Optimization of Hydrolysis-Acidogenesis Phase of Swine Manure for Biogas Production Using Two-Stage Anaerobic Fermentation

Chiu-Yue Lin,Chin-Chao Chen,Chun-Yi Lee,Pau Loke Show,Wai Siong Chai,Chyi-How Lay

doi:10.3390/pr9081324

Abstract

The traditional pig manure wastewater treatment in Taiwan has been low in methane production efficiency due to unstable influent concentration, wastewater volume, and quality. Two-stage anaerobic systems, in contrast, have the advantage of buffering the organic loading rate in the first stage (hydrolysis-acidogenesis phase), allowing a more constant feeding rate to the second stage (methanogenesis phase). Response surface methodology was applied to optimize the operational period (0.5–2.0 d) and initial operational pH (4–10) for hydrolysis and acidogenesis of the swine manure (total solid 5.3%) at 35 °C in batch operation mode. A methanogenesis verification experiment with the optimal condition of operational period 1.5 d and pH 6.5 using batch operation resulted in peak volatile acid production 7 g COD/L, methane production rate (MPR) 0.3 L-CH4/L-d, and methane yield (MY) 92 mL-CH4/g-CODre (chemical oxygen demand removed). Moreover, a two-stage system including a hydrolysis-acidogenesis reactor with the optimal operating condition and a methanogenesis reactor provided an average MPR 163 mL/L-d and MY 38 mL/g volatile solids, which values are 60% higher than those of a single-stage system; both systems have similar dominant methane-producing species of Firmicutes and Bacteroidetes with each having around 30%–40%. The advantages of a two-stage anaerobic fermentation system in treating swine manure for biogas production are obvious.

Highlights

The raw swine manure feedstock with the characteristics of chemical oxygen demand (COD) 37,934 mg/L, total solid (TS) 28,870 mg/L (2.9%, percentage by weight), volatile solids (VS) 21,190 mg/L, and NH3 -N 1310 mg/L was collected in an adjustment tank and settled for one day before applied as the feedstock for a two-stage anaerobic fermentation process
The results show that higher solid content can obviously enhance the accumulative methane production and methane production rate (MPR)
The highest MPR of 608 L/L-d was obtained from settled sludge feedstock, which is 1.14 and 4.37 times higher compared to raw swine wastewater (530 L/L-d) and supernatant liquid (139 L/L-d), respectively

Summary

Introduction

The swine industry in Taiwan was mainly small-scale and decentralized in the early stage, and most of the swine manure was applied in the form of liquid fertilizer or compost to provide nutrients for crops. The disposal of manure has become a major public concern due to its huge potential threat to public health and depletion of natural resources if improperly managed [1,2,3]. The hog numbers are about 5.5 million heads, and the daily livestock slurry quantity is about 163,000 m3 from all swine farms in Taiwan [4]. The methane production yields from swine manure have been reported as 403 mL CH4 /g

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Results

Conclusion