Enhanced mesophilic bio-hydrogen production of raw rice straw and activated sewage sludge by co-digestion

Agronomic and phytotoxicity test with biosolids from anaerobic CO-DIGESTION with temperature and micro-organism phase separation, based on sewage sludge, vinasse and poultry manure

This study deals with energy and agronomic valorisation by anaerobic co-digestion with temperature and microorganism phase separation of sewage sludge, vinasse and poultry manure, with the aim of achieving an integral waste management, obtaining bioenergy and biofertilizer that returns nutrients to the soil in a natural way. The yields obtained were 40 mL H2/gVS and 391 mLCH4/gVS. The resulting effluent showed more than 98 % removal of E. coli and Total Coliforms, as well as total removal of Salmonella. The results obtained in the phytotoxicity tests showed that all the proportions studied had phytostimulant and phytonutrient properties, with 20 % having the highest germination index (GI) with mean values of 145.30 %. Finally, the agronomic trial carried out with strawberry crops (Fragaria sp.) showed that the addition of this biosolid has fertilising properties and can be used as an agronomic amendment, with an increase of 145 % in fresh weight and 102.5 % in dry weight, and fruit production doubled with respect to the control. The ANOVA statistical study corroborated that there were significant differences in crop growth when applying different proportions of biofertilizer in the fertilizer. Therefore, these results show that this technology is promising and would contribute environmentally, socially and economically to the transfer towards a circular economy model.

Exploitation of microbial activities at low pH to enhance planetary health

Awareness is growing that human health cannot be considered in isolation but is inextricably woven with the health of the environment in which we live. It is, however, under-recognized that the sustainability of human activities strongly relies on preserving the equilibrium of the microbial communities living in/on/around us. Microbial metabolic activities are instrumental for production, functionalization, processing, and preservation of food. For circular economy, microbial metabolism would be exploited to produce building blocks for the chemical industry, to achieve effective crop protection, agri-food waste revalorization, or biofuel production, as well as in bioremediation and bioaugmentation of contaminated areas. Low pH is undoubtedly a key physical-chemical parameter that needs to be considered for exploiting the powerful microbial metabolic arsenal. Deviation from optimal pH conditions has profound effects on shaping the microbial communities responsible for carrying out essential processes. Furthermore, novel strategies to combat contaminations and infections by pathogens rely on microbial-derived acidic molecules that suppress/inhibit their growth. Herein, we present the state-of-the-art of the knowledge on the impact of acidic pH in many applied areas and how this knowledge can guide us to use the immense arsenal of microbial metabolic activities for their more impactful exploitation in a Planetary Health perspective.

Dark co-fermentation of rice straw and pig manure for biohydrogen production: effects of different inoculum pretreatments and substrate mixing ratio

Biohydrogen produced from agricultural waste through dark co-fermentation is an increasingly valuable source of renewable energy. Rice straw (RS) and pig manure (PM) are widely available waste products in Asia with complementary levels of carbon and nitrogen that together have a high biohydrogen production potential. However, no research has yet determined the ideal inoculum pretreatment method and mixing ratio for biohydrogen production using these resources. In this study, we tested biohydrogen production using three different inoculum pretreatment methods (acid, alkali and thermal) at five RS/PM ratios (1:0, 5:1, 3:1, 1:1 and 0:1, based on total solids). All three pretreatments promoted biohydrogen production with the increase of bioactivity of biohydrogen-producing organisms (compared with a control group), though acid was clearly superior to thermal or alkali. Using acid pretreatment and RS/PM ratio of 5:1 corresponded with a relatively low NH4+-N concentration (655.17 mg/L), a maximal cumulative biohydrogen production of 44.59 mL/g VS_added with a low methane production (<0.1%), a large butyric acid accumulation (1035.30 mg/L) and a biohydrogen conversion rate of 2.12%. The optimal pH for biohydrogen production from co-fermentation of RS and PM ranged from 5.0-5.5.

Enhancement of Biogas Production via Co-Digestion of Wastewater Treatment Sewage Sludge and Brewery Spent Grain: Physicochemical Characterization and Microbial Community

The present study intends to evaluate a synergy towards enhanced biogas production by co-digesting municipal sewage sludge (SS) with brewery spent grain (BSG). To execute this, physicochemical and metagenomics analysis was conducted on the sewage sludge substrate. The automatic methane potential test system II (AMPTS II) biochemical methane potential (BMP) batch setup was operated at 35 ± 5 °C, pH range of 6.5–7.5 for 30 days’ digestion time on AMPTS II and 150 days on semi-continuous setup, where the organic loading rate (OLR) was guided by pH and the volatile fatty acids to total alkalinity (VFA/TA) ratio. Metagenomics analysis revealed that Proteobacteria was the most abundant phyla, consisting of hydrolytic and fermentative bacteria. The archaea community of hydrogenotrophic methanogen genus was enriched by methanogens. The highest BMP was obtained with co-digestion of SS and BSG, and 9.65 g/kg of VS. This not only increased biogas production by 104% but also accelerated the biodegradation of organic matters. However, a significant reduction in the biogas yield, from 10.23 NL/day to 2.02 NL/day, was observed in a semi-continuous process. As such, it can be concluded that different species in different types of sludge can synergistically enhance the production of biogas. However, the operating conditions should be optimized and monitored at all times. The anaerobic co-digestion of SS and BSG might be considered as a cost-effective solution that could contribute to the energy self-efficiency of wastewater treatment works (WWTWs) and sustainable waste management. It is recommended to upscale co-digestion of the feed for the pilot biogas plant. This will also go a long way in curtailing and minimizing the impacts of sludge disposal in the environment.

Biohythane production and microbial characteristics of two alternating mesophilic and thermophilic two-stage anaerobic co-digesters fed with rice straw and pig manure

To investigate biohythane production and microbial behavior during temperature-phased (TP) anaerobic co-digestion (AcD) of rice straw (RS) and pig manure (PM), a mesophilic-thermophilic (M1-T1) AcD system and a thermophilic-mesophilic (T2-M2) AcD system were continuously operated for 95 days in parallel. The maximal ratio (8.44%v/v) of produced hydrogen to methane demonstrated the feasibility of biohythane production by co-digestion of RS and PM. T2-M2 exhibited higher hydrogen (16.68 ± 1.88 mL/gVS) and methane (197.73 ± 11.77 mL/gVS) yields than M1-T1 (3.08 ± 0.39 and 109.03 ± 4.97 mL/gVS, respectively). Methanobrevibacter (75.62%, a hydrogenotrophic methanogen) dominated in the M1 reactor, resulting in low hydrogen production. Hydrogen-producing bacteria (Thermoanaerobacterium 32.06% and Clostridium_sensu_stricto_1 27.33%) dominated in T2, but the abundance of hydrolytic bacteria was low, indicating that hydrolysis could be a rate-limiting step. The thermophilic acid-producing phase provided effective selective pressure for hydrogen-consuming microbes, and the high diversity of microbes in M2 implied a more efficient pathway of methane production.

Impact of mesophilic co-composting conditions on the quality of substrates produced from winery waste activated sludge and grape stalks: Lab-scale and pilot-scale studies

In this study, different amounts of a mixture of winery waste activated sludge and grape stalks were co-composted for 8 weeks, at lab-scale under different temperatures and aeration rates, and at pilot-scale. None of the experiments showed the occurrence of a thermophilic stage, even when the composting temperature was kept at 34 °C, which might suggest biological suppression by the acclimated mesophilic microorganisms ubiquitous to the winery waste activated sludge. The composted substrates were fully characterized by physicochemical analysis, plant growth tests and germination indexes using parsley (Petroselinum crispum) seedlings and seeds. Surprisingly, despite the higher volume reduction at lab-scale, it was the initial mixture and the mixture composted outdoors which presented the best horticultural qualities, with seedling survival rates of 88.9% and 87.0% and modified germination indexes of 54% and 161%, respectively. These findings shed some light on previous contradictory results and allow the development of new recycling strategies.

Biohydrogen production from co-fermentation of fallen leaves and sewage sludge

The co-fermentation of fallen leaves and sewage sludge was performed for the production of hydrogen at different mixing ratios. The experimental results indicated that the optimal mixing ratio of sludge to leaves was 20:80 (volatile solids (VS) basis), and the co-fermentation process showed a synergistic effect on biohydrogen production at this mixing ratio. The biohydorgen yield reached 37.8 mL/g-VS_added at the mixing ratio of 20:80, which was higher compared to the mono-fermentation of sludge (10.3 mL/g-VS_added) or the leaves (30.5 mL/g-VS_added). The VS removal was also highest (15.7%) at the mixing ratio of 20:80, which was higher compared to sludge mono-fermentation (6.2%) or leaves mono-fermentation (12.8%). Meanwhile, the co-fermentation process enhanced the biohydrogen production rate and led to a more efficient fermentation pathway. Microbial community analysis showed that the co-fermentation system enriched much more Clostridium, Bacillus and Rummeliibacillus genera, which was responsible for the synergistic effect on biohydrogen production.

Co-fermentation of sewage sludge with ryegrass for enhancing hydrogen production: Performance evaluation and kinetic analysis

The low C/N ratio and low carbohydrate content of sewage sludge limit its application for fermentative hydrogen production. In this study, perennial ryegrass was added as the co-substrate into sludge hydrogen fermentation with different mixing ratios for enhancing hydrogen production. The results showed that the highest hydrogen yield of 60mL/g-volatile solids (VS)_added was achieved when sludge/perennial ryegrass ratio was 30:70, which was 5 times higher than that from sole sludge. The highest VS removal of 21.8% was also achieved when sludge/perennial ryegrass ratio was 30:70, whereas VS removal from sole sludge was only 0.7%. Meanwhile, the co-fermentation system simultaneously improved hydrogen production efficiency and organics utilization of ryegrass. Kinetic analysis showed that the Cone model fitted hydrogen evolution better than the modified Gompertz model. Furthermore, hydrogen yield and VS removal increased with the increase of dehydrogenase activity.

Improved Treatment and Utilization of Rice Straw by Coprinopsis cinerea

As one of the most abundant renewable resources, rice straw is an attractive lignocellulosic material for animal feeding or for the production of biochemical. An appropriate pre-treatment technique is essential for converting rice straw to rich fodder or biofuel. Based on previous work, Coprinopsis cinerea can grow on rice straw medium and therefore it is useful for the treatment of rice straw. However, little is known regarding its degradation systems and nutrition values. In this study, we firstly found that C. cinerea could grow rapidly on rice straw without any additives by the production of a series of enzymes (laccase, cellulase, and xylanase) and that the microstructure and contents of rice straw changed significantly after being treated by C. cinerea. We propose that a possible underlying mechanism exists in the degradation. Moreover, C. cinerea has a high nutrition value (23.5% crude protein and 22.2% total amino acids). Hence, fermented rice straw with mycelium could be a good animal feedstuff resource instead of expensive forage. The direct usage of C. cinerea treatment is expected to be a practical, cost-effective, and environmental-friendly approach for enhancing the nutritive value and digestibility of rice straw.