The use of waste incineration with energy recovery is a matured waste-to-energy (WtE) technology. Waste incineration can reduce the volume and mass of municipal solid waste significantly. However, the generation of high volumes of polluting flue gases is one of the major drawbacks of this technology. Acidic gases are constituents in the flue gas stream which are deemed detrimental to the environment. The wet flue gas desulphurization (FGD) method is widely employed to clean acidic gases from flue gas streams, due to its high efficiency. A major setback of the wet FGD technology is the production of wastewater, which must be treated before reuse or release into the environment. Treating the wastewater from the wet FGD presents challenges owing to the high level of contamination of heavy metals and other constituents. Membrane distillation (MD) offers several advantages in this regard, owing to the capture of low-grade heat to drive the process. In this study the wet FGD method is adopted for use in a proposed waste incineration plant located in Ghana. Through a mass and energy flow analysis it was found that MD was well matched to treat the 20 m(3)/h of wastewater generated during operation. Thermal performance of the MD system was assessed together with two parametric studies. The thermal efficiency, gained output ratio, and specific energy consumption for the optimized MD system simulated was found to be 64.9%, 2.34 and 966 kWh/m(3), respectively, with a total thermal energy demand of 978.6 kW.

This investigation involves recent work on developing membrane distillation (MD) as a novel separation technology for flue gas condensate treatment in combined heat and power (CHP) applications. Flue gas condensate samples were obtained from municipal solid waste and bio-fuel fired CHP facilities and were tested in laboratory-scale air gap MD equipment. Separation efficiencies and other water quality parameters were measured, and the outcomes show that high-quality clean condensate can be recovered, i.e., conductivity <5 mS/m; total organic carbon <2 ppm; total hardness <0.15 °dH; pH ∼7.5; and turbidity <1 FNU. Strict discharge limits for cadmium could not be achieved in all trials. This aspect is examined in further detail with respect to potential mechanisms attributed to the non-ideal separation of contaminants below the parts per billion limit. Beyond this, an industrial scale district heating driven membrane distillation system was designed and analyzed. The estimated annual thermal energy demand was 88 GWh for treating 500,000 m³ of flue gas condensate per year, with an expected clean condensate cost of around 2.6 $/m³.

The European Union has placed a high priority on reaching the goals described in the 2030 Agenda for Sustainable Development. This aim has provided added momentum to member-state environmental regulatory authorities to further tighten the discharge limits of industrial wastewater. These measures strongly influence existing industrial practices as many traditional wastewater treatment methods cannot achieve these strict release limits. Moreover, industrial sectors are encouraged to employ a zero liquid discharge strategy for advanced wastewater management, particularly for process water reuse. Emphasis is thus now placed on improved water treatment systems to recover, reuse and release water in a manner that protects natural resources, guarantees stringent regulatory constraints and ensures financial viability. In this context membrane distillation (MD) is a promising industrial wastewater treatment technology capable of meeting these requirements while utilizing low-grade heat sources.

This thesis focuses on experimental investigations and techno-economic analysis of waste heat driven MD systems for water purification in two water-intensive industries: nano-electronics facilities and cogeneration plants. Samples collected at relevant facilities were tested in an air gap MD bench unit and a semi-commercial pilot plant, with a focus on separation efficiency and potential for achieving high recovery ratios. For the techno-economic analysis of the industrial scale system, the performance of the chosen semi-commercial unit was considered to evaluate the full-scale system operation in terms of thermal energy demand and expected water purification cost. Various thermal integration approaches were investigated while considering locally available heat sources to realize the energy requirements of the specific MD system. The selected case studies include: removal of tetramethylammonium hydroxide (TMAH) from photolithography process wastewater in nano-electronics industries; treatment of chemical mechanical planarization (CMP) process wastewater in nano-electronics industries; and water recovery through advanced flue gas condensate treatment from municipal solid waste incineration and biofuel fired cogeneration plants.

The results from nano-electronics wastewater treatment tests showed that high-quality permeate could be recovered while observing good to excellent separation efficiencies of analyzed contaminants. Moreover, the proposed advanced flue gas condensate treatment is also proved successful while removing the pollutants up to the concentration levels of parts per billion. The proposed pretreatment step, pH adjustment of MD feeds, enhanced ammonia removal efficiency in all cases. Compared to current practices, the separation efficiencies of the considered MD based processes are improved. The simulation results indicate that the required thermal energy for operating large scale MD systems is readily available via internal waste heat sources of nano-electronics facilities for handling typical volumes of the mentioned wastewaters. In cogeneration plants, district heating supply and return lines are well suited as the heat source and heat sink to manage industrial-scale MD systems effectively. The process economy shows that the unit water treatment cost is mainly constrained by thermal energy cost. In case when the price of heat is considered negligible, the unit water treatment cost is significantly lower than the competing technologies.

Den Europeiska Unionen har lagt högt prioritet på uppfyllelsen av de målen som finns i 2030 Agenda för Hållbar Utveckling. Denna ambition har gett ytterligare fart till medlemsländernas miljöförvaltningar för att strama åt utsläppsnivåer av industriella avloppsvatten. Dessa åtgärder har stor betydelse för existerande förhållningssätt i industrin eftersom många traditionella metoder för rening av avloppsvatten når inte de åtstramade utsläppsnivåerna. Dessutom finns det en uppmaning hos industrin att implementera strategier för noll utsläpp, framför allt för återanvändning av processvatten. Betoningen ligger på förbättrad vattenreningsteknik för återhämtning, återanvändning och utsläpp av vatten på det sättet som skyddar naturresurser, garanterar tuffa miljölagstiftningar och säkerställer ekonomin. I detta sammanhang är membrandestillering (MD) en lovande teknik för rening av avloppsvatten och är kapabel att bemöta dessa krav genom utnyttjandet av låg-temperatur värmekällor.

Denna avhandling fokuserar på experimentella undersökningar och tekno-ekonomiska utvärderingar av spillvärmedrivna MD-system för vattenrening i två vattenintensiva industrier: nano-elektronisk tillverkning och kraftvärmeverk. Vattenprover hämtade från relevanta anläggningar testades i en luftspalt MD rigg i bänkskala och hos en halv-kommersiell pilotanläggning, med fokus på separationsverkningsgrad och möjligheten att nå en hög grad av uppkoncentrering. För den tekno-ekonomiska analysen av ett system i industriellt skal undersöktes prestandan hos den valda halv-kommersiell enhet för att utvärdera drift i fullt skal gällande termiskt energibehov och förväntad kostnad för renat vatten. Olika termiska integreringssätt utvärderades med hänsyn till lokala värmekällor för att tillgodose energibehoven hos det specifika MD-systemet. De valda fallstudierna omfattar: avskiljning av tetrametylammonium hydroxid (TMAH) från fotolitografiska avloppsvatten i nano-elektronisk tillverkning; behandling av kemisk-mekanisk utjämning (CMP) avloppsvatten i nano-elektronisk tillverkning; och uppkoncentrering genom avancerad rening av rökgaskondensat från kraftvärmeverk med hushållsavfall och biobränsle som energikällor.

Resultat från rening av avloppsvatten hos nano-elektronisk tillverkning visade att permeat med hög kvalité kunde åstadkommits med hög separationsverkningsgrad hos de analyserade föroreningarna. Det föreslagna systemet för rening av rökgaskondensat var också framgångsrikt med avskiljning av föroreningar upp till miljarddelar. Förbehandlingen genom pH-justering av råvattnet ledde till förbättrad ammoniak-avskiljning i alla fallstudier. I jämförelse med dagens tekniker fanns det en förbättring med MD-teknik gällande separationsverkningsgrad. Resultaten från simuleringar för nano-elektronisk tillverkning visade att den nödvändiga termiskenergin finns tillgänglig för MD-system i stort skal genom utnyttjandet av intern spillvärme. Hos kraftvärmeverk passar fjärrvärmeledning och –returlinjor bra som värmekällor respektive värmesänka. Processekonomin visar att kostnaden för renat vatten är mest beroende av kostnaden för värmen. I de fall där värmekostnaden är noll ligger reningskostnaden mycket lägre än konkurrerande teknik.

Combined heat and power plants (CHP) require advanced pollution controls in order to ensure acceptable environmental performance. Flue gas condensate cleaning is a critical operation in this regard, enabling high separation efficiencies for particles, heavy metals, polyaromatic hydrocarbons, and other contaminants – all while enhancing the thermal output of the CHP unit. The current trend is to employ membrane technologies such as reverse osmosis (RO) for purification and water recovery. Although RO-based treatment is a proven and mature technology, there are several disadvantages. RO operates with very high pressure differences, causing high mechanical loading and subsequent deterioration of membrane performance and lifetime. Moreover, biofouling is a well-known problem with RO, often requiring extensive use of harsh pretreatment chemicals. Concerning the limitations of RO, there is a need to consider alternative cleaning methods. For the purpose, membrane distillation is introduced as a promising technology for flue gas condensate cleaning in this study. The experimental tests have been performed using an Air Gap Membrane Distillation (AGMD) bench scale unit in order to determine the potential of membrane distillation (MD) for flue gas condensate cleaning. The real flue gas condensate samples were collected from Stockholm Exergi plant. The results show that high quality condensate was recovered having conductivity ~0.5 mS/m, pH ~5, TOC <0.5 ppm, TDS <10 ppm, COD <5 ppm, turbidity <1 NTU, total hardness <0.1 °dH and alkalinity <2.4 mg HCO₃/L. Moreover, the outcomes present that MD also provides better performance as compared to RO in terms of contaminants concentration i.e., total ammonia <0.1 ppm, mercury <0.02 ppb, zinc <4 ppb and copper <1 ppb. Results from current study show that the treated condensate cannot only be reused as boiler water but disposing it into water bodies is also acceptable under strict environmental regulations.

In combined heat and power (CHP) plants, reverse osmosis (RO) based flue gas condensate treatment processes have shown several intrinsic problems including bio-fouling and higher electrical energy demand. In contrast, novel membrane separation techniques can operate at reduced electricity demand, provide better separation efficiency and are not prone to bio-fouling. As shown in our previous studies, membrane distillation (MD) has proven itself as a promising technique for such applications. MD is a thermally driven separation process where district heating (DH) can be considered as a viable heat source to comply with its required thermal energy demand. In the present study, a DH driven MD process is presented and evaluated. Performance model of MD system was first developed in MATLAB, based on previously performed experiments where semi-commercial air gap membrane distillation (AGMD) module was considered. This empirical model was then employed to design DH driven MD system in Aspen Plus for flue gas condensate cleaning at industrial scale. Furthermore, in order to evaluate the potential of the technology, feasibility study of the proposed system was performed. Results show the techno-economic viability of the presented DH integrated MD system. The estimated unit flue gas condensate treatment cost is found as low as 2.38 $/m³.

Wastewater from chemical mechanical planarization (CMP) processes in nano-electronics industries must be treated properly in order to fulfil local and international environmental regulations. This study is focused on a performance assessment of membrane distillation (MD) technology for CMP wastewater treatment. A new prototype of air gap membrane distillation (AGMD) module was utilized, with feed water consisting of CMP wastewater collected from imec, Belgium. The module was tested at different operating conditions (temperatures, flow rates and filtration time) and responses in terms of separation efficiency, permeate water quality, transmembrane flux, specific heat demand and exergy efficiency were determined. High quality permeate was produced in all trials, i.e. conductivity ~2.11 µS/cm, pH ~5.4, TOC ~1.13 ppm, IC ~0.24 ppm, TDS ~1.18 ppm and COD ~ 1.9 ppm; for most of the contaminants the separation efficiency was >99%. These findings clearly show that the resulting MD permeate does not exceed environmental regulations for release to recipient, and the permeate can even be considered for reuse. Moreover, the determined specific heat demand at different operating conditions was varying between 1390 and 2170 kWh/m3 whereas; the achievable exergy efficiency was ~19%.

The main challenge for implementing an industrial-scale membrane distillation (MD) system is its associated thermal power demand and resulting operational cost, which hinders the commercialization of the technology, even after forty years of its evolution and development. Nevertheless, an enormous amount of waste heat releasing from the nano-electronics facilities provides MD an opportunity to showcase its potential for treating industrial wastewater discharging from the facilities. In this work, a waste heat driven MD system for a plant capacity of 15 m3/h was analyzed in terms of its thermal power demand and unit wastewater treatment cost. The economic analysis was performed using the factored estimate method. The results show that the thermal power requirement of the industrial-scale MD system was 12.38 MW, and the unit water treatment cost can vary between 3-23 $/m3, based on plant type (i.e., retrofitted facility or new wastewater treatment facility).

Membrane distillation (MD) is a promising separation technology for the treatment of chemical mechanical planarization (CMP) wastewater releasing from nano-electronics industries. In order to determine the feasibility of the process at industrial scale, the most important factors are large-scale system evaluation and related economics. Since membrane distillation is a thermally driven process, therefore, different integration possibilities between an air gap membrane distillation (AGMD) system and low-grade heat sources are identified and analyzed in this work. Global mass and energy balances are conducted for the AGMD system for CMP wastewater treatment in a typical nano-electronics manufacturing facility. It is determined that around 100 GWh of thermal energy can be readily recovered via internal sources and reused to treat 120,000 m³ CMP wastewater/year with MD feed temperature of 80^◦C. Along with the technical feasibility of the system, the detailed economic evaluation has also been performed. Annual capital investment and operating cost showed that the expected CMP wastewater treatment cost can be as low as 3 $/m³ of treated water, which is estimated to be nearly 95% lower than the wastewater treatment cost from electro-chemical systems.

In cogeneration plants with wet scrubbing of exhaust gases, the resulting flue gas condensate passes through various treatment steps prior to its discharge to recipient water body or for use as boiler feed water. The present investigation examines membrane distillation (MD) as an alternative treatment method, potentially overcoming bio-fouling and other known drawbacks of established membrane technologies while making efficient use of available heat sources and sinks. Laboratory and pilot scale experiments are performed using air gap MD system where acid neutralization has been considered as a pretreatment step in order to avoid ammonia slip. Separation efficiency, transmembrane flux, specific heat demand and net heat demand were determined at different operating conditions. Resultant separation efficiency of the contaminants shows the successful application of MD for flue gas condensate treatment, achieving results that are comparable or even better than separation with reverse osmosis (RO). The obtained transmembrane flux varied between 1.6 and 7.2 L/m2h per module depending upon the hot and cold side temperatures. For various operating conditions, specific heat demand ranged from 400 to 1000 kWh/m3 per module and corresponding net heat demand was around 17.5–110 kWh/m³. The reconcentration study found that 92% of water could be recovered from the tested flue gas condensate. Process economy shows that estimated clean condensate production cost can be as low as 1.7 $/m³.

In nano-electronics industries, the wastewater from Chemical Mechanical Planarization (CMP) process is subjected to a special treatment due to the presence of abrasive chemicals (silica and alumina) and metal deposits (tungsten, copper and aluminum), in order to achieve effluent discharge requirements and to allow for recycling of deionized water. Therefore, the challenge faced by imec (Belgium) is to treat the CMP wastewater properly in an environmental friendly and economical manner by reducing discharge volumes of CMP wastewater, and recovering and recycling the clean water. In this regard, we proposed a novel CMP wastewater treatment method based on using membrane distillation technology. Membrane distillation (MD) is a promising thermally driven technology which is capable to achieve extremely high environmental performance while using waste heat sources. For this study, Xzero Air Gap Membrane Distillation (AGMD) lab unit has been employed to treat the CMP wastewater and to reuse the MD treated water (deionized water).  The wastewater samples are collected and analyzed in imec whereas tested at Xzero AB. During the tests, composition, concentration, pH, conductivity, total organic carbon (TOC), total dissolved solid (TDS) and chemical oxygen demand (COD) of feed, concentrate and permeate has been measured. The neutralization step was performed as a pretreatment prior to MD separation process.The results show that high quality water was recovered having major contaminants (silica, alumina, copper, aluminum and tungsten) concentration below the detection limit, conductivity ~ 2.11 μS/cm, pH~5.4, TOC~1.13 ppm, IC~0.247 ppm, TDS~1.38 ppm, COD~1.11 ppm. Based on the obtained results, it is clear that disposing the MD treated wastewater into water bodies is not only acceptable under environmental regulations but can also be reused further. The CMP wastewater volumes are reduced up to 4 times, as well. In addition, the proposed technology is tolerant to many treatment conditions as compared to the conventional treatment.