Strategy of mitigating ammonium-rich waste inhibition on anaerobic digestion by using illuminated bio-zeolite fixed-bed process

Review of energy self-circulation systems integrating biogas utilization with Powerfuels production in global livestock industry

Energy self-circulation systems, defined as energy systems incorporating the recycling utilization of waste biomass, have been proposed to reduce greenhouse gases emissions from livestock sector. In this study, a comprehensive review of the situation and challenges of biogas utilization in the livestock industry was provided. Moreover, two technological routes were proposed for a circular livestock system combined with Powerfuels production (CP-CLS), starting from biogas combustion for power generation and steam reforming to the sustainable development path of synthesizing, storing, and utilizing Powerfuels. The self-circulation capability and comprehensive benefits of the CP-CLS life cycle was discussed, along with future application scenarios and proposed standards for Powerfuels. To realize this potential, continuous research, development, and policy support are crucial. This study envisions the next generation of energy self-circulation systems, which expects to reduce the negative effect of livestock industry on climate change and promote sustainable development.

Significance of homogeneous operation in light-assisted fixed-bed bioprocess under ammonia stress: Optimization, long-term operation and metagenomic analysis

Activating microbes with light is a promising strategy for addressing ammonia-stressed anaerobic digestion (AD). However, as a critical in-process parameter, homogenous operation, in light-assisted AD amended by bio-fixed bed has received limited attention. This research endeavors to establish a uniform-illuminated biosystem and assess its practical feasibility through a 90-day semi-continuous operation at pilot scale under solar light illumination. With optimal stirring mode (intermittent stirring for 3 min every 15 min), robust methane yields were achieved across various organic loads, reaching 88.7-94.3% of theoretical yield under high ammonium stress (3500 mg/L). The metagenomic analysis unveiled that uniform illumination triggered synergistic effects in AD, fostering a diversified microbial consortium, enhancing carbohydrate and methane metabolism, and facilitating the formation of an electroactive bio-cluster. This study underscores the significance of homogenous illumination in AD systems for efficient waste-to-energy conversion, highlighting the implementation of solar light as a greener approach for scale-up application.

Combined effects of oxytetracycline concentration and organic loading rate on semi-continuous anaerobic digestion of swine wastewater

High concentrations of antibiotics in swine wastewater raises concerns about the potential adverse effects of anaerobic digestion (AD). Current studies mainly focused on the effects of various antibiotic concentrations. However, these studies didn't take into account the fluctuation of swine wastewater quality and the change of reactor operating conditions in practical engineering applications. In this study, it was found that in the operating systems with COD of 3300 mg/L and hydraulic retention time (HRT) of 4.4 days, the continuous addition of oxytetracycline for 30 days had no effect on the AD performance. Nevertheless, when COD and HRT were changed to 4950 mg/L and 1.5 days respectively, oxytetracycline at 2 and 8 mg/L increased the cumulative methane yield by 27% and 38% at the cost of destroying cell membrane, respectively, while oxytetracycline at 0.3 mg/L improved the performance and stability of AD. These results could be referred for practical engineering applications.

Natural Ecuadorian zeolite: An effective ammonia adsorbent to enhance methane production from swine waste

Anaerobic digestion (AD) of swine waste allows obtaining renewable energy, biofertilizer and the reduction of environmental impacts. However, the low C:N ratio of pig manure generates high concentrations of ammonia nitrogen in the digestion process, reducing methane production. Zeolite is an effective ammonia adsorbent; thus, in this research the ammonia adsorption capacity of natural Ecuadorian zeolite was studied under different operating conditions. Subsequently, its effect on methane production from swine waste was evaluated using three doses of zeolite, 1.0, 4.0 and 8.0 g, in 1 L batch bioreactors. The results showed that the Ecuadorian natural zeolite has an adsorption capacity of around 19 mgNH₃-N gZ^-1 when using ammonium chloride solution and, an adsorption capacity between 37 and 65 mgNH₃-N gZ^-1 using swine waste. On the other hand, the addition of zeolite had a significant effect on methane production (p < 0.01). The zeolite doses that provided the highest methane production were 4.0 and 8.0 g L^-1, which led to values of 0.375 and 0.365 Nm³CH₄ kgVS^-1, compared to the values of 0.350 and 0.343 Nm³CH₄ kgVS^-1 that were obtained for the treatments without addition of zeolite and using a dose of 1.0 g L^-1, respectively. Addition of natural Ecuadorian zeolite meant not only a significant increase on methane production in the AD of swine waste, but also a better quality of the biogas with higher percentages of methane and lower concentrations of H₂S.

Light stimulation strategy for promoting bio-hydrogen production: Microbial community, metabolic pathway and long-term application

Light stimulation strategy for promoting bio-H₂ production was firstly investigated with incandescent light. The light condition controlled by photon number (N_R, 0.63 × 10⁴-6.25 × 10⁴ μmol/(day∙L)) was applied to stimulate H₂ fermentation process. The optimal N_R of 3.75 × 10⁴ μmol/(day∙L) contributed to 1.4 folds H₂ yield of the dark reactor and promoted efficient H₂ producing pathway (acetate and nicotinamide adenine dinucleotide pathway) with increased microbial activities. Furthermore, the effect of light stimulation on microbial community was identified. Fervidobacterium, Coprothermobacter and OPB95 were the dominant genera that could be activated by light stimulation for promoting acetate pathway and contribute to higher H₂ production. Moreover, long-term operation showed more stable and higher H₂ production of light stimulated bioreactor than the dark one, which resulted from the light stimulated metabolic pathway, increased sludge conductance and promoted microbial immobilization. This novel light stimulation strategy is promising for future application on promoting bio-H₂ production.

Biomethane enhancement from corn straw using anaerobic digestion by-products as pretreatment agents: A highly effective and green strategy

The development of biogas projects feed by lignocellulosic biomass has been constrained by the high cost of pre- and post-treatment. In this study, a novel strategy for pretreatment by using two by-products, i.e., CO₂ and liquid digestate (LD), generated from anaerobic digestion (AD) was developed to overcome these shortcomings. Results showed that corn straw pretreated in LD pressurized under 1 Mpa CO₂ at 55 ℃ resulted in increased glucose and xylose contents and a 9.80% decrease in cellulose crystallinity. After 45 days of AD conversion, the methane yield increased by 50.97% compared with untreated straw. However, pretreatment in LD pressurized under 1 Mpa CO₂ at 170 ℃ produced 5-hydroxymethylfurfural and furfural, which led to a decrease in methane production from the straw in the subsequent AD conversion. The alteration of the microbial community in the pretreated slurry at 55 °C was another potential contributor to the enhanced performance of AD.

A developed hybrid fixed-bed bioreactor with Fe-modified zeolite to enhance and sustain biohydrogen production

In this study, we describe the development of a hybrid bioreactor with integrated chlorinated polyethylene (CPE) fixed-bed and zeolite as a microorganism nutrition carrier (MNC), aiming at enhancing and sustaining biohydrogen production during the anaerobic digestion (AD) process. In the batch test, the hybrid bioreactor achieved a maximum biohydrogen production of 646.3 mL/L. Accordingly, the hybrid bioreactor significantly enhanced biohydrogen production and maintained a stable performance for 50 days of semi-continuous operation. This result should be attributed to the CPE providing roughness surface and high porosity for microorganism immobilization, resulting in the enhancement of microbial quantity, confirmed by our scanning electron microscope and immobilized biomass analyses. Moreover, the element ratio significantly decreased, indicating that zeolite could provide metal cations for stimulating microbial bioactivity and growth, as well as contributing to superior biohydrogen productivity during the 50-day operation. In order to further enhance and sustain long-term biohydrogen production, raw zeolite was modified with iron. The hybrid-Fe bioreactor (CPE with Fe-modified zeolite) operated mainly following the acetate pathway and exhibited higher sustainability in improving biohydrogen production with a peak value of 1893.0 mL/L during a 72-day-lasting operation. The synergistic mechanism of the Fe-modified zeolite and CPE fixed-bed revealed that it could effectively induce favorable pathways and contribute to the synthesis of essential enzymes, micronutrient supplementation, electoral conductivity, and microbial immobilization for biohydrogen production. Therefore, a hybrid-Fe bioreactor could provide a unique alternative for the enhancement of hydrogen production for practical applications.

A new strategy to recover from volatile fatty acid inhibition in anaerobic digestion by photosynthetic bacteria

The accumulation of volatile fatty acids (VFAs) can decrease reactor pH and inhibit methane-producing process. For the first time, photosynthetic bacteria (PSB) were used to recover from VFAs inhibition (pH 6.0) of an anaerobic digestion system. After adding PSB for 12 days with and without light condition, the methane content recovered from 33.3% to 60.5% and from 32.1% to 59.3%, respectively; the pH increased to 7.1 and 6.8, respectively, the system alkalinity rapidly increased to 2238 and 1921 mg/L, respectively; the sCOD decreased from 5600 to 995 mg/L and from 5575 to 2025 mg/L, respectively; and the contents of formic acid, acetic acid, propionic acid and total VFA were greatly reduced. Microbial analysis found that PSB bioaugmentation could maintain microbial diversity of the system. PSB bioaugmentation could effectively relieve acids accumulation and stimulate methane production especially under light condition. It is also found that light could accelerate recovery with or without bioaugmentation.

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.

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

Anaerobic digestion (AD) is an important technology for the treatment of livestock and poultry manure. The optimal experimental conditions were studied, with deer manure as a fermentation material and mushroom residue as an inoculum. At the same time, methane production was increased by adding zeolite and changing the magnetic field conditions. The results showed that a 6% solid content was the best condition for producing methane. The optimal conditions for methane production were obtained by adding 35 g of mushroom residue to 80 g of deer manure at 35 °C. The addition of organic wastewater (OW) improved methane production. The result of improving the methane production factor showed that adding zeolite during the reaction process could increase the methane production rate. When the amount of zeolite was over 8% total solids (TSes), methane production could improve, but the rate decreased. Setting a different magnetic field strength in the AD environment showed that when the distance between the magnetic field and the reactor was 50 mm and the magnetic field strength was 10–50 mT, the methane production increment and the content of methane in the mixed gases increased.

A high-efficiency denitrification bioreactor for the treatment of acrylonitrile wastewater using waterborne polyurethane immobilized activated sludge

The performance of a laboratory-scale, high-efficiency denitrification bioreactor (15L) using activated sludge immobilized by waterborne polyurethane in treating acrylonitrile wastewater with high concentration of nitrate nitrogen (249mg/L) was investigated. The bioreactor was operated at 30°C for 220days. Batch denitrification experiments showed that the optimal operation parameters were C/NO₃^--N molar ratio of 2.0 using sodium acetate as electron donor and carrier filling rate of 20% (V/V) in the bioreactor. Stable performance of denitrification was observed with a hydraulic retention time of 30 to 38h. A volumetric removal rate up to 2.1kgN/m³·d was achieved with a total nitrogen removal efficiency of 95%. Pyrosequencing results showed that Rhodocyclaceae and Pseudomonadaceae were the dominant bacterial families in the immobilized carrier and bioreactor effluent. The overall microbial diversity declined as denitrifiers gradually dominated and the relative abundance of other bacteria decreased along with testing time.