Anaerobic co-digestion of swine manure with sweet potato or cassava in different C/N ratios

Lisandra Maraia Villa,Jorge De Lucas Junior,Natália Da Silva Sunada,Luana Alves Akamine,Ana Carolina Amorim Orrico

doi:10.1590/0103-8478cr20190734

Abstract

ABSTRACT: Anaerobic co-digestion (AcoD) of waste is a method of increasing methane (CH4) yield and improving biofertilizer quality. This study aimed to evaluate the best AcoD conditions for swine manure (SM) with sweet potato (SP) or cassava (C) in different amounts in semi-continuous biodigesters. Initially, using batch biodigesters, an AcoD test of the SM with SP or C was performed, adopting carbon/nitrogen (C/N) ratios of 10/1, 13/1, 17/1, and 22/1. Based on the results, a C/N ratio of 10/1 was chosen, which was the proportion that resulted in the highest reduction of volatile solids (VS) and specific biogas production. From these results, the experiment was carried out in semi-continuous biodigesters, consisting of three treatments (control (SM), SP 10/1, and C 10/1) with five replicates and a hydraulic retention time (HRT) of 30 days. Total solid (TS) and volatile solid (VS) reductions, biogas and CH4 yields, alkalinity, and volatile acidity were measured. The control treatment differed from the others and resulted in decreased biogas yield (752 LN.kgVSadded -1), CH4 (449 LN.kgVSadded -1), and CH4 content (59.7%). The AcoD treatments (SP and C) did not differ significantly for biogas yield (respectively, 901 and 883 LN.kgVSadded -1) and CH4 (respectively, 590 and 547 LN.kgVSadded -1); however, they differed in CH4 content (65.5% and 61.9% respectively). The treatments showed general reduction averages of 76.1% and 85.9% for TS and VS, respectively, with no statistical difference found between them. The AcoD of the SM with SP or C increased the production and quality of the biogas, increasing the concentration of CH4 therein.

Highlights

Pig farming, as an activity with high polluting power, has animal waste one of the most studied substrates in anaerobic digestion (AD)
For the inclusion of C in the substrates, the largest reductions of Total solid (TS) and volatile solids (VS) (45% and 56%) occurred in the 10/1 carbon and nitrogen (C/N) ratio, which did not differ from the distinct C/N ratios for the sweet potato (SP) and the control
The mean reduction of sugars for Anaerobic co-digestion (AcoD) was 88.4%, with a 90% reduction for the 80:20 ratio, which was verified as a harmonic combination of the substrates because it led to a higher production of biogas

Summary

Introduction

As an activity with high polluting power, has animal waste one of the most studied substrates in anaerobic digestion (AD). The addition of plant materials to the medium in the digestion of animal waste is indicated because it provides a balance in the C/N ratio and increases the efficiency of the AD process (HASSAN et al, 2017). These materials allowed an additional carbon supply compared to SM, which has a C/N ratio ranging from 6 to 8 (LORIMOR et al, 2000). The SM has a high buffering capacity, biodegradability, and ammonia concentration, factors that optimize the degradation process (MOLINUEVO-SALCES et al, 2012; MATA-ALVAREZ et al, 2014)

Objectives

Methods

Results