GB2413124A

GB2413124A - Glass filtration media

Info

Publication number: GB2413124A
Application number: GB0408196A
Authority: GB
Inventors: Howard Dryden
Original assignee: THIMS Ltd
Current assignee: THIMS Ltd
Priority date: 2004-04-13
Filing date: 2004-04-13
Publication date: 2005-10-19
Also published as: GB0408196D0

Abstract

A glass filtration media used as an alternative to sand for the enhanced treatment of water and wastewater. The filtration media is specifically manufactured from green and brown glass bottles. The glass granules are further enhanced by exposure to an acid to increase the surface area available on the glass granules for adsorption and catalysis. In wastewater treatment glass granules are used in a filter immediately after the biological process but before humus tank sedimentation, or in place of the humus tank sedimentation stage. The glass granules will mechanically filter the water and remove prescribed substances. The glass granules may be further processed by fluidized bed washing at a high oxidation potential to remove any contamination and to the sanitize the glass granules. The presence of dissolved oxygen or oxidising chemicals will enhance the surface catalytic properties by increasing still further, the free radical concentration on oxidation potential on the surface of the glass granules.

Description

1 2413124

WATER TREATMENT

The present invention relates to water treatment, and more particularly to an improved process for the treatment of wastewater, sewage effluent and drinking water, using active filtration glass granules With everincreasing levels of water consumption there is increased demand for more efficient and effective methods for treating sewage water to protect the receiving environment.

There is also an increasing problem of chemical contaminants from various sources in sewage water, which require special and costly treatment processes.

Conventional sewage water treatment generally comprises the following process steps: coarse screening . ë . primary sedimentation &-.

biological treatment :. secondary settlement (in humus tanks), and tertiary sand filtration. c. .

With such conventional treatments, the sand filtration stage if employed, is particularly susceptible to failure due to fouling by bacteria and contaminants present in the water.

It is an object of the present invention to avoid or minimize one or more of the above-mentioned problems and disadvantages.

It has now been found that a particular form of granular glass, conveniently referred to herein as active filtration glass granules, provides a particularly effective form of water filtration medium in sewage water treatment. More particularly we have found that such active filtration glass granules can effectively replace the secondary settlement stages, in a sewage water treatment system.

Thus in one aspect the present invention provides a method of and apparatus for, sewage water treatment consisting essentially of the following stages: coarse screening; . e primary sedimentation; biological treatment; and . active filtration glass granule filtration. .e

A. With the method and apparatus of the invention, not only is the apparatus substantially simplified, and the treatment process significantly enhanced, but significant further benefits are obtainable including improved chemical contaminant removal and sewage treatment works performance.

In more detail, the principal reason for sand filter failure is fouling of the sand by bacteria and contaminants present in the water. Active filtration glass granules actively resist biofouling and contamination which provides greatly improved filtration performance and allows active filtration granules to be used before secondary humus tank sedimentation.

The flow of water through a sand or active filtration glass granules filter has to be reversed for approximately 1 to 10 minutes, at intervals ranging from a few hours to several days, in order to clean the filter media. If any of the solids remain in the filter after the standard backflush period, then the solids will gradually accumulate, act as a food source for bacteria, and the filter performance will deteriorate until the filter fails. The time interval to . e . complete failure may be several days to years. The time .

interval is a function of the water quality, the filter media, filter design and operating procedures. In sewage effluent or grossly contaminated biologically active water, *.

: . sand filters cannot normally be used because the filter will rapidly fail due to biofouling. In clean water applications sand filters will also fail, but biofouling will take longer to occur.

Another significant benefit is improved solids removal efficiency. During the humus tank sedimentation phase, the oxygen content in the water will fall, and may become anaerobic. The bacteria floes being removed by the humus tank are aerobic bacteria. The bacteria floe therefore come under stress and shock from exposure to anoxic conditions. As a consequence of bacteria stress, the floes or bacterial colonies will have a tendency to break up into smaller colonies. Filtration of the water prior to the humus tanks therefore means that the bacteria floe being filtered by the active filtration glass granules filter are larger and more stable than the bacteria floe after the humus tank. Since the active filtration glass granules filter is tolerant of high solids loading, removal efficiency by active filtration glass granules filtration is better before humus tank solids separation as opposed to after the humus tanks. .e

A

A further benefit is avoidance of stressing of the bacteria . . recycled back to the beginning of the treatment system, by anoxic conditions. The bacteria will be in a better .

. condition as opposed to bacteria that would normally have been stressed by processing in a humus sedimentation tank.

Yet another benefit relates to the removal of prescribed substances from the sewage water. Prescribed substances are prescribed because they are concentrated by bioaccumulation in the ecosystem. These include compounds such as polychlorinated bi-phenols (PCB's). tri-butyltin (TBT) and dioxin (List 1 and List 2 prescribed substances). Bacteria in a sewage treatment works will certainly concentrate these substances. Bacteria are at the root of the ecosystem, and big-accumulation of toxins starts with the bacteria. The suspended bacteria solids removal efficiency of the active filtration glass granules filter is better before the humus tank rather than after the humus tanks. The removal of prescribed toxins is therefore improved with a solids removal process before the humus tank.

When aerobic bacteria are exposed to anoxic conditions a proportion of the bacteria will succumb and lyse in to the water thereby releasing their contents and prescribed substances back into the water. Organisms under serious . stress tend to discharge into the water, multiply or go into a dormant stage. In all cases a portion of the bacterial . cell biomass and their contents will be released back into the water. The application of active filtration glass . : granules prior to humus tank sedimentation therefore provides a mechanism for the removal of prescribed substance and bio- accumulated toxins from the discharge of sewage and industrial effluent.

The active filtration glass granules used in accordance with the present invention are obtainable from coloured glass, most conveniently from green and/or brown glass bottles. Other kinds of glass, including clear glass, plate glass, and flint glass should be avoided. The glass is in general, first reduced in size by crushing to a pellet size in the region of 3 to 10 mm, preferably around 4 to 8 mm, e.g. about 6 mm. The glass pellets are then further reduced in size by means of glass-onto-glass size reduction processing, conveniently using a vertical shaft impactor, or similar equipment, to produces sub-angular glass granules, in similar size grades to those used in sand filtration. Thus typically there would be used successive layers of the following grades: 4 to 8 mm (corresponding to 2 to 4 mesh size), 1 to 2 mm (8-16 mesh size), and 0.5 to 1.0 mm (16-32 mesh size).

-. - ., In order to avoid impairment of the valuable catalytic and e. * adsorptive properties of these active filtration glass granules, they should not be exposed to temperatures over 150 C. I.

. Active glass granules work by physically filtering the solids from the water and by adsorption of the solids onto the surface of the glass. The catalytic properties of active glass granules in the presence of oxygen, hydrogen peroxide, ozone, chlorine or other oxidizing agent, generates a high oxidation potential on the surface of the glass granules and thereby prevents bacteria from becoming established.

The adsorptive properties are due to the hydrolysed glass surface. (SiOH) on the glass surface reacts with free hydroxyl ions (OH-) in the water, forming Si(OH) 2- and leaving the glass surface negatively charged. The negative charge adsorbs positively charge particles, molecules and ions.

The catalytic properties are generated by metal ions such as ferric oxide and chromium oxides on the surface of the glass.

Other metal oxides present in the glass, or which may be bonded to the glass, if desired to further improve the properties of the active filtration glass granules, include titanium oxides, and transition element metal oxides, as discussed further herein below. The presence of metal oxides .. . on the surface of the glass granules enables the catalytic .e properties thereof. a :

The raw active filtration glass granules as described above - . may be used directly. If desired, though, they may be subjected to further processing to enhance their performance, including one or more of the following.

Fluidised bed fractionation using clean water to remove dust, small particles and flat particles, improves the particle shape and size distribution.

The fluidised water can be at a high oxidation potential using chlorine, chlorine dioxide, ozone, permanganate, bromine, or a strong oxidising agent. The oxidising agent will remove surface biological, organic and inorganic contamination and sanitize the glass granules The microstructure of the glass surface can be changed by low pH conditions using acids such as citric acid, ascorbic acid or other week organic acids. Hydrochloric acid, hydrofluoric acid and other strong acids can also be used in the process.

The acids dissolve the carbonates and salts in the glass to make a rough or porous structure, which has a high surface - . area. The higher the surface area the better the catalytic, ecce adsorptive and absorptive properties of the active filtration . glass granules. c

ate. Exposure to strong bases and high pH using, for example, sodium hydroxide, removes surface layers of the glass granules, exposing surface active sites.

Surface coatings can be bonded onto the glass to change the chemical characteristics of the active filtration glass granules. Chemical groups may include silicones and metals such as titanium dioxide can be added to increase catalytic and selective adsorption properties.

The active filtration glass granules are used in essentially the same manner as a conventional filter sand, with successive layers of progressively smaller mesh size. Thus generally there is provided a coarse base support layer with a thickness of the order of 100 to 200 mm, e.g. 150 mm; an intermediate layer (usually with a mesh size of 8-16) with a thickness of the order of 100 to 200 mm, e.g. 150 mm; and a finer filter layer (usually with a mesh size of 16-32) with a thickness of the order of 300 to 1500 mm, preferably 400 to 1000 mm, e.g. 750 mm.

In accordance with conventional practice, the active .

filtration glass granules filter stage of the invention, may ate also be periodically cleared of accumulated solids by . reversing the water flow, and returning the flushed out solids to the primary sedimentation stage or biological a. stage. .

The active filtration glass granules used in accordance with the present invention have the particular benefits of acting both as a mechanical filtration media and physically removing solids from the water, and also adsorbing charged particles, molecules and ions, as well as acting as a surface catalytic filter media.

In more detail, during the size reduction process, the molecular bonds holding the glass together are broken at the surface. This leaves on the surface of the glass, ions of oxygen, aluminium, silica, ferric oxide, chromium dioxide and other elements or compounds making up the composition of the glass. The breakage of the surface bonds results in an electrical in-balance at the glass surface. In an aqueous solution the glass develops a hydrolyzed negatively charged surface with a high zeta potential. This active surface attracts and adsorbs positively charged particles, positively charged and dipolar organic molecules, and metal ions. Also adsorbed are dipolar organic molecules, including proteins, hydrocarbons, as well as small particles such as viri, . . . bacteria, protozoa, crytosporidia and giardia oocysts. e ë.e

A. Certain chemical species present on the surfaces of the active filtration glass granules exhibit catalytic activity, - -e . such as oxides of iron, chromium titanium and most of the . transition elements. The catalyst works by dissociating molecules such as water and dissolved oxygen to form highly reactive free radicals. The free radicals are generated on the surface of the active filtration glass granules. The radicals can react with any chemical species that can be oxidised such metals and organic compounds. Metals are chelated and oxidised, whilst organic molecules are cracked into smaller, and generally less harmful, compounds.

Organic molecules present on the surface and in the cell wall of bacteria, viri, and protozoa are oxidised. The surface of active filtration glass granules is therefore rendered self- sterilising, and as a result is largely free of biofouling.

Cryptosporidian oocysts are rendered more susceptible to oxidation after they have passed through a sand filter media.

It is believed that the oocyst experiences physical damage to its cell wall, which gives a route by which the disinfectant (chlorine, ozone, Ultra Violet light or oxidising agents) is more effective. In sand filters, the sand normally becomes progressively coated with a layer of bacteria and the polysaccharide gelatinous material excreted by the bacteria. ce. .

The surface of the sand particles thereby becomes cushioned A. at a microscopic level and as a result, less damaging to the oocysts. The active filtration glass granules used in accordance with the present invention tend to be much more ..

free of bacteria, and as a result impact damage to oocysts will be more severe, thereby improving the effectiveness of the disinfectants used, and the safety of the water.

Active filtration glass granules can exert its catalytic action in any water type, however the presence of dissolved oxygen, or oxidising chemicals such as ozone, peroxide, chlorine, chlorine dioxide and bromine, will enhance the surface catalytic properties by increasing still further, the free radical concentration and oxidation potential on the surface of the glass granules.

It will be appreciated that in relation to the coarse screening; primary sedimentation; and biological treatment, stages, any form of these known in the art, may in general be used in the apparatus and process of the present invention.

Thus, for example, in the case of the biological treatment stage, there may be used trickle down flow biofiltration, fluidised bed biofiltration, or activated sludge systems. ë ë ë ë :. a sea. ae . .

Claims

1. A water filtration media manufactured from green or brown glass bottles and used in a filter for the treatment of water and wastewater that actively resists colonization by bacteria.

2. A water filtration media as in claim 1 that when used in a filter may replace or precede the humus tank sedimentation stage in a wastewater treatment process.

3. A glass filtration media as in claim 2 that prevents the release of chemicals and prescribed substances back into the water by not subjecting the bacteria to anoxic stress.

4. A glass filtration media as in the preceding claims with an active surface for the adsorption of chemicals, prescribed substances and small particles.

5. A glass filtration media as in the preceding claims with an active catalytic surface, which generates a zone of high oxidation potential on the surface of the media for the cracking of organic molecules and oxidation of metals.

6. A glass filtration media as in claim 5 that can by further enhanced by the synergistic action of oxidising chemicals and catalysts injected into the water before the glass filtration media. ë ace ë a e

as

7. The filter media as in the proceeding claims that provides an effective means of removing oocysts of protozoa such as *. cryptosporidia from water, or rendering them susceptible to oxidation. :.

8. A filtration media as in the preceding claims that has ,. enhanced surface active properties of catalysis and adsorption by exposure of the glass to an acid as part of the manufacturing process.