Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-06-16
2001-11-27
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C205S745000, C210S626000, C210S631000, C210S713000, C210S716000, C210S719000, C210S721000, C210S724000, C210S726000, C210S903000, C210S906000, C210S909000, C210S917000, C210S928000
Reexamination Certificate
active
06322701
ABSTRACT:
This invention relates to a water treatment process, in particular, to a process for the treatment of waste water containing chemically reducible dissolved organic and inorganic pollutants and suspended matter in particulate or colloidal form.
The process of the invention is particularly useful for the treatment of waste water from the wood, wood-based panel, paper-pulp and paper industries, as well as effluent from tanneries, oil wastes such as motor oil or olive oil wastes, dyehouses, fibre, textile and other industries which among other pollutants contain large concentrations of complex organic contaminants of large molecular weight, commonly referred to as macromolecules, along with large concentrations of suspended particles and which are, consequently, difficult to treat fully by the sole use of standard biological processes. A further specific application of the process is the reductive cleavage of nitrogenous and halogenated organic pollutants which may then be removed easily by conventional biological methods. Another application of the process is the removal of inorganic species, such as nitrate, nitrite and phosphate by their chemical entrapment in the form of insoluble compounds which may then be easily removed by precipitation. The net effect of the treatment proposed herein is the decrease in the overall load of pollutants present in a given waste water stream and the chemical conversion, commonly referred to as “softening”, of non-readily biodegradable pollutants through a generally complex set of redox reactions so that the stream is subsequently treated more fully, more effectively and at lower cost by conventional anaerobic and aerobic biological treatment processes, such as denitrification and activated sludge systems.
In the various stages of industrial manufacturing processes, such as wood treatment and papermaking, large amounts of water are employed. While significant improvements have been made in the conservation or reuse of water in these processes, it is still necessary to discharge a certain amount of waste water from the system. The process water effluent from processing and manufacturing plants is often a coloured, turbid and odorous liquor consisting of water, dissolved pollutants and particulate matter in suspension. The disposal of large quantities of such process effluents into adjacent streams and bodies of water can result in the pollution of the latter causing among other things the water to attain an objectionable colour and odour.
The composition of industrial wastewaters is typically quite complex often comprising tens or even hundreds of different chemical species in a dissolved, colloidal or particulate form. As a result, the overall quality of a certain waste water stream is conventionally measured by the combined use of lumped composition parameters which denote the overall concentration of entire groups of pollutants with a common characteristic (e.g., carbonaceous compounds, organic nitrogen, suspended solids, colour, odour, halogenated organics, total phosphorus, total phenols etc.) and actual concentrations of individual pollutants (e.g., various heavy metals etc.) which are specifically targeted due to the particularly harmful effects on living species. Among these quality markers, the overall load of oxidizable carbonaceous organic pollutants (the so-called “wastewater strength”) comprises most often the major concern with respect to water pollution and is, therefore, regulated quite strictly in most areas. The total concentration of oxidizable carbonaceous organic pollutants in a certain waste water stream is conventionally characterized by its Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD).
The Chemical Oxygen Demand (COD) of an aqueous sample is a measure of the oxygen consumption during the chemical oxidation of its organic carbonaceous components by a strong chemical oxidant under standard reaction conditions which ensure the oxidation of at least 95% of the total existing organic carbonaceous contaminants. When precautions are taken to minimize interferences by the oxidation of inorganic species, the COD can be employed to describe relatively accurately the total concentration of organic carbon present in a given aqueous stream.
The Biochemical Oxygen Demand (BOD) of an aqueous sample is a measure of the oxygen consumption during the biological oxidation of its organic carbonaceous components by an aerobic microbial culture and is determined using standardised laboratory procedures whereby the aqueous sample is contacted with an appropriate microbial culture for a predetermined time period. Since biological oxidation is a relatively slow process, the resulting BOD value depends on the contact time employed. A five-day contact period is conventionally employed, hence the nomeclature “5-day BOD or BOD
5
”. When precautions are taken to minimize interferences by the concurrent biological oxidation of certain inorganic species, such as sulphides, ferrous iron, and reduced forms of nitrogen (nitrogenous oxygen demand), the BOD can be employed as a measure of the total concentration of the biologically degradable organic carbon present in the given aqueous stream.
Based on the above definitions, the COD:BOD
5
ratio of a given wastewater denotes the ratio of total to biodegradable carbonaceous organic pollutants and may, thus, be used as a measure of its biodegradability. High COD:BOD
5
ratios suggest a large concentration of non-readily biodegradable carbonaceous organics which may not be treated by conventional aerobic biological treatment processes, such as activated sludge.
Typical COD values for untreated industrial waste waters range from 400 to 15,000 mg/L while the corresponding BOD
5
values from 80 to 4,000 mg/L. On the other hand, typical COD values for untreated municipal sewage range from 400 to 800 mg/L and BOD
5
values from 150 to 400 mg/L. It is evident that the COD:BOD
5
ratio of typical industrial waste waters is far in excess of 2:1 which is the corresponding value for municipal sewage and which, thus, provides a target for the pre-treatment of industrial process water effluents in order to allow an effective further treatment by conventional aerobic biological processes. Treated municipal effluents typically have COD values around 60 mg/L and BOD
5
15 mg/l (COD/BOD
5
=4:1).
Various physicochemical processes have been proposed for the treatment of process water from industrial manufacturing processes apart from the conventional biological treatments. These non-biological effluent treatment processes, such as filtration methods, advanced oxidation using ultraviolet light, peroxide and ozone, reverse osmosis, precipitation with polyelectrolyte, lime or alum, dissolved-air floatation, carbon adsorption and others, are effective in removing dissolved and particulate contaminants from such streams but are often either partially effective being able to remove only a relatively narrow range of pollutants or prohibitively expensive for use in treating industrial process water effluents, especially, from processes which generate large quantities of waste water, such as pulp and paper mills. The cost of large amounts of chemical reagents, high maintenance costs and expensive facilities along with their often limited scope have rendered these proposed solutions not attractive. A water treatment process has accordingly been sought that has a high level of efficiency, is able to remove a wide spectrum of pollutants and yet requires low investment and operational costs.
EP-A-0 151 120 discloses a method for the removal of heavy metals from an aqueous solution. The method comprises co-precipitating the heavy metal ions with a carrier precipitate that is formed in-situ within the aqueous solution.
In the field of dyestuff manufacture there have been proposals to purify contaminated water through the precipitation of ferric hydroxide to <<entrap contaminants>>. Metallic iron had been used in the 1950s to produce in-situ ferric hydroxide as a coagulant (Dr. H. Jung, Viersen, Ein Beitrag
Hruskoci Peter A.
Ladas & Parry
Thocar Ltd.
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