The remediation of groundwater with nitrate contamination in the water basins or in some farmlands is considered a very difficult task in the application of environmental sciences. The groundwater is accessed by drilling wells or boreholes to access the water at the water table. The extracted water has so many minerals and may not be fit for consumption. The groundwater needs to be treated to remove several minerals that make it very salty. It is considered a very crucial task in the environmental cleanup process (NRC 1994, NRC 2000). The ground water has recalcitrant contaminants such as the nitrate components that are quite difficult to remove using certain physical methods. Several researchers have come up with different techniques that can be used to remove the nitrate components in the groundwater. The previously researched and implemented techniques have performed poorly in the removal process such as pump-and-treat and the plum scale. The groundwater remediation on the basis of the regulatory limit is often a factor of 2 and 10 times the values of the nitrate concentration in the ground water. The remediation process seeks to obtain the polluted groundwater and process it to get clean water that is fit for human consumption and other related activities (Shuval & Gruener, 2002). Ground water provides a large portion of the drinking water consumed by the larger population of Americans. Statistics show that 15 percent of Americans consume ground water and the well owners have the mandate to ensure the safety of drinking water. The aquifers are polluted when there is leaching from rocks, pollutants carried down from the surface by percolating water, surface water recharge, inter-aquifer exchange, and direct mitigation. The aquifers are slowly recharged through precipitation. The groundwater becomes contaminated by natural causes free from human sources. As the water percolates through the soil matrix, it may carry pollutants down with it. The pollutants may naturally leach from rocks into the ground water. The ground water EPA rules are not applied on the private wells and the standards are a good basis for determining the drinking water quality from the maximum contaminant level. Some of the contaminants are arsenic, nitrates, perchlorate, and radionuclides.
To determine the nitrate removal using alginate floating beads in a water treatment system of groundwater.
To determine the conventional method and techniques employed in the determination of the nitrate reduction in pump and treat ground water systems.
To determine the merits of treating water using natural adsorbents as opposed to the chemical and electrical systems.
Nitrate contamination in groundwater
According to statistics in the UK, the largest portion of nitrate in groundwater is attributed to the diffused pollution from agricultural related practices. Part of it is caused when the sewage sludge is exposed to the land leaving atmospheric depositions and point sources. The first instance of nitrate saturation due to agriculture dates back to the agricultural intensification era as a result of the application of fertilizer. Many researchers have studied the impact of land practices on the nitrate leaching to the groundwater and as well the way the nitrate is able to move through the unsaturated regions of land to other sections. Boreholes and wells are the main sources of groundwater (Foster & Young, 2008). The users of the boreholes may constantly pour out the aquifers or water purifiers in the borehole to clean the water as a way of groundwater remediation. Some studies show that the concentrations of nitrate in groundwater in the areas where agriculture has been implemented are higher than in other regions. The rate at which the nitrate concentration is rising in the groundwater is given as 0.3 mg/l/year (Chilton & Foster, 2001). It is also estimated that during winter and spring, the nitrate fluctuation in groundwater in many regions demonstrates high concentrations than in other seasons due to higher water levels during these two seasons. As a result, a change in the climate attributes to the nitrate leaching through the soil to the water table and as a result it affects the ground water (NERC, 2017).
It is considered as one of the most prevalent water contaminants in the rural areas. It has health impacts such that mother who consume water with so much nitrate may bear children who get methemoglobinemia or the blue baby disease (Feig, Nathan, Oski, & Saunders, 2001). The nitrate levels affect the new born babies more than they affect adults. The nitrate that leaches through to the water tables originates from the constant use of fertilizers, septic that seeps through the land from the faulty sewerage system, the storage of manure as well as spreading operations. Some of the fertilizer component is not taken up by the plants and as a result, it is carried off especially during the rainy seasons and absorbed into the soils. The nitrogen components found in manure, either animal or plant manure is obtained from the septic systems where the groundwater is elevated to percolate through the groundwater.
Nitrate as a contaminant
Nitrogen comprises the largest portion of the atmospheric air. Its compounds such as nitrate are highly soluble anions that are easily leached into the ground during the surface runoff. The agricultural areas are mostly affected by the nitrate contamination due to farming using fertilizer inputs, animal feedlots and dairy products, the manufacture of chemicals and explosive by industries and improper disposal of the waste. The nuclear industry uses very large amounts of nitric acid to dissolve metals and other forms of actinides as well as the mining industry. The high nitrate levels in the pumped water for drinking purposes may cause a myriad of health complications such as the methaemoglobinaemia, Alzheimer’s disease, the vascular dementia, and multiple sclerosis in human beings (Priyamitra, Kuldeep, & Rohit, 2015). Researchers have come up with a number of techniques to remove the nitrate contamination from the pumped water. The techniques used are based on the chemical reaction with nitrates, absorption process, and ion exchange process. Other technologies available for treating the nitrate in groundwater are the reverse osmosis, the ion exchange, the chemical denitrification, the electro-dialysis, the distillation process, absorption from water and biological denitrification. The US Environmental protection agency, EPA, advocates for the reverse osmosis, electro-dialysis, and ion exchange techniques for nitrate removal in the water (Hemnat, 2013). The World Health organization, on the other hand, advocates for biological denitrification and the ion exchange. There is another technique that is successful in removal of different types of inorganic anions from waters due to adsorption using various materials as adsorbents (Bhatnagar & Sillanpaa, 2011). The nitrogenous fertilizers and the organic waste compounds contain very high Nitric ions due to organic garbage, livestock excreta and sewerage leaks. There is need to adopt a proper environmental management plan to control the groundwater pollution with immediate effect (Ayyasamya, Raakumarb, Sathishkumarc, Shanthid, & Leea, 2009). There are different forms of nitrogen that are found in waste water. The components of wastewater or groundwater are ammonia, nitrite, and nitrate. The organic nitrogen contains complex compounds in form of protein and amino acids for both plants and animals. The total inorganic nitrogen is the collective sum of ammonia, nitrite, and nitrate. The nitrogen cycle based on the total kjeldahl nitrogen,
The primary effluent or the secondary influent has organic nitrogen or ammonia and the secondary treatment using biological techniques. The nitrates may be removed by the biomass and the heterotrophic bacteria breakdown organics or proteins to ammonia. The bacteria may take up ammonia in the ratio,
The autotrophic bacterium utilizes the inorganic compounds with a carbon source. The heterotrophic bacteria breaks down organics and generate three components, nitrogen hydride, carbon (IV) oxide, and water. The effect of temperature on nitrification and the lower temperatures has the slower nitrification growth rate. There is a higher MLSS concentration and it may compensate for the lower temperature. It is also limited by the oxygen transfer, the high CRT problems, and maximum MLSS controllable. The anoxic environment enables the denitrification and the heterotrophic bacteria will use the oxygen from nitrates as they assimilate the BOD as it produces nitrogen gas,
The denitrification process has merits such as minimizing the rising sludge, it helps to recover oxygen, it recovers alkalinity, and may help control filamentous bacteria. When the temperature is at 17 degrees centigrade, the first step in conversion is slow while the second part is fast such that,
When there is cold water and the temperature reduces to 14 degrees centigrade,
The treatment of water in such temperatures tends to be quite difficult. The effect of temperature increment causes the denitrification process to speed up.
Removal of groundwater contaminants
One of the most common methods of nitrate removal from ground water is the pump-and-treat method for drinking water treatment. The pump-and treat method of nitrate removal is an ex-situ remediation method. The treatment process revolves around the treatment and extraction of contamination water from the subsurface followed. The method is commonly used in the areas where organic chemicals are used in the contaminated areas (Meyer, Swaim, Bellamy, Rittmann, Tang, & Scott, 2010). The method works for areas that have waste acquittal areas, creeks, surplus fertilizer and manure submission to the agricultural fields. The method address the high nitrate levels found in the lessening technologies and exclusion technologies. The reduction technologies have the biological denitrification and chemical denitrification by transforming the nitrate through reduction to the other nitrogen species which are innocuous nitrogen gas. The technique performs an anion exchange, reverse osmosis, and the electro-dialysis reversal which removes the nitrate and the constituents are found in the concentrated waste stream requiring disposal (Nuttall & Dutta, 2004).
The Tulare Lake Basin and Salinas Valley groundwater is infiltrated with nitrogen and the national water department of California has sought different techniques to clean the water and make it fit for consumption. Based on the soil and water sample tests, the maximum contaminant level for the nitrate compound is found to be 45mg per liter and further analysis shows that the nitrogen component is 10mg per liter. As highlighted in the basic overview, it is found that the consistent consumption of water with nitrate causes several health complications especially the ‘blue baby disease’. In health systems, the body absorbs the nitrate component of water and reduces it to nitrite with renders the hemoglobin unable to carry oxygen (AWWA, 2000). In the management of nitrate in potable water, there are both treatment and non-treatment options. When a feasibility analysis is carried out for the non-treatment options, there are a number of limiting factors that include the location, budget, source availability, and water quality may vary due to the fluctuation of the nitrate levels. The infiltration of fertilizer components into the groundwater and the leakage from the livestock feedlots and waste storage is one of the major contributors to the nitrate problems. Some of the treatment methods implemented in the management of nitrate for water treatment are the ion exchange, reverse osmosis, electro-dialysis and electro-dialysis reverse, and biochemical denitrification. The ion exchange technique is related to the water softener alternative that is used to soften hard water obtained from boreholes by replacing the divalent cations, the manganese and calcium ions with sodium ions. The transfer in the ion exchange vessel treatment results in stabilization and disinfection of the groundwater,
The result develops the sulfate ions for the anion exchange resins such that the nitrate selective resins are developed. Other the years, several studies have developed a number of tools to perform the ion exchange such as Dow’s CADIX and the Lenntech’s Ion Exchange Calculator. The process has been well embraced even at the industrial level as a treatment option. It has different levels of contaminant removal, selective nitrate removal, financial feasibility, and the use of small and large systems which enables portability and mobility. On the other hand, the technique leaves the potential for nitrate dumping and resin fouling which is a great position of pH adjustment and potential hazardous waste generation.
The management of the water treatment process is perceived on the research conclusions, capital and operational and maintenance costs, the caveats involved, as well as the latest improvements. When non-treatment alternatives are adopted, the best way to determine the proper management is by ensuring the well abandonment and proper destruction. Unfortunately, the water sources may not be sufficient hence the need to find a treatment alternative. In the identified water basins, a nitrate treatment system survey was conducted to determine the nitrate treatment levels. The data analysis was obtained as,
The process of groundwater remediation enables the management for nitrate using the conventional methods. The nitrate removal is a high cost operation which requires that the water treatment company make huge investments in the structures and ensure regular operations and maintenance of the equipment. The project requires that the different processes and techniques be employed to enable water treatment as well as the post treatment processes which tend to be more of chemical treatment to stabilize the pH levels of the systems. From the conventional techniques, unnatural methods, the only cost implications with respect to the biological denitrification are the maintenance of optimal conditions as well as the nutrient dose and management of the pretreatment and post-treatment in the portable water guidelines. The capital costs affect the land acquisition, housing, piping, storage tanks with the operation and maintenance costs inclusive of post treatment activities, sludge disposal, repair, extensive monitoring and maintenance, power, labor, and chemical use. There are higher capital costs compared to other techniques while the system footprint is large compared to the ion exchange systems. The process may not complete fully since the process does not allow for iteration and GHG production. Nitrate can be removed from water with means similar to arsenic. Treatment technologies include reverse osmosis, distillation, and ion exchange. These all function the same as was previously described with the exception that a different resin would be used for nitrate removal in the ion exchange column than what would be used for arsenic. Electro-dialysis is a fourth option.
Groundwater nitrate component may also be removed using the chitosan as an adsorbent. The environment has been gravely affected by the use of nitrogenous fertilizer inputs in agricultural farms especially those close to the rivers, and the improper disposal of industrial waste water into water bodies. In agriculture, fertilizers are used to improve yields. Some farmers use these fertilizers and later perform spread planting where the land is left bare for long periods of time especially in the maize, tobacco, and vegetables farming. Improper drainage systems cause a lot of damage to the groundwater and poor rational schemes for organic fertilizers in animal husbandry as well as the increased urbanization. This research aimed at studying the suitability of different forms of chitosan as an adsorbent in the nitrate component removal from the groundwater. The nitrate levels in groundwater were determined using the spectrophotometer, the IS code method, and the nitrates kit. There are various methods used in the nitrate removal from water based on chitosan adsorbent, using the ammonium ions from water as the natural absorbent, and the nitrate removal from water using the conifer tissues. The chitosan adsorbent is a nitrogenous polysaccharide that is comprised of the acetyl glucosamine and other glucosamine units. The adsorbent is obtained from chitin. Chitin is a common polymer found in the shellfish shells, insect exoskeletons, and the fungi cell walls. The adsorbent creases a web made of fiber to link the sediments in the three-dimensional matrix mode. The biological component has long filtration cycles at sediment loading rates which are above industry standards. The chemical composition of the chitin and the chitosan is as expressed below,
Conventional methods of removing nitrate
The treatment procedure uses a very strong base anion exchange resin. The raw water is taken through a pre-treatment system to remove any solid matter that may affect the resin. The groundwater, under test, with nitrate components is passed through the ion exchange vessel. The resin obtains the nitrate and displaces the chloride at surface sites which removes the nitrate compounds from water.
The technique is related to the water softener alternative that is used to soften hard water obtained from boreholes by replacing the divalent cations, the manganese and calcium ions with sodium ions. The transfer in the ion exchange vessel treatment results in stabilization and disinfection of the groundwater,
The result develops the sulfate ions for the anion exchange resins such that the nitrate selective resins are developed. Other the years, researchers have developed a number of tools to perform the ion exchange such as Dow’s CADIX and the Lenntech’s Ion Exchange Calculator. The process has been well embraced even at the industrial level as a treatment option. It has different levels of contaminant removal, selective nitrate removal, financial feasibility, and the use of small and large systems which enables portability and mobility. On the other hand, the technique leaves the potential for nitrate dumping and resin fouling which is a great position of pH adjustment and potential hazardous waste generation.
Reverse osmosis
It is another feasible nitrate removal technique that is adopted at both the municipal and residential user level. The method is used in the removal of nitrate, arsenic, sodium, chloride, and fluoride in particulate form and organic constituents. The treatment option forces water through a semi-permeable membrane under pressure such that the water passes through it and the contaminants are removed or impeded by the membrane. The illustration below demonstrates the reverse osmosis process,
The pressure levels are adjusted on the basis of the concentration of solute in the feed water. The rejection rate is dependent on the membrane’s capacity to remove nitrate compounds from the groundwater. The technique employs very thin film membranes with very high rejection rates and lower pressures than CTA membranes. The hollow fiber membranes are compact configurations with ultra-low pressure and RO membranes. These ultra-low pressure RO membranes have a higher rejection rate, water recovery and frequency cleaning state. The treatment process has lower operating pressures that are less costly and decrease the water recovery. The cost considerations for the process focus on the capital costs and the operations and maintenance costs of the system. The process produces high quality product water, multiple contaminant removal; as it performs a feasible automation with TDS removal and an application of POU.
Electro-dialysis
The treatment procedure includes the reversal electro-dialysis and the selective electro-dialysis of the groundwater obtained from wells and boreholes. The method passes an electrical current through stacks of anions and cation exchange membranes to remove nitrate components in the groundwater. The anion-impermeable cation exchange membrane traps the nitrate components in the recycled waste stream. The electrical signal stirs a movement of ions across the membranes such that each compartment has a cation of equivalent charge that leaves and maintains a charge balance for the components. The membranes are plated with anions and cations that enable the removal of nitrate components in the groundwater as illustrated below,
One good example of the water treatment especially where the water bodies are contaminated with nitrates is the use of crops. The crops are said to absorb from 50 to 90 percent of nitrate components in a given space to reduce the concentration. The system has selective membranes that perform both the monovalent and multivalent water recovery and frequency cleaning using the selective membranes. After the treatment process, the pH of the treated water is corrected to avoid corrosion of the pipes during transmission from source to end user. For the pH adjustment, the water treatment technique may use some chemicals to clean the water further. The electro dialysis employs very low chemical usage and the systems use quite long lasting membranes with selective removal of target species. The voltage control at the power input point defines the flexibility in the removal rate. On the other hand, the system requires very high levels of maintenance, has the need to vent gaseous by-products, and has the potential for precipitation especially where high water recovery and high system complexity is desired. Unfortunately, the treatment process is unable to remove the uncharged constituents in the water. The water treatment option has been improved over the years with modifications such as the selective electro dialysis and the reverse electro dialysis. This technology feeds water through alternating anion (negatively charged ion)- and cation (positively charged ion)-selective stacked membranes. Nitrate ions are drawn through the membrane pores with electrical currents. The nitrate is pulled from the water into a brine waste stream. This treatment process may not be a good option due to its complexity, costliness and potential prohibition by local codes as a nitrate-removal technology.
Biological denitrification
The use of biological reactors in the removal of nitrate, chromate, perchlorate, and the trace original components is an emerging trend in the field of water treatment. The process has been implemented since the 19th century in Europe and has been adopted by other nations globally. The denitrification process borrows from the natural process of the nitrogen cycle. The process changes the portable water treatment from a contaminated state to a consumption state. The reactors use the denitrifying bacteria to reduce the nitrate to innocuous nitrogen gas in anoxic conditions where oxygen is not present. The schematic below represents the biological denitrification process,
There is an electron donor that aids the denitrifying bacteria reduce the nitrate to nitrogen gas. The wastewater treatment orders that the substrate addition is not needed while the wastewater does not have sufficient carbon to denitrify the occurrence. The water treatment technique seeks to reduce the carbon substrate in the denitrification process. The feed water is made of the augmented and the reduction of the carbon substrates causes a reduction in the growth of microbes in the water and as a result the production of disinfectant by-products. Several countries have implemented the system and the data below shows the concentration of nitrate in groundwater that is processed by the technique,
The method is quite efficient in the elimination of biomass and dissolved organics, the potential for incomplete denitrification, augmented capital costs, and the sensitivity to the environmental conditions. The technique uses the substrate and nutrient dosing to perform the denitrification and the pH adjustment. After the nitrate components are removed, the carbon is adsorbed by the organic carbon removal and the residual substrate is achieved using the biological filtration. The water is, further, aerated, filtered, and disinfected. The process only incorporates chemical usage where there is potential pH alteration, substrate and nutrient accumulation, disinfection, and coagulant or polymer that meets turbidity standards. The method encounters a number of caveats in the operator training, the intermittent use of wells in the acclimation of micro-organisms, the post-treatment requirements, and the anoxic conditions.
The only cost implications with respect to the biological denitrification are the maintenance of optimal conditions as well as the nutrient dose and management of the pretreatment and post-treatment in the portable water guidelines. The capital costs affect the land acquisition, housing, piping, storage tanks with the operation and maintenance costs inclusive of post treatment activities, sludge disposal, repair, extensive monitoring and maintenance, power, labor, and chemical use. There are higher capital costs compared to other techniques while the system footprint is large compared to the ion exchange systems. The process may not complete fully since the process does not allow for iteration and GHG production. Nitrate can be removed from water with means similar to arsenic. Treatment technologies include reverse osmosis, distillation, and ion exchange. These all function the same as was previously described with the exception that a different resin would be used for nitrate removal in the ion exchange column than what would be used for arsenic. Electro-dialysis is a fourth option.
It should be noted that just because a technology may have a list of multiple contaminants it can treat, the list does not necessarily imply co-treatment capabilities if multiple contaminants are present in the source water. This is especially the case for ion exchange units. Although ion exchange is listed as a treatment option for all four contaminants of concern, a single unit would not be able to remove all contaminants at once. This is due to the contaminants competing with each other for exchange sites as well as the specificity of the resin. The type of resin used and the ability for the resign to be regenerated will impact the cost. Typically a unit’s cost will be between 400 and 1500 dollars. Installation and regular operation and maintenance costs were not considered in the price estimation. Reverse Osmosis is a treatment option for all contaminants discussed with the exception of radon. This method produces a large amount of wastewater and is traditionally only used to treat water for drinking and cooking. An RO unit ranges from 300 to 1000 dollars. A distillation unit can be purchased for a similar cost. Distillation can effectively remove arsenic, nitrate, radon and uranium from water. The main cost associated with this method is the energy required to heat the water to boiling.
Alginate structure and application
Alginate beads are biodegradable and bio-adhesive polymers. Alginate is made from the algae or the seaweeds. The alginates are hydrophilic, biocompatible in nature, biodegradable and totally non-toxic. The alginates can form gels in for the divalent and trivalent cations and anions. It forms a number of common gels that are implemented in the food industry, medical applications, and in the chemical industry. The alginate and algae-based polymers are used to improve the textures of food for instance, ice cream and chicken nuggets. In this research paper, the polymers are implemented as a water treatment technique when used as alginate beads. These gel beads are used to absorb the hazardous wastes from contaminated solutions and the beads are easy to collect from the ground water reserves and dispose. It is observed that the calcium alginate forms quite fast the moment the sodium alginate reacts with calcium chloride.
Some of the world producers of the alginate acid with very large capacities are Europe, Americas, and the Asia-Pacific regions. The alginates formed as a result of the chemical reaction highlighted above, the alginate beads may dissolve in water to increase the viscosity of the aqueous solution. There are some algal beads used in the characterization of the adsorbents once the experiment is commenced. The diameter of the algal beads is measured to be between 4 and 6 mm which are more efficient than the smaller ones which are rated at 2.8 mm diameter width. The pore size in this case, the algal beads, is estimated to be around 2-4 mm. Many researchers have affirmed these values through experiments on different samples. In a nutshell, the alginate beads chosen for the experiment were estimated to have diameters in the range of .
This determines the shape of the beads taking into consideration that the beads have pores which means that the surface area is not smooth. There are pseudo-plastic attributes demonstrated by the sodium alginate solution. The alginate beads are further developed using the cross equation, developed by Soong and Shen (1981) using the rheological data such that,
The water content of the beads is determined once the sample is dried and the constant weight is measured for specific sizes. The surface area of the chosen immobilized alginate bead tends towards 562.0034m2/g. The pore size is equally measured to amount to 14.4130 nm while the pore volume is estimated at 1.8421 cm3/g (Petrovic & Simonic, 2014). In the alginate beads production a number of tests trials are carried out with different sodium alginate concentration to determine the viscosity and the flow rate as illustrated in the table in the appendix A. the relationship between the surface tension and the concentration of the sodium alginate and density is as illustrated below,
The alginate beads are modified to either be drug loaded in rifampicin and the polymer coated as chitosan. The swelling behavior of the chitosan coated alginate beads is slightly greater than the uncoated alginate beads. The uncoated beads demonstrate the sharp increase in the swelling rate. The result of the swelling is the degradation of the beads which makes the beads performs poorly in terms of removing the nitrate compounds from the contaminated ground water. The chitosan coated beads depict slightly lesser swelling rate as it degrades. The beads are able to stay afloat when they are coated with either sodium or calcium ions. The coating improves the swelling rate as well as the adsorbence rate. The resulting gel beads find application in the field of pharmaceuticals in the coating of drugs such as the antibiotics and virus drugs. The use of alginate beads in the control of drug release such that the drug stability problems in oral delivery are resolved.
Alginate beads production
The alginate beads are developed alginate beads enables the use of spray drying, fluid bed coating, electrostatic deposition or the extrusion method where the manufacturing of particles for the controlled dimension and morphology is investigated. One common method for the development of the different final products used in the biomedical, pharmaceutical, and water treatment agents, is the laminar jet break-up or prilling. The procedure involves the breaking apart of the solution into an array of mono-sized drops. The breaking apart is enabled using the vibrating nozzle device. The resultant droplets fall into a polymer gelation solution in which they are solidified as beads. The procedure is crucial in the determination of cell immobility and the state of owning the mild operative conditions.
After the prilling process is completed, it is possible to obtain the mean diameters of the alginate beads from the hydrated bead micrometrics. The illustration below is based on data collected on the diameter and sodium alginate concentration in the prilling process,
During the production stage a number of observations were made when the concentration of sodium alginate was altered as expounded in the table below,
|
< 0.85 % (w/w) concentration |
Projected diameter < 1 mm |
|
0.85-2.5 % (w/w) concentration |
Projected diameter = 3-3.5 mm |
|
> 2.5 % (w/w) concentration |
Gel beads are difficult to produce |
This table guides the production of sodium alginate gel beads in the different concentrations of sodium alginate concentration in water. The equipment used in the production determines the flow rate based on the nozzle radius. To compute the viscosity of the thermo coupled sodium alginate flowing to the gelling bath at the nozzle, the radius of the nozzle is as,
Considering that there is laminar flow in the nozzle as the liquid flows from heating area to gelling bath, a Reynolds number is used as shown for the different sodium alginate concentrations as shown in appendix A. The Reynolds number is given as,
To illustrate the relationship between the viscosity of the solution flowing at the nozzle area and the hydrated beads generated,
Production and nitrate removal technique of floating beads
The alginate develops the hydrogels that are quite stable in the presence of certain divalent cations albeit needing heat even in low absorptions through the ionic interaction between the cation and the carboxyl functional group G units located on the polymer chains. Conferring to Sheridan (2000), the alginate is exceedingly hydrophilic and biocompatible while being quite economical in terms of capital costs and implementation or operation costs. When carboxyl groups are added to the chemical equation,
Procedure:
|
Formulation code |
Sodium alginate (gm) |
CaCO3 (gm) |
CaCl2 solution (%) |
|
F1 |
2.0 |
1.5 |
1 |
|
F2 |
2.5 |
1.5 |
1 |
|
F3 |
3.0 |
1.5 |
1 |
|
F4 |
3.5 |
1.5 |
1 |
|
F5 |
4.0 |
1.5 |
1 |
TWDB collects groundwater samples through its Ambient Groundwater Quality Sampling Program. From 1988 to 2004, TWDB staff tested 24,272 samples from 11,501 wells for nitrate. Of the total number of samples, 16 percent contained no detectable amounts of nitrate. Of the 20,498 samples found with detectable amounts, the median value was 4.0 milligrams/liter (mg/l); 1,141, or 5 percent of the total sample population, contained nitrate (as N) above the primary MCL of 10 mg/l.
The infrared spectroscopy is used to identify the incidence of functional groups in molecules for the specific functional groups in molecules. The spectrum of the sodium alginate tends to illustrate the broad peak of 3430 cm-1 and the vibrations stretch further to develop the C-H bonds. The technology alienation of the alginate beads from the effectiveness of the bacterial isolation causes a better inoculation in the water treatment. The alginate derivatives have been combined with other nutrients for a very long time alongside the surfactants, stabilizers, bulk and dispersal materials as well as the cryo-protectants (Bashan, 2006). The implementation of the alginate formulations in the systems causes easier nitrate removal from the ground water and it improve the economic feasibility for the organization.
There are micro-alginate and macro-alginate beads which are categorized on the basis of size. In agricultural applications, the seeds tend to alienate themselves a few centimeters from the plants. In water treatment, the alginate beads float on the water surface but they are useful in adsorbing the nitrate content in the water alongside other minerals such as the ammonium.
The alginates are hydrophilic, biocompatible in nature, biodegradable and totally non-toxic. The alginates can form gels in for the divalent and trivalent cations and anions. The following illustration demonstrates how the alginate beads are dropped into the contaminated water and after the beads absorb the contaminants, the beads rise up and float on the water surface with the aim of nitrate removal from the groundwater,
Alginate stability in groundwater resources
The researchers are constantly looking for natural alternatives in water treatment as opposed to the chemical implementations in water treatment alongside the other expensive techniques. The gel forming ability highly depends on the alginates that depend on the G-blocks binding divalent cations. The longer the time taken to gel determine the far the matter can shrink. The dye model of the beads has a great encapsulation efficiency that is way higher than that of the calcium such that the micro beads tend to swell while being gelled. The alginate beads react to the effects of the gelling action and in the low temperature; it is exhibited to have minor size changes as compared to the incubated ions in solutions. The beads are gelled and they stay stable for about 120 minutes. The beads have different properties and the larger the beads, measuring the diameter and the pore sizes, the faster it loses its stability after the gelling process. During incubation, where the room temperature is taken up as the ambient temperature, for the alginate properties for the different fields, the beads depict a dramatic shrinkage which reduces the size by about 25 percent. A number of environmental parameters affect the stability of the alginate beads in the water treatment process. For instance, the temperature in the surrounding, the Ph level of water, and the cross-linkers in the polymer during the gelling process affect the stability of the alginate beads regardless of the size. At the increased Ph rate of 2-3, the nitrate removal rate increases but at the rate of Ph 3-8. The properties of the alginate gel beads are demonstrated in the pollutants of the aquatic environment as specific tank reservoirs with ponds of contaminated ground water.
There are a number of factors that contribute towards the nitrate removal using the alginate beads such as the algae species from which the alginate is obtained, the media configuration, and diverse environmental strictures such as light radiance, Ph levels, and temperature. The media composition is based on the correlation of nutrients and the carbon sources made available. The algal treatment systems encounter a weakness while there is harvesting of the algal biomass which causes the immobilization technology that entraps the micro-algal cells into a matrix. The immobilization technology in the treatment of water depends on a number of factors such as the,
Bead concentration
Algal species (origin of the alginate)
Type of nitrogen source
Hard or soft water
Water treatment is not only about cleaning water for human consumption but also it’s important to have a recirculating an aquaculture system as opposed to the flow-through systems considering the waste discharge into the environment and to have a controlled volume. One of the main ways that the researchers have managed to ensure that the nitrate is removed from the drinking water is the use of immobilized floating calcium alginate. As stated in the literature review, the carboxyl groups are needed in the natural approach of the water treatment by nitrate removal. The adsorbents used have the carboxyl group components which are found within the alginate. The alginic acid is obtained from the natural seaweeds found on several water bodies. The acid is inexplicable in water and the carboxyl groups in the given acid can actively be involved in the ion-exchange.
The conventional water treatment methods are well to do at the pilot stage but they tend to be very expensive and they operate in a limited potential application. Several researchers, in this regard, tend to focus on other alternatives that can meet the same objective but more efficiently, with a friendly budget. The focus has shifted to the use of the new efficient and cost effective adsorbents from natural and biological materials or industrial waste. Some of the key adsorbents implemented to aid in the removal of the nitrate components of water are the carboxyl groups which bind the nitrate ions and as a result of the large surface area and uniform pore size distribution, the long range homogeneity of texture and modifiable surface chemistry the system is able to function as intended.
There are a number of biotechnical procedures in the environmental and agricultural implementations that are responsible for the immobilization of micro-organisms in alginate beads as well as in other polymers in the same cellular life. In the ground water treatment especially for the tertiary waste water, the chlorella, Spp. Exists together with the alginate beads. The alginate beads are basically implemented to immobilize the micro-organisms. The research work seeks to quantify the occurrence of the bacteria in waste water involved. The alginate beads are strengthened against the degradation by biological processes. The biologists may analyze its concentration in a compound and calcium chloride to get the alginate mixture. The Na-alginate-entrapped Nano-scale iron uses the Nano scale zero-valent iron entrapped in calcium beads that show a great state of aqueous arsenic treatment. There are common techniques used in the ground water remediation of arsenic components such as the coagulation/ precipitation, filtration, ion exchange, and the chemical precipitation. The calcium alginate material entraps microbial cells in the water treatment, pharmaceutical industry, and the microbial cells. The process involved is coagulation that enables the sedimentation and filtration. It is not very effective in arsenic removal but the ion exchange process has a better performance. The NZVI removes the groundwater contaminants using surface precipitation or adsorption when arsenic is in a pentavalent oxidation state. These particles become quickly dispersed in the mobile aquifer material. The nanoparticles affect the micro and higher organisms once presented in unreacted stages. An experiment is carried out to demonstrate that the NZVI particles do not lose their reactivity especially in the instance where they are entrapped within the beads. The illustration below shows the entrapment procedure,
The forces that affect the beads are based on the pore state of the beads as well as the weight. The buoyancy test is carried out to determine the floating time. The paddle type USP apparatus II is used to perform the test.
Agitation is done at 50 rpm and the temperature is maintained at .
The floating properties are studied to determine the buoyancy force as well as the time required for all the beads in the batch to sink. A surfactant is used in the test to simulate the surface tension of the ground water. There is a very short lag time and the beads are able to sink and float back in a span of 24 hours. The following FT-IR spectra demonstrates the behavior of the sodium alginate beads in the buoyancy test,
There are forces that affect the floatation of alginate beads in the groundwater under treatment. From the solutions obtained using the sodium alginate solutions, the viscosity was measured using the rotational rheometer that is based on Bohlin Instruments Division, UK. The procedure involves a cone-plate combination (CP 4/40) used as a measuring system. The density of the beads is measured using the glass picnometer (DISA, Milan, Italy).
Effect of CaCO3 and NaHCO3 on CO2 production
A cylinder is in this experiment to facilitate the removal of the nitrate ions at the bottom of the water and the beads are observed to NaHCO3 and CaCO3 so as to show the specific gravity of the alginate gel beads. The stability of the carbon (IV) oxide within the alginate gel beads is determined to be 1 percent of the alginate solution. All the alginate beads float on the groundwater surface at the beginning of the tests and they tend to sink as nitratethe contaminants are dissolved in an acidic solution. The dissolution of the Carbon (IV) oxide bubble in the solution is such that the bicarbonate ions are obtained and the floatability of the beads is lost. The beads float and only about 1 percent is left at the bottom. The beads alter the Ph of the solution and the formation of the CO2 bubbles float in the alginate gel beads controls the floating time. These gas bubbles are prepared by alginate gel beads from the solution that contain sodium hydro-carbonate at various Ph values and it is prepared to form a bead in the size of 0.15 to 0.25 mm in radius.
The sodium alginate tends to be soluble in cold or hot water and it belongs to linear block of polyanionic copolymers as shown in the illustration below (Sutherland, 1991),
The effect of the pH on the nitrate adsorption capacity of the Na-alginate beads in the production on CO2 bubbles from the alginate gel beads. The adsorption capacity of the contaminant against the pH from the Na-alginate beads and the CaCO3 bubbles for nitrate contaminant in water. The concentration of the adsorbent causes the alginate gel bead to act as the reagent so that the pH of the solution of the groundwater in the treatment chamber is acidic and the pH of the gel beads remains basic. Based on the alginate gel beads, the development of the new adsorbent is effected to remove the nitrate capacity and other ground water contaminants. The concentration of the nitrate ions at the bottom of the water is removed using the gel beads which rise thereafter and can be removed from the solution.
The NZVI experiment produces the average particle size with an average BET surface area of 25m2g-1. It takes 6 hours to produce the NZVI-entrapped Na-alginate beads. One can observe that the beads are porous and have adequate porosity for contaminant diffusion into the beads ((Bezbaruah et al. 2009). In the experiment, it was observed that the NZVI reduced the contamination by arsenic components sequentially from 9.385, 4438, and 1.457 mg per liter. In the experiment, it is observed that the Na-alginate beads are slightly deformed and the blanks are filled up during the uptake of the nitrate contamination in the treatment process. The surface area of the Na-alginate beads is normalized at the rate equation such that,
The reaction rate is constantly monitored and it is observed that there is a 95 percent confidence with the exception of 1 mg per liter arsenic contamination. The use of the NZVI particles to remove the arsenic components from the groundwater may ultimately cause huge ramifications on the water treatment or using the filter media. Further, more experiments were carried out to test the removal of the nitrate contamination from the groundwater using the NZVI as illustrated in appendix B.
It is observed that about 92 percent of the aqueous nitrate is removed when the Sodium alginate beads are implemented. When the environmental considerations are incorporated in the developed of the alginate beads using NZVI, it is concluded that the method may not be used for treatment of the groundwater for drinking purposes. In such instances, the NZVI beads are disposed after removing the contaminants from the solutions by disposing the nanoparticles for a safe way. When the nitrate contaminant is to be removed from the ground water, the Calcium carbonate and carbon dioxide bubbles are dissolved into the solution at a pH 3.0. The concentration of the nitrate determines the time taken by the alginate gel beads to be adsorbed in the water column. The adsorbent sinks to the bottom section of the treatment system and floats up as it collects the nitrate contaminants.
In the management of nitrate in potable water, there are both treatment and non-treatment options. When a feasibility analysis is carried out for the non-treatment options, there are a number of limiting factors that include the location, budget, source availability, and water quality may vary due to the fluctuation of the nitrate levels. The infiltration of fertilizer components into the groundwater and the leakage from the livestock feedlots and waste storage is one of the major contributors to the nitrate problems. Some of the treatment methods implemented in the management of nitrate for water treatment are the ion exchange, reverse osmosis, electro-dialysis and electro-dialysis reverse, biological denitrification, and chemical denitrification. The nitrate removal is a high cost operation which requires that the water treatment company make huge investments in the structures and ensure regular operations and maintenance of the equipment.
Effect of CO2 production and amount of nitrate adsorbed,
The amount of nitrate removed during the adsorption process as a percentage is represented as,
The equations represent
The effect of pH on the adsorption of the nitrate ions using the floating Na-alginate beads
The effect of contact time on the adsorption of nitrate
The effect of adsorbent dosage on adsorption of nitrate,
The implementation of alginate beads as adsorbents of the nitrate contaminant in groundwater requires that the adsorbent sinks to the bottom of the treatment system of the groundwater. The beads are expected to rise up as they adsorb the nitrate contaminants till they float on the water surface. The floating time is based on the amount of the calcium carbonate that develops the amount of Carbon dioxide bubbles that form a reagent that is based on the Ph of the solution. The effect of temperature on the % of extraction of nitrate ions is studied by increasing the temperature in the intervals of 10 K in the range 303 to 333 K, while keeping all other conditions of extraction at optimum levels, namely, pH: 6, contact time: 180 min, initial concentration of lead: 100 mg/L, rpm: 300, and adsorbent dosage: 20 g/L. Using the Freundlich model to determine the adsorption isotherms of the nitrate ions,
While the Langmuir model determines the adsorption capacity such that,
From the solutions in the experiment, it was observed that the R2 from the Freundlich and Langmuir models are 0.9534 and 0.9967 respectively. The adsorption ability of the Na-alginate beads in the removal of the nitrates from the contaminated groundwater is found to be 137.58 mg/g.
Conclusion
In a nutshell, the process of groundwater remediation enables the management for nitrate using the conventional methods. The nitrate removal is a high cost operation which requires that the water treatment company make huge investments in the structures and ensure regular operations and maintenance of the equipment. The project requires that the different processes and techniques be employed to enable water treatment as well as the post treatment processes which tend to be more of chemical treatment to stabilize the pH levels of the systems. From the conventional techniques, unnatural methods, the only cost implications with respect to the biological denitrification are the maintenance of optimal conditions as well as the nutrient dose and management of the pretreatment and post-treatment in the portable water guidelines.
Future Work
The implementation of alginate beads in the conservation and treatment of water at an industrial level with automation systems to add the beads, analyze their level of swelling and determine the removal and replenish strategy.
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