Nitrate in Drinking Water
Nitrate contamination in groundwaterBibek ChatterjeeRoll No- 414ER2015
Contents:-What is Nitrate?Source of NitrateEffects of nitrateCase studyRemedies for Nitrate
What is nitrate?Nitrate (NO3) is a naturally occurring chemical that made of nitrogen and oxygen. Nitrate (NO3) is a naturally occurring form of nitrogen (N) which is very mobile in water. A common example of an inorganic nitrate salt is potassium nitrate (saltpeter)Nitrate is a polyatomic ion with the molecular formula NO3 and a molecular mass of 62.0049 g/mol.Nitrate salts are found naturally on earth as large deposits, particularly a major source of sodium nitrate.Nitrites are produced by a number of species of nitrifying bacteria.It is the primary source of nitrogen for plants, and it occurs naturally in soil and water.
Major Source Of Nitrate:-
Nitrate ions found in freshwater samples result from a variety of natural and manmade sources likes
Agricultural run offMunicipal and industrial wastewaterAutomobile and industrial emissionsDecomposition of both plants and animalsAnimal feedlots and barnyards
Agricultural run off:-
Nitrate pollution is due to excessive amount of nitrate in surface or ground water as a result of agricultural practices.Farmers and home owners using nitrate bearing fertilizers often use a variety of pesticides and herbicides which may migrate to ground water supplies.Due to its high solubility in water, nitrate and nitrite are the most common contaminants in rural and suburban areas.
The anthropogenic sources are really the ones that most often cause the amount of nitrate to rise to a dangerous level.Waste materials are one of the anthropogenic sources of nitrate contamination of groundwater.Water moving down through soil after rainfall carries dissolved nitrate with it to ground water. In this way, nitrate enters the water.
Automobile and industrial emissions:-
The water pollutants include sewage, variety of both organic and inorganic pollutants that are coming out from different automobile and industrial area.This waste water also show nitrate pollution when it contaminated the water.Many things are emitted from this area,Including oils, greases, plastics plasticizers, metallic wastes, suspended solids, phenols, acids, salts, and some heavy metals like Cu, Cr, Cd, Hg, Pb are also discharged from industries
Source of Nitrate:-Nitrate levels can be high in streams and rivers due to runoff of nitrogen fertilizer from agricultural fields and urban lawns.Groundwater is susceptible to contamination from many different chemicals, including nitrate fertilizers, especially where the water table is shallow.Most of these contaminated ground waters flow into streams and rivers, causing elevated nitrate levels.
Source of Nitrate:-
Effect of Nitrate:-Nitrate levels of up to three parts per million in well water may be naturally occurring or possibly indicate some low level of contamination, but are considered to be safe for consumption.EPA has set a maximum contaminant level of 10 ppm for nitrate (NO3-N) for drinking waterNitrate levels above 10 ppm may present a serious health concern.Due to increase of nitrate level in water is affected on human health and also affect the aquatic life. Human health issues:-Methemoglobinemia:- Adults receive more nitrate exposure from food than from water. When its concentration high in body its help to oxidize the iron atoms in hemoglobin from ferrous iron (2+) to ferric iron (3+), rendering it unable to carry oxygen. This process can lead to generalized lack of oxygen in organ tissue of the body in infants of six months old or younger. The resulting illness is called methemoglobinemia, or "blue baby syndrome".
Human health issues:-Cancer:- Nitrate is converted to nitrite after ingestion, and this nitrite reacts with natural compounds to produce N-Nitroso compounds in the human stomach. Many of these N-Nitroso compounds are carcinogenic in human body so high nitrate levels in drinking water may increase cancer risks. Recent human epidemiologic studies have shown that nitrate ingestion may be linked to gastric cancer
Some research has suggested that nitrate may play a role in spontaneous miscarriages, thyroid disorders, birth defects, and in the development of some cancers in adults.
Nitrate effect on aquatic life:-
Excess nitrate in the water is a source of fertilizer for aquatic plants and algae. Excess plants in a body of water can create many problems. The growth of plants and algae create an unstable amount of dissolved oxygen.During the day, there will be usually be high levels of dissolved oxygen, and at night the levels of oxygen can decrease dramatically. This will create stressful conditions for fish. If the conditions persist for a long period of time, the stressed fish species may choose to leave that area or die off.High densities of algae will create a condition where sunlight cannot reach very far into the water. Since plants and algae require some sunlight, plants and algae not receiving sunlight will die off. These dead plant materials will settle to the bottom of the water and bacteria that feed on decaying organic material will greatly increase in numbers. These bacteria will consume oxygen and, therefore, the level of dissolved oxygen in this water will fall to levels that are too low for many aquatic insects and fish to survive.
Nitrate effect on aquatic life:-
Remedies for Nitrate1)Biological Treatment:-
Nitrate is commonly removed from wastewater in both industrial and municipal applications with biological treatment using nitrate-reducing (denitrifying) bacteria. Added methanol or a comparable carbon source typically serves as an electron donor for the bacteria. In this reaction, denitrifying bacteria reduce nitrate to nitrogen gas, oxidize methanol to carbon dioxide and create more bacteria (biomass). Including methanol demand for dissolved oxygen, approximately 3 mg/L of methanol is required for each mg/L of nitrate-nitrogen. Nitrogen gas and carbon dioxide, which are natural constituents of the atmosphere, passively vent from the treatment system
2) Reverse Osmosis:-The most common nitrate removal method for household use is reverse osmosis process. Reverse Osmosis Drinking Water Systems can be installed under the sink or in a mechanical room.This technology passes your water through a series of filters, one of which is the Reverse Osmosis Membrane(semipermeable membrane).Membranes used were made of cellulose acetate, polyamides and composite materials.The membrane will physically separate impurities from the water, including Nitrates. The good water is sent to a storage tank awaiting your use. Estimates are around 83 to 92% of the incoming nitrate are remove by this process.
Disadvantage of Reverse osmosis:-Reverse osmosis is expensive.Added to the equipment costs are the high energy costs for operation. Reverse osmosis is also a slow inefficient process, sometimes producing only a few gallons a day of purified water, while wasting up to 90 percent of the incoming water.
3) Distillation:-Is a traditional method for removing minerals and other components from water.Water is boiled, cooled and condensed. The condensed water is then free of solids, salts, heavy metals. Boiling the water also inactivates microorganisms.
Distillers also have limitations:-
Like reverse osmosis, distillation is a slow process.Distillation uses much energy and produces heat which taxes air conditioners in the summer months.Energy costs are about 30 % per gallon produced.Ultimately, these units require frequent cleaning to remove accumulated scales.
4) Electro-dialysis (ED) for denitrification:-In ED ions are transferred through membranes from a less concentrated to a concentrated solution by application of direct electric current. ED treated the water by selective removal of undesirable ions through a semi permeable membrane. An electro dialysis system required a supply of pressurized water [50-75 psi (345-578 kPa)].The nitrate removal efficiency of ED and RO processes was almost the same.A selective nitrate removal process was developed, NitRem, based on ED.The process was effective in reducing nitrate concentrations from 50 mg/L or more to less than25 mg/L. An attractive feature of the process was that it included the removal of nitrate without the addition of any chemicals.
5) Catalytic denitrification:-A catalytic process was developed for the removal of nitrite and nitrate from water.Palladium - alumina catalysts were effective in reducing nitrite to nitrogen (98%).The lead (5%), copper (1.25%), Al2O3 , catalyst were found to completely remove nitrate from water having an initial nitrate concentration of 100 mg/L.The reaction was completed in 50 min. The process operated effectively at a temperature of 10C and pH 6-8.
6) Ion exchange process:-The ion exchange process involved passage of nitrate water through a resin bed containing strong base anion (SBA) exchange resins on which nitrate ions were exchanged for chloride or bicarbonate ions until the resin exhausted. The exhausted resin was regenerated using a concentrated solution of sodium chloride or sodium bicarbonate.Fifteen ion exchange plants used in the united states 24 reduced nitrate from 18 to 6.8 mg/L.. Nitrate removal capacity of the resins was reduced by Silica and iron precipitates.Ion exchange process was found to be five times more economical in comparison to RO process.
7) Denitrification using a membrane bioreactor :-Immersed heterotrophic membrane bioreactor (MBR) produced high quality product water when NO3 contaminated water was flow through the lumen of tubular microporous membranes(0.1m). NO3 diffused through the membrane pores. Denitrification took place on the shell side of the membranes. The MBR achieved over 99% NO3- removal from the water.