Biogas plant – biowaste management

In recent years, the problem of increasing the amount of waste generated has become more and more important. The economic factor has a large impact on the increase in the amount of generated waste in households. After the introduction of selective biowaste collection, biogas plants will be one of the ways to process them.

Food waste – the problem of their reduction and management is raised by numerous global and local NGOs.

Poland is at the forefront of this disgraceful classification and we are in the 5th place (2017) of 9 million tonnes of discarded products and consumer raw materials. Each year, an average family of four loses about PLN 2,000-2500.

According to the Act of 14 December 2012 on waste (Journal of Laws 2013 item 21), waste is defined as “any substance or object which the holder discards or intends to discard or is required to discard.” Mixed municipal waste, on the other hand, is defined as “mixed municipal waste, even if it has undergone waste treatment operations that have not significantly changed their properties”. On the other hand, food waste usually includes overdue products, catering remnants, as well as parts of products and post-production residues withdrawn from sale. These wastes are characterized by specific properties and require proper management. It was calculated that in 2017, due to “wasted food”, the value was about EUR 14.5 billion for Poland alone. A value not so much puzzling as it is embarrassing. Wasted food accounts for 8% of greenhouse gases, and 9 million tonnes of wasted food in Poland is also harmful greenhouse gas emissions to the atmosphere. According to estimated estimates for 2017, the equivalent of the total carbon dioxide emission of all passenger cars traveling on Polish roads – about 22.77 million tons of CO2.

Biogas plants will be an increasingly needed element of the energy market and waste utilization in Poland. The implementation of biogas plants is a very sensible move both in economic terms and for the sake of ecology.

If you want to produce biogas, first of all you have to think about whether we have enough substrate. It would be best if we produce this green energy, use waste that arises from our main production, eg food.

Biogas is obtained in the process of anaerobic digestion of plant biomass, animal waste, organic waste or sewage sludge. It should be remembered that biogas is a gas mixture consisting mainly of methane and carbon dioxide, as well as some impurities in the form of hydrogen sulphide, nitrogen, oxygen and hydrogen. The composition of biogas and its calorific value depend on the substrates used for its production.

Each of the installations used for biogas production is characterized by an individual design, adapted to different composition of the batch material. By producing biogas we can use, among others, waste from the food, dairy, sugar, pharmaceutical, cosmetics, biochemical, paper and meat industries. Biogas is also produced from animal waste, plant debris, grass clippings and waste or food scraps. For the production of biogas you can also use target crops, so-called energy crops such as: grass, clover, potatoes, corn, oilseed rape, sunflower and others.

In most existing biogas installations, the basic substrate is maize silage. But due to its high price, alternatives are sought for it like grass silage and waste from agro-food processing.

Regardless of the substrate, its degree of fermentation and biotransformation of organic compounds in methane is important. This is helped by hydrolytic enzymes that accelerate the distribution of large particles into substances with simpler structures, facilitating their absorption and conversion into methane by bacteria.

Bacteria secrete enzymes and thanks to them obtain the necessary substances. Initially, they break down macromolecular proteins, peptides, polysaccharides to simpler compounds that change into organic acids, alcohols, aldehydes, and these in turn are converted into biogas components: CH4, CO2, O2, H2S and others.

Providing raw material for biogas plants should meet the basic criteria:

the region intended for obtaining the raw material should not be too large
effective transport logistics,
the obtained raw material should be suitable for biogas production, so as not to transport raw material with a low content of organic dry matter, important due to the production of biogas,
the individual raw materials obtained should come from one place in sufficient quantity to secure effective transport through large-capacity vehicles.
From the point of view of the input raw material, there are basically two main types of biogas plants: a biogas plant intended for the processing of deliberately grown biomass and a biogas plant intended for the processing of agricultural and municipal waste.

In the case of a “waste” biogas plant, you can count on waste from maintaining public green areas (except for wood):

household waste
garden waste,
food products after their shelf-life
bio-waste from supermarkets,
wastes from the food industry (bakeries, distilleries, sugar factories, breweries, meat plants), waste from farming of commercial goods (liquid manure, manure, bedding, poultry droppings, etc.).
The minimum amount of material required to operate the biogas plant is 10 t / day, however, only from 20 t / day the biogas plant is profitable. This stock should be properly selected, because the appropriate ratio of nitrogen and phosphorus organic substances should be maintained: CHSK: N: P – (300 – 500): 6.7: 1 and the amount of organic dry matter and humidity.

Due to this, information about suppliers from whom the input raw material will be collected should be obtained already at the design stage, or the working media used by the supplier should be agreed to enable the waste to be processed in the anaerobic digestion process.

All input raw materials should be adequately pre-prepared (eg bones should be ground into meat-bone meal), raw materials requiring sanitization should be in accordance with the applicable legislation hygienized before entering the biogas plant.

If the input raw materials contain large amounts of nitrogen, there is a risk of ammonia forming, eliminating the necessary bacterial flora. Liquid manure and sewage usually contain little dry matter, poultry excrements contain little organic dry matter (poultry also adopts sand and plaster with food) and antibiotics (compound feed ingredient), which may disturb the bacterial flora, so pig waste may contain disinfectants, threatening the regular movement of the biogas plant. A very valuable energy input is a fat-containing mass, however, it should not be the only raw material. It is necessary to pay attention to the sulfur content in these wastes, eg in waste from the dairy industry, in distillery vats and in the waste from breweries there may be sulfur compounds. Biogas plant, in which the bacterial flora is subject to liquidation creates major problems. The entire content of fermentation tanks is in this case dangerous waste, which is subject to applicable law in the field of hazardous waste management.

The biogas plant should be built in such a way as to ensure adequate conditions for the development of anaerobic microorganisms that progressively degrade the organic mass to biogas:

humid environment
preventing air access,
preventing light access,
constant temperature,
pH value,
supply of nutrients,
large contact surfaces,
loading of the fermentation space,
even substrate delivery,
degassing the substrate.
A large number of different biogas plant solutions can be reduced to several typical technological solutions, varying depending on:

charging method (dose, flow),
the production process (one-stage, multi-stage),
substrate consistency (solid, liquid).
The structure of the main elements of the biogas production line should include:

source of organic materials,
acceptance and pre-preparation of material,
anaerobic fermentation tanks for liquid material,
biogas tip,
Mud tip.
Currently, designing a single-stage biogas plant is not profitable. The optimal technical solution for a waste biogas plant is a two-stage biogas plant with a computer controlled process of dosing and mixing of the input raw material, with a continuous supply of input raw material and collection of solid residue after the fermentation process. For the first stage of biogas plant, horizontal or vertical fermentation tanks are used, with both types having their own advantages and disadvantages.

For the second stage of biogas plant, mostly vertical fermentation tanks are designed. A very important factor is the planned retention time of the raw material in the tank, which then results in the calculation of the dimensions of the fermentation tank. In agricultural biogas plants the retention time of the raw material is on the first stage of 30 days, whereas in waste biogas plants this time is up to 100 days. The retention time on the second stage is even longer, although the biogas yield from the second stage is only 10-20% of the total amount of biogas produced, which in turn requires a large built-up area and investment funds. Only in this way can you build and operate a well-functioning biogas plant, which is not a source of odor, stable performance and quality end product, not only in the form of biogas, but also organic fertilizer. Mud tip is intended for a fermented residue from the second stage. The digested mass is then dewatered and transferred for ripening in the composting process.

It is only in this way that the prepared material can be used as an organic fertilizer, provided that the requirements for limit values ​​of heavy metals are met. This problem can be solved only through the required quality of the input raw material. In a regularly operated biogas plant there are no problems with material hygienization.

Ways of using biogas energy:

direct combustion (cooking, lighting, cooling, heating, drying, heating of drinking water, etc.),
electricity production and heating of a heat conveyor,
electricity production and heating of a heat conveyor, production of cold,
drive internal combustion engines or turbines to obtain mechanical energy,
use of biogas in fuel cells.

At present, cogeneration of heat and electricity is one of the most typical ways of using biogas not only from biogas plants, but also on landfills for municipal waste and on silt tip in sewage treatment plants. The electrical efficiency of cogeneration units is usually 35-45%. Part of the heat produced can be used to maintain a constant temperature in the fermentation tank, in the case of a thermophilic process (55 ° C). The biggest problem regarding the use of heat is low gas temperature and a large distance from potential heat consumers. The temperature of cooling water from the cogeneration engine is ca. 90 ° C, after reaching the heating network only 80 ° C. Water can be heated using the produced gas, however, close to the biogas.

The economic aspect of waste processing is one of the most important parts of waste management system planning.

There are two types of income for biogas plants: income from marketing and income related to the disposal and disposal of waste.

The by-product of the biogas plant is a liquid fertilizer phase in the form of a liquid stable fertilizer with a similar effect. If the biogas plant does not have its own agricultural land on which this fertilizer can be used, it should cooperate with farmers.

Due to the requirements of the EU Council Directive 1999/31 / EC “regarding landfills” in relation to the acceptance of biodegradable waste in landfills, it is obvious that in the near future facilities for the treatment of biodegradable waste will be designed and built. One of the most perspective, though at the same time, most expensive options is a biogas plant. Biogas plant is a complicated and expensive device and when designing it is necessary to take into account not only the possibility of obtaining subsidies, but also the quality, availability and quantity of input material, resulting in specific technologies and exploitation possibilities, mainly related to the sale of biogas and manure . Even partial errors in the design can lead to deterioration of operating parameters, to unpleasant odors, disruptive to the environment, unstable biogas production, problematic or even impossible use of residues from the fermentation process and, finally, losses worth several million. Regularly conducted biogas plant is not a source of undesirable odor, characterized by constant efficiency of quality biogas.

Examples of biogas plants in the Kujawsko-Pomorskie Voivodeship

At Torun, a biogas plant is located in a landfill. The landfill has been closed since 2009 and the only activity being carried out there is the recovery of landfill gas. The released biogas is burned in three kogenetrators with a total power of 1324 KWe (thermal and electric energy is generated). Up to 82 biogas wells have been built for biogas intake. At present, this installation is ending its operation.
The agricultural biogas plant in Starorypina, operating since 2013, has a capacity of 1.9 MW. The local farmers use the biogas plant in Starorypina because it created very good cooperation conditions for them. For the hosts who sign a contract for the cultivation of maize with it, the company “Biogazownia Rypin” guarantees seeds, sowing services, harvesting and transport of collected raw material. And also, very importantly, the farmer is guaranteed a minimum price of corn before signing the contract. Pig breeders no longer worry about unpleasant odors released during the slurry spreading on the fields, because the biogas plant uses it for the production of biogas, and gives off the fermentate substrate without odor. The nearby town of Rypin also benefited from the creation of the biogas installation in Starorypin. Its owners have built a heat pipeline at their own cost, connecting their biogas plant with the Rypina heating network, which belongs to the Miejskie Przedsiębiorstwo Energetyki Cieplnej. Thanks to this, heat produced from biogas is used to heat many buildings in Rypin.

A cogeneration biogas plant with an electric power of 1.36 MW and a thermal power of 1.54 MW. The installation was located in industrial areas (after a former sugar factory) in the town of Mełno. The project has achieved tangible benefits for the Investor himself as well as for the socio-economic environment with which he operates directly.
Biogas plant in Liszków, commune Rojewo, Kujawsko-Pomorskie, with the planned total installed capacity of 2,126 MW and a total area of ​​2.3 ha. At present, the owner of the facility is an energy company ENEA. The technology used in the biogas plant comes from the German company Schmack Biogas AG. Designed by Aufwind as intake for corn silage, it currently produces energy from waste.
Bioelektrownia Buczek Sp. z o.o. started operations in the field of electricity production and waste utilization in 2014. Currently, the start-up phase has been completed and electricity production is at the level of 80 – 90% of the nominal power (1.8 MW). It operates based, inter alia, on the decision of Starosty Świecki of November 13, 2014 within the scope of the integrated permit for waste neutralization and recovery; Decision No. 38/2014 of the District Veterinary Surgeon in Świecie of 23/10/2014 in the field of processing animal by-products in biogas using pressure sterilization.