Air Pollution Control ( APC ) residues are the solid end product of the fluke gas intervention equipment installed on incinerators ( this study refers specifically to APC Residues from incinerators managing Municipal Solid Waste – MSW ) . They comprise the fly ash from incineration ( in-between and all right classs ) together with the reagents ( chiefly lime and activated C ) used in the fluke gas intervention. Therefore, they contain:
Therefore they are classified as risky waste.
Approximately 170,000t/y ( Technology Strategy Board 2009 ) of such residues are produced in the UK – 3-4 % of the entire waste mass incinerated ( Environment Agency, 2002 ) . This tunnage is turning as more waste is incinerated to bring forth electricity and heat, and to cut down landfill. While increased energy recovery and reduced landfill are worthwhile in themselves, accomplishing them has created the job of the risky APC residues. In the UK the prevailing finish for these residues has been landfill, but this option is under menace from fastening landfill Waste Acceptance Criteria, and lifting landfill revenue enhancements, so new solutions are required.
There are assorted treatment/recovery options available for APC residues. However these raise other concerns, chiefly:
The overall end is to place cost-efficient direction options for APC residues, within Waste Acceptance Criteria. The ultimate aims of implementing such options are shown in Requirements ( Appendix 1 ) . For this survey, the particular the aims are:
The range is focused on APC residues from municipal waste incineration. It is assumed that current incineration engineering and operating conditions apply, with waste of current composing, ensuing in residues of current composing. The aims have been pursued in the context of current UK and EU ordinance. This is explained in footings of the waste direction hierarchy in table 1.
This study has been structured to give an overall reappraisal of the direction options for the Air Pollution Control residue, intended to supply a inside informations of the findings related with work taking to give recommendations on its intervention.
Chapter 1. Background and range.
Chapter 2. Introduction to the residues, overview of major direction schemes, legislative facets, and environmental issues
Chapter 3. Detailss on the residue intervention techniques, operation rules, and development position
Chapter 4. Appraisal on the recovery and use techniques, operation rules, and development position.
Chapter 5. Overview of position for available solutions, certification degree, assessment attack for environmental impacts, lineation of of import facets for consideration, qualitative and quantitative comparing of each intervention processes.
Chapter 6. Recommendations
System Engineering Management Plan ( SEMP ) is listed in Appendix 2. This is an lineation of system demands and mechanisms for verifying whether the demands are met. It will supply an overview to incorporate different proficient elements of the undertaking. The program will besides depict the activities, procedures and tools used to guarantee an accomplishment of the undertaking outcomes to the client and other stakeholders. Press Release is placed in Appendix 3 and this would organize a footing of a promotion run for the undertaking.
APC residues come from the cleaning procedure of the gaseous emanations, which are produced during the incineration. Dry and semi-dry scrubber systems are used in the cleansing procedure and affect the injection of an alkalic stuff to take acid gases, particulates and fluke gas condensation ( Sabbas et al. 2003 ) . Finally, fabric filters in baghouses are used, where the all right particulates, i.e. the APC residues are focalized and removed from the gaseous emanations ( Sabbas et al. 2003 ) . It is estimated that APC residues represent 2-5 % of the original waste on a wet footing and their production in the UK is about 128,000 metric tons per annum ( Amutha Rani et al. , 2008 ) . In general, APC residues from municipal solid waste incineration ( MSWI ) consist of fly ash, C and calcium hydroxide and contain dioxins and furans ( Amutha Rani et al. , 2008 ) . They are extremely alkalic stuffs ( pH 12.0-12.6 ) and they comprise important concentration of heavy metals, salts and micro-pollutants ( Sabbas et al. 2003 ) . Depending on the initial waste composing, the incinerator and the air pollution control system, their composing may change significantly ( Amutha Rani et al. , 2008 ) . The typical scope of APC residues composing is shown in table 2.
The APC residues are characterized as risky wastes ( 190107* , harmonizing to the EWC ) due to their chemical content and their impact on the environment, chiefly by leaching.
Regulations and statute law on waste direction in the UK have evolved well over the old ages as a consequence of designation of new pollutants, public wellness and environmental concerns, economic sciences and technological promotion ( Pocklington, 1997 and McDougall et Al, 2001 ) . This averment suggests that statute law and ordinances play a major function in guaranting sustainable waste direction. In add-on, the constitution of statute law on waste direction shows the radically altering perceptual experience of worlds and communities towards the environmental impact of human activities ( Pocklington, 1997 ) . Today, ordinances and statute law provide a model for efficient handling of risky wastes such as APC residue. Amutha Rani et Al ( 2008 ) observed that sustainable direction of APC residues depend on the execution of UK and EU waste direction statute law.
Approximately 80 % of the environmental statute law in the UK have their beginnings in the European Commission Torahs ( Pocklington, 1997 ) . The bing legislative and regulative model for APC waste direction in the UK and EU include:
However, the treatment on the regulative and legislative model for this undertaking focuses chiefly on the UK Landfill directive and EA counsel on categorization of risky wastes. These topics are pertinent within the boundary of this undertaking more so as Landfill disposal is common in the UK. Besides IPPC directive is discussed briefly to foreground the functions public engagement and deployment of best available techniques in run intoing our aims.
The cardinal aims of these statute law and ordinance are to:
This diagram illustrates the relationships between the established regulative model and phases in the APC direction procedure. There is no specific statute law covering recovery or reclassification of APC residue in the UK ( ESA 2004 ) . Quina et Al ( 2008 ) besides points out that statute law for recycling APC has non yet been established in the UK.
This Directive purposes at set uping agencies to forestall or cut down emanations into air, H2O and land ( IPPC, 2008 ) . Hence this directive is important as it suggests assorted methods of incineration and intervention that could cut down the impact of APC residues on the environment during incineration, intervention or landfill. The IPPC Directive is based on four rules viz. :
The BAT refers to the most effectual methods of operation that would cut down environmental impact and enhance consequences such as doing residues from incineration less risky. In the BAT, optimising resources and tackling or salvaging energy are prioritized ( Gargulas N. and Mentzis A, 2007 ) . Besides, the BAT is flexible and no footings are imposed since it recognizes that different conditions apply in different instances. The Best Available Techniques Reference ( BREF ) is a mention papers on proficient input needed to find the BAT to be adopted. This BREF contains proficient information on available agencies of handling APC residues such as sintering, vitrification, stabilisation and hardening. This undertaking has considered the BATs to APC intervention and these methods are discussed in chapter 3. However, there are no BATs available for landfills. Notwithstanding, Landfill operators and APC intervention workss require licenses issued by the Environment Agency with public support to guarantee that there are no wellness or environmental impacts as a consequence of their activities ( Macleod C. et Al 2006 and IPPC 2008 ) .
The function of the populace is important in this directive. Article 15 of the Directive, gives the public full privileges to take part in determination devising processes taking to the issue of licenses for installing of workss, and for transporting out proficient and administrative alterations. This facet is really of import particularly in the proper undertaking planning and executing ( see SEMP ) . Therefore the installings of APC intervention installations and the method involved are tailored to run into public demands every bit good as legislative demands. All jeopardies inherent in operating APC intervention installations shall be made known to the populace in conformity to this directive. Besides the result of conformity trials on intervention installations with respect to environmental impact shall be made public ( IPPC 2008 ) . Therefore, it can be argued that since the populace are cardinal stakeholders in this undertaking, good public perceptual experience is needed in conformity with the IPPC directive to guarantee sustainable direction of APC residues.
The kernel of this counsel is to separate different sorts of wastes based on their physical and chemical belongingss which include their toxicity or risky nature.
The Hazardous Waste Directive ( HWD ) , council directing 91/689/EC and the Revised European Waste Catalogue ( EWC ) form the regulative model for this counsel. The HWD purposes at specifying “ risky wastes to guarantee the right direction and ordinance of such waste ” ( EA Hazardous Waste 2008, pg 5 ) . This directing identifies 14 risky belongingss of wastes, therefore risky wastes are classified H1 – H14 harmonizing to their risky belongingss ( EA, Hazardous waste 2008 ) . The EWC codification is derived from the industry and procedure bring forthing the waste, and the type of waste ( EA risky waste 2008 ) .
APC residues are categorized as risky wastes with absolute entry ( Rani et al 2008 and ESA 2004 ) . Under the European Waste Catalogue ( EWC ) , APC residues fall under the class of wastes from incinerators ( waste direction installations ) that have a generic codification ’19 ‘ . The specific codification for solid wastes generated from gas intervention such as APC residues is 19 01 07.
Wastes ensuing from the intervention of the APC residues such as the partly stabilized APC residue, the glassy stuff etc are besides categorized as risky with absolute entry ( EA risky waste 2008 ) . However, when trials confirm that the components of treated waste have become less or not risky, they can be reclassified as risky wastes with mirror entry or non-hazardous as the instance may be ( EA Hazardous waste 2008 ) . Solidified and partially stabilized wastes are coded 19 03 06 and 19 06 04 severally with absolute entries, while vitrified wastes from flue gas intervention are assigned the codification 19 04 02.
The primary aims of the landfill directive are:
Rigorous steps and criterions have been set to cut down the load and trust on landfill ( EA counsel on landfill, 2006 ) .
Landfills are classified into three classs: non-hazardous, inert and risky landfills ( Landfill ( England and Wales ) Regulations, 2002 )
For APC residues, a cardinal demand in the Directive prior to landfill is to execute trials to find its long term and short term leaching behavior and to transport out intervention to cut down its toxicity ( EA counsel on landfill, 2006 ) . This undertaking suggests that the demand for intervention of APC residues augments the instance for researching potencies for recovery or reclassification of the residues.
Article 6 degree Celsius ( three ) of the Directive reflects our purpose to do APC residues at least “ stable non-reactive ” risky wastes ( SNRHW ) or wholly non-hazardous through efficient intervention techniques such as vitrification, rinsing, stabilisation and plasma engineering. SNRHW are known to hold low leaching potencies ( EA counsel on landfill, 2006 ) . Treated APC residues with leaching behaviour equivalent to those of non-hazardous waste can be disposed at designated non-hazardous landfill topic to run intoing the relevant waste credence standards ( EA counsel on landfill, 2006 and Landfill ( England and Wales ) Regulation, 2002 ) .
APC residues must run into the waste credence standards ( WAC ) for a designated landfill after intervention. Schedule 1 of the Landfill ( England and Wales ) ( Amendment ) Regulation 2004, stipulates the process and standards for disposing or accepting waste at landfills.
The WAC is intricately designed to cover with the proficient demand of wastes such as APC residues designated for landfills in the UK ( England and Wales ) . It besides aims at commanding the disposal of wastes into landfill which is a common pattern in the UK. Technically, the WAC ensures that the numerical leaching features of APC residue are determined prior to disposal at landfill ( EA Guidance on Landfill 2006 ) . Thus, after their compulsory intervention, APC residues must run into the relevant waste credence standards before they are accepted into landfill. The leaching features include: the elements and compounds in APC residue and their leaching belongingss ( in mg/kg or L/S ) and the risky nature of the APC residue ( EA Guidance on Landfill, 2006 ) . The Environment bureau is responsible towards guaranting that the standards for peculiar landfills are met. Predating the WAC is the Waste credence process.
The Waste credence process for APC requires basic word picture, conformity testing and on-site confirmation ( EA Guidance on Landfill 2006 ) . The basic word picture is done to find the physical and chemical features of the waste ( EA Guidance on Landfill 2006 ) . Incineration workss are responsible for transporting out the basic word picture of the APC residues since they produce the APC while the landfill operator ensures that conformity testing and on-site confirmation are done ( EA Guidance 2006 ) . Approved trials are defined in schedule1 portion 2 of the landfill ordinance 2004 and they include trials for finding treated APC composing and leaching behavior. The conformity trials are carried out to verify if leaching bound degrees predicted in the basic word picture are believable.
Besides researching chances for reuse of APC residues and recovery of valuable stuffs from the residues, this undertaking besides aims to handle APC residues to run into at least the waste credence standards for SNRHW to enable disposal at a non-hazardous landfill. Amendment 14 of the Landfill ( England and Wales ) ordinance 2004 states the standards for disposing SNRHW in the non-hazardous landfill.
There is no specific statute law on the reuse of wastes such as the APC residues in the UK. Notwithstanding, the UK without incineration web ( www.ukwin.org.uk ) tagged the usage of fly ash and APC residues for building works as “ irresponsible ” . Thus it can be suggested that “ re-use ” is implied in this clause every bit good. However, if it is good proven that APC residues can be managed sustainably without any long or short term environmental reverberations, it will pave manner for arguments to beef up the bing regulative frame and besides re-focus the positions of environmental militants toward the chances in the residues.
ESA study ( 2004 ) argues the proviso of regulative certainty by the authorities is necessary in heightening investing towards sustainable direction of APC residues. The study besides suggests that investings will concentrate on dependable APC intervention engineerings. There are several scientific developments for pull offing APC residues pioneered by waste direction companies such as Techtronic in the UK.
Most of the APC residues ( around 88 % ) ( Environmental Agency, 2002 ) produced in the UK, are disposed of into landfills. During their disposal or any sort of use or handling, a figure of environmental impacts can be caused.
Dust emanations are represented as a possible hazard, due to the size of the APC residues atoms ( 0.001-1 millimeter ) ( Sabbas et al. , 2003 ) . Despite the easy scattering of these all right atoms, a study by the Environmental Agency at a figure of landfill sites in the UK testifies that their concentrations are within the recommended air quality aims ( Environmental Agency, 2002 ) .
Gas production is another possible environmental impact related to the disposal of APC residues. Gas is produced by metallic aluminium hydration ( Sabbas et al. , 2003 ) and because of that, some detonations have been reported ( Sabbas et al. , 2003 ) . However, the production of gas is significantly lower compared to the production of the municipal solid waste landfills, due to their low biodegradable content of the APC residues.
The major environmental impact is the leaching production of APC residues The leaching behavior of the elements present in APC residues is the chief beginning of environmental concern. Leachates can do pollution of dirt, groundwater and surface H2O organic structures. The leaching behaviour of the APC residues is really complex and depends on a batch of parametric quantities. The pH and the liquid to solid ( L/S ) ratio of the residues that will happen in the landfill site are of import factors which affect determine their leaching behaviorbehaviour every bit good as the handiness of the elements which are contained in the APC residues.
The pH depends on the features of the leaching fluid and the waste, i.e. APC residues, and is the cardinal factor of many elements ‘ leachability. Leaching of most major elements ( e.g. Al, Ca, S, Mg ) and heavy metals ( e.g. Cadmium, Pb, Zn ) are strongly pH-dependent ( Astrup et al. , 2006 ) . This dependence of the pH causes a important trouble on the anticipation of the leaching behaviorbehaviour. Generally, APC residues carry on their pH in alkaline values for a long clip ( many 1000s of old ages ) ( Astrup et al. , 2006 ) . However, their pH lessenings as the clip base on ballss and the APC residues are washed by the infiltrating H2O ( the neutralize capacity decreases ) ( Astrup et al. , 2006 ) . Therefore, the anticipation of the landfills pH and thereby the leaching behaviorbehaviour of the residues in over a long term period is complex.
The L/S ratio represents ‘the sum of the leachate that comes in contact with a given sum of APC residues ‘ ( Sabbas et al. 2003 pp what page? ) and depends on the features of the APC residues and the climatic conditions, the hydrology and the hydrogeology of the country ( Sabbas et al. 2003 ) . Normally, as the clip of disposal passes the value of the L/S ratio becomes higher for a peculiar application site. Due to this contact the belongingss of the waste every bit good as the leaching behaviorbehaviour of the waste alteration. Therefore, the value of this ratio is a really of import parametric quantity for the leachate content.
The handiness for leaching is a parametric quantity, which characterizes the peculiar waste and represents a fraction of the entire content of contaminations in the waste itself ( Sabbas et al. 2003 ) . The typical values of the handiness for the APC residues are shown in table 2 and they can supply a theoretical appraisal of the maximal release of a contamination in a period of 1000 to 10000 old ages ( Sabbas et al. 2003 ) .
The anticipation of the leaching behavior and the rating of the environmental impact of APC residues are based on leaching trials. Leaching values for the APC residues originating from leaching trial are summarized in table 4.
The first leachate from APC residues is normally characterized from soluble salts ( e.g. chlorides, hydrated oxides of Ca, Na and K ) and trace component such as Pb and Mo ( Sabbas et al. , 2003 ) . Contrary to the high solubility of this elements, the solubility of toxic organic compounds is believed to be non high due to their hydrophobic nature and their low concentration in APC residues ( from decently operated MSWI workss ) ( Sabbas et al. , 2003 ) .
Long term leachate concentrations are normally lower than the initial or they may stay atto the same degree. The lone exclusions are the elements Al and Zn, which concentrations in the leachate are increase vitamin D inover a long term period ( Astrup et al. , 2006 ) .
As it is explained above the leaching behavior of the APC residues depends on the environmental conditions and alterations during the clip of the disposal. Thus, an analytical anticipation of the long term leaching behavior is really hard and it should be based on a combination of ‘information on leaching rules, leaching trials, field measurings, simulation of mineral alterations and speciation ‘ ( Sabbas et al. , 2003 page figure pls ) . Due to the complexness of the long term leaching behavior, the informations available in literature are limited.
In the UK the disposal of any waste to landfill is regulated ( see ordinances subdivision ) . By and large, the landfills are classified as suited for risky, non-hazardous or inter wastes and, for each of these types of landfill, peculiar leaching bound values ( Waste credence standards, WAC ) are defined and should be achieved for any waste are to be landfilled. Table 5 shows the leaching bound values ( WAC ) for the three types of landfill sites and if they are compared with the values in table 4, it becomes obvious that APC residues can non be landfilled without a anterior intervention.
APC residues are assorted with effluent to organize a coagulated merchandise. During this intervention the residues react with the CO2 from the ambiance cut downing the pH to values between 8 and 9. This commixture besides eliminates the scattering of the APC residues atoms. After this intervention, the APC residues reach the WAC and they are landfilled into monofill cells at a risky waste landfill. This procedure is used by a intervention works in GloucesstershireGloucestershire, from which most of the APC residues treated by this method in the UK are coming.
In this disposal method the APC residues are loaded in certain capsules and pitted 170m below the surface ( Amutha Rani et al. , 2008 ) . The disposal in salt mines can take topographic point for a long term. They are characterized as ‘well isolated, really dry, with stable ambiance and natural gas-impermeable salt beds ‘ ( Clement, 2000 ) . Salt mine for this intent is located in Cheshire, England, where a major per centum of the APC residues, produced in the UK, are stored ( Amutha Rani et al. , 2008 ) .
Due to the commixture of waste acid ( normally HCl ) and APC residues, the lime content of the APC residues is convertedsed into less risky constituents ( CaCl2 ) and the concentrations of Zn and Pb are reduced. Furthermore, the pH is at high degrees, forestalling the salts release. Therefore, the concluding mixture from this procedure is non-hazardous and it is described as sludge from a physico/chemical intervention ; it is classified as EWC codification 190206 and can be disposed of in non-hazardous landfills.
The aim of Ash rinsing procedure is to pull out a figure of minerals from the APC residue obtained after Municipal Solid Waste incineration and thereby decrease the leachability of assorted compounds staying in the residue. The procedure besides aims to better the quality of the residue obtained for farther re-use applications or to cut down the overall content of waste traveling to the landfill. Harmonizing to Quina et Al ( 2001 ) , ash lavation, acid leaching, electro-chemical procedure and thermic intervention are some of the most widely used methods for pull outing metal values from the APC residues.
The separation techniques studied in this subdivision are ash rinsing with MgSO4, bioleaching utilizing Asphergillus Niger Fungi and leaching utilizing pull outing agents. Each procedure has different requirements, operation clip and cost, aims and hazards associated with them.
The procedure aims to use the optimal parametric quantities for rinsing APC residue by using minimal energy and H2O. This procedure uses multi-stage rinsing procedure to decrease the leaching of chloride and sulfate salts present in APC residue and thereby guaranting that the sum of harmful substance nowadays in effluent is reduced. The effluent produced is recycled and re-used in the procedure utilizing using a rapid spray vaporization technique which runs on the waste heat produced from pumps, turbines and incineration furnace. Figure 3a showsrepresent the overall procedure diagram of operation.
The research conducted by Zhang et Al ( 2008 ) shows that the leachability of the heavy metals and chlorides present in APC residue depends on its pH degree. The pH of the solution, when MgSO4 is added during the rinsing procedure, may be controlled by the formation of gypsum as shown in Eq ( 1 ) .
Ca ( OH ) 2 + MgSO4 CaSO4 + Mg ( OH ) 2… … … … … … … .. ( 1 )
This procedure is considered to be a biohydrometallurgical attack to pull out heavy metals from APC residue. It is considered to be a ‘green engineering ‘ because of it makes usage of the natural ability of micro-organisms to interrupt down solid compounds into soluble and extractible signifier by enzymatic oxidization or decrease. The procedure uses the acids secreted by Aspergillus niger fungi such as oxalic acid, citric acid and gluconic acids to pull out the heavy metals present. Water-washing was is used as a pre-treatment before the bioleaching procedure to cut down the bio-leaching period from 30 to 20 yearss and to pull out the maximal sum of chloride and sulfate salts. Figure 4 shows an overall procedure diagram for the bioleaching procedure. Bioleaching is a low cost and low energy ingestion attack.
This procedure uses leaching agents other than H2O for pull outing heavy metals like Zn and Pb. The efficiency of the extraction agent depends on heavy metals of involvement, the concentration of the pull outing solution, the pH and the liquid/Solid ratio used. The end of the procedure is obtain a solution in which the concentrations are high plenty to enable farther separation or recovery.
The leaching media used for this procedure are
The pick of these leaching media was based on their ability to organize a complex with metal ions. Table 6 compares the efficiency of the aforesaid leaching agent in pull outing the heavy metals from APC residue. Figure 5 represents the overall procedure diagram.
The most widespread leaching method used for APC residues is acidic leaching utilizing strong mineral acids such as HCl and H2SO4. However, due to the high alkalinity of APC residues, big sums of acids are needed which consequences in problem with storage and handling.
Furthermore, the reaction of APC residue with mineral acids is really exothermal and it has a high rate of discharge of anionic concentration into effluent.
The lavation procedure is really efficient in taking about 90-100 % of the H2O soluble chloride salts along with some of the sulfate salts present in APC residue with a few exclusions such as Pb, Cu, Hg, Sr and Ca. These heavy metals have to be removed utilizing leaching media or bioleaching. Unfortunately, the rinsing procedure does non impact the per centum of dioxins present in APC residues. These dioxins can be broken down into simpler compounds by heating the APC residue to a temperature of 800-900^ ( o ) C during the drying of ash after rinsing procedure.
Furthermore, the rinsing procedure reduces the entire volume of APC residue by 20-30 % and increases its denseness. This is due to the fact that these soluble chloride salts are responsible for keeping together some of the atoms in APC residues.
The chief disadvantage of the lavation procedure is its demand for big measures of H2O. However, this job canit is suggested that this job can be overcome by recycling and re-using this H2O within the incineration works utilizing using a AquaSonics RSETM ( Rapid Spray Evaporation ) or other H2O purification system. The advantage of utilizing the Rapid Spray Evaporation technique is that it can be run utilizing the waste heat from incineration operation and from heat generated from a Combined Heat and Power ( CHP ) works
Furthermore, the extracted metals from the rinsing procedure can be sold as mineral ore for pull outing the chlorides and other metals such as K and Na. These extracted chloride salts can be used for industry of Cl which is used in garments, paper and other industries.
Washing procedure can ever be supplemented by methods such as stabilization and thermic intervention methods ( vitrification and sintering ) . The advantage of such systems will be discussed in the undermentioned chapters.
Stabilization aims to cut down the mobility of the metals such that the hazard of leaching will consequently be lessened in the landfill. [ Quina et Al. 2008 ] Stabilisation is non effectual when there are soluble salts that APC residues frequently contain hence happening of unwanted leaching over clip. [ Quina et Al. 2008 ]
Chemical stabilisation involves the binding and immobilization of the risky metal ions in the pollutants with “ stabilising agent ” to do it thermodynamically stable. ( Ecke et al. 2000 ) The procedure frequently comprises of several sub-processes, get downing with H2O extraction, so followed by chemical reaction and completed with dewatering. ( ISWA 2008 ) ( californium. Figure 6 )
Hardening helps to cut down the risky nature through capsulation, with the purposeconcept of cut downing thee surface country and permeableness for contact. Hardening is besides treated as a stabilisation procedure, as activities of the metal ions will greatly be reduced. ( ISWA 2008 ) . In effect, hardening creates a physical barrier and this helps to minimise the impact of heavy metals on the environment. ( Quina et al. 2008 ) . ( cf. Figure 7 )
Solidification/Stabilization ( S/S ) was developed establishing on the combination of hardening and stabilisation. It was normally used because of their enhanced efficiency. The leachability toxicity degree from the S/S procedure was found to be lower than hardening or stabilisation on its ain. S/S begins with the usage of hardening transforming harmful substance into solid with the usage of cement or pozzolanic stuffs to avoid risky chemical contact with the natural environment. Chemicals such as Na silicate or soluble phosphates would be used to alter the contaminations into less harmful signifier, since the nomadic risky ions had been “ stabilised ” . ( Ecke et al. 2000 ) Both processes purpose to diminish the rate of disintegration of the metal in landfill and it had to be closely monitored to follow with the current criterions for timely rectification if required. However, the efficiency of disrupting the nomadic metal ions depends on the method used so as the belongings of the cement and asphalt used for hardening. ( cf. Figure 7 )
The chief job of APC residue is about the high degrees of soluble chloride salts, which is one of the ground of doing leaching, and possible taking to dirty, land, surface H2O taint. ( Dimech et al. 2009 )
Therefore, chloride leaching informations, monetary value of cement ( CEMI ) and the cement content ( CEMI ) are presented in Figure 9 to analyze the consequence of cement on chloride leaching in relation to the usage of cement for altering the belongingss of APC residue. The consequence from the survey is traveling to be used for look intoing the possibilities of utilizing APC residue for other intents instead than directing it to landfill.
As noted from the findings, the concentration of chloride lessenings while the monetary value of the cement additions. Since the monetary value of the cement correlates with the cost of the intervention, that implies, in order to accomplish an effectual remotion of chloride, the intervention cost will be expensive, which is non a feasible solution. Furthermore, the concentration drops quickly at the get downing without any add-on of cement, but the APC residue is non stabilized. Following on, it is non practical to pay a difference of & A ; lb ; 90 ( & A ; lb ; 150 – & A ; lb ; 60 ) to obtain an undistinguished decrease in 20 and 50 wt % of CEMI/APC residue ( cf. Figure 94 ) . Furthermore, the volume of the APC contained cement will take up much country in the landfill and this is non desirable. ( Lampris et al. 2009 in Gaynor 2010 )
As a consequence, it is non executable and economic to utilize cement to pull off the APC residue. Therefore, this helps to extinguish two methods, S/S and hardening for intervention of this residue.
The literature ( Quina et al, 2007 ; Amutha Rani et Al, 2007 ( 2 ) ) identifies 3 types of thermic intervention:
is defined as “ the bonding of next surfaces of atoms in a mass of pulverization or a compact by heating. Sintering strengthens a pulverization mass and usually produces compaction and, in powdery metals, recrystallization. ” ( About.com: metals, 2010 ) In this instance there are illustrations where this is carried out under force per unit area, others without. Sintering is discussed as a direct agency of handling the APC residues, and as a secondary procedure after vitrification.
is defined as “ the procedure of change overing a stuff into a glassy formless solid that is free from crystalline construction. This can be achieved through the add-on of heat or debut of an linear. Vitrification occurs at the glass passage temperature which is lower than the thaw point. ” ( About.com: chemical science, 2010 ) In this instance this is achieved in a furnace – either fuel-fired or electric ( including plasma-arc ) , and requires the add-on of “ flux ” ( glass cullet, silicon oxide and aluminum oxide, or bottom ash ) to accomplish the right glass belongingss. Vitrification may straight handle APC residues, or may necessitate a pre-washing phase to take salts, peculiarly Chloride.
is similar to vitrification but without the add-on of flux, ensuing in a less homogenous stuff. There is treatment of runing procedures used in Japan ( Quina et al, 2007 ; Amutha Rani et Al, 2007 ( 2 ) ; Jung and Osako, 2009 ) and the potency for metal recovery. In Japan these procedures are normally applied to combined underside and fly ash, and in some instances to the natural MSW itself, so they are non straight comparable to APC residues in the UK. Advice from Tetronics ( Tetronics, 2010 ) , who operate such procedures in Japan and ( through a sister company ) in retrieving metal from automotive fumes accelerators in the UK, is that metal recovery is improbable to be economic in the UK. This option is non developed farther.
The chief end product of all these procedures is an inert stuff in which the staying metals are bound into the construction and leaching degrees are really low. The mass of this stuff is typically around the mass of the entrance APC residue, but the stuff is much denser ( 3-4 times ) . This is at least an inert stuff for landfill, and has the potency for recovery as a edifice stuff, replacing sum. Other higher value recovery chances ( usage in ceramics, metal recovery ) are less good proven.
Operating temperatures required vary between 800 and 1600oC, some with extra heat intervention, and all with the drawn-out heating/cooling governments that such high-temperature industrial works typically requires. So all require important energy input – for illustration plasma-arc intervention utilizations ( in steady province operation ) around 13MWh per metric ton of APC residue ( Tetronics, 2010 ) . The energy is an of import economic consideration, non merely as a high absolute cost, but as a potentially increasing cost in the hereafter, depending on C taxes/trading etc. Where this is electrical energy it may be advantageous to co-locate the intervention procedure with the incinerator, taking advantage of the electricity generated on site in the context of Renewable Duty Certificates ( ROCs ) , although that merely reduces the power available for sale so there is still a net demand for extra power coevals. Energy needs to be considered beyond the economic consequence, in footings of CO2 emanations.
While right incineration operation should cut down these carcinogens to xxxxxxx, any staying hints in the APC residues will be destroyed by the high temperatures in the thermic procedures.
All these procedures generate their ain fluke gases, incorporating volatile constituents of the APC residues, necessitating fluke gas cleansing, and ensuing in a little measure of residuary waste. Limited specific information is available from the literature, and farther tests are required in this country:
An advantage of electric thermic intervention over fuel-fired is the much lower gas flow rate ( because there is no demand for a burning air flow ) , cut downing the measure residue carried over.
Five possible procedures are shown in figures 10 – 14: ( Diagrams to follow )
Figure 10 Fuel-fired sintering ( Lee et al, 1999 ) , with the option of farther heat-treatment ( Boccaccini et al 1995 ) . This reports lab-scale work and does non quantify mass-balance, economic sciences, or waste watercourses. Recovery would be from the regenerator pebbles, a more hard procedure than the wet scrubbers and bag filters proposed elsewhere. This is non considered farther.
Figure 11 Wash followed by Sintering ( Dimech, 2008 ) . This reports lab-scale work with aggregate balance information. It does non see waste watercourses ( including the liquid wastewater from rinsing ) . There are a big figure of process stairss, including suppression and pressure. Further treatment to follow after treatment with David Deegan.
Figure 12 Plasma-arc vitrification ( Amutha Rani et Al, 2007 ( 1 ) ) . This reports pilot-scale work done in coaction between Tetronics Ltd and Imperial College London. This option was explored farther in treatment with Tetronics ( Teronics, 2010 ) . Unlike other mentions to vitrification, this allows thermic intervention without pre-washing, with the Cl extracted as ( salable ) HCl in a proprietary procedure measure. This is the lone option with cost information available – & A ; lb ; 100/t of APC residues ( Gomez et al, 2009 ) , consisting & A ; lb ; 60/t operating cost, & A ; lb ; 40/t amortization of capital. From this a capital cost of around & A ; lb ; 10-15M is estimated for a 30Kt/y ( see appendix x ) . The client has farther information on the economic sciences of this option from Tetronics, given under confidentiality understanding. Further treatment to follow after treatment with David Deegan.
Figure 13 Plasma-arc vitrification followed by sintering ( Roether et al 2009 ) . Further treatment to follow after treatment with David Deegan
Figure 14 Wash followed by plasma-arc vitrification. Further treatment to follow after treatment with Anup and David Deegan
APC residues are the byproduct from MSW incineration. APC residue is classified as risky waste due to its high content of heavy metals and soluble salts. Particular interventions are ever required for APC residues. However, the rise of APC residues is attendant on the addition of MSW. It leads to a gradual addition in landfill revenue enhancement. Therefore, directing the APC residues to landfill is non an ideal method. Use and recovery would be an alternate method to manage the monolithic sum of APC residues. Although appropriate use and recovery can minimise the environmental impacts of APC residues, there are a limited figure of use and recovery solutions available at present.
The present elements of APC residues may be recovered and used once more by suited recovery methods. Thos The cured elements can be used in other industrial procedures. The purpose of recovery is to bring forth a stuff which can replace a similar natural stuff and used in a similar manner.
Vaporization can be used to retrieve salts from treated waste H2O from wet scrubbers. A extremely concentrated salt solution or re-crystallized salt can be produced through this procedure. Those workss without any permission for discharge of waste H2O can execute with this procedure. Salt can besides be straight recovered from washed APC residues. Salts can be besides extracted by acidic solution.
Acidic extraction is used for disintegration of solid stuffs. Most of the heavy metals present in APC residues are much soluble at low pH solution which consequences in improved heavy metals remotion. However, the quality of the cured metals is varied due to the composing of solution used. Further interventions may be required for upgrading the quality of metals.
Besides, appropriate control of those runing procedures of APC residues may assist to retrieve specific metal stages which depend on usage of temperatures. ( Astrup et al. , 2008 )
“ Use is characterized by permutation of stuffs in merchandises or applications to which the residues can lend with utile belongingss. ” ( Astrup et al. , 2008 pp. ten ) The dominant principals of using APC residues are ( one ) widening bing landfill capacity ( and therefore cut downing disposal costs ) and ( two ) the ability to make from APC residues value-added merchandises that conform to regulative demands for direction and usage ( such as permutation for natural sums ) . The composing of APC residues has the similar indispensable constituents for cement. It is normally used to replace cement in concrete. APC resides are besides suggested to be utilized as fill stuff or sums. The high contents of soluble salts and potency for H coevals may take to the troubles on replacing APC residues straight for cement.
Substituting APC residues for cement in concrete for building industries has been widely used, such as shore protection blocks, unreal reefs, etc. Compare with adding cement into APC residues for hardening, replacing APC residues for cement is comparatively hard. The strength development and subsiding clip are straight affected by the sum of replacements. ( Geiker et al. , 2006 ) Metallic Al in APC residues can bring forth H under damp conditions. ( Astrup et al. , 2006 ) As a consequence, clefts and decomposition of concrete with APC residues may go on. APC residues are besides used for backfilling of mines to avoid prostration. It is done in German salt mines.
Filler stuffs can be used in embankments, main road inclines, noise barriers, etc. However, the pozzolanic belongingss of APC residues consequences in up taking H2O can do indurating the stuff. It is now by and large non accepted due to the changing of environmental facets.
Using APC residues in bituminous constructions can stabilise the residues and minimise leaching. ( Ali et al. , 1996 ; Sawada et al. , 2001 )
Glass-ceramic features stuffs can be formed intermixing washed APC residues with sodium carbonate calcium hydroxide glass and waste electrostatic precipitator dust incorporating boracic oxide. It can bring forth a heavy glass-ceramic stuff with a hardness of 4.5GPa. It can be used in high value building merchandises due to the high denseness and hardness. ( Dimech et al. , 2008 )
APC residues are alkalic in nature which can move as a neutralisation capacity of acidic waste stuffs. In Norway, it is utilized on the acerb waste from the Ti industry ( NOAH, 2003 ) . The staying merchandises after neutralisation are so landfilled. This use is besides carried out in the United Kingdom ( Veolia, 2007 ) .
APC residues require interventions before disposal which varies the disposal costs since the intervention procedure costs varies with economic sciences. Table 1x shows the entire disposal costs varied in different states. One of the cardinal factors for use is the comparative cost of disposal against use.
In commercial applications, soluble phosphates are used as a stabilisation procedure. The entire disposal costs for untreated APC residues are typically ˆ71.25/tone and ˆ77.25/tone for treated APC residues. However, the interventions for APC residues may be ˆ49.5/tone.
APC residues are classified as risky waste which requires particular interventions before landfill. Most heavy metals are of course stable except they are being utilized. Recovery and use are more ideal to pull off those APC residues in order to minimise the environmental impact. However, they are an ecological and economic challenge. Due to the variable chemical and physical features of APC residues from different MSW incineration workss, they affect the credence of APC residues in re-use applications.
The cured salts and metals are able to bring forth gross for the MSW incineration workss. However, the content of both cured stuffs extremely depend on the intervention processes. Economic alterations twenty-four hours by twenty-four hours, there is no exact figure available for the costs of recovery and use. It is difficult to foretell the entire costs of recovery and use.
APC Air Pollution Control
BAT Best Available Technique
BREF Best Available Technique Reference Document
CEMI Portland cement, Cement type I
EDTA Ethylene Di-amine Tetra Acetate
EWC European Waste Catalogue
H2SO4 Sulphuric acid
HCl Hydrochloric acid
HNO3 Nitric acid
L/S ratio liquid to solid ratio ( L/mg )
LOS Loss of Size
MSW Municipal Solid Waste
NH4NO3 Ammonium nitrate
RSE Rapid Spray Technique
SEMP Systems Engineering Management Plan
WAC Waste Acceptance Criteria
Figure 1 Overall System Diagram Showing System Boundary.
Figure 2 The regulative model in APC residues direction
Figure 3 Procedure diagram for ash rinsing with MgSO4
Figure 4 Procedure diagram for bioleaching with H2O rinsing pre-treatment
Figure 5 Procedure diagram for leaching with pull outing agents
Figure 6 Procedure Diagram for Stabilization
Figure 7 Procedure Diagram for Solidification
Figure 8 Procedure Diagram for Solidification/Stabilization
Figure 9 Chloride Leaching vs. Cement Content vs. Price californium. Table 1
Figure 10 Fuel-fired sintering
Figure 11 Wash followed by Sintering
Figure 12 Plasma-arc vitrification
Figure 13 Plasma-arc vitrification followed by sintering
Figure 14 Wash followed by plasma-arc vitrification
Table 1 Scope of Project, shown in footings of the Waste Management Hierarchy
Table 2 Chemical content of APC residues
Table 3 Availability of APC residues
Table 4 Range of concentrations typically leached utilizing the L/S= 10 EU conformity leaching trial for farinaceous wastes BS EN 12457-3
Table 5 Landfill waste credence standards ( WAC ) for farinaceous wastes
Table 6 Fraction of APC residue constituent released after 24h leaching.