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The main purpose of the publication was to show the differences in revenues, costs and profits when using manure directly as a fertilizer (after storage) or as a substrate for a biogas plant equipped with a cogeneration unit, and then using the digestate for fertilization purposes. The comparison includes cost, revenue and profit streams throughout the year. It also takes into account the introduction of additional co-substrates in order to increase the yield of biogas (biomethane), and thus the profits from the future investment. Forecasts of the profitability of biogas investments were presented, taking into account the reduction of greenhouse gas emissions, i.e. methane and nitrous oxide, which are several dozen or even almost 300 times more harmful to the atmosphere than carbon dioxide. The economic, energy and ecological accounts of manure management can serve as guidelines for pre-investment analysis when considering investments in biogas plants. In addition, the published data indicate that the energy management of cow manure is of great importance when estimating the carbon footprint of the entire dairy production. It should be expected that in the near future such solutions will become more and more popular almost all over the world. Input parameters of substrates, gaseous emissions and biogas (and biomethane) yields were obtained from own research (cow manure samples were taken from a working farm) and from literature sources, e.g. these were international and national IPCC (Intergovermetal Panel on Climate Change) protocols.

The amendment to the Polish Renewable Energy Act creates great opportunities for the development of the biogas market in Poland. Years of experience in biogas production in Western Europe and the development of biogas installations in Poland indicate the requirement to look for alternative substrates to those produced from dedicated crop production (mainly maize silage). Feasible solutions include the use of biodegradable waste from agriculture or industry as well as municipal landfill sites. The usage of these substrates in the methane fermentation process offers low cost, high biogas production and the safe management of biowaste. The arguments for using them in biogas installations are persuasive. This article presents new approaches of biogas plant installation solutions which allows for the effective fermentation of biowaste from animal and vegetable production, from the agro-food industry and from municipal waste

The research aimed to analyse the influence of diesel oil temperature on NOx emission level. The tests were carried out on a test stand equipped with a 9.5 kW multi-fuel compression-ignition engine. The stand is an experimental cogeneration unit discharging the produced energy into the power grid. The measurements were carried out under the D1 test procedure provided by ISO 8178-4 for testing engines operating at a constant speed. As a result of statistical analysis of the results obtained, significant differences were found in the u specific values of nitrogen oxides emission gained for particular phases of D1 tests, when the engine was fed with diesel fuel of different temperatures. The results obtained confirmed the possibility of limiting the specific emission of NOx only when the engine is running at 75% of its nominal torque. An increase in NOx emissions was recorded for the remaining loads.

Household wastewater is a problem, especially in areas with a dispersed settlement where there is no wastewater collection system or wastewater treatment plant. In this case, it is necessary to build a local or onsite wastewater treatment plant. This paper is an attempt to analyse the possibility of using recycled shredded ABS plastic (acrylonitrile butadiene styrene) as packing media in an experimental vertical flow filter for use in on-site wastewater treatment plants. Studies have shown that shredded recycled ABS is a promising filtration material that has several features important in the treatment process, like a large surface area, high mechanical strength and chemical inertness. The system was operated with a hydraulic load of 50 dm3/m2 (3 months). BOD5 (biochemical oxygen demand), COD (chemical oxygen demand), and total suspended solids (TSS) reduction efficiency in the primary effluent was high; 94.4%, 77.8%, and 92.8%, respectively.

In modern agricultural biogas plants, the biowaste are increasingly used for biogas production. Food waste are also widely used in larvae breeding. This is important because, based on biowaste, its proper management and green energy production is possible. This study aims to determine the biogas and methane efficiency of Hermetia illucens larvae that were fed using food waste. In the research on biogas and methane efficiency, Hermetia illucens larvae were used. The total solids (TS) of the substrate equals 30.35%, and volatile solids (VS) content was 92.31% of TS. The larvae were fed only by plant origin food waste. The obtained substrates were homogeneous. The experiment was carried out under mesophilic anaerobic digestion conditions – 39°C in the 21-chamber biofermentor set in the Institute of Biosystems Engineering in Poznań University of Life Sciences. The anaerobic digestion process in the batch reactor ran correctly. Fermentation inhibition was not detected. Biogas efficiency for larvae amounted to 198.75 m3∙Mg-1 fresh mass (FM). On the other hand, methane efficiency, amounted to 127.73 m3∙Mg-1, at methane concentration of 64.27%. Based on the research, it was found that the larvae feeding food waste can be used directly as anaerobic digestion in the bioconversion process.

The biogas production constitutes one of renewable energy sources (RES) . In addition, wastes are preferred for energy production. In the case of some wastes, e.g. poultry manure, it is difficult to conduct anaerobic digestion in monofermentation. The aim of this work was to plan the biogas plant, in which the main substrate is the waste from a poultry farm. The scope of work included: preparation of a biogas plant technological project, determining the amount of biogas and methane that can be produced annually on the example of the selected poultry farm, performing the energy and financial calculations for the current conditions prevailing on the renewable energy market in Poland. The installation project assumed the location of a biogas plant at an existing poultry farm – the source of the substrate. The micro-biogas plant includes a fermentation tank with a capacity of 500 m3 and storage of digestate pulp with a capacity of 700 m3. The assumed power biogas plant will generate 112 kW of electricity and 120 kW of heat. The installation will operate in a single-stage mesophilic technology (39ºC), which will avoid incurring additional costs related to heating and the construction of additional fermentation tanks. The use of poultry manure by anaerobic digestion provides benefits through biogas technology. It is necessary to examine the technology in terms of biogas production, which is carried out under better sanitary and environmental conditions. This work was undertaken to investigate the environmentally friendly removal of poultry manure through biogas technology to obtain the best economic effect, and employ it further, e.g. as a fertilizer.

The article discusses the impact of nutrients from sewage on the state of the sewage receiver. Bioremediation was carried out through the use of effective microorganisms. The potential recovery of valuable mineral and organic substances in the form of fertilizers was also examined. The Słoneczko Reservoir is a bathing area and serves many people in the summertime as a place of water recreation. Water quality deteriorated intensively from 2006 as a result of illegal wastewater discharge and the impact of fecal pollution from bathers. The high concentration of nutrients in the water was the cause of the eutrophication process and blooms of cyanobacteria, which pose a threat to human health in the bathing area. The bathing area was also closed many times by sanitary services as a result of exceeding the number of Escherichia coli and Enterococcus faecalis in the water. At the bottom of the reservoir, there was a layer of sediments with a thickness of 30&ndash, 70 cm. Thus, the processes of anaerobic decomposition generated odor, causing nuisance in the reservoir area. Water transparency varied from 30 to 50 cm, due to the accumulation of suspensions and biomass of planktonic algae. The reservoir was subjected to microbiological bioremediation in 2017 and 2018 to polluted water treatment and to reduce the organic content of bottom sediments. Already after the first application of biopreparations putrefactive odors and the eutrophication process disappeared at the end of the 2017 summer season. Bioremediation reduced the value of E. coli and E. feacalis to the acceptable level. After the second application in 2018, the organic fraction of the bottom sediments was reduced to a very low level and the water transparency reached the bottom (maximum depth was 2.2 m) throughout the entire bathing area. The effect of the water remediation was maintained until 2019, and the surface water quality remained at a very good level. An important aspect in this case is also the exploitation of bottom sediments, because they are rich in nutrients and organic matter, and therefore it may have some potential as a fertilizer. The recovery of nutrients can be used in plant or pot production. However, they contain compounds that degrade quickly, causing unpleasant odors and threatening the environment. Thus, they should be managed and handled in an environmentally friendly and sustainable way.

Barbotage reactors such as airlift reactors (ALR) and bubble column reactors (BCR), due to their two-phase flow systems, were investigated in many research papers. In their basic design variants, they are typically used to lift, mix, and aerate liquids, while, when equipped with additional elements in hybrid variants, their individual properties, i.e., lifting, mixing, and aeration of liquids, can significantly change with the same reactor geometry. The object of this study was to develop a hybrid barbotage reactor in various structural design variants. The structure consisted of a barbotage column of 50 mm in diameter, used to transport a water&ndash, air mixture outside the reactor (so-called external loop). The installation was additionally equipped with a nozzle in order to improve mixture aeration and circulation efficiency. The nozzle was mounted at various heights of the column pump segment. Additionally, the reactor was equipped with s moving bed in two variants (20% and 40% reactor capacity) in order to determine its effect on the mixture aeration and circulation conditions. Based on the measurement results, aeration curves were prepared for various structural design and column packing variants of the reactor. Properties of the two-phase mixture were determined for both parts&mdash, ALR and BCR. Technological and energy parameters of the aeration process were calculated, and the results obtained for the individual structural design variants were compared. It was found that, for the most advantageous design, in terms of aeration efficiency, the aeration nozzle should be placed in the mid-length of the pump segment of the barbotage column, irrespective of the hybrid reactor packing rate with the moving bed. The reactor packing with the moving bed resulted in a decreased mean water velocity in the reactor. For most analyzed structural design variants, the respective packing with the moving bed had no significant effect on aeration efficiency. Only for one structural design variant did the lack of packing significantly improve oxygen levels by as much as approximately 41%.

The aim of this paper was to determine the energetic and economic aspects of a 499 kW power biogas plant powered by substrates in three different scenarios: typical arable crops (maize silage), dedicated energy crops (sorghum silage) and agricultural waste biomass (maize straw). The obtained results show that methane productivity of tested substrates is closely connected with its dry matter content– which was especially significative in case of pig slurry (only 1.30 $\mathrm{m}^{3}\mathrm{C}\mathrm{H}_{4}$/Mg of fresh matter). In consequences methane productivities of tested substrates had strong influence on its masses needed for feeding planned biogas plant (from 11,250 Mg to 20,430 Mg). The research have shown the big differences of the substrates costs in analyzed scenarios: the most costly scenario II was over 180 kEuro more expensive than III scenario. Taking into account 15 years period of guarantied subsidies in Poland, this difference can reach in total 2.71 mln Euro.

The aim of the work was to compare composting technology and anaerobic digestion in the case of manure from dairy cows. The research was carried on the case study farm in Wielkopolska Region (Western Poland) specialized in milk production (600 cows). The results have shown that both analyzed scenarios can give the additional profits to a studied dairy farm. However, the anaerobic digestion can provide more than twice a higher profit (315.6 kEuro) comparing to the composting scenario (148 kEuro). In composting, the biggest part of the generated heat is lost and only 36% can be recovered, which influences on profit decreasing up to 75.5 kEuro (instead of 201.7 kEuro theoretically). The amounts of energy produced in anaerobic digestion technology by CHP unit is almost equal for electricity (1601 MWh) and for heat (1680 MWh). However, the electric energy has several times higher value than heat because of additional subsidies paid by the state.

Air pollution is the result of natural processes and intense urban development. The volatile substances undesired emission causes environmental threats such as acid rain, aggravated greenhouse effect or the ozone depletion. Moreover, the pollution released into the air are harmful to the human respiratory system, eyes and skin. This paper presents the body of analyses conducted in Poznań between 2015-2017 on the changes in the local emission concentration of PM10 and PM2.5. The data concerning the emission of suspended particulates were provided by the meteorological station on Polanka St. in Poznań. The research included correlation analysis. The results point to a steady decrease in the amount of produced particulates. It was also noted that the emissions of PM10 and PM2.5 change seasonally, with the highest levels in the autumn and winter. Furthermore, the amount of emitted suspended particulates is correlated with the temperature, hence it is supposed that the main source of air pollution in Poznań are low-efficiency heaters and boilers.

The interest in biogas production in Poland is growing rapidly. This is mostly due to the fact that there is a need for handling and managing the increasing quantities of diverse bio-waste generated by industry and agriculture. Therefore, good laboratory practices and correct preparation of batch tests are very important for planning of a full-scale biogas plant. The aim of the paper was to determine the effect of mixing in the laboratory batch reactors on the biogas yield of maize straw under thermophilic conditions. The scope of this work included: (1) the analysis of basic physical and chemical parameters and (2) laboratory determination of biogas and methane yield from anaerobic digestion of maize straw with different frequencies of mixing. The obtained biogas and methane yield from the thermophilic fermentation of maize straw mixed every day was 381.89 m3•Mg-1 FM and 184.97 m3•Mg-1 FM, respectively. The results of this study confirmed the effect of no mixing inside reactors. In the batch test a decrease in biogas and methane yields was observed, by approx. 60 m3•Mg-1 and approx. 28 m3•Mg-1, respectively.

Primary energy sources have limited deposits and their exploitation has a negative impact on the environment. Biofuels production is an efficient and profitable method of environmentally-friendly energy production in terms of economic reasons. In recent years use of renewable energy sources (RES) in the Polish energy balance can be noticed. The main sector in which can be observed a dynamic growth is the biomass market, with the solid biofuel market in particular. The aim of this research was to perform an economic and energy analysis of briquettes and pellets production. The obtained results of economic analyzes have shown that the individual production of solid biofuels from digestate is more profitable than using sawdust as a substrate. The costs of producing solid biofuels from solid fraction of digested pulp, as well as their calorific value, make the discussed substrate to be used to produce energy. The calorific value of the solid biofuel produced from the digested pulp solid fraction (DSF) can be compared to the calorific value of biofuel generated from sawdust. The digested pulp can be considered as an alternative to the sawdust in the production of solid biofuels.

Post-mining areas require reclamation. The main aim of reclamation is to restore the soil as a basic element of the terrestrial ecosystem. This paper presents the results of an evaluation of the enzymatic activity of soils formed on an afforested heap from an opencast sulphur mine. Six research sites were selected on the overburden heap of the Piaseczno sulphur mine, afforested 50 years ago. They differed in the type of soil in the subsoil and in the species composition of the stand. The activity of dehydrogenases, phosphatases, urease, total organic carbon, and total nitrogen was determined and statistical analysis of the obtained results showed that the activity of the evaluated enzymes in the soils formed in the reclaimed areas was significantly dependent on the type of substrate and the species composition of the plants. The activity of the evaluated enzymes was significantly positively correlated with the content of total nitrogen and the C/N ratio, and the activity of phosphatases and urease with the total organic carbon content. Within soils developed on the same texture, the influence of stand species was revealed. In soils formed on clay, the soils under the beech stand and under the birch stand were characterized by higher activity of enzymes. The soil developing under the stands of European larch and red oak was characterized by higher enzymatic activity on weakly clayey sands. On loose sands, the activity of dehydrogenases and urease was significantly higher under acacia robinia than under hornbeam.

The article presents the research made on the effects of methods of pressure-thermal agglomeration of corn bran, as well as the influence of processing parameters on selected physicochemical properties and biogas efficiency. Corn bran moistened to four levels of moisture content was used for the tests: 20%, 25%, 30% and 35% of dry matter. The pressure-thermal treatment was carried out with the use of a Brikol SJ25 pellet maker and a TS-45 single-screw extruder. In the tests of the extrusion-cooking process, three rotational speeds of the extruder screw were applied: 70, 90 and 110 rpm. The following characteristics were examined: efficiency of the extrusion-cooking and pelleting process, as well as the energy consumption. The water absorption index (WAI), the water solubility index (WSI), bulk density, kinetic strength, structure analysis by the ART/FTIR method, energy potential and the efficiency of cumulated biogas and cumulated methane per dry mass, as well as fresh mass and fresh organic matter and a series of microscopic pictures were completed. The analysis of the ATR/FTIR infrared spectra of the tested pelleted and extruded samples showed clear changes at the molecular level. Biogas production of extruded corn bran increased by several percent, as compared to untreated material.

Renewable energy sources (RES) become more and more popular. In Poland, biomass has the highest energy potential among all RES. Methane fermentation is one of possible ways to use it. The aim of the study was to perform energy and economic calculations for the biogas plant installation project in an existing farm situated in the Wielkopolska voivodeship. Because of the small area of the farm and the type of production, the calculations were carried out for micro-installation biogas plants. During the preparation of the project the production potential of the substrates was determined, allowing for further analyses. It was calculated that the electrical power of the designed biogas plant was 8.10 kW, with a total annual production of biogas at 29 471 m3. The obtained amount allows to generate in the cogeneration system 66 450 kWh of electricity and 71 190 kWh of heat energy. Some of the energy produced can be used on the farm and its surplus sold to the grid, which will allow for financial and environmental benefits.

Combustion of diesel oil and liquid biofuels in self-ignition engines is related to the emission of harmful gases to the atmosphere (i.e. nitrogen, carbon or sulfur oxides). These compounds, emitted in significant quantities, pose a threat to human life and health, as well as to the natural environment. The goal of our research was to investigate the influence of temperature of the waste cooking oil methyl ester on the nitrogen oxides emission in the self-ignition engine. This is to help determine if the use of biofuel thermal activation can be used to reduce nitrogen oxides emissions. Experiments carried out on the test bench in relation to harmful nitrogen compounds (NOx). The emission of exhaust gases from a diesel engine fed with methyl esters of the cooking oil was measured. The measurements were made in accordance with ISO 8178-4. From the obtained test results it can be concluded that it is worth equipping the engine with installation for preheating the fuel before its injection, but the optimal value of fuel temperature reducing emissions is at least 70°C.

The composting of sewage sludge and maize straw mixtures was investigated in this study. The aim was to analyze the influence of different proportions of sewage sludge and maize straw in the mixtures on composting process dynamics (expressed by heat production) and gas emissions. The results showed that all examined mixtures reached a strong thermophilic phase of composting; however, the lowest dynamic of temperature growth was observed in the case of the biggest sewage sludge content (60% of sewage sludge in the composting mixture). The ammonia concentration inside bioreactor chambers was directly related to the content of sewage sludge in the composted mixture. Excessive contents of sewage sludge had a considerable effect on very low C/N ratios and high losses through ammonia emissions. Tests were carried out in reactors with a capacity of 160 dm3 under controlled conditions. All mixtures were aerated by the average air-flow of about 2.5 dm3∙min−1, i.e., the minimum air-flow that allows a temperature of about 70 °C to be reached and a sufficiently long thermophilic phase, which ensures proper composting.

Maize has great potential, especially as a substrate for biofuels production. The aim of this paper is to analyze the possibility of usage in methane fermentation maize straw harvested in different weather conditions, which had an influence on different physical parameters, mainly the dry mass content. The research has shown that maize straw harvested in Central-Eastern Europe can have a broad spectrum of dry mass content, which is related to diverse weather conditions during autumn. However, independently from moisture content, maize straw can be a good (for more wet material) or very good (for more dried straw) substrate for the biogas plant. With the methane productivity reaching 201&ndash, 207 m3/Mg of fresh mass, this material is a significantly better substrate than that typically used in Europe maize silage (approximately 105 m3/Mg FM). It was noted that the retention time for maize straw (36&ndash, 42 days) is longer than in the case of maize silage (less than 30 days). However, this difference is quite small and can be accepted by the biogas plant operators.

Untargeted metabolite profiling was performed on chicken manure (CHM), swine manure (SM), cattle manure (CM), and their respective digestate by XCMS coupled with MetaboAnalyst programs. Through global chemical profiling, the chemical characteristics of different digestates and types of manure were displayed during the anaerobic digestion (AD) process. As the feed for AD, CM had less easily-degradable organics, SM contained the least O-alkyls and anomerics of carbohydrates, and CHM exhibited relatively lower bio-stability. The derived metabolite pathways of different manure during the AD process were identified by MetaboAnalyst. Twelve, 8, and 5 metabolic pathways were affected by the AD process in CHM, SM, and CM, respectively. Furthermore, bioactive compounds of digestate were detected, such as amino acids (L-arginine, L-ornithine, L-cysteine, and L-aspartate), hormones (L-adrenaline, 19-hydroxy androstenedione, and estrone), alkaloids (tryptamine and N-methyltyramine), and vitamin B5, in different types of manure and their digestates. The combination of XCMS and MetaboAnalyst programs can be an effective strategy for metabolite profiling of manure and its anaerobic digestate under different situations.

This paper deals with wastewater treatment systems placed in motorway service areas (MSAs). In the years 2008-2009 eight of such facilities installed on the stretch of the A2 motorway between Poznań and Nowy Tomyśl were examined and analyzed. The system consists of a septic tank, a submerged aerated biofilter and an outflow filter. The volume of traffic on the highway was analyzed, the amount of water use was measured and peak factors were calculated. On this basis it was concluded that the inflows to the wastewater treatment systems in many cases exceeded the nominal design values. Based on the analysis of effluent quality it was found that the effects of plant operation in large part did not meet the requirements. It was found that the bioreactor aeration system and the design of the suspension separator (outflow filter) should be modified. One of the solutions was to use the soil-reed bed for wastewater treatment. The treatment of wastewater from the MSAs is a task that must take into account the unusual character of these facilities and the atypical quality of the effluent.

The aim of the article was to determine the feasibility and advisability of the use of secondary filters applied before discharge of wastewater into the ground in the context of the fulfillment of the conditions of the current Regulation of the Minister of Environment of 18 November 2014 on the conditions to be met during the discharge of wastewater into the water or the ground and on substances particularly harmful to the aquatic environment. Due to expected in practice, an application and popularity, as compared variants, reactors having a very simple construction were used. The average values of removal of BOD5, COD and total suspended solids for three secondary filters technologies: biological trickling filter with natural ventilation, sand filter and nonwoven filter were compared. Additionally, as a fourth option a simple mathematical model has been presented. This model allows to estimate of BOD5 at the outflow from biological trickling filter and to verify the empirical data. Despite a large usefulness, it is rarely used in our country. It has been found the possibility of reduction of the infiltration area (surface area after reduction is 38–63% of the initial value) due to the application of secondary filters. In the case of a high initial demand of the terrain area for drainage localization the benefit in costs resulting from the reduction (several thousand of PLN) or may even significantly exceed the cost of buying and installing a cheap secondary filter. In addition, reduction the occupied area of the lot (in extreme cases up to 100 m2) by using the secondary filter allows to use the unoccupied space for other purposes, and thus gives additional economic advantage.

The typical tests of biogas efficiency require a great deal of time and are quite expensive. Thus, there is a necessity to develop tools for estimating the energy value of silage more quickly. This paper describes the application of a prediction model based on artificial neural networks to estimate the methane production from various substrates in the form of silages. For this prediction, basic silage parameters were used. The learning file contained input data such as the kind of silage, pH, dry matter, organic dry matter, conductivity and fermentation time. The output data in the database sheet contained the cumulative methane production. The prediction model of methane production that was created was a Radial Basis Function (RBF) with 5 inputs, 2 neurons in a hidden layer and 1 output. However, the resulting optimal prediction model has 73% of the quality of the network with a Root Mean Square Error (RMSE) less than 3%. This is a satisfying result, which can be increased significantly by enhancing the model with the addition of a new analysis of silages. The RBF model created can help to estimate the energy value of different silages quickly and without the necessity of expensive, long-term analysis.

Large amounts of municipal sewage sludge are generated every year. Composting is one of the most popular and cost-effective methods of handling this waste. It is particularly important to carry out the composting of sewage sludge in an efficient way. The identification of the stage of early maturity of composted material is crucial. The objective of this study was to check the possibility of using convolutional neural networks to classify the early maturity of compost made from sewage sludge and rapeseed straw. The literature review showed that this specific and modern type of neural network had not been investigated for this purpose before. A mixture of these two substrates, composted for 25 days in 7 experiments, was the research material. Images of the material samples were acquired in a dedicated photo station illuminated with: visible light, ultraviolet light, and mixed visible and ultraviolet light. For each acquisition variant 1312 images were obtained. On the basis of the acquired images, 25 convolutional neural networks with one convolutional layer and a varied number of convolution filters were developed to determine the stage of early maturity of the material. Their classification error ranged from 0.51% to 17.77%. The best classification result was obtained for the model containing 16 convolution filters and based on images of the material acquired in mixed visible and ultraviolet light. The results presented in this paper have shown that convolutional neural networks are an adequate tool to assess compost maturity. Such models may provide a simplified and cost-effective approach to the approximate evaluation of the early maturity of compost.

Paper presents a method of using EPANET solver to support manage water distribution system in Smart City. The main task is to develop the application that allows remote access to the simulation model of the water distribution network developed in the EPANET environment. Application allows to perform both single and cyclic simulations with the specified step of changing the values of the selected process variables. In the paper the architecture of application was shown. The application supports the selection of the best device control algorithm using optimization methods. Optimization procedures are possible with following methods: brute force, SLSQP (Sequential Least SQuares Programming), Modified Powell Method. Article was supplemented by example of using developed computer tool.

Along with the development of environmental friendly technologies, an increasing interest in generating the electricity and heat from renewable sources has been observed in Poland. Perfect example of such installations are agricultural biogas plants, where methane fermentation produces high-energy gas fuel i.e. biogas. Before investing, it is necessary to perform a detailed studies of the biogas efficiency of the substrates used. The proper run of fermentation process, as well as the high biogas production related to the operation, depend on many factors, including the mixing inside the reactor. The DIN 38 414-S8 standard, commonly used in the tests, assumes the mixing of the whole eudiometric sets, used in accredited laboratory units, which due to their uniform construction may cause problems. The aim of the study was to determine the effect of laboratory mixing in the fermentation reactor on the biogas efficiency of the maize straw. The experiment tests were performed in the Laboratory of Ecotechnologies, in the Poznan, in accordance with the current standard DIN 38 414-S8.The obtained research results confirmed the effect of mixing inside the fermentation reactors on the biogas efficiency of the maize straw.

Sewage sludge contains organic and biogenic substances that should be used. These materials may also contain toxic substances and heavy metals, and therefore require proper management in accordance with applicable law. Sewage sludge disposal is important for the protection of the environment, but also for the costs associated with the disposal of sludge. There are many technologies that are designed to use the properties of sewage sludge. It should be emphasized, however, that the proposed sewage sludge management technologies require investment outlays. In the present situation, research experiments have been carried out in the Environmental Technology Laboratory of the University of Environmental and Life Sciences in Poznan, indicating the possibility of efficient use of sewage sludge in the methane fermentation process. The use of sewage sludge in the fermentation mix allows the fertilizer to be obtained in the form of fermentation pulp, which also has the same properties as natural fertilizers. It should also be noted that the effect of physicochemical changes is the production of biogas, which is the source of electricity and/or heat. The economic sustainability of the use of sludge (taking into account the current costs of their disposal) is unequivocally positive when co-fermented in an appropriate proportion. The results show that sewage sludge can be successfully used in biogas plants as a co-substrate of fermentation mix. Therefore, the use of sewage sludge in biogas plants not only allows for the safe management and production of fertilizers, but also for the "green" energy.