Guide to Effective Waste Management

waste-mountainThe best way of dealing with waste, both economically and environmentally, is to avoid creating it in the first place. For effective waste management, waste minimization, reuse, recycle and energy recovery are more sustainable than conventional landfill or dumpsite disposal technique.

Waste Minimization

Waste minimization is the process of reducing the amount of waste produced by a person or a society. Waste minimization is about the way in which the products and services we all rely on are designed, made, bought and sold, used, consumed and disposed of.

Waste Reuse

Reuse means using an item more than once. This includes conventional reuse where the item is used again for the same function and new-life reuse where it is used for a new function. For example, concrete  is a type of construction waste which can be recycled and used as a base for roads; inert material may be used as a layer that covers the dumped waste on landfill at the end of the day.

Waste Recycling

Recycling of waste involves reprocessing the particular waste materials so that it can be used as raw materials in another process. This is also known as material recovery. A well-known process for recycling waste is composting, where biodegradable wastes are biologically decomposed leading to the formation of nutrient-rich compost.

Waste-to-Energy

As far as waste-to-energy is concerned, major processes involved are mass-burn incineration, RDF incineration, anaerobic digestion, gasification and pyrolysis. Gasification and pyrolysis involves super-heating of municipal solid waste in an oxygen-controlled environment to avoid combustion. The primary differences among them relate to heat source, oxygen level, and temperature, from as low as about 300°C for pyrolysis to as high as 11 000°C for plasma gasification. The residual gases like carbon dioxide, hydrogen, methane etc are released after a sophisticated gas cleaning mechanism.

MSW incineration produce significant amounts of a waste called bottom ash, of which about 40% must be landfilled. The remaining 60% can be further treated to separate metals, which are sold, from inert materials, which are often used as road base.

The above mentioned techniques are trending in many countries and region. As of 2014, Tokyo (Japan) has nineteen advanced and sophisticated waste incinerator plants making it one of the cleanest cities. From the legislature standpoint, the country has implemented strict emission parameters in incinerator plants and waste transportation.

The European Union also has a similar legislature framework as they too faced similar challenges with regards to waste management. Some of these policies include – maximizing recycling and re-use, reducing landfill, ensuring the guidelines are followed by the member states.

Singapore has also turned to converting household waste into clean fuel, which both reduced the volume going into landfills and produced electricity. Now its four waste-to-energy plants account for almost 3% of the country’s electricity needs, and recycling rates are at an all-time high of 60%. By comparison, the U.S. sent 53% of its solid waste to landfills in 2013, recycled only 34% of waste and converted 13% into electricity, according to the US Environmental Protection Agency.

Trends in Waste Collection

Since the municipal solid waste can be a mixture of all possible wastes and not just ones belonging to the same category and recommended process, recent advances in physical processes, sensors, and actuators used as well as control and autonomy related issues in the area of automated sorting and recycling of source-separated municipal solid waste.

Automated vacuum waste collection systems that are located underground are also actively used in various parts of the world like Abu Dhabi, Barcelona, Leon, Mecca and New York etc. The utilization of the subsurface space can provide the setting for the development of infrastructure which is capable of addressing in a more efficient manner the limitations of existing waste management schemes.

AI-based waste management systems can help in route optimization and waste disposal

This technique also minimizes operational costs, noise and provides more flexibility. There are various new innovations like IoT-enabled garbage cans, electric garbage trucks, waste sorting robots and mechanisms etc are also being developed and deployed at various sites.

Conclusion

Waste management is a huge and ever growing industry that has to be analyzed and updated at every point based on the new emergence of threats and technology. With government educating the normal people and creating awareness among different sector of the society, setting sufficient budgets and assisting companies and facilities for planning, research and waste management processes  can help to relax the issues to an extent if not eradicating it completely. These actions not only help in protecting environment, but also help in employment generation and boosting up the economy.

Biomethane Utilization Pathways

biomethane-transportBiogas can be used in raw (without removal of CO2) or in upgraded form. The main function of upgrading biogas is the removal of CO2 (to increase the energy content) and H2S (to reduce risk of corrosion). After upgrading, biogas possesses identical gas quality properties as  natural gas, and can thus be used as natural gas replacement. The main pathways for biomethane utilization are as follows:

  • Production of heat and/or steam
  • Electricity production / combined heat and power production (CHP)
  • Natural gas replacement (gas grid injection)
  • Compressed natural gas (CNG) & diesel replacement – (bio-CNG for transport fuel usage)
  • Liquid natural gas (LNG) replacement – (bio-LNG for transport fuel usage)

Prior to practically all utilization options, the biogas has to be dried (usually through application of a cooling/condensation step). Furthermore, elements such as hydrogen sulphide and other harmful trace elements must be removed (usually trough application of an activated carbon filter) to prevent adverse effects on downstream processing equipment (such as compressors, piping, boilers and CHP systems).

Although biogas is perfectly suitable to be utilized in boilers (as an environmental friendlier source for heat and steam production), this option is rather obsolete due to the abundance of alternative sources from solid waste origin.

Most Palm Oil Mills are already self-reliant with respect to heat and steam production due to the combustion of their solid waste streams (such as EFB and PKS). Consequently, conversion to electricity (by means of a CHP unit) or utilization as natural gas, CNG or LNG replacement, would be a more sensible solution.

The biogas masterplan as drafted by the Asia Pacific Biogas Alliance foresees a distribution in which 30% of the biomethane is used for power generation, 40% for grid injection and 30% as compressed/liquefied fuel for transportation purpose (Asian Pacific Biogas Alliance, 2015).

For each project, the most optimal option has to be evaluated on a case to case basis. Main decision-making factors will be local energy prices and requirements, available infrastructure (for gas and electricity), incentives and funding.

For the locations where local demand is exceeded, and no electricity or gas infrastructure is available within a reasonable distance (<5-10 km, due to investment cost and power loss), production of CNG could offer a good solution.

Moreover, during the utilization of biogas within a CHP unit only 40-50% of the energetic content of the gas is converted into electricity. The rest of the energy is transformed into heat. For those locations where an abundance of heat is available, such as Palm Oil Mills, this effectively means that 50-60% of the energetic content of the biogas is not utilized. Converting the biogas into biomethane (of gas grid or CNG quality) through upgrading, would facilitate the transportation and commercialisation of over 95%  of the energetic content of the biogas.

Within the CNG utilization route, the raw biogas will be upgraded to a methane content of >96%, compressed to 250 bar and stored in racks with gas bottles. The buffered gas (bottles) will be suitable for transportation by truck or ship. For transportation over large distances (>200km), it will be advised to further reduce the gas volume by converting the gas to LNG (trough liquefaction).

Overall the effects and benefits from anaerobic digestion of POME and utilization of biomethane can be summarized as follows:

  • Reduction of emissions i.e. GHG methane and CO2
  • Reduced land use for POME treatment
  • Enhanced self-sufficiency trough availability of on-site diesel replacement (CNG)
  • Expansion of economic activities/generation of additional revenues
    • Sales of surplus electricity (local or to the grid)
    • Sales of biomethane (injection into the natural gas grid)
    • Replacement of on-site diesel usage by CNG
    • Sales of bottled CNG
  • Reducing global and local environmental impact (through fuel replacement)
  • Reducing dependence on fossil fuel, and enhances fuel diversity and security of energy supply
  • Enhancement of local infrastructure and employment
    • Through electrical and gas supply
    • Through Fuel (CNG) supply

Co-Authors: H. Dekker and E.H.M. Dirkse (DMT Environmental Technology)

Note: This is the second article in the special series on ‘Sustainable Utilization of POME-based Biomethane’ by Langerak et al of DMT Environmental Technology (Holland). The first article can be viewed at this link

Biogas Upgradation Methods

Upgradation of biogas is primarily achieved by carbon dioxide removal which then enhances the energy value of the gas to give longer, driving distances with a fixed gas storage volume. Removal of carbon dioxide also provides a consistent gas quality with respect to energy value. The latter is regarded to be of great importance from the vehicle manufacturers in order to reach low emissions of nitrogen oxide.

At present four different methods are commercially used for removal of carbon dioxide from biogas, either to reach vehicle fuel standard or to reach natural gas quality for injection to the natural gas grid. These methods are:

  • Water absorption
  • Polyethylene glycol absorption
  • Carbon molecular sieves
  • Membrane separation

Water Scrubbing

Water scrubbing is used to remove carbon dioxide but also hydrogen sulphide from biogas since these gases is more soluble in water than methane. The absorption process is purely physical. Usually the biogas is pressurized and fed to the bottom of a packed column where water is fed on the top and so the absorption process is operated counter-currently.

Polyethylene Glycol Scrubbing

Polyethylene glycol scrubbing is a physical absorption process. Selexol is one of the trade names used for a solvent. In this solvent, like in water, both carbon dioxide and hydrogen sulphide are more soluble than methane.

The big difference between water and Selexol is that carbon dioxide and hydrogen sulphide are more soluble in Selexol which results in a lower solvent demand and reduced pumping. In addition, water and halogenated hydrocarbons (contaminants in biogas from landfills) are removed when scrubbing biogas with Selexol.

Carbon Molecular Sieves

Molecular sieves are excellent products to separate specifically a number of different gaseous compounds in biogas. Thereby the molecules are usually loosely adsorbed in the cavities of the carbon sieve but not irreversibly bound. The selectivity of adsorption is achieved by different mesh sizes and/or application of different gas pressures.

When the pressure is released the compounds extracted from the biogas are desorbed. The process is therefore often called “pressure swing adsorption” (PSA). To enrich methane from biogas the molecular sieve is applied which is produced from coke rich in pores in the micrometer range. The pores are then further reduced by cracking of the hydrocarbons. In order to reduce the energy consumption for gas compression, a series of vessels are linked together.

Pressure swing adsoprtion process for biogas upgradation

The gas pressure released from one vessel is subsequently used by the others. Usually four vessels in a row are used filled with molecular sieve which removes at the same time CO2 and water vapour.

Membrane Purification

There are two basic systems of biogas purification with membranes: a high pressure gas separation with gas phases on both sides of the membrane, and a low-pressure gas liquid absorption separation where a liquid absorbs the molecules diffusing through the membrane.

  • High pressure gas separation

Pressurized gas (36 bar) is first cleaned over for example an activated carbon bed to remove (halogenated) hydrocarbons and hydrogen sulphide from the raw gas as well as oil vapour from the compressors. The carbon bed is followed by a particle filter and a heater. The raw gas is upgraded in 3 stages to a clean gas with 96 % methane or more.

The waste gas from the first two stages is recycled and the methane can be recovered. The waste gas from stage 3 (and in part of stage 2) is flared or used in a steam boiler as it still contains 10 to 20 % methane.

  • Gas-liquid absorption membranes

Gas-liquid absorption using membranes is a separation technique which was developed for biogas upgrading in the recent past. The essential element is a micro-porous hydrophobic membrane separating the gaseous from the liquid phase. The molecules from the gas stream, flowing in one direction, which are able to diffuse through the membrane will be absorbed on the other side by the liquid flowing in counter current.

The absorption membranes work at approx. atmospheric pressure (1 bar) which allows low-cost construction. The removal of gaseous components is very efficient. At a temperature of 25 to 35°C the H2S concentration in the raw gas of 2 % is reduced to less than 250 ppm.

Food Waste Management

The waste management hierarchy suggests that reduce, reuse and recycling should always be given preference in a typical waste management system. However, these options cannot be applied uniformly for all kinds of wastes. For examples, food waste is quite difficult to deal with using the conventional 3R strategy.

Of the different types of organic wastes available, food waste holds the highest potential in terms of economic exploitation as it contains high amount of carbon and can be efficiently converted into biogas and organic fertilizer.

There are numerous places which are the sources of large amounts of food waste and hence a proper food waste management strategy needs to be devised for them to make sure that either they are disposed off in a safe manner or utilized efficiently. These places include hotels, restaurants, malls, residential societies, college/school/office canteens, religious mass cooking places, communal kitchens, airline caterers, food and meat processing industries and vegetable markets which generate food residuals of considerable quantum on a daily basis.

anaerobic_digestion_plant

The anaerobic digestion technology is highly apt in dealing with the chronic problem of food waste management in urban societies. Although the technology is commercially viable in the longer run, the high initial capital cost is a major hurdle towards its proliferation.

The onus is on the governments to create awareness and promote such technologies in a sustainable manner. At the same time, entrepreneurs, non-governmental organizations and environmental agencies should also take inspiration from successful food waste-to-energy projects in Western countries and try to set up such facilities in cities and towns.

How Modern Technology is Transforming Urban Development

Australia is famous the whole world over for its incredible scenery and stunning countryside, from the arid yet beautiful outback to the shimmering sands of the Gold Coast, but the country is also home to some of the world’s favourite cities. Australia’s population is growing, and so urban development and planning is becoming ever more important. The way we plan, design and build our urban centres has changed rapidly over the last decades thanks to evolving needs, environmental concerns and rapidly advancing technology.

It is this combination that is helping Australian towns and cities lead the way when it comes to urban generation and regeneration.

More Accurate Surveying

Thorough surveying is the key to successful development, and it was once a laborious and time-consuming process, and therefore by necessity, an expensive one too. One modern invention has transformed this task completely, as the most forward thinking planners now utilise unmanned aerial surveying techniques.

Using the latest high-powered drones, planners and developers can now get a much more accurate and holistic picture of the land that they plan to build on. The highly detailed maps produced from the air allow clients to make more informed decisions quicker than they would otherwise have been able to, thus helping to ensure that projects come in on time and on budget.

Greener Developments

Many Australians are becoming increasingly concerned about the effect that mankind is having upon the environment, and the effects of climate change can be seen across this nation and beyond. That’s why surveyors and designers have to be very careful when planning urban developments, as it’s imperative that expanding urban centres don’t adversely impact upon our ecology or the incredible animal life that also calls Australia its home.

Today’s leading urban surveying companies put green issues at the heart of the work, using the latest computer modelling techniques to thoroughly assess the impact of an urban development upon the environment surrounding it; in this way, it’s possible to maintain the equilibrium between the need to develop new urban spaces and the need to protect our ecosystems.

Bringing Greater Benefits to Urban Dwellers

There are many factors to be considered when planning an urban development, as well as the green concerns mentioned above. It’s essential for planners to be able to make accurate assessments of what benefits their development will bring to the people who live within it and upon its neighbourhood, and this involves careful study of a wide range of metrics and projections.

The highly detailed maps produced from the air allow clients to make more informed decisions quicker

Whilst this remains a specialist and highly important job, the appearance of specialist computer programmes now allow planners to make an economic and demographic assessment that’s more accurate than ever before.

Expert urban planners know how essential it is to use all of the technological innovations now available to them, from unmanned aerial surveying, to high tech demographic assessment tools and greener planning software. This is why new urban developments bring benefits for residents and businesses, and for the economy as a whole, while still protecting the rural areas and environment that make Australia the envy of the world.

Dyne Testing and its Usefulness

Dyne Testing is a technology, a method to measure surface wettability. The low surface wettability of polymer-based substrates is the sign of poor adhesion of inks, glues and coatings. Thus, to obtain the optimum amount of adhesive it is necessary to increase the surface energy of the substrate which can be done by surface treatment with either Corona or Plasma. It will result in good wetting of the material over the surface of the substrate and hence, it improves adhesion.

For the optimum adhesion, while printing, gluing, or coating the various substrates, it is necessary to obtain high surface energy which can be obtained by Dyne Testing Markers. The fluid that is present in the Dyne Testing markers is based on ISO 8296 method for measuring the surface energy of polythene film.

When the Dyne Testing Pens are being applied to the surface, the liquid will form a continues film or will form a small trail of droplets. If it is being stretched as a film for at least 3 seconds, the substrate will have a minimum surface energy of that ink value which will be expressed in mN/m (Dynes).

The exact surface energy (Dyne level) can be determined by applying a range of increasing or decreasing values of Dyne test pens thereby taking the steps to improve its condition.

The Dyne Test Pen may lose its accuracy for which there are 3 reasons:

  1. It could get contaminated with the foreign substance
  2. It could evaporate quicker than it is expected to be
  3. And the third reason is ageing, during which chemical reactions take place among the constituents.

The experts have also faced the problem with the ageing of Dyne Testing Equipment. If their hue or color density are almost past their expiration date, it is advisable to replace them as stated by experts. The lower Dyne value states that the value stated on the bottle does not match true surface tension. You must be sure that retains the substrate used for the measurements are to be kept well sealed, free from contamination, and stored under laboratory conditions.

The ideal Dyne Testing Pen should be:

  • easy to handle,
  • perfect for the quick spot checks on the production floor,
  • very easy to read,
  • no subjectivity for this type of test,
  • no wiping off necessary,
  • lasting display of result, and
  • very striking coloring.

Conclusion

The Dyne Testing Kit by Ice-equipment.com is based on valve tip applicator and not the magic marker type. The quick test 38 pen is our most popular product amongst all and it is available in a bright red ink. This is the quick test pen which serves to check the surface treatment of all plastic substrates.

It has a shown an effect onto the material such that a stroke of the pens leaves a full line on the material if the material’s surface energy is below 38 Dynes/cm. Also, as mentioned above if the materials surface energy is below 38 Dynes/cm, the fluid will form small drops on the surface. The fluid applied to the surface will dry within seconds; it does not need to be wiped off anymore.

4 Reasons Why Inflatable Packer is a Must Have

Non-stop operating challenges in the field of the gas, oilfield, and underground mining has led the inflatable technology to become a mainstream go-to solution for those in jobs of high-pressure drilling, borehole measurement, and tunneling. And it is none other than the inflatable packers that have been extensively catering to the niche since a decade now. The best thing about these tools is that they easily pass through restrictions and they are extremely sturdy to stand all the extremities and challenges of their projects.

With these tools rapidly gaining the ground in almost all parts of boring, sealing and mechanical jobs, it’s probably time to take a look at what makes these testing powerhouses really an unmatched solution in the field of special civil engineering and geotechnical studies. There are a plenty of informative and reliable sources, including http://www.aardvarkpackers.com/products-list/inflatable-packers/ and others that can tell you how these tools work and benefit their users.

What is an Inflatable Packer

As the name suggests, an inflatable packer is a plug equipment that can be extended and used in a wide array of decommissioning projects more specialized in terms of hole temperature and washouts etc. These plugs are both robust and versatile in nature and can be deployed where activities like hydraulic fracturing and high-pressure permeability require an in-depth planning and execution.

It’s the pipe that makes the main body of the packer and its the outside of the pipe that can inflate multiple times its original diameter to offer the space needed for all conventional jobs like coil tubing, pumping injections, tubes, and more.

Types of Inflatable Packers

When you have a clear idea about the job, it will be easy to choose your kind of pick from a wide selection of packers. They are many types, though…

  1. Fixed end packers
  2. Single or sliding end packers available in three styles, non reinforced, partially reinforced or fully reinforced
  3. Steel fortified
  4. Wire-line packers
  5. Custom packers (metal or other combinations)

Remember, every job needs an inflatable tool that can serve the bespoke purpose.

Uses of Inflatable Packers

As already mentioned earlier, inflatable packers are used in a wide range of energy-optimized fields, including groundwater projects, dewatering, high-pressure mining, contamination, block caving, core drilling, rock blasting and other kinds of stress testing

However, below mentioned is a list of broad range applications where these inflated tools are hugely deployed…

  1. Multi-depth ground consolidation
  2. Unconsolidated material consolidation
  3. Solid rock consolidation
  4. Improvement of mechanical properties
  5. Underground soil injections
  6. Lifting injections
  7. Sealing projects
  8. Injections in foundations

So, now that you know about most of the high-key projects where packers are used, there are certain unique features that make a packer ideal for a job.

  1. Extension capability of the packer’s hose,
  2. High-pressure rating
  3. The interior measurement of the pipe
  4. The exterior measurement of the pipe
  5. Longness of the sealing section that complies with the uneven borehole

The real advantage of having an inflated tool with an increased number of features is that it will make sure you can use it in multifaceted projects.

Advantages of inflatable packers

There are four main reasons that make these tools a must-have. They are as follows:

  1. Inflatable packers are reusable

Yes, most of their parts can be used for a great number of times. All the parts from a mandrel, inflation point, rubber element to connectors are exchangeable and their models are available in different lengths.

  1. Material parts are built sturdy

A non-welded packer is made robust and its patented and reinforcing ribs offer a tighter grip in the target areas to withstand challenges and vulnerabilities during and post inflation. What’s more, the packer ensures a uniform inflation between its metal ribs to offer maximum efficiency at disposal operations.

  1. Good use in inconsistent contact pressure

The packer’s metal ribs offer reinforcing anchoring in the end subs. This allows the inflatable tool to optimize its pressure differential holding capacity in varying depths.

  1. Flawless and safe sealing

While the ribs and the high-quality threads of an inflatable packer offer a greater surface preparation, eliminating any need for using crossover sub, welding or epoxy, the larger expansion range of a packer’s valve system provides an extra room for the fluid and the sealing functions, What’s more, all its material tubes and check valves can be cleaned easily when you separate them.

But the benefits of using these tools don’t end just here. There are a tall-list of other advantages too when you buy a packer of this type.

Final Thoughts

In a nutshell, inflatable packers prove extremely efficient where a perfect decommissioning job can add hundreds of thousands of dollars to the ever-flourishing energy industry. Their proven track records make them a must-have for projects like test injections, geological boring, water pressure control and special cases like plugging and abandoning wells just to name a few. The good news is, nowadays these tools are made available just a click away. Just go through the specifications carefully and pick the one that best suits your niche.

Major Considerations in Biopower Projects

In recent years, biopower (or biomass power) projects are getting increasing traction worldwide, however there are major issues to be tackled before setting up a biopower project. There are three important steps involved in the conversion of biomass wastes into useful energy. In the first step, the biomass must be prepared for the energy conversion process. While this step is highly dependent on the waste stream and approach, drying, grinding, separating, and similar operations are common.

In addition, the host facility will need material handling systems, storage, metering, and prep-yard systems and biomass handling equipment. In the second step, the biomass waste stream must be converted into a useful fuel or steam. Finally, the fuel or steam is fed into a prime mover to generate useful electricity and heat.

One of the most important factors in the efficient utilization of biomass resource is its availability in close proximity to a biomass power project. An in-depth evaluation of the available quantity of a given agricultural resource should be conducted to determine initial feasibility of a project, as well as subsequent fuel availability issues. The primary reasons for failure of biomass power projects are changes in biomass fuel supply or demand and changes in fuel quality.

Fuel considerations that should be analyzed before embarking on a biomass power project include:

  • Typical moisture content (including the effects of storage options)
  • Typical yield
  • Seasonality of the resource
  • Proximity to the power generation site
  • Alternative uses of the resource that could affect future availability or price
  • Range of fuel quality
  • Weather-related issues
  • Percentage of farmers contracted to sell residues

Accuracy is of great importance in making fuel availability assumptions because miscalculations can greatly impact the successful operation of biomass power projects. If biomass resource is identifies as a bottle-neck in the planning stage, a power generation technology that can handle varying degrees of moisture content and particle size can be selected.

Technologies that can handle several fuels in a broad category, such as agricultural residues, provide security in operation without adversely affecting combustion efficiency, operations and maintenance costs, emissions levels, and reliability.

Consistent and reliable supply of biomass is crucial for any biomass project

Identification of potential sources of biomass fuel can be one of the more challenging aspects of a new biomass energy project. There are two important issues for potential biomass users:

  • Consistent and reliable biomass resource supply to the facility
  • Presence of harvesting, processing and supply infrastructure to provide biomass in a consistent and timely manner

Biomass as an energy source is a system of interdependent components. Economic and technical viability of this system relies on a guaranteed feedstock supply, effective and efficient conversion technologies, guaranteed markets for the energy products, and cost-effective distribution systems.

The biomass system is based on the following steps:

  • Biomass harvesting (or biomass collection of non-agricultural waste)
  • Preparation of biomass as feedstock
  • Conversion of biomass feedstock into intermediate products.
  • Transformation of intermediates into final energy and other bio-based products
  • Distribution and utilization of biofuels, biomass power and bio-based products.

Medical Waste Management in Developing Countries

medical-waste-managementHealthcare sector is growing at a very rapid pace, which in turn has led to tremendous increase in the quantity of medical waste generation in developing countries, especially by hospitals, clinics and other healthcare establishments. The quantity of healthcare waste produced in a typical developing country depends on a wide range of factors and may range from 0.5 to 2.5 kg per bed per day.

For example, India generates as much as 500 tons of biomedical wastes every day while Saudi Arabia produces more than 80 tons of healthcare waste daily. The growing amount of medical wastes is posing significant public health and environmental challenges across the world. The situation is worsened by improper disposal methods, insufficient physical resources, and lack of research on medical waste management. The urgent need of the hour is to healthcare sustainable in the real sense of the word.

Hazards of Healthcare Wastes

The greatest risk to public health and environment is posed by infectious waste (or hazardous medical waste) which constitutes around 15 – 25 percent of total healthcare waste. Infectious wastes may include items that are contaminated with body fluids such as blood and blood products, used catheters and gloves, cultures and stocks of infectious agents, wound dressings, nappies, discarded diagnostic samples, swabs, bandages, disposal medical devices, contaminated laboratory animals etc.

Improper management of healthcare wastes from hospitals, clinics and other facilities in developing nations pose occupational and public health risks to patients, health workers, waste handlers, haulers and general public. It may also lead to contamination of air, water and soil which may affect all forms of life. In addition, if waste is not disposed of properly, ragpickers may collect disposable medical equipment (particularly syringes) and to resell these materials which may cause dangerous diseases.

Inadequate healthcare waste management can cause environmental pollution, growth and multiplication of vectors like insects, rodents and worms and may lead to the transmission of dangerous diseases like typhoid, cholera, hepatitis and AIDS through injuries from syringes and needles contaminated with human.

In addition to public health risks associated with poor management of biomedical waste, healthcare wastes can have deleterious impacts on water bodies, air, soil as well as biodiversity. The situation is further complicated by harsh climatic conditions in many developing nations which makes disposal of medical waste more challenging.

The predominant medical waste management method in the developing world is either small-scale incineration or landfilling. However, the WHO policy paper of 2004 and the Stockholm Convention, has stressed the need to consider the risks associated with the incineration of healthcare waste in the form of particulate matter, heavy metals, acid gases, carbon monoxide, organic compounds, pathogens etc.

In addition, leachable organic compounds, like dioxins and heavy metals, are usually present in bottom ash residues. Due to these factors, many industrialized countries are phasing out healthcare incinerators and exploring technologies that do not produce any dioxins. Countries like United States, Ireland, Portugal, Canada and Germany have completely shut down or put a moratorium on medical waste incinerators.

Alternative Treatment Technologies

The alternative technologies for healthcare waste disposal are steam sterilization, advanced steam sterilization, microwave treatment, dry heat sterilization, alkaline hydrolysis, biological treatment and plasma gasification.

Nowadays, steam sterilization (or autoclaving) is the most common alternative treatment method. Steam sterilization is done in closed chambers where both heat and pressure are applied over a period of time to destroy all microorganisms that may be present in healthcare waste before landfill disposal. Among alternative systems, autoclaving has the lowest capital costs and can be used to process up to 90% of medical waste, and are easily scaled to meet the needs of any medical organization.

Advanced autoclaves or advanced steam treatment technologies combine steam treatment with vacuuming, internal mixing or fragmentation, internal shredding, drying, and compaction thus leading to as much as 90% volume reduction. Advanced steam systems have higher capital costs than standard autoclaves of the same size. However, rigorous waste segregation is important in steam sterilization in order to exclude hazardous materials and chemicals from the waste stream.

Microwave treatment is a promising technology in which treatment occurs through the introduction of moist heat and steam generated by microwave energy. A typical microwave treatment system consists of a treatment chamber into which microwave energy is directed from a microwave generator. Microwave units generally have higher capital costs than autoclaves, and can be batch or semi-continuous.

Chemical processes use disinfectants, such as lime or peracetic acid, to treat waste. Alkaline digestion is a unique type of chemical process that uses heated alkali to digest tissues, pathological waste, anatomical parts, or animal carcasses in heated stainless steel tanks. Biological processes, like composting and vermicomposting, can also be used to degrade organic matter in healthcare waste such as kitchen waste and placenta.

Plasma gasification is an emerging solution for sustainable management of healthcare waste. A plasma gasifier is an oxygen-starved reactor that is operated at the very high temperatures which results in the breakdown of wastes into hydrogen, carbon monoxide, water etc. The main product of a plasma gasification plant is energy-rich syngas which can be converted into heat, electricity and liquids fuels. Inorganic components in medical wastes, like metals and glass, get converted into a glassy aggregate.

Biomass Gasification Power Systems

Biomass gasification power systems have followed two divergent pathways, which are a function of the scale of operations. At sizes much less than 1MW, the preferred technology combination today is a moving bed gasifier and ICE combination, while at scales much larger than 10 MW, the combination is of a fluidized bed gasifier and a gas turbine.

Larger scale units than 25 MW would justify the use of a combined cycle, as is the practice with natural gas fired gas turbine stations. In the future it is anticipated that extremely efficient gasification based power systems would be based on a combined cycle that incorporates a fuel cell, gas turbine  and possibly a Rankine bottoming cycle.

Integrated Gasification Combined Cycle

The most attractive means of utilising a biomass gasifier for power generation is to integrate the gasification process into a gas turbine combined cycle power plant. This will normally require a gasifier capable of producing a gas with heat content close to 19 MJ/Nm3. A close integration of the two parts of the plant can lead to significant efficiency gains.

The gas from the gasifier must first be cleaned to remove impurities such as alkali metals that might damage the gas turbine. The clean gas is fed into the combustor of the gas turbine where it is burned, generating a flow of hot gas which drives the turbine, generating electricity.

Hot exhaust gases from the turbine are then utilised to generate steam in a heat recovery steam generator. The steam drives a steam turbine, producing more power. Low grade waste heat from the steam generator exhaust can be used within the plant, to dry the biomass fuel before it is fed into the gasifier or to preheat the fuel before entry into the gasifier reactor vessel.

Schematic of integrated biomass gasification combined cycle

The gas-fired combined cycle power plant has become one of the most popular configurations for power generation in regions of the world where natural gas is available. The integration of a combined cycle power plant with a coal gasifier is now considered a potentially attractive means of burning coal cleanly in the future.

Biomass Fuel Cell Power Plant

Another potential use for the combustible gas from a biomass gasification plant is as fuel for a fuel cell power plant. Modern high temperature fuel cells are capable of operating with hydrogen, methane and carbon monoxide. Thus product gas from a biomass gasifier could become a suitable fuel.

As with the integrated biomass gasification combined cycle plant, a fuel cell plant would offer high efficiency. A future high temperature fuel cell burning biomass might be able to achieve greater than 50% efficiency.