Solid Wastes in the Middle East

The high rate of population growth, urbanization and economic expansion in the Middle East is not only accelerating consumption rates but also increasing the generation rate of all  sorts of waste. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita solid waste generation. The gross urban waste generation quantity from Middle East countries is estimated at more than 150 million tons annually.

Saudi Arabia produced 13 million tons of garbage in 2009. With an approximate population of about 28 million, the kingdom produces approximately 1.3 kilograms of waste per person every day.  According to a recent study conducted by Abu Dhabi Center for Waste Management, the amount of waste in UAE totaled 4.892 million tons, with a daily average of 6935 tons in the city of Abu Dhabi, 4118 tons in Al Ain and 2349 tons in the western region. Countries like Kuwait, Bahrain and Qatar have astonishingly high per capita waste generation rate, primarily because of high standard of living and lack of awareness about sustainable waste management practices.

In Middle East countries, huge quantity of sewage sludge is produced on daily basis which presents a serious problem due to its high treatment costs and risk to environment and human health. On an average, the rate of wastewater generation is 80-200 litres per person each day and sewage output is rising by 25 percent every year. According to estimates from the Drainage and Irrigation Department of Dubai Municipality, sewage generation in the Dubai increased from 50,000 m3 per day in 1981 to 400,000 m3 per day in 2006.

Waste-to-Energy Prospects

Municipal solid waste in the Middle East is mainly comprised of organics, paper, glass, plastics, metals, wood etc. Municipal solid waste can be converted into energy by conventional technologies (such as incineration, mass-burn and landfill gas capture) or by modern conversion systems (such as anaerobic digestion, gasification and pyrolysis).

At the landfill sites, the gas produced by the natural decomposition of MSW is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. In addition, the organic fraction of MSW can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.

Anaerobic digestion is the most preferred option to extract energy from sewage, which leads to production of biogas and organic fertilizer. The sewage sludge that remains can be incinerated or gasified/pyrolyzed to produce more energy. In addition, sewage-to-energy processes also facilitate water recycling.

Thus, municipal solid waste can also be efficiently converted into energy and fuels by advanced thermal technologies. Infact, energy recovery from MSW is rapidly gaining worldwide recognition as the 4th R in sustainable waste management system – Reuse, Reduce, Recycle and Recover.

Ultrasonic Pretreatment in Anaerobic Digestion

Anaerobic digestion process comprises of four major steps – hydrolysis, acidogenesis, acetogenesis and methanogenesis. The biological hydrolysis is the rate limiting step and pretreatment of sludge by chemical, mechanical or thermal disintegration can improve the anaerobic digestion process. Ultrasonic disintegration is a method for breakup of microbial cells to extract intracellular material.

Ultrasound activated sludge disintegration could positively affect sludge anaerobic digestion. Due to sludge disintegration, organic compounds are transferred from the sludge solids into the aqueous phase resulting in an enhanced biodegradability. Therefore disintegration of sewage sludge is a promising method to enhance anaerobic digestion rates and lead to reduce the volume of sludge digesters.

The addition of disintegrated surplus activated sludge and/or foam to the process of sludge anaerobic digestion can lead to markedly better effects of sludge handling at wastewater treatment plants. In the case of disintegrated activated sludge and/or foam addition to the process of anaerobic digestion it is possible to achieve an even twice a higher production of biogas. Here are few examples:

STP Bad Bramstedt, Germany (4.49 MGD)

  • First fundamental study on pilot scale by Technical University of Hamburg-Harburg, 3 years, 1997 – 1999
  • reduction in digestion time from 20 to 4 days without losses in degradation efficiency
  • increase in biogas production by a factor of 4
  • reduction of digested sludge mass of 25%

STP Ahrensburg, Germany (2.64 MGD)

  • Preliminary test on pilot-scale by Technical University of Hamburg-Harburg, 6 months, 1999
  • increase in VS destruction of 20%
  • increase in biogas production of 20%

STP Bamberg, Germany (12.15 MGD)

  • Preliminary full-scale test, 4 months, 2002 2) Full-scale installation since June 2004
  • increase in VS destruction of 30%
  • increase in biogas production of 30%
  • avoided the construction of a new anaerobic digester

STP Freising, Germany (6.87 MGD)

  • Fundamental full-scale study by University of Armed Forces, Munich, 4 months, 2003
  • increase in biogas production of 15%
  • improved sludge dewatering of 10%

STP Meldorf, Germany (1.06 MGD)

  • Preliminary full-scale test, 3 months, 2004 2) Full-scale installation since December 2004
  • increase in VS destruction of 25%
  • increase in biogas production of 25%
  • no foam or filamentous organisms present in the anaerobic sludge digester

STP Ergolz 2, Switzerland (3.43 MGD)

  • Full-scale test, 3 months, 2004
  • increase in VS destruction of 15%
  • increase in biogas production of 25%

STP Beverungen, Germany (2.64 MGD)

  • Full-scale test, 3 months, 2004/2005
  • increase in VS destruction of 25%
  • increase in biogas production of 25%

To sum up, ultrasonication has a positive effect on sludge solubilisation, sludge volume, biogas production, flock size reduction and cells lyses. Ultrasonic pretreatment enhances the subsequent anaerobic digestion resulting in a better degradation of volatile solids and an increased production of biogas.

The use of low power ultrasound in bioreactors may present a significant improvement in cost reduction. Therefore, ultrasonic pretreatment enhances the subsequent anaerobic digestion resulting in a better sludge digestion and efficient recovery of valuables.