Tertiary Treatment and Recycling of Waste Water, Research Paper Example

Summary

The purpose of this research project was to look at the methods by which waste-water treated by a primary and secondary treatment procedure can be further purified using a tertiary sewage treatment procedure in order to be reclaimed for use or to be released into the environment with a minimum impact.  A tertiary treatment can be useful in order to reduce the amount of pollutants that are released into the environment, especially in environmentally sensitize areas such as coral reefs, swamps, marshes and other wetlands. Sewage in water comes from both commercial and residential sources. Household sewage water comes from toilets, baths and sinks and can contain substances such as soaps, cleaners, food and other household waste products as well as human waste. Industrial sewage can contain a number of chemicals and dyes that are byproducts of production. While primary and secondary treatments will reduce the amount of large solids and biodegradable matter in the water, they are often not sufficient to remove chemicals, dyes and excess nitrogen and phosphorus. In addition, sewage water often contains excess amounts of organic carbon. In order to judge how just how much an effluent has, its Biological Oxygen Demand (BOD) is measured. If an effluent has a high BOD, it will more likely cause oxygen depletion in the water system, causing algal blooms and consequent anaerobic conditions. A tertiary sewage treatment is performed after the effluent has been treated with a primary and secondary treatment in order to remove non-biodegradable organic pollutants as well as nitrogen and phosphorus salts, which are mineral nutrients and trigger algal and bacterial blooms (http://www.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/streem/methods.htm).

Before a tertiary treatment is performed, the effluent is first subjected to a primary treatment and a secondary treatment. Primary waste-water treatment is a process called sedimentation. The waste-water is placed into a holding tank where sediment is allowed to settle to the bottom, where large scrapers remove it. Grease and oils will rise to the top and are removed with top scrapers. The sedimentation tank must be of sufficient dimensions to effectively remove a majority of the floatables and sludge. “A typical sedimentation tank may remove 60% to 65% of suspended solids and from 30% to 35% of the BOD from the sewage (http://en.wikipedia.org/wiki/Sewage_treatment). From here the effluent is removed and placed in another enclosure in order to be subjected to a secondary treatment method.

Secondary treatments are designed to removed biological content such as food, soaps, detergents and human waste from the waste-water Secondary treatment, called fixed-film or suspended-growth systems, are biological methods that use organisms such as bacteria and protozoa which consume biodegradable soluble organic contaminants (http://en.wikipedia.org/wiki/Sewage_treatment).

Both these methods have one goal in common, and that is to bring “aerobic microorganisms, organic matter in waste-water and oxygen together(http://www.brighthub.com/environment/science-environmental/articles/68537.aspx).” This process allows biological oxidation to occur in the treatment pond rather than in a lake, river or stream where it naturally would if released untreated.

While primary and secondary treatments can clean waste-water sufficiently for release into some ecosystems, there are other ecosystems which are far too delicate to release this water into. Waste-water effluent that has been treated by primary and secondary treatments can still contain high levels of BOD, suspended solids, ammonia (NH3) that is toxic to fish, depletes oxygen and supports biological growth, nitrate (NO3) another nutrient that is toxic to babies, phosphorus which is also a nutrient and disease causing pathogens including bacterias and viruses (www.aowatc.uwa.edu/Tertiary%20Treatment.ppt).

Tertiary treatment is necessary when waste-water is going to be released into areas where it will be harmful to the environment and affect public health, such as when it will be mixing with drinking water.  “water reclamation is achieved in varying degrees, but only a few large-scale plants are reclaiming water to near-pristine quality (http://www.waterencyclopedia.com/Tw-Z/Wastewater-Treatment-and-Management.html).” Tertiary treatment methods include coagulation sedimentation to further remove solids suspended in the effluent, filtration, reverse osmosis and biological processes that remove excess nutrients (http://www.sheffy6marketing.com/index.php?page=tertiary-treatment).

In addition to the tertiary treatment of the waste-water effluent, it is also necessary to address the issue of sludge produced by tertiary waste-water treatment. Sludge is produced from all of the sewage treatment steps. Sludge from primary waste-water treatment typically consists of organic solids and grits. Primary sludge is typically processed with additional thickening, stabilized, conditioning and de-watering procedures then disposed of or reused. Secondary treatment produces sludge is typically biological sludge since secondary treatments are biological in nature. Since secondary sludges result from aerobic biological treatments, they are typically more difficult to thicken and dewater than primary sludges. Adding lime, iron and aluminum salts to secondary sludge can help to process it (http://outreach.engineering.uga.edu/publications/Ch03-SolidsHandlingProcesses.pdf).

Tertiary sludge can contain either biological or chemical bi-products and will need to be processed depending on the specific contaminants contained in the sludge. Processing the sludge will also release excess water which can be re-captured and sent back for further purification. Typically the first step to treating tertiary sludge it to concentrate the sludge or thicken it. This involves removing as much of the water content as possible, and is done by either gravity thickening, flotation or centrifugation (http://outreach.engineering.uga.edu/publications/Ch03-SolidsHandlingProcesses.pdf).

Gravity: Treating the tertiary sludge by gravity starts with pumping the sludge into a circular tank so that the solids can be separated out from the liquids by settling. The removed liquid is removed and sent back for further treatment. Gravity methods can typically reduce sludge volume by half.

Dissolved Air Flotation (DAF): to remove solids involves attaching air bubbles to the solids suspended in the effluent.  To help in flocculation of the solid particles, polymers are added to the effluent, usually ones that are synthetic organic, long chain and water soluble. Polyacrylamide is the most widely used polymer for DAF tertiary sludge treatments.

Centrifugation: In order to treat tertiary sludge with centrifugation, the sludge is fed into a rotating bowl where the solids are separated from the liquid. A large, rotating internal screw removes dewatered sludge out of one end of the bowl and water out of the other end. Centrifugation can thicken sludge to approximately 20% of its original volume.

Biological tertiary treatments can be an effective way to remove unwanted contaminants from waste-water such as phosphorus and nitrogen. Both of these are mineral supplements that, when released into a waterway in excess amounts, can cause excess algal and bacterial blooms in rivers and streams where it is released. Biological treatments allow the natural process of the breakdown of nitrogen and phosphorus to be done in a controlled setting as a tertiary treatment.

The use of plants has been shown to be a very promising as a biological tertiary treatment for waste-water. There are numerous ways in which plants can be used to remove nutrients from the water, from the installation of a pond to the creation of an artificial wetland that mimics natural processes in order to break down nutrients in the waste-water before it is released into the environment. The use of plants to filter waste-water is called phytoremediation. This process can be especially beneficial to developing nations that do not have the resources to invest into a water treatment plant. An example of the effectiveness of this type of tertiary treatment was shown in the report “Phytoremediation and Wetland for Tertiary Treatment of Pulp and Paper Mill Wastewater” by W. Wirojanagud and N. Tantemsapya (http://home.kku.ac.th/netnapid/publication/2005/Taiwan%2005.pdf). Phytoremediation was investigated as a solution to cleaning up water released from a pulp and paper mill located in northeastern Thailand which was damaging the crops of local farmers. The main contaminant in the effluent which needed to be removed was organic solids. The researchers used native salt tolerant plants, Brassica alboglabra, Asparagus officinalis var. altilis L., Brassica alboglabra Bailey, Ocinum sanctum, Ixora congesta Roxb and Phyllanthus amarus. These plants were chosen not only for their effectiveness in breaking down the organic solids from the waste-water but also because these plants were able to be used by the locals for local handicrafts and for enhancing landscape management. This type of tertiary treatment is preferable for regions where tertiary treatment is needed but where cost inhibits implementation of a tertiary treatment facility.

Nitrogen and other nutrients that are often present in waste-water can also be effectively removed with biological tertiary waste water treatments. Biological nitrogen removal processes include using organisms to uptake the nitrogen into their cell mass, converting the nitrogen into nitrate via nitrification processes, and converting it to nitrogen gas via denitrification (www.aowatc.uwa.edu/Tertiary%20Treatment.ppt). Nitrification can be difficult to control in a tertiary treatment setting as the bacteria needed perform the nitrification are sensitive and susceptible to a variety of conditions, including a specific dissolved oxygen concentration, pH, temperature and the concentration of NH4 and NO2. Biological denitrification involves denitrifying bacteria that consume carbon aerobically, obtaining their energy from the conversion of NO3- to N2 gas, using a carbon source inherent in the waste-water This process requires a low to no oxygen concentration, a carbon source (usually the BOD in the waste-water), a neutral pH and a high concentration of nitrate. The process can take place in either a denitrification reactor or in a combined carbon oxidation-nitrification-nitrification reactor.  (www.aowatc.uwa.edu/Tertiary%20Treatment.ppt).

A study by Kimochi, Masada, Mikami, Tsuneda and Sudo  (http://www.iwaponline.com/wst/05804/0847/058040847.pdf) explored the effectiveness of using natural zeolite ceramics and aquatic plants, in particular the reed Phragmites australis in removing nitrogen from sewage at domestic waste-water treatment facilities. The study concluded that the water purification system with zeolite ceramics and reeds could keep higher nitrogen removal efficiency for a long time. Zeolite ceramics would be useful when nitrogen compound, NH4N, in particular, in the influent was higher (http://www.iwaponline.com/wst/05804/0847/058040847.pdf).” Zeolites also showed promising results at being effective in removing tertiary butyl alcohol (TBA) from waste-water (http://www.wpi.edu/Pubs/ETD/Available/etd-042908-232630/unrestricted/Butland_Tricia_Thesis.pdf). TBA comes from the breakdown of methyl tert butyl ether (MTBE), a  blending agent used in fuels, and is a health hazard and suspected carcinogen. TBA can be broken down by anaerobic bacteria, however the conditions needed for the bacteria to flourish are difficult to maintain. Zeolites were found to be an effective at removing this contaminate safely from water.

This process is similar to lagooning, where aerobic lagoons are colonized with native macrophytes, such as reeds, and small filter feeding invertebrates such as Daphnia sp. and Roifera sp.(http://wastewater-treatment.org/component/content/article/40-wastewater-treatment/55-tertiary-treatment.html). Constructed wetlands can also be created as a tertiary waste-water treatment. This method has recently been implemented at Davis University in California. In the paper, “Construction of a Wetland to Accept Tertiary Treated Wastewater at the University of California, Davis Experimental Ecosystem (2003)”, the author Cynthia Fowler lays out a design plan for constructing a wetland in order to accept treated waste-water from the campus and use it to create a wetland that would closely mimic natural ones from the area, resulting in an ultimate discharge of water that would be of a significantly lower BOD (http://www.des.ucdavis.edu/faculty/Richerson/ESP%20110%20Project%20example.pdf).

Willow trees have been used to remove heavy metals and nutrient contaminates from waste-water in Belgium (http://www.brdisolutions.com/pdfs/bcota/abstracts/6/151.pdf). The study, entitled “Tertiary Waste Water Treatment Using Short Rotation Willow Coppice in Belgium”, looked at the effectiveness of planting willows at a high density of 10 to 20,000 plants per hectare. The trees act like a biological filter media and effectively removed nitrogen, potassium and phosphorus from waste-water With this method, the trees are harvested every 2 to 5 years and replanted, doubling as a source of renewable energy.

The common water hyacinth (Eichhornia crassipes) can also be used as phytoremediation and is especially beneficial for removing heavy metals from water. A report entitled “Heavy Metal Phytoremediation by Water Hyacinth at Constructed Wetlands in Taiwan” by Liao and Chang (http://www.apms.org/japm/vol42/v42p60.pdf) showed how this fast growing water plant can effective absorb cadmium, lead, copper, zinc and nickel from wetlands. Since the water hyacinth is fast growing and adaptable to a number of environments, it is a cost effective and environmentally friendly way to remove toxic heavy metals from waste-water.

Phytoremediation can also be achieved using simple plants such as algae. The effectiveness of the aerial microalga Trentepohlia aurea was presented by Abe, Imamaki and Hirano in the report “Removal of Nitrate, Nitrite, Ammonium and Phosphate Ions from Water by the Aerial Microalga Trentepohlia aurea.” This algae grows well in solutions where there is a high concentration of ammonium, nitrate and phosphate ions and effectively removes them from the solution as it grows. Trentepohlia aurea was again studied in another report, “Development of Laboratory-Scale Photobioreactor for Water Purification by Use of a Biofilter Composed of the Aerial Microalga Trentepohlia aurea (Chlorophyta).” The study (http://www.springerlink.com/content/a1j7413245050941/) concluded that a photobioreactor made from Trentepohlia aurea immobilized on a glass plate filter was effective in removing inorganic nitrate and phosphate from waste-water solution.

Phosphorus is another nutrient present in waste-water that can cause eutrophication when released into waterways in excess amounts. There are several ways to remove excess phosphorus, biologically and chemically. Phosphorus can be removed using specific bacteria in a process known as enhanced biological phosphorus removal. In this process the bacteria, called PAO’s (polyphosphate accumulating organisms) are “selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20% of their mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value (http://www.sheffy6marketing.com/index.php?page=tertiary-treatment).” Chemical removal can be used by precipitation the phosphorus out of the effluent using salts, iron, alum or lime. This method is not without consequences, since the precipitated sludge will contain the added chemicals and can be expensive to treat and dispose of (http://www.sheffy6marketing.com/index.php?page=tertiary-treatment).

Algal ponds are a biological tertiary treatment of waste-water that is effective in removing phosphorus. A study done in South Africa by Charles Digby Wells (2005) entitled “Tertiary Treatment in Algal Ponding Systems” (http://eprints.ru.ac.za/206/1/wells-msc.pdf) studied an algal pond system for nine years to determine the effectiveness of this type of tertiary treatment in removing unwanted contaminants, pathogens and nutrients from waste-water. The high rate algal pond (HRAP) studied was determined to achieve nutrient and organic removal that was comparable to conventional waste-water treatments. Phosphorus and ammonia was consistently removed at high rates, as was the bacteria E.coli. After treatment, the effluent was of a quality that allowed it to be used for irrigation. HRAP was again demonstrated to be an effective process to remove excess phosphorus in a study by Wells and Rose (http://www.ewisa.co.za/literature/files/264%20Wells.pdf), “Disinfection and Nutrient Removal in the Independent High Rate Algal Pond (IHRAP).”

A 1995 study entitled, “Nanofiltration as a Tertiary Treatment for Phosphate Removal from Wastewater (http://www.faculty.ait.ac.th/visu/Data/AIT-Thesis/Master%20Thesis%20final/Roy%20pdf%2095.pdf)” investigated using nanofilters to remove phosphate from waste-water as an alternative to chemical procedures. Nanofiltration (NF) is the use of filters made from multiple layer thin-film composites of organic polymer. They have very small pore sizes that average 2 nanometers. Results showed that NF removed up to 95% of phosphorus whereas conventional methods only removed up to 90%. NF also has the ability to remove salts, heavy metals, dyes, viruses, bacteria and parasites.

Dissolved air flotation (DAF) can be used to remove phosphorus and microbes from waste-water as well as from sludge. DAF’s use as a tertiary water treatmentas studied by Koivunen and Heinonen-Tanski in their paper, “Dissolved Air Flotation (DAF) for Primary and Tertiary Treatment of Municipal Wastewaters” (http://www.deepdyve.com/lp/medline-abstracts/dissolved-air-flotation-daf-for-primary-and-tertiary-treatment-of-yOj0txiMLU). The study showed that the use of polyaluminum chloride was effective at removing phosphorus at a rate of 55% up to 81% and has produced reductions of enteric microbes from 90% to 99%.

Semi permeable membranes made of either biological or synthetic materials can be used effectively for tertiary waste-water treatment. Reverse osmosis is a filtration method that is able to filter out a range of large molecules and ions using a selective membrane. It is similar to membrane filtration which is also used for tertiary waste-water treatment except that reverse osmosis involves a diffusive mechanism and separation efficiency is dependent on the concentration of contaminates in the effluent, as well as factors such as pressure and water flux rate (http://en.wikipedia.org/wiki/Reverse_osmosis). Reverse osmosis and membrane filtration both have a wide range of applications in tertiary waste-water treatment.  It is especially useful in purifying drinking water. Usually RO membranes are combined with activated carbon filters, chemical additives and UV lamps in water purification systems.

While both NF and RO methods have been used successfully, a study undertaken by Ben Amar, Kechaou, Palmeri, Deratani, and Sghaier entitled “Comparison of Tertiary Treatment by Nanofiltration and Reverse Osmosis for Water Reuse in the Denim Textile Industry” (http://www.ncbi.nlm.nih.gov/pubmed/19497667) compared the two techniques to determine which was more efficient in removing contaminants from water from a factory specializing in dyeing denim. The study determined that NF allowed a higher yield and produced water that was acceptable for reuse.

Membrane nanofilters have also been used to treat effluent from palm oil mills. In a report entitled “Membrane Bioreactor Technology for Tertiary Treatment of Palm Oil Mill Effluent (POME) the effectiveness of bio-filters as an effective tertiary waste-water treatment was examined. Membrane bioreactor systems (MBR) create an absolute barrier against suspended solids. MBR also filters out chlorine resistant pathogens, such as Cryptospovidium and Giardia.  When MBR is used as a tertiary treatment for waste-water from a POME mill, the waste-water is able to be reused. By contrast, chemical methods to treat POME mill effluent, as shown in the report “Tertiary Treatment of Palm Oil Mill Effluent (POME) Using Chemical Coagulation” (http://www.efka.utm.my/thesis/IMAGES/3PSM/2008/JKAS1/mohdfahdliaa040111ttt.pdf) showed a much lower success rate. Chemicals tested were ferrous sulfate and aluminum sulfate. In addition to having a lower removal rate of both COD and color, the chemicals are then taken into the sludge and must then be treated again.

Bacterial biofilms have also shown promising use as a tertiary treatment for waste-water. Bacteria from the Nitrospirae group and the Acidobacteria group have been found to thrive in ammonia rich effluent and to oxidize nitrite and ammonia in the waste-water. Some of the drawbacks of biofilms include hygiene issues and clogging from colonies that reproduce prolifically. Biofilms and their benefits and drawbacks is examined in the report “Characterization of Bacterial Biofilm Communities in Tertiary Treatment Processes for waste-water Reclamation and Reuse” by Shoji, Ochi and Ozaki (2008). (http://www.ncbi.nlm.nih.gov/pubmed/18824800)

Another type of filter used for filtering tertiary waste-water is the use of disc filters. Innovative disc filter technology was used effectively by a waste-water treatment plant in Frankfort, Illinois to meet guideline for total suspended solids in its tertiary effluent (http://www.wwdmag.com/Tertiary-Treatment-Today-article11039).  Disc filters at the plant took water than came in averaging 81.66 mg/L and discharged water with an average of only 4mg/L. Disc filter technology uses fabric membranes to filter effluent. They have the benefit of being more environmentally friendly than conventional tertiary treatment methods and are also easy to install and cost effective.

Stainless steel filters have also been used to effectively treat domestic waste-water. The effectiveness of these filters was examined in the study “Experimental Study of Domestic Sewage Treatment with a Metal Membrane Bioreactor” (2005) by Zhang, Qu, Liu, Yang, Zhang, Furukawa and Yamada (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFX-4HBRP0T-B&_user=10&_origUdi=B6TFX-4HBRP0T-F&_fmt=high&_coverDate=06/20/2005&_rdoc=1&_orig=article&_origin=article&_zone=related_art&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=9b253c95352b4a644789ae2e63e686ae). Stainless steel filters are not only effective, removing up to 97% of COD but the filters could also be easily cleaned with a NaClO solution with a pH of 12. Stainless steel filters are proving to be a cost effective and efficient tertiary waste-water treatment method.

Activated carbon has also been used to filter tertiary waste-water to make it suitable for reuse. Granular filtration mimics nature and uses activated carbon of various sizes in order to filter out suspended solids, dissolved solids, turbidity and COD. This method was studied by Vargas and Moreira and results were presented in their report “Adsorptive Filtration of Waste-water for Tertiary Treatment and Water Reuse” (http://www.enpromer2005.eq.ufrj.br/nukleo/pdfs/0537_enpromer_2005_vargas.pdf). Results showed that the granular filtration method using adsorbent carbon was effective in removing 85 to 90% of color and turbidity from the waste-water effluent.

Chemical methods have been described briefly and cannot be omitted as being useful in tertiary waste-water treatment. Various chemicals can be used to remove solids from waste-water effluent. Drawbacks, however, include the fact that the chemicals are then transferred to the sludge which must then be treated as well. The chemicals used to treat waste-water are rarely benign.

A final stage of tertiary treatment of waste-water is disinfection, which is also sometimes called “effluent polishing.” Disinfection is used to reduce the number of live microorganisms present in the water. The specific process used depends on environmental variables, such as the cloudiness of the water, its pH, where it will be discharged and how it will be used. Some of the common forms of disinfection include adding chlorine to the water and treating it with ozone and ultraviolet light. Chlorine is used for treating drinking water because of its safety, low cost and history of effectiveness. However, it cannot be used to treat waste-water that will be discharged into the environment because chlorine is deadly to aquatic life and it can react with residual organic material and generate chlorinated-organic compounds that are also hazardous to the environment.

Disinfecting waste-water with ultraviolet, or UV, light is an environmentally friendly alternative to using chemicals such as chlorine or iodine. When treated with UV light, bacteria, viruses and other pathogens can be damaged to the point where they are incapable of reproduction. However, there are some drawbacks to the process, including the high cost of maintaining UV lamps. As well, the effluent needs to be highly treated and contain a minimum amount of solids, which would shield the microorganisms making the treatment less effective.

Treating effluent with ozone, or O3 gas, is another chemical free alternative disinfecting agent. In this process, ozone is passed through the effluent and oxidizes most organic material it encounters. The main disadvantage of this technique is the high cost of maintaining the ozone generation equipment (http://wastewater-treatment.org/component/content/article/40-wastewater-treatment/55-tertiary-treatment.html). Ozone can also be combined with peroxide, UV or other reactions taking place under high pH conditions in what is known as advanced oxidation processes (AOP). Hydrogen peroxide will break down pollutants by making them unstable through the production of free radicals. The unstable pollutants are then more susceptible to the ozone attack, aiding in the overall effectiveness of the oxidation process (http://www.otsil.net/articles/waste%20water%2002.pdf). Ozone has been used beneficially in all four stages of waste-water treatment. “Ozone during the preliminary stage is used for detoxification. Ozone at the secondary stage is used for sludge reduction (http://www.otsil.net/articles/waste%20water%2002.pdf).” Ozone has also been used to treat waste-water prior to a secondary treatment (http://www.freepatentsonline.com/4178239.html) as a pretreatment. Ozone will breakdown non-biodegradable material into biodegradable material, making the secondary treatment more effective. In addition, zone has the added benefit of removing up to 90% of most investigated compounds, such as pharmaceutical contaminants (http://www.otsil.net/articles/waste%20water%2002.pdf).

The success of ozone devices for tertiary waste-water treatment was presented in a study conducted by P.K. Jin, X.C. Wang and G. Hu entitled “A Dispersed-Ozone Flotation (DOF) Separator for Tertiary Wastewater Treatment” (http://netedu.xauat.edu.cn/jpkc/szy/wlzy/7/A%20dispersed-ozone%20floatation%20%28DOF%29%20separator%20for%20tertiary%20wastewater%20treatment.pdf) examined the use of a compact DOF device for treating tertiary waste-water for re-use purposes. The DOF separator combined three processes, coagulation, ozonation and flotation. The results were very positive, as the device achieved a high level of removal of organic contaminants as well as color removal, at which it was successful at a rate of 84%. The device was also successful at inactivating bacteria and coliform.      Ozone has also been used effectively to treat waste-water from the leather industry, which typically has high pollution levels. The report “Ozone generation by Silent Electric Discharge and its Application in Tertiary Treatment of Tannery Effluent” by Balakrishnan, Arunagiri and Rao (http://cat.inist.fr/?aModele=afficheN&cpsidt=13706052) discuss the effectiveness of ozone in removing color, odor, hydrogen sulfide, iron and manganese from tannery effluent.

The use of nanotechnologies has emerged as a variety of effective and useful methods of tertiary waste-water treatment. The use of nanotechnology and its uses in waste-water treatment was addressed in a report by the National Network for Environmental Management Studies, a fellowship program managed by the Environmental Education Division of the EPA. The report, entitled “Emerging Nanotechnologies for Site Remediation and waste-water Treatment” (Watlington, 2005) discusses the various uses for nanotechnology in waste-water treatment. “In terms of [waste water treatment] site remediation, the development and deployment of nanotechnology for contaminant destruction has already taken place. Nanoscale iron particles and the subsequent derivatives (bimetallic iron particles and emulsified iron) represent a viable commercially available nanotechnology for remediation (http://www.clu-in.org/download/studentpapers/K_Watlington_Nanotech.pdf).” Diverse nanotechnologies including dendritic polymers and functionalized ceramics show promise in allowing for more efficient, and environmentally friendly, waste-water treatment that will allow for water to be re-used more effectively.

One nanotechnology that is showing great promise is the use of carbon nanotubes. Carbon nanotubes are effective in removing heavy metal ions from drinking water. The tubes are made of hematite and are non toxic as well as recyclable and useable. The capsules can be re-configured using heat treatment and sonification (http://www.nanowerk.com/spotlight/spotid=15136.php). When placed in water, heavy metal ions are attracted to the cores and become trapped in the small cavities. Carbon tubes can easily absorb lead and chromium ions. A report entitled “Carbon Nanotubes – The Promising Adsorbent in Waste-water Treatment” appeared in the Journal of Physics Conference in 2007.

In addition to heavy metals, carbon nanotubes are also effective at removing organic compounds from waste-water. Organic compounds, such as polychlorinated biphynyls (PCB’s), poly-aromatic hydrocarbons (PAH’s), dioxins and endocrine disrupting compounds (EDC’s) pose a serious health problem and are not easily removed from waste-water with conventional methods.  A study entitled “Cyclodextrin Polyurethanes Polymerised with Carbon Nanotubes for the Removal of Organic Pollutants in Water” (http://www.wrc.org.za/Knowledge%20Hub%20Documents/Water%20SA%20Journals/Manuscripts/2008/01/WaterSA_2008_01_2198.pdf) (Salipira, Mamba, Krause, Malefetse, and Durbach, 2008) showed that the polymerised carbon nanotubes were highly effective in removing organic compounds from waste-water. The carbon nanotubes, though expensive to produce, did have the benefit of being recyclable. However, the structural integrity of the carbon nanotubes was compromised after prolonged recycling. Another drawback encountered with the carbon nanotubes were that they were only effective when the concentrations of organic pollutants were low.

Carbon nanotubes, while effective, are not without controversy. There have been numerous studies that show that the carbon nanotubes are toxic so some microorganisms, ones that are not targeted with waste-water treatment. While every effort is made to reclaim the carbon nanotubes from the effluent and sludge of during waste-water treatment, because of their nanoscale some of the tubes will ultimately be released into the environment where they have the potential to reek havoc on natural ecosystems. A study was undertaken in Canada in 2008 to determine the toxicity of carbon nanotubes on a culture of Tetrahymena thermophila (http://www.physorg.com/news132996964.html). After exposure, the protozoa’s ability to ingest and digest bacteria was hindered. These protozoa are an ecologically important part of water ecology at many levels. A similar study was released in 2009 by Kang, Mauter, and Elimelech entitled “Microbial Cytotoxicity of Carbon-Based Nanomaterials: Implications for River Water and Waste-water Effluent.” The results of their study also confirmed the toxicity of carbon nanotubes on organisms in aquatic systems.

Nickel oxide nanosheets have a polar surface that can be used to attract contaminants out of waste-water effluent. The effectiveness of the NiO nanosheets is comparable to that of activated carbon. Once used, the contaminant can be burned off of the nanosheet and the sheet can then be reused. The sheets are especially effective at absorbing dyes used in industrial processes including paper manufacturing, cloth dyeing and leather treatment. A report on the NiO nanosheets appeared in the journal Nanotechnology in 2009 (http://www.physorg.com/news165655977.html).

Conclusion and Recommendations

Water conservation is one of the most important issues facing the environment today and finding effective solutions for cleaning water for re-use and human consumption is of vital importance. Tertiary treatments are necessary for ensuring that water released into the environment is of the best quality possible, with as few contaminates as possible so that its effect on the natural ecosystem is minimal. The types of tertiary treatments available are numerous and the one that is necessary depends on the contaminants in the effluent as well as the cost of the system and the resources available for the treatment.

When reclaimed, waste-water can be used for irrigating crops and human use and consumption. This allows for less water to be wasted and puts less stress on aquifers, rivers and lakes. In waster stressed areas, and in times of drought, this can be especially beneficial. By implementing a good water treatment system, reclaimed water will help to keep communities from suffering from water shortages.

The most effective choices for tertiary treatment should be the ones that offer the most effective contaminant removal while having the least impact on the environment. Chemical solutions and nanotechnologies such as carbon nanotubes offer impressive results yet have a strong negative impact on the environment, making them less attractive as effective tertiary treatments. Phytoremediation, treatment with ozone gas, UV radiation, reverse osmosis and various membrane filters all are effective tertiary waste water treatments that are also gentle on the environment.

Cost is also a major factor that must be included in the decision of which tertiary treatment to implement. Many of the areas in need of effective tertiary waste-water treatment plans are developing and third world nations. In poor areas of Latin America, Africa and southeast Asia, it is not cost effective to implement systems such as reverse osmosis no matter how effective a solution it is. Treatment plants that are expensive to maintain are simply not feasible options in these areas. Here, options like phytoremediation can be extremely beneficial since these systems use native plants and need little maintenance to be effective. Once implemented, locals can be trained to maintain the system and, which will basically run itself.

The type of tertiary treatment that will be most effective will also highly depend on the types of contaminants in the water. Waste-water that contains only solid organic contaminants, such as from domestic sources, will require a different treatment than waste-water from industrial factories that contains dyes, chemicals and organic compounds. A complete assessment of the waste-water effluent needs to be undertaken to determine the type of contaminants and their concentration before any type of tertiary treatment is implemented. This way the best treatment can be chosen for the waste-water.

Waste-water recovery and reuse is vital to the health of the Earth and the future of mankind. Clean water is a resource that man cannot live without and cities, industry and population growth is continuing to stress water supplies around the world. Implementation of ecologically sound tertiary waste-water treatment methods is an action that will positively affect the future, and ensure that clean water is a legacy that can be passed down to future generations.