Suchergebnisse

This PhD work deals with the upgrading and use of two kinds of ashes, bioash from cocombustion of wood/straw and fly ash from municipal solid waste incineration (MSWI), in the production of bricks. The overall aim is to use these secondary resources prior to natural resources, and by the upgrading to reduce adverse environmental effects caused by the brick making process and at the same time to have a high material quality of the bricks. Two Danish bioashes from co-combustion of straw and wood were studied. They were collected from Enstedværket and Vordingborg Kraftvarme A/S, both combined heat and power plants. The bioashes had Cd concentrations of 9.0-9.7 mg/kg TS, which exceeds the limiting value of 5 mg/kg TS for the ash for agriculture purposes. The use of the ashes directly in brick production results in a loss of plant nutrients, mainly potassium. Potassium is generally present in the water-soluble fraction, which is in practice already being recovered from e.g. straw ash for use as fertilizer by water leaching and other chemical treatments to precipitate dissolved heavy metals prior to use. The scope of this PhD work is on using the water washed ash as resource. The water washed bioashes had a Cd concentration varying between 20 and 67 mg/kg TS. The enrichment of other heavy metals, such as As, Cr, Ni, Pb and Zn, was also observed due to the high ash dissolution ranging from 75% to 88% of the initial mass. Considering the enrichment effect of water washing on heavy metals, recycling of the washed bioashes is problematic from an environmental point of view. Removal of heavy metals from the washed ashes was carried out by electrodialytic remediation (EDR). The results showed that the Cd bound in the two studied bioashes was EDR extractable. After 10-14 days electrodialytic extraction, the Cd concentration in both the raw and the washed ashes originating from Enstedværket CHP was reduced to below 2 mg/kg (with removal rate >95%); and, after 7 days EDR, the Cd concentration in the washed bioash originating from Vordingborg CHP was reduced from 63.7 to 21.4 mg/kg TS. Pb had a removal rate ranging between 12% and 67% from the Enstedværket CHP ash, which shows that Pb in the bioashes was harder to remove than Cd. A two-compartment electrodialytic cell with anode placed in the ash suspension was tested and facilitated the extraction of Pb by creating a faster acidification process. The results showed that prewash with water before EDR stabilized the ash properties, and the removal of Cl resulted in good separation of e.g. Cd, Pb and Ni by hindering the formation of chlorine complexes. The XRD analysis showed that the ashes from Enstedværket CHP underwent dramatic changes in the main mineral compositions: from KCl and K2SO4 in the raw ashes, to quartz and carbonates and sulfates after water washing, and finally to mainly quartz in the ashes after EDR treatment. In relation to the use of the treated bioashes in the production of bricks at sintering temperature 1000 °C, substituting 25% clay in the small brick pellets (~2 g) with the washing-EDR treated bioashes resulted in pellets with higher porosity, higher water absorption, and less total shrinkage compared to the pure clay pellets. The water absorption of the pellets increased with increasing ash content, but decreased with increasing sintering temperature. Increasing sintering temperature also led to the decrease in porosity and the increase in bulk density. In addition, by increasing sintering temperature the leaching of heavy metals from the fired pellets containing bioash, in particular As and Cr, could also be minimized to a level that allows the clay pellets to be reused or landfilled as nonhazardous waste at the end of service life. The bricks also had good material qualities. For instance, when fired at 1100 °C for 1 h, the pellets with 25% treated fly ash from Enstedværket CHP met the water absorption requirement for building bricks in accordance with ASTM C62-13a. When fired at 1100 °C, the pellets with 20% treated ash from Vordingborg CHP showed acceptable leaching of heavy metals such as As, Cd, Cr, Ni, Pb and Zn, allowing the bricks to be used in construction work. The use of the bioashes in the production of clay bricks is technically possible, after being treated first by water washing to extract plant nutrients, and then by EDR to extract easily mobilized Cd and the mobile fraction of other heavy metals to lower the leaching to acceptable low levels. The recycling of MSWI fly ash faces challenges from technical, legislative, environmental and economical aspects. Thus, identifying options allowing use of the resources retained in the ash is necessary. Direct use of MSWI fly ash in the production of bricks leads to air pollution (e.g. the emission of volatile heavy metals) and the loss of metal resources (e.g. Zn), and also causes heavy metal leaching from the bricks themselves. Zn was the metal with the highest concentration in the MSWI fly ash studied, followed by Pb. Water washing was also applied to remove the soluble salts in the MSWI fly ash in the present work. Approximately 19% of the ash was dissolved in water. It was found that Pb and Zn had relatively higher concentrations in the leachate after washing than the other heavy metals, probably due to the presence of chlorine complexes of Pb and Zn in the ash. The raw MSWI fly ash and the washed ash were alkaline; whereas EDR could lower pH to the acidic range, resulting in elevated leaching of Cd and Zn after EDR. At same time, the Cr leaching could be reduced, which was related to the pH and redox potential of the treated ash. Up to 59% of Zn and 6% of Pb were extracted by EDR for 7-12 days compared to less than 0.6% extraction by water washing. However, the extraction of Cr was generally low, because Cr was strongly bound in the ash. The major fraction of Cr remained bound in the ash even after different EDR treatments including one, two and three step treatments, involving ash suspension alkalization by the cathode reaction and acidification by the anode reaction and/or water splitting. The Cr extraction rate was improved by combining different electrodialytic cells to achieve first acidification (especially to pH below 4) and then alkalinity generation. The improvement was mainly due to the combined extraction of Cr(III) at low/oxidizing condition (e.g. anode reaction taking place in the ash suspension) and extraction of Cr(VI) at high pH/reducing condition (e.g. cathode reaction taking place in the ash suspension). Thermal treatment was conducted on the pure EDR-treated ash at 1000 °C for 1 h. The results showed that during thermal treatment the slightly acidic to neutral ashes (pH 5-6.5) were realkalized. The thermal treatment reduced the leaching of most heavy metals by solidification, and possibly also by evaporation; however, the leaching of As and Cr were still problematic and did not meet the limiting values for the ash being reused in construction work. It was found that the removal of Ca by EDR resulted in a decrease in the leaching of Cr after thermal treatment, but an increase in As leaching. However, minimizing leaching from the thermally treated ash (especially of Cr) could be obtained when optimizing the combined water washing and EDR prior to the thermal treatment. In addition, the evaporation of especially Pb during thermal treatment was significantly reduced by water washing and EDR pre-treatment. Handmade bricks (50 mm × 50 mm × 50 mm) incorporating the MSWI fly ash treated after water washing and EDR, had higher porosity, lower compressive strength and higher soluble salts content compared to the 100% clay brick when sintered at 1000 °C for 6 h. Still the washing-EDR treatment significantly improved the properties of the fired fly ash-clay bricks compared to the properties of the bricks incorporating the untreated ash. The results indicated that the MSWI fly ash could be fit for the studied clay replacement at low substitution ratio i.e. 5%, as the bricks with this substitution met the technical requirements for bricks (properties: weight loss during firing 11.3%; density 1.63 g/cm3; apparent porosity 41%; water absorption 25.5%; and compressive strength 8 N/mm2). The leaching of heavy metals from all the bricks with ash content up to 20% sintered at 1000 °C for 6 h met the requirement for landfilling as mineral waste. Even better was that the fly ash-clay brick with 5% ash content might be reused in construction work at the end of service life as the heavy metal leaching was low enough to allow this, and thus these bricks could be reused directly. Even though washing-EDR treatment reduced the Cr leaching from the fired bricks compared to that from the bricks with the untreated ash, the fine fraction in the ash was shown to significantly contribute to the leaching of Cr. Thus, fractionation of the treated MSWI fly ash was beneficial to its recycling in particular of the less toxic fraction.

Produktion af vedvarende energi fra forbrænding af træflis og træpiller er i Danmark steget fra 5,7 PJ til 16 PJ i perioden 2000-2015 og yderligere stigninger forventes i de kommende år. I 2012 blev der i Danmark genereret omkring 22.300 tons træaske. I dag bliver størstedelen af asken deponeret, til trods for at den danske lovgivning muliggør anvendelse af træasken til jordbrugsformål som gødning og/eller som erstatning for kalk i skovene og i landbruget. Den kemiske sammensætning og udvaskningsegenskaberne af 16 forskellige træasker indsamlet fra ti danske fjernvarmeanlæg blev undersøgt. På trods af den relativt store variation i indholdet af næringsstoffer og spormetaller var de overordnede niveauer sammenlignelige med typiske data i litteraturen for andre asker fra forbrænding af træ, også i relation til udvaskning. Generelt opfyldte træaskerne de danske kvalitetskriterier, hvilket indikerer, at askerne kan anvendes til jordforbedring i skovene. Tages der i stedet udgangspunkt i EU's modtagelseskriterier for affald til deponering svarer udvaskningen fra træaskerne til en klassificering som enten "ikke-farligt affald" eller "farligt affald". Dette indikerer, at genanvendelsen af asken i skovbrug kan udgøre et potentielt miljøproblem, særligt i forhold til udvaskning af Cr og Se. Udvaskning af næringsstoffer og forureningselementer fra to udvalgte asker (én blandet aske bestående af bund- og flyveaske, samt én flyveaske) blev undersøgt ved forskellige pH-niveauer såvel som i forhold til den kort- og langsigtede udvaskning via kolonneforsøg. Sure jordbundsforhold typisk for danske skove resulterede i væsentlig højere udvaskning af Cd, Mg, Zn and P sammenlignet med udvaskningen ved askernes naturlige pH-forhold (mere end to størrelsesordner højere). Udvaskningen af Cl, K, Na og S var relativ uafhængig af pH, høj i starten af udvaskningsperioden, og sandsynligvis styret af tilgængeligheden af disse elementer i askematricen. Udvaskningen af Ca, Cr, Mg, Sb, V og Zn var derimod fordelt over en længere periode (og et højere liquid-to-solid, L/S, forhold) med forskelle på mindst én størrelsesorden mellem den akkumulerede udvaskning ved L/S 10 L/kg og L/S 1000 L/kg. Relativt store P-mængder (33-48 % af indholdet i de to asketyper) kunne opløses ved ekstraktion med ammoniumcitrat, hvilket indikerer, at træaskerne har potentiale som P-supplement til jorden. Udvaskningen af elementer som Al, Ba, Ca, Fe, Mg, Si, P and S var styret primært af askemineralernes opløselighed. De identificerede mineraler svarede til tilsvarende mineralfaser fundet i litteraturen for andre træasker, såvel som for asker fra forbrænding af affald. Udvaskningen af sporstoffer som Cu, Cr, Pb og Zn kunne beskrives ved en kombination af mineralernes opløselighed, adsorption til Al/Fe (hydr-) oxider og kompleksbinding til opløst organisk stof. En række forbehandlingsmetoder, nemlig hærdning (også kendt som modning) og granulering, blev undersøgt i forhold til ændringer i askernes kemiske sammensætning og udvaskningsegenskaber. Granulering af askerne dannede relativt hårde partikler og medførte en reduceret udvaskning sammenlignet med aske i løs form; en effekt som formentlig skyldes ændringen i specifikt overfladeareal. Granulering af asken vil reducere støvdannelsen ved udspredning til jordbrugsformål. Hærdning påvirkede askens mineralstruktur, mens askernes samlede bufferkapacitet (alkalinitet) i praksis forblev uændret. Udvaskning fra kolonneforsøg viste, at den hærdede aske havde et pH-niveau omkring to enheder lavere end for den friske aske samt en lavere udvaskning af alkalinitet. Udvaskningen af As, P, Sb and V var højere efter hærdning, mens udvaskningen af Ba, Ca, Pb, og Zn var reduceret til koncentrationer tæt på eller under detektionsgrænsen. Hærdning af askerne blev vurderet som en relativ simple og hurtig forbehandlingsproces. Det anbefales, at hærdningen gennemføres under kontrollerede forhold før udspredning af askerne, da hærdningen vil kunne mindske askernes reaktivitet og den samlede udvaskning. Påvirkningen af nærings- og spormetallernes mobilitet via porevandet i jorden blev undersøgt i en række kolonneforsøg med både aske og jord. De øverste to jordlag fra en dansk næringsfattig skovbund blev undersøgt med tilsætning af tre forskellige askeniveauer: 3, 9 og 30 tons/ha. Asketilførslen øgede frigivelsen af næringsstoffer som K og P igennem hele eksperimentet svarende til udvaskning over ca. otte år i felten. En øget udvaskning af Cl, K, Mg, og S blev observeret inden for en infiltration svarende til de første 500 L/m2 (svarende til mindre end to år). Selvom en stigning i den udvaskede mængde af As og Cu blev observeret fra kolonnerne (fra 2,2 til 5,0-5,8 mg/m2 for As og 2,0 til 4,9-7,6 mg/m2 for Cu) var koncentrationsniveauerne generelt i overensstemmelse med de danske grundvandskvalitetskriterier. Effekterne fra 3 og 9 tons/ha var begrænsede og sammenlignelige, mens tilførslen af 30 tons/ha indikerede væsentlig højere udvaskning af K, Mg, S og Si inden for de første 500 L/m2 (mere en fem gange større mængder end i kontrolforsøgene uden aske). Den lave mobilitet af spormetaller såsom Cd, Cr, Ni, Pb og Zn indikerer dog, at potentialet for akkumulering af disse elementer i jorden bør undersøges nærmere. Baseret på resultaterne kan en høj tilførsel på 30 tons/ha ikke umiddelbart anbefales. ; The combustion of wood chips and wood pellets for the production of renewable energy in Denmark increased from 5.7 PJ to 16 PJ during the period 2000-2015, and further increases are expected to occur within the coming years. In 2012, about 22,300 tonnes of wood ashes were generated in Denmark. Currently, these ashes are mainly landfilled, despite Danish legislation allowing their application onto forest and agricultural soils for fertilising and/or liming purposes. During this PhD work, 16 wood ash samples generated at ten different Danish combustion plants were collected and characterised for their composition and leaching properties. Despite the relatively large variations in the contents of nutrients and trace metals, the overall levels were comparable to typical ranges reported in the literature for other wood combustion ashes, as well as with regards to leaching. In general, the composition of the ashes complied with Danish ash quality criteria, indicating that they may be applied onto forest soil. However, according to EU landfill waste acceptance criteria, the leachates corresponded to "non-hazardous" or "hazardous" waste, thereby suggesting that recirculation of the same ashes to forestry land may constitute an environmental issue as a result of leaching, especially with regards to Cr and Se. The release of nutrients and contaminants from two selected wood ash samples (corresponding to one mixed ash sample and one fly ash sample) was estimated based on selected pH conditions and data for both short- and long-term leaching. Acidic conditions relevant for typical forest soils in Denmark indicated considerably higher releases of Cd, Mg, Zn and P compared with releases of the natural ash pH (more than two orders of magnitude difference). The leaching of Cl, K, Na and S was rather pH-independent, high during the initial leaching and most likely governed by the availability of these elements in the ash matrix. On the other hand, the leaching of Al, Ba, Ca, Cr, Mg, Sb, V and Zn was distributed over a wider liquid-to-solid (L/S) interval and differences of at least one order of magnitude were shown between the observed cumulative releases at L/S 10 L/kg and L/S 1000 L/kg. Relatively large fractions of P (i.e. 33 % and 48 % of the fly ash and mixed ash P contents, respectively) were observed to dissolve after extraction with neutral ammonium citrate, which indicated the potential use of wood ashes as a P supplement for the soil. The release of major elements such as Al, Ba, Ca, Fe, Mg, Si, P and S was governed mainly by mineral solubility. The most likely minerals governing the release of these elements were found to be in general agreement with mineral phases identified in the literature for other wood combustion ashes, but also municipal solid waste incineration ashes. The leaching of trace elements, such as Cu, Cr, Pb and Zn, was described adequately as a combination of mineral solubility, adsorption onto Al/Fe (hydr-) oxides and complexation with dissolved organic matter. The influence of common ash pre-treatments, such as hardening (also known as ageing or maturing) and granulation, on ash chemistry, liming potential and leaching behaviour was investigated through a series of laboratory experiments. Ash granules were relatively hard (barely breakable by finger-pinching) and demonstrated a reduced leaching compared to loose ashes, an effect that appeared to be related to the specific surface area granules. Ash granules may be used in actual field applications to minimise dust generation. Hardening affected the mineralogical structure of the ashes, but their overall acid neutralisation capacity remained practically constant. Column leaching tests showed that hardened ashes presented pH levels about two units lower than fresh ashes and a reduced leaching of alkalinity. The leaching of As, P, Sb and V increased after hardening, while the leaching of Ba, Ca, Pb and Zn was generally reduced to concentration levels below or close to limit of quantitation levels. Ash hardening was observed to be a relatively simple and fast treatment. Preferably, this process should be carried out under controlled conditions, before the ashes are applied, as this will minimise their overall reactivity as well as the leaching of most trace elements. The effects of ash application on the mobility of nutrients and trace elements in soil pore water were evaluated through a series of column experiments. The two uppermost soil horizons of a Danish nutrient-poor forest soil were tested against three ash dosages, namely 3, 9 and 30 tonnes/ha. Ash application promoted the release of nutrients such as K and P during the entire duration of the experiment, corresponding to about eight field-scale years. A short-term release of Cl, K, Mg and S was also observed within the first 500 L/m2 of infiltrating water (corresponding to fewer than two years on the field scale). While an overall increase in the leached amounts of As and Cu from the organic soil horizon were observed in the case of ash application (from 2.2 to 5.0-5.8 mg/m2 for As and from 2.0 to 4.9-7.6 mg/m2 for Cu), their concentration levels in the percolating soil solutions was generally within Danish groundwater quality criteria. Though the effects of both the 3 and 9 tonnes/ha dosages were limited and comparable, the use of 30 tonnes/ha indicated considerably larger amounts of K, Mg, S and Si within the first 500 L/m2 (at least five times larger than the soil controls). Furthermore, because of the low mobility of many trace elements, such as Cd, Cr, Ni, Pb and Zn, potential accumulation of these elements on the forest floor should be evaluated. Consequently, such high dosages cannot be recommended based on these experiments.

Verden over er de globale klimaforandringer på den politiske dagsorden, og der er et stigende behov for strategier, som kan mindske udledningen af drivhusgasser. En kilde til udledningen af drivhusgasser er deponeret affald, hvor nedbrydningen af organisk kulstof danner metan. Emissionen af deponigas er meget dynamisk med en stor rumlig og tidslig variation. Der er derfor behov for udvikling af innovative teknologier til både måling og håndtering af deponigas, som kan hjælpe i den nødvendige konceptuelle forståelse af, hvad der styrer gastransporten og udledningsprocesserne. En metanbalance kan opstilles på baggrund af den dannede metans forskellige migrations veje, som inkluderer opsamling med henblik på energiudnyttelse eller afbrænding, horisontalt udslip til naboejendomme, metanoxidation i dæklaget samt emission til atmosfæren. En god konceptuel ramme for udarbejdelsen af en håndteringsstrategi for et deponi er en metan massebalance. Størstedelen af nærværende Ph.d. projekt blev udført i forbindelse med et nedlukket dansk deponi (Hedeland deponi, Roskilde). Mange års intensive undersøgelser har været gennemført på Hedeland deponi, for bedre at forstå under hvilke forhold den dannede deponigas spredes og emitteres til atmosfæren. En håndteringsstrategi, der tager højde for både sikkerheden for naboerne og de negative effekter på klimaet, er nødvendig. En metan massebalance for deponiet kan give et overblik og vise betydningen af de enkelte migrations veje i forhold til hinanden. Som en del af dette Ph.d. projekt er der opstillet en metan massebalance for Hedeland deponi baseret på de store mængder data, der er indsamlet i forbindelse med de mange års undersøgelser, og som dækker årene 2013-2015. Metandannelsen blev modelleret ved brug af en multifase-model baseret på førsteordens nedbrydningshastigheder (Afvalzorg) og den gennemsnitlige metandannelse blev fundet til 67 ±8.6 kg h-1. Metanindvindingen, emissionen og den horisontale migration viste sig at udgøre 38% af den modellerede dannede metan, og de bidrog med en lige stor andel hver (hhv. 9 ±2,9, 8 ±4,1 and 9 ±2,4 kg h-1). Metanoxidation i dæklaget blev identificeret som den spredningsvej, der kunne lukke metanbalancen, og den udgjorde 62% af den dannede metan. Der var adskillige indikationer, som støttede en høj oxidationsrate i dæklaget på Hedeland deponi herunder en lav total emissionsrate bestemt ved brug af sporgasmetoden og få emissions-hotspots med forhøjede koncentrationer af metan på overfladen (fundet ved en overflade screening med en flammeioniserings detektor). Identifikation af emissions-hotspots med lossepladsgas er grundlaget for etableringen af emissionsbegrænsende teknologier så som biocovers. En drone udstyret med at termokamera blev testet på to danske deponier (Hedeland deponi og Audebo deponi) som et muligt screeningsværktøj, der vil kunne imødegå den store rumlige og tidslige variation i lossepladsgas emissionen. Sammenhængen mellem udledningen af lossepladsgas (metan og kuldioxid), overfladetemperaturen målt med termokameraet og jordtemperaturen i 5 og 10 cm dybde blev undersøgt i et testområde på hver er de to deponier. På Hedeland deponi blev der ikke fundet nogen sammenhæng mellem emission af deponigas og overfladetemperaturene. Desuden var de fundne overfladefluxe meget begrænsede, hvor gennemsnitsfluxen for de fire målekampagner var begrænset til 1,3 ±16 g CH4 m-2 d-1. En gennemsnitlig metanflux på 371 ±1337 g CH4 m-2 d-1 blev fundet for Audebo deponi for de fem gennemførte målekampagner. Derudover blev der fundet højere temperaturer både på overfladen og i 5 og 10 cm dybde i de samme områder, hvor de højeste overfladefluxe af deponigas var målt, hvilket indikerer, at termokameraet vil kunne være i stand til at identificere emissioner af deponigas under de rette forhold. En minimumsflux på 150 g CH4 m-2 d-1 fra et område på mindst 1 m2 blev fundet som den nedre grænse for hvornår et termokamera er i stand til at identificere et emissions-hotspot med deponigas på et typisk dansk deponi. En fortynding af deponigas med luft vil ofte resulterer i et metanindhold i den fortyndede deponigas som er for lavt til at gassen kan udnyttes. Dog vil der ofte stadig være behov for at minimere de negative effekter på miljøet og for menneskers sikkerhed. Kilderne til fortyndet deponigas kan være afværgesystemer imod den horisontale spredning af deponigas, emissioner fra perkolat- og overvågningsbrønde eller ved at luft trænger ned i dæklaget på deponiet. En kosteffektiv begrænsningsteknologi for fortyndet deponigas kan være mikrobiel oxidation i et biofilter med aktiv tilførsel af gas. Denne teknologi blev testet i et kompostbaseret åbent pilotskala filter på Hedeland deponi konstrueret i en 30 m3 container. Filteret blev tilført deponigas fortyndet med luft til en metankoncentration på mellem 5 og 10 vol.%. Filteret blev testet i fem flowkampagner med den samme metankoncentration i indløbet i alle fem kampagner, men med en stigene metantilførsel, der resulterede i en tilførsel på mellem 106 og 794 g CH4 m-2 d-1. Den højeste fundene metanoxidationsrate var 460 g CH4 m-2 d-1 med en oxidationseffektivitet på 58%. Den højeste samlede oxidationseffektivitet, der blev fundet var 87%, og en højere effektivitet blev aldrig opnået på grund af væsentlig præferentiel transport langs siderne mellem komposten og containervæggen til trods for de installerede blokader designet til at begrænse det selektive flow. Dog viste gasprofiler i komposten en metanoxidation på næsten 100%. Test med en sporgas understøttede disse resultater og viste en metanoxidation på 86% 10 cm under filteroverfladen ved flowkampagne 5, hvor der gennemsnitligt blev tilført 701 ±47 g CH4 m-2 d-1 til filteret. På Hedeland deponi er der installeret tre afværgesystemer for at afskære den horisontale spredning af lossepladsgas til beboelsesejendommene på nabogrundene. I 2017 blev der målt et gennemsnitlig metanindhold i den oppumpede gas fra alle tre anlæg på 0,53 ±0,55 vol.% og med et indhold af ilt på over 10 vol.% i de fleste tilfælde. Håndteringen af den oppumpede afværgegas i det testede pilotskala biofilter vil resultere i en metan tilførsel på 717 g CH4 m-2 d-1. På grund af den høje pumperate på 80 m3 h-1 vil gassens opholdstid i filteret dog kun være på 3 minutter, hvilket forventes at være mindre end den nødvendige opholdstid. Ti filtre med det samme volumen som det testede filter er nødvendigt for at øge opholdstiden til 30 min. Et foreslået alternativ kunne være et 111 m2 biofilter indbygget i deponiets slutafdækning, som vil resultere i den samme mængde metan tilført pr. arealenhed som til de ti containere. Et biofilter indbygget i dæklaget kan også være en løsning på problemerne med det selektive flow ved containerløsningen. ; Climate change is on the political agenda worldwide, and abatement strategies for greenhouse gas emissions are a necessity. One source of greenhouse gas emissions is landfills, as the degradation of organic carbon in landfilled waste generates methane. Landfill gas emission patterns show high spatial and temporal variability, but the development of innovative technologies for both monitoring and mitigation will help in the much-needed conceptual understanding of governing gas transport and emission processes. A methane mass balance can be established based on the individual migration pathways for the generated methane, including methane recovery for energy utilisation or flaring, lateral migration to neighbouring plots, methane oxidation by microorganisms in the cover and emissions seeping into the atmosphere. A methane mass balance forms a good conceptual framework for setting up a mitigation strategy for a landfill. The main part of this PhD project was conducted in relation to a closed Danish landfill (Hedeland landfill, Roskilde, Denmark). Many years of intensive investigations have been conducted at Hedeland landfill to understand better the migration and emission patterns of methane generated at the site. A mitigation strategy has to be established, which takes into consideration both the safety of local residents and the negative impact on global warming from landfill gas migration and emission. A methane mass balance for the landfill could provide a valuable overview and show the individual importance of each migration pathway. As part of this PhD project, a methane mass balance was established for Hedeland landfill based on data from many years of investigation, covering the years 2013-2015. Methane generation was modelled based on a multi-phase, first-order degradation kinetics (Afvalzorg) model, with average methane generation determined at 67±8.6 kg h-1. Methane recovery, emission and lateral migration were found to cover 38% of the modelled methane generation, each accounting for an equal share (9 ±2.9, 8 ±4.1 and 9 ±2.4 kg h-1, respectively). Methane oxidation in the cover was identified as the migration pathway capable of closing the mass balance and accounting for the remaining 62% of the generated methane. Several indications supported a high oxidation rate in the landfill cover at Hedeland, including a low total emission rate, which was determined using the tracer gas dispersion method and a few emission hotspots with elevated methane concentrations at the surface (identified by screening the whole landfill surface, using a flame ionisation detector). Identification of landfill gas emission hotspots is the basis for establishing emission abatement technologies such as biocovers. To overcome the high spatial and temporal variability of landfill gas emissions, a screening tool based on an unmanned aerial system mounted with a thermal infrared (TIR) camera was tested at two Danish landfills (Hedeland and Audebo landfills). The correlation between landfill gas emissions (methane and carbon dioxide), surface temperatures obtained with the TIR camera and soil temperatures at 5- and 10-cm depths was investigated in an established test area at each of the two sites. At Hedeland landfill, no correlation was found between gas emissions and surface temperatures. In addition, identified methane surface fluxes were very limited, with an average for the four measuring campaigns of only 1.3 ±16 g CH4 m-2 d-1. An average methane flux of 371 ±1337 g CH4 m-2 d-1 was found at Audebo landfill for five measuring campaigns. Furthermore, elevated temperatures at both the surface and at 5- and 10-cm depths were found in the same area as where the highest landfill gas surface fluxes were measured, thus indicating that in the right conditions the TIR camera could be used for delineating landfill gas emissions. A minimum flux of 150 g CH4 m-2 d-1 from an area of at least 1 m2 was established as the limit for the TIR camera being able to delineate a landfill gas emission hotspot at a typical Danish landfill. When landfill gas is mixed with air it dilutes, often with a methane content too low for utilisation. However, mitigation is still needed to minimise the negative impacts on the environment, and to ensure human health and safety. Sources to dilute landfill gas could be remediation systems for lateral migration, emissions from leachate and monitoring wells or from air penetrating the cover of the landfill. A cost-efficient mitigation technology for dilute landfill gas could be microbial oxidation in an actively loaded biofilter. This technology was tested in an open-bed pilot-scale compost filter at Hedeland landfill, constructed in a 30 m3 container. The filter was loaded with landfill gas diluted with ambient air to a methane concentration of between 5 and 10 vol.%. The filter was tested in five flow campaigns with the same methane inlet concentration and an increasing methane load between 106 and 794 g CH4 m-2 d-1. The highest observed methane oxidation rate was 460 g CH4 m-2 d-1 with an oxidation efficiency of 58%. Overall, oxidation efficiencies of more than 87% were never achieved, due to substantial preferential flows at the transition point between the compost and container wall despite an attempt to design the container with blockers against preferential flows. However, pore gas profiles showed methane oxidation of 100% in the compost material. These results were supported by tracer gas tests showing an average methane oxidation of almost 86% at 10 cm below the surface of the filter in flow campaign 5, where the load had an average of 701 ±47 g CH4 m-2 d-1. At Hedeland landfill, three remediation systems have been installed to cut off laterally migrating landfill gas from reaching residential houses on neighbouring plots. In 2017, an average methane content of 0.53 ±0.55 vol.% in off-gas from these remediation systems was observed, accompanied by an oxygen content in most cases above 10 vol.%. Treatment of the remediation off-gas in the constructed pilot-scale biofilter would result in a methane load of 717 g CH4 m-2 d-1. Nevertheless, the gas retention time would only be 3 min, due to the high pump flow rate of 80 m3 h-1, which is thought to be below a critical gas retention time. To increase the retention time to 30 min, ten containers similar to the tested filter would be needed. A suggested alternative could be a 111 m2 biofilter embedded in the landfill cover, which would result in the same load as the ten containers. An embedded biofilter is also expected to be able to overcome the challenges of preferential flows experienced in the tested container solution.

This report is a synthesis of the technical assistance (TA) and recommendations, carried out by the World Bank water and sanitation program (WSP) since September 2014. To achieve the target of 100 percent improved sanitation, there is a national drive to improve fecal sludge management (FSM). This TA recognizes that to achieve the goals it is necessary to support the development of national FSM policies, regulations, and guidelines, while also improving capacity at the local level by supporting the implementation of improved FSM models in target cities. The objective of the TA was to provide government with tested advice on how to scale up improved septage management nationwide through: (i) improvement of septage management in three cities through the application of new management models (local level); and (ii) assistance to national government in training and capacity building and the formulation of policies and regulations to improve septage management at scale (national level). This report is structured as follows: chapter one is the executive summary; chapter two gives the background to sanitation in Indonesia and to fecal sludge management in particular; chapter three provides an overview of the TA approach; chapter four gives details of the implementation of the TA; chapter five summarizes the lessons learned; and chapter six outlines the recommendations and next steps.

Along with economic growth and improved living standards, waste from households, industries, and commercial or service establishments is expected to increase rapidly over the next years. Managing this waste is a hard challenge for the Government of Vietnam because of its substantial cost and lack of awareness and participation of people and businesses. Wastes can be classified according to: their form (wastewater, solid waste); their origin (industrial wastes, agricultural wastes, urban (municipal) wastes); and their hazardous nature (non-hazardous or hazardous).