Chemical Treatment of Liquid Waste Streams
John Poullain, P.E.
online course provides general guidelines for treating industrial and hazardous
liquid waste streams by chemical and physical chemical processes. The guidelines
assist in the selection of remedial actions for treating hazardous and toxic
waste (HTW) contaminants. The methods include precipitation, flocculation, sedimentation,
neutralization, oil-water separation, reverse osmosis and ultrafiltration. 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. 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.
At the conclusion of this course, the student will:
This course is intended for civil engineers and planners.
Benefit to Attendees
The student will
become familiar with the various types of physical and chemical methods used
for treating contaminated liquid waste streams at industrial and 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
chemical methods are presented. Potential environmental risks caused by a treatment
method and basic considerations for minimizing risks are discussed.
This course provides
general technical guidelines and methods for the treatment of liquid waste by
chemical and physical chemical treatment methods. The treatment methods include
precipitation, sedimentation, flocculation, other methods and methods used in
combination. Heavy metals in solution are removed, partly mineralized and partly
collected as a semi solid or sludge and separated from the liquid waste. Heavy
metals such as mercury, lead and cadmium are from industrial discharges, landfills
and mining operations and other sources.
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, industrial discharges, city street runoff, mining activities and effluents generated by landfills and 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 or preprocessing treatment may be necessary to remove any component, 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 chemical 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.
There are many treatment methods, which function by various chemical and physical means or in combinations. All methods are sensitive to heavy metals, oil and grease by varying degrees. Methods such as ultrafiltration can handle suspended solids better than other methods such as reverse osmosis. Physical processes treat suspended solids either by allowing them to settle out (sedimentation) or to float to the top naturally. Or the process may use stirring or agitating actions to cause particles to contact each other and stick together without or with chemical additives (flocculation). Chemical flocculant additives produce larger particles. Particle flotation can be aided with dissolved air under pressure or under vacuum conditions (dissolved air flotation). Chemical processes include precipitation, flocculation, neutralization and solidification. Membrane processes include reverse osmosis and ultrafiltration and other filtration systems.
a. Reverse Osmosis (RO) A RO plant processes waste water streams by forcing the feed water through semipermeable membranes into separate streams, a stream of purified water and a stream of concentrated dissolved solids removed from the feed water. The RO plant typically consists of pre-filters, multi-stage simplex or duplex pumps to generate osmotic pressure, RO membrane and element modules and control panels housing pressure gauges, flows, alarms and meters. Many are skid mounted, which makes them applicable to small installations and easy to install. The plants can remove dissolved solids, organic material, bacteria, viruses and ionic groups and are used to treat waste water, beverage and brewing liquor, food and boiler feed water and for desalination. A disadvantage is the reject water can equal 25 % of the feed water. Unless the reject water can be reused or a more suitable membrane arrangements are used, the RO operation cost may be prohibitive. Computer programs are used to study the feed water to select a suitable membrane configuration. Also the membrane will have to be cleaned of foulants and scale caused from organics, microbiological matter, silica, iron or calcium deposits. Alkalines, organic acids or disinfectants accomplish cleaning. Use of chemical are minimized compared to demineralized ion exchange processes. Suspended solids in the feed water may require filtration or ultra filtration for removal prior to RO treatment.
b. Ultrafiltration (UF) The UF and RO processes are similar but UF differs by using different types of membranes with varying porosities which provides a more specialized treatment and aid in water pre-treatment. Both UF and RO are membrane and pressure driven processes. UF however operates at a lower pressure than RO. UF can process and remove nitrates, hardness, bacteria, protozoa and viruses and reduce turbidity. It is used in the pharmaceutical industry, potable water for feed sources, water re-use and recycling for industry. Filtration systems minimize the suspended solids in cooling tower systems, which keeps the system clean and improves cooling efficiency. RO, UF and other membrane processes, nanofiltration and microfiltration, can use permeable or semipermeable membranes. Most use cross flow operation.
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, exothermic reactions, 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.
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.
This course is based primarily on Chapter 4, Section I (par 4.10- 4.17 and 4.21) 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, 31 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 (par 4.10-4.17 and 4.21), "Treatment
of Liquid Waste Streams" and C-3, "Treatment
You need to open or download above documents to study this course.
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.
Chemical 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 waste water treatment plants, equipment and various physical and chemical