A method for denitrification of nitrate-contaminated water using a wetland treatment system

Abstract

The invention relates to a method for denitrification of nitrate-contaminated water using wetland water treatment systems. The removing of the nitrates from the contaminated water is done by using ethanol efficiently as a supplementary energy source. The structure and substrates used in the wetland ponds as well as experimental results are provided.

Description

A METHOD FOR DENITRIFICATION OF NITRATE-CONTAMINATED WATER USING A WETLAND TREATMENT SYSTEM

[0001] FIELD OF THE INVENTION

[0002] The invention relates to a method for denitrification of nitrate-contaminated water using wetland water treatment systems. More specifically, the invention relates to a wetland water treatment method for removing nitrate contaminated water using ethanol efficiently as a supplementary energy source.

[0003] BACKGROUND OF THE INVENTION

[0004] Nitrates in groundwater are major pollutes in many areas of the world and cause adverse health effects when consumed in drinking water. The most pronounced adverse health effect caused by nitrates is methemoglobinemia. Nitrates can also be of a major health concern when urban and / or agricultural wastewater is purified to be used as potable water.

[0005] Various physical and chemical-based methods have been developed for removing nitrates from nitrate-contaminated water, such as reverse-osmosis, nanofiltration, and electrodialysis. These methods have proven to be expensive to operate, to have poor selectivity in denitrification processes and in some cases, to produce toxic wastes that have to be dealt with.

[0006] Biological denitrification based methods are relatively inexpensive to operate, produce not-toxic nitrogen gas and have high selectivity for nitrates, meaning that a very low-concentration of nitrate in the treated water can be obtained without major technological efforts.

[0007] In order to operate, bio-denitrification based methods rely on the enzymatic activity of bacteria. In biological based water treatment facilities, the bacteria are typically grown in biofilms on submerged inert in particles of free-floating bacterial- formed aggregates in anaerobic conditions and need an energy source (“electrondonors” in chemical terms), to keep their metabolism functioning and the denitrification process going. Bio-denitrification process can either be heterotrophic or autotrophic. For heterotrophic bacteria, an organic carbon source such as methanol, ethanol or acetic acid has to be supplied. For autotrophic bacteria, inorganic compounds, such as sulfur and hydrogen, must be made available.(Source of information: website: https: / / www.ncbi.nlm.nih.gov / pmc / articles / PMC3880027 / . J Environ Health Sci Eng. 2013; 11: 35. Biological nitrate removal processes from drinking water supply-a review By: Anoushiravan Mohseni-Bandpi, David Jack Elliott and Mohammad Ali Zazouli.)

[0008] An efficient method for the bio-removal of nitrate from contaminated water, using a simple-to-construct and simple to operate water treatment system, is constructing wetland systems. Ethanol is an efficient energy source for heterotrophic bacteria in constructed wetland systems.

[0009] An example of adding ethanol for maintaining the bio -denitrification process in wetlands is given in: CN106542635 (Weizhong et al): “Artificial wetland system with enhanced nitrogen removal function”.

[0010] The invention is a bio-denitrification wetland system that is inexpensive and simple to construct and uses ethanol as an additional energy source for the heterotrophic bacteria while being substantially more efficient than the bio-denitrification wetland systems previously disclosed.

[0011] SUMMARY OF THE INVENTION

[0012] The method for nitrate removal (“denitrification”) from contaminated water using wetland treatment systems. The invention combines one or more bottom-sealed aerobic ponds for denitrification and one or more bottom-sealed “polishing” aerobic ponds. While the denitrification ponds denitrifies the nitrate components found in the water by anaerobic microorganisms, the polishing ponds remove by microorganism the organic components from the water after the aerobic treatment. The inflow capacity, inflow nitrate concentration, and the outflow requested concentration determine thenumber and size of the ponds. It is also affected by intervening parameters (such as other contaminants, if there are, and by temperature). The term “sealed” refers to the bottom of the ponds, constructed to prevent water leaks to the ground.

[0013] Sealing the wetland ponds is done with clay, liners, or cement, according to ease of implementation and cost. No toxic materials (like Bitumen liners) are utilized.

[0014] The ponds’ dimensions are typically, but in no way, limited to: length of 40 by 20 meters. The depth of the anaerobic pond is typically 0.70 meters, and the aerobic, “polishing pond”, is typically 0.90 meter. Commonly, yet again, in no way limited, the length, width and depth of the ponds varies by plus / minus 10%, Changes can be made according to topography and other relevant considerations, such as the porosity of the substrate mixture, the organic load, temperature, and types of plants grown (see Table 4 of experiments). The key factor of determining the length of the anaerobic ponds is the efficiency of the dispersion and penetration of the to-be-treated water on the top of and into the layer of the substrate in the ponds. The length of the aerobic (“polishing”) ponds is minimally 4 meters. All the data presented in the tables in the embodiment section refers to anaerobic ponds of the wetland system.

[0015] In the anaerobic ponds, referred to as “vertical ponds” (shown as (10A) in the figures) the treated water is dispersed on the top layer of the substrate and seeps downwards to the bottom of the pond. In the aerobic, “polishing” ponds, referred to as “horizontal ponds” (shown as (10B) in the figures) the treated water streams in the substrate in a horizontal path till it flows out of the system.

[0016] Different components constitute the substrate used as wetland pond fillers for biofilm growing surfaces. The substrate components are, but are not limited to, basalt gravel, perforated clay, fly ash, and pine bark. Fly ash and pine bark have low hydraulic conductivity, which is countered with the perforated clay and gravel. The perforated clay has to be of agricultural grade (as opposed to insulation clay products, which may contain materials that cannot be in contact with water treated for agricultural use or potable water).

[0017] The pond filler components are typically mixed together in proportions that vary, depending on both inflow and outflow concentration and the total suspended solids (TSS) content of the inflow.

[0018] Presently the components used in the experiments described in the embodiments and their supply source is provided:

[0019] Fly ash: residue from coal burning power stations. The Material typically comes as a fine powder.

[0020] Pine bark: purchased from Alfarroxo Trading LDA at Figueira da Foz, Figueira Da Foz 3090-380 Portugal. Size of particles used: any size ranging from 15 to 60 mm.

[0021] Perforated clay: purchased from the Laterlite Company at Via Vittorio Veneto 30, 43046 Rubbiano di Fomovo (PR), Italy. Particles size used 10-20 mm.

[0022] Basalt gravel: purchased from local quarries in Israel. Size of particles used: 14- 19 mm. The basalt gravel can be exchanged by other hard rock material.

[0023] Ethanol: used industrial grade purity, obtained from various sources.

[0024] High nitrate concentration is defined as higher than 150 mg / liter.

[0025] High TSS concentration is defined as higher than 100 mg / liter.

[0026] The percentages of the components of the substrates given below refer to percent on total volume of the substrates.

[0027] The substrate in the anaerobic pond (10A in the figures) is typically, of but not limited to: a mixture of 20% perforated clay, 70% basalt (or other hard stone material), plus 10% pin bark placed on the top surface of the pond. The substrate of the pond enables water from the top surface to readily penetrate and pass through the substrate toward the bottom of the pond. On the way down, the water wets the surfaces of the particles in the substrate, enabling the formation of covering biofilms.

[0028] The substrate in the aerobic pond (10B in the figures) is typically, of but not limited to: a mixture of 10% ash, 30% basalt gravel (or other hard stone material), 40% pine bark and 10% perforated clay. The substrate in the pond enables the rapid horizontal streaming of water coming into the aerobic pond from the anaerobic pond.

[0029] The concentration of the components of the substrate in the anaerobic pond may vary, depending on the temperature and the containments in the to-be-treated water to: perforated clay between 15% and 25%,, basalt gravel between 55% and 85%, ine bark between 5 % and 15% .

[0030] The concentration of the components of the substrate in the aerobic pond may vary, depending on the temperature and the containments in the to-be-treated water to:perforated clay between 5% and 15% , basalt gravel between 30% and 50%, pine bark between 30 % and 50% fly ash is between 5 % and 15% .

[0031] The ethanol of wetland nitrate-contaminated denitrification waler treatment system of claim 1, wherein, the amount of said ethanol added in said anaerobic pond is between 0.05-0.5 gr of ethanol to every 1 gr of dissolved nitrate calculated to be in the to-be-treated water.

[0032] The concentrations of the components that constitute the substrate of the ponds commonly, yet again, in no way limited, is changed to adjust to different and types of TSS / organic substances load varies by plus / minus 20%,.

[0033] Ethanol is administered to the anaerobic pond through a dozing pump controlled by the nitrate monitoring and control box and is dependent on the concentration of the nitrate entering the treatment pond(s). The ethanol used is of industrial grade purity.

[0034] Experimental results showed that when using basalt gravel as a wetland pond filler, 2.5 gram of ethanol were required for every 1 gr of nitrate removal. The same ration of were reported for non- wetland systems. Experiments in wetland water treatment systems, using a combination of fly ash, pine bark and perforated clay, resulted in the consumption of (only) between 0.05-0.5 gr of ethanol to reduce 1 gr of dissolved nitrate, depending on temperature and the required outcome. The unexpected experimental results, which are the basis of the invention, showed a substantially more efficient ethanol consumption than previously disclosed for wetland treatment systems. It was also found that adding ethanol in the invention's treatment wetland system induces the bio-denitrification process without residuals of nitrite and TOC (total organic carbon dissolved in the water).

[0035] The length-to-width measures of the ponds need to take into account the hydraulic conductivity of the substrate. If more organic substrate components are needed, the hydraulic section, (designated (10A) in the figures) must be wide and the length short. Retention time is between 5 to 10 hours, depending mainly on the inflow concentration.

[0036] The aerobic polish pond / s, (designated (10B) in the figures), are designed as tidal-flow ponds, thus requiring a pump or a siphon, allowing it to be flooded and emptied in intervals. It has to contain well-aerated substrates like perforated clay.

[0037] It should be noted that nitrate contaminated water can be denitrified by the wetland system of the invention to a concentration regulatorily-acceptable in potable water while keeping the minerals of health significance (such as calcium , magnesium, and iodine) in the treated water. Regulation for drinking water varies from 70 mg / 1 (Israel) to 50 (Europe) and 40 (most of the USA). Internationally, nitrate concentration in drinking water regulations are in a process of change, aiming at 10 mg / 1.

[0038] Optionally, for the wetland water treatment systems, post treatment disinfection is done according to local regulations which vary from one location to another. In the case of potable water, the disinfection is particularly strict and thorough.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals.

[0041] Fig. 1 is a schematic illustration of the various components and the connection between them in a wetland water treatment system for the denitrification of nitrate- contaminated water. The water treatment system shown from above.

[0042] Fig. 2 is a schematic cross-cut, from the side illustration, of the various components and the connection between them in a wetland water treatment system for the denitrification of nitrate-contaminated water shown in Fig. 1. For graphical purposes the treatment system is shown divided into two segments, that are a single entity.

[0043] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0044] It should be clear that the description of the embodiments set forth in this specification serves only for a better understanding of the invention, without limiting its scope.

[0045] The invention is a wetland nitrate contaminated denitrification water treatment system composed of at least one sealed pond for denitrification and one or more polish aerobic ponds. The denitrification pond is filled with substrates made of a mixture of:fly ash, pine bark, perforated clay and basalt gravel. The nitrate-contaminated water treated by the wetland water treatment system is exposed to denitrification bacteria in anaerobic conditions, and ethanol is added to the treated water in sufficient amounts to be consumed by said denitrification bacteria in the process of utilizing the nitrate for their metabolic requirements while removing the nitrate from the water. The Ethanol is administered continuously through a dozing pump controlled by the nitrate controller, to optimize ethanol amount to inflow nitrate level.Experiments were conducted to determine the favorable conditions to remove nitrate from water using the above-mentioned composition of substrate components. It was determined that no more than 25% basalt gravel will be used if TSS is high. If there is an additional organic matter, fly ash should be avoided even at the cost of less efficient reduction.

[0046] Presently the general structure of a wetland water treatment system for the denitrification of nitrate-contaminated water experimented with is explained. Fig. 1 is a schematic illustration of the various components and the connection between them in the wetland water treatment system (10), shown from above. Fig. 2 is a schematic illustration of the components and the connection between them shown in Fig. lin the wetland water treatment system (10), shown from above. . For graphical purposes (only) the wetland treatment system is shown in Fig. 2 divided into two segments, (10A) and (10B), that are a single entity (10).

[0047] The wetland system (10) is divided into two ponds: a vertical pond (12) and a horizontal pond, also refeed to as “a polishing pond” (14).

[0048] The figures illustrate polluted water entering the wetland system via a pipe (16). A pump (18) feeds the vertical pond (12) with the incoming inflow water. The water passing through the pump (18) receives doses of ethanol, pumped into the sewage by a dosing pump (20). The dosing pump obtains the ethanol from an ethanol supply container (21). The water with the ethanol enters pond (12) by tube (16) and is dispersed throughout the top surface area of pond (12) by a series of tubes (17). The tubes have connected to them spray nozzles (17A) that distribute the ethanol-water solution. The wetland substrate (15) that fills pond (12) is composed of: 20% clay, 70% basalt (particles 14-19 mm) and 10% pine bark. The sewage water with the ethanolseeps through the substrate of pond (12 ) from top to bottom and flows via tube (22) that runs along the length of the bottom of pond (12) by gravitational force into horizontal pond (14). Along tube (22), at the bottom of pond (12), are openings that facilitated the entrance of water to the tube. The polluted water, on its way to pond (14), pass through a separation tank (23) in which the heavier than water suspended particles sediment and are removed. On entering pond (14), the water is dispersed on the top surface of the edge of the substrate (19) that fill pond (14). The substrate (19) that fills the pond is composed of: 40% basalt (particle 14-19 mm), pine bark 40%, clay 10% and ash 10%. The sewage water seeps through the substrate (19) and streams towards the bottom edge of pond (14). “The bottom edge” being the bottom of the edge of the pond on the opposite side of the entrance of the sewage water. The water exits pond (14) via tube (24) from the edge of pond (14) by gravitational force. In order to control and maintain the water level in pond (14) the water passes through a “balancing pool” (71) before being discharged. “Balancing pool” (71) has a tube like configuration which is sealed at its bottom. Water enters balancing pool” (71) at the horizontal level of tube (24) and leaves balancing pool (71) via tube (72), positioned at the height / level in which the level / height of the water in pond (14) is kept in order to maintain the pond functioning. The wet environment of the substrates in both ponds ((12) and (14)) and the nutrients from the streaming water, enable the growth of vegetation of the surface of both ponds (30). To facilitate the streaming of the treated sewage water in the ponds ((12) and (14)) by gravitational force in the ponds, from pond (12) to pond (14) and out of pond (14), pond (14) is positioned at a higher elevation than pond (14).

[0049] Given below are the results of denitrification experiments using the treatment system of the invention:

[0050] TABLE 1Wetland area at a minimum temperature of 5 degrees Celsius, Target purification: 40 mg / 1 with no other contaminants.

[0051] TABLE 2Wetland area at a minimum temperature of 5 degrees Celsius, inflow concentration: 80 NO3 mg / 1 with no other contaminants.

[0052] TABLE 3Weight of added ethanol in grams to reduce 1 gram of NO3 at a minimum temperature of 5 degrees Celsius. Target purification: 40 NO3 mg / 1 with no other contaminants.TABLE 4Maximum length of a pond (12) in relation to total substrate porosity.The porosity is defined in the percentage of water contained by the pond-filling substrate components and is the most straightforward measure to predict the hydraulic conductivity of the substrates.

[0053] It should also be clear that a person skilled in the art, after reading the presented specifications, could make adjustments to the above-described embodiments that would still be covered by the invention.

Claims

CLAIMS aim:1) A wetland nitrate-contaminated denitrification water treatment system comprising at least one bottom-sealed anaerobic denitrification pond, and at least one bottom-sealed aerobic polishing pond, wherein both ponds are filled with substrates for the water treatment, whereby, to-be-treated water from said anaerobic denitrification pond streams gravitationally to said aerobic polishing pond and streams gravitationally out of said aerobic polishing pond, wherein, the said substrate in the anaerobic denitrification pond comprises a mixture of: perforated clay, basalt gravel with pine bark layer on the top surface of the substrate, wherein, the said substrate in the aerobic polishing pond comprises a mixture of: fly ash, perforated clay, basalt gravel and pine bark layer, wherein, ethanol is added to the treated water in said denitrification pond.2) The perforated clay of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said perforated clay in said anaerobic pond is between 15% and 25% by volume.3) The basalt gravel of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said basalt gravel in said anaerobic pond is between 55% and 85% by volume.4) The pine bark of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said pine bark in said anaerobic pond is between 5 % and 15% by volume.5) The perforated clay of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said perforated clay in said aerobic pond is between 5% and 15% by volume.6) The basalt gravel of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said basalt gravel in said aerobic pond is between 30% and 50% by volume.7) The pine bark of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said pine bark in said anaerobic pond is between 30 % and 50% by volume.8) The pine bark of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said pine bark in said anaerobic pond is between 30 % and 50% by volume.9) The fly ash of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the concentration of said pine bark in said aaerobic pond is between 5 % and 15% by volume.10) The ethanol of wetland nitrate-contaminated denitrification water treatment system of claim 1, wherein, the amount of said ethanol added in said anaerobic pond is between 0.05-0.5 gr of ethanol to every 1 gr of nitrate calculated to be dissolved in the to-be-treated water, in sufficient amounts to be consumed by anaerobic denitrification bacteria to remove nitrate from the water.11) The basalt gravel of said wetland nitrate contaminated denitrification water treatment system of claim 1, wherein the basalt gravel is exchanged for other hard rock material.12) The wetland nitrate contaminated denitrification water treatment system of claim 1, wherein said denitrification water treatment system treats nitrate contaminated water nitrate to purified potable water.

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