Berrysmith Foundation

Proposed food waste management system

The food waste collection and treatment system recommended by the Berrysmith Foundation comprises the following elements:

  • A household wheeled bin designed for aerobic composting, with a kitchen caddy, composting liners for the caddy, and carbon based material for addition to the caddy or bin to ensure aerobic composting is achieved.
  • A reduced pick up cycle of pre-composted material (timeframe subject to trials and could be 12 weeks and up to six months)
  • Disposal of partially composted material to a composting plant for finishing

The Foundation notes that the Council organic waste assessments did not identify the wheeled bin composting system as an option for increasing times between collections and pre-treating material; Bokashi is mentioned in brief, but is not explored in detail. Aerobic composting bin systems are available internationally and Council needs to consider this option for management of the future food waste collection.

There are a number of options available for both collection and storage of food waste which need to be explored in more detail and trialled to ensure the approach is optimal for achieving necessary behaviour change and maximum diversion rates. The basic system is detailed below, and options identified.

Pre-composting system

Wheeled composting bins

The proposed bin is a 120-140 litre composting wheeled bin, such as that designed by Sulo or ssi-Schaefer. These bins are a standard part of the range provided by these companies and are formed from injection moulded plastic. They look very similar to the Council’s existing wheeled bin stock. They include air vents and a base plate, which allows for the material to remain aerated, aiding break down of material and moisture loss.

The bins range in size and the ideal capacity is to be determined. However, a smaller capacity bin is recommended to avoid its use for garden waste material and to allow for handling over a 12 week period.

The image below provides an indicative view of a compost wheelie bin, showing layers of material.

Composting Bin Cross-section

For further information on wheeled composting bins refer:

Kitchen Collection

The collection system proposes to offer each household a kitchen caddy with compostable bin liners to support maximum rates of diversion of food waste. According to the background studies prepared for the Auckland Waste Assessment report, the option which provides for the highest rates of diversion includes both a caddy and liners.

A trial undertaken by Christchurch City Council prior to the establishment of its organics collection system found that the frequency of plastic bag contamination fell once each household was provided with BioFilm bags. That trial found that the most common reasons given for preferring the BioFilm bags and green ventilated kitchen bins were: no smell, no mess, fly proof, no condensation or smelly liquid in the bottom of the bin, no need to clean the bin each time it was emptied, the bin looks better in the kitchen, the bin was easier to use, and the kerbside bin was cleaner.

Kitchen bin liners are to encourage use, and to avoid cross contamination of the waste stream with plastic bags; to avoid perceived 'mess' households are likely to introduce plastic bags to the food waste stream. Council needs to make available approved bin liners, which are clearly distinguishable as such. These could be supplied direct to households, or made available via retail outlets.


The kitchen caddy can either be in the form of a sealed caddy (with or without a liner) or a vented unit (which requires a liner) that allows for moisture loss. Using the breathable system the water content of kitchen scraps can be reduced by around 20% in 14 day period, reducing weights for collection.

Options need to be explored to determine which system results in the greatest diversion rates, as well as the number of bags required by households and the best way to distribute them.

The image on the right is of the vented kitchen caddy with breathable liner, which is recommended for achieving maximum diversion rates.

Carbon material

To create suitable conditions for pre-treatment of food waste material and to minimise the potential for odour generation (due to anaerobic conditions), households would be provided with high carbon dry matter to add to the collection receptacle. This provides an aeration medium to ensure aerobic (and odourless) conditions are maintained.

The amount of material to be added will be determined to ensure correct aeration and the stage at which it will be added (i.e. in the kitchen caddy or in the main receptacle would be determined based on household behaviour, as well as the type of collection system used in the kitchen).

How this material will be made available to households will also need to be worked through; this may be by request, via retail outlets or as allocation made during bin collection.

Collection regime

A household collection timetable of every 12 weeks is proposed, with bin capacity to allow for 24 weeks material storage. Over this period much of the material in the bins will be composted, with only the faction nearer the top of the bin requiring further composting treatment.

Background studies to the waste plans appear to follow overseas models where weekly pick up of food waste only is considered the 'best' model for processing efficiency. However, this model is most efficient for processing of food waste by anaerobic digestion; a process that is not likely to be cost effective in Auckland. Therefore, weekly pick up becomes less suitable due to collection logistics and the availability of treatment locations.

A more frequent collection regime for food waste than for general waste is shown to improve diversion rates. However, background studies do not appear to consider the impact of diversion when direct versus indirect costs for collection, as are proposed in Auckland, are applied. Therefore, it is possible that a similar or less frequent collection cycle can result in increased diversion when combined with pricing incentives. This is particularly the case when issues associated with management of the bin system are taken into account.

A weekly collection regime of wet organic material, as currently proposed, will result in householders needing to clean their bins regularly to remove kitchen waste remnants. A pre-composting system with less frequent pick up results in drier material, and a reduction in wet and odorous bin residue, as well as reduced bin cleaning requirements for householders.


Research undertaken in the preparation of this submission has found no use of pre-composting systems in the municipal collection of food waste. The most obvious comparison to the proposed system is use of the EM (effective microorganism) Bokashi systems, which are utilised in some municipalities, and most notably in Korea and Japan, although extended collection regimes do not appear common.

In 2002 the Christchurch City Council trialled the use of a Bokashi system for kerbside collection. Waste was collected weekly, and the comparison was for waste to be collected using bio-insert bags. The Bokashi system was reported to have worked well. However, at the end of the trial the bio-insert bag option was favoured due to the fact that collection bins remained cleaner and more hygienic looking.

A 2007 report by the New South Wales Department of Environment and Conservation reviewed food and organic waste collections in a number of jurisdictions in Australia, Europe and North America. This report includes details of the use of aerobic bins, which have been trialled in several areas including Bexley, UK and Broken Hill, Australia.

The Bexley trial concluded that the aerobic bins offered a clear performance advantage over other tested systems. The bin supplied adequate ventilation for aerobic decomposition and drying of the added organic materials while in the standard bin, anaerobic conditions were prevalent. Significantly higher rates of weight loss were observed with the bio-insert (aerobic bin) in winter, spring, and summer compared to the standard bin. Further, the contents of the bio-insert bin were less compacted, drier and more uniform than the contents of the standard bin. The better condition of organics collected in the bio-insert were considered likely to cause fewer problems for compost facility operators receiving the feedstock.

The trial also concluded that while a collection frequency of four weeks was feasible for green organics, if food organics was also collected, a two week collection frequency was recommended to prevent the build up of excessive leachate and odours.

The Broken Hill trial also used a bio-insert bin, and collected food waste weekly. The Council found that residents did not need to put the bins out weekly as there were no reports of odour, and waste volume was quickly reduced. A fortnightly collection regime was recommended.

The waste disposal agent, responsible for collection and treatment of the organic material, reported being impressed with the results of the Bio-insert, stating that it assisted the composting and vermiculture operations because material was delivered in an aerobic state.

The trials indicate a clear advantage of the use of an aerobic bin for collection in terms of condition of material, weight loss, and reduced odour. With the addition of carbon material, this scenario is expected to improve further and use of a pre-composting system warrants further investigation and trial.

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