In Terms of Waste Management, Biological Waste Treatment Can Deal With All Our Needs. Municipal waste is defined as domestic and other waste which may resemble domestic waste by its properties. According to the Environmental Protection agency it is the "household, commercial waste and non-process industrial waste".
According to the National Waste Report 2007 (EPA 2007), the production of municipal waste rose to 0.4% to 3,397,683 tonnes. The recycling of this waste increased to 36.5% but the disposal of waste to landfill also increased by 1.7%. An increase in composting in the home place was observed to 34,470 tonnes. The number of biodegradable municipal waste disposed to landfill also increased by 4% to 1,475,077 tonnes. This figure demonstrates that Ireland is moving further away from the first target set by the Landfill Directive which was to implement less than one million tonnes of biodegradable municipal waste to be land filled by the year 2010.
This level of waste in 2007 along with the urgent need for businesses to reduce their costs in 2009, demonstrates the necessity for the continued assistance for the resource conservation initiatives with regards waste, water and energy such as the National Waste Prevention Programme.
(Strive 2007-2013) In Ireland, landfill disposal has been the main means in the past the disposal of municipal solid waste. However, according to European Legislation (Council Directive of the Landfill of Waste-"Landfill Directive") there is a requirement that alternative treatment methods must be introduced and employed to pre-treat all waste before land filling and for the reduction of landfill use.
In achieving this, a waste hierarchy was constructed for the implementation of the development of national waste policies and waste management plans designed to move away from the dependence with landfills. The most favoured option is the prevention and reduction of waste followed by reuse and recycling and lastly its final disposal.
Biological treatment can contribute to option/step of the waste hierarchy such as recycling, energy recovery and disposal.
The biological treatment of waste converts the organic fraction of the waste into a more stable material. This is achieved by either aerobic or anaerobic processes (microbes that perform in the presence or absence of oxygen). The anaerobic treatment involves a process known as "anaerobic digestion" which produces a partly stabilised organic material and methane gas which in turn can be used for electricity generation. These treatment methods can be applied singly of in combination, for example, the product from anaerobic digestion can be further treated by aerobic composting processes. The overall biological treatment process produces a stabilised organic substance that can be land filled or used in limiting land application as a soil container. Biological waste treatment can be associated with wastewater treatment, air and gaseous waste streams, soil microbiology and biogeochemical cycling and composting. In Ireland, currently the main focus is on mechanical-biological treatment and will be the main focus throughout as mechanical biological treatment may be the main focus in helping Ireland's need.
The term "Mechanical -Biological Treatment" deals wit a broad range of distinct technologies that can be combined to treat residual municipal solid waste. According to Juniper Consultancy Services Ltd (2005) MBT: A guide for Decision makers- processes, politics and markets, defined mechanical-biological treatment waste as the process that "partially processes mixed household waste by mechanically removing some parts of the waste and biologically treating others, so that the residual fraction is smaller and more suitable for a number of possible uses". It involves mechanical and biological treatment processes. The mechanical treatment refers to minimizing, sorting and separating to recover various recyclable elements from the residual waste stream and to prepare the waste stream for further treatment, which makes them more suitable for disposal.
The arrangement of mechanical biological treatment is determined by the specific performance of the plant. Mechanical- biological treatment plants can be used for:
Producing a stabilised organic fraction
Producing a recovered fuel for energy generation
Recovering recyclable material
Mechanical biological treatment involves two stages. Stage one represents the mechanical treatment which deals with residual of municipal solid waste. Stage two (a), which is the biological treatment, is the aerobic and anaerobic processes with mechanical assistances, for example mixers, turners and stirrers. Stage 2 (b) then involves biological treatment, usually aerobic, with mechanical assistance.
In Ireland, an environmental impact statement is required for planning application which comprises of screening and scoping. A facility with a capacity of over 100,000 tonnes per year for disposal, treatment or recovery of waste may be considered an importance.
Mechanical biological treatment has a role in assisting Ireland to comply with the diversion targets set out in the Landfill Directive. The Irish Government have set out clear targets in relation to renewable energy and greenhouse gas emissions. Biological treatment has a vital role to play in the achievement of these targets. Waste management activities between 1990-2004 contributed to 2.6% of overall greenhouse gases. Landfills were the significant source of the greenhouse gas emissions due to the release of methane.
Mechanical Biological treatment can contribute to the reduction of methane emissions by the biodegradation of organic material from landfills to a required stable standard. Due to the Kyoto Protocol, Ireland has agreed to limit its emissions by 2012; biological waste treatments can help achieve this. Also, by the EU directive, Ireland is trying to achieve the generation of its domestic electricity to 13.2% by renewable sources by 2010. Mechanical Biological treatment may achieve this by
The thermal treatment of recovered fuel material by the means of the biomass, which is deemed a renewable source.
The generation of heat and electricity achieved by the combustion of anaerobic digestion which produces biogas in a gas fired engine as part of a combined heat and power plant.
This contribution that biological waste can make in helping Ireland reaching its targets for biodegradable waste from landfill in the future is dependent on the waste composition of the residual waste which includes:
Waste sources, whether it is urban or rural
Social and economic factors
Type of user charged employed
Demographics
Collection regime (bin collecting).
It is important when determining the performance of a mechanical biological treatment facility for Ireland over the next few years, to continue national surveys to understand the changing composition of residual waste. Also when assessing the performance it is critical to understand and capture it in an Irish context as comparisons to other EU countries would not be a sufficient comparison.
However all European Union countries with the framework of the community action programme on the environment have the same waste management policy with a set of actions laid out to be taken at a community level to prevent pollution from waste. These aims include:
Reduce the quantity of nonrecoverable waste and prevent it originating.
Recover, recycle and reuse waste for energy and raw materials.
To manage non-recoverable waste and dispose of it by a safe manner.
With biological waste treatment, regulations, aims and legislations are of a significant importance to the satisfactory development for a market by helping the environment and at the same time improving the quality of life in a community. The research and community dealing with biological treatment of deal with three factors to ensure satisfactory control;
Recycling of waste: research area on fermentation and hydrolysis.
Energy and biomass: use of waste to produce energy.
Environment:
Biological treatment of water pollutants; use of sluges in agriculture.
Methods for evaluating the toxicity of waste of human beings and other animals.
Biotechnology: bioreactors.
These three programmes in research and development show the multi- disciplinary nature and complexity of biotechnology. However modern technologies have made huge advances due to the increasing demand for more sufficient technologies and the cost of processing to improve this and continue looking for new ones.
To enhance the process of biological waste treatment is to increase the rate of conversion. The aim of achieving this is to make the process more profitable. There are two ways in accomplishing this;
To increase the conversion rate per unit mass of biomass, organisms and enzymes.
To increase the volumetric conversion.
These two means are important in making biotechnology profitable and competitive.
Within the characteristics of the microbial species, a rise in temperature increases the biochemical conversion rate and a surplus of important nutrients ensures maximum growth rate. Recycling of biomass in a reactor also makes the process more efficient and advances in these have been undergone to achieve this.
The main aim can be the production of biomass or another compound, when the substrate is is often in excess and not limiting. Also, the conversion of waste materials where low concentration substrates are limited. A good example of both of these goals is biomethanation which involves the production of methane with the reduction of waste strength. Ultimately, it is the production of valuable material (biomass) or the reduction of waste stream (composting).
The physical reactor design and methods of the system can account for the overall reaction rate also. These include:
Hydraulic regime
Batch operation
Aeration
Recycle of biomass
Carrier for biomass
Temperature.
Environmental factors also play a significant role in reaction rates for biological and chemical reaction, these include:
Temperature
pH
Nutrients
Toxic substances
Moisture.
For optimum temperature, which is in a range of 30-40°, an increase in reaction rate is observed. A temperature dependency is the usual for pure culture or for homogeneous, mixed culture of bacteria.
pH is a big factor in all reactions. Usually, in many biotechnology processes the basic structure is well buffered, which limits pH variations. Nutrients can also affect biological reaction rates. Nitrogen and phosphorous are vital nutrients as is sulphur and some metals. Toxic substances that may be contained in raw wastewater can reduce the biological activity. These can be organic compounds and metals. The intensification of biological waste treatment makes the process more efficient. (Biotechnology of Waste Treatment and Exploitation 1987)
A common debate is the comparison of environmental aspects between mechanical biological treatment and waste with an incineration-centric waste management system. An environmental assessment was carried out with the UK environment agency's WRATE life cycle assessment to compare these. Five waste-management scenarios were looked at.
Baseline: landfill centric involves dry recyclables sent to material recovery facility, the organic waste is aerobically treated to produce compost and the residual bin is sent directly to landfill without treatment.
Scenario 1: Aerobic mechanical biological treatment centric; dry recyclables sent to material recovery facility, organic waste is aerobically treated to produce compost, the residual bin is sent for mechanical biological treatment recovering ferrous metal, a fuel with an aerobic step. Stabilised waste sent to landfill. The high calorific value fraction is separated and used for fuel.
Scenario 2: Anaerobic Mechanical biological treatment centric; dry recyclables sent to material recovery facility for recycling, aerobic waste treated for composting, residual bin sent for mechanical biological treatment recovering ferrous metal with an anaerobic stabilisation step while yielding a biogas. Stabilized waste sent to landfill, high calorific value fraction used for fuel.
Scenario 3: Thermal Centric; same as above but no recovery of ferrous metal, and the residual bin is sent for treatment by incineration with energy recovery. Incinerator fly ash is sent to landfill and bottom ash is recycled as aggregate.
Scenario 4: Thermal (Power only) Centric; Same as above, only difference is the residual bin is sent for treatment by incineration with energy recovery as electricity exported to the national grid.
This shows that the treatment of residual waste with biological treatment supports an environmental benefit over land filling or incineration. However also shows a benefit due to recycling. The disposal of untreated solid wastes to landfill is a significant disadvantage.
There are four main long term outlets for the management of mechanical biological treatment;
Stabilised organic fraction
Solid recovered fuel product
Ferrous/non-ferrous metallic outputs
Anaerobic digestion biogas.
All offer significant advantages in biological treatment of waste.
Along with mechanical biological treatment, composting is a very important factor in biological treatment of waste streams. As shown from the EPA 2007 annual waste report, composting in the home place was observed to 34,470 tonnes. Composting which is a traditional biological method has seen a huge increase in the last number of years. Composting involves the decomposition or degradation of organic waste by microbial action under certain conditions such as warm temperature, moisture and aerobic conditions however anaerobic conditions have also been know. Composting can be involved along mechanical biological treatment as seen in the five scenarios.
Many types of composting methods have been developed to handle various types of waste. These include onsite composting, vermicomposting, in-vessel composting, aerated windrow composting and aerated static pile composting. Composting is now seen as an applicable option as a significant application of biological waste treatment. The increasing problems due to pollution from incineration and land fills have lad composting to be implemented in legislation policies all across the globe. A study conducted in the UK in October 2009, observed that the composting industry was a huge success and further growth is predicted. The market turned over £164 million in the year and 4.5million tonnes of waste were composted. Most of the organic waste was municipal waste and agriculture seemed to be the biggest market for the composting with restoration and landscaping following closely. The drive in the market is due to local authority, food waste collections. The managing director of AFNOR (Association for organic recycling) by whom the study was taken by, commented that waste will now and in the future, be seen as a valuable asset and not a problem, due to composting and sources for renewable energy such as anaerobic digestion.
Another biological waste treatment is treatment for wastewater by activated sludge systems and biotowers. The activated sludge system involves organic matter of waste water providing an energy source for new cells in a heterogeneous mixture of microorganisms this is known as synthesis. Carbon is converted by the microorganisms to cell tissue and oxidation occurs to form carbon dioxide and water, known as respiration. Subsequently, nitrification may occur in an activated sludge system as a number of microorganisms may exist to obtain energy from oxidising ammonium nitrogen. A main advantage of an activated sludge system is that the final effluent does not require high dilution for final disposal, easy to manage and it is the most common wastewater treatment method used and is used on a worldwide basis.
Biological treatment of waste is not only a seen as a treatment of waste but also as a source for renewable energy. This is the reason for biological waste treatment being implemented in so many government policies. Irish mational policy has recognized that role that biological treatment of waste can play in the role for waste management, especially with regards to Mechanical-biological treatment of waste. This can be seen in the national policy documents Waste Management: Changing our ways 1998, Preventing and Recycling 2002, Waste Management-Taking Stock and Moving Forward 2004, National Biodegradable Waste Strategy 2006 and Renewable Energy Development 2006. These documents all highlight the need for Ireland to move forward in Biological Treatment of Waste as it can deal with all our needs by abiding by EU legislations, Kyoto agreement and to move forward in renewable energies.
