The performance and archaeal community shifts in a modified anaerobic baffled reactor treating sweet potato starch wastewater at ambient temperatures

Shengjun Xu,Shanghua Wu,Xuliang Zhuang,Guoqiang Zhuang,Shuanglong Ma,Zhihui Bai,Cancan Jiang

doi:10.1038/s41598-017-15421-6

Abstract

A conventional anaerobic baffled reactors (ABRs) treating high strength sweet potato starch wastewater at ambient temperatures resulted in acidification and bad performances. After modification, the acidification was remitted and COD removal efficiencies reached 92.73% at high temperatures and were maintained at 71.19% at low temperatures. Moreover, as much as 1.014 ± 0.056 L CH4/L/d were collected at Stage III. The q-PCR results revealed that the largest methanogen populations emerged at Stage III as well, which was 5.29 × 108 mcrA copies per milliliter sludge. A comparable shift in the archaeal community structure at different stages and acetoclastic methanogens Methanosaeta predominated the archaeal community in every compartment in Stages I (63.73%) and II (48.63%). Finally, the net energy gains analysis at mesophilic, thermophilic, and ambient temperature revealed that modified ABR at ambient temperature was not only economical but also profitable and could generated 3.68 KJ energy per gram COD removed.

Highlights

China is the world’s largest sweet potato (Ipomoea batatas Lam) producer with the output exceeding 100 million tons in 2011, accounting for ~90% of global production[1]
The decline in chemical oxygen demand (COD) removal efficiency might have been caused by decrease of pH in the first two compartments in the conventional anaerobic baffled reactors (ABRs) and influence the utility of organic matters in sweet potato starch wastewater (SPSW). pH optima for hydrolytic and acidogenic bacteria is between 5.5 and 6.517–19 and methanogenic microorganisms is around pH 720–22
After modification, the acidification was remitted in the front compartments and the pH was maintained at 5.61 ± 0.17 in the first compartments compared with 4.62 ± 0.14 in the conventional ABR

Summary

Introduction

China is the world’s largest sweet potato (Ipomoea batatas Lam) producer with the output exceeding 100 million tons in 2011, accounting for ~90% of global production[1]. The wide application is because of its various advantages, e.g., simple construction, good performance, low sludge yields, energy production, and low cost[5,7,8] Another important advantage of the ABR is its ability to separate acidogenesis and methanogenesis longitudinally along the course of the reactor and achieve greater overall COD removal efficiencies than many other anaerobic reactors under the same conditions[9,10]. The relatively high costs of anaerobic SPSW treatment has limited its application, while operated at low temperatures (10–15 °C), a fall in overall COD removal efficiency is usually observed in ABR performance, even when fed low strength wastewater (4000 mg/LCOD)[11]. We hung plastic membranes in each reaction compartment to increase the attachable area for bacterial and enhanced the reaction rate After these improvements, the performance of the modified ABR treating high strength SPSW was investigated at ambient temperatures. Quantitative methanogen community shifts and changes in archaeal community structure in relation to operation conditions at ambient temperatures was monitored by real-time PCR and high-throughput 16 S rRNA gene sequencing, respectively

Methods

Results

Conclusion