Patent Application
20180282190
The present invention seeks to provide improved methodologies and systems for water treatment.
There is thus provided in accordance with a preferred embodiment of the present invention a clogging resistant biofilm-based water treatment system, including a membrane-enclosed water flow pathway including at least one water-impermeable, oxygen-permeable membrane wall portion extending along the pathway and at least another wall portion extending along at least part of the pathway, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and biofilm growth and clogging does not take place along the another wall portion.
In accordance with a preferred embodiment of the present invention the at least another wall portion includes at least one water-impermeable, oxygen-impermeable wall portion extending along at least part of the pathway, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and clogging does not take place along the water-impermeable, oxygen-impermeable wall portion.
Preferably, the at least another wall portion includes a plurality of water-impermeable, oxygen-impermeable wall portions interspersed with water-impermeable, oxygen-permeable wall portions and extending along at least part of the pathway, and biofilm growth and consequent clogging which prevents water flow but not oxygen permeation generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and clogging which prevents water flow generally does not take place along the water-impermeable, oxygen-impermeable wall portions, such that water to be treated can flow along generally the entire length of the pathway notwithstanding biofilm clogging of the plurality of water-impermeable, oxygen-permeable membrane wall portions into engagement with the biofilm on the water-impermeable, oxygen-permeable wall portions and oxygen diffuses into the biofilm.
Preferably, a surface area of the water-impermeable, oxygen-permeable membrane wall portion is at least 80% of the surface area of the at least part of the pathway.
In accordance with a preferred embodiment of the present invention the at least one water-impermeable, oxygen-impermeable wall portion extends continuously along at least part of the pathway. Additionally or alternatively, the at least one water-impermeable, oxygen-impermeable wall portion includes plural water-impermeable, oxygen-impermeable wall portions. Additionally or alternatively, the at least one water-impermeable, oxygen-impermeable membrane wall portion is formed of the at least one water-impermeable, oxygen-permeable membrane overlaid with an oxygen-impermeable layer. Preferably, the oxygen-impermeable layer is formed from at least one of an adhesive, a heat laminatable surface; and a thermoplastic polymer.
In accordance with a preferred embodiment of the present invention the plurality of water-impermeable, oxygen-impermeable wall portions and the plurality of water-impermeable, oxygen-permeable wall portions extends continuously along at least part of the pathway. Additionally or alternatively, a cumulative width of the oxygen-permeable membrane wall portions is greater than the cumulative width of the plurality of water-impermeable, oxygen-impermeable wall portions.
Preferably, the wall portion surface area of the plurality of water-impermeable, oxygen-impermeable wall portions is between 20% and 50% of the wall portion surface area of the plurality of water-impermeable, oxygen-permeable wall portions. Additionally or alternatively, the width of each of the plurality of water-impermeable, oxygen-impermeable wall portions is between 10-50 mm. Additionally or alternatively, the plurality of water-impermeable, oxygen-impermeable membrane wall portions are formed of the at least one water-impermeable, oxygen-permeable membrane overlaid with an oxygen-impermeable layer.
In accordance with a preferred embodiment of the present invention the membrane-enclosed water flow pathway includes an upstream region, including a plurality of water-impermeable, oxygen-permeable membrane wall portions extending along the pathway interspersed with a plurality of water-impermeable, oxygen-impermeable wall portions extending along at least part of the pathway, wherein biofilm growth and consequent clogging which prevents water flow but not oxygen permeation generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and clogging which prevents water flow does not take place along the water-impermeable, oxygen-impermeable wall portions, such that water to be treated can flow along generally the entire length of the pathway notwithstanding biofilm clogging of the plurality of water-impermeable, oxygen-permeable membrane wall portions into engagement with the biofilm on the water-impermeable, oxygen-permeable wall portions and oxygen diffuses into the biofilm, and a downstream region including a water-impermeable, oxygen-permeable membrane wall portion.
In accordance with a preferred embodiment of the present invention the membrane-enclosed water flow pathway has a cross-sectional configuration defining a pair of generally parallel mutually spaced sides, separated by at least a minimum transverse separation and the plurality of water-impermeable, oxygen-impermeable wall portions each having a width which is at least twice as large as the minimum transverse separation.
There is also provided in accordance with another preferred embodiment of the present invention a clogging resistant biofilm-based water treatment method including causing water to be treated to flow along a membrane-enclosed water flow pathway including at least one water-impermeable, oxygen-permeable membrane wall portion extending along the pathway and at least another wall portion extending along at least part of the pathway, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and biofim growth and clogging does not take place along the another wall portion.
There is further provided in accordance with yet another preferred embodiment of the present invention a clogging resistant biofilm-based water treatment method including causing water to be treated to flow along a membrane-enclosed water flow pathway including at least one water-impermeable, oxygen-permeable membrane wall portion extending along the pathway and at least one water-impermeable, oxygen-impermeable wall portion extending along at least part of the pathway, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and clogging does not take place along the water-impermeable, oxygen-impermeable wall portion.
Preferably, the causing water to be treated to flow includes causing water containing organic material and ammonium compounds to flow along the pathway.
In accordance with a preferred embodiment of the present invention at an initial process phase most of the organic material is oxygenated in a first region of the pathway, at a second process phase, biofilm growth clogs at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway, such that the water to be treated, containing organic material, travels through the first region to a second region of the pathway, at a third process phase, clogging of at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway, generally blocks oxygen supply to the biofilm along the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway, causing at least partial disintegration of the biofilm along the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway and resulting at least partial unclogging thereof and at a fourth process phase, biofilm growth clogs at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the second region of the pathway, such that the water to be treated, containing organic material, travels along the at least one water-impermeable, oxygen-impermeable membrane wall portion through the second region to a third region of the pathway.
Alternatively, at an initial process phase most of the organic material is oxygenated in a first region of the pathway, at a second process phase, biofilm growth clogs at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway but does not clog at least most of the at least one water-impermeable, oxygen-impermeable membrane wall portion in the first region of the pathway, such that the water to be treated, containing organic material, travels along the at least one water-impermeable, oxygen-impermeable membrane wall portion through the first region to a second region of the pathway, at a third process phase, clogging of at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway, generally blocks oxygen supply to the biofilm along the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway, causing at least partial disintegration of the biofilm along the at least one water-impermeable, oxygen-permeable membrane wall portion in the first region of the pathway and resulting at least partial unclogging thereof and at a fourth process phase, biofilm growth clogs at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the second region of the pathway but does not clog at least most of the at least one water-impermeable, oxygen-impermeable membrane wall portion in the second region of the pathway, such that the water to be treated, containing organic material, travels along the at least one water-impermeable, oxygen-impermeable membrane wall portion through the second region to a third region of the pathway.
Additionally, at a fifth process phase clogging of at least most of the at least one water-impermeable, oxygen-permeable membrane wall portion in the second region of the pathway, generally blocks oxygen supply to the biofilm along the at least one water-impermeable, oxygen-permeable membrane wall portion in the second region of the pathway, causing at least partial disintegration of the biofilm along the at least one water-impermeable, oxygen-permeable membrane wall portion in the second region of the pathway and resulting at least partial unclogging thereof.
In accordance with a preferred embodiment of the present invention most of the ammonium compounds are oxygenated in regions of the pathway which are downstream of the first and second regions.
Preferably, the duration of the initial process phase is less than six months. Additionally or alternatively, duration of the second process phase is less than six months. Alternatively or additionally, the duration of the third process phase is less than six months.
In accordance with a preferred embodiment of the present invention the second and third process phases at least partially overlap in time. Additionally or alternatively, at least some of the initial, second, third and fourth process phases at least partially overlap in time.
There is yet further provided in accordance with still another preferred embodiment of the present invention a clogging resistant biofilm-based water treatment method including causing water to be treated to flow along a membrane-enclosed water flow pathway including a plurality of water-impermeable, oxygen-permeable membrane wall portions extending along the pathway interspersed with a plurality of water-impermeable, oxygen-impermeable wall portions extending along at least part of the pathway, wherein biofilm growth and consequent clogging which prevents water flow but not oxygen permeation generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and clogging which prevents water flow does not take place along the water-impermeable, oxygen-impermeable wall portions, such that water to be treated can flow along generally the entire length of the pathway notwithstanding biofilm clogging of the plurality of water-impermeable, oxygen-permeable membrane wall portions into engagement with the biofilm on the water-impermeable, oxygen-permeable wall portions and oxygen diffuses into the biofilm.
Preferably, the causing water to be treated to flow includes causing water containing organic material and ammonium compounds to flow along the pathway.
In accordance with a preferred embodiment of the present invention a cumulative width of the oxygen-permeable membrane wall portions is greater than the cumulative width of the plurality of water-impermeable, oxygen-impermeable wall portions.
There is even further provided in accordance with another preferred embodiment of the present invention a water-impermeable, oxygen permeable membrane system including a water flow pathway including a first water-impermeable, oxygen-permeable membrane wall portion extending along at least part of the pathway and having an inside surface and an outside surface and a second water-impermeable wall portion extending along at least part of the pathway, the second wall portion being sealed to the inside surface of the first wall portion at along part of its periphery thereby to define at least part of the water flow pathway and being configured to define an air-flow pathway between the outside surface of the first wall portion and an adjacent surface of the second wall portion and to define a water-flow pathway between the inside surface of the first wall portion and an adjacent surface of the second wall portion.
Preferably, the second water impermeable wall portion includes an oxygen-permeable membrane.
In accordance with a preferred embodiment of the present invention the second water impermeable wall portion includes a wall portion having greater thickness and greater stiffness than the first water-impermeable, oxygen-permeable membrane wall portion.
Preferably, the first water-impermeable, oxygen permeable membrane wall portion and the second water-impermeable wall portion are wound together in a spiral-wound configuration. In accordance with a preferred embodiment of the present invention the first water-impermeable, oxygen permeable membrane wall portion and the second water-impermeable wall portion are stacked together.
In accordance with a preferred embodiment of the present invention the second water impermeable wall is oxygen-impermeable.
Preferably, the second wall portion includes at least one of plastic netting and dimpled sheet. Additionally, the second wall portion comprises at least one of a bi-planar and a tri-planar plastic netting. In accordance with a preferred embodiment of the present invention the second wall portion comprises a dimpled sheet including one sided or double sided dimples.
In accordance with a preferred embodiment of the present invention the air flow pathway has a transverse distance of between 4-10 mm between the outside surface of the first wall portion and the adjacent surface of the second wall portion. Additionally or alternatively, the water flow pathway has a transverse distance of 2-8 mm between the inside surface of the first wall portion and the adjacent surface of the second wall portion.
There is also provided in accordance with still another preferred embodiment of the present invention a water treatment system, including a membrane-enclosed water flow pathway receiving contaminant-containing water to be treated and at least one contaminant precipitating chemical, wherein at least one contaminant is precipitated along the water flow pathway and a back-flow cleaning subsystem operative to back-flush at least part of the membrane-enclosed water flow pathway, thereby removing therefrom the at least one precipitated contaminant.
Preferably, the contaminant-containing water contains phosphate, the contaminant precipitating chemical includes ferric cations and the precipitated contaminant includes ferric phosphate. In accordance with a preferred embodiment of the present invention the contaminant-containing water contains sulfide, the contaminant precipitating chemical includes at least one of ferric and aluminum cations and the precipitated contaminant includes at least one of ferric sulfide and aluminum sulfide. Preferably, the contaminant-containing water contains at least one heavy metal, the contaminant precipitating chemical includes a base and the precipitated contaminant includes metal hydroxides.
In accordance with a preferred embodiment of the present invention the membrane-enclosed water flow pathway forms part of an aerobic biological water treatment system. Additionally or alternatively, the back-flow cleaning subsystem includes an air scouring subsystem operative along at least part of the membrane-enclosed water flow pathway.
There is further provided in accordance with yet another preferred embodiment of the present invention a water treatment method including causing contaminant-containing water to be treated and at least one contaminant precipitating chemical to flow through a membrane-enclosed water flow pathway, wherein at least one contaminant is precipitated along the water flow pathway and back-flushing at least part of the membrane-enclosed water flow pathway, thereby removing therefrom the at least one precipitated contaminant.
Preferably, the contaminant-containing water contains phosphate, the contaminant precipitating chemical includes ferric cations and the precipitated contaminant includes ferric phosphate. In accordance with a preferred embodiment of the present invention the contaminant-containing water contains sulfide, the contaminant precipitating chemical includes at least one of ferric and aluminum cations and the precipitated contaminant includes at least one of ferric sulfide and aluminum sulfide. Preferably, the contaminant-containing water contains at least one heavy metal, the contaminant precipitating chemical includes a base and the precipitated contaminant includes metal hydroxides.
In accordance with a preferred embodiment of the present invention the membrane-enclosed water flow pathway forms part of an aerobic biological water treatment system. Additionally or alternatively, the back-flushing includes air scouring along at least part of the membrane-enclosed water flow pathway.
There is yet further provided in accordance with still another preferred embodiment of the present invention a clogging resistant biofilm-based water treatment method including causing water to be treated, containing both dissolved organic material and ammonium compounds, to be mixed with sludge, producing a first mixture containing suspended biomass and resulting in adsorption by the sludge of at least most of the dissolved organic material, following the adsorption, separating the sludge having adsorbed thereon the dissolved organic material, from liquid, which contains the ammonium compounds, causing the liquid to be treated to flow along an oxygen-permeable membrane-enclosed, water impermeable water flow pathway, thereby biologically nitrifying the ammonium compounds in the liquid, following the nitrifying, mixing the liquid containing nitrified ammonium compounds with the sludge having adsorbed thereon the dissolved organic material to create a second mixture, thereby producing denitrification of the nitrified ammonium compounds and oxidation of the organic material which had been adsorbed onto the sludge and following the denitrification, separating the sludge from water, wherein the water has substantially decreased amounts of dissolved organic material and ammonium compounds as compared with the water to be treated.
Preferably, the first mixture has suspended biomass at a concentration of at least 1000 mg/liter. Additionally or alternatively, the method also includes utilizing the sludge separated from the water following the denitrification to be mixed with the water to be treated, which contains both dissolved organic material and ammonium compounds.
In accordance with a preferred embodiment of the present invention the oxygen-permeable membrane-enclosed, water impermeable water flow pathway includes an elongated membrane enclosed generally horizontal flow path for water including an inlet for water to be treated at a first end of the horizontal flow path, an outlet for treated water on a second end of the horizontal flow path and an oxygen permeable membrane, defining a tubular water pathway having an inside surface exposed to water and an outside surface exposed to ambient air, the oxygen permeable membrane supporting a biofilm on the inside surface, the oxygen permeable membrane being arranged to define at least one generally vertical airflow passageway communicating with the outside surface. Additionally, the horizontal flow path is spirally wound and the at least one generally vertical airflow passageway has a generally spiral cross section. Additionally or alternatively, the generally horizontal flow path and the at least one generally vertical airflow passageway are enclosed within a generally vertical cylindrical enclosure. In accordance with a preferred embodiment of the present invention the generally horizontal flow path has a tapered top surface region.
In accordance with a preferred embodiment of the present invention mutually adjacent inside surfaces of the tubular water pathway are separated by at least one interior spacer. Additionally or alternatively, mutually adjacent outside surfaces of the tubular water pathway are separated by at least one exterior spacer.
In accordance with a preferred embodiment of the present invention mutually adjacent outside surfaces of the tubular water pathway are separated by a transverse distance of 4-20 mm. Additionally or alternatively, the spacer includes at least one of: drainage netting, reinforcement mesh, a screen and a three-dimensional plastic mesh grid.
There is also provided in accordance with another preferred embodiment of the present invention a clogging resistant biofilm-based water treatment method including causing water to be treated to flow initially along a first upstream membrane-enclosed water flow pathway portion including at least one upstream water-impermeable, oxygen-permeable membrane wall portion extending along the first upstream membrane-enclosed water flow pathway and thence along a downstream membrane-enclosed water flow pathway portion including at least one downstream water-impermeable, oxygen-permeable membrane wall portion extending along the downstream membrane-enclosed water flow pathway, upon clogging of the first upstream membrane-enclosed water flow pathway portion, causing water to be treated to flow along at least one second upstream membrane-enclosed water flow pathway portion including at least one upstream water-impermeable, oxygen-permeable membrane wall portion extending along the first upstream membrane-enclosed water flow pathway and thence along the downstream upstream membrane-enclosed water flow pathway portion including at least one downstream water-impermeable, oxygen-permeable membrane wall portion extending along the downstream membrane-enclosed water flow pathway, upon subsequent unclogging of the first upstream membrane-enclosed water flow pathway portion, causing water to be treated to flow initially along a first upstream membrane-enclosed water flow pathway portion including at least one upstream water-impermeable, oxygen-permeable membrane wall portion extending along the first upstream membrane-enclosed water flow pathway and thence along a downstream upstream membrane-enclosed water flow pathway portion including at least one downstream water-impermeable, oxygen-permeable membrane wall portion extending along the downstream membrane-enclosed water flow pathway.
Preferably, the method also includes at least partially unclogging the first upstream membrane-enclosed water flow pathway portion. Additionally, the at least partially unclogging the first upstream membrane-enclosed water flow pathway portion includes at least one of terminating flow of water to be treated through the first upstream membrane-enclosed water flow pathway portion for a sufficient duration to provide acceptable partial unclogging by aerobic endogenous decay, causing gas bubbles to scour the first upstream membrane-enclosed water flow pathway portion and circulating fluid through the first upstream membrane-enclosed water flow pathway portion, thereby creating shear forces which dislodge biofilm from the first upstream membrane-enclosed water flow pathway portion.
In accordance with a preferred embodiment of the present invention the water treatment method also includes discharging treated water directly from the membrane-enclosed water flow pathway without filtering.
In accordance with a preferred embodiment of the present invention the water treatment method also includes discharging treated water directly from the membrane-enclosed water flow pathway, the treated water having a suspended solids concentration of less than 50 mg/liter. Preferably, the water treatment method also includes discharging treated water directly from the membrane-enclosed water flow pathway, the treated water having a suspended solids concentration of less than 35 mg/liter.
There is still further provided in accordance with even a further preferred embodiment of the present invention a water treatment system including at least one settling pond receiving water to be treated, at least one oxidation pond receiving water from the at least one setting pond and a membrane-enclosed water flow pathway receiving water from the at least one oxidation pond and discharging water back to at least one of the at least one settling pond and the at least one oxidation pond and including at least one water-impermeable, oxygen-permeable membrane wall portion extending along the pathway, wherein clogging normally does not take place along the water-impermeable, oxygen-permeable membrane wall portion.
Preferably, the membrane-enclosed water flow pathway also includes at least one other wall portion, wherein biofilm growth and consequent clogging does not take place along the at least one other wall portion. Additionally or alternatively, the at least one other wall portion includes at least one water-impermeable, oxygen-impermeable wall portion extending along at least part of the pathway, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and clogging does not take place along the water-impermeable, oxygen-impermeable wall portion.
In accordance with a preferred embodiment of the present invention the water treatment system also includes at least one settling pond receiving water to be treated and at least one oxidation pond receiving water from the at least one setting pond, the membrane-enclosed water flow pathway receiving water from the at least one oxidation pond and discharging water back to at least one of the at least one settling pond and the at least one oxidation pond.
The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:
Reference is now made to
In each of
As seen in each of
In accordance with a preferred embodiment of the present invention, air circulation is provided through the interior of module 100 by means of conduits 120 connecting air flow generator such as a blower or a fan 122 to top apertures 116. The air is provided to top apertures 116, flows through the interior of module 100 and is discharged or vented through circumferentially distributed bottom apertures 118.
It is a particular feature of the invention that circulation may be provided without the need for conduits 120 and air flow generator 122, by means of a naturally occurring air flow resulting from temperature differences between the temperature of the water being treated and the ambient air within modules 100. It is appreciated that in this case, top apertures 116 in top cover 106 may be replaced by circumferentially distributed apertures formed in cylindrical wall 114. If, for example, the ambient air is hotter than the water being treated, a downward air flow will take place from circumferentially distributed top apertures (not shown) to circumferentially distributed bottom apertures 118 and if the ambient air is cooler than the water being treated, an upward air flow will take place from circumferentially distributed bottom apertures 118 to circumferentially distributed top apertures (not shown).
Alternatively, as described hereinbelow with reference to
In accordance with a preferred embodiment of the present invention, each of modules 100 includes a membrane-enclosed water flow pathway 130 including at least one water-impermeable, oxygen-permeable membrane wall portion 144 extending along the pathway and at least another wall portion extending along at least part of the pathway 130, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and biofilm growth and clogging does not take place along the other wall portion. An entrance 131 of the water flow pathway 130 is coupled to inlet manifold 102. An exit 133 of the water flow pathway is coupled to outlet manifold 104.
Turning specifically to
Preferably, water impermeable oxygen-permeable membrane wall portions 144 comprise a fabric formed of a first polymer, extrusion coated with a second polymer. The coating is preferably applied to the water facing side of the fabric and typically has a thickness of between 5 and 20 microns. Preferably, the first polymer is a dense polyolefin, such as polyethylene or polypropylene, or a polyester. In a preferred embodiment of the water-impermeable, oxygen permeable membrane the fabric formed of a first polymer is a non-woven fabric, such as Tyvek®, commercially available from Dupont. In one embodiment of the water impermeable oxygen-permeable membrane wall portions 144, the second polymer is an alkyl-acrylate. The function of the second polymer coating is to substantially seal the fabric formed of a first polymer to passage of water with a small additional resistance to oxygen passage by diffusion therethrough. It is noted that alkyl-acrylates are compatible with polyolefin fabrics and specifically polyethylene fabrics for coating by extrusion. Alternatively, the second polymer is poly-methyl-pentene, which is compatible with polyester fabrics for coating by extrusion.
Strip 146 preferably extends along at least the part of the water flow pathway 130 wherein buildup of a thick biofilm normally takes place. Strip 146 may extend further along the water flow pathway in order to enable reversing the flow direction or increasing the feed rate or in order to deal with an unexpected increase in organic material load passing through the water flow pathway.
Preferably, strip 146 has an oxygen permeability which is lower by more than one order of magnitude than that of oxygen-permeable membrane wall portion 144. Strip 146 may be realized, for example by coating a corresponding strip of the water-impermeable, oxygen-permeable membrane wall portion 144 with an oxygen-impermeable material, such as a contact adhesive, ink, drying adhesive, hot adhesive. Strip 146 alternatively may be in the form of a strip of a generally low permeability polymer such as polyethylene or polypropylene, heat laminated onto oxygen-permeable membrane wall portion 144 or arranged on oxygen-permeable membrane wall portion 144 and held thereon by coiling of the sleeve.
Strip 146 may be made of a pressure sensitive tape such as duct tape. It should be noted that strip 146 should be chosen to be adhesive or adherent to water-impermeable, oxygen-permeable membrane wall portion 144.
It is further noted that oxygen impermeable strip 146 may be applied on either or both of the water side and the air side of oxygen permeable wall portion 144. The choice of the side on which to apply the non-permeable material is generally made based on production process considerations.
Preferably an additional spacer 147 is coiled outside of and together with pathway 130. Coiled spacer 143 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent inside walls of pathway 130, thus allowing water movement between adjacent wall surfaces of the coiled membrane-enclosed water flow pathway 130. Similarly, coiled spacer 147 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent outside walls of pathway 130, thus allowing air movement between adjacent outside wall surfaces of the coiled membrane-enclosed water flow pathway 130.
The nettings for either of spacers 143 and 147 are preferably bi-planar- or tri-planar. The dimpled sheets for either of spacers 143 and 147 can include one sided or double sided dimples. The thickness of spacers 143 and 147 can be between approximately 1-20 mm and most preferably is between 5-10 mm Spacers 143 and 147 are made of a water durable material having a compressive strength of above 2 ton/m2, most preferably above 20 ton/m2. Preferably the material is suitable for coiling at a diameter of at least 200 mm Preferred materials for the spacers include plastic materials such as polyethylene, polyethylene terephthalate (PET), polypropylene, polyamide and polyacetal. Spacers 143 and 147 may be identical, similar or dissimilar.
The water inlet and outlet flows in the embodiment of
Turning specifically to
Preferably, strips 156 have an oxygen permeability which is lower than that of oxygen-permeable membrane wall portion 154 by more than one order of magnitude. Strips 156 may be realized, for example by coating a corresponding strip of the water-impermeable, oxygen-permeable membrane wall portion 154 with an oxygen-impermeable material, such as a contact adhesive, ink, drying adhesive, hot adhesive. Strip 156 alternatively may be in the form of a strip of a generally low permeability polymer such as polyethylene or polypropylene, heat laminated onto oxygen-permeable membrane wall portion 154 or arranged on oxygen-permeable membrane wall portion 154 and held thereon by coiling of the sleeve.
Strips 156 may be made of a pressure sensitive tape such as duct tape. It should be noted that strips 156 should be chosen to be adhesive or adherent to water-impermeable, oxygen-permeable membrane wall portion 154.
It is further noted that oxygen impermeable strips 156 may be applied on either or both of the water side and the air side of oxygen permeable wall portion 154. The choice of the side on which to apply the non-permeable material is generally made based on production process considerations.
Preferably an additional spacer 157 is coiled outside of and together with pathway 130. Coiled spacer 153 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent inside walls of pathway 130, thus allowing water movement between adjacent wall surfaces of the coiled membrane-enclosed water flow pathway 130. Similarly, coiled spacer 157 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent outside walls of pathway 130, thus allowing air movement between adjacent outside wall surfaces of the coiled membrane-enclosed water flow pathway 130.
The nettings for either of spacers 153 and 157 are preferably bi-planar- or tri-planar. The dimpled sheets for either of spacers 153 and 157 can include one sided or double sided dimples. The thickness of spacers 153 and 157 can be between approximately 1-20 mm and most preferably is between 5-10 mm. Spacers 153 and 157 are made of a water durable material having a compressive strength of above 2 ton/m2, most preferably above 20 ton/m2. Preferably the material is suitable for coiling at a diameter of at least 200 mm Preferred materials for the spacers include plastic materials such as polyethylene, polyethylene terephthalate (PET), polypropylene, polyamide and polyacetal. Spacers 153 and 157 may be identical, similar or dissimilar.
The water inlet and outlet flows in the embodiment of
Reference is now made to
Reference is now made to
In the embodiment presented in
Reference is now made to
It is to be appreciated that
Table I below presents examples of dimensions of full scale embodiments of the present invention as described hereinabove with reference to
It is seen from a consideration of
For settled municipal wastewater in a moderate climate, typically Phase 2 extends for one to three months from the initial supply of water to be treated to the pathway 130. In regions III and IV nitrification takes place, and removal of organic material is generally at rate smaller than or equal to the endogenous decay rate of the biofilm microbiological population.
At a phase designated as Phase 3, the biofilm growth is such that in region I, the entire pathway 130, other than the portion thereof bounded by oxygen-impermeable strips 146 is blocked. Once this occurs, the rate of biofilm buildup in region II increases, due to the fact that an increasing amount of organic material in the water reaches region II. As a consequence, region III also receives a higher organic material loading than in Phase 2 similar to the organic material load that region II received during Phase 2.
For settled municipal wastewater in a moderate climate, typically Phase 3 is reached within 2-4 months from the beginning of Phase 2.
In region IV the buildup is significantly slower than in regions II and III. The reason for this is that most of the organic material in the water to be treated is already depleted by passing through upstream regions II and III, and does not reach region IV, wherein the remaining organic material, load is only sufficient to support the endogenous decay rate of a thin biofilm.
At Phase 4, the biofilm growth is such that in region II, the entire pathway 130, other than the portion bounded by oxygen-impermeable strips 146 is blocked by the biofilm.
Importantly, at Phase 4, this blockage prevents the flow of water, which contains the organic material, from reaching most of the biofilm and therefore the lack of organic material, sufficient to support the biofilm in region I, causes the biofilm in region I to decay and disintegrate, while significant biofilm buildup continues at regions II and III other than along oxygen-impermeable strips 146. Disintegration typically takes several weeks to one month in moderate climates. The water to be treated passes through region I between strips 146 and substantially all of the organic material reaches regions II and III.
Once all of the pathway 130 along region II is blocked other than that portion thereof bordered by oxygen-impermeable strips 146, significant biofilm buildup begins at region III other than along oxygen-impermeable strips 146, due to the fact that an increasing amount of organic material in the water reaches region III. In region IV the buildup remains generally the same as in Phases 2 and 3, which is a generally steady state level at which the passageway 130 does not become blocked.
In a moderate climate, typically Phase 4 extends for about one month from the end of Phase 3. During Phase 4, in region IV the biofilm buildup is significantly slower than in regions II and III. The reason for this is that most of the organic material in the water to be treated is already depleted in region II and III and does not reach region IV wherein the remaining organic material load is only sufficient to support the endogenous decay rate of a thin biofilm.
At a phase designated as Phase 5, the lack of organic material in region I, causes the biofilm to fully disintegrate, while the lack of organic material to support biofilm growth in region II causes the biofilm in region II to begin to decay and disintegrate, while significant biofilm growth continues at region III and is renewed in region I, upon completion of disintegration of the previously built up biofilm other than along oxygen-impermeable strips 146 thereat. Disintegration typically takes several weeks to one month in moderate climates. Water to be treated bypasses region II between strips 146 and substantially all of the organic material reaches regions III and IV.
Typically Phase 5 covers up to one month from the end of Phase 4. In region IV. During Phase 5, in region IV the biofilm buildup is significantly slower than in regions I and III. The reason for this is that most of the organic material in the water to be treated is already depleted in region I and III and does not reach region IV, wherein the remaining organic material load is only sufficient to support the endogenous decay rate of a thin biofilm.
At a phase designated Phase 6, it is seen that in region I there is an increased buildup of biofilm along the interior surfaces of walls 144 except along strips 146, while in region II the biofilm continues to disintegrate due to lack of organic material. Significant biofilm growth continues at region III other than along oxygen-impermeable strips 146, causing all of the pathway 130 at Region III to become blocked other than that portion thereof bordered by oxygen-impermeable strips 146. Once all of the pathway 130 in Region III is blocked other than that portion thereof bordered by oxygen-impermeable strips 146, significant biofilm growth appears at regions I and II other than along oxygen-impermeable strips 146. Typically Phase 6 covers one to two months from the end of phase 5.
At a phase designated Phase 7, it is seen that in region I there is an further buildup of biofilm along the interior surfaces of walls 144 except along strips 146. Once the entire pathway 130 in region I is blocked other than that portion thereof bordered by oxygen-impermeable strips 146, significant biofilm buildup occurs at region II other than along oxygen-impermeable strips 146. In region III, the biofilm is seen to disintegrate due to lack of organic material and biofilm buildup is renewed upon completion of disintegration of the previously built up biofilm other than along oxygen-impermeable strips 146 thereat.
Typically Phase 7 covers one to two months from the end of phase 6.
At a phase designated Phase 8, it is seen that in region II there is a further buildup of biofilm along the interior surfaces of walls 144 except along strips 146. Once the entire pathway 130 in region II, other than that portion thereof bordered by oxygen-impermeable strips 146, is blocked, significant biofilm buildup occurs at region III other than along oxygen-impermeable strips 146. In region I, the biofilm is seen to disintegrate due to lack of organic material and biofilm buildup is renewed, other than along oxygen-impermeable strips 146, upon completion of disintegration of the previously built up biofilm, and region IV the buildup biofilm remains at a steady state level. Typically Phase 8 covers one to two months from the end of Phase 7.
It is appreciated that the sequential phases described generally hereinabove are repeated throughout operation of the system.
Reference is now made to
It is to be appreciated that
It is seen from a consideration of
For settled municipal wastewater in a moderate climate, typically Phase 2 covers one to three months from the initial supply of water to be treated to the pathway 130.
At a phase designated as Phase 3, the biofilm growth is such that in region I, the entire pathway 130, other than the portions bounded by oxygen-impermeable strips 156, is blocked.
As distinct from the situation in the embodiment of
Accordingly, a greater biofilm buildup does not take place in region II as clogged region I removes most of the load of organic material from the water passing therethrough, thus limiting the amount of organic material reaching region II.
It is appreciated that the sequential phases described generally hereinabove are repeated throughout operation of the system.
Reference is now made to
As seen in
A first layer 162 is in the form of a water-impermeable, oxygen-permeable membrane wall portion having an inside surface (not shown) and an outside surface 166. A second layer 168 is in the form of a water-impermeable wall portion having an inside surface 170 and an outside surface 171, which is sealed to the first layer 162 along at least part of its periphery, thereby to define the spacing for at least part of the water flow pathway 130.
Outside surface 171 of second layer 168 is shaped to define air-flow pathways between the outside surface 166 of the first layer 162 and an adjacent surface of the coiled second layer and preferably includes an array of mutually parallel elongate protrusions 172. Inside surface 170 of second layer 168 is shaped to define a water-flow pathway between the inside surface of first layer 162 and an adjacent inside surface 170 of the coiled second layer and preferably include a plurality of dispersed dimples 174.
The water inlet and outlet flows in the embodiment of
The mutually parallel elongate protrusions 172 can have a height of between approximately 1-20 mm in thickness and most preferably between 2-8 mm. The plurality of dispersed dimples 174 can have a height of between approximately 4-20 mm in thickness and most preferably between 4-10 mm.
Preferably the second layer 168 is formed of a material, which is suitable for coiling up at a diameter of at least 250 mm Preferred materials for the second layer 168 include plastic materials such as polyethylene, polyethylene terephthalate (PET), polypropylene, polyamide and polyacetal.
Reference is now made to
It is to be appreciated that the embodiment of
As seen in
As seen in each of
In accordance with a preferred embodiment of the present invention, air circulation is provided through the interior of cubical enclosure 210 by means of conduits 220 coupled to top apertures 216 and to circumferentially distributed bottom apertures 218 and which provide a flow of air from an air flow generator 222, such as a fan.
It is a particular feature of the invention that circulation may be provided without the need for conduits 220 and air flow generator 222, by means of a naturally occurring air flow resulting from temperature differences between the temperature of the water being treated and the ambient air within modules 200. It is appreciated that in this case, top apertures 216 in top cover 206 may be replaced by circumferentially distributed apertures formed in circumferential wall 214. If, for example, the ambient air is hotter than the water being treated, a downward air flow will take place from circumferentially distributed top apertures (not shown) to circumferentially distributed bottom apertures 218 and if the ambient air is cooler than the water being treated, an upward air flow will take place from circumferentially distributed bottom apertures 218 to circumferentially distributed top apertures (not shown).
In accordance with a preferred embodiment of the present invention, each of modules 200 includes a membrane-enclosed water flow pathway 230 including at least one water-impermeable, oxygen-permeable membrane wall portion extending along the pathway and at least another wall portion extending along at least part of the pathway 230, wherein biofilm growth and consequent clogging generally takes place along the water-impermeable, oxygen-permeable membrane wall portion and biofilm growth and clogging does not take place along the other wall portion. An entrance 231 of the water flow pathway 230 is coupled to inlet manifold 202 and an exit 233 of the water flow pathway is coupled to outlet manifold 204.
Turning specifically to
Strip 246 preferably extends along at least the part of the water flow pathway 230 wherein buildup of a thick biofilm normally takes place. Strip 246 may extend further along the water flow pathway in order to enable reversing the flow direction or increasing the feed rate or in order to deal with an unexpected increase in organic material load passing through the water flow pathway process performance.
Preferably, strip 246 has an oxygen permeability which is lower by more than one order of magnitude than that of oxygen-permeable membrane wall portion 244. Strip 246 may be realized, for example by coating a corresponding strip of the water-impermeable, oxygen-permeable membrane wall portion 244 with an oxygen-impermeable material, such as a contact adhesive, ink, drying adhesive, hot adhesive. Strip 246 alternatively may be in the form of a strip of a generally low permeability polymer such as polyethylene or polypropylene, heat laminated onto oxygen-permeable membrane wall portion 244 or arranged on oxygen-permeable membrane wall portion 244 and held thereon by folding of the sleeve.
Strip 246 may be made of a pressure sensitive tape such as duct tape. It should be noted that strip 246 should be chosen to be adhesive or adherent to water-impermeable, oxygen-permeable membrane wall portion 244.
It is further noted that oxygen impermeable strip 246 may be applied on either or both of the water side and the air side of oxygen permeable wall portion 244. The choice of the side on which to apply the non-permeable material is generally made based on production process considerations.
Preferably an additional spacer 247 is provided outside of and folded together with pathway 230. Spacer 243 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent inside walls of pathway 230, thus allowing water movement between adjacent wall surfaces of the membrane-enclosed water flow pathway 230. Similarly, spacer 247 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent outside walls of pathway 230, thus allowing air movement between adjacent outside wall surfaces of the folded membrane-enclosed water flow pathway 230.
The nettings for either of spacers 243 and 247 are preferably bi-planar- or tri-planar. The dimpled sheets for either of spacers 243 and 247 can include one sided or double sided dimples. The thickness of spacers 243 and 247 can be between approximately 1-20 mm and most preferably is between 5-10 mm Spacers 243 and 247 are made of a water durable material having a compressive strength of above 2 ton/m2, most preferably above 20 ton/m2. Preferably the material is suitable for folding at a diameter of at least 2 inches. Preferred materials for the spacers include plastic materials such as polyethylene, polyethylene terephthalate (PET), polypropylene, polyamide and polyacetal. Spacers 243 and 247 may be identical, similar or dissimilar.
The water inlet and outlet flows in the embodiment of
Turning specifically to
Preferably, strips 256 have an oxygen permeability which is lower than that of oxygen-permeable membrane wall portion 254 by more than one order of magnitude. Strips 256 may be realized, for example by coating a corresponding strip of the water-impermeable, oxygen-permeable membrane wall portion 254 with an oxygen-impermeable material, such as a contact adhesive, ink, drying adhesive, hot adhesive. Strip 256 alternatively may be in the form of a strip of a generally low permeability polymer such as polyethylene or polypropylene, heat laminated onto oxygen-permeable membrane wall portion 254 or arranged on oxygen-permeable membrane wall portion 254 and held thereon by folding of the sleeve.
Strips 256 may be made of a pressure sensitive tape such as duct tape. It should be noted that strips 256 should be chosen to be adhesive or adherent to water-impermeable, oxygen-permeable membrane wall portion 254.
It is further noted that oxygen impermeable strips 256 may be applied on either or both of the water side and the air side of oxygen permeable wall portion 254. The choice of the side on which to apply the non-permeable material is generally made based on production process considerations.
Preferably an additional spacer 257 is folded outside of and together with pathway 230. Spacer 253 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent inside walls of pathway 230, thus allowing water movement between adjacent wall surfaces of the membrane-enclosed water flow pathway 230. Similarly, spacer 257 is typically a plastic netting or dimpled sheet, which maintains a spacing between adjacent outside walls of pathway 230, thus allowing air movement between adjacent outside wall surfaces of the membrane-enclosed water flow pathway 230.
The nettings for either of spacers 253 and 257 are preferably bi-planar- or tri-planar. The dimpled sheets for either of spacers 253 and 257 can include one sided or double sided dimples. The thickness of spacers 253 and 257 can be between approximately 1-20 mm and most preferably is between 5-10 mm Spacers 253 and 257 are preferably formed of a water durable material having a compressive strength of above 2 ton/m2, most preferably above 20 ton/m2. Preferably the material is suitable for folding at a diameter of at least 2 inches. Preferred materials for the spacers include plastic materials such as polyethylene, polyethylene terephthalate (PET), polypropylene, polyamide and polyacetal. Spacers 253 and 257 may be identical, similar or dissimilar.
The water inlet and outlet flows in the embodiment of
Reference is now made to
The water treatment system of
The system of
Examples of some suitable precipitating chemicals, also known in the art as coagulants, are: ferric chloride, aluminum sulfate, sodium aluminate. Sodium sulfide is an example of a precipitating chemical useful for precipitation of heavy metals. Mixing of the precipitating chemical into the water may be performed in any suitable known manner.
It is seen that water to be treated, mixed with the precipitating chemical, passes through each water flow pathway 270 from an inlet 275 to a treated water outlet 276. Treated water outlets 276 of water flow pathways 270 are preferably coupled via piping 277 and a valve 278 to an effluent tank 279 having an effluent outlet 280.
Turning additionally to
Along at least part of the water flow pathway 270 there is disposed a perforated conduit 272. It is a function of perforated conduit 272 to diffuse air into the water flow pathway 270 either or both before and during periodic backflushing. The diffusing of pressurized air through holes of perforated conduit 272 into the water flow pathway 270, fluidizes the precipitated solids, thereby enabling them to be washed out during backflushing.
Back flushing is performed periodically in order to discharge solids that accumulate in and along the flow pathway with time, preferably by a controller 284, which initiates back flushing based on sensing pressure along the flow pathway 270 and/or according to preset time intervals. Controller 284 operates a backflush pump 285; a backflush outlet valve 286, coupled to a backflush outlet 287; a pressurized air valve 288, coupling a source of pressurized air 274 to perforated conduit 282 and valves 261 and 278.
Back flushing is performed periodically in order to discharge solids that accumulate in and along the flow pathway with time. The back flushing may be initiated by a controller 284 according to pressure measurement or constant time intervals or both. During back flushing, wastewater inlet valve 261 and treated water outlet valve 278 are closed, while drain valve 286 is opened, and back flushing pump 280 is operated. Preferably, pressurized air valve 292 is opened prior to back flushing and more preferably pressurized air valve 292 remains open to provide mixing and fluidization of the solids in the water during at least part of the back flushing. Back flushing is terminated according to any of a preset time or a measured quantity of water drained or draining water turbidity. Upon termination of the back flushing, back flushing pump 280 is stopped, drain valve 286 is closed, pressurized air valve 292 is closed and treated water outlet valve 278 together with wastewater inlet valve 261 are opened. Back flushing is terminated by controller 284 at a preset time after initiation or based on sensed quantities of backflushed material reaching backflush outlet 292 or the sensed turbidity of the backflushed liquid. Back flushing outlet from drain is preferably directed to subsequent processing such as thickening, dewatering and discharge.
Reference is now made to
The water treatment system of
It is appreciated that the water containing dissolved ammonium compounds received at biofilm-based water treatment subsystem 310 is supplied through an inlet manifold 312 to a plurality of membrane enclosed water flow pathways 314 and flows therethrough as indicated by arrows A to a nitrified water outlet manifold 316, thereby reducing the quantity of ammonium compounds in the water and thereby nitrifying the water.
In the biofilm-based water treatment subsystem 310, a biofilm that consumes the ammonium compounds is built up on the interior walls of membrane enclosed water flow pathways 314 and thus oxidizes the ammonium compound contained in the water flowing therethrough to nitrates. The organic material load in the water that reaches the biofilm-based water treatment subsystem 310 is relatively low due to earlier adsorption thereof by contact with the activated sludge. As a result, the biofilm buildup on the interior walls of enclosed water flow pathways 314 is relatively thin and water flow pathways 314 does not get clogged.
Water from nitrified water outlet 316 is preferably supplied to a denitrification tank 306 together with sludge from separator 304. In denitrification tank 306, the nitrified water is mixed with the activated sludge containing adsorbed non-oxidized organic material. As a result the activated sludge oxidizes the organic material using nitrates to complete both processes of denitrification and organic materials oxidation.
Optionally, if oxidation of organic material is limited by nitrate concentration, an additional aeration may be provided. In some embodiments intermittently by diffusers placed in the denitrification tank. In other embodiments continuously by an additional aeration tank downstream the denitrification tank and upstream the sludge—liquid separator.
Denitrified water from denitrification tank 306 is preferably supplied to a sludge-liquid separator 322. Treated water from the separator 322 is preferably employed as an effluent through effluent outlet 324. Most of the sludge from separator 322, which sludge consumed most of the organic material, is returned to mixing and adsorption tank 302 while a small fraction of the sludge is removed from the system via a sludge outlet 328. The fraction of sludge removed from the bottom of separator 322 is adjusted to maintain a desired constant concentration of sludge in tanks 302 and 306.
Reference is now made to
The alternative clogging resistant biofilm-based water treatment system of
Downstream subsystem 405 does not generally become clogged by growth of a thick biofilm along at least part of the flow pathway of the units 406 therein. Clogging is prevented by the reduction of most of the load of organic material contained in the water by operating units 404 in upstream subsystem 403, which as a result become clogged by growth of a biofilm therein.
Upon clogging of one or more operating units 404 of upstream subsystem 403, typically after 2-4 months, the flow of water to be treated is redirected to non-operating units 404 of upstream subsystem 403 preferably automatically by a valve assembly 410. During the time period that clogged units 404 of upstream subsystem 403 are non-operative, they become unclogged due to endogenous decay.
The time required for this decay can be optionally shortened by various means, including, for example: addition of chemicals such as a hypochlorite solution, caustic soda solution or specific enzymes. Water may be circulated through the non-operative units 404 in order to provide mixing and turbulence. As a further option, air may be periodically sparged into the units 404 in order to provide shearing and turbulence and thus shorten the decay time.
Valve assembly 410 is preferably controlled by a controller 420, which either operates on a fixed time schedule or on the basis of sensed clogging based on inputs from one or more pressure sensors 422, to redirect a flow of water to be treated from one or more current operating units 404 to one or more currently non-operating units 404.
Each of the units 404 of biofilm-based water treatment upstream subsystem 403 preferably includes a pathway whose length is 20-40% of the combined length of the entire water treatment flow path, including that incorporated in one of upstream units 404 and in downstream subsystem units 406. Most preferably, the length of the flow path in each of the upstream units 404 is 10-30 meters, and the length of the flow path of the downstream unit 406 is 40-70 meters.
Treated, partially purified water output from the upstream operating biofilm-based water treatment units 404 of upstream subsystem 403 is supplied to downstream biofilm-based water treatment subsystem 405, preferably via one or more non-return valves 430, to complete the water treatment process.
In a preferred embodiment, the partially treated water 440 from upstream subsystem 403 is supplied to operational tank 442, from which it is pumped by pump 444 to downstream subsystem 405 for further treatment thereof.
Reference is now made to
In one embodiment, as seen in
In a different embodiment, no settling pond is provided or alternatively a different conventional pretreatment is utilized upstream the oxidation pond.
Subsystem 510 is preferably constructed and operative as described hereinabove with reference to
Following such nitrification, nitrified water from membrane-supported biofilm-based water treatment subsystem 510 is circulated back to one or more oxidation pond 504 or to another upstream or downstream oxidation pond (not shown) for denitrification thereof.
A first advantage of the above-described process is higher effluent quality than obtained in the conventional process, resulting from the increased aeration by the biofilm-based water treatment subsystem 510. A further advantage of the process is the use of the nitrates that are dissolved in the water, which nitrates are circulated to the oxidation pond 504, as an oxidant, thereby enhancing the oxidation process in the one or more oxidation ponds 504.
It is noted that clogging of the subsystem 510 by biofilm buildup does not generally occur, due to the relatively low load of organic material in the effluent of the oxidation pond 504, which is supplied to system 510, as a result of the partial removal of organic material that takes place in the one or more oxidation ponds 504.
Subsystem 510 may optionally be backflushed with effluent from oxidation pond 504 or from a point downstream thereof. Backflushing of subsystem 510 is normally required in order to dispose of suspended solids that settle along the flow pathway or excess solids that slough off of the biofilm therein. Backflushing is generally performed by reversal of the flow direction through the flow pathways of units 520 of subsystem 510. During normal operation valves 506 and 512 are open whereas valves 516 and 518 are closed. During backflushing of at least part of units 520 of subsystem 510, valves 506 and 512 are closed whereas valves 516 and 518 are open. The switching between the normally open valves 506 and 512 and normally closed valves 516 and 518 is preferably controlled by a controller (not shown) according to any of inlet pressure or preset time intervals. Backflushing water outlet 522 is preferably discharged to settling pond 502, or to a different point upstream the oxidation pond 504.
It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes combinations and subcombinations of features described above as well as modifications and improvements thereof that are not in the prior art.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IL2016/050932 | 8/25/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62209891 | Aug 2015 | US |
