Anaerobic Digestion Technology for Methane Production Using Deer Manure Under Different Experimental Conditions

Research on the impact mechanism of changes in the production of medical solid waste in China before and after COVID-19

The changes of medical solid waste (MSW) output in recent years have had a significant impact on the spread of the virus. There is a high-risk transmission of MSW in various stages such as storage, transportation, and treatment during the COVID-19. To cope with the risks brought by the epidemic, normalized prevention consumes a large amount of protective clothing, medical masks, goggles, packaging bags, and other related medical supplies. There is a significant uncertainty in the amount of MSW output that poses a risk of COVID-19 infection in the event of an emergency, which increases the difficulty of collecting and handling epidemic prevention MSW. The analysis of MSW data from 2000 to 2022 found a stable growth trend before 2019. However, the MSW data was a sudden increase trend from 2020 to 2022, and the COVID-19 in China was characterized by an initial stage, an outbreak stage, and a stable growth stage. The range of MSW output during the epidemic was (1.19-1.75) × 106 t a-1. The amount of MSW was approximately 1.19 × 106 t a-1 during the normalized epidemic period, and its treatment cost was as high as 3.57 × 109 yuan (RMB)·a-1. The distribution of MSW output was uneven due to factors such as climate conditions, population data, and local economy. This study has important reference value for epidemic medical material reserves and MSW treatment.

Spent Mushroom Substrate Hydrolysis and Utilization as Potential Alternative Feedstock for Anaerobic Co-Digestion

Valorization of lignocellulosic biomass, such as Spent Mushroom Substrate (SMS), as an alternative substrate for biogas production could meet the increasing demand for energy. In view of this, the present study aimed at the biotechnological valorization of SMS for biogas production. In the first part of the study, two SMS chemical pretreatment processes were investigated and subsequently combined with thermal treatment of the mentioned waste streams. The acidic chemical hydrolysate derived from the hydrothermal treatment, which yielded in the highest concentration of free sugars (≈36 g/100 g dry SMS, hydrolysis yield ≈75% w/w of holocellulose), was used as a potential feedstock for biomethane production in a laboratory bench-scale improvised digester, and 52 L biogas/kg of volatile solids (VS) containing 65% methane were produced in a 15-day trial of anaerobic digestion. As regards the alkaline hydrolysate, it was like a pulp due to the lignocellulosic matrix disruption, without releasing additional sugars, and the biogas production was delayed for several days. The biogas yield value was 37 L/kg VS, and the methane content was 62%. Based on these results, it can be concluded that SMS can be valorized as an alternative medium employed for anaerobic digestion when pretreated with both chemical and hydrothermal hydrolysis.

Methods for Intensifying Biogas Production from Waste: A Scientometric Review of Cavitation and Electrolysis Treatments

This article presents future trends in research using microbiological methods to intensify bioprocesses for biogas production. The pretreatment by combinations of physical and chemical methods, such as cavitation and electrolysis, is considered. The approach of the article involved reviewing the residual area on the intensification technologies of anaerobic digestion with current methods to improve the quality and quantity of biogas. The most valuable reported positive results of the pretreatment of biological raw materials in the cavitation process were reviewed and are presented here. A model of the effect of electrolysis on the species diversity of bacteria in anaerobic digestion was developed, and changes in the dominance of the ecological and trophic systems were revealed on the basis of previous studies. The stimulating effect on biogas yield, reduction in the stabilization period of the reactor, and inactivation of microorganisms at lower temperatures is associated with different pretreatment methods that intensify anaerobic digestion. More research is recommended to focus on the electrolysis treatment of different types of waste and their ratios with optimization of regime parameters, as well as in combination with other pretreatments to produce biomethane and biohydrogen in larger quantities and in better qualities.

Properties of Animal-Origin Ash—A Valuable Material for Circular Economy

In the presented paper, two types of animal-origin biomass, cow dung and chicken litter, are characterized in terms of combustion-related problems and ash properties. It was found that these parameters strongly depend on the farming style. Whether it is cow dung or chicken litter, free-range raw materials are characterized by higher ash contents than industrial farming ones. Free-range samples contain chlorine at lower levels, while industrial farming samples are chlorine rich. Free-range samples are characterized by the predominant content of silica in the ash: 75.60% in cow dung and 57.11% in chicken litter, while industrial farming samples contain more calcium. Samples were classified by 11 “slagging indices” based on the ash and fuel composition to evaluate their tendencies for slagging, fouling, ash deposition and bed agglomeration. Furthermore, an assessment was made against the current EU law regulations, whether the ashes can be component materials for fertilizers. The phosphorus concentration in the investigated ashes corresponds to 4.09–23.73 wt% P2O5 and is significantly higher in industrial chicken litter samples. The concentrations of Hg, Cu, As, Ni, Cd and Pb in all samples are below the limits of the UE regulations. However, concentrations of Cr in all samples and Zn in industrial chicken litter exceed these standards.

Investigation of technology for composting mixed deer manure and straw

Composting is an effective method for utilizing agricultural straw waste and livestock manure resources. Using deer manure and corn straw as raw materials, the changes in various indexes were studied during composting under different initial C/N ratios, initial moisture contents, and particle sizes of corn straw, and compost maturity was evaluated. Moisture content, total organic carbon content, and C/N ratio all declined during composting, while total nitrogen, total phosphorus, total potassium, pH, germination index, and electrical conductivity increased. The grey relational analysis method was used to evaluate maturity. The results showed that a mixture of stalk and deer manure with initial moisture content of 55%, initial C/N ratio of 30:1, and a straw particle size of 1.5-3.5 cm constituted the optimal experimental conditions. Taguchi analysis indicated that initial moisture content exerted the greatest influence on compost maturity, followed by initial C/N ratio and crushed straw particle size. This study provides an important reference for the utilization of compost derived from a mixture of livestock manure and straw.

Zeolite addition to improve biohydrogen production from dark fermentation of C5/C6-sugars and Sargassum sp. biomass

Thermophilic biohydrogen production by dark fermentation from a mixture (1:1) of C5 (arabinose) and C6 (glucose) sugars, present in lignocellulosic hydrolysates, and from Sargassum sp. biomass, is studied in this work in batch assays and also in a continuous reactor experiment. Pursuing the interest of studying interactions between inorganic materials (adsorbents, conductive and others) and anaerobic bacteria, the biological processes were amended with variable amounts of a zeolite type-13X in the range of zeolite/inoculum (in VS) ratios (Z/I) of 0.065–0.26 g g⁻¹. In the batch assays, the presence of the zeolite was beneficial to increase the hydrogen titer by 15–21% with C5 and C6-sugars as compared to the control, and an increase of 27% was observed in the batch fermentation of Sargassum sp. Hydrogen yields also increased by 10–26% with sugars in the presence of the zeolite. The rate of hydrogen production increased linearly with the Z/I ratios in the experiments with C5 and C6-sugars. In the batch assay with Sargassum sp., there was an optimum value of Z/I of 0.13 g g⁻¹ where the H₂ production rate observed was the highest, although all values were in a narrow range between 3.21 and 4.19 mmol L⁻¹ day⁻¹. The positive effect of the zeolite was also observed in a continuous high-rate reactor fed with C5 and C6-sugars. The increase of the organic loading rate (OLR) from 8.8 to 17.6 kg m⁻³ day⁻¹ of COD led to lower hydrogen production rates but, upon zeolite addition (0.26 g g⁻¹ VS inoculum), the hydrogen production increased significantly from 143 to 413 mL L⁻¹ day⁻¹. Interestingly, the presence of zeolite in the continuous operation had a remarkable impact in the microbial community and in the profile of fermentation products. The effect of zeolite could be related to several properties, including the porous structure and the associated surface area available for bacterial adhesion, potential release of trace elements, ion-exchanger capacity or ability to adsorb different compounds (i.e. protons). The observations opens novel perspectives and will stimulate further research not only in biohydrogen production, but broadly in the field of interactions between bacteria and inorganic materials.

Preparation of ceramsite from municipal sludge and its application in water treatment: A review

Municipal sludge is a solid waste material, and resource utilization is the optimal way to dispose of this material. The amount of municipal sludge produced in China is large, and it can be used in the preparation of ceramsite. The content of Al₂O₃ in drinking water treatment sludge is significantly higher than that in wastewater treatment sludge, while the content of K₂O, Na₂O and MgO in the two kinds of sludge is similar. When sludge is used to prepare ceramsite, the amount of sludge in most raw materials for ceramsite is less than 50%. The bulk density of the prepared sludge ceramsite is less than 1000 kg m^-3, and the highest water absorption rate is close to 40%. The leaching content of heavy metals in municipal sludge-based ceramsite is within the standard health safety limit, and heavy metals are better stabilized. The fitting effect of the pseudo-second-order kinetic equation of the dynamic adsorption of sludge ceramsite is obviously better than that of the pseudo-first-order kinetic equation. Sludge ceramsite used in bio-filter media and constructed wetland (CW) substrates is good able to purify wastewater. In the future, the preparation method of municipal sludge ceramsite and purification research of CW substrates based on sludge ceramsite need to be further improved.

Effects of additives on nitrogen transformation and greenhouse gases emission of co-composting for deer manure and corn straw

Compost can realize the recycling of organic waste. However, it also emits NH₃ and greenhouse gases (GHGs) to the environment, which leads to nitrogen loss and global warming. Adding additives to compost can alleviate the emission of NH₃ and GHGs. The mechanism of nitrogen transformation and GHGs emission was studied with deer manure and corn straw as compost substrate, and biochar and zeolite as additives. The results showed that the addition of zeolite in compost is good for prolonging high-temperature composting time. The addition of zeolite reduced the transformation of NH₃-N and the N₂O emission. The addition of zeolite is beneficial to reduce nitrogen loss during composting. CH₄ emission is an important factor affecting the global warming potential of composting, and it is necessary to improve ventilation conditions in order to alleviate anaerobic. This study is of great significance to reduce nitrogen loss and improve composting effect.

Application of zeolites for biological treatment processes of solid wastes and wastewaters - A review

This review reports the use of zeolites in biological processes such as anaerobic digestion, nitrification, denitrification and composting, review that has not been proposed yet. It was found that aerobic processes (activated sludge, nitrification, Anammox) use zeolites as ion-exchanger and biomass carriers in order to improve the seattlebility, the biomass growth on zeolite surface and the phosphorous removal. In the case of anaerobic digestion and composting, zeolites are mainly used with the aim of retaining inhibitors such as ammonia and heavy metals through ion-exchange. The inclusion of zeolite effect on mathematical models applied in biological processes is still an area that should be improved, including also the life cycle analysis of the processes that include zeolites. At the same time, the application of zeolites at industrial or full-scale is still very scarce in anaerobic digestion, being more common in nitrogen removal processes.