Wastewater Treatment Plants

Planning, Design, and Operation, Second Edition

Syed R. Qasim

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351405164
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

Step-by-step procedures for planning, design, construction and operation:
* Health and environment * Process improvements* Stormwater and combined sewer control and treatment* Effluent disposal and reuse* Biosolids disposal and reuse* On-site treatment and disposal of small flows* Wastewater treatment plants should be designed so that the effluent standards and reuse objectives, and biosolids regulations can be met with reasonable ease and cost. The design should incorporate flexibility for dealing with seasonal changes, as well as long-term changes in wastewater quality and future regulations. Good planning and design, therefore, must be based on five major steps: characterization of the raw wastewater quality and effluent,
pre-design studies to develop alternative processes and selection of final process train,
detailed design of the selected alternative,
contraction, and
operation and maintenance of the completed facility.
Engineers, scientists, and financial analysts must utilize principles from a wide range of disciplines: engineering, chemistry, microbiology, geology, architecture, and economics to carry out the responsibilities of designing a wastewater treatment plant. The objective of this book is to present the technical and nontechnical issues that are most commonly addressed in the planning and design reports for wastewater treatment facilities prepared by practicing engineers. Topics discussed include facility planning, process description, process selection logic, mass balance calculations, design calculations, and concepts for equipment sizing. Theory, design, operation and maintenance, trouble shooting, equipment selection and specifications are integrated for each treatment process. Thus delineation of such information for use by students and practicing engineers is the main purpose of this book.

1

Introduction

1-1 HISTORICAL BACKGROUND

In the early 1800s, the United States was a sparsely populated, underdeveloped country. Human waste was generally disposed of by either pit privies or open drainage ditches. The dramatic increase of population and industries in urban areas and public awareness of the connection between human diseases and waste disposal needs made it necessary for municipalities to improve waste management practices. Work on the first sanitary sewer in the United States was begun in Chicago in 1855, 12 years after the world’s first sanitary sewerage system was completed in Hamburg, Germany. Various types of wastewater treatment technologies were used: trickling filter in 1901, Imhoff tank in 1909, liquid chlorine for disinfection in 1914, and activated sludge in 1916. By 1948 wastewater treatment plants served some 45 million Americans out of a total population of 145 million.^1,2

1-2 CURRENT STATUS

In 1956 Congress enacted the Federal Water Pollution Control Act, which established the construction grants program. Under the 1972 Amendments to the Federal Water Pollution Control Act (Public Law 92–500) and Clean Water Act of 1977 (Public Law 95–217), thousands of municipal wastewater treatment facilities have been constructed or expanded across the nation to control or prevent water pollution.^3,4 The law established the National Pollutant Discharge Elimination System (NPDES), which calls for limitation on the amount or quality of effluent and requires all municipal and industrial discharges to obtain permits. The interim goal is to achieve water quality in natural waters, which provides for the protection and propagation of fish, shellfish, and wildlife and provides recreation in and on the water. The law authorized billions of dollars for construction grants. Pursuant to the mandates of 1987 Clean Water Act Amendments, the federal construction grants program was converted to State Revolving Fund (SRF), which provided loans to municipalities for construction of wastewater treatment facilities. Also, regulations for stormwater discharges, combined sewer overflows, and disposal of sewage sludge have been established. The 1992 Needs Survey Report to Congress indicated that there were a total of 15,613 wastewater treatment facilities serving a total of 181 million people. Out of these, 1,981 facilities have no discharge; 868 facilities provide less than secondary; 9,086 facilities provide secondary; and 3,678 facilities provide higher than secondary level of treatment. It is estimated that by the year 2012, there will be 18,966 facilities serving 251 million people.⁵

Effluent treatment of liquid waste increased the quantity of sludge or residuals for handling and disposal. Residuals management practices trailed the development of liquid processing alternatives. The significant developments in sludge management technology over the past 50 years were heated anaerobic digestion and utilization of digestion gases; gravity, dissolved air flotation, and centrifuge for sludge thickening; sludge drying beds, vacuum filter, belt filter and centrifuge for dewatering; and landfilling, incineration, and composting for sludge disposal.

During the last 20 years, contemporary design has emphasized secondary treatment, primarily to control the carbonaceous and nitrogenous oxygen-demanding pollutants, and suspended solids. The treatment strategies for phosphorus and nitrogen removal were limited to highly-restricted waters. Toxicity control has emerged only recently as a design consideration.

Many innovations in screening, degritting, clarification, aeration and mixing, sludge bulking control, biological nutrient removal (both suspended and attached growth), and sludge stabilization and beneficial recycling of biosolids have taken place in the last decade and provide cost savings and system improvements. All these innovative technologies have been tested under EPA-funded programs.

1-3 FUTURE DIRECTIONS

Many technological advances have been achieved in the wastewater treatment field as a result of concepts and policies promulgated by environmental laws and guidelines. A great deal has been learned regarding process design and construction, operation and maintenance, problems associated with improper site selection, and plant design. In the next decade there will be some shift in strategy for new plants and upgrading of existing facilities. Major changes are expected in process design, wastewater reclamation and reuse, and sludge disposal and reuse. New directions and concerns are evident in several interrelated areas of wastewater treatment fields: (1) health and environmental concerns, (2) improvement in treatment processes, (3) control and treatment of stormwater and combined sewer overflows, (4) effluent disposal and reuse, (5) biosolids disposal and reuse, and (6) on-site treatment and disposal of small flows.

1-3-1 Health and Environmental Concerns

Wastewater treatment works must not be the ugly duckling in the community but, rather, a good neighbor. In the past, odors, dust, noise, erosion, and unsightly conditions created public doubts and uneasiness about the nearby municipal wastewater treatment works. It is unacceptable to create new environmental problems.⁶ Therefore, future planning and designs of wastewater treatment facilities will emphasize techniques to minimize adverse environmental impacts and objections by neighborhood residents. Furthermore, active public participation programs will be an integral part of the decision-making process at all stages of the planning, design, construction and operation of wastewater treatment facilities.⁷

Currently, the release of volatile organic compounds (VOCs) and volatile toxic organic compounds (VTOCs) found in wastewater are of great concern in the operation of a collection system; wastewater treatment process selection, design, and operation; and sludge processing and disposal. Also, odors are one of the most serious environmental concerns for the public. Furthermore, in addition to being odorous, the hydrogen sulfide can cause accelerated corrosion of sewers and preliminary and primary treatment facilities. Great emphasis is therefore being placed on plant site selection, process selection, compact layout, covered and multistory process design, and even underground facilities. Such concepts reduce the atmospheric exposure of the wastewater. The air from the treatment facilities is collected and treated prior to discharge into the atmosphere. Concepts like these in plant design address VOCs, odors, and other environmental issues.

1-3-2 Improvements in Treatment Processes

In the past, extensive research activity in the search for improved processes for wastewater treatment and sludge management has resulted in a rapid growth in technology. Enhanced knowledge of fundamentals has permitted the engineers to adapt to innovative alternative technologies for improved process designs. The empirical methods commonly used in the past are inadequate for interpreting data and optimizing the processes. Laboratory and pilot plant studies will be utilized to develop process design parameters and kinetic coefficients for industrial and joint industrial-municipal wastewater treatment facilities. Future process designs may incorporate energy conservation, compact degritter, fine screens to replace primary sedimentation, sludge bulking and foaming control, biological nutrient removal, natural systems, improved methods of sludge thickening and dewatering and biosolids utilization, incineration, and codisposal with municipal solid wastes.

In addition to improved process design, great emphasis will be given to plant operation and maintenance to optimize the treatment costs. Energy saving measures and value engineering reviews are being emphasized to reduce capital and operation costs of the treatment facility.

1-3-3 Control and Treatment of Stormwater and Combined Sewer Overflows

The discharge of stormwater runoff and other nonpoint sources and combined sewer overflows (CSOs) to the receiving waters have resulted in contamination problems that often have prevented the attainment of water quality standards. The contaminants found in stormwater and CSOs include bacteria, nutrients, solids, biochemical oxygen demand (BOD), metals, and other potentially toxic organic constituents. Implementation of pollution control measures for stormwater runoff and CSOs will require management of stormwater drainage area, combined wastewater collection and detention basins, and wastewater treatment plants. In response to the need for solving these problems, engineers have used a variety of stormwater runoff and CSO control methods, including construction of new separate sewers and stormwater drainage systems, treatment at the combined sewer outlet, and storage followed by treatment under dry-weather conditions.

Approaches for reducing pollution from stormwater and CSOs are now in the development and evaluation phases. It is anticipated, however, that in many cases the benefits obtained from construction of treatment works for these purposes will be small compared with the costs. On the other hand, there are techniques for control and prevention that can be more cost-effective. The policy of the EPA is, therefore, not to use construction grants for treatment works to control pollution from stormwater and CSOs, except under unusual conditions, where the project clearly has been demonstrated to meet the planning requirements and criteria developed for CSOs. Chapter 26 is devoted exclusively to these issues.

1-3-4 Effluent Disposal and Reuse

Great emphasis is being given to the opportunities for effluent reuse. In many cases treatment plants have been located so that a portion of effluent is reused for irrigation of golf courses, highway medians, city parks, and landscape watering; effluent reused as industrial cooling water; groundwater recharge; and an indirect water supply through discharge into rivers, lakes, and reservoirs. Great attention is given to the environmental effects of constituents such as nutrients, refractory organics, toxic compounds, and microorganisms and how these constituents are safely assimilated into the aquatic, as well as terrestrial, environment. Mathematical modeling techniques are used to assess the assimilative capacity of these systems and thus to predict the impacts of the proposed reuse or discharge. A higher level of treatment may often be necessary to achieve the desired reuse objectives. Many effluent reuse and disposal options are covered in Chapter 15.

1-3-5 Biosolids Disposal and Reuse

Large quantities of sludge are produced with utilization of advanced wastewater treatment technology. There is an urgent need to find better methods of solids processing, reuse, and disposal. Landfilling and incineration of dewatered sludge is of great concern because of potential groundwater and air pollution problems. New regulations will restrict land application because of lower limits that will be imposed on certain heavy metals. This will mean tighter industrial pretreatment regulations to reduce certain heavy metals in the sludge. As a result of new regulations on biosolids utilization, solids processing has become one of the most significant challenges to the wastewater treatment plant designers and managers. Land application of biosolids is presented in Chapter 19.

1-3-6 On-site Treatment and Disposal of Small Flows

During the 1970s great emphasis was given to areawide wastewater planning and management in an effort to (1) use best practicable waste treatment technology and (2) produce revenues through use of effluent and sludge. Experience has shown that centralized facilities may require pumping of wastewater long distances from different portions of the service area and thus may be in general energy- and resource-intensive. Also serious odors, dust, noise, and other environmental problems developed in the community, as a result of processing large quantities of wastewater and sludge at one location.

In recent years, the concept of satellite wastewater treatment has been reevaluated in the overall context of economics, innovative energy-efficient technology, and reuse of effluent and sludge locally, or sludge alone being pumped to a central location for processing. Also, individual on-site treatment and disposal systems have received greater attention. This topic is covered in Chapter 25.

1-4 PLANT DESIGN

The task of planning and designing wastewater treatment works is not simple. It involves understanding of service area, sources of wastewater and the resulting characteristics, plant site, conveyance system, and treatment processes for the liquid and residues. Many nontechnical factors such as legal issues, regulatory constraints, public participation, effluent, and sludge disposal and reuse may influence planning and design. Furthermore, most of the facilities are designed to provide service over the plant’s life expectancy (20 years or more). During this extended time span, technology may improve, new laws may be passed, new regulations may be issued, and economic factors may change. The engineers must consider these possibilities and should favor processes that are sufficiently flexible to remain useful in the face of changing technology, regulations, economics, and wastewater characteristics.

During the design phase of a plant, it is important to recognize that the overall performance of a wastewater treatment facility is the result of combined performances of many components utilized in the overall process train. The designers must understand the design implications and performance of the individual processes and how these processes may affect one another under normal and adverse operational conditions. As an example, failure to remove solids produced within the treatment processes will eventually cause degradation of effluent quality. Likewise, hydraulic overload to the sludge-processing systems may increase the solids in the sidestream, which is returned to the plant as a recirculating load, thus adversely affecting the influent quality to be treated.

In spite of the multitude of regulations and standards that treatment plants must comply with, the theory and design principles of wastewater treatment processes such as screening, sedimentation, biological waste treatment, nutrient removal, filtration, demineralization, and sludge processing systems have not changed over half a century. What has changed, however, are many tools that both designers and operators have at their disposal. New equipment has improved efficiency and reliability. Computers have bestowed the gifts of alacrity and accuracy in design and operation. Now...