An international organic food waste system in “Full scale co-digestion of waste water sludge and food waste: Bottlenecks and possibilities” by D. Bolzonella, J. E. Drewes, K. Koch, L. D. Nghiem (2017) refers to a case study in Oberding, Germany at a ‘centralised food waste processing plant’ discussing the challenges and opportunities to the system. Back in Australia, my current workplace, Hornsby RSL Club, last month placed a Pulpmaster 5000 in there main back of house area. Being part of the system gives me a unique first hand experience.
Initially the Oberding plant was a treatment plant for ‘slaughter house waste’ from 1940 (Bolzonella, Drewes, Koch, Nghiem 2017). Not until 1995 did the plant begin to accept food waste (Bolzonella, Drewes, Koch, Nghiem 2017). In 2001 an outbreak of foot and mouth disease in the UK originally but fast spread to Europe changing Oberding pre-treated food waste to anaerobic digestion (Bolzonella, Drewes, Koch, Nghiem 2017). ‘Each year, about 10,000 t of expired food and 60,000 t of food waste from commercial customers e.g. restaurants, canteens and supermarkets are collected’ within a 200km radius of the plant (Bolzonella, Drewes, Koch, Nghiem 2017). ‘The average gate fee was 30 €/t (in 2016)’ (Bolzonella, Drewes, Koch, Nghiem 2017).
‘Oberding has a specialised fleet of trucks able to accommodate three different bin sizes (i.e. 120, 240, 1000 L)’ (Bolzonella, Drewes, Koch, Nghiem 2017). Customers can choose to have clean bins or use a bag system, the trucks are fitted with a high pressure water cleaning equipment attached to the truck (Bolzonella, Drewes, Koch, Nghiem 2017).
‘Food waste is unloaded to a live bottom feeder using customised fork lifts equipped with a tilting rack that can accommodate several bins together. The bins are automatically cleaned with high pressure water, then steam-cleaned on a conveying belt before returning to service. The mixture of water and food waste is macerated by a hammer mill. Plastic materials are removed by a drum sieve while other heavy inert materials (e.g., broken glass and ceramic, bones, metals) are removed by gravity. The plant operator estimates that inert materials account only for about 3% of the input. After maceration, the food waste slurry is transferred into a pressurised vessel where it is heated to 120 °C by steam for at least 15 min. The heated liquid food waste is then centrifuged for oil recovery. Some canteens and restaurants do not separate fat, oil and grease from food waste. Thus, oil recovery by centrifugation accounts for 6–7% of the total food waste input. The pre-treated liquid food waste is stored in insulated reservoirs and delivered to a number of co-digestion plants (including agricultural biogas plants) using tankers with insulation capacity to maintain a temperature of at least 90 °C.’
(Bolzonella, Drewes, Koch, Nghiem 2017).
Oberding Plant System Diagram (Bolzonella, Drewes, Koch, Nghiem 2017)
Not all parts of the process are possible to complete at the Oberding Plant however this excerpt above gives great insight into what’s in the process to treat and separate the organic food waste.
The only machine available from Pulpmaster is the Pulpmaster 5000 (Pulpmaster 2017). The machine is a little larger than a washing machine size with a connection to a tank that’s accessible via truck. The Pulpmaster converts the organic food waste into slurry. In the case of the RSL the tank is located in the loading dock, this is where patrons aren’t in contact with the tank in case there is an issue of smell or over flow. The Pulpmaster machine notifies the Pulpmaster office with an SMS or email when it reaches 80% full to schedule a truck to come pick it up (Pulpmaster 2017). Once the tank reaches 100% it will stop processing organic food waste until it is emptied. The truck transports it to a site where it is recycled.
Slurry Machine (McManis 2017)
Tank (McManis 2017)
Every day the machine is used. Its busiest periods are during lunchtime service 12pm – 2:30pm and dinner service 5:30pm – 9:30pm when the floor attendants are collecting plates. The chefs use the Pulpmaster throughout the day from their preparing of food to the end of the day when food service is complete at 9:30pm when they’re cleaning the kitchen.
The prep kitchen, the main kitchen and plate scraping for a day would produce 4 purple organic food waste bins each with a volume of 20L. Equalling about 240L. This doesn’t include the other café kitchen, tapas kitchen or functions. Taking the other kitchens into account the machine in one day would convert about 340L of organic food waste to slurry. Using the Calculator on the Pulpmaster website the total Greenhouse Gas Saved is 1027 kg.
Calculator (Pulpmaster 2017)
As a system it reduces the amount of organic food waste going into the bins with the general waste. However it does take staff a little longer for the plates to be scraped into separate bins but that little extra time saves the RSL the cost on the general waste bins. There’s a small margin in it but from an environmental point of view and ethical point of view The RSL is doing their bit to help.
The international example gives great insight into what happens to the organic food waste once it has been collected from the producer where as the local example shows what happens at a baseline level, what the accumulation is over a significant period of time? The other area that needs to be considered is at what point do you choose between the money it takes to service the organic food waste and the environmental gain? I believe many businesses are reluctant to invest in organic food waste management systems because the costs are too high. The reward of environmental benefit doesn’t out way the risk of debt.
(Bolzonella, Drewes, Koch, Nghiem 2017)
- D. Bolzonella, J. E. Drewes, K. Koch, L. D. Nghiem 2017, Full scale co-digestion of wastewater sludge and food waste: Bottlenecks and possibilities, Renewable and Sustainable Energy Reviews, Volume 72, May 2017, viewed 17 June 2017, <http://www.sciencedirect.com/science/article/pii/S1364032117300771>.
- Hornsby RSL Club 2017, Environmental, viewed 17 June 2017, < https://www.hornsbyrsl.com.au/environmental>.Pulpmaster 2017,
- Hornsby RSL Club 2017, Sustainability Policy, viewed 17 June 2017, <https://www.hornsbyrsl.com.au/files/site_uploads/Sustainability_Policy.pdf>.
- Pulpmaster 2017, Pulpmaster 5000, viewed 17 June 2017, <http://pulpmaster.com.au/products/pulpmaster-4000>.