Israeli biological municipal solid waste (MSW) treatment company Arrow Ecology is hoping to offer its low-cost ArrowBio biological waste treatment system to the South African waste market.
Arrow Ecology sales manager Ofer Ben Ami explains to Engineering News that the ArrowBio process is a patented technology that succeeds in treating unsorted MSW to recover materials from the waste, as well as producing biogas, which is an alternative, clean and green energy for municipal transportation and power plants.
“The process has been tested for six years in a laboratory and in field tests at a semi-industrial plant near Hadera, in Israel,” he says.
The plant, in Tel Aviv, has been operational since December 2003 and has been approved by scientists from Europe, the US and Australia as being more effective and economical than all other existing MSW treatment methods, he notes.
“Arrow Ecology has won a $150-million contract in Sydney, Australia, with local partner and solid waste processing and disposal service provi- der WSN Environmental Solutions. Arrow Ecology has also been awarded a Los Angeles tender for MSW treatment, with the contract being prepared for signing soon,” says Ben Ami.
Through Arrow Ecology’s local partner in Mexico, the company won a long-term contract for a plant in Pachuca, Mexico, and its techno- logy has been declared one of the two best available technologies by waste removal company Waste Management, of the US.
Ben Ami mentions that the main advantages of the technology include the production of high-quality biogas (70% methane), which is an envi- ronment-friendly fuel that can be used for power plants and municipal transportation.
The technology recovers 80% to 90% of all waste materials, including metals, plastics, cardboard and glass, which can be recycled, and there is no need for the presorting of waste.
The system decreases air, water and ground pollution and leaves no unpleasant odours, and also lowers the effect of global climate change caused by methane gas from landfills. Methane production is also increased when sorted organic material is received.
Ben Ami explains that the ArrowBio process is an integrated solution that receives sorted or unsorted MSW as an input, eliminating the need for prior separation or classification of mixed waste.
“The waste is delivered by trucks and, after presorting large materials such as cardboard, it is dumped into a large vat, where water is present to assist with the first separation by gravity of different materials,” he says.
The preliminary liquid-based waste prepa- ration and separation stage is based on the principle that inorganic materials, such as metals and glass, as well as organic materials, have a specific weight that is greater than [that of] water, while plastics and biodegradable organic matter have a specific weight gravity that is equal to or less than [that of] water.
The heavy components that sink to the bottom are separated from the organic stream. These include ferrous metals, nonferrous metals and glass.
These materials travel down a processing line, where they are separated by a number of methods, including magnetic force, eddy current, shredders, screens and hydrocrushers. The remaining materials are returned to the water vat and go through the light materials process.
The light organic waste already separated from the heavy components is transported by conveyor into a pipe, where it is washed by strong water streams. After rough screening, the smaller elements are channelled to a hydrocrushing unit.
Larger items go to a sorting conveyor, where the polyethylene terephthalate and high-density polyethylene are screened out manually – the metals by magnets, while the film plastic is blown out by an air sifter. All the other waste goes into a rough shredder and then the hydrocrusher.
Biodegradable material enters the filtering systems where residual contaminants are filtered out. The grit, sand, broken glass and small metal elements are screened out using a settling vat. Larger elements enter a secondary air sifter and are either returned for a second cycle in the system, or expelled from the system for landfill.
The remaining energy-rich organic watery solu- tion, referred to as biological soup, contains bio- degradable material, organic matter and paper that can be treated in the bioreactors to yield noncontaminated fertiliser, water and biogas.
During the biological reaction, the fluid undergoes another two processes, which are orchestra- ted through naturally occurring microorganisms.
In the first bioreactor tank, acidogenic fermentation transforms complex organic material into simpler organic acids and fatty acids. This acid-rich organic matter is heated to between 36 ˚C and 40 ˚C and transported to the methano- genic fermentation reactor for anaerobic degradation of the organic materials and the generation of clean fertiliser, water and biogas.
“Some of the biogas is used for energy needs and for heating the methanogenic tank and the rest is sold as ‘green energy’. Fertiliser is sold to farmers and nurseries and the water is purified and sent back to the beginning of the process,” says Ben Ami.
He concludes that the environmental aspects of this system include no carbon pollution, no unpleasant odours, the ability to treat excess water to municipal standards, and the production of a high-quality organic fertiliser.