Sustainable management and recycling of anaerobic digestate solid fraction by composting: A review.

The aim of the study was to review and discuss the management and recycling of anaerobic digestate solid fraction by composting process in the context of circular bioeconomy and sustainable development. The conversion of the solid fraction into compost can be recognized as novel process-enhancing supplements for land reclamation. Moreover, the solid fraction of the digestate is a valuable substrate for compost production, both as a monosubstrate and as a valuable additive for other raw materials to enrich in organic matter. These results should serve as reference point to target adjusting screws for anaerobic digestate solid fraction by composting process improvement, its implementation in modern bioeconomy perspective as well as provide a guideline for effective waste management.

Production of compost from logging residues.

The implementation of forest management generates logging residue which can be used in several ways. One of the option is to use of logging residue in the composting process. Therefore, this study determined the possibility of producing compost based on logging residue and the produced fertilizer used to fertilize forest nurseries. Pine chips and sewage sludge were used for carrying out the study. The compost, as well as the leachate produced during composting, were characterized by high NPK content. The leachate collected at the end of the experiment was characterized by nitrogen content of approximately 6500 mg‧dm-3, phosphorus of approximately 450 mg‧dm-3, and potassium of approximately 500-700 mg‧dm-3. In contrast, the compost produced contained approximately 0.57 g‧kg-1 nitrogen, approximately 0.39 g‧kg-1 phosphorus, and approximately 0.24 g‧kg-1 potassium. The disadvantage in terms of the usefulness of the resulting fertilizer in forest nurseries is its pH, which exceeded 9.0.

The effects of inflow of agricultural biogas digestate on bivalves' behavior.

This study focused on the reaction of bivalve molluscs to biogas digestate, which is a waste product of an increasingly developing biogas production in rural areas worldwide. The effects of biogas digestate on aquatic organisms are not fully known, and neither this substance nor any types of manure were tested in the monitoring based on valvometry, which is a biomonitoring method based on bivalve behavior. The change in bivalves functioning in biogas digestate inflow was studied using three different diluted digestate concentrations. Exposure to the highest concentration of digestate induced a decline of mean shell opening and activity time of Unio tumidus species. A significant difference in behavioral patterns was recorded during the first 10 min after exposure to the digestate. A Gradual decreasing tendency of shell opening levels was apparent under the highest concentration reaching 55% compared to the pretreatment value. Also, a decreasing tendency was observed under the medium concentration (82.4% of initial level) after 2 h, while an increase in shell opening levels was recorded in the most diluted digestate. This research work proved that the inflow of biogas digestate has significant impact on bivalves' behavior. Unio tumidus is a sensitive indicator of biogas digestate inflow in the aquatic environment. Moreover, it proved that the opening and closing activities over time depend on the concentration of the digestate. Therefore, the mollusk bivalves might be utilized in early warning systems to detect organic pollutants in water.

The Influence of Corn Straw Extrusion Pretreatment Parameters on Methane Fermentation Performance.

The aim of the study is to determine the energy consumption of the extrusion-cooking process of corn straw under various conditions (screw speed, moisture content), water absorption measurements and water solubility indices as well as biogas efficiency evaluation. The extrusion-cooking of corn straw was carried out using a single screw extruder with L/D = 16:1 at various rotational screw speeds (70, 90, and 110 rpm) and with various initial moisture content of raw material (25 and 40%). Prior to the process, the moisture content of the raw material was measured, and next, it was moistened to 25 and 40% of dry matter. For example, at 70 rpm extruder screw speed, the temperature range was 126-150 °C. Energy consumption of straw pretreatment through extrusion-cooking was assessed in order to evaluate the possibility of using the process in an agricultural biogas plant. Biogas and methane efficiency of substrates after extrusion was tested in a laboratory scale biogas plant and expressed as a volume of cumulative methane production for fresh matter, dry matter, and dry organic matter. Pretreated corn straw moistened to 25% and processed at 110 rpm during the extrusion-cooking processing produced the most advantageous effect for methane and biogas production (51.63%) efficiency as compared to corn straw without pretreatment (49.57%). Rotational speed of the extruder screw influenced biogas and methane production. With both dry matter and dry organic matter, the increase of rotational speed of the extruder screw improved the production of cumulated biogas and methane. Pretreatment of corn straw has a positive effect on the acquisition of cumulated methane (226.3 Nm3 Mg-1 for fresh matter, 243.99 Nm3 Mg-1 for dry matter, and 254.83 Nm3 Mg-1 for dry organic matter). Preliminary analysis of infrared spectra revealed changes in the samples also at the molecular level, thus opening up the possibility of identifying marker bands that account for specific degradation changes.

Lignin Transformation of One-Year-Old Plants During Anaerobic Digestion (AD).

The aim of the research is to identify the changes which occur in lignin from miscanthus and sorghum, one of the main biomass components, as a result of an anaerobic digestion (AD) process. The percentage content and structure of lignin before and after the fermentation process were analysed using biomass harvested in two growing periods-before and after vegetation. It was shown that plants at different developmental stages differ in lignin content. During plant growth, the lignin structure also changes-the syringyl-to-guaiacyl ratio (S/G) increases, whereas the aliphatic and aromatic structure ratio (Al/Ar) decreases. The AD process leads to an increase in percentage lignin content in cell walls, and the increase is higher for plants harvested during vegetation. It has been shown in studies that the methane fermentation of miscanthus and sorghum produces waste containing a large amount of lignin, the structure of which is altered relative to native lignin. The quantity and the new, simplified structure of lignin create new possibilities for using this aromatic polymer.

An effective method of utilizing vegetable waste in the form of carriers for Trichoderma strains with phytosanitary properties.

It has been assumed that compost from savoy cabbage and rapeseed straw is a good substrate for discrimination of the reproduction potential of Trichoderma strains. This hypothesis was verified based on a two-stage incubation experiment. The prepared mixture was fermented in a bio-reactor for 11 weeks. In the second experiment, the mature compost was inoculated with four strains of Trichoderma and a spore concentration of 104 and 106, and then incubated for four weeks. The biomass of autogenic fungi reached a maximum of 12.5 mg∙g-1 DM in the cooling phase. The variability in temperature during composting significantly affected NH3 emission. The pH of mature compost from cabbage wastes, as a result of the elevated NH3 emission reached the alkaline range. The survival of the Trichoderma fungi introduced into the alkali substrate was a result of strain sensitivity to the high pH of the compost and to the initial inoculum density. The adaptation potential of Trichoderma harzianum to the alkali milieu depended on the pH stabilization of the substrate by this fungi, provided the spore inoculum density was 106. The strains of Trichoderma atroviride responded negatively, regardless of the inoculum density, to the alkaline pH of the substrate and to self-induced changes in the compost pH.

Biochar to reduce ammonia emissions in gaseous and liquid phase during composting of poultry manure with wheat straw.

Composting of poultry manure which is high in N and dense in structure can cause several problems including significant N losses in the form of NH3 through volatilization. Biochar due to its recalcitrance and sorption properties can be used in composting as a bulking agent and/or amendment. The addition of a bulking agent to high moisture raw materials can assure optimal moisture content and enough air-filled porosity but not necessarily the C/N ratio. Therefore, amendment of low C/N composting mixtures with biochar at low rates can have a positive effect on composting dynamics. This work aimed at evaluating the effect of selected doses of wood derived biochar amendment (0%, 5% and 10%, wet weight) to poultry manure (P) mixed with wheat straw (S) (in the ratio of 1:0.4 on wet weight) on the total ammonia emissions (including gaseous emissions of ammonia and liquid emissions of ammonium in the collected condensate and leachate) during composting. The process was performed in 165L laboratory scale composting reactors for 42days. The addition of 5% and 10% of biochar reduced gaseous ammonia emission by 30% and 44%, respectively. According to the obtained results, the measure of emission through the condensate would be necessary to assess the impact of the total ammonia emission during the composting process.

Co-composting of poultry manure mixtures amended with biochar - The effect of biochar on temperature and C-CO2 emission.

Biochar as an amendment could have an impact on composting dynamics. This study investigated the effect of the addition of biochar (B) to poultry manure (P) mixed with wheat straw (S) (i.e. P:S, P:S+5%B and P:S+10%B) on temperature and carbon dioxide emission. For temperature studies a modified equation for net degree-hour parameter DHnet (°Chday(-1)) was proposed. The modified equation takes into account ambient temperature. The highest daily temperatures DHnet were observed on day 2 and the mixture with the highest addition of biochar (P:S+10%) reached the max temperature. The period of thermophilic temperatures (40°C>) was shorter for mixtures amended with biochar. The addition of biochar increased C-CO2 emission and the total C-CO2 emission were higher about 6.9% and 7.4% for P:S+5%B and P:S+10%B, respectively.