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Sand FiltersSand Filters direct the fluid into the top of their tank and onto a bed of specified sand. As the fluid makes it's way through the bed of sand media, the contaminants become captured at the top of the media. The fluid makes it's way downward through the bottom of the tank and is discharged at at outlet pipe or manifold. In order to remove the captured contaminants, flow is reversed. This fluidizes the sand media and backwashes the contaminants through the tank's inlet into a disposal discharge line. The problem is that water is also dumped down the drain in order to remove the contaminants from the system. This backwash occurs for a minimum of 3 minutes a day plus any time the pressure differential in the tank becomes too high
THEADSORPTIONTREATMENTOFMICROPOLLUTANTSINWATER Adsorption is the adhesion of molecules onto the surface of an adsorbent solid using various processes of differing intensity (using Van der Waals forces of attraction = physical adsorption, or same type forces which are involved in the formation of chemical attractions = chemical adsorption).
In wastewater treatment, activated carbon is widely proposed for adsorption of the micropollutants. This material can either be in granular form in a filter or in powder form usually in an activated carbon contactor/separator.
mmonia removal from highly concentrated wastewaters can be accomplished by air or steam stripping. Ammonia stripping is the best known with the most extensive applications in concentrated wastewater treatment (e.g. landfill leachate, supernatants of anaerobic digestion processes, specific flows of the petrochemical industry), while very few applications in sewage treatment are known.
In ammonia stripping, lime or some other caustic substance is generally added to the wastewater until pH reaches 10.8-11.5 standard units, converting ammonium hydroxide ions to ammonia gas according to equilibrium reaction: Efficiency of ammonia stripping depends mainly on pH and temperature, in addition to the dimensioning criteria of the process (e.g. liquid rate, air/liquid ratio, packing height, packing characteristics). Air stripping is more common and more often applied than steam stripping, which is a quite similar process, with the difference that it requires operating temperatures higher than 95°C (Tchobanoglous et al., 2003). Steam stripping is usually adopted when ammonia recovery is economically attractive. It should be considered that the resulting free dispersion of ammonia into the atmosphere may be unacceptable in many areas due to air quality concerns or regulations; in such cases, air stripping units are coupled with absorption towers which capture the released ammonia. In modern facilities, absorption onto sulfuric acid solutions allows the production of ammonium sulfate, which could constitute a marketable product (base fertilizer). Figure 2 shows typical flow diagrams of the stripping process with air and steam. Stripping is a relatively simple operation, as it only requires that pH and temperature remain stable enough. Its disadvantages are mainly related to the formation of CaCO3 scale on the tower packing, resulting in a progressive loss of stripping performance, with the need of frequent chemical cleaning operations (Viotti and Gavasci, 2015). Furthermore, air stripping cannot be performed in freezing conditions when icing of the lower packing strata may occur, resulting in a dramatic reduction of process performance. Closed loop systems are designed to avoid this risk. Air stripping is often used in the treatment of municipal solid waste (MSW) landfill leachate (or groundwater polluted by the same leachate). An example of the process is represented in Figure 3.
fter the contaminated water enters the column, it flows down the column and through the packing countercurrent to the air stream. The packing serves to increase the amount of contact between the two streams, and enhances the stripping as a result. After leaving the column, the air is either distributed into the atmosphere, or is collected for purification. Air stripping columns contain either trays or packing, depending on the application. These trays and packing are the same as those used in distillation and absorption columns.
Assuming pH and air temperature remain stable, the operation is relatively simple and unaffected by wastewater fluctuation. • Ammonia stripping creates no backwash or regeneration. • Ammonia stripping is unaffected by toxic compounds that could disrupt the performance of a biological system. • Ammonia stripping is a controlled process for selected ammonia removals.
Ammonia stripping does not remove nitrite and organic nitrogen. • Air pollution problems
Zeolites have been found effective in many water, waste water and industrial applications as molecular filters which can distinguish molecules at the ionic level. For example, the natural zeolite clinoptilolite is selective for the ammonium ion in preference to other ions present in solution. A filtered waste water can be passed through a bed of zeolite to effect a 90-97% ammonium removal.
Ion exchange using zeolites is a technologically simple process for ammonia removal. Zeolites have a porous structure that can accommodate a wide variety of cations (e.g. Na+, K+, Ca2+, Mg2+ and others). Zeolite minerals differ in Si and Al content. Natural zeolites (aluminosilicates) particularly used are clinoptilolite and modernite. Clinoptilolite, the most common and abundant high-siliceous zeolite (Si:Al ratio equal to 5.7) is usually employed as ion exchange medium. It has a two-dimensional channel system that allows the mineral to act as a molecular sieve. For this reason it has high sorption and ion-exchange capacity, ion exchange selectivity, catalytic activity and structural temperature stability up to 700-750°C
The mechanism of ammonia-nitrogen removal by clinoptilolite is based on cationic ion exchange. But ammonia can be also removed through adsorption in the structural pores of the zeolite. The efficiency of ammonia removal is strongly affected by temperature: the higher the temperature, the higher the removal efficiency achieved. Regarding pH, the removal capacity of clinoptilolite is approximately constant between 4 and 8, diminishing rapidly outside this range (US-EPA, 1971a; b). Clinoptilolite and other zeolite minerals easily adsorb potassium, ammonia, calcium, sodium, magnesium and other ions. Therefore, high cationic concentration of the solution will reduce ammonia removal capability. In demonstration studies on municipal wastewaters containing about 20 mgNH3-N L-1, an average ammonia removal of 95.7% was reached (US-EPA, 1971a; b). Another important advantage of zeolite applied to water treatment is its high porosity when compared to other minerals: this results in good hydrodynamic properties (head loss through zeolite filters is 1.5 2.0 times smaller than that in sand filters) and adsorption properties; furthermore its high capacity allows for adsorption of other contaminants (e.g. phytoplankton and bacteria). Both natural and synthetic zeolites can be regenerated with solutions containing high concentrations of calcium ions. The regenerant is a relatively small volume of liquid with high ammonia concentrations. Ammonia-rich eluate can be stripped, recovered by chemical absorption or destroyed by electrolysis producing chlorine which reacts with the ammonia to produce nitrogen gas (Figure 7).
Breakpoint chlorination is a widely used process that oxidizes ammonia to nitrogen gas, thus removing it from wastewaters. This process is practical only as an effluent polishing technique, not for the removal of high levels of nitrogen. When chlorine is added to wastewater containing ammonia-nitrogen, it initially reacts with hypochlorous acid to form chloramines. Continued addition of chlorine after "breakpoint" (occurring when free chlorine residual is formed) converts chloramines to nitrogen gas. The overall breakpoint reaction is given as: Proceed to file 300048CN
It has important role in nitrogen removal from wastewater during treatment. The biological conversion of ammonium to nitrate nitrogen is called Nitrification. It is autotrophic process i.e. energy for bacterial growth is derived by oxidation of nitrogen compounds such as ammonia. In this process, the cell yield per unit substrate removal is smaller than heterotrophs. Nitrification is a two-step process. In first step, bacteria known as Nitrosomonas can convert ammonia and ammonium to nitrite. These bacteria known as nitrifiers are strictly aerobes. This process is limited by the relatively slow growth rate of Nitrosomonas. Next, bacteria called Nitrobacter finish the conversion of nitrite to nitrate.
Denitrification is an anoxic process which takes place in the absence of dissolved oxygen. The nitrate and nitrite produced during nitrification become the oxygen source for heterotropic bacteria which will tilise the availabe BOD
Phosphoric acid, pyrophosphate, atp
s the pH value of the wastewater increases beyond about 10, excess calcium ions will then react with the phosphate, to precipitate in hydroxylapatite:
The common element in EBPR implementations is the presence of an anaerobic tank (nitrate and oxygen are absent) prior to the aeration tank. Under these conditions a group of heterotrophic bacteria, called polyphosphate-accumulating organisms (PAO) are selectively enriched in the bacterial community within the activated sludge. These bacteria accumulate large quantities of polyphosphate within their cells and the removal of phosphorus is said to be enhanced. Generally speaking, all bacteria contain a fraction (1-2%) of phosphorus in their biomass due to its presence in cellular components, such as membrane phospholipids and DNA. Therefore as bacteria in a wastewater treatment plant consume nutrients in the wastewater, they grow and phosphorus is incorporated into the bacterial biomass. When PAOs grow they not only consume phosphorus for cellar components but also accumulate large quantities of polyphosphate within their cells. Thus, the phosphorus fraction of phosphorus accumulating biomass is 5-7%. This biomass is then separated from the treated water at end of the process and the phosphorus is thus removed. Thus if PAOs are selectively enriched by the EBPR configuration, considerably more phosphorus is removed, compared to the relatively poor phosphorus removal in conventional activated sludge systems.
Chlorine is widely used in drinking water treatment for the disinfection of surface and groundwater. It is a strong oxidising agent and reacts with any organic matter present in the water. Most common Advantages: low cost & effective Disadvantages: chlorine residue could be harmful to environment
What happens when chlorine gas or hypochlorite enters the water:
Produces hypochlorous acid and hypochlorite ion oxidizes organics and inorganics in solution changes pH (up with hypochlorite and down with chlorine gas) produces chlorinated byproducts when combined with natural organic matter produces chloramines when ammonia or organic nitrogen is present.
Two species of free chlorine: HOCl and OCl.
OCl and HOCl are both measured together as “free chlorine”.
The equilibrium of hypochlorous acid and hypochlorite is a function of pH.
Free chlorine is the most effective form of chlorine for disinfection.
The most effective form of free chlorine is hypochlorous acid. One study: These results have been confirmed by several researchers that concluded that HOCl is 70 to 80 times more effective than OCl- for inactivating bacteria. (Culp/Wesner/Culp, 1986).
In other words, where it takes 2 minutes to destroy 99% of E. Coli with 0.1 ppm hypochlorous acid, it takes 150 minutes to accomplish the same thing with hypochlorite ion. One system’s chlorine residual of 0.4 ppm is different from another’s in its ability to kill bacteria.
One disadvantage with chlorine disinfection is that of free and combined chlorine residues being toxic to aquatic organisms. There is also potential for the formation of organo-chlorinated derivatives. These derivates are of particular concern, as they tend to be relatively toxic, persistent and bioaccumulative.. However, in spite of the apparent ability to form such compounds, the operational results from major sewage treatment plants show that the actual levels of these compounds in the treated wastewater are very low
It is a highly reactive oxidising 72 TREATME4T OF WASTE WATER agent and rapidly forms free radicals on reaction with water. It is generated on-site in ozone generators by passing dry air or oxygen through a high voltage electric field. The gas is bubbled through the water being treated and any remaining ozone in, the off-gas is destroyed either catalytically using metal oxide catalysts or in a furnace heated to 300°C. Ozone reacts with organic matter in the waste water and this ozone demand must be satisfied before efficient disinfection commences. Disinfection is typically achieved within 5 minutes at dosage rates of 5-50 mg 0311, depending on the level of treatment received by the waste water (that is, on how much organic matter is remaining).
Advanced wastewater treatment
Nikka Nissa Z. Lopez
To remove residual nutrients
To remove pathogens
To reduce total dissolved solids
* To remove residual
To remove refractory organic compounds
The most common for the removal of ammonia from
Biological Nitrification and Denitrification
The conversion ammonium to gaseous phase and then
dispersing the liquid in air, thus allowing transfer of the
ammonia from wastewater to the air
Addition of lime
The pH must be greater than 11 for complete conversion
Air stripping column shown is used to
remove ammonia from water and
waste water feedstreams.
Packed Tower Air Stripper
A filtered waste water
can be passed through a
bed of zeolite to effect a
Breakpoint chlorination is a widely used process that
oxidizes ammonia to nitrogen gas
Nitrification followed by Denitrification to covert
nitrogen ammonia finally to gaseous nitrogen
Biological Nitrification and
The biological conversion of ammonium to nitrate
Denitrification occurs when oxygen levels are
depleted and nitrate becomes the primary electron
acceptor source for microorganisms.
Denitrification process requires the following:
Phosphorus in waste exists in three forms :
polyphosphate and (H4P2O7 )
organic phosphate (ATP, ADP)
Could be done thru:
Biological Phosphorus Removal
Chemical precipitation is used to remove the inorganic
forms of phosphate by the addition of a coagulant to
wastewater .The multivalent metal ions most commonly
Calcium is added as a lime (Ca(OH)2):
Precipitation by Calcium
Alum or hydrated aluminium sulphate is widely used
precipitating phosphates and aluminium phosphates
(AlPO4). The basic reaction is:
Precipitation by Aluminum
Ferric chloride or sulphate and ferrous sulphate also
know as copperas, are all widely used for phosphorous
removal. The basic reaction is:
Precipitation by Iron
A sewage treatment configuration applied to activated
sludge systems for the removal of phosphate.
BPR is achieved by : „
Growing phosphorus-accumulating organisms (PAOs)
In anaerobic to aerobic conditions
Enhanced biological phosphorus
Chlorine may be applied in a number of forms such as
chlorine gas, sodium hypochlorite or chlorine dioxide
Chlorine disinfection works through oxidation of cell
walls leading to cell lysis (bacterial) or inactivation of
functional sites on the cell surface
Strong oxidizing agent
Free and combined chlorine residues are toxic to aquatic
The potential formation of organo-chlorinated
low cost & effective
Ozone gas (03) can be used as a disinfectant even
though it does not leave a residual in the water being
safer than chlorination
fewer disinfection by-product
the elimination of odors
Involves passing a film of wastewater
within close proximity of a UV source
Damage the genetic
structure of bacteria,
viruses and other
Advantages: no chemicals
are used, high efficiency
against a wide range of
maintenance of the UV-