Indoor Air Pollution Control Solutions PDF

# Indoor Air Pollution Control ## Cynthia Maharani ## Khaled Abass ### Department of Environmental Health Sciences ### College of Health Science ### University of Sharjah ## 6 Solutions to Reduce Indoor Air Pollution - **Regular Maintenance:** To avoid excessive repairs or an expensive replaceme...

# Indoor Air Pollution Control ## Cynthia Maharani ## Khaled Abass ### Department of Environmental Health Sciences ### College of Health Science ### University of Sharjah ## 6 Solutions to Reduce Indoor Air Pollution - **Regular Maintenance:** To avoid excessive repairs or an expensive replacement air conditioning and/or heating unit, always keep up with routine maintenance and inspections. - **Routine Clean:** It’s recommended that you clean your air conditioning or heating unit filters once every four to six weeks to avoid indoor air pollution and impurities. - **Improve Ventilation:** Blocked air ducts, or gaps in ventilation system could allow unwanted debris, dust, and moisture to buildup within HVAC unit causing indoor air pollution. - **Control Moisture:** Moisture leads to more mold, odors, and respiratory issues caused by lack of indoor air quality. To improve these issues, you need to maintain proper moisture levels. - **Use Natural Cleaners:** Sometimes the things we clean our homes with end up being the source of indoor air pollution. Household cleaners contain chemicals and toxins that are harmful to humans. - **Add Indoor Plants:** Indoor plants are a breath of fresh air. Fresh oxygen can be supplied to your home by incorporating household plants. Many house plants even filter the air. ## Introduction - Indoor air pollution has traditionally received less attention than outdoors pollution despite indoors pollutant levels are typically twice higher, and people spend 80-90% of their life in increasing air-tight buildings. - More than 5 million people die every year prematurely from illnesses attributable to poor indoor air quality, which also causes multi-million losses due to reduced employee’s productivity material damages, and increased health system expenses. - Indoor air pollutants include particulate matter, biological pollutants and over 400 different chemical organic and inorganic compounds, whose concentrations are governed by several outdoor and indoor factors. - Prevention of pollutant is not always technically feasible, so the implementation of cost-effective active abatement units is required. - Up to date no single physical-chemical technology is capable of coping with all indoor air pollutants in a cost effective manner. - **Key figures:** - 1 out of 10 deaths related to pollution diseases - 5.5 million people die prematurely due to indoor air pollution (2013) - 49% of the cities do not meet WHO pollution guidelines - $1.43 trillion - Costs associated to air pollution in Europe (2010) - $42.9 billion – Corresponded to Spain - 15% reduction of employee's productivity by low indoor air quality - These effects will be even more critical due to the continuous growth of major cities. Indeed, about 90% of the population worldwide lives in urban areas exposed to air quality levels that exceed the WHO guidelines, which are typically based on PM pollution. - The latest studies on human exposure to indoor pollution revealed that indoor environments could be at least twice as polluted as outdoor environments. - Indeed, the air in an urban street with average traffic might actually be cleaner than the air in a living room. - Many buildings rely entirely on mechanical ventilation to recirculate indoor air with a greatly reduced outdoor air dilution level, leading to the accumulation of indoor pollutants. - A recent commission report estimated that nearly 3 billion people worldwide are daily exposed to poor indoor air quality (IAQ) caused by the use of solid fuels for cooking, heating and lighting. - This report concluded that household air pollution is a major contributor to global figures for morbidity and mortality, with major effects on respiratory and cardiovascular systems. ## Main Sources of Pollutants at Homes | Location | Pollutants | |---|---| | Outdoor | VOCs, O3, PM, NOx, microorganisms, pollen | | Office | O3 from electronic devices; VOCs from office supplies | | Kitchen | CO, PM and VOCs from cooking and heating devices; VOCs from cleaning products | | Garage | PM, NOx, CO and VOCs from car exhaust; VOCs from stored paints, adhesives, solvents, lubricants, herbicides and cleaning products; mold | | Construction materials | HCHO and fibers from insulating materials, dust, asbestos and VOCs | | Bedroom | dust and microorganisms; VOCs from furniture and personal care products; naphthalene from insect repellers | | Bathroom | mold, microorganisms and excessive moisture; VOCs from cleaning agents, cosmetics and personal care products | | Living room | HCHO and BTEX from furniture, carpets and air fresheners; CO, PM and VOCs from fireplaces and burning stoves | ## Prevention of Indoor Air Pollutant Emission - Among the different approaches to control indoor air quality, prevention of pollutant formation and emission rank first in terms of cost-effectiveness. - Several strategies to prevent the emission and to decrease the concentration of gas pollutants in indoor environments have been proposed. - Overall, ventilation is the easiest measure to prevent the accumulation of indoor pollutants. - Indoor pollutant concentrations typically decrease when increasing outdoor air exchange rate unless outdoor pollutant concentrations are high (such as in areas with intense traffic or industrial activities). - Mechanical ventilation systems introduce outdoor fresh air into the building, which dilutes the concentration of indoor air pollutants. - Some sources can be sealed or removed by professionals, like asbestos and other insulation fibers. - Smoking bans are also a very effective measure since tobacco smoke is a source of multiple harmful chemicals in elevated concentrations. - Adequate control of the relative humidity and temperature is crucial to control the emissions of organic pollutants from indoor materials. - In this context, air conditioning systems can control the temperature and relative humidity, potentially using smart systems to automatize ventilation or heating depending on the indoor atmosphere (high CO2 levels, low temperatures) or occupants’ activities. - Many indoor air pollutants, including PM, NOx or CO, are emitted during combustion processes at homes, such as cooking or heating. - Increased ventilation rates and the reduction of these combustion gases from cooking stoves, boilers or fireplaces prevent indoor pollutant accumulation. - Combustion devices in buildings must be regularly checked and maintained to prevent malfunctioning and emissions of harmful pollutants to the indoor atmosphere - Highly polluting fuels like biomass or kerosene need to be replaced by more efficient fuels such as natural gas or electricity at homes. - Some VOCs are emitted from common construction materials. The manufacture of some wooden-based materials, like plywood or fiberboard, often implies the utilization of resins and varnishes that contain formaldehyde and other VOCs. - Paints, coatings, glues, plastics and other construction materials include VOCs (usually BTEX) as solvents or additives. - Some of these emissions can be prevented by using low-emitting materials like improved plastics and paints (phenol resins instead of urea resins, polyurethane coatings, etc.) - Occupancy of buildings should be avoided during several weeks after construction or renovation, as pollutant emissions from these sources typically decrease in time until reaching low emission steady state levels. Indeed, pollutant concentrations were found higher even four months after renovation. - Similarly, emissions of VOCs from paints, adhesives, cleaning products and fuels can be partially mitigated by properly sealing and storing these liquid materials and minimizing storage periods to prevent leakages and emissions. - Overall, a good ventilation ensuring indoor-outdoor air exchange is a feasible solution to solve most of the problems related with the accumulation of indoor pollutants, especially when the source of the pollutant is known and is not a continuous emission (e.g. cooking, painting, refurbishment). Additionally, ventilation is the best option in terms of cost-effectiveness. - To prevent emissions, it is necessary to determine the possible sources in indoor areas, such as combustion devices, stored paints and solvents or construction materials, and keep them properly maintained or discarded. Manufacturer recommendations must be followed to avoid undesired emissions. ## Physical-Chemical Technologies for Indoor Air Treatment - Active reduction units can be installed in order to lower or eliminate the levels of indoor air contaminants. - Traditionally, these devices consisted of physical chemical technologies such as filters or ozonisers installed as part of a central heating and ventilation system or operated as portable units. - Real-time sensing has been applied to these devices to optimize their performance. These sensors on-line monitor ambient conditions (temperature, humidity, concentrations of key pollutants) and activate the units based on the need of the occupants and their activities, with the subsequent energy saving. - Mechanical filtration, based on the forced circulation of air through a fibrous material where pollutants are captured, is the simplest and most popular method for PM removal. PM removal efficiencies depend on several factors such as the type and material of the filter or the air flow. - These filters need regular replacements to maintain the capture efficiency, prevent the re-emission of pollutants and to avoid the growth of microorganisms on the organic matter trapped in the filter material. - Electronic filtration is based on the attraction of negatively charged particles to a plate with opposite polarity, where particles are retained. - Two commercial devices are available: electrostatic precipitators ionizing pollutant particles and ion generators dispersing into the air ions that will subsequently attach to pollutants. - This technology exhibits higher operating costs than mechanical filtration (particularly ion generators) and requires an active removal of the particles accumulated on the plates. - The efficiencies achieved by electronic filters are lower than those provided by mechanical filtration. - Adsorption consists of the capture of organic and inorganic volatile pollutants on the surface of an adsorbent material. The most popular materials are activated carbon and zeolites, although alumina, silica gel or polymers are also used. - These adsorbent materials can be even incorporated in construction materials, which are easy to integrate in interior surfaces. - A high relative humidity and the inherent variability of pollutant levels in indoor environments decrease the efficiency of adsorption filters. - In addition, the adsorption specificity of the material with one pollutant may inhibit the efficient adsorption of other gas pollutants. - These systems can also accumulate microorganisms hazardous to human health. - **Overall, there is no single physical-chemical technology capable of coping with all indoor air pollutants in a cost-effective manner, which requires the use of sequential technology configurations at the expenses of superior capital and maintenance costs.** ## Biological Based Purification Methods - **The performance of conventional physical-chemical methods for indoor air purification is hampered by the diversity and the variability of VOCs in indoor environments.** - **However, these limitations represent an opportunity for biological based purification systems.** - Biotechnologies are based on the action of microorganisms or plants, which are able to eliminate or transform the gas pollutants by utilizing them as energy and/or carbon source for cell replication. - Overall, indoor air pollutant biodegradation relies on the action of oxidative enzymes, which function at ambient pressure and temperature without the need of additional chemicals. - In botanical technologies, both plant and soil microenvironment are responsible of pollutant degradation. - On the other hand, gas-water contactors are based on the biocatalytic action of suspended or immobilized microorganisms, which bio-convert air pollutants into CO2, H2O and new microorganisms. These microorganisms need to be integrated by diverse, versatile and adaptive microbial communities of bacteria, fungi, microalgae or yeasts able to remove simultaneously a wide spectrum of pollutants at variable concentrations without generating undesirable by-products. - Biotechnologies have been successfully developed for industrial applications, where varying concentrations of multiple gas pollutants from different sources are cost-effectively treated. - Biological-based purification systems for indoor air would improve the energy efficiency of buildings, while providing additional benefits in indoor environmental quality such as aesthetic and psychological improvements. - botanical biofiltration could have additional economic, environmental and social benefits, including remarkable psychological impacts of ‘greening’ the indoor space with plants. ## Schematic Operational Configurations of Different Air Purification Biotechnologies - **PB-BTF – Plant based Biotrickling filters** - **Biofilter** - **Bioscrubber** - **Biotrickling filter** - **Capillary bioreactor** - **Membrane bioreactor** - **Microalgae reactor** ## Plant Based Biotrickling Filters - BP-BTF: The application of botanical systems to indoor environments has been shown effective for removing VOCs. - Botanical technologies can be divided into passive (e.g. potted plants) or active (plant based biotrickling filters, PBTFs) systems. - Passive systems rely on the diffusion (spreading) of gas pollutants, which is a slow process typically present in indoor environments. - Active systems incorporate mechanical ventilation devices to increase the availability of the gas pollutants. - PBTFs system, the polluted air is forced to flow though the aerial parts and roots of hydroponic plants (does not use soil) to maximize the removal of pollutants. - Additional benefits of these active systems such as decreasing indoor temperature and increasing relative humidity. - While CO2, SOx, NOx and O3 appear to be taken up directly through the stomates of plants during daylight, VOCs are mostly degraded by microorganisms present in the rhizosphere. - A symbiotic relationship between plants and microorganisms may be achieved. ## Biofiltration - Biofiltration is a well-known and proven method for the removal of gas pollutants. - In biofilters (BFs), microorganisms are immobilized in a packing media, traditionally an organic material like compost, irrigation is irregular, and moisture and nutrients are retained by the biofilm and the packing media. - BFs are the preferred option for the treatment of hydrophobic pollutants based on the occurrence of a direct contact between the biofilm and the air emission. ## Bioscrubbers - Bioscrubbers consist of two separate units, where pollutants are initially transferred in absorption unit from the gas phase to an aqueous phase, which is recirculated to a second unit where microorganisms growing in suspension. - This configuration provides high efficiencies for hydrophilic pollutants. ## Membrane Bioreactors - Membrane bioreactors are based on the separation of gas and liquid phase by a membrane. - A nutrient solution, containing the pollutant degrading microorganisms, is continuously recirculated at one side of the membrane, while the contaminated air flows on the other side. - An attached biofilm might be formed on the aqueous side of the membrane. - The pollutants diffuse from the gas side through the membrane and are biodegraded by the microorganisms in the biofilm or in the bulk cultivation medium. ## Capillary Bioreactors - Capillary bioreactors are a new approach on the abatement of gas pollutants. - Capillary bioreactors are engineered as parallel straight microchannels, with a maximum internal diameter of 5 mm in air-water reactors (air bubbles and liquid slugs). - The mass-transfer of gas pollutants is enhanced by the internal circulation within liquid slugs, which increases the contact between the gas and the liquid phase. This configuration improves the gas-liquid mass-transfer (much higher than conventional stirred systems). - This technology achieve better results than traditional bioreactors. Although capillary bioreactors are promising solutions for indoor air purification, some problems such as the long-term maintenance needs to be solved. ## Microalgae Reactors - Microalgae fix CO2 during photosynthesis using light as energy source while releasing O2 to the ambient air. - While plants can also perform photosynthesis, algae are much more effective in this process because of the simpler cell structure and higher light utilization efficiencies. - Algae photobioreactors may be a feasible solution for indoor environments with elevated CO2 levels such as offices, schools or shopping centers. - Some species of microalgae are also able to use hydrocarbons from the environment to obtain carbon and energy (heterotrophic metabolism), and even exhibit a mixed metabolism depending on the environmental conditions. ## Summary - Currently, there is not a single physical-chemical technology that can efficiently address all challenges related to indoor air purification. - Biological based purification systems are promising solutions to overcome the limitations of indoor air treatment. - Modern building regulations are based on promoting energy savings, which entails a reduction in air exchange and therefore increases the concentration of indoor pollutants. - Regulations and recommendations in the field of modern construction should find a compromise between the progress in building tightness and the guarantee of a good IAQ, leading to a parallel decrease of buildings energy requirements. - **The implementation of biotechnologies in indoor spaces would have benefits in IAQ, which at the end would lead to an increased comfort and health of the users and a reduction in the energy expenses of the buildings.**