses biological activity in a controlled aerobic environment to stabilize sludge by destroying organic material.  The heat produced by the process destroys pathogens sufficiently to meet Class “A” requirements if specified time and temperature requirements are met.  Composting may be practiced using either raw sludge or digested sludge.  Because of odor concerns (and related siting issues), it has been assumed that the sludge would be digested prior to composting.  This is the most common practice in the U.S. 

Several methods are available for performing the compost operation including aerated static piles, windrowing or in-vessel composting systems.  Facility requirements and cost estimates are based on aerated static piles, similar to the process currently used in Coeur d’Alene, Idaho.  Figure 7‑4 provides a schematic of the overall sludge processing concept.

Figure 7‑4.  Alternative B-3 - Composting

The product produced by composting is much drier than that produced by Alternatives B-1 and B-2, and contains partially decomposed wood chips that are added as an amendment in the process.  The product is suitable for use as a landscaping material on either large scale commercial projects or a home-by-home basis. 

Applicability to Spokane County

The long-term viability of composting in the Spokane region has been demonstrated by the City of Coeur d’Alene’s program, which has successfully operated since 1989. Coeur d’Alene has a contract with a local landscaping company to distribute the compost.  The material is then used in commercial and home landscaping projects in the region. 

A key issue for a new composting operation would be whether there is sufficient market demand to support two local programs.  Given the size of the local population, it appears that there would be adequate demand, but a market survey should be conducted if this alternative proves highly attractive.

A second key issue for a compost operation involves land requirements and siting.  For a 12 mgd program, a minimum of 20-acres is recommended for an aerated static pile operation.  By way of comparison, Coeur d’Alene has a 17-acre site for a compost operation that will eventually serve a plant flow of 12 mgd.  This site is adequate, but not generous, considering buffering and setback requirements. 

From an operational standpoint, it would be desirable to combine the compost site with a treatment plant site; however, given the limited availability of large sites for a new treatment facility, it would likely be difficult and expensive to find an urban site that can meet both functions.  More likely, a remote composting site would be needed. Siting the compost facility may be challenging because of potential concerns regarding odor generation, dust and truck traffic.

Implementation

Facility Requirements at the Treatment Plant – Treatment facility requirements would be identical to those described for Alternative B-1 with the following exception:

·        Storage requirements for liquid, digested sludge would be reduced from 7 to 3 days.  The smaller volume allows dewatering operations to be discontinued over long weekends.  Long detention times for icy road conditions are not likely to be needed since the haul distance will be much shorter.  Coeur d’Alene has not had a problem with this issue.

Facility Requirements for Hauling Biosolids – The number of truckloads of sludge produced each week would be the same as described for Alternatives B-1. 

Compost Facility Requirements – Compost facility requirements are based on an operation similar to Coeur d’Alene’s in which wood chips would be used as the bulking agent.  Key requirements are summarized in Table 7‑16 and discussed below:

·        A compost unloading area is needed to provide short-term storage of the digested, dewatered sludge.

·        Covered storage sheds are needed for both new wood chips and recycled wood chips that have been screened from the finished compost. Approximately 6 cubic yards of wood chips will be combined with each yard of dewatered biosolids.

·        Mechanical sludge blending equipment is needed to mix the sludge and amendment material.  This equipment should be placed in a covered structure adjacent to the active compost piles.

·        A front end loader is needed for material handling and creation of the active compost piles.

·        A covered area is needed for the active compost piles.  Space requirements are based on a 21-day compost period and 7-foot high piles.

·        Mechanical aeration and piping systems are needed to aerate the active compost piles and the curing piles.

·        Biofilters are needed to treat odorous off-gases from the compost operation.

·        Screening equipment is needed to recover amendment material from the composted mixture.

·        Storage area is needed for a 30-day curing period for the composted biosolids.

·        Additional storage area is needed for the finish product unless the end user promptly removes the material.

·        The entire compost, curing and storage area must be paved and equipped with site drainage systems to prevent runoff.  The site drainage should be piped to a sewer or a drainage collection sump for subsequent pumping and haul to a wastewater treatment plant.

Table 7‑16. Alternative B-3 Compost Facility Requirements

End Use Requirements – Final end use requirements depend on how the compost is marketed and distributed.  Some communities, like Tacoma, bag the compost for retail distribution and sales.  This requires a fairly elaborate production effort. Other communities, such as Coeur d’Alene, sell all or most of the compost to one or more commercial landscaping companies.  These companies assume responsibility for removing the material from site on a bi-weekly or monthly basis, and all subsequent distribution efforts.  For this analysis, it is assumed that the latter approach would be taken. 

Estimated Costs – Costs estimates are provided only for the 12 mgd of capacity associated with the new treatment plant.

Capital Costs.  Capital costs for treatment facilities and equipment needed for sludge haul and application are summarized in Table 7‑17.

Table 7‑17.  Capital Costs for Alternative B-3

Land Costs.  Land costs are associated with the space requirements for the solids handling facilities at the new treatment plant and a remote compost site.  For this analysis, it is assumed that the treatment facility would be sited in an urbanized location in the Spokane Valley.  Based on 5 acres and a unit cost of $100,000 per acre, the cost would be $500,000.  It is likely that the compost facility would be located in a more remote area with lower land prices.  Based on 20 acres and a unit cost of $20,000 per acre, the cost would be $400,000.

O&M Costs.  Operations and maintenance costs for Alternative B-3 are shown in Table 7‑18.  The estimates are based on an average plant flow of 8.5 mgd during the first 20 years of operation (5 mgd initial flow, and 12 mgd in 2025).

Table 7‑18.  Annual O&M Costs for Alternative B-3

          1.           Based on an average plant low of 8.5 mgd.

Agreements with End Users.  Based on Coeur d’Alene’s experience, the market price for sale of the finished compost to local landscape companies is in the range of $3 to $6 per cubic yard.  Using a $5/cu yd value and the compost production associated with an 8.5 mgd plant flow, an annual revenue of $45,000 would be generated.

Present Worth.  A 20-year present worth value for Alternative B-3 is presented in Table 7‑19.

Table 7‑19.  Present Worth for Alternative B-3

Anticipated Result

Implementation of this alternative would produce a Class “A” that is highly desirable for use in landscaping and gardening use.  Although a market analysis is needed, it is likely that sufficient demand would exist for this material despite the presence of a similar operation in Coeur d’Alene. If odors were minimized, the process would likely be well-accepted by the community.  The composting process is more labor intensive and requires more land area than Alternatives B-1 and B-2. Revenues from the compost would offset only a fraction of the extra cost to produce the material.

Given the higher cost of composting, implementation of this alternative would need to be driven by 1) the County encountering difficulty in finding users for less expensive biosolids products or 2) the public’s desire to produce a material with more widespread uses.

7.2.6        Alternative B-4: Treatment at SAWTP

Concept

In this alternative, no solids treatment facilities would be provided at the new 12 mgd treatment facility.  Instead, all solids generated at the plant would be directed to the SAWTP for centralized solids processing.  There are two potential approaches to accomplishing this:

·        Return all sludge produced to the sewer system for subsequent conveyance to SAWTP.  This practice is commonly employed for “scalping” plants that generate water for reuse, particularly in Southern California.

·        Build a new pipeline to directly convey the removed sludge to the SAWTP.

The first approach was dropped from consideration for two reasons:

·        Conveying the solids through the existing collection system could result in a higher level of untreated solids escaping to the Spokane River during CSO events.  Although, most current overflows would not be affected by this practice, the CSO at the entrance to the SAWTP would be impacted.

·        Returning the sludge to the sewer increases solids and organic loading on the liquid treatment system at the SAWTP.  Organic removal capacity is one of the key factors limiting the ability to expand the SAWTP.

·         

The direct force main concept is illustrated in Figure 7‑5.  In this approach, dilute primary, secondary and chemical sludge would be combined and pumped to the SAWTP.  Given the anticipated length of the pipeline, an intermediate booster station may be required.  At the SAWTP, the sludge would discharge to a receiving tank, and would then pass through the thickening, digestion and dewatering systems.  Although the sludge flow would not go directly to the SAWTP liquid process, the underflows from the thickening and dewatering processes would be recycled to the liquid stream for treatment.  While this would increase loading on the liquid process, the impact would be much lower than if the sludge was conveyed to the SAWTP using the gravity sewer system.

Applicability to Spokane County

This alternative appears technically feasible.  Variations of this concept have been implemented in other locations, such as San Diego, Vancouver, Washington and Washington County, Oregon.  At the SAWTP, it appears that the solids handling facilities could be expanded to handle the loadings from an additional 12 mgd of plant flow, although more detailed analysis is needed to confirm this.  

The driving forces for this concept would be (1) reduced land requirements at the new treatment plant, (2) greater ease in siting a new treatment plant by eliminating processes that have higher potential for odor generation, and (3) consolidating solids processing in one location to benefit from operational efficiencies.

Implementation

Facility Requirements for Conveyance – Conveyance facilities would include the following components:

·        A 0.6 mgd pumping station at the new treatment plant (based on maximum-month flows).

·        A ferric chloride feed system at the sludge pumping station.  This would be used to control odors and hydrogen sulfide formation in the force main.

·        An 8-inch diameter force main.  If the new treatment plant were located in the Mid-Valley area, a length of approximately nine miles would be needed.  Much of the pipeline would be routed through developed neighborhoods or business districts.

·        Air/vacuum relief stations equipped with odor control facilities at high points along the force main.

Facility Requirements for Treatment at SAWTP – It is anticipated that the SAWTP solids handling process would be expanded using the same technologies described earlier in this chapter under the heading “Existing Solids Treatment and Reuse”. A new 100,000-gallon receiving tank would be needed upstream of the thickening process to facilitate blending with the SAWTP sludge.  The final product would be a Class “B” biosolids that would be land applied.

A detailed analysis of the increased recycle streams on the liquid process has not been conducted.  For this analysis, it has been assumed that no new capital facilities would be required, but chemical and energy costs would increase.

Conveyance of the sludge though a long force main would generate high odors in the material discharged to the SAWTP.  More extensive odor control facilities would be needed to handle this impact.

Institutional Arrangements - Implementation of this alternative would require a revised interlocal agreement between the County and City.  Also, permitting and easements would be required for the sludge force main and booster pumping station.

Estimated Costs – Cost estimates for this alternative were more difficult to derive because the concept impacts liquid and solids treatment facilities at the SAWTP.

Capital Costs.  The capital improvements for solids handling facilities would take place at the SAWTP rather than at a new treatment plant.  Although the technology selection at the SAWTP may be slightly different than that identified for Alternative B-1, the overall facility requirements are similar.  To simplify the analysis, it has been assumed that the capital cost of treatment facilities at SAWTP would be approximately 90 percent of the costs identified for Alternative B-1.  The 10 percent savings results from the economy of scale of building larger tankage at SAWTP and the ability to use existing infrastructure at that plant. 

The cost of the conveyance facilities must be added to the treatment costs.  Table 7‑20 summarizes capital costs for Alternative B-4.
 

Table 7‑20.  Capital Costs for Alternative B-4

Land Costs.  This alternative reduces land requirements at the new treatment plant, but consumes space at SAWTP.  The SAWTP property has a relatively high value since the treatment plant has significant site constraints.  Consequently, the value of land required was assumed to be the same as Alternatives B-1 and B-2, which is $500,000.  The cost of easements for the sludge pipeline is included in the capital cost for the pipeline.

O&M Costs.  Operations and maintenance costs for Alternative B-1 are shown in Table 7‑21.  The estimates are based on an average plant flow of 8.5 mgd during the first 20 years of operation (5 mgd initial flow, and 12 mgd in 2025).  The cost of solids handling at SAWTP was assumed to be 90 percent of that estimated for Alternative B-1.  The projected savings would result from greater staffing efficiency at a larger plant.

Table 7‑21.  O&M Costs for Alternative B-4

                           1.      Based on an average plant low of 8.5 mgd.

Agreements with End Users.  In this alternative, it is assumed that the biosolids would be provided at no cost to the end users.  Consequently, neither cost not revenue would be associated with this transaction.

Present Worth.  A 20-year present worth value for Alternative B-1 is presented in Table 7‑22.

Table 7‑22.  Present Worth for Alternative B-4

Anticipated Result

Implementation of this approach would allow implementation of a “liquid only” plant at a new location, facilitating the siting and permitting process.  However, this benefit would be offset by the need to site, permit and construct the sludge pipeline.  Consolidating the solids handling facilities at SAWTP may slightly reduce capital and operating costs for these facilities; however, the cost of building, operating and maintaining the force main, plus the operational impacts on the SAWTP liquid treatment processes would offset these savings.

7.2.7        Alternative B-5: Privatized Management

Concept

In this alternative, the County would contract with a privately operated biosolids management company.  The County would be responsible for partially treating the sludge to a condition that is acceptable for delivery to the private operator.  The vendor would then remove the sludge from the County’s facilities, haul it to an off-site location, further process the material, and either dispose of or reuse the final material.  The County would pay the vendor a price per unit of sludge removed, usually on the basis of dollars per wet ton.

On a national basis, private vendors use a range of technologies to process the biosolids, including composting, alkaline (lime) treatment, and drying/pellitization.  In most cases, a dewatered, unstabilized sludge is acceptable for their purposes.  For some compost operations, or for conditions with long sludge hauls, a dewatered, stabilized sludge is required.  Analysis of this alternative is based on the assumption that the County would need to provide a dewatered, unstabilized sludge to the private vendor.  This concept is shown in Figure 7‑6.

Applicability to Spokane County

An investigation was conducted to identify private vendors offering biosolids management services in the Eastern Washington/Northern Idaho region.  At this time, the only active vendor in the area appears to be EKO Compost, located in Missoula, Montana.  EKO’s clients include several small to mid-size communities in the Inland Northwest, including Post Falls, Idaho.  Based on discussions with EKO personnel, this company anticipates adding several new contracts with communities in Idaho and Montana within the next few years that would cause their compost operation to reach capacity.  Because of this, the company officials were hesitant to offer potential pricing terms because they were uncertain they could handle the additional load associated with a 12 mgd treatment plant.

Although no other locally-active vendors were identified, the County could likely gain interest from other nationally and regionally based firms by issuing a request for proposals for privatized management of biosolids. 

Figure 7‑6.  Alternative B-5 – Privatized Management

Implementation

Facility Requirements at the Treatment Plant – As stated earlier, on-site treatment requirements would be vendor specific.  For initial evaluation purposes, it has been assumed that the sludge streams would be thickened, stored as a liquid, and dewatered.  The on-site liquid sludge storage would provide a 10-day detention time to provide a “wide spot” in case sludge hauling was interrupted due to weather or other causes.   On-site storage of dewatered sludge would be limited to a sludge-loading hopper with a one-day detention time.  The private vendor would be responsible for off-site dewatered sludge storage.  Facility requirements are summarized in Table 7‑23.
 

Table 7‑23. Alternative B-5 Facility Requirements

                        1.         Design criteria based on maximum month loading conditions

EKO compost has indicated that they accept dewatered, undigested sludge.  The sludge produced at Post Falls is undigested, but the nature of the liquid treatment process (extended aeration) produces a fairly stable raw sludge.  With the liquid treatment concept presented in Figure 7-1, a less stable raw sludge will be produced.  As a result, it may be necessary to digest this material to prevent unacceptable odor levels during the long haul to the compost site. 

Agreement with Private Vendor.  Implementation of this alternative would require an agreement with a private vendor.  The terms and length of these agreements can vary widely depending on the needs of the utility and the level of competition available.  At a minimum, the agreements specify the responsibilities of the parties and an agreed upon unit price for removal and disposal/reuse of the sludge.

Estimated Costs.  Costs estimates are provided only for the 12 mgd of capacity associated with the new treatment plant.

Capital Costs.  Capital costs for treatment facilities are summarized in Table 7‑24 for the cost of this alternative with and without sludge digestion.  Capital costs associated with sludge haul and further processing would be included in the vendor contract.

Table 7‑24.  Capital Costs for Alternative B-5

Land Costs.  Land costs are associated with the space requirements for the solids handling facilities at the new treatment plant.  For this analysis, it is assumed that the facility would be sited in an urbanized location in the Spokane Valley.  With the privatized operation, land requirements would be reduced to about 2 acres.  Based on a unit cost of $100,000 per acre, the cost would be $200,000.

O&M Costs.  Operations and maintenance costs for Alternative B-5 (exclusive of the vendor agreement) are shown in Table 7‑25.  The estimates are based on an average plant flow of 8.5 mgd during the first 20 years of operation (5 mgd initial flow, and 12 mgd in 2025).

Table 7‑25.  Annual O&M Costs for Alternative B-51

1.         Based on an average plant low of 8.5 mgd.

Agreement with Vendor.  Initial estimates of vendor costs are based on the price that Post Falls currently pays EKO Compost - $42 per wet ton plus additional cost associated with a longer haul.  Based on a 25-percent solids content in the dewatered sludge, this would equate to $190 per dry ton of solids.  At the sludge production rate associated with an 8.5 mgd plant flow, the annual cost would be $355,000.

Present Worth.  A 20-year present worth value for Alternative B-5 is presented in Table 7‑26.
 

Table 7‑26.  Present Worth for Alternative B-5

Anticipated Result

Use of a private biosolids management company reduces facility requirements, initial capital costs and property needs for a new treatment plant.  By making the plant footprint smaller and by eliminating processes with odor generation potential, this alternative may make it easier to site a new treatment facility.

Reliance of a private vendor greatly reduces the County’s control.  Should the vendor become financially unstable or encounter other difficulties, the County may need to quickly find an alternative method of disposing its biosolids.  This is a particular concern in a region such as Spokane where there are few private vendors operating.

7.2.8        Alternative B-6:  Co-Incineration with Solid Waste

Concept

In this alternative, the County would transport dewatered sludge to the regional Waste-to –Energy Plant for co-incineration with solid waste.  This approach would be attractive because it would take advantage of the existing incineration facilities and reduce the biosolids to a low-volume product (ash).

Applicability to Spokane County

Based on initial investigation of this alternative, several issues were identified that could render the concept difficult to implement, undesirable to operate, or otherwise unattractive to the community:

·        The Waste-to Energy Facility is not designed to inject this type of material into its furnace (municipal solid waste is fed by a crane).

·        The low heat value of the biosolids would likely have a negative impact on the plant’s energy production. 

·        A private vendor (Wheelabrator) currently operates the facility and their contract currently does not allow biosolids incineration. 

·        Addition of the biosolids would increase air emissions, which may be unacceptable to regulators and the public.

For these reasons, this alternative was removed from further consideration. 

7.3        Discussion of Alternatives Relative to Evaluation Criteria

The biosolids management alternatives were compared relative to one another using the evaluation criteria developed for this planning effort.  Alternative B-6 (Co-Incineration with Solid Waste) was not included in this comparison since it was found to be fatally flawed.

A summary of the comparison is presented in Figure 7‑7, using a modified “Consumer Reports” rating system.  Key considerations are presented in the following sections, with emphasis placed on factors that strongly differentiate the alternatives.  In reviewing the findings, it is important to remember that each of the alternatives is based on 10 mgd of Class “B” biosolids production at the SAWTP, and 12 mgd of biosolids management using the concepts addressed by the alternatives.

7.3.1         Capacity

This criterion focuses on the ability of the alternative to be implemented quickly to meet near-term requirements, and the alternative’s ability to meet projected capacity requirements for 25 and 50 year planning horizons.

Alternatives B-1 and B-2 fare well against this criterion.  It appears that agreements with end users could be implemented quickly to allow use of the biosolids once the new plant comes on line.  Also, there is adequate agricultural land within a reasonable haul distance of the plant to allow expansion of the program to handle 2050 sludge generation rates.  Sufficient property must be acquired at the new plant site to allow future expansion of the sludge treatment processes.

Alternative B-3 (composting) fares well in terms of being able to continue a reuse program long into the future, providing that market survey results confirm that the addition of a second compost supply in the region would not saturate the market.  Given the potential difficulty of siting a new compost facility, this operation may not be on-line when the new treatment plant becomes operational.  This would require an interim reuse or disposal method, such as Class “B” land application.

Alternative B-4 (convey to SAWTP) rates poorly in terms of providing a solution beyond the Year 2025.  This is due to the site constraints at SAWTP, which  limit the ability to expand solids processing facilities.  Also, the sludge conveyance facilities may be limited in capacity unless they are oversized when initially installed.  Consequently, expansion beyond Year 2025 requirements may necessitate construction of solids handling facilities at the new treatment plant site.

The ability of Alternative B-5 (private operation) to meet Year 2025 and 2050 capacity requirements is uncertain.  It depends on the stability and capacity of the vendor, and the affordability of the contract terms.

Figure 7‑7.  Comparison of Biosolids Management Alternatives with Evaluation Criteria
 

7.3.2        Technical/Operations

This criterion addresses whether the concept has a proven record of performance, and examines the technical reliability and operational complexity of the alternative.

Alternative B-1 rated the highest because it has the lowest complexity and has a long, wide-spread record of success in the region.

The two Class “A” alternatives (B-2 and B-3) involve more operationally complex technologies.  Of these, composting is more widely practiced and has a more proven record of success than pre-pasteurization.  The latter approach has been implemented in only a few treatment plants in the U.S.  Advantages of Alternative B-3 include simpler end use agreements and reduced monitoring and reporting requirements, particularly if all the material was contracted to a single user.

Alternative B-4 is similar to B-1 in terms of the reliability and simplicity of the treatment and reuse process; however, it adds the complexity of the sludge conveyance system.

From the County’s perspective, Alternative B-4 (privatization) would rate high in terms of operational simplicity, but would rate lower in terms of proven performance.  With respect to technical reliability, most vendors use well-established processes with proven track records.

7.3.3        Conveyance

The biosolids alternatives do not impact the existing sewer conveyance system.  Alternative B-4, which includes construction of a force main to SAWTP, would parallel the existing interceptor system.

7.3.4        Implementation

This criterion addresses implementation challenges such as permitting and approval requirements, difficulty of siting, and property and easement requirements.

Assuming a qualified, reliable private vendor can be contracted with, Alternative B-5 rates the highest against this criterion.

Alternatives B-1 and B-2 are identical in terms of implementation challenges.  The major obstacle would be finding a site to encompass both liquid and solids treatment facilities. For land application programs, a significant implementation issue is the ability to negotiate cooperative agreements with farmers for the amount of land needed.  If such agreements cannot be obtained, the County would have the option to purchase property, but this would increase cost and may not be politically acceptable in some circumstances.

Alternative B-3 requires siting and acquiring a second site to house the compost operation, increasing the implementation difficulty. 

Alternative B-4 reduces property requirements at a new treatment plant site, at least for the next 20 years.  However, this alternative involves siting and easement acquisition for a 9-mile pipeline through urban areas.

7.3.5        County Control of Destiny

In Alternatives B-1, B-2 and B-3, the County has full control of the biosolids management program associated with a new plant.  While these alternatives are dependent on other entities to a certain extent – farmers in Alternatives B-1 and B-2 and a landscape contractor in B-3 – the County retains ownership of the biosolids and is in a position to execute other contracts if their current contractors default.

Alternative B-4 requires the County to implement a revised interlocal agreement with the City, reducing the County’s ability to directly control implementation.  Furthermore, while it is unlikely that the City would default on its contract, the County has no other alternative for biosolids management should the City become unable to treat the County’s sludge. 

In Alternative B-5, the County would have the authority to enter into an agreement with a third party, but would then become dependent on that party for handling the biosolids produced.

7.3.6        Risk

There is some risk involved in all the alternatives.  Alternative B-5 (privatized management), has the most significant risk because it relies on a private vendor.  This vendor could become insolvent during the course of the contract or sharply raise prices, making this solution unaffordable. 

All of the land application programs have some risk associated with conversion of farmland to other uses; however, there is a large quantity of land within a reasonable distance of Spokane that is zoned to remain agricultural long into the future. 

Potential risk associated with changing regulations is addressed under the next criterion.   

7.3.7        Regulatory Compliance

All of the alternatives have been developed to comply with current federal and state regulations for biosolids management; however, those alternatives producing Class “B” biosolids (B-1 and B-4) have a somewhat higher risk associated with future regulatory change than those producing Class “A” biosolids (B-2, B-3 and B-5). This is because some experts in the field of biosolids management are projecting that, at some future date, EPA may tighten the requirements for or even prohibit the application of Class “B” biosolids.  Should this occur, the solids processing facilities at both the SAWTP and a new treatment plant could be modified to produce a Class “A” biosolids, either by adding high-temperature processes (such as pre-pasteurization), or by composting the digested sludge.

7.3.8        Water Resource Enhancement

Water resources would not be significantly impacted by any of the proposed alternatives.  All alternatives reuse biosolids and return moisture to the soil either by land application on farmland or by use for landscaping and gardening.  The privately operation alternative was rated slightly lower than the others because the benefits of biosolids reuse may occur in a remote location, rather than in the Spokane area.

7.3.9        Environmental Impact

Groundwater, surface water, and fisheries would not be significantly impacted by any of the alternatives.  Only land application sites that meet the requirements for buffers to groundwater and surface water bodies would be used in Alternatives B-1, B-2 and B-4. 

Similarly, the proposed alternatives are unlikely to have a significant effect on bird and wildlife habitat. 

Soil quality in areas where biosolids are land applied is improved by adding both moisture and nutrients.  Biosolids are loaded at sustainable rates.  Typically, nitrogen loading is the controlling factor on application rate. 

Non-point water quality would not be significantly impacted by any of the biosolids management alternatives.  Land application sites must meet minimum requirements for slope, reducing the risk of runoff in a storm event. 

7.3.10    Community Impact

With respect to construction activities, Alternative B-5 would appear to have the least impact and Alternatives B-3 and B-4 would have the most impact.  Alternative B-3 would require construction activities at two sites, increasing disruption.  While Alternative B-4 reduces construction activity at the new plant site, it increases activity at SAWTP and requires construction of a long pipeline.  Often, pipeline construction is more disruptive to a community than plant construction.

All of the alternatives are designed to be protective of public health.  The composting alternative (Alternative B-3) would result in greater contact between the finished product and the public, but would provide a higher level of pathogen reduction in the biosolids treatment process.  With land application of Class B sludge (Alternative B-1) there is some potential for public contact, but these programs take place at relatively remote locations with limited access. The potential for contact would be limited primarily to workers who have received training.  For the land disposal options (Alternative B-1 and Alternative B-2), the potential for contact also would be limited primarily to workers at the wastewater agencies and the landfill operation.  Alternative B-5 would involve the haul of undigested sludge; however, public contact would only occur in the event of an accident or a spill.

All of the alternatives appear to be compatible with future land uses in the area.   The land application alternatives require substantial amounts of farmland.  If cooperative agreements with farmers are implemented, the land application practice does not alter land ownership or use.

Protection of air quality is an important concern with any biosolids management program.  The two primary considerations are odor control and minimization of dust from operations such as composting.  Odors can result during the treatment, storage, conveyance and application of biosolids.  

·        Treatment.  For all alternatives, odor control facilities have been included for the biosolids treatment.  Alternative B-2 (thermal treatment) has a higher potential for odor generation than those options using mesophilic digestion. The composting alternative (B-3) has a greater potential for dust generation than the other management alternatives given the nature of the operation, which involves moving and turning of compost piles.

·        Storage.  Odor generation associated with sludge storage is impacted by the period of storage required, the level to which the sludge has been stabilized, and the level of odor control provided at the storage facility.  Alternative B-5 minimizes sludge storage requirements since the biosolids can be sent to the end use year-round.  By contrast, Alternative B-1 (Class “B” treatment) and Alternative B-2 (Class “A” treatment) requires that sludge be stored for up to six months.  For alternatives producing Class “A” sludge, storage requirements depend on the timing of demand for the finished product.  In a compost operation, a non-offensive product can be stored for several months without significant odor generation. 

·        Sludge Pipelines.  Sending untreated sludge through a long pipeline would generate strong odors.  These can be controlled to some extent with chemical treatment; however, odorous venting would occur at high points along the pipeline.  Odor control devices can be placed at each vent location to reduce the impact on the surrounding neighborhood.

·        Hauling.  Odor potential from transport is related to the degree of stabilization of the biosolids being hauled, the degree to which the material is contained within the truck, the haul distance, and the amount of development or potential for exposure to the public along the haul route.  Hauling of undigested sludge (Alternative B-5) presents the greatest odor potential.

·        Application.  Odor generation at the application site is generally a lesser problem than that associated with treatment, storage or transport.  If the material is objectionable, it must be incorporated into the ground shortly after being applied

All of the alternatives would have similar noise impacts on the surrounding community. 

All of the alternatives involve truck haul of dewatered biosolids.  Alternatives B-5 would have the greatest haul length (potentially to Montana); whereas Alternative B-3 would have the shortest haul.

None of the proposed alternatives will have a significant impact on open space or recreation/resource awareness.  The compost product may be used as a soil amendment on parks and open spaces.

7.3.11    Economics

A comparative summary of capital costs, operating costs, end-user costs or revenues, and total present worth costs for the alternatives is presented in Table 7‑27.

Table 7‑27.  Summary Comparison of Costs

1.                    Cost based on 8.5 mgd

2.                    Revenue from compost sales or off-site costs for private biosolids haul and processing