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Guidelines for Treatment of Liquid Waste Streams

John Poullain, P.E.

Course Outline

This two-hour online course provides general guidelines for treating hazardous liquid waste streams by air stripping and biological processes. The guidelines assist in the selection of remedial actions for treating hazardous and toxic waste (HTW) contaminants. Air stripping, a mechanical method using lagoons and packed towers, is discussed. Biological methods include trickling filters, rotating biological contactors, activated sludge systems and waste stabilization ponds. The basis for selecting a treatment method, criteria for optimum performance, advantages and disadvantages are presented for consideration. Other methods for treating contaminated liquid waste, thermal, desorption, solidification, stabilization, incineration and evaporation are not discussed in this course. Certain biological methods are used to treat contaminated soil and sludge as well as liquid waste streams. Remedial actions performed at a contaminated site must comply with federal and state regulations.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this three-hour course, the student will:

Intended Audience

This course is intended for civil engineers and planners.

Benefit to Attendees

The student will become familiar with air stripping and biological methods used for treating contaminated liquid waste streams at hazardous and toxic waste sites. The basic guidelines for the design and operation of the treatment methods are considered. The advantages and disadvantages and guidance in the selection of suitable treatment methods are discussed. Variations of biological methods are presented. Potential environmental risks caused by a treatment method and basic considerations for minimizing risks are discussed.

Course Introduction

This course provides general technical guidelines and methods for the treatment of liquid waste by physical and biological methods. Physical treatment methods include air or stream stripping and absorption or both methods used in combination. Biological treatment methods use the action of microbes similar to that of ecosystems but at much faster rates. Organics in solution are removed, partly mineralized and partly collected as a semi solid or sludge and separated from the liquid waste. Treatment of liquid waste render such waste and any residues left from treatment methods non-hazardous and safer to dispose of, to transport or to store. Liquid waste includes; leachates, ground water, surface water and effluents generated by other treatment measures. Liquid wastes vary considerable depending on the type of activity generating them; waste from the oil industry contains oily substances and hydrocarbons while galvanic industries generate heavy metals. Ground water may be contaminated from fuel storage, chemical leakage, fuel spills, underground pipeline failures, runoff of chemical preservatives, uncontrolled disposal of HTW materials and other sources. Contaminants include chlorinated, aromatic or polycyclic hydrocarbons, solvents, ammonia, hydrogen sulfide or heavy metals.

Liquid waste treatments can be grouped into primary or preliminary, secondary, and tertiary. Preliminary treatment may be necessary to remove any object, stone or wood that would damage or reduce the efficiency of the treatment unit and to separate solids from the liquid stream to lower the BOD before continuing with secondary treatment. Secondary treatment methods are the subject of this course. Tertiary treatment is used to remove nitrogen, phosphorous or to disinfect pathogenic microorganisms to a safe level for downstream release.
Air stripping treatment consists of pumping the contaminated water into a column or tower as a fine spray which drips downward on the packing inside the tower. Air is sucked into the tower, flows through the water spray which "strips" the dissolved contaminants from the feed water. The contaminants can be volatile gasses or low- boiling liquids. Packing maximizes the surface area to provide greater contact between the feed water and air. To be efficient there must be constant contact between the water and air. Pollutant laden air is exhausted from the tower and cleaned as required by activated charcoal or thermal destruction to prevent air pollution. Packing material is made from plastic, wood or ceramic and the stripping units are made from polyethylene, stainless steel or plastic coated steel.

There are many biological treatment methods, which function by various means, but all are based on incorporating microorganisms' to treat organic chemicals, nutrients and colloidal solids. All methods are sensitive to heavy metals, oil and grease by varying degrees. Some methods, rotating biological disks and trickling filter, can handle suspended solids better than soluble ones while others, activated sludge and waste stabilization ponds or lagoons, are intolerant of suspended solids.

Main features of some of the biological treatment methods are described below.

a. Activated sludge. Consists of primary sedimentation, an aeration tank or basin with mechanical stirring and a settling tank to clarify the liquid waste. Aeration devises use submerged diffusers that release compressed air and mechanical surface aerators that introduce air by agitating the liquids' surface. The liquid and microorganisms are next passed to a settling tank or clarifier. Microorganisms are separated from the liquid by sedimentation and the clarified liquid exits as purified wastewater. A portion of the resulting sludge is recycled to the aeration tank to maintain a high level of mixed-liquor suspended solids (MLSS). The remainder of the sludge is removed and processed for safe disposal, adding to the solids produced in primary sedimentation. Several variations of the basic process commonly used are discussed.

b. Trickling filter. Consists of a basin or tower filled with rocks or synthetic media. The liquid waste is applied or trickled over the media and microorganisms attach to the media to form a biological layer or fixed film. The film of microbes metabolizes organic matter. Depending on the wastewater and ambient air temperatures, oxygen is supplied to the film by airflow through the media. Forced air may also be used. As new organisms grow, the biofilm thickens, sloughs off and is separated from the liquid in a clarifier. The clarified liquid is discharged as effluent and a portion, sludge, is recirculated to improve hydraulic distribution of the wastewater.

c. Lagoons or Waste stabilization ponds. They are slow, relatively inefficient and require large capacities and long aeration times. Lagoons are basically biological ponds in which solids settle the dissolved and non-settling waste is degraded by microbes. They tend to fill as waste material is decomposed. The ponds are excavated and require liners to prevent infiltration and migration of the contaminants. The four main types include aerobic, anaerobic, aerated and facultative ponds. Aerobic ponds need larger surface areas because they need shallower depths to provide complete oxygen distribution to maintain aerobic decomposition. Aerated ponds can be deeper than aerobic ponds because of the artificial aeration systems used.

The advantages and disadvantages of various liquid waste treatment methods are compared. The treatment methods cause certain environmental risks and other concerns for consideration. Considerations for selecting a treatment method include operation costs, experience of personnel, odors and treatment performance. Environmental risks include inadequate treatment, contaminated sludge residue, effluent or leakage from treatment units and air pollution. Leachate, migration of contaminants, runoff and wind erosion can contaminate the subsoil, groundwater and nearby surface water.

Remedial actions at hazardous waste sites consist of on site control, on site treatment, on site storage or off site disposal or combinations of these. On site and off site landfill disposal is a viable option when the volume of HTW material is within the feasible or economic limits of available technology. Remedial actions must comply with the regulatory guidelines of the Department of Defense Environmental Restoration Program (DERP), the Formerly Used Defense Sites (FUDS) Program, Resources Conservation and Recovery Act (RCRA), the US Environmental Protection Agency (EPA) and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA or commonly called "superfund"). Waste sites must be investigated for a wide range of conditions, including ground water levels, surface drainage and subsurface ground conditions.

Course Content

This course is based primarily on Chapter 4, section I (par 4.1- 4.5) and C- 3, "Treatment Technology Terms", of the US Army Corps of Engineers Manual, "Technical Guidelines for Hazardous and Toxic Waste Treatment and Cleanup Activities", EM 1110-1- 502 (1994 Edition, 30 pages), PDF file.

The link to the Engineers Manual is "Technical Guidelines for Hazardous and Toxic Waste Treatments and Cleanup Activities", Chapter 4, Sections I, "Treatment of Liquid Waste Streams" and C-3, "Treatment Technology Terms".

You need to open or download above documents to study this course.

Course Summary

State and federal regulations have to be complied with at industrial and hazardous and toxic waste sites in order to remove any threat to human health, welfare or to the environment. Hazardous and toxic waste includes materials defined as hazardous waste, hazardous substance and pollutants. Among HTW substances are heavy metals, including lead, cadmium and mercury, PCBs, dioxins, chlorine, sulfur, potassium and explosives. Air stripping and biological treatment methods discussed can be used to remediate contaminated liquid waste streams generated by mismanagement of HTW disposal materials or from other hazardous treatment methods. Such waste after being rendered non-hazardous can then be safely disposed, transported or stored.


For additional technical information related to this subject, please refer to:
Describes water waste treatments, chemical and physical treatment processes.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.