The Budapest South wastewater treatment plant in Budapest is one of the most self-sufficient in the world – fueled by sewage sludge and easy degradable biowaste.
Nowadays, some wastewater treatment plants don’t just stick to treating wastewater, they also produce resources such as recycled water, fertilizers for agriculture and green energy. Veolia’s Hungarian subsidiary, Budapest Sewage Works (FCsM), has developed an ingenious co-digestion system that has increased its production of biogas and made it almost completely energy self-sufficient. Here’s how...
Budapest South is a wastewater treatment plant that serves a population of 1.8 million and has been using sewage sludge to produce biogas for more than 50 years. In 2004, Veolia decided to improve the site's energy efficiency and so maximize self-sufficiency. But there was a problem - the quantity of organic matter available on site was not sufficient to achieve the objective. New sources of biowaste were needed.
Industry, supermarkets and local restaurants all produce large quantities of organic waste – and they don’t know what to do with it! Unsold food, production waste, used cooking oil and fat... the solution was obvious: recover this waste, mix it with sludge to feed the plant digester and produce more energy through co-digestion. But the challenge lay in finding a way to efficiently treat the still packaged out of date food products that can’t be put in a digester as they are. Moreover the unpacked product and also other organic wastes has to be prepared for co-fermentetion, they cannot feed directly into the digesters.
Still in its packaging, but recyclable
In order to solve the associated problems, Veolia developed and patented an innovative technology that separates the organic waste from its plastic packaging (inert material), called Ecrusor. Installed in the Budapest South plant in 2007, the Ecrusor system grinds and sorts biodegradable waste to produce biogas through anaerobic digestion. It separates liquid and solid organic waste (out of date food products, unused ingredients, kitchen waste, etc.) from the packaging and transforms it into a homogeneous paste suitable for digestion and easily mixed with the sludge. The packaging residue is chopped up for incineration or landfill storage.
The results are telling - electricity consumption in the Budapest South plant fell 20% and more energy in the form of biogas is recovered. The plant, which now generates four times more biogas (from 6,000 to 24,000 Nm3 per day) than before, also produces three times more electricity (from 4,500 to 14,000 MWh per year) making it in average 90% energy self-sufficiency. In the low consumption period of the plant the produced electrical energy is more than the electrical consumption of the plant, so from middle the middle of 2016, the extra biogas do not need to flare, but the extra energy above 100% can be sold and it is fed into the national electrical grid, which makes further significant savings for the company.
Main picture: Phototheque VEOLIA - Stéphane Lavoué