Management of Process Solids, Sludges, and Residuals

Abstract

Solids, sludges, and residuals are generated during decentralized wastewater system operations. These materials need to be properly handled, appropriately treated and safely disposed of or beneficially used. This chapter describes the different types of solids, sludges, and residuals that are often generated in decentralized systems and highlights options for treatment and disposal or use.

Slides of Chapter 15: Decentralized Water Reclamation

15.1.1 Chapter 15: Management of Process Solids, Sludges, and Residuals

Contents

• 15-1. Introduction

• 15-2. Septage

• 15-3. Waste biological solids

• 15-4. Granular media

• 15-5. Vegetation

• 15-6. Excreta and fecal sludge

• 15-7. Summary

15.1.1.1 15-1. Introduction

• ■ Solids, sludges and residuals are generated during operation and maintenance of decentralized wastewater systems

  • • Commonly encountered materials are listed in Tables 15.1 and 15.2 and include:

    Table 15.1 Characteristics of process solids, sludges and residuals that can be generated during operation and maintenance of decentralized wastewater treatment systems

    Table 15.2 Characteristics of solids and other materials that can be generated during use of decentralized wastewater treatment systems

    • ○ Septage

    • ○ Waste biological solids

    • ○ Granular media

    • ○ Vegetation

    • ○ Excreta (including diverted urine) and fecal sludge

  • • Example generation rates are given in Tables 15.3 and 15.4

    Table 15.3 Estimated quantities of solids produced in three unit operations commonly used in decentralized wastewater treatment systems

    Table 15.4 Estimates of the quantities of materials generated in source separated waste streams that can occur in decentralized wastewater treatment systems

• ■ The quantity and character of these materials can be very important and may influence the selection, design and implementation of a decentralized system

• ■ Management of solids, sludges and residuals is critical

  • • Effective management can help ensure:

    • ○ Protection of public health and environmental quality

    • ○ Beneficial recovery of organic matter, nutrients, and energy content

  • • Management encompasses:

    • ○ Proper removal, handling, and transport

    • ○ Appropriate processing, treatment and ultimate disposition

    • ○ Safe recovery and use of media with resource value

  • • Federal and state regulations can govern management

    • ○ Requirements can dictate what treatment and disposal/use options are feasible for a particular situation and set of circumstances

• ■ Focus of Chap. 15

  • • Chapter 15 is focused on the characteristics and approaches for treatment and disposal or use of:

    • ○ Septage

    • ○ Waste biological solids

    • ○ Granular media

    • ○ Vegetation

    • ○ Excreta (including diverted urine) and fecal sludge

  • • For the process principles and design of specific treatment unit operations, the reader is referred to other Chapters in this book and to design manuals and reference literature (e.g., USEPA 2003, WEF 2012, Strande et al. 2014, Tchobanoglous et al. 2014)

15.1.1.2 15-2. Septage

• ■ Description of septage

  • • Septage can be defined to include the contents removed from septic tanks, portable vault toilets, holding tanks, and similar facilities

  • • In this section, the focus is on septage removed from septic tanks

    • ○ Septage generation is discussed in Chap. 6

    • ○ Example generation rates in lb of solids per 1000 gal treated are given in Table 15.3 for a residential versus a commercial source

  • • Septage can be described as partially digested anaerobic sludge and fats, oils, and greases, and other materials that have accumulated in a septic tank during routine operation over a period of time (e.g., 3 to 10 yr or more)

• ■ Characteristics of septage

  • • Septage is typically a waste liquid with 3–10 wt.% solids

    • ○ It contains high concentrations of organics, nutrients, and microorganisms as well as grease, hair, stringy materials, and extraneous debris

  • • Septage composition

    • ○ Major constituents are listed in Table 15.5 and pathogenic microorganisms are shown in Table 15.6

      Table 15.5 Concentrations of major constituents in septage removed from septic tanks serving households (USEPA 1984, 1999)

      Table 15.6 Concentrations of microorganisms in domestic septage (USEPA 1984)

    • ○ Septage can contain trace organic compounds (Table 15.7)

      Table 15.7 Concentrations of ten trace organic compounds observed in septic tank solids from residential dwellings and commercial and institutional establishments (after Conn et al. 2006)

    • ○ For some commercial or institutional sources, septage can contain higher levels of organics and heavy metals

    • ○ The composition of septage can vary widely between different sources and even from load to load from the same source

• ■ Treatment and disposal/use of septage

  • • In the United States, septage management is specified in Federal (40 CFR Part 503) and State requirements

    • ○ Management programs vary by states and municipalities

    • ○ Tracking or manifest systems help prevent illegal dumping

    • ○ Procedures help ensure proper treatment and disposition

  • • Two options are commonly used for treatment and disposal/use of septage in the United States

    • ○ Land application and potential integration with agriculture

    • ○ Treatment at a municipal wastewater treatment plant

    • ○ Tables 15.8 and 15.9 highlight these two options and Fig. 15.1 presents several illustrative photographs

      Table 15.8 Two options commonly used for treatment and disposal/reuse of septage in the United States

      Table 15.9 Land application approaches for septage produced in the United States (USEPA 1999)

      Fig. 15.1

      

      Photographs of septage removal and management options

  • • Septage can also be treated in dedicated treatment operations to enable safe disposal or use

    • ○ The primary goal is to stabilize the septage by removing excess liquid, decomposing organic matter, and destroying pathogens

      • * Once stabilized, the treated septage may be used as a soil amendment, be land applied, or be landfilled

      • * Disposition depends on the requirements of applicable regulations and the local situation

    • ○ Examples of treatment operations used for septage in the United States and similar countries are presented in Table 15.10

      Table 15.10 Example treatment operations used for septage produced in the United States (USEPA 1999)

    • ○ Due the pervasive use of septic tanks in urbanized areas in developing countries, specialized approaches such as outlined in Table 15.11 have been developed and used under these circumstances

      Table 15.11 Example treatment approaches for septage produced in developing regions^a

  • • Treatment of septage and other wastewater solids can generate biosolids

    • ○ “Biosolids are the nutrient-rich organic materials resulting from the treatment of sewage sludge (the name for the solid, semisolid or liquid untreated residue generated during the treatment of domestic sewage in a treatment facility)”^a

    • ○ Biosolids are categorized into levels based on the residual levels of pathogens and heavy metals after treatment (Tables 15.12 and 15.13)

      Table 15.12 Classification of biosolids generated from sludge treatment in the United States

      Table 15.13 Pathogen density standards for biosolids classification in the United States (CFR 40 Part 503)

    • ○ Biosolids are intended to be used as a soil amendment or integrated into agricultural applications for recovery of organic matter and nutrient content (Fig. 15.2)

      Fig. 15.2

      

      Class A biosolids produced from wastewater treatment plant sludge in Chicago, Illinois (source: Chicago Tonight, 11 Aug 2014)

      ^a Source: http://water.epa.gov/polwaste/wastewater/treatment/biosolids/

  • • Composting as a treatment operation to produce biosolids

    • ○ Compositing is an aerobic thermophilic biological process involving bacteria, fungi, and actinomycetes

      • * Composting can be accomplished using within-vessel, static aerated pile, or open windrow operations (Figs. 15.3 and 15.4)

        Fig. 15.3

        

        Photographs of septage composting using (a) in-vessel or (b) windrow composting. (Photographs courtesy of Robert Rubin)

        Fig. 15.4

        

        Photograph of aerated bin composting of septage along with fats, oils and greases. (Photograph courtesy of Robert Rubin)

      • * Composting at high temperature for a minimum period of time can stabilize organic solids and reduce pathogen levels (Table 15.14)

        Table 15.14 Time and temperature requirements for composting of wastewater solids in the United States according to 40 CFR Part 503

15.1.1.3 15-3. Waste Biological Solids

• ■ Description of waste biological solids

  • • Waste biological solids are produced in different unit operations for wastewater treatment

    • ○ Waste activated sludge (WAS) is produced during suspended or attached growth in aerobic treatment units (Chap. 7) and membrane bioreactors (Chap. 9)

    • ○ Waste biological solids are also produced due to attached growth and sloughing that can occur in recirculating porous media biofilters (Chap. 8)

  • • Example generation rates in lb of solids per 1000 gal treated are given in Table 15.3 for a residential versus a commercial source

• ■ Characteristics of waste biological solids

  • • WAS consists of biomass and organic and inorganic solids in a wastewater liquid matrix at a concentration of 1–2 % by wt.

    • ○ The generation rate and composition of WAS varies widely depending on the wastewater being treated and the type and operational features of the unit operation in which it is generated, including:

      • * Influent wastewater composition and BOD removal efficiency desired

      • * Suspended growth versus attached growth

      • * Solids retention time, temperature, and mixed liquor volatile suspended solids concentration in the bioreactor

    • ○ Tables 15.15 and 15.16 present basic composition data for WAS

      Table 15.15 Concentrations of major constituents in waste activated sludge removed from activated sludge systems receiving domestic wastewaters^a

      Table 15.16 Concentrations of microorganisms in waste activated sludge

    • ○ Heavy metals and trace organic compounds (see Table 15.7) can also be present, particularly during treatment of commercial and institutional wastewaters

  • • Waste biological solids also can be generated in some recirculating porous media biofilters

    • ○ The microorganisms attached to the porous media can grow to the point where there is excess biomass that intermittently or continuously sloughs off the media

    • ○ There is limited data on the quantity and composition of these biomass solids as they are often retained and removed in other solids handling operations

      • * e.g., pumped out and removed along with septage as it is pumped from an upstream septic tank, the effluent from which is the influent to the PMB

    • ○ It would seem the quantity of PMB biomass that sloughs off per unit volume of wastewater treated would be much lower than that of WAS while the composition could be equal or more concentrated

• ■ Treatment and disposal/use of waste biological solids

  • • In the United States, management of waste biological solids is specified in Federal (40 CFR Part 503) and State requirements

  • • Options for management are similar to those used for septage and include:

    • ○ Land application and potential integration into agriculture

    • ○ Treatment at a wastewater treatment plant

    • ○ Treatment in a specialized sludge treatment facility (e.g., a composting operation)

  • • Tables 15.8, 15.9, 15.10, 15.11, and 15.14 provide a description of each of these methods

15.1.1.4 15-4. Granular Media

• ■ Description of granular media solids and residuals

  • • Varied types of granular material used in unit operations can become waste products or treatment residuals, e.g.:

    • ○ The top few inches of a single pass sand filter that becomes clogged with a biomat and requires replacement

    • ○ Filtralite P or Polonite^® mineral media from a packed bed that is used for phosphorus sorption and the media becomes exhausted and requires replacement

    • ○ Media from a peat biofilter that is spent and requires replacement

• ■ Characteristics of granular media solids and residuals

  • • The quantities and characteristics of granular media waste products and treatment residuals is highly varied

    • ○ Table 15.17 and Fig. 15.5 provide some insight through a few examples

      Table 15.17 Examples of granular media solids and residuals generated during decentralized wastewater treatment and water reclamation^a

      Fig. 15.5

      

      Illustration of granular media solids and residuals that might be generated during maintenance functions for an old soil absorption system or a single pass sand filter

• ■ Treatment and disposal/use of granular media solids and residuals

  • • Feasible options depend on the type of media involved (Table 15.17) and applicable Federal and state regulations

    • ○ Some media will most often be disposed of as a fill material for construction or land development or as a solid waste for landfilling, e.g.:

      • * Gravel removed from a hydraulically failed soil absorption system

      • * Sand removed from the clogged infiltrative surface zone of a single pass sand filter

    • ○ Some media can be regenerated and reused, e.g.:

      • * Filtralite P or Polonite® granules that were used as a sorbent for P could be processed (e.g., storage for a period of time) and then used as a source of P in agriculture

      • * GAC media that was used as a sorbent for trace organic chemicals could be regenerated and reused as a sorbent

15.1.1.5 15-5. Vegetation

• ■ Description of vegetation

  • • Vegetation grows during certain types of wastewater treatment

    • ○ Vegetation grows in constructed wetlands and other plant-based systems as well as during landscape drip dispersal

    • ○ Vegetation may or may not need to be cut and removed from the site to enable normal operation

    • ○ However, for true long-term removal of organic matter and nutrients from a site, vegetation generally needs to be cut and removed periodically

  • • Vegetation is often present and important to processes that occur during land application of different wastewater solids and sludges

    • ○ Vegetation that grows in a wastewater solids or sludge amended setting is often used for beneficial purposes (e.g., animal grazing, food crops)

• ■ Characteristics of vegetation

  • • The types of vegetation vary depending on the system

    • ○ Vegetation that grows in constructed wetlands can include various types of macrophytes

    • ○ Vegetation that grows in some plant-based systems and areas with landscape drip dispersal can include various types of grasses, shrubs, and trees (e.g., willow trees)

    • ○ Vegetation that grows in areas that are amended with waste solids and sludges or irrigated with reclaimed water can include various types of grasses and crops

  • • The quantity and characteristics of vegetation generated during routine operation varies based on situation-specific factors include growing conditions and harvesting methods

    • ○ In general the quantity of vegetation harvested for common unit operations (e.g., constructed wetlands, soil treatment units, landscape drip dispersal units) will be limited

• ■ Treatment and disposal/use of vegetation

  • • Trees that are removed from a site can be chipped and used as a source of bioenergy in chip burning systems

  • • Grasses and small woody species can be processed through composting in a fashion similar to yard waste

    • ○ Processing and treatment can occur at the household or small business scale or in a more centralized location

    • ○ Composting is a common method that can be used and includes:

      • * Cutting and chopping to reduce the particle size of the materials

      • * Mixing the vegetation with an organic matter

      • * Composting and aerobic biodegradation

        • – Need to provide for proper moisture content, carbon:nitrogen ratio, and oxygen levels over a sufficient period of time

      • * Use of the compost product as a soil amendment

  • • Vegetation that grows at a site that is amended with wastewater solids or sludges or irrigated with reclaimed water

    • ○ Methods of treatment and disposal/use depend on the situation and what, if any, beneficial outcome there is for the vegetation

      • * Example beneficial outcomes include:

        • – Where vegetation can be used for grazing or feeding animals

        • – Where vegetation is a food crop for humans

    • ○ Treatment of the vegetation generated may or may not be required based on the intended use and the composition of the vegetation (heavy metals, trace organics)

    • ○ At a minimum, there are normally waiting periods before the vegetation is used

      • * In the United States, the 40 CFR Part 503 Rules specify waiting periods between biosolids application ends and the crop can be harvested that range from 30 days for animal grazing to 38 months for crops consumed raw

15.1.1.6 15-6. Excreta and Fecal Sludge

• ■ Description of excreta and fecal sludge^a

  • • Excreta including diverted urine

    • ○ Excreta consists of the human wastes generated during use of waterless toilets (Table 15.18, Fig. 15.6)

      Table 15.18 Features and functions of several waterless toilet options^a

      Fig. 15.6

      

      Photographs of a few waterless toilet options

    • ○ Urine diverting toilets can be used to capture urine separately and enable its processing for nutrient recovery (N, P, K, S)

    • ○ Waterless toilets and urine diverting toilets are widely used in some regions of the world but so far they have been infrequently used in houses and businesses in the United States and many other developed countries

    • ○ Example generation rates for excreta and diverted urine are given in Table 15.4

      ^a Note: Chapter 4 describes source separation and the use of alternative toilet systems including waterless toilets and urine diverting toilets.

  • • Fecal sludge

    • ○ One definition is broad and encompasses more than just excreta:

      “Faecal sludge (FS) comes from onsite sanitation technologies, and has not been transported through a sewer. It is raw or partially digested, a slurry or semisolid, and results from the collection, storage or treatment of combinations of excreta and blackwater, with or without greywater. Examples of onsite technologies include pit latrines, unsewered public ablution blocks, septic tanks, aqua privies, and dry toilets. Faecal sludge management (FSM) includes the storage, collection, transport, treatment and safe enduse or disposal of FS. FS is highly variable in consistency, quantity, and concentration.”—Strande et al. (2014)

    • ○ In Chap. 15, the definition of fecal sludges is restricted as follows:

      • * Fecal sludge consists of human wastes combined with a very small volume of water and it is generated when flush water is used and the toilet is connected to a vault or tank

      • * Example toilets include pour-flush toilets and ultra low-volume gravity- or vacuum-flush toilets that can use only 0.2–0.5 gal of water per flush

• ■ Characteristics of excreta

  • • Excreta

    • ○ The quantity and composition of excreta depends on the age, health status, diet, and activity of the individual

      • * Example generation rates are given in Table 15.4

    • ○ Tables 15.19 and 15.20 present data on the basic characteristics of excreta as well as graywaters

      Table 15.19 Water and nutrient loads contributed in separated sources with no dilution for urine and feces (Otterpohl et al. 2003)

      Table 15.20 Mass loadings per capita for organic matter and nutrients in blackwater (urine and feces) as measured in the United States and Norway and reported elsewhere in Europe

  • • Feces alone

    • ○ An individual can excrete about 80–200 lb/year/cap of fecal solids with a moisture content of 50–90 % by wt. (Table 15.4)

    • ○ Feces is typically made up of microorganisms, undigested food and fiber, fats, proteins, and inorganic matter

    • ○ Microorganisms in feces are mostly high numbers of nonpathogenic bacteria but pathogens can be present (Table 15.21)

      Table 15.21 Incidence and concentration of enteric viruses and protozoa in feces in the United States

  • • Urine alone

    • ○ An individual can excrete about 80–200 gal/year/cap of urine each year (Table 15.3)

    • ○ Urine is an aqueous solution (>95 % water) of dissolved constituents including: urea, Cl, Na, K, and other dissolved ions plus inorganic and organic compounds (proteins, hormones, metabolites)

    • ○ Microorganisms can be present in urine depending on the health status of the individual generating the urine

      • * Urine in the bladder is normally sterile

        • – However, during passage through the urinary tract urine can pick up microorganisms

      • * If an individual has an infection his/her urine can contain infectious microorganisms

      • * Table 15.22 presents the estimated level of pathogens in urine and the importance of urine as a transmission route for infectious disease

        Table 15.22 Pathogens that may be excreted in urine (WHO 2006)

  • • Diverted urine

    • • The composition of urine generated through use of urine-diverting toilets (UDT) contains substantial concentrations of valuable nutrients (N, P, K, S) (Table 15.19)

      • * But urine from UDTs can also contain pathogens and trace organic compounds

    • ○ Pathogens in urine

      • * The composition depends on the users health status and the potential for fecal contamination of the urine generated

      • * If an individual has an infection, pathogens can be excreted in his/her urine (Table 15.22)

      • * The occurrence of pathogens in urine is also highly dependent on the level of fecal contamination of the urine

        • – Fecal contamination of urine is relatively common in UDTs and can result in fecal pathogens being present in diverted urine

    • ○ Urine can contain trace organic compounds including endocrine disrupting substances

      • * Substances can be biogenic in origin or result from the use of pharmaceuticals and personal care products

      • * The compounds present and their concentrations depend on the users generating the urine and their personal behaviors

      • * The following are examples of the substances that have been reported (Mitchell et al. 2013)

        • – Caffeine—stimulant

        • – Carbamazepine—anticonvulsant

        • – Ibuprofen, Naproxen—analgesic anti-inflammatory

        • – Estrone, Estriol—estrogens

        • – 4-acetamidophenol—analgesic

        • – Triclosan—anti-bacterial and anti-fungal

        • – Diclofenac—anti-inflammatory

  • • Fecal sludge

    • ○ The composition of fecal sludge generated from ultra low-volume water-flush toilets depends on two major factors

      • * The type of excreta contributed (feces alone or feces plus urine) and its composition

      • * The volume of water used per flush

    • ○ An estimate of fecal sludge composition can be made using the data given in Tables 15.19, 15.20, and 15.21

      • * An adjustment to the concentrations in fecal sludge can be made for the volume of dilution water added from the use of a specific type of water-flush toilet

• ■ Treatment and disposal/use of excreta or fecal sludge

  • • Treatment during accumulation and storage

    • ○ In some waterless toilet designs human waste can undergo varying degrees of decomposition during periods of accumulation and holding

      • * For example during holding in a ventilated or aerated vault there can be evaporation of water, a degree of biological degradation, and some inactivation of pathogens

    • ○ In some waterless toilet designs heat can be added to help evaporate excess liquid

      • * For example, some types of composting toilets can have an electric heating element that is used to heat the human wastes during holding

    • ○ Table 15.23 presents data on die-off of pathogens in feces during storage and in soil and Table 15.24 presents guidance on the required storage prior to use of excreta and fecal sludges

      Table 15.23 Estimated pathogen survival times during storage of feces and in soil (WHO 2006)

      Table 15.24 Recommendations for storage treatment of dry excreta and fecal sludge before use at the household or municipal levels (WHO 2006)

  • • Treatment of exreta or fecal sludge after removal

    • ○ For most toilet system designs, excreta and fecal sludge are typically removed from a self-contained waterless toilet or an associated vault or holding tank

      • * For example, a vault used with dry toilets may be emptied mechanically by pumping (or manually by excavation in developing regions) when the vault becomes full of human waste

    • ○ Depending on the toilet design and storage conditions further treatment may be required before safe disposal or use

      • * Tables 15.8, 15.9, 15.10, 15.11, and 15.14 present several treatment and disposal/use options for septage and waste activated sludge and under some circumstances these same options can be appropriate for excreta and fecal sludges

      • * Table 15.25 presents several low cost options for treatment of fecal sludges that have been recommended for applications in developing regions

        Table 15.25 Low cost options for treatment of fecal sludge in developing regions (WHO 2006)^a

  • • Safe use of treated excreta and fecal sludge

    • ○ What is considered “safe” and suitable for a specific end use depends on the situation and risks as well as applicable regulatory requirements

      • * e.g., WHO recommendations for safe use of treated excreta and fecal sludge in agriculture are given in Table 15.26

        Table 15.26 WHO guidelines for use of excreta and fecal sludge in agriculture (WHO 2006)

• ■ Treatment and disposal/use of diverted urine

  • • Treatment during accumulation and storage of urine

    • ○ Diverted urine is normally collected in a container

      • * During storage, urea and other organics in urine are degraded by bacteria

      • * NH₃ is released and the pH increases to 9 or higher

    • ○ Due to the high pH that develops during storage, urine can undergo changes in composition

      • * Significant N may be lost by volatilization in open containers

      • * Some P will precipitate out as calcium phosphate solids

      • * Pathogens can be killed or inactivated

      • * Some trace organics can be degraded but pharmaceutical residues can persist

  • • Treatment after urine is collected

    • ○ Treatment during simple longer-term storage

      • * Recommended storage times for urine based on pathogen content and use as a fertilizer are given in Table 15.27

        Table 15.27 Recommended guideline for storage times for urine mixture based on estimated pathogen content and recommended crop for larger systems^a

      • * It is also recommended that urine be carefully incorporated into soil as a fertilizer to avoid volatilization and loss of NH₃

    • ○ Treatment by different processes prior to disposal/use

      • * Physicochemical processes have been tested including:

        • – Combined electrodialysis, microfiltration, ozonation

        • – Phosphorus recovery by struvite precipitation

        • – Ammonia stripping

        • – Acidification and solar evaporation

        • – Nitrification/distillation

        • – Electrolysis

      • * However, as of this writing full-scale applications of these processes have been very limited

15.1.1.7 15-7. Summary

• ■ Solids, sludges and residuals are generated during operation and maintenance of decentralized systems and include:

  • • Septage and waste biological solids

  • • Granular media from various unit operations

  • • Vegetation that is cut and harvested

  • • Excreta and fecal sludge and diverted urine

• ■ Effective management is critically important to ensure:

  • • Protection of public health and environmental quality

  • • Recovery of organic matter, nutrients, and energy content

• ■ Treatment can occur during accumulation and storage and by an array of unit operations and systems to enable safe disposal or beneficial use