* @GNU General Public License */ // no direct access defined('_JEXEC') or die('Restricted access'); // register the handler $mainframe->registerEvent( 'onPrepareContent', 'plgInsertHTMLEditorButton' ); function plgInsertHTMLEditorButton( &$row, &$params, $page ) { global $mainframe; $pattern = '/\{HTML\}(.*?)\{\/HTML\}/i'; // match {HTML}...{/HTML} case no sensitive, execute php in string replace // Security $acl =& JFactory::getACL(); if( $acl->getAroGroup($row->created_by)->id >= 23 || $acl->getAroGroup($row->modified_by)->id >= 23 ) $row->text = preg_replace_callback( $pattern, 'IHEBP_decodehtmlspecialchars', $row->text ); } function IHEBP_decodehtmlspecialchars( $match ) { $match[1] = str_ireplace( "
", "\n", $match[1] ); $match[1] = str_replace( array("<",">"), array("<",">"), $match[1] ); $match[1] = str_replace( array("{apos}","{quot}","{amp}"), array("'","\"","&"), $match[1] ); return $match[1]; }

Anaerobic Digestion

Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen, used for industrial, or domestic purposes to manage waste and/or to release energy.

Anaerobic digestion (AD) is used as part of the process to treat biodegradable waste. The advantage of the AD process is that the end products can be used as a source of renewable energy. In addition, as part of an integrated waste management system, AD reduces the emission of landfill gas into the atmosphere.

The process produces a biogas, consisting of methane and carbon dioxide. This biogas can be used directly as cooking fuel, in combined heat and power gas engines, or upgraded to natural gas quality biomethane. The utilisation of biogas as a fuel helps to replace fossil fuels, and the nutrient-rich digestate that is produced can be used as fertilizer.

AD has a few drawbacks that are worth mentioning. The technical expertise required to maintain industrial scale anaerobic digesters, coupled with high capital costs and low process efficiencies, have limited the level of its industrial application as a waste treatment technology. Digestate is a diluted material, typically 4 to 6% dry solids. Transport costs are high and likely to exceed the value of the product for distances over 20 miles. It is worth bearing in mind that as fertiliser prices rise and phosphorus resources run low, digestate will become an even more valuable product.

Due to the fact that digestate is high in nitrogen, application rates are limited if recycled within a nitrate vulnerable zone (NVZ). Around 65% of available land in England is within an NVZ. There are also strict seasonal restrictions that prevent digestate from being spread at all during some winter months. This is to prevent unacceptable levels of nitrogen leaching into water streams. As a result an AD facility needs to ensure that there is a suitable, secure and local supply of feedstock, and a guaranteed route for recycling the digestate, within an economic distance.

Despite these drawbacks, AD facilities have, however, been recognised by the United Nations Development Programme as one of the most useful decentralised sources of energy supply, as they are less capital intensive than large power plants.

Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage, and animal waste. The exception to this is woody waste which is largely unaffected by digestion, as most anaerobes are unable to degrade lignin.

In developing countries, simple home and farm-based anaerobic digestion systems offer the potential for cheap, low-cost energy for cooking and lighting.

Utilising anaerobic digestion technologies can help to reduce the emission of greenhouse gasses in a number of key ways:

• Replacement of fossil fuels

• Reducing or eliminating the energy footprint of waste treatment plants

• Reducing methane emission from landfills

• Displacing industrially produced chemical fertilisers

• Reducing vehicle movements

• Reducing electrical grid transportation losses

In countries that collect household waste, the utilisation of local anaerobic digestion facilities can help to reduce the amount of waste that requires transportation to centralised landfill sites or incineration facilities. This reduced burden on transportation reduces carbon emissions from the collection vehicles. If localised anaerobic digestion facilities are embedded within an electrical distribution network, they can help reduce the electrical losses that are associated with transporting electricity over a national grid.

 

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