Review of Domestic Septage and Municipal Wastewater Treatment Plant Residuals Management

Transcription

1 Final Report No Prepared for: PEI Department of Fisheries, Aquaculture, and Environment Review of Domestic Septage and Municipal Wastewater Treatment Plant Residuals Management November 2001 ISO 9001 Registered Company

2 Executive Summary Proper treatment and disposal of wastewater generates residual materials in the form of septage and sludge. Current disposal practices for septage and sludge include collection by licensed septic tank pumpers and disposal by land spreading. Licensed sludge and septage haulers are regulated by the Sewage Disposal Regulations issued under the Environmental Protection Act and the Atlantic Canada Standards and Guidelines for the Collection, Treatment, and Disposal of Sanitary Sewage. The current disposal methods and regulations are consistent with those in other Canadian Provinces. However, with current regulations in the United States and some provinces becoming increasingly stringent, the long-term viability of current sludge and septage disposal practices is questioned. Ultimate disposal options were developed based on the degree of stabilization of the material. The volume of material generated in PEI which fall into these categories is presented in the table below. Volume of Wastewater Residuals Requiring Disposal Classification Volume (m 3 /yr) Kings County Prince County Queens County Total (PEI) Stabilized Material 4,633 1,324 5,652 11,609 Partially Stabilized Material 3,839 8,691 10,380 22,910 Unstabilized Material Ultimate disposal of the organic fraction of wastewater treatment residuals produced in PEI will continue to be on the land for the foreseeable future. This suggests that the current disposal method, land spreading, will remain relatively unchanged. However, in order to minimize the risks associated with this practice, several options were investigated to provide treatment of materials prior to land spreading. The evaluation of these options led to the conclusions drawn as a result of the study which include: Current septage and wastewater treatment plant residual disposal methods are similar to those in use in other jurisdictions. The main difference between practices in PEI and those in other jurisdiction include: The allowance of direct disposal of unstabilized septage The absence of application limits on septage spreading Improvements in current practices can be achieved through relatively minor changes to regulations. CBCL Limited Consulting Engineers Executive Summary i

3 The recommendations that followed these conclusions are grouped by material type and listed below: Stabilized Material Landspreading of stabilized material should remain as the preferred disposal method for these materials. Application rates and methods will remain subject to the Atlantic Canada Standards and Guidelines Manual for the Collection, Treatment, and Disposal of Sanitary Sewage. Partially Stabilized Material The current certificate of approval process should continue for the disposal of wastewater lagoon residuals. Septage should be stabilized prior to land spreading. Stabilization methods could include one of the following: Alkali addition at the source Co-Treatment with domestic sewage Composting Removal of non-biodegradable products should be included as a requirement when utilizing alkali addition at the source as the stabilization method. The annual issuance of septage disposal licenses should include a disposal site application which identifies the area where spreading is to occur as well as the amount of material which will be spread. The current practice of discharging septage to private holding ponds should be discontinued and holding ponds decommissioned. Unstabilized Material Dewatering and composting of unstabilized material from mechanical treatment plants without stabilization facilities should continue. Holding tank material should continue to be treated at municipal wastewater treatment plants. Further Study Stabilization utilizing either co-treatment with domestic sewage or composting require further study to develop capital costs, operating costs, management options, and pump-out rate impacts of central septage processing facilities. Specific sites must be identified such that transportation, treatment, and disposal costs can be estimated with some degree of accuracy. Given that a number of municipal treatment plants in major centers are currently undergoing upgrading projects, co-treatment could potentially be incorporated into the design of the upgrade. CBCL Limited Consulting Engineers Executive Summary ii

4 Contents Executive Summary...i Contents iii Chapter 1 Introduction Introduction Background...1 Chapter 2 Generation Study Sources of Sludge and Septage Wastewater Residuals Generation and Characterization Septage Wastewater Treatment Lagoon Sludge Mechanical Secondary Treatment Primary Treatment Plant Residuals Classification of Materials for Disposal...8 Chapter 3 Wastewater Residuals Disposal Disposal Options Current Practice in Prince Edward Island Current Practice in Other Jurisdictions Ontario New Brunswick Nova Scotia United States Restrictions on Disposal Stabilization Metals Nutrients Method of Application...16 Chapter 4 Options for Treatment and Disposal General Treatment Methods...17 CBCL Limited Consulting Engineers Contents iii

5 4.2.1 Digestion Processes Alkaline Stabilization Composting Development of Disposal Strategies Stabilized Material Partially Stabilized Material Unstabilized Material...23 Chapter 5 Conclusions and Recommendations Conclusions Recommendations...24 CBCL Limited Consulting Engineers Contents iv

6 Chapter 1 Introduction 1.1 Introduction CBCL Limited was retained in June 2001 by the Prince Edward Island Department of Fisheries, Aquaculture and Environment (PEIFAE) for the completion of a study to evaluate current practices utilized for the disposal of domestic septage and sludge and make recommendations regarding requirements for future modifications. This report has been developed in accordance with our proposal dated 6 April 2001, the original terms of reference, and subsequent discussions with PEIFAE staff. 1.2 Background Proper treatment and disposal of wastewater generates residual materials in the form of septage and sludge. Residents who reside in the unserviced areas of PEI are responsible for the operation and maintenance of on-site sewage disposal systems. When the septic tank has to be pumped, the homeowner contracts with a licensed septic tank cleaner to empty the tank and dispose of the contents which typically contain grease, sludge, and clear effluent which collectively are termed septage. Sludge generally contains settleable material removed from the wastewater and biomass generated at central wastewater treatment plants. Depending upon the treatment process utilized at each plant, sludge may require removal continuously or on a periodic basis which can vary from a few days to several years. Current disposal practices for septage and sludge include collection by licensed septic tank pumpers and disposal by land spreading or surface disposal in designated septage holding ponds. Licensed sludge and septage haulers are regulated by the Sewage Disposal Regulations issued under the Environmental Protection Act which set out setback criteria for designated disposal areas, but do not regulate the quantity of material which may be applied or the method of disposal. Septage holding ponds are not addressed in these regulations and typically are not constructed to any particular standard which would provide the necessary public health safeguards to make this an acceptable practice. Guidelines related only to the disposal of sludge are provided in the Atlantic Canada Standards and Guidelines for the Collection, Treatment, and Disposal of Sanitary Sewage. These guidelines describe acceptable metal concentrations and sludge application rates for aerobically and anaerobically digested material. Although these guidelines are available at this time, their use is not widespread among those responsible for the disposal of the sludge, which are primarily licensed septage pumpers. CBCL Limited Consulting Engineers Introduction 1

7 The current method of disposal is common in the other Canadian Provinces. However, current regulations in the United States do not permit land spreading of some materials currently being spread and would place additional restrictions on other materials. As new Canadian regulations often mirror existing US regulations, the long-term viability of current sludge and septage disposal practices is questioned. Therefore, the main objective of this study will be to develop septage and sludge treatment and disposal methods which are manageable under the current and developing PEI wastewater/ solid waste industry, and will be acceptable under both current and potential future regulations. CBCL Limited Consulting Engineers Introduction 2

8 Chapter 2 Generation Study 2.1 Sources of Sludge and Septage The province of PEI has a population of approximately 135,000 that reside in one of three counties, Kings, Prince, and Queens. Wastewater treatment and disposal is provided with central collection and treatment systems in most communities with rural residents being serviced by on-site wastewater treatment and disposal. The serviced population distribution is presented in Exhibit 2.1. Exhibit 2.1 Population Distribution Area Central Wastewater On-Site Treatment Total* Collection and Treatment and Disposal Kings County 5,270 14,290 19,560 Prince County 17,270 27,300 44,570 Queens County 42,820 27,610 70,430 Total 65,360 69, ,560 * Population data taken from 1996 census results Sludge and septage generation can be estimated based upon typical generation rates which vary depending upon treatment type and (central or on-site) as well as the treatment process utilized at the central treatment facility. Central wastewater treatment is provided by a number of different processes throughout PEI. Exhibit 2.2 presents the types of treatment and the serviced population for each. Exhibit 2.2 Central Wastewater Treatment Types Treatment Process Serviced Population Kings County Prince County Queens County Total (PEI) Wastewater Treatment Lagoons 1,770 7,770 12,990 22,530 Secondary Mechanical Treatment Plants 3,500 1,000 1,330 5,830 Primary Treatment Plants 0 8,500 28,500 37,000 Generation rates and typical solids concentrations of the residuals produced for the above processes are listed in Exhibit 2.3. In some cases, additional solids handling procedures are utilized which decrease sludge volume through further degradation of the organic fraction or physical dewatering of the material. Additional generation rates and solids concentrations are provided where these processes are utilized. CBCL Limited Consulting Engineers Generation Study 3

9 Exhibit 2.3 Sludge Generation and Typical Solids Content Process Solids Production (kg/m 3 treated) Typical Solids Concentration (% Solids) Wastewater Treatment Lagoons Secondary Mechanical Treatment with aerobic digestion Primary Treatment with anaerobic digestion with vacuum filtration These solids production estimates can be utilized to generate sludge volumes provided the volume of wastewater treated at the facility is known. In the development of the sludge generation tables presented in the following sections, wastewater flows have been estimated by allowing 0.34 m 3 of wastewater per capita per day which is the domestic wastewater production rate stated in the Atlantic Canada Standards and Guidelines Manual for the Collection, Treatment, and Disposal of Sanitary Sewage. Septage generation is typically estimated at a yearly generation rate of approximately 0.23 m 3 per capita. The solids content of septage is approximately 1.5 %. 2.2 Wastewater Residuals Generation and Characterization Each of the materials generated has specific characteristics that dictate their potential treatment and disposal options. The following sections describe the volume of residuals generated by County as well as provide some of the more significant properties of each material in terms of their application to potential treatment and disposal options Septage Septage can be defined as the liquid and solid material removed from a septic tank. It generally includes wastes derived from toilet, bath and shower, sink, garbage disposal, dishwasher, and washing machine. The volume of septage generated in PEI is tabulated in Exhibit 2.4. CBCL Limited Consulting Engineers Generation Study 4

10 Exhibit 2.4 Septage Generation Area Solids Generation (kg/yr) Septage Volume (m 3 /yr) Kings County 49,350 3,290 Prince County 94,200 6,280 Queens County 95,250 6,350 Total 238,800 15,920 Septage characteristics can vary widely from household to household. A survey of domestic septage characteristics performed by the USEPA has produced typical characteristics that are presented in Exhibit 2.5. Exhibit 2.5 Typical Septage Characteristics Parameter Concentration (mg/l) Biochemical Oxygen Demand (BOD) 6,500 Chemical Oxygen Demand (COD) 30,000 Total Kjeldahl Nitrogen (TKN) 600 Ammonia Nitrogen (NH3 N) 100 Total Phosphorus 210 Fats, oil, and grease 5,600 Alkalinity 1,000 Total Solids (TS) 34,000 Total Volatile Solids (TVS) 25,000 Total Suspended Solids (TSS) 15,000 Total Volatile Suspended Solids (VSS) 9, Wastewater Treatment Lagoon Sludge Two types of wastewater treatment lagoons exist on PEI, stabilization ponds, and partial mix aerated lagoons. Both treatment systems provide aerobic secondary treatment, however, stabilization ponds supply oxygen with passive aeration through algal photosynthesis and wave action while aerated lagoons utilize mechanical aeration systems including blowers and diffusers. Both systems provide large basin volumes where both raw wastewater solids and biomass produced by the treatment process can settle out to form sludge deposits. These sludge deposits accumulate over time even though they are partially digested due to anaerobic decomposition of organic material on the pond bottom. Sludge generation in these systems is tabulated in Exhibit 2.6. CBCL Limited Consulting Engineers Generation Study 5

11 Exhibit 2.6 Wastewater Treatment Lagoon Residuals Area Serviced Population Solids Generation (kg/yr) Sludge Volume (m 3 /yr) Kings County 1,770 21, Prince County 7,770 96,426 2,411 Queens County 12, ,206 4,030 Total 22, ,597 6,990 Although the generation volumes are presented on a yearly basis, handling of the material can be difficult, as it is not removed from the basins on a yearly basis. Sludge is typically left to accumulate until it interferes with the treatment process which can take years depending upon the amount of inorganic material in the raw wastewater as well as the loading rate of the treatment facility. Many of the lagoon treatment plants in PEI were constructed between 1960 and 1980 and currently require sludge removal. The material requiring removal contains inorganic material, older inert materials, and raw to partially digested newer organic material. The disposal of this material can be complicated due to the requirement of disposing of large volumes over a relatively short time frame as well as the putrescibility of the newer material. Very little sludge characterization information is available for classifying this material. Typically sludge disposal operations for treatment lagoons are handled on a case by case basis due to the relatively infrequent nature of their occurrence Mechanical Secondary Treatment A number of mechanical secondary treatment plants have been constructed in PEI. These consist of both package activated sludge and rotating biological contactor (RBC) treatment plants. Both systems are predominantly aerobic biological processes designed to convert the finely divided and dissolved organic matter in wastewater into flocculent settleable biological cell tissue (biomass) which can be removed in secondary clarification tanks. The two systems differ in that the activated sludge plants are suspended growth systems and the RBC plants are attached growth systems. Suspended growth systems utilize aeration and mixing to keep microorganisms in suspension and achieve a relatively high concentration of these microorganisms (biomass) through the recycle of biological solids. Attached growth systems provide a surface (medium) on which the microbial layer can grow and expose this surface to wastewater for adsorption of organic material and to the atmosphere and/or artificial aeration for oxygen. CBCL Limited Consulting Engineers Generation Study 6

12 Both systems produce sludge at roughly equivalent rates. Most package plants have either an aerated sludge holding tank or aerobic digester as part of the process and therefore some reduction in sludge production has been allowed for. An estimate of mechanical secondary treatment plant residuals produced in PEI is presented in Exhibit 2.7. Exhibit 2.7 Mechanical Secondary Treatment Plant Residuals Area Serviced Population Solids Generation (kg/yr) Sludge Volume (m 3 /yr) Kings County 3,500 69,496 4,633 Prince County 1,000 19,856 1,324 Queens County 1,330 26,408 1,761 Total 5, ,760 7,717 Sludge produced by mechanical secondary plants is typically partially to fully digested depending upon both the retention time of the aerobic digester or holding tank as well and the average temperature during the holding period. Typical characterization data for aerobic treatment plant residuals are presented in Exhibit 2.8. Although the data as presented is useful, it should be noted that sludge quality will vary widely. Exhibit 2.8 Typical Secondary Sludge Characteristics Parameter Concentration (mg/l) Total Solids (TS) 10,000 Total Volatile Solids (TVS) 7,500 Total Nitrogen (TN) 300 Total Phosphorus 500 Fats, oil, and grease 700 Alkalinity Primary Treatment Plant Residuals Primary treatment plants contain large basins that allow particulate matter contained in the raw wastewater to be removed through settling. Settled solids are collected with mechanical scrapers and then pumped for further processing, dewatering, or direct disposal. Primary treatment plants are located in the cities of Charlottetown and Summerside. The Charlottetown plant utilizes anaerobic digestion for stabilization and volume reduction purposes. The Summerside plant does not stabilize its sludge on-site, however it does dewater the raw sludge with vacuum filter prior to transport for further processing at the East Prince Waste Management CBCL Limited Consulting Engineers Generation Study 7

13 Facility composting site. Sources and quantities of primary treatment plant residuals are presented in Exhibit 2.9. Exhibit 2.9 Primary Treatment Plant Residuals Area Serviced Population Solids Generation (kg/yr) Sludge Volume (m 3 /yr) Kings County Prince County 8, , Queens County 28, ,054 3,891 Total 37, ,830 4,566 Primary treatment residuals are composed of the solids that readily settle out of the raw wastewater. These solids tend to consolidate more readily to form a thicker material that can be further dewatered with relative ease. Typical characterization data for primary sludge is presented in Exhibit Exhibit 2.10 Typical Primary Sludge Characteristics Parameter Undigested Primary Digested Primary Sludge (mg/l) Sludge (mg/l) Total Solids (TS) 50, ,000 Total Volatile Solids (TVS) 35,000 45,000 Total Nitrogen (TN) 1,250 3,000 Total Phosphorus 800 2,500 Fats, oil, and grease 7,500 15,000 Alkalinity 600 3, Classification of Materials for Disposal When discussing options for ultimate disposal of wastewater residuals, a number of different classifications are utilized. Classifications of materials can describe the degree of stabilization of the material and/or the state of the material whether it is liquid or dewatered. Stabilized wastewater residuals are typically referred to as biosolids, while unstabilized material is referred to as raw sludge. The volume of material generated in PEI which fall into these categories is presented in Exhibit For the purpose of this study, secondary mechanical plant sludge will be considered stabilized while wastewater treatment lagoon sludge and septage will be considered partially stabilized. Untreated primary sludge and holding tank material will be classified as unstabilized. CBCL Limited Consulting Engineers Generation Study 8

14 Exhibit 2.11 Material Classifications Classification Volume (m 3 /yr) Kings County Prince County Queens County Total (PEI) Stabilized Material 4,633 1,324 5,652 11,609 Partially Stabilized Material 3,839 8,691 10,380 22,910 Unstabilized Material CBCL Limited Consulting Engineers Generation Study 9

15 Chapter 3 Wastewater Residuals Disposal 3.1 Disposal Options The disposal of wastewater residuals is an issue in all regions where wastewater treatment is practiced. The ultimate disposal of the material will be on the land, in the air, or in the water. With ocean dumping of sludge being prohibited in Canada and sludge incineration being both costly and questionable in terms of environmental impact, land based disposal options will be preferable for Prince Edward Islands wastewater treatment residuals. The key issue then becomes how to regulate the method of incorporating the material into the land. Wastewater residuals can be spread directly or treated prior to spreading. Exhibit 3.1 indicates the basic wastewater residuals management options. Land Spreading Land Disposal Trench/Lagoon/Landfill Burial Subsurface Incorporation Untreated Residuals Co-Treatment Addition to Liquid Stream Addition to Sludge Stream Addition to Both Streams Independent Treatment Stabilization Lagoon Composting Conventional Biological Treatment Aerobic Digestion Anaerobic Digestion Lime Stabilization Chlorine Oxidation Exhibit 3.1 Wastewater Residuals Management Options These options result in two basic residuals management approaches, re-use and disposal. The re-use approach involves the recycling of the residuals to take advantage of all or part of its constituents. The most common reuse option practiced today includes application on agricultural land where the nutrient value can be used in crop fertilization and the organic content as a soil conditioner. Disposal options include burial either separately or CBCL Limited Consulting Engineers Wastewater Residuals Disposal 10

16 with municipal solid waste. As the province of PEI is moving away from the burial of organic material it appears that the application of the organic material on agricultural land is the disposal option that should be focused upon. 3.2 Current Practice in Prince Edward Island Septage and wastewater treatment plant residuals are addressed by two current documents. The Environmental Protection Act Sewage Disposal Regulations apply to both septage and wastewater treatment plant residuals. They provide the means of regulating septic tank pumpers through a licensing program as well as setting out the requirements for disposal sites. This document does not address the quality and volume of material which may be spread on an approved site with the exception of prohibiting the land spreading of sewage holding tank contents which is termed unstabilized sewage in the regulations. The second document available in the Province which applies is the Atlantic Canada Standards and Guidelines Manual for the Collection, Treatment, and Disposal of Sanitary Sewage. This document is more specific in terms of quality and quantity of material that can be spread. As this document is a guideline document its primary use is as a reference as it is limited from a regulatory standpoint. The document is also specific to domestic sewage sludge and does not apply to septage. 3.3 Current Practice in Other Jurisdictions Land spreading of wastewater residuals is widespread in jurisdictions other than PEI. A summary of how other jurisdictions are regulating the disposal of wastewater residuals follows. Focus will be on practices which alter somewhat from the current method of practice in PEI Ontario The Province of Ontario treats septage and wastewater treatment plant residuals separately. The main document related to land spreading of wastewater residuals is the Guidelines for the utilization of Biosolids and Other Wastes on Agricultural Land. This document specifically deals with biosolids which are defined as stabilized municipal sewage sludge. Septage is not addressed in this document. These guidelines describe the restrictions for site selection, biosolids quality requirements, application rates, and monitoring requirements. Both disposal sites and the waste material must be approved and a certificate of Approval be issued before routine spreading of the wastes can occur. In Ontario, septage is regulated by the Waste Management Act and is disposed of at approved Waste Management Sites. Land spreading of septage is not permitted. In some cases, the organic components of septage CBCL Limited Consulting Engineers Wastewater Residuals Disposal 11

17 may be incorporated into other materials such as compost or biosolids that can then be land spread provided the combined material meets the applicable regulations New Brunswick The province of New Brunswick also handles sludge and septage separately. New Brunswick issued Guidelines for Issuing of Certificates of Approval for the Utilization of Wastes as Soil Additives which address land spreading of biosolids and industrial wastes. However, septage is not addressed in this document. Although not specifically covered by regulations, current practice in New Brunswick is to encourage the disposal of septage at municipal wastewater treatment plants with approved septage receiving facilities. In this manner, undesirable components of the septage are removed and landfilled and the organic component becomes incorporated in the biosolids that can then be land spread. Where acceptable municipal plants are not within acceptable hauling distances, septage holding and treatment facilities are established that treat the liquid portion of the septage and retain the solid fraction indefinitely Nova Scotia The province of Nova Scotia is similar to PEI in that it utilises a guidelines document for domestic wastewater treatment plant residuals and a separate document for septage. The Nova Scotia interim septage handling guidelines regulate quantity and quality issues which are not addressed in the PEI regulations. However, the quality restrictions and loading rates are identical to the sludge regulations which are included in the Nova Scotia Guidelines for Collection, Treatment, and Disposal of Sanitary Sewage from which the Atlantic Guidelines were developed United States All of the US states must comply with USEPA CFR Rule 503. The EPA CFR 503 defines requirements for land spreading of biosolids and domestic septage. Regulatory requirements for land spreading of biosolids and septage include pollutant limits, management practices, pathogen and vector attraction reduction requirements, and frequency of monitoring. Regulatory requirements for land spreading of septage are not as extensive as those for biosolids. Septage can be spread without treatment provided that a number of restrictions be observed including limiting public and animal access to the site for 30 days. By treating the septage with the addition of alkali material, grazing and public access restrictions are removed. CBCL Limited Consulting Engineers Wastewater Residuals Disposal 12

18 Individual States may have regulations which are more stringent than CFR 503, however all states must meet a minimum of the CFR 503 requirements. 3.4 Restrictions on Disposal The land spreading of septage and wastewater treatment plant residuals is subject to a number of different restrictions. A discussion of the restrictions as well as a comparison of restricted levels from different jurisdictions follows Stabilization Stabilization of wastewater treatment residuals refers to the biological or chemical processing of the material to reduce the number of pathogens including bacteria, parasites, protozoa, and viruses, as well as odour potential. However, even stabilized material will contain some pathogens and therefore some site restrictions will still be required. In most jurisdictions, all material is required to be stabilized prior to land spreading. However, some jurisdictions will allow the land spreading of unstabilized or partially stabilized material provided additional restrictions are adhered to. The definition of stabilized wastewater residuals varies from jurisdiction to jurisdiction. A number of definitions for stabilized residuals are listed in Exhibit 3.2. In addition to stabilization of wastewater residuals, USEPA CFR 503 has introduced the concept of reducing pathogens to levels greater than ar achieved through traditional stabilization practices. This has allowed a reduction in restrictions for use for some materials. CBCL Limited Consulting Engineers Wastewater Residuals Disposal 13

19 Exhibit 3.2 Stabilization Requirements Area New Brunswick Ontario Atlantic Provinces USEPA CFR 503 Septage Class B Biosolids Class A Biosolids Definition Stabilized material is that which has been processed by the stabilization methods of lime stabilization, aerobic digestion, or anaerobic digestion. Materials processed by MOE approved anaerobic and aerobic digestion processes are considered stabilized. Other stabilization methods require review on an individual basis. Material is considered stabilized if volatile solids in the sludge have been reduced by at least 38% during the treatment of the sludge, the specific oxygen uptake rate (SOUR) of the sludge is less than 1.5 mg O2/h.g of total sludge on a dry weight basis corrected to 20 o C, or a homogeneous mixture with a minimum ph of 12 after 2 hours of vigorous mixing is produced through the addition of alkaline material. Septage may be stabilized by raising the ph to 12 or higher for a minimum of 30 minutes with the addition of alkali material. Class B Biosolids are produced by processes that significantly reduce pathogens (PSRP s) as defined in the regulations. Alternatively Class B Biosolids are defined as material which have less than 2,000,000 MPN per gram of material on a dry weight basis. Class A Biosolids are produced by processes that further reduce pathogens (PFRP s) as defined in the regulations. Alternatively Class A Biosolids are defined as material which have less than 1,000 MPN per gram of material on a dry weight basis Metals Wastewater residuals can contain varying amounts of metals. At low concentrations, metals can be beneficial to plant growth however at high concentrations, some metals can be toxic to humans, animals, and plants. Therefore, based on risk assessment techniques, almost all regulations dealing with land spreading of wastewater residuals will contain restrictions related to both metal concentrations and additive metal loading for successive applications. A comparison of these concentrations and additive loading rates are tabulated below. The information in these tables applies to wastewater treatment residuals only with the exception of CFR 503 which also applies to septage. CBCL Limited Consulting Engineers Wastewater Residuals Disposal 14

20 Exhibit 3.3 Metal Concentration Limits Pollutant Concentration Limit (mg/kg dry weigt basis) Nova Scotia New Brunswick Ontario* USEPA CFR 503 Arsenic Cadmium Cobalt n.c. Chromium 2,800 1,100 2,800 1,200 Copper 1, ,700 1,500 Lead 1, , Mercury Molybdenum Nickel Selenium Zinc 4,200 1,850 4,200 2,800 n.c. no criteria criteria for Ontario are the present requirements. Guidelines also include long term targets which are significantly lower than the present requirements. Exhibit 3.4 Cumulative Metal Application Limits Pollutant Concentration Limit (kg/ha) Atlantic Canada Nova Scotia Ontario USEPA CFR 503 Arsenic Cadmium Cobalt n.c. Chromium ,000 Copper ,500 Lead Mercury Molybdenum n.c. Nickel Selenium Zinc ,800 n.c. no criteria Nutrients Nutrients present in wastewater residuals include nitrogen, phosphorus, potassium, and others that are essential for plant growth and are responsible for the beneficial properties of the material. Nutrient levels are CBCL Limited Consulting Engineers Wastewater Residuals Disposal 15

21 key in the determination of application rates as excessive nutrient levels due to high application rates can result in environmental contamination of ground and surface water. Therefore the development of application rates restrict nutrient loading to prevent this type of contamination. Nitrogen is the main nutrient of concern when applying wastewater treatment residuals to agricultural lands. Most regulations require that nitrogen application does not exceed the agronomic rate of the crop being cultivated which is roughly equivalent to the annual nitrogen fertilizer requirement for the crop planted. The guidelines for Ontario and Atlantic Canada further restrict nitrogen applications to a maximum of 135 kg/ha and 160 kg/ha, respectively Method of Application The method of application can provide additional protection, specifically when applying lower quality materials or applying materials in sensitive areas. Special application methods include subsurface injection or incorporation into the soil within a specified time frame typically from 6 24 hours. Instances where special application methods have been called for in the guidelines reviewed include; Application of untreated septage Application of wasetwater lagoon residuals Applications in areas where runoff controls are required Application on floodplains Application where odour controls are required By incorporating the material into the soil as quickly as possible a barrier is placed between vectors and the material and moisture is taken from the material into the soil minimizing the potential for odour generation. CBCL Limited Consulting Engineers Wastewater Residuals Disposal 16

22 Chapter 4 Options for Treatment and Disposal 4.1 General Ultimate disposal of the organic fraction of wastewater treatment residuals produced in PEI will continue to be on the land for the foreseeable future. This suggests that the current disposal method, land spreading, will remain relatively unchanged. However, in order to minimize the risks associated with this practice, several options are available to provide treatment of materials prior to land spreading. This should allow the process to become more sustainable and help to avoid public scrutiny. Because of the variable nature of the materials requiring disposal, development of a single treatment and disposal method common to all materials is unlikely. Therefore, following a description of the treatment methods available, strategies for the main types of materials identified in Chapter 2 will be developed. 4.2 Treatment Methods Treatment of biosolids prior to disposal relies on it s application as well as the regulations and guidelines within that region. As a general rule, the greater the level of treatment the more options available for disposal. Treatment technologies with the most potential for use on Prince Edward Island are described below Digestion Processes Aerobic Digestion Stabilization in this process occurs from the destruction of degradable organic components and the reduction of pathogen organisms by aerobic, biological mechanisms. The objectives of the aerobic digestion process, include production of a stable product by oxidizing organisms and other biodegradable organics, reduction of mass and volume, reduction of pathogen organisms, and conditioning for further processing. Wastewater residuals that are agitated with oxygen to maintain aerobic conditions for a specific mean cell residence time at a specific temperature will achieve the required degree of stabilization. A minimum mean cell residence time of 45 days is required in Atlantic Canada with up to 120 days required for full digestion. CBCL Limited Consulting Engineers Options for Treatment and Disposal 17

23 Anaerobic Digestion Anaerobic digestion is the solubilization and reduction of complex organic substances by microorganisms in the absence of oxygen. The purposes of anaerobic digestion are to produce stabilized biosolids, reduce pathogens, reduce biomass quantity by partial destruction of volatile solids, and produce a usable gas as a by-product. The microorganisms responsible for the conversion of organic substances to methane, carbon dioxide, trace gases, and stabilized biosolids can be divided into three groups, each responsible for a separate function: solubilization, acid formation, and methane formation. Proteins, lipids, carbohydrates, and other complex organics are solubilized by hydrolysis. These products are then converted to short-chain organic acids including acetic, propionic, and lactic acid. These acids are then converted to methane, carbon dioxide, and other trace gases by methanogens. Anaerobic stabilization accomplishes substantial reductions in pathogen concentration. Anaerobic digestion has been shown to reduce detectable viruses by one to four orders of magnitude, with the higher reductions achieved at thermophilic operating ranges Alkaline Stabilization The addition of alkaline chemicals is a reliable method of stabilization. The most common chemical additive is lime. In recent years other chemical additives have been introduced, all guaranteeing advantages over traditional lime stabilization. This section describes the lime stabilization processes as well as new alkaline stabilization techniques. Alkaline stabilization has been used in numerous biosolids management programs. Some of the most common situations include: Short haul distances to end-use or disposal sites, Stabilization facilities at small plants, Plants with highly variable solids production, and Septage disposal. The main advantages of alkaline stabilization processes are they are reliable, reduce odours, low in capital cost, compact, and easier to operate than other stabilization processes. The primary disadvantage of alkaline stabilization, as compared with digestion, is that there is no reduction in solid mass. This increase in mass may increase the costs of transportation for usage and disposal. In alkaline stabilization processes, alkaline material is added to untreated sludge in sufficient quantity to raise the ph to 12 or higher. The high ph CBCL Limited Consulting Engineers Options for Treatment and Disposal 18

24 creates an environment that is not conducive to the survival of microorganisms. As a result, the sludge will not putrefy, create odours, or pose a health hazard, so long as the ph remains high. New methods of alkaline stabilization using materials other than lime have recently been developed. Most of the processes are proprietary and rely on additives such as cement kiln dust, lime kiln dust, portland cement, or fly ash. Advanced treatment includes the addition of other chemicals, a higher chemical dose, and supplemental drying Composting Composting is a process in which organic material undergoes biological degradation to a stable end product. A properly composted sludge may be used as a soil conditioner in agricultural or horticultural applications or for final disposal. Sludge that has been properly composted decomposes into a sanitary, humus-like material with approximately 20 to 30 percent of the volatile solids converted to carbon dioxide and water. Raw, digested, or chemically stabilized solids may be composted. The process has also been proven effective for organic residuals from the paper, pharmaceutical, and food processing industries. The bulking agent or amendment may be a wide variety of materials including other wastes such as wood wastes, yard wastes, paper, agricultural residue, wood ash, and animal bedding. Composting is a relatively simple process that can be performed outdoors in most climates. In order to control odours, and reduce operating costs, many facilities are constructed under structures, in fully enclosed buildings, or in entirely mechanised facilities. The primary objective of composting is to produce a fertilizer-like product that can be beneficially used. The compost must meet regulatory and public health requirements and be attractive for some end use. 4.3 Development of Disposal Strategies Disposal strategies are required for each of the following categories of wastewater residuals; 1. Stabilized Material 2. Partially Stabilized Material 3. Unstabilized Material The options available for each of these material are described below. CBCL Limited Consulting Engineers Options for Treatment and Disposal 19

25 4.3.1 Stabilized Material Stabilized wastewater treatment residuals are produced at most of the mechanical secondary treatment facilities as well as the Charlottetown primary treatment facility. All of these materials are produced in the liquid form and are landspread by licensed septic tank cleaners under the current sewage disposal regulations and Atlantic Canadian Guidelines. While this is the preferred method of disposal, the current method of regulation only controls the disposal site and not the quantity and quality of material that is spread. These materials could be processed to further reduce pathogens and decrease site restrictions for application by composting or drying. However, as this material would ultimately be disposed of on similar lands as it is now, this further processing would seem unnecessary Partially Stabilized Material Partially stabilized wastewater treatment residuals are produced at wastewater lagoons and septic tanks. This material accounts for the largest volume of material produced in PEI at approximately 65% of all residual by volume. Although grouped in the same category these materials are not very similar in either their composition or their generation patterns. Therefore, they will be treated separately here. Wastewater Lagoon Residuals Wastewater lagoon residuals are a difficult material to handle because these materials are only generated periodically in large volumes over a short period of time, construction of facilities to treat this material is not practical. Also, the degree of stabilization of this material is quite high when compared with other partially stabilized material such as domestic septage. Considering that in many cases the material has accumulated over a period of greater than 20 years, in all likelihood less than 5% of the material will fail to meet stabilization requirements. Some jurisdiction will allow land spreading of wastewater lagoon residuals without further treatment. In some cases, restriction such as ph adjustment, incorporation into the soil within a specified time frame, or storage of material for six months prior to disposal have been applied. In PEI, the most effective means of managing this material will be through the disposal approval process. Each facility applying for a disposal permit could supply the volume of material, characterization data, and the disposal location. With this information, disposal operations can be approved on a case by case basis. As the amount of lagoon residual disposal that has occurred is minimal, costs are not well developed. Although a more extensive approval process would justify an increase in disposal CBCL Limited Consulting Engineers Options for Treatment and Disposal 20

26 application costs it should not have any impact on the overall cost of the disposal project. Septage Septage contains two components, a solids fraction and a liquid fraction. The solids fraction is the component requiring disposal while the liquid fraction is only removed from the tank because these two components can not be effectively separated at the source with conventional pumping equipment. The solids fraction of septage can potentially contain undesirable inorganic non-biodegradable material such as rags and plastics. A number of options exist which would result in a more stable material being landspread, thus providing for a more sustainable septage management program. These include: 1. Stabilization by alkali addition at the source 2. Co-treatment with domestic sewage 3. Composting Stabilization by alkali addition at the source involves the addition of alkali material to raise the ph of the septage-alkali mixture to greater than 12 for a minimum of 30 minutes prior to disposal. This generally requires approximately kg of hydrated lime (Ca (OH) 2 ) for every 5,000 liters of septage. This mixture can then be land spread in a manner consistent with current operation. When utilizing alkali addition at the source for stabilization, the septage hauler should have a means of removing non-biodegradable products prior to land spreading. This typically achieved by discharging septage through a simple screen or basket located on the truck between the discharge pipe and the splash plate (or ground if no splash plate installed). Collected trash should be lime stabilized and sent to a sanitary landfill. Co-treatment with domestic sewage requires a septage handling facility to be constructed at an existing wastewater treatment plant. The receiving station screens out undesirable plastics and rags and grinds up organic material before introducing the pre-treated septage into the influent of the treatment plant. Septage solids then become incorporated into the wastewater treatment plant sludge and the liquid fraction is treated and released in the effluent. For this solution to be effective the treatment plant must provide a minimum of secondary treatment and have excess capacity in both its solids and liquids processes. The introduction of septage can have negative impacts on domestic treatment plants resulting in odours, CBCL Limited Consulting Engineers Options for Treatment and Disposal 21

27 additional wear on mechanical solids pumping and processing equipment, and degradation of effluent quality. Composting of septage will also require that either a septage handling facility be constructed to dewater and pre-treat septage, or that specialized vehicles be utilized that collect only the solids fraction of the septage and return the liquid fraction to the septic tank. Septage dewatering vehicles have capital costs in excess of $300,000 and as a number of these vehicles would likely be required, this option does not seem to have much potential. Septage dewatering requires a facility to be constructed in an area serviced by a secondary treatment plant with the capacity to treat the liquid fraction of the dewatered septage. Septage would be received, screening and grinding would be performed to remove plastics, rags, etc, chemical addition would take place, followed by physical dewatering. Septage dewatering can be performed by gravity separation in screened dewatering boxes, or by mechanical dewatering equipment. The dewatered septage is then transported to the composting site where it is co-composted with municipal solid waste. When co-composting wastewater residuals and municipal solids waste it is important to monitor metal content in the wastewater residuals as the disposal criteria for compost is more restrictive than for wastewater residuals as presented in Exhibit 4.1. Typical metal contents in septage are included for comparison. Exhibit 4.1 Comparison of Metal Criteria for Compost and Wastewater Residuals Pollutant Concentration Limit (kg/ha) Typical Wastewater Criteria CCME Class A Compost CCME Class B Compost Typical Septage Composition Arsenic Cadmium Cobalt Chromium 2, , Copper 1, Lead 1, Mercury Molybdenum Nickel Selenium Zinc 4, , CBCL Limited Consulting Engineers Options for Treatment and Disposal 22

28 All three options describe above will stabilize the septage prior to landspreading. However, costs related to each option vary considerably. A comparison of capital and operating costs are included in Exhibit 4.2 Exhibit 4.2 Septage Stabilization Costs Stabilization Option Capital Cost ($) Treatment Cost ($/m 3 ) Additional Transportation Cost Alkali Stabilization < $5,000 per 5 No hauler Co-Treatment with $400, Yes Municipal Wastewater Dewatering & Composting $850, Yes Septage receiving and dewatering facilities have been designed for a capacity of 10,000 m 3 per year or roughly 65% of all septage generated on PEI. The cost differential for the three options clearly indicates a preference for alkali stabilization by the septage hauler. However, if this option is deemed unacceptable, additional costing can be performed to determine the most cost effective of the other two options Unstabilized Material Unstabilized material generated on PEI includes holding tank material and dewatered primary sludge from the Summerside Wastewater Treatment Plant. Holding tank material is considered sewage and therefore must be disposed of at a wastewater treatment plant. Residuals from the Summerside Wastewater Treatment Plant are currently co-composted with municipal solid waste at the East Prince Waste Management facility. This is an effective means of treating and disposing of this material and should continue when the composting operation is relocated to Brookfield. New wastewater treatment facilities typically are required to provide stabilization facilities on-site and therefore the volume of this material is not expected to increase. However, if additional unstabilized material is generated on PEI, dewatering and composting is the most practical and sustainable method of treatment and disposal available at this time. CBCL Limited Consulting Engineers Options for Treatment and Disposal 23