Successful and stable operation of anaerobic thermophilic co-digestion of sun-dried sugar beet pulp and cow manure under short hydraulic retention time

Biodesulfurization of landfill biogas by a pilot-scale bioscrubber: Operational limits and microbial analysis

Biogas serves as a crucial renewable energy vector to ensure a more sustainable energy future. However, the presence of hydrogen sulfide (H2S) limits its application in various sectors, emphasizing the importance of effective H2S removal techniques for maximizing its potential. In the present study, the limits of a pilot-scale bioscrubber for biogas desulfurization was study in a real scenario. An increase in the superficial liquid velocity resulted in significant improvements in the H2S removal efficiency, increasing from 76 ± 8% (elimination capacity of 6.2 ± 0.5 gS-H2S m-3 h-1) to 97.7 ± 0.5% (elimination capacity of 8 ± 1 gS-H2S m-3 h-1) as the superficial liquid velocity increased from 50 ± 3 m h-1 to 200 ± 8 m h-1. A USL of 161.4 ± 0.5 m h-1 was able to achieve outlet H2S concentrations as low as 3 ± 1 ppmv (H2S removal efficiency of 97 ± 1%) for 7 days. High superficial liquid velocity favoured the aerobic H2S oxidation reducing the nitrate demand. The maximum EC reached throughout the operation was 50.8 ± 0.6 gS-H2S m-3 h-1 (H2S removal efficiency of 96 ± 1%) and a sulfur production of 60%. Studies in batch flocculation experiments showed sulfur removal rates up to 97.6 ± 0.9% with a cationic flocculant dose of 75 mg L-1. Microbial analysis revealed that the predominant genus with sulfo-oxidant capacity during periods of low H2S inlet load was Thioalkalispira-sulfurivermis (61-69%), while in periods of higher H2S inlet load, family Arcobacteraceae was the most prevalent (11%).

Long hydraulic retention time mediates stable volatile fatty acids production against slight pH oscillations

The effect of operational conditions on the stability of acidogenic fermentation (AF) devoted to volatile fatty acids (VFAs) production still presents numerous gaps to achieve high yields and fully understand the responses of open microbiomes associated to this technology. To cope with that, this investigation was designed to assess the stability of VFAs production via AF of agro-food wastes at high hydraulic retention times (HRTs) (20 and 30 d) and pH oscillations (5.8-6.2). Similar bioconversion efficiencies (∼50 %) were reached regardless of the HRT, revealing that HRT of 20 d can be considered as a threshold from which, no further improvement was achieved. The combination of long HRTs, 25 °C and acid pHs promoted a robust microbiome that resulted in a stable outcome against pH variations, being Clostridiales order identified as key player of AF stability. These conditions mediated a high selectivity in the VFAs production profile, with acetic and butyric acids, prevailing in the VFAs pool (∼80 % of total VFAs) at HRT 20 d. The selection of appropriated conditions was shown to be critical to maximize the hydrolysis and acidogenesis of the substrate and attain a stable effluent against pH oscillations.

Enrichment and balancing of nutrients for improved methane production using three compositionally different agro-livestock wastes: Process performance and microbial community analysis

Balanced nutrition is important for maximizing anaerobic digestion (AD) performance. Herein, the strategy of balancing sugar-fiber-nitrogen nutrients was first established for improved methane production by co-digesting two agricultural and one livestock wastes with complementary compositional properties, such as banana pseudo-stem (BPS), sugarcane baggage (SCB), and chicken manure (CM) having high sugar, fiber and nitrogen contents, respectively. The maximum methane yield was 186.5 mL/g VS_added with a mixture of 45.7% BPS, 26.2% SCB and 28.1% CM (with 1: 11.3: 0.3 of sugar to fiber to nitrogen ratio), increasing by 16.1%, 53.3%, 122.6% than those of mono- BPS, SCB, and CM, respectively. The co-digestion process remained stable under an organic load of 4 g VS/(L·day), which was attributed to the predominant presence of Bacteroidetes, Proteobacteria, Thauera, uncultured_bacterium_p_Aegiribacteria, and hydrogenotrophic methanogens. This study provides a deeper understanding of the co-digestion with agricultural and livestock wastes from the perspective of nutrient balance.

Biological acidification of pig manure using banana peel waste to improve the dissolution of particulate phosphorus: A critical step for maximum phosphorus recovery as struvite

Traditional disposal of agricultural bio-waste such as pig manure and banana peel waste poses an environmental nuisance. The uncontrolled disintegration of these waste materials decomposes to toxic effluent and methane a greenhouse gas twenty-one times more potent than carbon dioxide at trapping heat in the atmosphere, which is detrimental to the climate by elevating temperatures. Agricultural bio-waste is rich in nutrients that include nitrogen and phosphorus. Selectively separating these nutrients from the solid phase to produce high value products has been envisaged as an effective method of waste valorisation. This study aims to investigate the solubilisation of phosphorus (P) during anaerobic digestion (AD) of pig manure with banana peel waste as the co-substrate. The objective was to enhance the biological dissolution of the phosphorus from solid pig manure to the aqueous phase as this is envisaged to subsequently ease the recovery of P as a concentrated product via crystallization. Thereafter, phosphorus is used as a slow-release mineral fertilizer. Biological acidification was effective in reducing the pH to less than 6.50 from an initial pH of 7.28 at higher doses of BPW >100 g/L. Maximum dissolution of total phosphorus of 75% was observed at a pH of 5.40. Multiple regression analysis was used to correlate pH, banana peel waste concentration, and the anaerobic digestion time (ADT) to optimize the dissolution of P as this was deduced to be occurring at a low pH. A 2^nd order polynomial was deduced to best fit the data with an R² value of 0.90. The p values for the HRT and banana peel waste concentration were both <0.05 showing that both variables had a strong influence on the pH.