Biofilter

Biofiltration is a pollution control technique using living material to capture and biologically degrade process pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air.



Examples of biofiltration include;

* Bioswales, Biostrips, Biobags, Bioscrubbers, and Trickling filters
* Constructed wetlands and Natural wetlands
* Slow sand filters
* Treatment ponds
* Green belts
* Living walls
* Riparian zones, Riparian forests, Bosques



Control of air pollution

When applied to air filtration and purification, biofilters use microorganisms to remove air pollution. The air flows through a packed bed and the pollutant transfers into a thin biofilm on the surface of the packing material. Microorganisms, including bacteria and fungi are immobilized in the biofilm and degrade the pollutant. Trickling filters and bioscrubbers rely on a biofilm and the bacterial action in their recirculating waters.

The technology finds greatest application in treating malodorous compounds and water-soluble volatile organic compounds (VOCs). Industries employing the technology include food and animal products, off-gas from wastewater treatment facilities, pharmaceuticals, wood products manufacturing, paint and coatings application and manufacturing and resin manufacturing and application, etc. Compounds treated are typically mixed VOCs and various sulfur compounds, including hydrogen sulfide. Very large airflows may be treated and although a large area (footprint) has typically been required -- a large biofilter (>200,000 acfm) may occupy as much or more land than a football field -- this has been one of the principal drawbacks of the technology. Engineered biofilters, designed and built since the early 1990s, have provided significant footprint reductions over the conventional flat-bed, organic media type.



One of the main challenges to optimum biofilter operation is maintaining proper moisture throughout the system. The air is normally humidified before it enters the bed with a watering (spray) system, humidification chamber, bioscrubber, or biotrickling filter. Properly maintained, a natural, organic packing media like peat, vegetable mulch, bark or wood chips may last for several years but engineered, combined natural organic and synthetic component packing materials will generally last much longer, up to 10 years. A number of companies offer these types or proprietary packing materials and multi-year guarantees, not usually provided with a conventional compost or wood chip bed biofilter.

Although widely employed, the scientific community is still unsure of the physical phenomena underpinning biofilter operation, and information about the microorganisms involved continues to be developed. A biofilter/bio-oxidation system is a fairly simple device to construct and operate and offers a cost-effective solution provided the pollutant is biodegradable within a moderate time frame (increasing residence time = increased size and capital costs), at reasonable concentrations (and lb/hr loading rates) and that the airstream is at an organism-viable temperature. For large volumes of air, a biofilter may be the only cost-effective solution. There is no secondary pollution (unlike the case of incineration where additional CO2 and NOx are produced from burning fuels) and degradation products form additional biomass, carbon dioxide and water. Media irrigation water, although many systems recycle part of it to reduce operating costs, has a moderately high biochemical oxygen demand (BOD) and may require treatment before disposal. However, this "blowdown water", necessary for proper maintenance of any bio-oxidation system, is generally accepted by municipal POTWs without any pretreatment.

Biofilters are being utilized in Columbia Falls, Montana at Plum Creek Timber Company's fiberboard plant. The biofilters decrease the pollution emitted by the manufacturing process and the exhaust emitted is 98% clean. The newest, and largest, biofilter addition to Plum Creek cost $9.5 million, yet even though this new technology is expensive, in the long run it will cost less overtime than the alternative exhaust-cleaning incinerators fueled by natural gas (which are not as environmentally friendly). The biofilters use trillions of microscopic bacteria that cleanse the air being released from the plant.

Water treatment



Trickling filters have been used to filter water for various end uses for almost two centuries. Biological treatment has been used in Europe to filter surface water for drinking purposes since the early 1900s and is now receiving more interest worldwide. Biological treatment methods are also common in wastewater treatment, aquaculture and greywater recycling as a way to minimize water replacement while increasing water quality.

For drinking water, biological water treatment involves the use of naturally occurring micro-organisms in the surface water to improve water quality. Under optimum conditions, including relatively low turbidity and high oxygen content, the organisms break down material in the water and thus improve water quality. Slow sand filters or carbon filters are used to provide a place on which these micro-organisms grow. These biological treatment systems effectively reduce water-borne diseases, dissolved organic carbon, turbidity and colour in surface water, improving overall water quality.

Use in aquaculture



The use of biofilters are commonly used on closed aquaculture systems, such as recirculating aquaculture systems (RAS). Many designs are used, with different benefits and drawbacks, however the function is the same: reducing water exchanges by converting ammonia to nitrate. Ammonia (NH4+ and NH3) originates from the brachial excretion from the gills of aquatic animals and from the decomposition of organic matter. As ammonia-N is highly toxic, this is converted to a less toxic form of nitrite (by Nitrosomonas sp.) and then to an even less toxic form of nitrate (by Nitrobacter sp.). This "nitrification" process requires oxygen (aerobic conditions), without which the biofilter can crash. Furthermore, as this nitrification cycle produces H+, the pH can decrease which necessitates the use of buffers such as lime.

From http://en.wikipedia.org/

Best available technology

Best available technology (or just BAT) is a term applied with regulations on limiting pollutant discharges with regard to the abatement strategy. Similar terms are best available techniques , best practicable means or best practicable environmental option. The term constitutes a moving targets on practices, since developing societal values and advancing techniques may change what is currently regarded as "reasonably achievable", "best practicable" and "best available".

A literal understanding will connect it with a "spare no expense" doctrine which prescribes the acquisition of the best state of the art technology available, without regard for traditional cost-benefit analysis. In practical use the cost aspect is also taken into account.

Best practicable means was used for the first time in UK national primary legislation in section 5 of the Salmon Fishery Act 1861 and another early use was found in the Alkali Act Amendment Act 1874, but before that appeared in the Leeds Act of 1848.

The BAT concept was first time used in the 1992 OSPAR Convention for protection of marine environment of North-East Atlantic for all types of industrial installations.

Some doctrine deem it already acquired the status of customary law.

In the United States, BAT or similar terminology is used in the Clean Air Act and Clean Water Act.

European Union directives

Best available techniques not entailing excessive costs (BATNEEC), sometimes referred to as best available technology, was introduced with the 1984 Air Framework Directive (AFD) and applies to air pollution emissions from large industrial installations.

In 1996 the AFD was superseded by the Integrated pollution prevention and control directive (IPPC), 96/61/EC, which applies the framework concept of Best Available Techniques (BAT) to the integrated control of pollution to the three media air, water and soil.

In the European Union directive 96/61/EC emission limit values were to be based on the best available techniques, as described in item #17: "Whereas emission limit values, parameters or equivalent technical measures should be based on the best available techniques, without prescribing the use of one specific technique or technology and taking into consideration the technical characteristics of the installation concerned, its geographical location and local environmental conditions; whereas in all cases the authorization conditions will lay down provisions on minimizing long-distance or transfrontier pollution and ensure a high level of protection for the environment as a whole.

The directive includes a definition of best available techniques in article 2.11:

"best available techniques" shall mean the most effective and advanced stage in the development of activities and their methods of operation which indicate the practical suitability of particular techniques for providing in principle the basis for emission limit values designed to prevent and, where that is not practicable, generally to reduce emissions and the impact on the environment as a whole:

- "techniques" shall include both the technology used and the way in which the installation is designed, built, maintained, operated and decommissioned,
- "available" techniques shall mean those developed on a scale which allows implementation in the relevant industrial sector, under economically and technically viable conditions, taking into consideration the costs and advantages, whether or not the techniques are used or produced inside the Member State in question, as long as they are reasonably accessible to the operator,
- "best" shall mean most effective in achieving a high general level of protection of the environment as a whole.

United States environmental law

The Clean Air Act requires that certain facilities employ Best Available Control Technology to control emissions.

...an emission limitation based on the maximum degree of reduction of each pollutant subject to regulation under this Act emitted from or which results from any major emitting facility, which the permitting authority, on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such facility through application of production processes and available methods, systems, and techniques, including fuel cleaning, clean fuels, or treatment or innovative fuel combustion techniques for control of each such pollutant.

The Clean Water Act (CWA) requires issuance of national industrial wastewater discharge regulations (called "effluent guidelines"), which are based on BAT and several related standards.

...effluent limitations for categories and classes of point sources,... which (i) shall require application of the best available technology economically achievable for such category or class, which will result in reasonable further progress toward the national goal of eliminating the discharge of all pollutants. ...Factors relating to the assessment of best available technology shall take into account the age of equipment and facilities involved, the process employed, the engineering aspects of the application of various types of control techniques, process changes, the cost of achieving such effluent reduction, non-water quality environmental impact (including energy requirements), and such other factors as the Administrator deems appropriate.

A related CWA provision for cooling water intake structures requires standards based on "best technology available."

...the location, design, construction, and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental impact.

From http://en.wikipedia.org/

Best Available Control Technology

Best Available Control Technology (BACT) is a pollution control standard mandated by the United States Clean Air Act. The U.S. Environmental Protection Agency (EPA) determines what air pollution control technology will be used to control a specific pollutant to a specified limit. When a BACT is determined, factors such as energy consumption, total source emission, regional environmental impact, and economic costs are taken into account. It is the current EPA standard for all polluting sources that fall under the New Source Review guidelines and is determined on a case-by-case basis.

The BACT standard is significantly more stringent than the Reasonably Available Control Technology standard but much less stringent than the Lowest Achievable Control Technology standard.

From http://en.wikipedia.org/

Baffle spray scrubber

Baffle spray scrubbers are a technology for air pollution control. They are very similar to spray towers in design and operation. However, in addition to using the energy provided by the spray nozzles, baffles are added to allow the gas stream to atomize some liquid as it passes over them.

A simple baffle scrubber system is shown in Figure 1. Liquid sprays capture pollutants and also remove collected particles from the baffles. Adding baffles slightly increases the pressure drop of the system.

This type of technology is a part of the group of air pollution controls collectively referred to as wet scrubbers.

A number of wet-scrubber designs use energy from both the gas stream and liquid stream to collect pollutants. Many of these combination devices are available commercially.

A seemingly unending number of scrubber designs have been developed by changing system geometry and incorporating vanes, nozzles, and baffles.

Particle collection

These devices are used much the same as spray towers - to preclean or remove particles larger than 10 μm in diameter. However, they will tend to plug or corrode if particle concentration of the exhaust gas stream is high.

Gas collection

Even though these devices are not specifically used for gas collection, they are capable of a small amount of gas absorption because of their large wetted surface.

From http://en.wikipedia.org/

Aerobic granulation

The biological treatment of wastewater in the waste water treatment plant often accomplished by means of the application of conventional activated sludge systems. These systems generally require large surface areas for implantation of the treatment and biomass separation units due to the usually poor settling properties of the sludge. In recent years, new technologies are being developed to improve this system. The use of aerobic granular sludge is one of them.

Aerobic granular biomass

A definition to discern between an aerobic granule and a simple floc with relatively good settling properties came out from the discussions which took place at the “1st IWA-Workshop Aerobic Granular Sludge” in Munich (2004) and literally stated that:

“Granules making up aerobic granular activated sludge are to be understood as aggregates of microbial origin, which do not coagulate under reduced hydrodynamic shear, and which settle significantly faster than activated sludge flocs”(de Kreuk et al. 2005)"

Formation of aerobic granules



Granular sludge biomass is developed in Sequencing Batch Reactors (SBR) and without carrier materials. These systems fulfil most of the requirements for their formation as:

Feast - Famine regime: short feeding periods must be selected to create feast and famine periods (Beun et al. 1999), characterized by the presence or absence of organic matter in the liquid media, respectively. With this feeding strategy the selection of the appropriate micro-organisms to form granules is achieved. When the substrate concentration in the bulk liquid is high, the granule-former organisms can storage the organic matter in form of poly-β-hydroxybutyrate to be consumed in the famine period, being in advantage with the filamentous organisms.

Short settling time: This hydraulic selection pressure on the microbial community allows retaining granular biomass inside the reactor while flocculent biomass is washed-out. (Qin et al. 2004)

Hydrodynamic shear force : Evidences show that the application of high shear forces favours the formation of aerobic granules and the physical granule integrity. It was found that aerobic granules could be formed only above a threshold shear force value in terms of superficial upflow air velocity above 1.2 cm/s in a column SBR, and more regular, rounder, and more compact aerobic granules were developed at high hydrodynamic shear forces (Tay et al., 2001 ).

Advantages

The development of biomass in the form of aerobic granules is being recently under study for its application to the removal of organic matter, nitrogen and phosphorus compounds from wastewater. Aerobic granules in aerobic SBR present several advantages compared to conventional activated sludge process such as:

Stability and flexibility: the SBR system can be adapted to fluctuating conditions with the ability to withstand shock and toxic loadings

Excellent settling properties: a smaller secondary settler will be necessary, which means a lower surface requirement for the construction of the plant.

Good biomass retention: higher biomass concentrations inside the reactor can be achieved, and higher substrate loading rates can be treated.

Presence of aerobic and anoxic zones inside the granules to perform simultaneously different biological processes in the same system (Beun et al.. 1999)

The cost of running a wastewater treatment plant working with aerobic granular sludge can be reduced by at least 20% and space requirements can be reduced by as much as 75% (de Kreuk et al.., 2004).

Treatment of industrial wastewater

Synthetic wastewater was used in most of the works carried out with aerobic granules. These works were mainly focussed on the study of granules formation, stability and nutrient removal efficiencies under different operational conditions and their potential use to remove toxic compounds. The potential of this technology to treat industrial wastewater is under study, some of the results:

* Arrojo et al. (2004) operated two reactors that were fed with industrial wastewater produced in a laboratory for analysis of dairy products (Total COD : 1500-3000 mg/L; soluble COD: 300-1500 mg/L; total nitrogen: 50-200 mg/L). These authors applied organic and nitrogen loading rates up to 7 g COD/(L·d) and 0.7 g N/(L·d) obtaining removal efficiencies of 80%.

* Schwarzenbeck et al. (2004) treated malting wastewater which had a high content of particulate organic matter (0.9 g TSS/L). They found that particles with average diameters lower than 25-50 µm were removed at 80% efficiency, whereas particles bigger than 50 µm were only removed at 40% efficiency. These authors observed that the ability of aerobic granular sludge to remove particulate organic matter from the wastewaters was due to both incorporation into the biofilm matrix and metabolic activity of protozoa population covering the surface of the granules.

* Cassidy and Belia (2005) obtained removal efficiencies for COD and P of 98% and for N and VSS over 97% operating a granular reactor fed with slaughterhouse wastewater (Total COD: 7685 mg/L; soluble COD: 5163 mg/L; TKN: 1057 mg/L and VSS: 1520 mg/L). To obtain these high removal percentages, they operated the reactor at a DO saturation level of 40%, which is the optimal value predicted by Beun et al. (2001) for N removal, and with an anaerobic feeding period which helped to maintain the stability of the granules when the DO concentration was limited.

* Inizan et al. (2005) treated industrial wastewaters from pharmaceutical industry and observed that the suspended solids in the inlet wastewater were not removed in the reactor.

* Tsuneda et al. (2006) , when treating wastewater from metal-refinery process (1.0-1.5 g NH4+-N/L and up to 22 g/L of sodium sulphate), removed a nitrogen loading rate of 1.0 kg-N/m3·d with an efficiency of 95% in a system containing autotrophic granules.

* Usmani et al. (2008) high superficial air velocity, a relatively short settling time of 5-30 min, a high ratio of height to diameter (H/D=20) of the reactor and optimum ogranic load facilitates the cultivation of regular compact and circular granules.

* Figueroa et al. (2008), treated wastewater from a fish canning industry. Applied OLR were up to 1.72 kg COD/(m3·d) with fully organic matter depletion. Ammonia nitrogen was removed via nitrification-denitrification up to 40% when nitrogen loading rates were of 0.18 kg N/(m3·d). The formation of mature aerobic granules occurred after 75 days of operation with 3.4 mm of diameter, SVI of 30 mL/g VSS and density around 60 g VSS/L-granule

* Farooqi et al. (2008), Wastewaters from fossil fuel refining, pharmaceuticals, and pesticides are the main sources of phenolic compounds. Those with more complex structures are often more toxic than the simple phenol. This study was aimed at assessing the efficacy of granular sludge in UASB and SBR for the treatment of mixtures of phenolics compounds. The results indicates that anaerobic treatment by UASB and aerobic treatment by SBR can be successfully used for phenol/cresol mixture, representative of major substrates in chemical and petrochemical wastewater and the results shows proper acclimatization period is essential for the degradation of m - cresol and phenol. Moreover, SBR was found as a better alternative than UASB reactor as it is more efficient and higher concentration of m cresols can be successfully degraded.

Pilot research in aerobic granular sludge

Aerobic granulation technology for the application in wastewater treatment is widely developed at laboratory scales. The large-scale experience is still limited but different institutions are making efforts to improve this technology:

* Since 1999 DHV Water, Delft University of technology (TUD), STW (Dutch Foundation for Applied Technology) and STOWA (Dutch Foundation for Applied Water Research) have been cooperating closely on the development of the aerobic granular sludge technology (Nereda). Based on the results obtained, a pilot plant was started up in September 2003 in Ede (Netherlands). The heart of the installation consists of two parallel biological reactors with each a height and diameter of 6 m and 0.6 respectively and a volume of 1.5 m3.

* From the basis of the aerobic granular sludge but using a contention system for the granules, a sequencing batch biofilter granular reactor (SBBGR) with a volume of 3.1m3 was developed by IRSA (Istituto di Ricerca Sulle Acque, Italy). Different studies were carried out in this plant treating sewage at an Italian wastewater treatment plant.

* The use of aerobic granules prepared in laboratory, as a starter culture, before adding in main system, is the base of the technology ARGUS (Aerobic Granules Upgrade System) developed by EcoEngineering Ltd.. The granules are cultivated on-site in small bioreactors called propagators and fill up only 2 to 3% of the main bioreactor or fermentor (digestor) capacity. This system is being used in a pilot plant with a volume of 2.7 m3 located in one Hungarian pharmaceutical industry.

* The Group of Environmental Engineering and Bioprocesses from the University of Santiago de Compostela is currently operating a 100 L pilot plant reactor.

The feasibility study showed that the aerobic granular sludge technology seems very promising (de Bruin et al., 2004. Based on total annual costs a GSBR (Granular sludge Sequencing Batch Reactors) with pre-treatment and a GSBR with post-treatment proves to be more attractive than the reference activated sludge alternatives (6-16%). A sensitivity analysis shows that the GSBR technology is less sensitive to land price and more sensitive to rain water flow. Because of the high allowable volumetric load the footprint of the GSBR variants is only 25% compared to the references. However, the GSBR with only primary treatment cannot meet the present effluent standards for municipal wastewater, mainly because of exceeding the suspended solids effluent standard caused by washout of not well settleable biomass.

From http://en.wikipedia.org/

AdBlue

AdBlue is the registered trademark for AUS32 (Aqueous Urea Solution 32.5%) and is used in a process called selective catalytic reduction (SCR) to reduce emissions of oxides of nitrogen from the exhaust of diesel engined motor vehicles. As the name AUS32 would suggest, it is a 32.5% solution of high-purity urea in demineralised water that is clear, non-toxic and is safe to handle. However, it can be corrosive for some metals, and must be stored and transported using the correct materials. The AdBlue trademark is currently held by the German Association of the Automobile Industry (VDA), who ensure quality standards are maintained in accordance with ISO 22241 specifications.

AdBlue is carried onboard SCR-equipped vehicles in specially designed tanks, and is dosed into the SCR system at a rate equivalent to 3–5% of diesel consumption. This low dosing rate ensures long refill periods and minimises the tank's impact on chassis space. On-highway SCR systems are currently in use throughout Europe, in Japan, Australia, Hong Kong, Taiwan, Korea, New Zealand and Singapore. The United States Environmental Protection Agency‎'s (US EPA) 2010 legislation will limit NOx to levels that will require North American trucks to be equipped with SCR post-2010. The current generic name in North America for AUS32 is diesel exhaust fluid (DEF). Some trucking industry OEMs have already developed branded SCR solutions, such as Daimler's BlueTec.

All European truck manufacturers currently offer SCR equipped models, and the future Euro6 emission standard is set to reinforce the demand for this technology. SCR systems are sensitive to potential chemical impurities in the urea solution, therefore, it is essential to maintain high standards of AdBlue quality according to the ISO 22241 standard.

The use of SCR technology in Europe made it necessary to develop an AdBlue supply infrastructure. AdBlue is available from thousands of service stations, this locator finder

is updated monthly with new Retail sites selling AdBlue. It can also be purchased in canisters of 5 or 10 litres (1.1 or 2.2 imp gal; 1.3 or 2.6 USgal) at service stations. Larger quantities of AdBlue can be delivered in, for example, 208 litres (46 imp gal; 55 US gal) drums, 1,000 litres (220 imp gal; 260 US gal) Intermediate Bulk Containers (IBCs), and bulk.

From http://en.wikipedia.org/

Vehicle inspection in the United States

In the United States, vehicle safety inspection is goverened by each state individually. 18 states have a periodic (annual or biannual) safety inspection program, while Maryland requires an inspection prior to registration or transfer of ownership only.

Under the Clean Air Act (1990), states are required to implement vehicle emission inspection programs in metropolitan areas whose air quality does not meet federal standards. The specifics of those programs vary from state to state. Some states, including Kentucky and Minnesota, have discontinued their testing programs in recent years with approval from the federal government.

In most states, such inspections are done at state-operated garages, usually near the local DMV office. Pennsylvania is a notable exception, instead opting to have privately-owned garages doing inspections with approval from PennDOT. The flip side to this though is that some independently-run garages will do what is commonly known in Pennsylvania as a "lick-'em-and-stick-'em", which simply has the person pay the inspection fee and has the sticker replaced without actually checking the vehicle. This is illegal in Pennsylvania, which among other penalties could lead to a fine for the garage and a revocation of their inspection privileges. Other independently-run garages as well as chains like Pep Boys, Midas, and car dealerships are more stringent and follow PennDOT guidelines for inspections.

States and Federal Districts with periodic (e.g., annual) vehicle safety inspections

* Delaware (every year or every two years; brand new cars are exempt for the first four years provided the car remains with the same owner. Older cars registered as antiques do not require emissions testing.)
* District of Columbia (every two years; the requirement for safety inspection for private cars will end October 1, 2009)
* Hawaii (every year, except brand new vehicles receive an inspection valid for two years, emergency vehicles, school vehicles, rental cars, vehicles used in public transportation, and other, every six months)
* Louisiana (every year; emission test in the Baton Rouge metropolitan area parishes of Ascension, East Baton Rouge, Iberville, Livingtston and West Baton Rouge)
* Maine (every year; emission test in Cumberland County)
* Massachusetts (safety inspection and emissions testing annually). In 2008 the tailpipe test for 1995 model year and older vehicles was discontinued, vehicles without OBD-II systems receive a visual check of exhaust components
* Mississippi (safety inspection every year)
* Missouri (Odd numbered model year renews in odd numbered year, even model year renews in even year, except new vehicles not previously titled which are exempt during the model year and the year following, or vehicles displaying historical plates, which are completely exempt.; emissions testing in St. Louis city, St. Louis County, St. Charles County, Franklin County, and Jefferson County)
* New Hampshire (annually, emissions testing for model year 1996 and newer vehicles))
* New Jersey (safety and emissions testing every two years, brand new cars are exempt for the first four years. Effective 2010, the new car four-year exemption will transfer to the next owner if sold before the end of the four years . Older cars registered as antiques do not require emissions testing. Diesel cars under 10000 lb are also exempt.
* New York (annual safety and emissions). Model year 1996 and newer vehicles are subject to an OBD-II emissions inspection while older cars receive a visual check of exhaust components. Vehicles registered in the five boroughs of New York City as well as Long Island, Westchester County and Rockland County require a tailpipe smog-test if they are not OBD II equipped. All OBD II vehicles in those areas (1996 model year or newer) require only the OBD II test. And any vehicle 26 model years old or more does not require an emissions check of any sort. Newly registered vehicles from another state with a current inspection sticker are exempt until the out-of-state sticker expires or for one year, whichever is sooner.
* North Carolina (every year; emissions inspections in 48 of 100 counties (1996-newer, except new cars), exempting diesels and cars 35 years or older. Starting Nov 1, 2008 there won't be an inspection decal issued upon passing. )
* Pennsylvania every year for most vehicles; every six months for tractor-trailers, school vehicles (including school buses and school vans), motor coaches, mass transit buses, ambulances, fire department trucks, etc.; emissions inspections every year in 25 of 67 counties (stricter in the Pittsburgh and Philadelphia metro areas) (no emission inspection for diesel vehicles))annual inspection, emission, and semi-annual inspection stickers are color-coded, which tells which month of the year they expire. This makes it easier for police to be aware of expired stickers.
* Rhode Island (safety and emission inspection every two years)
* Texas (every year; emission test in the largest urban areas - Houston Metro, Dallas Metroplex, Austin, San Antonio, and El Paso)
* Utah (every two years for the first eight years, then every year)
* Vermont (every year)
* Virginia (every year; emission inspection every two years in urban and suburban jurisdictions in Northern Virginia)
* West Virginia (every year - safety)

States with safety inspection only required prior to sale or transfer

* Alabama
* Maryland (emission inspection required every two years in all counties)(not required in every county. The VEIP testing network consists of 18 centralized inspection stations located in 13 counties and Baltimore City)

States which only require federally mandated emissions inspections

* Arizona (Phoenix and Tucson metro areas only) annually, depending on age and type of vehicle)
* California (for most ZIP codes, every two years for all vehicles made after 1975 which are more than six years old)
* Colorado (in some localities, every year or two, depending on age and type of vehicle)
* Connecticut (every two years)
* Georgia (metropolitan Atlanta area only, every year, most recent three model year cars are exempt)
* Illinois every two years after the vehicle is four years old (Chicagoland and eastern suburbs of St. Louis, Missouri)
* Indiana (Lake and Porter counties only, every two years)
* New Mexico (Albuquerque metro area)
* Nevada (Clark County and Washoe County areas)
* Ohio (Cuyahoga, Geauga, Lake, Lorain, Medina, Portage, and Summit counties only) cars that are four years old or less do not have tested, after that period they have to tested. Testing is based on a odd-even year system. If a car was bought in 2000, it wont tested until 2010, if a car was purchased in 2003, then it will need to be tested in 2009. Franklin County (Columbus) and Hamilton County (Cincinnati) will also have be under emission testing effective in 2010. Ohio does not charge a fee for emission testing, due to Ohio's tobacco settlement.
* Oregon (Portland and Medford metro areas only)
* Tennessee in conjunction with annual registration renewal (Davidson, Hamilton, Rutherford, Sumner, Williamson or Wilson counties and city of Memphis only)
* Washington (urban areas of Clark, King, Pierce, Snohomish and Spokane counties)
* Wisconsin (Kenosha, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha; every two years)

States requiring an inspection only when bringing a vehicle from another State or jurisdiction

* Nebraska (all vehicles, ATVs, minibikes and trailers brought into Nebraska from Out-of-State)

States without safety or emissions inspections

* Alaska
* Arkansas
* Florida
* Idaho (Ada County has a county level program that requires testing)
* Iowa
* Kansas
* Kentucky
* Michigan
* Minnesota
* Montana
* North Dakota
* Oklahoma
* South Carolina
* South Dakota
* Wyoming

From http://en.wikipedia.org/