Membrane distillation (MD) integrated with a district heating network (DHN) to supply the heat demand has been investigated in a bioethanol production plant (BP). The specific application considered here is ethanol recovery from fermentation off-gas (CO₂) scrubber water, where the main objective of this study was to develop an air gap MD system that is driven by heat from DHN, thereby offloading the steam-driven distillation column. Experiments conducted on an MD laboratory facility combined with data from the bioethanol industry were used to assess the technological and economic feasibility of this integrated MD-DHN-BP system. Comparisons were also made between the distillation column and MD units regarding heat demand and economic savings. Results of the study showed that MD could be a competitive technology for ethanol recovery given that low-grade heat such as from district heating network or waste heat is accessible.

Despite the country's rural electrification programme, kerosene is the predominant source for lighting, and unsustainable and polluting woody biomass is virtually the only option available for cooking. The rural population also struggles with unsafe drinking water in terms of widespread arsenic contamination of well water. The present work has taken an integrated approach in an attempt to mitigate problems through small-scale polygeneration, a concept linking renewable energy sources to these energy needs via novel energy conversion systems.

Anaerobic digesters (AD) for biogas production are promising in the rural setting, and field surveys have identified problems in the construction, maintenance and operation of existing AD, particularly in overall performance of household digesters. Based on these results, a number of operational and technological improvements are suggested for employing digesters in polygeneration units. This study also examines one approach for small-scale, low cost arsenic removal in groundwater through air gap membrane distillation, a thermally-driven water purification technology.

Integration of biogas production with power generation and water purification is an innovative concept that lies at the core of feasibility analyses conducted in this work. One of the case studies presents a new concept for integrated biogas based polygeneration and analyzes the techno-economic performance of the scheme for meeting the demand of electricity, cooking energy and safe drinking water of 30 households in a rural village of Bangladesh. The specific technologies chosen for the key energy conversion steps are as follows: plug-flow digester; internal combustion engine; and membrane distillation. One major concern is local feedstock availability for the digester, since a single feedstock is impractical to serve both cooking, lighting and water purification systems. In this circumstance solar PV could be a potential option for integrated hybrid systems.

Bangladesh har varit föremål för en svår energikris (bristande el- och gasnät) de senaste tre decennierna. Landsbygden, som innefattar 75 % av befolkningen, har varit särskilt drabbad. Trots landets elektrifieringsprogram av landsbygden är fotogenlampor den företrädande ljuskällan, medan förorenande och ohållbar träbaserad biomassa är praktiskt taget det enda alternativet för matlagning. Landsbygden kämpar samtidigt mot osäkert dricksvatten, på grund av utbredd arsenikförgiftning av brunnsvatten, med negativa hälsoeffekter som följd. Tillgång till ren energi och säkert dricksvatten är verkliga behov bland de fattiga på landsbygden, för ökad välfärd. Detta arbete antar ett integrerat tillvägagångssätt för att försöka lösa dessa problem genom småskalig polygenerering. Detta koncept länkar samman förnyelsebara energikällor av biomassa och sol med energibehoven, genom nya energiomvandlingssystem.

Anaerobiska rötkammare för biogasproduktion är lovande för landsbygdsmiljö, även om det för närvarande råder en betydande klyfta mellan den tekniska och kostandseffektiva potentialen och faktisk implementering på grund av bristande tekniskt kunnande och tillgång på råmaterial, höga installations- och driftkostnader, och begränsade användartillämpningar. Intervjuundersökningar visar på problem i konstruktion, underhåll och drift av befintliga anaerobiska rötkammare. Särskilt den generella prestandan hos hushållsrötkammare identifieras som bristfällig. Utifrån dessa resultat föreslås en rad drift- och teknikförbättringar för att utnyttja rötkammare i polygenereringssystem.  

Denna studie undersöker även en metod för småskalig och kostnadseffektiv arsenikrening av grundvatten genom membrandestillation med luftspalt (Air Gap Membrane Distillation, AGMD), vilket är en termiskt driven vattenreningsteknik. Resultat från en experimentell undersökning visar att den undersökta AGMD-prototypen är kapabel att uppnå utmärkt separationseffektivitet med hänsyn till arsenikrening. Parametriska studier med fokus på varierande kylvattentemperatur illustrerar möjligheten att integrera AGMD-teknik i diverse termiska system.

Integrering av biogasproduktion med kraftproduktion och vattenrening är ett innovativt koncept som utgör kärnan av förstudierna utförda i detta arbete. En av studierna visar ett nytt koncept för biogasbaserad polygenerering och analyserar den techno-ekonomiska prestandan av metoden för att möta efterfrågan av elektricitet, matlagningsvärme och säkert dricksvatten för 30 hushåll i en Bangladeshisk by på landsbygden. De specifika tekniker som valts för energiomvandlingsstegen är följande: plugg-flödesrötkammare, förbränningsmotor och en AGMD-enhet. Termodynamisk utvärdering inklusive mass- och energibalans av systemet undersöktes tillsammans med produktionskostnaden för elektricitet, matlagningsgas, och säkert dricksvatten. Även återbetalningsperiod och internräntan undersöktes. För att bemöta energi- och arsenikproblemen i Bangladesh, indikerar resultaten att detta polygenereringssystem är mycket mer konkurrenskraftigt och lovande (med avseende på produktionskostnaderna) jämfört med andra tillgängliga tekniker. Ett viktigt problem för rötkammaren är tillgången till lokalt råmaterial, eftersom en ensam källa till råmaterial är opraktiskt för att tillgodose efterfrågan från både matlagning, belysning och vattenrening. I detta fall kan solceller vara ett potentiellt alternativ för integrerade hybridsystem. Teknisk värdering och optimering har genomförts för elektricitet med verktyget HOMER (Hybrid Optimization of Multiple Energy Resources), för ett polygenereringssystem beläget i byn Panipara i Faridpur. Resultaten visar att systement kan tillgodoses det dagliga elektricitetsbehovet och samtidigt producera 0.4 m³ matlagningsbränsle och 2-3 L/person rent dricksvatten. Kostnadsuppskattningar visar att denna metod är högst gynnsam jämfört med andra förnyelsebara alternativ (t ex vind-, vatten-, biobränslebaserad- eller geotermisk energi).

Water purification is an important separation process that can be found in various industrial applications. Process water quality varies between applications, but the trend of increased reuse or recycling of process streams in combination with stricter emission regulations lead to additional needs for water purification in the future. Membrane technology such as reverse osmosis, ultrafiltration and nanofiltration are often employed. However even if these technologies are mature there is still a need to explore alternatives that can lead to more robust performance, lower energy consumption, reduced environmental effects, and lower costs. Membrane Distillation (MD) is such an alternative. The process is heat driven and can be paired up with district heating when a high degree of purity is desired.The purpose of this project is to develop MD’s role within a district heating perspective. The following three sub-goals have been investigated:Sub-goal

Sub-goal 1 considered a mapping of water purification in relevant industrial processes. Various possible application areas were identified, including treatment of flue gas condensate, ultrapure water, processes in the food industry, reconcentrating, desalination, and others. Three case studies with relevance to MD driven by district heating were identified for further analysis.Sub-goal 2 encompassed system analyses and optimization studies for the particular case studies:

• Wastewater treatment at Astra Zeneca in Södertälje. It is theoretically possible to place MD between the district heating network and end users in order to achieve advanced treatment for a smaller wastewater line. The district heating demand would increase by about 7-13%, and costs (excluding retrofitting) are estimated to increase by 60% compared to the available treatment method (activated carbon).• Reconcentrating of ethanol from CO2 scubber water at Agroetanol inNorrköping. The concept involves off-loading of the distillation column via introduction of MD technology. Exchange between steam (distillation column) and district heating (MD system) is roughly balanced which implies significant cost savings potential with MD.• Water purification and reconcentrating at Arla Foods, Kalmar facility. A poor thermal integration yields a high district heating demand for MD in this particular application.For sub-goal 3 experimental investigations were conducted for two MD prototypes. A newer generation of MD prototype showed a marked reduction in heat losses with increase in yield, which in turn leads to lower energy demand.

In this study, membrane distillation integrated with district heating network has been investigated for applications in a bioethanol production plant. The specific application considered was recovery of ethanol from CO₂ scrubber water, where the main objective of this study was to develop an air gap membrane distillation system that is driven by heat from district heating network, to offload the distillation column. Experiments on membrane distillation lab unit along with data from the industry were used to assess the technologic and economic feasibilities of this system. Comparisons were also made between the distillation columns and membrane distillation units in terms of heat demand and economic savings. Results of the study showed that MD can be a competitive technology for ethanol concentration depending on availability of low-grade heat like district heating or waste heat.

Bangladesh has been facing severe energy crises (lack of electricity and gas supply network) during the last three decades, especially in rural areas. These areas are characterized by their often inefficient use of woody biomass, mainly for cooking purposes. To avoid the resulting environmental degradation and achieve sustainable development, access to clean and affordable energy is essential. Upgrading existing biomass resources (i.e., animal manure, crop residues, kitchen waste and green wastes) to biogas shows significant promise in this respect. This article presents a review of the current status of biogas digester technology in Bangladesh with focus on households in rural areas, covering 75% of the total population. Currently there exists a substantial gap between technical and cost-effective potential and the achievable potential due to lack of technical knowledge, high installation and operation costs, feedstock availability and limited end user applications. As a result only one percent of the overall biogas potential, estimated at 14.5x10⁶ m³/yr, has been achieved despite government programs for promoting digester installation. Via in-field surveys this review has identified problems in the construction, maintenance and operation of biogas digesters, particularly in overall performance of household digesters. Based on these results a number of operational and technology improvements are suggested. Three digester implementation scenarios are introduced, and performance and cost estimates are projected to 2040. The most ambitious scenario leads to a five-fold increase in biogas output as compared to today’s levels; levelized energy costs can be halved with proper choice of digester technology.

Despite the country's rural electrification program, kerosene is the predominant source for lighting, and woody biomass is virtually the only option available for cooking. The rural population also struggles with unsafe drinking water in terms of widespread arsenic contamination of well water. Biogas plants and pV are individually impractical to serve both cooking, lighting and water purification systems, and their combined applications are extremely limited. This study considers a holistic approach towards tackling both of these issues via integrated renewable energy-based polygeneration employed at the village level. The polygeneration unit under consideration provides electricity via a pV array and animal and agriculture waste-fed digester, which in turn is coupled to a gas engine. Excess digester gas is employed for cooking and lighting, while waste heat from the process drives a membrane distillation unit for water purification. Technical assessments and optimization have been conducted with HOMER (Hybrid Optimization of Multiple Energy Resources). Results show that daily electricity demand can be met with such a system while simultaneously providing 0.4 m3 cooking fuel and 2e3 L pure drinking water. Cost estimates indicate that this approach is highly favorable to other renewable options. The pay back period of such system is between 3 and 4 years.

Despite the country's rural electrification program, kerosene is the predominant source for lighting, and woody biomass is virtually the only the option available for cooking. Aside from this energy service challenges the rural population also struggles with unsafe drinking water in terms of widespread arsenic contamination of well water. Access to electricity, clean cooking gas, and safe drinking water services are genuine needs of the rural poor and are essential to improving welfare. These needs can be addressed individually or using an integrated approach. This study considers a holistic approach towards tackling both of these issues via integrated renewable energy-based polygeneration employed at the community level. The polygeneration unit under consideration provides electricity via a pV array and cow dung-fed digester, which in turn is coupled to a gas engine. Excess digester gas is employed for cooking and lighting, while waste heat from the process drives a membrane distillation unit for water purification. The system is sized to serve a community of 52 households (Pani Para, Faridpur District) with 14 kWe peak demand and 250 kWh/day primary electricity loads. Technical assessments and optimization have been conducted with HOMER. Results show that electricity demand can be met with such a system while simultaneously providing 0.4 m(3) cooking fuel and 2-3 L pure drinking water per person per day. Cost estimates indicate that this approach is highly favorable to other renewable options.

Access to electricity, clean energy, and safe drinking water services are genuine needs of the rural poor for their welfare. These needs can be addressed either individually or in an integrated approach. Biogas digesters are promising in the rural setting and integration of biogas production with power generation and water purification is an innovative concept that could be applied in remote areas of Bangladesh. This paper presents a new concept for integrated biogas based polygeneration and analyzes the techno-economic performance of the scheme for meeting the demand of electricity, cooking energy and safe drinking water of 30 households in a rural village of Bangladesh. The specific technologies chosen for the key energy conversion steps are as follows: plug-flow digester; internal combustion engine; and air-gap membrane distillation. Mass flows and energy balance, levelized cost of producing electricity, cooking gas and safe drinking water as well as the payback period of such a polygeneration system were analyzed. The results indicate that this polygeneration system is much more competitive and promising (in terms of levelized cost) than other available technologies when attempting to solve the energy and arsenic-related problems in Bangladesh. The payback period of such system is between 2.6 and 4 years.

Arsenic contamination in shallow tubewell water is a serioushealth issue in Bangladesh and other Southeast Asian countries.Rural and remote areas in these locations continue toface tremendous challenges in providing access to affordableand safe arsenic-free drinking water. In recent years, intensiveefforts have been undertaken to identify appropriate technologiesfor arsenic removal. This study examines one approach byinvestigating the application of suitable membrane technologies,specifically air gap membrane distillation (AGMD), asa promising method for small-scale, low cost deployment. Theobjective of this study was to test an AGMD commercial prototype(nominal capacity of 2 L/hr) with three different feedstocks:arsenic-containing groundwater (medium concentration) andarsenic-spiked tap water (medium and high concentrations).Results show that the tested AGMD prototype is capable ofachieving excellent separation efficiency, as all product watersamples showed arsenic levels well below WHO accepted limits(10 μg/L) even for initial concentrations over 1800 μg/L.Parametric studies with focus on variation of coolant temperatureillustrate the possibility of integrating AGMD in variousthermal systems.