A few years ago, when the City of Oslo set bold new climate targets of halving CO2 emissions from the 1990 level by 2030, rubbish collection was identified as a major challenge standing in the way of achieving the target - not just because waste disposal contributes to CO2 emissions, but because source separation is a proven method of increasing environmental awareness.

With the exception of separate paper, hazardous waste, metal and glass collections, all household waste was sent for incineration in the domestic plants of Klemetsrud and Haraldrud, or plants in Sweden. A major expansion of district heating in Oslo from the two waste incineration plants was needed in order to meet the target of halving. It was therefore decided to increase the waste incineration capacity of the Klemetsrud plant with a third furnace and to speed up expansion of the district heating distribution network. Considerable increases in source separation and recycling, particularly of all plastic and organic food residues, were needed. But the challenge was to achieve this in existing housing without burdening yards and streets with additional waste disposal containers.

Experience from other Optibag plants
EnvacOptibag’s system of source separating waste into different coloured bags for subsequent optical separation in a central facility had already been operational at various sites in Norway and Sweden for several years. Pre-separated waste in different coloured bags are deposited in a common container or in existing rubbish chutes, eliminating the need for extra storage space for the fractions.

Containers are then collected in the conventional way and transported to the separation plant. The Optibag system can also be combined with Envac’s underground waste transport system, enabling the use of a single inlet for several fractions. An example of this is found in the northern Norwegian town of Tromsö, as detailed in Envac Concept No. 2:06. (see www.envacconcept.com)

Based on experience from Optibag facilities elsewhere in Norway, the City of Oslo’s optical sorting system was implemented on 1 October 2009 with a pilot study in which 20,000 households started to use source separation of food residues and plastic. The first ordinary rollout to 20,000 households started in October 2010 and has since continued at a rapid pace. Since then, 20,000 new households a month have been provided with bags and information materials. Two types of bags are being distributed to households - blue bags for plastic and green bags for organic food residues. All other waste is placed in ordinary plastic bags or loose in the rubbish bins.

The optical separation plant in Haraldrud separates 30 tonnes an hour with a cleanness requirement of 97% and a separation requirement of 95%. The blue bags with plastic are sent for plastic recycling and the green bags with food residues are currently sent to a biogas plant in Vänersborg.

High source separation motivation
“Households have been highly motivated to start separating waste into the coloured bags,” says Jannicke Gerner Bjerkås, communications manager at Energigjenvinningsetaten EGE (energy recovery department). “Quality varies a little from area to area, so in some areas we need to distribute more information.” The City of Oslo waste management department is responsible for informing the public, distributing coloured bags and collecting mixed waste, while the EGE is responsible for the separation and recycling of waste. “We will reach full capacity of 100,000 tonnes per annum in our existing Optibag plant in Haraldrud on 1 November 2011. At the beginning of June 2012, the next Optibag plant in Klemetsrud will be fully operative,” says Petter Thorbeck, project manager for the separation plant at EGE. The Klemetsrud plant will have the capacity to separate 50,000 tonnes of waste a year.

Biogas for the vehicles
At the same time, EGE is building a biogas plant in the Municipality of Nes. The plant is designed for 50,000 tonnes a year and will only break down food residues that can be converted into biogas cleaned for vehicle biogas and residues used as bio-fertilizers. Consideration is also being given to constructing a plant for the production of liquid biogas to facilitate distribution.

Good example for other towns and cities in the world The Optibag system is a central element of the City of Oslo’s waste disposal system and an important part of achieving the city’s environmental targets. No other large town has consistently invested in optical separation more than Oslo. Many towns and cities around the world face similar challenges, implementing source separation in existing buildings without additional storage facilities. Therefore, experience from the full scale expansion of Optibag for 600,000 inhabitants and 340,000 households in Oslo will be of great interest to many densely populated and climate conscious cities. “And so far, things have gone very well,” says Jannicke.

The system
Households and other users, such as restaurants, shops, etc are provided with coloured bags. Each colour corresponds to a waste fraction, e.g. green is for food residues, red for paper, yellow for paper packaging, blue for plastic and orange for residuals. All waste bags are deposited in the same waste chute/bin/container. They are then collected by an ordinary refuse collection vehicle and taken to the Optibag plant.

The mixed waste bags are emptied into reception pockets and transported by conveyor belt, where the separation process starts. Until then, no bag separation is performed.

Once on the conveyor belt, the bags are automatically sorted using camera technology that recognises the colour of the bags. The bags are transported to a rejection device that recognises the colour and a rejection paddle removes the bags to an underlying conveyor belt.

The belt carries the sorted materials to containers, container compactors, ball presses or to other forms of processing.