No abstract

An investigation was performed to study the emissions of state of the art small-scale residential heating appliances. The different combustion systems were compared at optimal combustion conditions. A comprehensive characterization of released organic species of all combustion systems was performed. An approach was performed to estimate the toxicity of the emitted particulate matter by the content of polycyclic aromatic hydrocarbons (PAHs). It is based on the proposal of the German Research Foundation (DFG) that the health risk is proportionally summarized by different PAHs with different health risk potentials. This approach allows for a rough but fast comparison of different furnaces by the calculation of the toxic equivalent (TEQ) value in addition to the emission of particulate matter (PM). Best results were obtained by combusting wood as pellets in a modern pellet boiler (PM = 11−13 mg MJ −1 and TEQ = 0.12−0.75 μg MJ −1 ). On the opposite of the emission scale, the toxic potentials of the typical log wood stove were found to be about 2 orders of magnitude higher (PM = 67−119 mg MJ −1 and TEQ = 14−28 μg MJ −1 ) compared to the pellet boiler, despite optimized combustion conditions.

The impact of combustion conditions on emission factors and characteristics of log wood combustion was investigated. Two different kinds of log woods (spruce and beech) and one kind of briquette (spruce sawdust) were used to study differences in emission behavior depending upon the wood type. Beech wood was used to examine additionally the impact of different moisture contents and maloperation on emissions of fine particulate matter (PM). Therefore, wood logs with three different levels of moisture content were used. Maloperation was simulated by an overload scenario and an air deficiency scenario. Toxicity equivalent (TEQ) values were calculated for the different combustion conditions. It was found that PM mass varies only by a factor of 8 at a maximum, whereas TEQ values can vary more than a factor of 80 (regular beech wood combustion, 6 μg MJ −1 ; beech wood combustion in an overloaded combustion chamber, 500 μg MJ −1 ). In particular, wood with a higher moisture content (19%) released high amounts of intermediate products from lignin and cellulose degradation. The PM emissions in this case were the highest among the tested operation conditions, especially during the initial (cold start) inflaming (660 μg MJ −1 ), but were not in correspondence with the toxicity potential. The TEQ (37 μg MJ −1 ) in that case was much lower than during maloperation.

There are many factors to consider for the design of appropriate water treatment systems including: cost, the concentration and type of biological and/or chemical contamination, concentration limits at which contaminant(s) are required to be removed, required flow rate, level of local expertise for on-going maintenance, and social acceptance. An ideal technology should be effective at producing clean, potable water; however it must also be low-cost, low-energy (ideally energy-free) and require low-maintenance. The use of packed beds containing metallic iron (Fe 0 filters) has the potential to become a cheap widespread technology for both safe drinking water provision and wastewater treatment. for decentralized water treatment particularly in the developing world. A design for safe drinking water to a community of 100 people is also discussed as starting module. It is suggested that Fe 0 filters have the potential for significant worldwide applicability, but particularly in the developing world. The appropriate design of Fe 0 filters, however, is site-specific and dependent upon the availability of local expertise/materials.

This study characterizes the decrease of the hydraulic conductivity (permeability loss) of a metallic iron-based household water filter (Fe0 filter) for a duration of 12 months. A commercial steel wool (SW) is used as Fe0 source. The Fe0 unit containing 300 g of SW was sandwiched between two conventional biological sand filters (BSFs). The working solution was slightly turbid natural well water polluted with pathogens (total coliform = 1950 UFC mL−1) and contaminated with nitrate ([NO3−] = 24.0 mg L−1). The system was monitored twice per month for pH value, removal of nitrate, coliforms, and turbidity, the iron concentration, as well as the permeability loss. Results revealed a quantitative removal of coliform (>99%), nitrate (>99%) and turbidity (>96%). The whole column effluent depicted drinking water quality. The permeability loss after one year of operation was about 40%, and the filter was still producing 200 L of drinking water per day at a flow velocity of 12.5 L h−1. A progressive increase of the effluent pH value was also recorded from about 5.0 (influent) to 8.4 at the end of the experiment. The effluent iron concentration was constantly lower than 0.2 mg L−1, which is within the drinking-water quality standards. This study presents an affordable design that can be one-to-one translated into the real world to accelerate the achievement of the UN Sustainable Development Goals for safe drinking water.