Comparison Between Single and Two-Stage Anaerobic Digestion of Vegetable Waste: Kinetics of Methanogenesis and Carbon Fl
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ORIGINAL RESEARCH
Comparison Between Single and Two‑Stage Anaerobic Digestion of Vegetable Waste: Kinetics of Methanogenesis and Carbon Flow Dinh Pham Van1 · Fujiwara Takeshi2 · Giang Hoang Minh1 · Song Toan Pham Phu3 Received: 14 May 2019 / Accepted: 21 October 2019 © Springer Nature B.V. 2019
Abstract This study aims to compare the performance and kinetics between the single-stage anaerobic digestion (SAD) and the twostage anaerobic digestion (TAD) of vegetable waste (VW). The SAD was performed using continuously stirred tank reactors. Meanwhile, the TAD experiment was set up using a combined system involving a continuously stirred tank for hydrolysis/ acidogenesis and an upflow reactor for methanogenesis. The hydrolytic reactor operated as a batch process with a retention time (RT) of 9 days, while the methane reactor was a continuous process operation with RT of 20 days. Both TAD and SAD were controlled at a temperature of 36 °C. The SAD experiments lasted for 143 days, and were characterised by the kinetic rate constant k = 0.02 day−1 which was much lower than that for the TAD (k = 0.66 − 2.16 day−1). The SAD seemed to be inhibited by high concentration of free ammonia and low inoculum to substrate ratio; herein, only 17.8–22.3% of the initial carbon could be converted into biogas (equivalent to 91–110 Nml/g-VSadded) with low methane content (44.1–48.7%). Meanwhile, TAD converted 41.67% initial carbon to biogas (equivalent to 299.0–374.6 Nml/g-VSadded) with high methane content (71.68–81.0%). Moreover, methanogenesis in the TAD was highly stable which enabled the digestion process to return to normal state within a few days, even though the concentrations of the influent increased to double (6.5–24.5 g-COD/l). As per these results, the TAD was much more stable, faster, and stronger than the SAD. Graphic Abstract
Keywords Anaerobic digestion · Single-stage digestion · Two-stage digestion · Vegetable waste Extended author information available on the last page of the article
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Statement of Novelty This paper provided a new approach for evaluations and comparisons between single-stage digestion and two-stage digestion. In which, the kinetic rate constant, which determines the rate of reaction processes, was used as a good indicator. Moreover, the fate of carbon, which reveals the proportion of biogas conversion, was employed for performance assessments. This study is also like a guideline for an in-depth evaluation of both single-stage digestion and two-stage digestion.
Introduction Vegetable waste (VW) is generated daily in large amounts globally as a natural consequence of agricultural and food industrial activities [1, 2]. European Union alone annually produces 89 million tons of fruit and vegetable waste and this value is expected to further significantly increase [3]. It is highly biodegradable, and when discarded into landfills or dumping sites, it inevitably causes natural anaerobic digestion (AD) leading to various environmental and human health problems such as odour pollu
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