WATER AND WASTWATER TREATMENT
INTRODUCTION
Although not often thought of as a commodity (or, for that matter, not thought about at all), water is a commodity —a very valuable commodity. In this report, it is our position that with the passage of time, potable water will become even more valuable. Moreover, with the passage of even more time, potable water will be even more valuable than we might imagine. It may be possibly comparable in pricing, gallon for gallon, to what we pay for gasoline, or even more. Earth was originally allotted a finite amount of water —we have no more or no less than that original allotment today. It logically follows that, in order to sustain life as we know it, we must do everything we can to preserve and protect our water supply. We also must purify and reuse the water we presently waste (i.e., wastewater).
THE PARADIGM SHIFT
Historically, the purpose of water supply systems has been to provide pleasant drinking water that is free of disease organisms and toxic substances. In addition, the purpose of wastewater treatment has been to protect the health and well being of our communities. Water and waste water treatment operations have accomplished this goal by
(1) Prevention of disease and nuisance conditions;
(2) Avoidance of contamination of water supplies and navigable Waters.
(3) Maintenance of clean water for survival of fish, bathing, and recreation.
(4) Generally conservation of water quality for future use.
The purpose of water supply systems and wastewater treatment processes has not changed. However, primarily because of new regulations the paradigm has shifted. These include:
1. Protection against protozoan and virus contamination
2. Implementation of the multiple barrier approach to microbial control
3. New requirements of the Ground Water Disinfection Rule, the Total Coli form Rule and Distribution System, and the Lead and Copper Rule
4. Regulations for trihalomethanes and disinfection by-products (DBPs).
FOCUS
Ø Optimization of Treatment Process
Ø Trained & Certified Plant Operators
Ø Source Protection
Ø Sound Distribution System Management
Ø A Second Dose of Disinfectant
Ø Cross-Connection Control
Ø Continuous Monitoring & Testing
KEYWORDS USED IN OUR REPORT
Coagulating agents - Wastes that are removed by this process are classed as suspended or colloidal. Colloids consist of small particles that are constantly moving; gravity does not cause them to settle out. Coagulating agents, e.g. alum and ferric chloride, reduce the effects of electrical charges which keep the particles of waste separate from each other. The particles then join together to form masses called flocs. These flocs then rise to the surface or settle to the bottom. Flocculating agents are frequently used to bond flocs together - this speeds the rate at which they rise to the surface or settle to the bottom.
Equalization - Equalization systems contain large reservoirs together with piping and treatment processes. These systems minimize fluctuations in wastewater flows and thus give stability, ensuring that wastewater treatment is carried out under the best possible conditions.
Flocculating agents - Flocculating agents are routinely used in municipal and industrial wastewater treatment in conjunction with clarifiers. There are many proprietary surfactant-type polymers designed for this purpose, although inorganic chemicals such as ferric chloride may also be used
Neutralization - Blending acidic and basic wastes is a function of most equalization systems. This action (neutralization) is essential before wastes are directed to biological treatment processes where microorganisms feed on organic substances. Extreme changes in pH often kill microorganisms.
Suspended solids removal - The removal of suspended matter is generally the most important process in the treatment of effluents and leachates from sediment remedial alternatives because most of the contaminants in water residues are associated with the solid particles. An effective solids removal system can significantly reduce contaminant concentrations, leaving behind only those contaminants that are dissolved or associated with colloidal material. Solids removal is a frequently required pretreatment for processes that remove dissolved contaminants (e.g., ion exchange, carbon adsorption). The primary technology types for suspended solids removal are sedimentation and filtration.
Solid residues - Solid residues include the bulk of sediment solids following treatment as well as smaller fractions of solids separated from the sediments or produced by the treatment processes. For most remedial alternatives involving a properly designed and thorough treatment system, the treated solids will not require additional treatment and can be disposed using the technologies
Residue management - Residues are materials, products, or waste streams generated by components of a sediment remedial alternative. Residues may be water, wastewater, solids, oil fractions, or air and gas emissions. The management of these residues may involve treatment, containment, or discharge to the environment. The types of residues anticipated from most sediment remedial alternatives and management options for them are discussed in various sections of this book. Some sediment treatment technologies may generate unique residues, requiring special management considerations. At minimum, the inert solid particles that were present in the original, untreated sediment will still be present following the application of any treatment technology.
Chemistry used
Dry Alum: The commercial dry alum most often used in wastewater treatment is known as filter alum, and has the approximate chemical formula Al2(SO4)3.14H20 and a molecular weight of about 600. Alum is white to cream in color and a 1 percent solution has a pH of about 3.5. Dry alum is not corrosive unless it absorbs moisture from the air, such as during prolonged exposure to humid atmospheres. Therefore, precautions should be taken to ensure that the storage space is free of moisture.
Solution of alum in water produces:
Hydroxyl ions become available from ionization of water:
Al2SO4--------Al+3+SO42-
H2O ------------H+ OH-
The aluminum ions (A13+) then react:
2Al+3 + 6 0H------- 2 Al(OH)3
Al2(S04)3 + Na2C0 3 + 3H2O-------2Al(OH)3- + 3 CO2
Al2(S04)3 + 3 Ca(OH)2----------------2 Al(OH)3 +3 CaSO4
Ferrous chloride: It is a liquid which is available in the form of waste pickle liquor from steel processing. The liquor weighs between 9.9 and 10.4 lb/gal and contains20 percent to 25 percent FeCl2 or about 10 percent available Fe2+.A 22 percent solution of FeC12 will crystallize at a temperature of - 4F. The molecular weight of FeC12 is 126.76. Free acid in waste pickle liquor can vary from 1 percent to 10 percent and usually averages about 1.5 percent to 2.0 percent. Ferrous chloride is slightly less corrosive than ferric chloride
Lime: Lime is among a family of chemicals which are alkaline in nature and contain principally calcium, oxygen and, in some cases, magnesium. In this grouping are included quicklime, dolomitic lime, hydrated lime, dolomitic hydrated lime, limestone, and dolomite. The most commonly used additives are quicklime and hydrated lime, but the dolomitic counterparts of these chemicals (i.e., the high-magnesium forms) are also widely used in wastewater treatment and generally similar in physical requirements.
Soda Ash: Soda ash, Na2CO3 is available in two forms. Light soda ash has a bulk density range of 35 to 50 lb/cu ft and a working density of 41 lb/cu ft. Dense soda ash has a density range of 60 to 76 lb/cu ft and a working density of 63 lb/cu ft. The pH of a 1 percent solution of soda ash as 11.2. It is used for pH control and in lime treatment
