Published in frozen food europe 9,10/2015 Can leftover food and food waste only be collected in wet waste garbage cans or are there other al-ternative systems? Which benefit do they offer a kitchen chef and what does it cost? Can he pre-treat his industrial water before discharging it into the sewage system and therefore save money? There are isolated systems for the treatment and storage of leftover food; industrial water can be recycled. But: how fast will the investments pay for themselves?
Waste water and leftover food (waste from the production of food and leftover food from plates) are valuable recyclable materials for operators of biogas plants, however for cooks they are frequently a smutty topic. It is uncomfortable for them to deal with it. It entails costs and above all, gets on their nerves when food controllers or water authorities not only criticize them, but also impose fines. But: even though this discussion is very unpopular, it is mandatory because cooking is inseparably connected to leftover food and waste water and can pollute the environment considerably. That’s why efficient and environmentally friendly solutions are absolutely essential.
Recycling Carts – Alternative Systems
Many cooks collect their production waste and leftover food in wet waste garbage cans, whose handling causes substantial costs and whose storage and collection are often borderline in hygienic terms. Simple wet waste systems will frequently pay for themselves within about four years already after several hundred meals a day.
Homogenizing Pumping Systems
Homogenizing pumping systems are isolated systems like the vacuum suction systems mentioned be-low, but technically significantly easier. Pipes connect the storage tank to the input station, which is frequently placed in the scullery. Its cutting unit chops up the leftover food (also hard materials like bones) into small particles and thereby reduces the volume of wet waste by down to 50%. Liquid is necessary for this, which comes partly from the chopped cells and partly from infiltration water (5 to 10% of the volume of the wet waste), which is fed in. The viscous suspension that comes from the biomass is fed into the tank by the pump, which is also housed in the input station. It is stored there in it uncooled until it is emptied – but usually not longer than six weeks. Then several input stations can be connected to each other, if they are not set too far apart. A system, which consists of an input station, tank, and piping costs c. 20,000 €, not including the installation, which costs approximately 2,000 €.
These systems also have a central tank. It is connected to one or several input stations for leftover food with piping. These can be set several hundred meters wide apart without a problem. This system is also isolated. If a filling hopper should be emptied, the system builds up a vacuum, which pulls the leftovers into the tank immediately at the touch of a button, and with relatively little energy. A large dough hook churns the substrate steadily until the tank is emptied; it doesn’t have to be either cooled or mixed with water. The investment costs of a system are between 80,000 and 500,000 € depending on the size of the tank (>3 m3), the number of input stations, the length of the piping, and the structural conditions.
A Look Behind the Scenes of a Large Kitchen
As an example, let’s imagine a large central kitchen in Southern Germany, which delivers meals to 120 branches on 365 days. The kitchen team produces for them 650 portions of breakfast and supper as well as 1,100 dinners per calendar day. The disposal is organized in the following way: there is a vacuum suction system with a 3 m3 tank installed in the operations (investment volume incl. chipper for vegetables, stalks, etc: 120,000 €). The grease interceptor also holds 3 m3. The branches collect their leftover food in garbage cans. Presently, the kitchen chef has to spend just under 12,000 € per year for the disposal of wet waste and around 14,000 € for waste water including emptying the grease interceptor. The contracts run from three to five years. Afterwards, he issues new tenders for the entire package. Currently, he pays 68,50 €/m3 for the bulk material from the tank. The difference between the offers is 1.50 €/m3 – an extremely low value, which points to forbidden cartel agreements. In addition, a number of providers bill the traveling time separately. The price margin is larger with the disposal of wet waste; currently, emptying a 120 l garbage can costs 12,80 €. Projected to a cubic meter, it is therefore 56% more expensive than that of the tank. The grease interceptor is emptied once in a quarter. The kitchen chef has to pay 60 €/m3 for that. It is decisively important for the kitchen chef that the manufacturer of his vacuum suction unit offers an efficient 24 hour service all year long. Because: if the unit breaks down, no wet waste can be disposed of. From the experiences of the kitchen chefs, the unit is relatively sensitive and breaks down time and again.
Leftovers – Valuable, Recyclable Materials for Biogas Plants
Biogas is a mixture comprised of methane (< 60%) and oxygen. It is manufactured in biogas plants from the biomass of annual plants and organic waste like, for instance, leftover food. This so-called “suspen-sion” is cut up into small pieces in the first step and yields dry matter of 25%. In the second step, the solids, which are larger than 12 mm, are sorted out, in the third step the fine particles, which are more than 1 mm. In a fermentation process under exclusion of oxygen, the mass is converted into gas or electric energy. This is either used for itself and/or fed into the public supply network. The residual mass of this process that cannot be used anymore is used as high-grade fertilizer in farming. Whoever would like to have their leftover food processed in a biogas plant, has to pay c. 40 € a freight ton for this. That is approximately the content of 7 to 8 wet waste garbage cans at 120 l.
Waste Water – Very Dirty Water is Wickedly Expensive
A kitchen operation in a German metropolis discharged 10 m3 waste water daily into the sewage system in the past few years. In a week, it exceeded the limiting values of admissible lipophilic (fat-soluble) substances by 50 mg/l on all days. It had to pay a surcharge for heavy polluters of 17,000 € for this. This example shows the great importance of the topic “waste water”.
Water protection is not only in the European Water Framework Directives, RL 2000/60/EG, but is also regulated in many national laws, standards, and other regulations. In Germany, the municipal waste water regulations for work in commercial kitchens are crucially important. The representatives from regional authorities (for instance, cities, communes, or regional districts) are particularly vigilant in this matter, because they have treat their sewage systems with care due to their often very dilapidated condition. The sewage systems, in particular, are only seldom up to date and cause considerable costs. Due to their bad condition, they often can’t bear any additional strain, which arises, for instance, by cleaning agents, but especially by fat and lipophilic substances. Emulsions, in other words fine mixtures from liquids like dressings, soups, milk or sauces are particularly critical. They form small fat droplets, which disperse in water and usually pass through the grease interceptor. In Germany, the limiting values for the discharge of these lipophilic substances are generally 250 to 300 mg/l waste water; some municipalities require clearly lower values, for example, 100 mg/l. In these cases, the grease interceptor alone can’t usually solve the problem anymore. In order to be able to discharge the waste water into the sewage system in the required or even in a clearly better and therefore cost-cutting quality in spite of these problems, it has to be pretreated, for instance, in mechanical or chemical flotation systems, biological alternative treatments, or neutralizing systems, which are placed mainly between the grease interceptor and the connection to the sewage system.
This issue arises presumably not only in Germany but in many Europe countries. That’s why it is mandatory that every commercial kitchen discharges its waste water into the sewage system solely with a grease interceptor, which withholds animal and vegetable fats and avoids odor accumulation and corrosion. In Germany, the authorities control discharging rigorously and recognize very quickly if a kitchen violates the rules. Whoever doesn’t adhere to the specifications, has to pay considerable penalties (see above). Grease interceptors have to be serviced annually and undergo a general inspection every five years. These technical examinations are to be documented in the operations diary as well as each emptying of the system.
Providers of Systems for the Disposal of Leftover Food
Bendig & Krause, http://www.abfall-ade.de
Rothenburg / Müller-Jessen, http://www.rothenburg-gmbh.de/wet-waste-disposal-systems.html