Wastewater Sludge

Physical and Biological Properties

Mass Balance Calculation Wastewater

Raw primary sludge particle size distribution is greater than 7 mm (5 to 20 ), 1 to 7 mm (9 to 33 ), and smaller than 1 mm (50 to 88 ), of which about 45 is less than 0.2 mm. In activated sludge, the approximate distribution is 90 below 0.2 mm, 8 between 0.2 and 1 mm, 1.6 between 1 and 3 mm, and 0.4 over 3 mm. The organic part of the sludge decays more rapidly, with an increase in the quantity of finely dispersed and colloidal particles and bound water resulting in a decrease in the separation...

Chemical Conditioning

Thickener Cross Section

Chemical conditioning is the most common conditioning process for sludge thickening and dewatering. Conditioning by adding chemicals can be viewed as coagulation or flocculation by neutralization of colloidal surface charge by oppositely charged organic polymers or inorganic chemicals. Particle size is the most important characteristic of the dewaterability of sludge. By adding chemicals, the particle size increases and the bound water decreases. Different sludges have different dewatering...

Dry Lime Stabilization

In dry lime stabilization (also known as postlime stabilization), dry lime (hydrated lime or quicklime) is mixed with dewatered sludge cake to raise the pH of the mixture. The process requires adequate mixing to avoid pockets of putrescible material and to produce a homogeneous mixture. An effective mixer is a pug mill in which two screw conveyors or paddle mixers rotate in opposite directions. Other types of mixers include plow blender, paddle mixer, and screw conveyor. Figure 6.3 shows the...

Dewatered Sludge Percent Solids

Figure 6.4 Theoretical quicklime dosages for class A and class B dry lime stabilization. lower line shows the dose required for class B pH requirements, and the upper line shows the dose for class A temperature requirements. The figure shows that the quicklime requirement for class B stabilization theoretically increases with increased solids, whereas the quicklime requirement for class A stabilization decreases with increased solids. This is because of the predominance of the heating...

Dry Lime Mixing

Mixing of dewatered sludge cake and lime (or other alkaline materials) is the most critical component of dry lime stabilization. The goal is to provide intimate contact between the sludge cake and lime and to produce a homogenized product. The mixing step is typically accomplished using a mechanical mixer such as a pug mill, plow blender, paddle mixer, or screw conveyor. Dewatered sludge and lime are introduced at the head end of the mixer. Sludge cake with a low moisture content and in large...

References

AWWA (1983), Standard for Quicklime and Hydrated Lime, AWWA B202-83, American Water Works Association, Denver, CO. Bitton, G., et al. (1980), Sludge Health Risks of Land Application, Ann Arbor Science Publishers, Ann Arbor, MI. Christensen, G. L. (1982), Dealing with the Never-Ending Sludge Output, Water Engineering and Management, Vol. 129, p. 25. -(1987), Lime Stabilization of Wastewater Sludge, in Lime for Environmental Uses, Gutschick, K. A. (Ed.), ASTM, Philadelphia. Farrell, J. B., et al....

The Main Advantages of Sludge Drying Beds

Table Screen Draining

Drying beds are the most widely used method of municipal wastewater sludge dewatering in the United States. They have been used for more than 100 years. Although the use of drying beds might be expected in small plants and in warmer, sunny regions, they are also used in several large facilities and in northern climates. In the United States, a majority of wastewater treatment plants with less than 5-mgd capacity use drying beds for biosolids dewatering.

Sludge Quantities And Characteristics

Various Types Sludge Treatment

2.1.4 Other wastewater residuals 2.2.4 Attached growth system sludge 2.3.3 Physical and biological properties Municipal wastewater is generated not only from the domestic use of water, but also from commercial establishments and from industries such as chemical or petrochemical, food and beverage processing, metal processing, pulp and paper, textile, automobile, and pharmaceutical. Therefore, the characteristics of wastewater vary from one municipality to another based on the unique mix of...

Chemical Sludge

Chemicals are widely used in wastewater treatment to precipitate and remove phosphorus and in some cases to improve the efficiency of suspended solids removal. Chemicals can be added to raw wastewater, to a secondary biological process, or to secondary effluent, in which case tertiary filters or tertiary clarifiers are used to remove the chemical precipitates. Although theoretical rates of chemical sludge production can be estimated from the anticipated chemical reactions, competing reactions...

Introduction

Thickening is a process to increase the solids concentration of sludge and decrease its volume by removing a portion of the water. The thickened sludge remains in the fluid state and is capable of being pumped without difficulty. The purpose of reducing the volume by thickening is to increase the efficiency and decrease the costs of subsequent sludge-processing steps. Thickening of waste activated sludge is important because of its high volume and low solids concentration. Thickening from 1...

Belt Filter Press

Belt Conveyor System For Biosolids

A belt filter press (BFP) is a continuous-feed sludge dewatering machine with two porous moving belts that has a gravity drainage zone and mechanically applied pressure zones. Belt filter presses have been used in Europe first for dewatering paper pulp and later modified to dewater wastewater sludge. It was introduced in North America in the mid-1970s, mainly because of its ability to dewater secondary sludge economically, and its reduced energy requirements compared to centrifuges and vacuum...

Supernatant

Supernatant from an anaerobic system generally contains high concentrations of dissolved and suspended solids, organic materials, nitrogen, phosphorus, and other materials. When returned to the treatment plant influent, these materials may impose an extra load on the liquid treatment processes. Table 5.6 presents reported characteristics of supernatant from two-stage digestion systems at different wastewater treatment plants. These characteristics represent a summary of the wide range of data...

Liquid Lime Stabilization

Image Stabilisation Method Using Lime

In liquid lime stabilization (also known as prelime stabilization), lime slurry is mixed with liquid sludge to produce class B biosolids. Figure 6.2 is a schematic of a liquid lime stabilization system. This is usually a batch treatment system in which the contact tank for mixing lime slurry with liquid sludge is Figure 6.2 Typical liquid lime stabilization process schematic. Figure 6.2 Typical liquid lime stabilization process schematic. sized, based on the quantity of sludge and the number of...

Incineration

Story Car Garage With Apartment

Incineration is complete combustion, which is the rapid exothermic oxidization of combustible elements in sludge. Dewatered sludge will ignite at temperatures of 420 to 500 C (788 to 932 F) in the presence of oxygen. Temperatures of 760 to 820 C (1400 to 1508 F) are required for complete combustion of organic solids. In the incineration of sludge, the organic solids are converted to the oxidized end products, primarily carbon dioxide, water vapor, and ash. Particulates and other gases will also...

Design Considerations

The most important aspects of the design of a thermal drying system are discussed in the following sections. Moisture Content of Feed Sludge Thermal evaporation of water from sludge requires considerable energy. The amount of fuel required to dry sludge depends on the amount of water evaporated. As mechanical dewatering methods are more efficient than thermal drying methods per volume of water removed, it is imperative that a dewatering step precede thermal drying so that overall energy...

Methods of Thermal Drying

Thermal Heat Flow Collision

Dryers are commonly classified on the basis of the predominant method of transferring heat to the wet solids being dried. These methods are convection (direct drying), conduction (indirect drying), radiation (infrared drying), or a combination of these. In convection (direct drying), heat transfer is accomplished by direct contact between the wet sludge and hot gases. The heat of the inlet gas provides the latent heat required for evaporating the liquid from the sludge. The vaporized liquid is...

B Cross Section of a rectangular tank Figure 311 Dissolved air flotation system

Settling Tank Figures

The floatation tank can be circular or rectangular and made of steel or concrete. Smaller tanks are usually steel and come completely assembled. For large installations requiring multiple tanks or large tanks, concrete tanks are more economical. Rectangular tanks have several advantages over circular units. In rectangular tanks, skimmers skim the entire surface and the flights can be closely spaced, allowing more efficient skimming. In a rectangular tank, bottom sludge flights are usually...

Pressure Filter Press

Minute Set Bulked Sludge Wastewater

Pressure filter press dewatering is a batch process in which dewatering is achieved by forcing the water from the sludge under high pressure. It produces a cake that is drier than that produced by any other dewatering alternative. Another advantage is that the high solids capture results in good filtrate quality. Disadvantages include high capital cost, relatively high operation and maintenance costs, high chemical costs, and a large area requirement for the equipment in small wastewater...

Process Theory

Aerobic digestion of excess activated sludge may be considered to be a continuation of the activated sludge process. Figure 4.1 illustrates this process graphically. When the soluble substrate (food) is completely oxidized by the microbial population, the microorganisms begin to consume their own protoplasm to obtain the energy for cell maintenance. This phenomenon of Figure 4.1 Relationship among BOD, MLVSS, oxygen utilization, and nutrients. (From Lue-Hing et al., 1998.) Figure 4.1...

InVessel Process

Reactores Horisontales Para Compostaje

An in-vessel composting system is a confined process in which composting is accomplished inside an enclosed container or basin. It produces a more stabilized and consistent product in less process time because of its ability to control environmental conditions, such as airflow, temperature, and oxygen concentration. It also affords better containment and control of odors. Detention time in a reactor varies from 10 to 21 days depending on the system supplier's recommendations, regulatory...

Pathogen and Vector Attraction Reduction

Pathogens are disease-causing organisms such as certain bacteria, fungi, viruses, protozoans and their cysts, and intestinal parasites and their ova. Vector attraction is the characteristic of sewage sludge that attracts rodents, flies, mosquitoes, or other organisms capable of transporting infectious agents. Subpart D of Part 503 covers alternatives for reducing pathogens in sewage sludge and domestic septage, as well as options for reducing the characteristic of sewage sludge that attracts...

Anaerobic Digestion173

5.1.1 Advantages and Disadvantages, 174 5.1.2 Theory of Anaerobic Digestion, 175 5.2.1 Solids and Hydraulic Retention Times, 177 5.3.3 Thermophilic Digestion, 185 5.4.3 Solids Retention Time, 189 5.4.4 Volatile Solids Reduction, 190 5.5 System Component Design, 191 5.6 Operational Considerations, 205 6.1.1 Advantages and Disadvantages, 214 6.2.1 Liquid Lime Stabilization, 217 6.2.2 Dry Lime Stabilization, 218 6.2.3 Advanced Alkaline Stabilization Technologies, 220 6.3.1 Sludge Characteristics,...

Aerated Static Pile Process

Part The Hair Detailed Look

The identifying feature of the aerated static pile system is a grid of aeration piping for forced aeration. A blower or fan aerates the pile. The aerated static pile process consists of mixing of dewatered sludge with a bulking agent (usually, wood chips), construction of the composting pile over the grid of aeration piping, composting, screening of the compost, and curing and storage. Figure 7.5 shows an aerated static pile process of composting. The aeration grid is usually made of 100- to...

Advanced Alkaline Stabilization Technologies

Technologies using materials other than lime for alkaline stabilization have been used by a number of municipalities. These technologies are modifications of traditional dry lime stabilization, and most of them use materials such as cement kiln dust, lime kiln dust, portland cement, or fly ash. The most common modifications are the supplemental drying and addition of other chemicals or bulking agents. The principal advantages of advanced alkaline stabilization processes include (1) the product...

Examples Of Composting In Europe

Minute Set Bulked Sludge Wastewater

Several examples of different types of composting systems that have been in use in Europe are described below. All these systems are open-air processes, mostly on asphalt pavements. In Finland, two wastewater treatment plants (city of Lappeenranta and city of Loensiy) compost sludge mixed with ground bark as the bulking agent at a ratio of 1 1 by volume in 3-m-high windrow piles. Every three weeks, piles are shoveled over by scoop loader. After two weeks of processing the temperature rises to...

Autothermal Thermophilic Aerobic Digestion

Aerobic Digester

Autothermal thermophilic aerobic digestion (ATAD) is a sludge digestion process that is capable of achieving a high degree of stabilization and pathogen reduction. The process is characterized by high reaction rates achieved at a thermophilic temperature of 40 to 70 C. The temperatures are attained by using the heat released by the exothermic microbial oxidation process. Approximately 15,000 kJ of heat is generated per kilogram of volatile solids destroyed. In a completely mixed and aerated...

Technological Improvements

Cabinetry Detail Drawings

The principal author of this book, together with the Medical Hygiene Institute in Russia and several wastewater treatment plants, conducted research on aerobic sludge digestion (Turovskiy, 2001). The object of this research was to obtain sanitarily harmless biosolids with an effective sludge digestion technology that was also cost-effective. Thickening Experiments with activated sludge thickening were conducted with samples from treatment plant thickeners using simulators. The thickening of...

System Design Considerations

Factors that must be considered in designing conventional aerobic digesters include method of operation, tank volume and detention time, tank design, and aeration and mixing equipment. Typical design criteria for aerobic digestion are presented in Table 4.1. Method of Operation The two primary operational modes for conventional aerobic digesters are batch or continuous operation, referring to the manner in which supernatant is withdrawn from the process. Figure 4.3 shows cross sections of...

Activated Sludge

In an activated sludge process, the important variables in quantifying the sludge produced that must be wasted daily are the amount of substrate (BOD or COD) removed, the mass of microorganisms in the system, and the non-biodegradable inert suspended solids in the influent to the system. Figure 2.4 shows a typical activated sludge system with these and other variables noted. The variables can be assembled into two simple equations as follows Px net growth of biomass expressed as volatile...

Theoretical Aspects Of Composting

The Composting Process

For the best results in a composting process, it is important to have appropriate mixing of sludge cake with bulking agents and recycled materials. For the process to operate in good condition, it needs to have the optimum mass balance, moisture, temperature, pH, nutrients, and air. Figure 7.11 shows a mass balance diagram that can be used for all three composting systems windrow, aerated static pile, and in-vessel. In the diagram A' weight of ready compost in one day A weight of recycled...

Process Design Considerations

Factors that govern the process design of conventional aerobic digesters include feed sludge characteristics, temperature, volatile solids reduction, oxygen requirements, and mixing. Other system design considerations and operational considerations are discussed later in this chapter. Feed Sludge Characteristics Because the aerobic digestion process is similar to the activated sludge process, the same concerns, such as variations in influent characteristics and materials that are toxic to...

Examples Of Composting In The United States

Aerated Static Pile Composting

In the United States, studies of windrow and aerated static pile composting were conducted in the mid-1970s in Beltsville, Maryland, and in Carson, California. As of 2003, there were more than 200 wastewater sludge composting facilities in the United States. Most of the composting facilities are aerated static pile systems, and some are in-vessel systems. Windrow composting is rarely used because of the potential odor generation and the large area requirement. The city of Eustis, Florida, uses...

Other Wastewater Residuals

In addition to sludge, three other residuals are removed in wastewater treatment process screenings, grit, and scum. Although their quantities are significantly less than those of sludge in volume and weight, their removal and disposal are very important. Screenings include relatively large debris, such as rags, plastics, cans, leaves, and similar items that are typically removed by bar screens. Quantities of screenings vary from 4 to 40 mL m3 (0.5 to 5 ft3 MG) of wastewater. The higher...

Surface Disposal

A surface disposal site is an area of land on which wastewater solids are placed for disposal. Examples of surface disposal practices include the following Sludge-only landfills (monofills) Sludge lagoon used for final disposal Surface application sites where wastewater solids are applied at rates in excess of the agronomic rate Surface disposal of wastewater solids differs from land application in that it principally uses the land for final disposal instead of using the solids to enhance the...

Composting Process

Aerobic Composting Process

Composting of wastewater sludge is an aerobic biothermal process that decomposes the organic constituents. It can be described by the formula C6H12O6 + 6O2 6CO2 + 6H2O + 674 kcal It can also be performed as an anaerobic process described by the formula The aerobic process provides a higher caloric content. It goes much faster than the anaerobic process, and decomposition of the organic constituents produces a stable humuslike material. Microbiology Composting represents the combined activity of...

Organic Content

In general, the higher the sludge's organic content, the greater the quantity of heat released during composting. This greater quantity of heat results in the thermophilic phase (55 to 65 C) being reached earlier in the composting process. Raw sludge typically contains 60 to 80 organic material while digested sludge contains only 30 to 50 organic material. Since raw sludge (from primary clarifiers and secondary clarifiers) contains more organic material than digested sludge, it is reasonable to...

High Rate Digestion

In the 1950s, several improvements to low-rate digestion were developed, resulting in a high-rate anaerobic digestion system. Heating, auxiliary mixing, thickening the raw sludge, and uniform feeding, the essential elements of a high-rate digestion system, act together to create a uniform environment. As a result, the tank volume is reduced and the stability and efficiency of the process are improved. Figure 5.6 shows the basic layout of this system. Heating Heating is essential because the...

Two Stage Digestion

Supernate Wastewater

Two-stage digestion is carried out in a high-rate digestion tank coupled in series with a second tank (sometimes called a secondary digester), as shown in Figure 5.7. The second tank is neither heated nor mixed. Its main function is to allow gravity concentration of digested solids and decanting of supernatant liquor. Decanting reduces the volume of digested sludge, requiring further processing and disposal. A secondary digester fitted with a floating cover can also provide storage for digested...

Solids and Hydraulic Retention Times

The most important factor in sizing the anaerobic digester is that the bacteria be given sufficient time to reproduce and metabolize volatile solids. The key parameters in providing sufficient time are the solids retention time (SRT), which is the average time the solids are held in the digester, and the hydraulic retention time (HRT), which is the average time the liquid sludge is held in the digester. They can be defined operationally as follows SRT, in days, is equal to the mass of solids in...

Windrow Process

In the windrow process, dewatered sludge mixed with a bulking agent is formed in long parallel rows or windrows. The width of a typical windrow is 2 to 4.5 m (6 to 14 ft) at the base and the height is 1 to 2 m (3 to 6.5 ft). Depending on the characteristics of the equipment used for mixing and turning of the windrows, the cross section of the pile may be triangular or trapezoidal. Windrow composting is commonly performed at open outdoor sites. However, in areas of significant precipitation, it...

Attached Growth System Sludge

The microorganisms in attached growth secondary treatment systems such as trickling filters and rotating biological contactors (RBCs) are biochemically similar to microorganisms that predominate in activated sludge systems. Consequently, the biomass production from attached growth systems and activated sludge systems is roughly similar when compared on the basis of kilogram of biomass produced per kilogram of substrate removed. Therefore, equations that predict solids production in an attached...

Composting

In sludge composting, a biothermal process takes place in which microorganisms reduce the sludge organics. This aerobic process is accompanied by a rise in temperature to 50 to 72 C and a decrease in the moisture content of the sludge. The quantity of sludge organics reduced during composting averages 25 . The reduction of 1.0 kg of sludge organic creates an average 21 MJ of heat. Taking into account the heat losses and the heating of compost material, it is necessary to spend approximately 4 M...

Theory of Anaerobic Digestion

Anaerobic digestion involves several successive stages of chemical and biochemical reactions involving enzymes and a mixed culture of microorganisms. The process comprises three general degradation phases hydrolysis, acido-genesis, and methanogenesis. Figure 5.1 is a simplified representation of the reactions involved in anaerobic digestion. Figure 5.1 Schematic of reaction in anaerobic digestion. Figure 5.1 Schematic of reaction in anaerobic digestion. In the first phase of anaerobic...

Two Phase Digestion

Acid Phase Digestion

As discussed in Section 5.1.2, anaerobic digestion involves two major phases hydrolysis and acid formation together, and methane production. In the three preceding high-rate digestion processes, both phases take place in a single reactor. In two-phase digestion, the two major phases are divided into separate tanks coupled in series. Pilot studies (Ghosh et al., 1975 Lee et al., 1989) and data from two full-scale facilities (Ghosh et al., 1995) have shown that better sludge digestion can be...

Comparison Of Thermal Drying And Composting

In recent years, thermal drying and composting have become useful technologies for the preparation of class A biosolids. Let us examine three sludge-processing schemes, shown in Figure 9.4, to compare the heat consumption of these two technologies. Let the quantity of raw primary and thickened activated sludge be 800 m3 d with 4 dry solids. Figure 9.4 Sludge processing schemes. Figure 9.4 Sludge processing schemes. heat necessary for sludge digestion (800 m3 d)(106Mj m ) heat obtained by sludge...

Composting Methods

Generalised Schematic Composting

There are three classifications of sludge composting Aerated static pile process In the windrow process, the dewatered sludge is agitated periodically for aeration. Agitation also controls the temperature and produces an end product that is uniform. In the aerated static pile process, air is blown through the materials using a blower. In-vessel composting systems are proprietary systems in which composting is performed in a reactor with air forced through the reactor, but with or without...

Composting Mixture

Sludge Composting Device

The new technology requires quicklime to be mixed with the dewatered sludge just prior to adding a bulking agent (sawdust, wood chips, bark, etc.) and recycled compost. Refer to Figure 7.13 for the schematic of the proposed 1.Hopper with conveyor for dewatered sludge 2.Silos for quicklime with processing unit and pneumatic pumping of lime 3.Hopper for bulking agents and recycled compost 6.Discharge conveyor for mixture to be composted 11. Cover over composting piles 1.Hopper with conveyor for...

Design Application Rates

Application rates for biosolids can be limited by nitrogen or by pollutants (heavy metals listed in Table 10.1). For most biosolids that are land applied TABLE 10.2 Typical Slope Limitation for Land Application 0-3 Ideal, no concern for runoff or erosion of liquid or dewatered 3-6 Acceptable, slight risk of erosion surface application of liquid or dewatered biosolids is acceptable. 6-12 Injection of liquid biosolids required for general cases, except in closed drainage basin and or when...

Heavy Metals

Russian studies on the influence of biosolids on harvest, crop quality, and migration of heavy metals from biosolids into soil and from soil into plants (Goldfarb et al., 1983 Turovskiy, 1988) established that absorption of heavy metals by plants depends on the following Mobility of heavy metals in sludge. Nickel, cadmium, and zinc are the most movable metals, but different methods of treatment may change the mobility of heavy metals in sludge. When treated by lime, for instance, the major part...

Process Description 721 Factors Influencing Composting

Bio Solids Affect The Local Populations

Composting represents the combined activity of a succession of mixed populations of bacteria, actinomycetes, and fungi at different stages of the process. The principal factors that affect the biology of composting are moisture, temperature, pH, nutrient concentration, and oxygen supply. Moisture Decomposition of organic matter depends on moisture. Less than 40 moisture may limit the rate of decomposition. The optimum moisture content is 50 to 60 . Moisture content is also important for the...

Units Of Measure

Wastewater Sludge Processing, By Izrail S. Turovskiy and P. K. Mathai Copyright 2006 John Wiley & Sons, Inc. A.2 Abbreviations for U.S. Customary Units A.2 Abbreviations for U.S. Customary Units A.3 Conversion from SI Units to U.S. Customary Units pounds per thousand cubic foot per day Some of the units listed are metric units commonly used in environmental engineering. Some of the units listed are metric units commonly used in environmental engineering. A.4 Conversion from U.S. Customary...

Conveyance and Storage of Biosolids

Biosolids land application always requires the biosolids to be conveyed to the ultimate location. Successful biosolids land application programs should also have provisions to deal with daily biosolids production at wastewater treatment plants in the event that biosolids cannot be land-applied immediately. This contingency plan generally involves storage. Transportation Biosolids may be transported by pipeline, truck, barge, rail, or a combination of these. The method of transportation chosen...